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Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
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9
Source Reduction and Control

KEY POINTS IN CHAPTER 9

This chapter reviews what is known about management options for reducing nutrient supply to coastal environments. It finds:

  • Nutrient loads to coastal areas can be reduced by a variety of means, including improvements in agricultural practices, reductions in atmospheric sources of nitrogen, improvements in treatment of municipal wastewater (including tertiary treatment in some cases), and better control of diffuse urban nutrient sources such as runoff from streets and storm sewers (including both structural and passive controls). Regional stormwater control facilities, use of wetlands as nutrient sinks, better forest management to limit nitrogen export, enhancement of circulation in coastal waterways, and biological treatment also offer promise in some settings.

  • Options to minimize nutrient export from agricultural areas include manure management strategies, careful estimation of native nutrient availability and crop requirements, and supplemental fertilizer application timed to meet crop demand. Watershed-scale implementation of best management practices needs to be targeted to ensure maximum reduction in nitrogen and phosphorus export. Post-implementation monitoring should be done to assess effectiveness.

  • Lasting reductions in nutrient export from agriculture can be encouraged by focusing on consumer-driven programs and education, as well as on-farm production. Farmers’ decisions are often influenced by regional or even global economics. At these scales, farmers have little or no control over these economic pressures and the resulting changes in nutrient flows and distribution. New ways of using incentives to help farmers implement innovative source reduction and control are needed.

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
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  • A positive side effect from regulatory initiatives to reduce NOx emissions, targeted to minimize ozone and acid rain, is a reduction in the atmospheric contribution to nutrient loading in estuaries. The need to minimize coastal eutrophication should be a component of air pollution control strategies. Unfortunately, current NOx emission efforts are aimed principally at control during the summer because of emphasis on ozone and smog formation; for eutrophication, year-round emission controls are necessary.

  • A wide variety of methods, with variable effectiveness, are available to reduce urban point and nonpoint sourced nutrients. Natural options (enhancement of coastal wetlands) are one of a range of management tools.

Many factors contribute to nutrient over-enrichment, and thus there are many avenues by which the associated loads might be reduced. The effectiveness of any method depends, in part, on how large a contribution the source in question makes: minor improvements to major sources can sometimes offer more overall improvement than eliminating some minor nutrient source. Accurate information about relative contributions is essential if policymakers are to prioritize control efforts. Again, the federal actions called for in Chapter 2 would greatly strengthen efforts by local, state, and regional decisionmakers to successfully prioritize control efforts.

Nutrient over-enrichment in coastal waters is inextricably linked to human activities within estuarine areas as well as upstream, which in turn are tied to management and policy decisions. Conversely, physical, chemical, and biological impacts can be reduced by more effective control of anthropogenic inputs to the watershed, for instance by reducing loadings from agricultural, urban, or atmospheric sources. Figure 9-1 illustrates the significant effects that changes in tillage practices can have on nitrogen and phosphorus in a watershed. This chapter explores management strategies designed to reduce nutrient inputs. Because agricultural runoff is one of the greatest challenges in nutrient control, considerable attention is focused on control of agricultural sources, followed by control of atmospheric sources, urban sources, and control by other mechanisms.

AGRICULTURAL SOURCES

The goal of efforts to reduce nitrogen and phosphorus loss from agriculture to water is to increase nutrient use-efficiency. To do this, farmers attempt to balance the input of nutrients into a watershed from feed and fertilizer with outputs in crop and livestock produce, and also to manage the level of nitrogen and phosphorus in the soil. Reducing nutrient loss in agricultural runoff can be achieved by both source and transport control measures (Table 9-1). In general, there are reliable ways to reduce the transport of sediment-bound phosphorus from agricultural land by controlling erosion, and, to a lesser extent, there are methods to control nitro-

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

FIGURE 9-1 Annual nitrogen and phosphorus loss into the Little Washita River from a wheat-dominant and grass-dominant sub-watershed. Note the reduction in both nutrients after the eroding gullies in the grass watershed were treated in 1984 and conventional tillage was replaced with no-till in 1983 in the watershed growing wheat (modified from Sharpley and Smith 1994; Sharpley et al. 1996).

gen leaching to groundwater and the transport of dissolved phosphorus in runoff. However, less attention has been directed toward source management of nutrients because controlling nutrients at the source typically requires significant extra labor and thus is an economic burden to the farmer.

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

TABLE 9-1

Practice

Description

Source Measures

Feed additives

Enzymes increase nutrient utilization by animals

Crop genetics

Low phytic-acid corn reduces phosphorus in manure

Manure management

Compost, lagoons, pond storage; barnyard runoff control; transport excess out of watershed

Rate added

Match crop needs

Timing of application

Avoid autumn and winter application

Method of application

Incorporated, banded, or injected in soil

Crop rotation

Sequence different rooting depths

Manure amendment

Aluminum reduces NH3 loss and phosphorus solubility

Soil amendment

Flyash, iron oxides, gypsum reduce phosphorus solubility

Cover crop and residues

If harvested can reduce residual soil nutrients

Plowing stratified soils

Redistribution of surface phosphorus through profile

Transport Measures

Cultivation timing

Not having soil bare during winter

Conservation tillage

Reduced and no-till increases infiltration and reduces soil erosion

Grazing management

Stream exclusion, avoid overstocking

Buffer, riparian, wetland areas, grassed waterways

Removes sediment-bound nutrients, enhances denitrification

Soil drainage

Tiles and ditches enhance water removal and reduce erosion

Strip cropping, contour plowing, terraces

Reduces transport of sediment-bound nutrients

Sediment delivery structures

Stream bank protection and stabilization, sedimentation pond

Critical source area treatment

Target sources of nutrients in a watershed for remediation

TABLE 9-1 Best management practices designed to control nonpoint sources of agricultural nutrients (unpublished table from A. Sharpley).

Source Management
Animal Feeding of Nitrogen and Phosphorus

Both nitrogen and phosphorus are important dietary nutrients for animals and have a key role in various metabolic functions (NRC 1989). Most feedstuffs do not contain adequate nitrogen and phosphorus to meet the needs of growing animals; thus additional nutrient supplements are brought onto the farm. The nutritional goal is to feed adequate nitrogen

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

and phosphorus to meet the animal’s requirements while minimizing excretion. Recommended dietary requirements of nitrogen and phosphorus have been established by the National Research Council (NRC) and are routinely updated (e.g., NRC 1989). Although studies show these requirements to be accurate, many farms routinely over feed nitrogen and phosphorus (Shaver and Howard 1995; Wu and Satter 1998). Because about 70 percent of the nitrogen and phosphorus in feeds is excreted, routine overfeeding of nitrogen and phosphorus animals contributes to nutrient surpluses on farms (Isserman 1990; Morse et al. 1992; Wadman et al. 1987).

It is common to supplement poultry and pig feed with mineral forms of phosphorus because of the low digestibility of phytin, the major phosphorus compound in grain. This supplementation contributes to phosphorus enrichment of poultry manures and litters. Enzyme additives for livestock feed that will increase the efficiency of uptake from grain during digestion are now being tested. Development of such enzymes would be cost-effective in terms of livestock weight gain and it is hoped that lowering mineral phosphorus supplementation of feed would reduce the phosphorus content of manure. One example is the use of phytase, an enzyme that allows the digestive systems of chickens and hogs to absorb phosphorus from grains. Ertl et al. (1998) showed a 23 percent reduction in excretion of phosphorus by poultry fed “low-phytic acid” grain compared to those fed normal corn grain.

Another approach to balance farm phosphorus inputs and outputs is to increase the quantity of phosphorus in corn that is available to poultry and pigs. Corn can be genetically engineered to decrease unavailable phytate-phosphorus, which contributes as much as 85 percent of phosphorus in corn grain. Ertl et al. (1998) manipulated the genes controlling phytate formation in corn and showed that phytate-phosphorus concentrations in “low-phytic acid” corn grain were as much as 51 percent less than in normal grain. There was a 23 percent reduction in excretion of phosphorus by poultry fed the “low-phytic acid” grain compared to those fed the “wild type” corn grain. Thus, the use of low-phytate corn in poultry and pig feed can increase the assimilation of phosphorus and other phytate-bound minerals and proteins.

Reducing Off-Farm Inputs of Nitrogen and Phosphorus

The accumulation of nutrients on many animal feeding operations where on-farm crop production is supplemented by feed inputs is generally not as great as in other operations where the animals depend primarily on off-farm feed. The distinguishing feature among these animal operations is the breakdown between the amount of crops produced on a

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

farm (and the potential nutrient utilization by those crops) and the animal numbers on the farm, because the manure applied to crop fields will include both nutrients coming from those fields and from imports of off-farm feeds. The application of imported nutrients to crop fields can compensate for those lost in marketed products and manure handling operations and help to sustain the farm, but the additional nutrients can also be the source of excess nutrient loading. Nevertheless, restricting feed purchases to maintain the balance of nutrients can limit herd size and economic return if all manure from the herd must be applied to the farm cropland (Westphal et al. 1989).

Improving Nutrient-Use Efficiency

Management practices that improve nutrient-use efficiency are vital for minimizing losses to ground and surface waters. Specific best management practices (BMPs) for nitrogen and phosphorus vary from region to region due to large-scale differences such as climate, geology, depth to water, and irrigation or drainage practices, and also due to small-scale differences such as soils, cropping systems, and past field history. Therefore, BMPs for nitrogen and phosphorus will necessarily be site-specific and should be prescribed by a technical advisor who has a good knowledge of local nutrient cycles. This task often is assigned to state and federal extension agencies or soil conservation agencies.

Nitrogen

Nitrogen sources and reduction control strategies for Mississippi River Basin inputs to the Gulf of Mexico have been outlined by the National Oceanic and Atmospheric Administration (NOAA 1999b). Even though the major inputs of nitrogen and phosphorus to agricultural systems in this region are via fertilizer rather than manure, the principles of increasing nutrient-use efficiency are appropriate to other regions of the United States. Loadings to surface waters in the Upper Mississippi River and Ohio River sub-basins occur primarily by infiltration of water beyond the crop rooting zone into deeper soil layers, where it is collected by subsurface tile drains. In other basins, the primary pathway for nitrate loading to surface waters is groundwater seepage and irrigation return flow. Reduction of nitrate loading to surface waters in the Mississippi River basin can be achieved by reducing nitrate sources and controlling drainage (NOAA 1999b).

Although the selection of BMPs for nitrogen must depend on the specific hydrologic setting, field, and source of nitrogen, there are some basic nitrogen management principles that apply if the goal is to mini-

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

mize nitrogen losses to ground or surface water. The most fundamental principle is to supply only the nitrogen needed to meet the needs of the next crop, and to apply it in synchrony with crop use. Steps in applying this principle include:

  • estimating the nitrogen requirement of the next crop (expected yield);

  • evaluating nitrogen available from native sources (soil nitrogen mineralization, residual soil nitrate, irrigation water, etc.);

  • subtracting the available native nitrogen from the crop nitrogen requirement to estimate supplemental nitrogen needs;

  • determining the most appropriate source of supplemental nitrogen (manure, fertilizer, crop residues); and

  • determining the most efficient and practical management practice for the specific source of supplemental nitrogen (rate, time, and placement of the nitrogen).

Crop nitrogen requirement

Selection of the expected yield goal is one of the most critical BMPs for nitrogen, because most fertilizer and/or manure application rates are based directly on anticipated yield. Several studies have shown that farmers, or those advising them, often have unrealistic yield expectations and that resultant over-fertilization with nitrogen can be directly related to long-term increases in groundwater nitrate.

The most direct way to integrate overall site-specific factors is to calculate the average yield of the specific soil-crop system over the past 3 to 5 years. One can then adjust the average yield for unusual conditions (eliminating unusually wet or dry years), for current conditions (stored soil moisture, planting date, tillage practices, etc.), or for new technologies (new varieties, new irrigation, etc.), and then calculate a final estimate of expected yield. In any case, it is important to base the estimated yield on “real world conditions” (i.e., actual field yields) to avoid excess nitrogen applications.

Native nitrogen availability

The second step is to evaluate nitrogen available from native sources (i.e., sources that are not directly manageable by the farmer). These sources include nitrogen present in the root-zone as inorganic nitrate, nitrogen released through organic matter decomposition (mineralized nitrogen), nitrogen contributed through water sources (irrigation), and nitrogen from atmospheric inputs. The most recent tools for including

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

native sources of nitrogen are the pre-sidedress nitrate test and the leaf chlorophyll meter (Magdoff et al. 1984; Meisinger et al. 1992; Schepers et al. 1992). The chlorophyll meter essentially measures the “greenness” of a specific leaf, from which the need (or lack of need) for more fertilizer nitrogen or potential for over fertilization can be estimated.

Management of nitrogen source (rate, placement, and timing)

The above steps produce an estimate of the appropriate nitrogen rate for a realistic yield of the next crop, which is the basic principle behind efficient nitrogen use. The final step is to manage the selected nitrogen source in a manner to supply nitrogen in phase or balance with crop demand. For fertilizer nitrogen, this is a relatively easy task because it can be applied just before the period of rapid crop nitrogen uptake.

Applying nitrogen when needed does not itself ensure adequate control of losses. For instance, one study showed that losses from unfertilized cereal crops were not much less than losses where fertilizer had been applied at the economic optimum input, with both resulting in nitrate concentrations in excess of the European Community limit of 10 mg nitrate-nitrogen l−1 (Sharpley and Lord 1998). This is because nitrate leached during winter is largely derived from that mineralized by the soil during late summer and autumn, when crop uptake is small especially in arable systems. This mineralization is affected little by fertilizer inputs. It is only when inputs exceed crop uptake capacity (usually close to the economic optimum) that excess fertilizer nitrogen contributes directly to losses. The economic optimum application of nitrogen for most crops exceeds offtake, resulting in a small positive balance. Within grazing systems, nitrogen surpluses are often a large proportion of the total fertilizer input, because most of the nitrogen consumed in grazing is redeposited as urine and dung. This nitrogen is not efficiently recycled because some of it is not immediately available and it is deposited unevenly over the field. Thus for nitrogen, enforcing a balance of inputs against removals could seriously reduce productivity, cause significant economic penalties, and would not in itself solve the nitrate problem.

Specific improvements in management may include: (1) reducing rates of nitrogen fertilizer by following fertilizer guidelines developed by land-grant universities, (2) switching from fall to spring or split applications, (3) changing the form of fertilizer nitrogen from anhydrous ammonia to slow-release urea fertilizers, (4) switching from broadcast to banded or incorporated application methods, (5) calibrating fertilizer application equipment, and (6) applying nitrification inhibitors (CENR 1997).

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×
Phosphorus

The long-term use of commercial fertilizers and manures has increased the phosphorus status of many agricultural soils to optimum or excessive levels. This, of course, was the intended goal of phosphorus fertilization, to remove soil phosphorus supply as a limitation to agricultural productivity. However, for many years actions taken to achieve this goal did not consider the environmental consequences of phosphorus loss from soil to water. The constraint on phosphorus buildup in soils from commercial fertilizer use was usually economic, with most farmers recognizing that soil tests for phosphorus were an accurate indicator of when to stop applying fertilizer phosphorus. Some “insurance” fertilization has always occurred, particularly in high value crops, such as vegetables, tobacco, and sugar cane. However, the use of commercial fertilizers alone would not be expected to grossly over fertilize soils because farmers would cease applying fertilizer phosphorus when it became unprofitable. Today’s concerns with phosphorus are caused by the realization that soils that are considered “optimum” in soil test phosphorus (or perhaps only slightly over fertilized) from a crop production perspective may still provide environmentally significant quantities of phosphorus in surface runoff and erosion.

Basing manure application on estimates of soil phosphorus and crop removal of phosphorus can reduce the buildup of soil phosphorus but can present several technical and economic problems to many farmers. A soil test phosphorus-based strategy could eliminate much of the land area with a history of continual manure application from further manure additions, as several years are required for significant depletion of high soil phosphorus levels. This would force farmers to identify larger areas of land to use the generated manure, further exacerbating the problem of local land area limitations. In addition, farmers relying on manure to supply most of their crop nitrogen requirements may be forced to buy fertilizer nitrogen to supplement foregone manure nitrogen.

As phosphorus is relatively immobile in soil compared to nitrogen, timing of application is less critical in BMP development for phosphorus than nitrogen. However, methods of phosphorus application are important. Rotational applications of phosphorus designed to streamline fertilizer operations may leave large amounts of available phosphorus in the surface, and should be avoided in areas of the landscape at risk of erosion or surface runoff. Efficient management of phosphorus amendments to soils susceptible to phosphorus loss involves the subsurface placement of fertilizer and manure away from the zone of removal in surface runoff, and the periodic plowing of no-till soils to redistribute surface phosphorus accumulations throughout the root zone. Both practices may indirectly

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

reduce the loss of nitrogen and phosphorus by increasing crop uptake and yield, which affords a greater vegetative protection of surface soil from erosion. However, these measures are often unrealistic for a farmer to implement. For example, subsurface injection or incorporation in rocky soils may be difficult, and without manure storage, farmers who contract out the cleaning of poultry houses will have little flexibility for when manure or litter is applied.

Manure Management

As discussed in Chapter 5, animal wastes are a major part of the nutrient over-enrichment problem, and management efforts are complicated by the long distances that feedstocks are transported. Managing nutrients from manure is often more difficult than from fertilizer, due to uncertainties in initial composition (e.g., ration, animal age, etc.), losses during storage or handling (e.g., ammonia volatilization), uncertainties of application rates (e.g., uncalibrated spreaders, uneven applications), difficulty in spreading manure to a growing crop without causing crop damage, greater gaseous nitrogen losses with manure after application, and time pressures producers face because of weather uncertainties.

It is also important for manure management to know the approximate decomposition rate of the organic nitrogen, so as to minimize nitrogen loss in groundwater. This is generally estimated as a decay series for the particular type of manure. An example of a decay series for solid beef manure would be 40 percent mineralized the first year, 25 percent of the remaining nitrogen the next year, 6 percent the next year, and so on (Gilbertson et al. 1979).

The last step is to calibrate the manure spreader. Obviously it does little good to know the crop nitrogen need, the manure composition, the likely ammonia loss, and the decomposition rate, if one cannot apply the calculated rate of manure accurately. Manure spreader calibration programs in Maryland and Pennsylvania frequently find that farmers are applying two to five times more manure than they originally estimate. Educational materials for spreader calibration can significantly improve manure nitrogen utilization, and further improvements could be obtained with monitoring or incentives.

Farm advisors and resource planners now recommend testing manure for nitrogen and phosphorus, and soils for phosphorus, prior to land application of manure. However, nitrogen-based manure management plans are still based on crop needs. Without these determinations, farmers and their advisors can underestimate the fertilizer value of manure. Soil test results can also demonstrate the positive and negative long-term effects of manure use and the time required to build-up or deplete soil

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

nutrients. For instance, they can help a farmer identify the soils in need of fertilization, those where moderate manure applications may be made, and those fields already containing excess nitrogen and phosphorus where manure should not be applied.

Commercially available manure amendments, such as slaked lime or alum, can help in manure management. Such amendments can decrease ammonia volatilization, which can significantly affect export to estuaries (Chapter 5), and at the same time lead to improved animal health and weight gains. Amendments can also decrease the solubility of phosphorus in poultry litter by several orders of magnitude and decrease dissolved phosphorus, metal, and hormone concentrations in surface runoff at least 10 fold (Moore and Miller 1994; Moore et al. 1995; Shreve et al. 1995; Nichols et al. 1997). Perhaps the most important benefit of manure amendments for both air and water quality would be an increase in the nitrogen:phosphorus ratio of manure, by reducing nitrogen loss because of ammonia volatilization. An increased nitrogen:phosphorus ratio of manure would more closely match crop nitrogen and phosphorus requirements.

One approach to better manure management would be to establish a mechanism to facilitate movement of manures from surplus to deficit areas. At present, manures are rarely transported more than 10 miles from where they are produced. But mandatory transport of manure from farms with surplus nutrients to neighboring farms where nutrients are needed would face several significant obstacles. First, it must be shown that manure-rich farms are unsuitable for manure application, based on soil properties, crop nutrient requirements, hydrology, actual nutrient movement, and proximity of sensitive water resources. Second, it must be shown that the recipient farms are more suitable for manure application. The greatest success with re-distribution of manure nutrients is likely to occur when the general goals of nutrient management set by a national (or state) government are supported by consumers, local governments, the farm community, and the livestock industry involved. This may initially require incentives to facilitate subsequent transport of manures from one area to another.

This may be a short-term alternative if nitrogen-based management is used to apply the transported manures. If this happens, soil phosphorus in areas receiving manures eventually may become “excessive.” To date, however, large-scale transportation of manure from producing to non-manure producing areas is not occurring. The main reasons for this are the high transportation costs and concern that avian diseases will be transferred from one farm (or region) to the next. Consequently, there is a need to develop a means to ensure the biosecurity of any manure transportation network that is developed, and in general to seek ways to over-

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

come existing obstacles to better manure management (e.g., incentives and disincentives).

Composting is another potential management tool to improve manure distribution. Although composting tends to increase the phosphorus concentration of manures, the volume is reduced and thus transportation costs are reduced. Additional markets are also available for composted materials. Finally, there is interest in using some manures as sources of bioenergy. For example, dried poultry litter can be burned directly or converted by pyrolytic methods into oils suitable for use to generate electric power. Liquid wastes can be digested anaerobically to produce methane that can be used for heat and energy. As the value of clean water and cost of sustainable manure management is realized, it is expected that alternative entrepreneurial uses for manure will be developed, become more cost-effective, and, thus, create expanding markets. Research is needed to speed the development of these types of technologies and approaches.

Transport Management

Once water and sediment begin to move in the landscape, taking with them the phosphorus originally applied as fertilizer and/or manure, the quantities that reach the stream can be reduced by any feature that slows flow and/or encourages infiltration or sediment trapping. Such transport management measures include terracing, contour tillage, cover crops, buffer strips, riparian zones, and impoundments. These transport measures are generally more efficient at reducing particulate phosphorus rather than dissolved phosphorus. However, such approaches only work where subsurface pathways of phosphorus loss are unimportant. Furthermore, by encouraging infiltration of surface runoff, which may be enriched with phosphorus, the problem is simply translated from surface to subsurface delivery. While uptake by plant roots and adsorption onto soil particles may delay the delivery of phosphorus to surface waters, such mechanisms may be ineffective in soils with a high hydraulic conductivity (e.g., sands) or where macropore or drainflow is important.

For nitrogen, losses can also be reduced by improved water management, including adoption of controlled drainage or sub-irrigation methods, switching from furrow irrigation to surge irrigation or sprinkler irrigation with fertigation, and the use of irrigation scheduling techniques (Skaggs and Gilliam 1981). Nitrate losses can also be reduced by control of water table depth by managing tile drain spacing and depth and by control structures on the tile drain outlets, to limit tile flow when the potential for nitrate may be greatest (Gilliam et al. 1979; Kladivko et al. 1991; Zucker

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

and Brown 1998). Moving the runoff through anoxic sediments (e.g., in wetlands) can also help remove nitrogen through denitrification.

Careful selection of the type and sequencing of crops in a rotation, taking into account the timing and position in the soil profile of residual nitrate, rooting depth, and soil-water movement, can maximize nitrogen-use efficiency and minimize nitrate leaching potential (Sharpley et al. 1992). Crop cover during the period of agricultural runoff will therefore reduce losses of both nitrogen and phosphorus. For nitrogen, the critical period is autumn, to allow plants to take up nitrogen mineralized in soils after harvest. In temperate regions, autumn-sown cereals usually do not take up much nitrogen before winter. However cover crops established immediately after harvest (and killed in winter or early spring) can be highly effective (Shepherd and Lord 1996). Data from farms within the United Kingdom Nitrate Sensitive Areas Scheme show that such crops are compatible with commercial farming systems, relatively inexpensive to manage, and can reduce nitrate losses by about 50 percent (Sharpley and Lord 1998).

For phosphorus, crop cover at any time during the period when agricultural runoff can occur will help protect against total phosphorus loss but will be less effective against losses of dissolved phosphorus (Sharpley and Smith 1991). Crop residues can be as effective as crop cover in reducing erosion or surface runoff, and hence protecting against phosphorus loss. Equally, anything that keeps the surface rough, such as plowing, can be effective. However creation of fine seedbeds, as are required for winter cereals, has been shown to increase erosion. This is especially the case where cultivations are up-and-down slopes.

Cultivation may promote mineralization of nitrate, especially where plant residues with high nitrogen content are present. Thus, delaying autumn plowing can reduce leaching losses. Cereal straw, conversely, because of its high carbon:nitrogen ratio, may actually reduce leaching losses slightly by using soil nitrate in the early stages of decomposition.

Riparian zones play an important role in reducing non-point sources of nitrogen and phosphorus, can increase wildlife diversity and numbers, and improve aquatic habitat and diversity via shading. In addition to acting as physical buffers to sediment-bound nutrients, plant uptake captures nitrogen and phosphorus, resulting in a short-term accumulation of nutrients in non-woody biomass as well as a long-term accumulation in woody biomass (Peterjohn and Correll 1984; Fail et al. 1986; Correll and Weller 1989; Groffman et al. 1992). Even more importantly, denitrification of nitrogen in riparian zones is a significant mechanism for decreasing nitrogen (Jacobs and Gilliam 1985; Pinay et al. 1993). Denitrification rates of 30 to 40 kg N ha−1 y−1 have been measured for natural riparian forests in the United States. Most denitrification occurs in the top 12 to 15 cm of the

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

soil. Within a riparian zone, the fastest rates occur at the riparian-stream boundary where nitrate enriched water enters organic surface soil (Cooper 1990).

The effectiveness of riparian zones as nutrient buffers can vary significantly. For instance, the route and depth of subsurface water flow paths though riparian areas can influence nutrient retention. Riparian zones are most efficient when sheet flow occurs, rather than channelized flow. The key to successful denitrification in riparian wetlands is for the water to flow (not too quickly) through the surface layer of waterlogged, wetland soils, where denitrification is fed by the high input of organic carbon from the wetland plants and where oxygen is low to zero.

In several locations of the coastal plain of the Chesapeake Bay watershed, average annual terrestrial boundary nitrate concentrations of 7 to 14 mg NO3-N l−1 decrease to 1 mg NO3-N l−1 or less in shallow groundwater near streams (Lowrance et al. 1995). However, in the same area, a single site with a nitrate concentration of 25 mg NO3-N l−1 at depth had a concentration of 18 mg NO3-N l−1 in shallow groundwater at the stream. Lowrance et al. (1984b), who estimated annual denitrification rates to average 31 kg N ha−1 yr−1 in the top 50 cm of soil, measured denitrification rates between 1.4 kg N ha−1 yr−1 in a riparian zone adjacent to an old field (which received no fertilizer) to 295 kg N ha−1 yr−1 under conditions of high nitrogen and carbon subsidies. Such results illustrate the potential for denitrification in riparian zones, the high spatial variability that can be expected, as well as the importance of carefully managing riparian areas.

Usually, farm nitrogen inputs can be more easily balanced with plant uptake than can phosphorus, particularly where confined animal operations exist. In the past, separate BMP strategies for nitrogen and phosphorus have been developed and implemented at farm or watershed scales. Because of differing chemistry and flow pathways of nitrogen and phosphorus in soil and through the watershed, these narrowly targeted strategies often are in conflict and lead to compromised water quality remediation. For example, basing manure application on crop nitrogen requirements to minimize nitrate leaching to groundwater increases soil phosphorus and enhances potential phosphorus surface runoff losses. In contrast, reducing surface runoff losses of phosphorus via conservation tillage can enhance nitrate leaching (Sharpley and Smith 1994).

Nitrogen and phosphorus transport management strategies may differ because nitrogen losses can occur from any location in a watershed, while areas prone to surface runoff contribute most to phosphorus loss. Nitrogen also volatilizes to the atmosphere, whereas, phosphorus does not. Hence, remedial strategies for nitrogen may be applied to the whole watershed, whereas the most effective phosphorus strategy would be a combination of simple measures over the whole watershed to avoid

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

excessive nutrient buildup, thereby limiting losses in subsurface flow, and more stringent measures to the most vulnerable sites to minimize loss of phosphorus in surface runoff. Thus, BMPs must consider both nitrogen and phosphorus sources and export pathways at farm and watershed scales.

Implementing Remedial Measures

Since the early 1980s, several studies have investigated the long-term (7 to 10 yr) effectiveness of BMPs to reduce nitrogen and phosphorus export from agricultural watersheds (National Water Quality Evaluation Project 1988; USDA and ASCS 1992; Goldstein and Ritter 1993; Richards and Baker 1993; Bottcher and Tremwell 1995). These studies quantified nutrient loss prior to and after BMP implementation or attempted to use untreated watersheds as control. Overall, these studies showed BMPs reduced nutrient export. However, it is evident that several factors are critical to effective BMP implementation. These factors include targeting watersheds that will respond most effectively to BMPs, identifying critical source areas of nutrient export, as well as accounting for both watershed and estuary response time and equilibration (capacity to buffer added nitrogen and phosphorus).

The time of watershed or estuary response to BMP implementation is particularly important for phosphorus, due to its long residence time in ecosystems, compared to nitrogen. Watersheds may become saturated with phosphorus where animal feeding operations are concentrated (Lander et al. 1997; USDA and EPA 1999). Studies have shown that even where phosphorus applications are stopped, elevated soil phosphorus can take up to 20 years to decline to levels at which crops will respond to applications (McCollum 1991). Also, internal recycling of phosphorus in estuarine sediments can supply sufficient phosphorus to maintain eutrophic conditions in phosphorus-sensitive waters.

Watershed Identification and Cost-Effectiveness

Because resources are limited, local decisionmakers often focus management efforts on those watersheds that will provide the greatest reduction in nitrogen and phosphorus loss following BMP implementation. Otherwise, overall nutrient inputs to an affected waterbody may not be decreased sufficiently. Similarly, farmers make decisions about on-farm management approaches based on cost-effectiveness, which is affected by many things.

Model simulation and field studies provide data illustrating that the cost-effectiveness of BMPs varies (Table 9-2). Although protection of

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

TABLE 9-2

Best Management Practice

Phosphorus Loss (kg ha−1 yr−1)

Cost-Effectiveness ($ kg P saved−1)

None

10.0

 

Contour cropping

6.3

1.7

Terraces

3.2

4.7

Conservation tillage

3.9

0.8

Vegetative buffer areas

2.5

1.1

Manure management

2.8

3.3

All BMPs

1.8

4.9

TABLE 9-2 Cost-effectiveness of BMPs for reducing phosphorus losses from continuous corn with a 5 percent slope and 140 kg P ha-1 yr-1 manure broadcast. Conservation tillage achieves significant phosphorus control with good cost-effectiveness, while manure management is less cost-effective (modified from Meals 1990).

riparian areas with buffers and manure management can reduce runoff phosphorus more than tillage management, conservation tillage is often a more cost-effective measure. These generalized examples emphasize the need to determine the load reduction required for a given watershed and waterbody to select appropriate BMPs. Clearly, construction of terraces, which are initially expensive, may in some cases be a viable option. However, careful selection and integration of different practices can improve overall cost-effectiveness. Cost-effectiveness includes the cost of land taken out of production.

In another example, Meals (1990) evaluated the effect of several manure BMPs on phosphorus export from two watersheds in the LaPlatte River basin draining into Lake Champlain, Vermont. BMPs included barnyard runoff control, milkhouse waste treatment, and construction and use of manure storage facilities. Phosphorus losses were lower than before BMPs. For both watersheds, barnyard runoff control resulted in the greatest reduction in phosphorus export and was the most cost-effective BMP (Table 9-3). The results of this simple cost-effectiveness analysis have important implications for formulating remediation strategies. If a watershed project was being developed with limited funding, the cost-effectiveness analysis could help target a watershed that would provide the greatest impact for the money invested (Meals 1990). For instance, if a choice had to be made between the two Vermont watersheds shown in Table 9-3, watershed 1 would have been selected based on better cost-effectiveness ratios.

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

TABLE 9-3

 

Watershed 1

Watershed 2

Management

Phosphorus Reduction (kg)

Effectiveness ($ kg P−1)

Phosphorus Reduction (kg)

Effectiveness ($ kg P−1)

Barnyard runoff control

311

4

78

14

Milkhouse waste treatment

34

12

11

32

Waste storage facility

154

269

14

1,963

Total

567

77

103

282

TABLE 9-3 Comparison of cost-effectiveness of animal waste management BMPs for two watersheds in the LaPlatte River Basin project, Vermont, 1980 to 1989 (modified from Meals 1990). Simple cost-effectiveness analysis can be key to helping farmers implement strategies that contribute the greatest benefits to watershed protection, and for targeting actions in watersheds where they can have the most impact.

If regional assessments are to identify critical source areas within large regions, results obtained from experimental sites as well as model estimates have to be scaled up. The accuracy of regional estimates depends on how good our experimental results or models are and how reliable available regional data are describing the factors governing nutrient transport. In addition to regional assessments, models can be used to make comparative studies on the effectiveness of different remedial measures.

Targeting Within a Watershed

Once an area has been selected for remediation, the next step is selection of appropriate BMPs. Using cost-effectiveness ratios like those outlined in Table 9-3, BMP implementation can be prioritized. For the example of the two Vermont watersheds in Table 9-3, the most effective BMP installation priority would be barnyard runoff control, followed by milkhouse waste treatment, and then animal waste storage facilities. Without careful targeting of critical nutrient source controls within a watershed, BMPs may not produce the expected reductions in nitrogen and phosphorus export.

The importance of targeting BMPs within a watershed or basin is shown by several studies in the Little Washita River watershed (54,000 ha) in central Oklahoma (Sharpley and Smith 1994). Nutrient export from two subwatersheds (2 and 5 ha) were measured from 1980 to 1994, while

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

BMPs were installed on about 50 percent of the main watershed. Practices included construction of flood control impoundments, eroding gully treatment, and conservation tillage. Following conversion of conventional-till (moldboard and chisel plough) to no-till wheat in 1983, nitrogen export was reduced 14.5 kg ha−1 yr−1 (3 fold) and P loss 2.9 kg ha−1 yr−1 (10 fold) (Figure 9-1; Sharpley and Smith 1994). A year later, eroding gullies were shaped and an impoundment constructed in the other subwatershed. Both nitrogen and phosphorus loss decreased dramatically (5 and 13 fold, respectively) (Sharpley et al. 1996). There was no effect of BMP implementation, however, on phosphorus of nitrogen concentration in flow from the main Little Washita River watershed (Figure 9-1). A lack of effective targeting of BMPs and control of major sources of phosphorus and nitrogen export in the Little Washita River watershed contributed to no consistent reduction in watershed export of phosphorus or nitrogen.

Apparently, there is a minimum threshold level of implementation that must be achieved before a significant response to BMPs occurs. For instance, in the LaPlatte River Basin, Vermont example (Meals 1990), animal waste control measures were implemented during the early 1980s. These BMPs included control of barnyard runoff, milkhouse waste treatment, and construction of waste storage facilities. However, there was no apparent reduction in either dissolved or total phosphorus concentration in runoff with increasing percent of animals in a watershed under a BMP (dashed lines; Figure 9-2). If the runoff phosphorus values for watersheds where less than 50 percent of the animals were under BMPs are not considered, then both dissolved and total phosphorus in runoff were decreased significantly. The low values of implementation (less than 42 percent) represent the initial years of land treatment when BMP implementation was incomplete.

Selecting a Best Management Practice

The cost-effectiveness of BMPs for reducing nitrogen and phosphorus loss varies with both types of practice and among watersheds. Remediation strategies are ongoing processes, in which BMP selection and operation should be reevaluated regularly to optimize nutrient export reductions.

Research into the effectiveness of BMPs has shown that they can be successful in reducing overall loads, but will not necessarily be adequate during extreme snowmelt or rainfall events. For instance, Meals (1990) studied BMPs in an agricultural watershed leading to Lake Champlain, which is sensitive to phosphorus loadings. Surprisingly, this analysis showed an increase in phosphorus export from the Mud Hollow Brook watershed following BMP implementation (Figure 9-3). Further analysis

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

FIGURE 9-2 Mean annual phosphorus concentration in watershed runoff as a function of the percentage of watershed animals under BMPs in the LaPlatte River basin, Vermont (modified from Meals 1990).

FIGURE 9-3 Effect of BMP implementation on total and dissolved phosphorus loss from Mud Hollow Brook watershed, Vermont, 1985 to 1989, with and without inclusion of extreme flow events. Positive values indicate an increase in phosphorus loss and negative values and decrease in phosphorus loss with BMP implementation (modified from Meals 1990).

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

revealed that annual phosphorus export was dominated by one or two extremely high flows (greater than the 95th percentile of all recorded stream flows) that were generally associated with snowmelt or intense rainfall events (Meals 1990). These few extreme events had a dramatic effect on the overall assessment of BMP impact on phosphorus export. When these events were not included in the analysis, BMPs reduced dissolved and total phosphorus export as anticipated. Effective remediation strategies should consider such extreme events in situations where they can dominate phosphorus export.

Incentives for BMP Adoption

As noted in Chapter 8, policies to promote source reduction can be based on either a voluntary approach or a regulatory approach. A voluntary approach has the advantage of promoting a more cooperative environment for encouraging adoption of, for example, BMPs. However, if the voluntary approach involves significant subsidies or cost-sharing to induce adoption, it will require the regulator or manager to raise funds to finance the subsidies and will generally result in product prices that do not fully reflect the total cost of production (including environmental costs). Nonetheless, voluntary approaches have been used successfully to promote source reduction and recent experience suggests these approaches could play an important role in reducing nutrient loadings.

There are several sources of technical assistance and financial programs to help defray the costs of constructing or implementing BMPs (EPA 1998e). Some of these sources are Conservation Technical Assistance, Conservation Reserve Program, Environmental Quality Incentives Program, Special Water Quality Incentives, Wetland Reserve Program, and Wildlife Habitat Incentive Program. Also, stakeholder alliances have been developed among state, federal, and local groups, producers, and the public to identify problems, focus resources, and implement BMPs in Chesapeake Bay and the New York City watershed, for example.

ATMOSPHERIC SOURCES

As discussed in Chapter 5, atmospheric deposition is a significant source of nitrogen loadings to some estuaries and other coastal waters, particularly in the northeastern United States. The deposition can be directly to the surface of the waterbody or onto the watershed with subsequent export to the estuary. This nitrogen deposition onto the watershed with export to downstream waters is more important than deposition directly onto the waterbody for many estuaries where the ratio of watershed area to estuary area is high. Both deposition of ammonia/

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

ammonium and of oxidized nitrogen compounds can be important. (NOTE: Deposited oxidized nitrogen compounds are denoted NOy as opposed to NOx, which denotes emitted compounds.) In the United States, most of the ammonium deposition comes from agricultural sources, particularly from animal wastes but also from volatilization of fertilizers, while the oxidized nitrogen comes principally from the combustion of fossil fuels.

For nitrogen deposition directly onto the water surface of an estuary, reductions in the sources of nitrogen to the atmosphere are the only possible approach to control. For nitrogen deposition onto the watershed, reductions in sources to the atmosphere may still be the easiest and most effective approach for control, but other options are possible, such as encouraging denitrification in riparian wetlands (discussed earlier in the context of controlling nitrogen runoff from agricultural fields), managing the composition of tree species in forests so as to reduce nitrogen export, and treating runoff from urban streets (where atmospheric nitrogen deposition is particularly high).

The reduction of atmospheric ammonium deposition requires better management of animal wastes to decrease the volatization of ammonia to the atmosphere, as is discussed earlier in this chapter. For the deposition of oxidized nitrogen compounds, the emission of nitrogen oxides (NOx) must be controlled. In tropical areas, agricultural practices can also contribute greatly to the emissions of these compounds, but in the United States, most NOx emissions originate from the burning of fossil fuels. These emissions originate from both point (stationary) and nonpoint (mobile) sources. The primary stationary sources are electric utilities and industrial facilities, while the primary mobile sources are motor vehicle emissions. Nationally, NOx emissions rose rapidly with post-war economic activity. However, due primarily to regulation of NOx emissions under the Clean Air Act, national emissions have been roughly constant since 1980 (EPA 1999c).

Reduction in atmospheric nitrogen deposition is directly related to reductions in NOx emissions. NOx emissions can be reduced either by burning less fossil fuel or by removing NOx from the combustion exhaust. For mobile sources, reductions in fossil fuel consumption can result from a number of different mechanisms (e.g., Calvert et al. 1993; Krupnick 1993). One obvious mechanism is a reduction in the number of vehicle miles driven. Incentives to reduce mileage can be created through promotion of mass transit or car pooling. Individuals can be expected to make transportation mode choices by comparing a number of factors, including convenience and price. The more expensive car travel is, the less individuals are likely to use it. Thus, incentives for either reductions in overall travel or for switching to alternative transportation modes can

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

be created through increases in the price of gasoline (Haughton and Sarkar 1996; Goldberg 1998). Gasoline prices can be increased through increases in gasoline taxes. However, the effectiveness of a tax depends on the responsiveness of demand to price increases. Empirical evidence suggests that demand is relatively unresponsive to price increases in the short run, although the responsiveness is greater in the long run (Espey 1998).1 Thus, while gasoline taxes may generate significant revenue that can be used to finance pollution abatement, it is likely that the tax increase would have to be large in order to induce a significant change in driving behavior. Such a large price increase could have undesirable distributional consequences, since gasoline taxes are generally thought to be regressive (Chernick and Reschovsky 1997).

A second potential mechanism for reducing fuel consumption is increasing miles per gallon of fuel (i.e., increasing the fuel efficiency of cars). This is the aim behind the Corporate Average Fuel Efficiency (CAFE) standards (Goldberg 1998). Overall reductions in the cost of meeting these standards can be achieved by allowing firms to average emissions across their fleets or to trade emissions with other firms (Kling 1994).2 A requirement that all vehicles meet a common emission standard in terms of grams per mile suggests that improvements in fuel economy per se may not generate reductions in vehicle emissions (NRC 1992). Although this is true for new cars (Khazzoom 1995), a recent study by Harrington (1997) finds that, as cars age and the emission control equipment breaks down, better fuel economy is strongly associated with low emissions, at least for CO and HC. If vehicle emissions in fact vary considerably by year, make and size (Kahn 1996), reductions in total emissions can be achieved by changing the composition of the existing automobile fleet. Incentives can be provided for early retirement of high-emission vehicles (Alberini et al. 1995, 1996). Reductions of this type may, however, be offset by emission increases due to the increased popularity of high-emission sport utility vehicles, which are currently subject to less stringent emission restrictions than passenger cars (0.7 grams per mile versus 0.4 grams per mile for passenger cars).

Reductions in fossil fuel consumption can also result from the development and use of vehicles that rely on alternative power sources, such as methanol (Krupnick and Walls 1992; Michaelis 1995; Hahn and Borick 1996; Kazimi 1997) or ethanol (Michaelis 1995; Rask 1998). Given current markets conditions, these alternatives do not appear to be very cost-

1  

The greater long run responsiveness is due to the impact that higher prices have on automobile purchases. As consumers replace their automobiles, higher gasoline prices can encourage them to purchase more fuel efficient cars.

2  

See Chapter 8 for a discussion of the economic implications of allowing firms to trade pollution allowances.

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

effective and hence are unlikely to be adopted voluntarily. If these sources are preferred from a social point of view, based on a full cost accounting that includes the environmental costs of alternative fuels, some mechanism for inducing private adoption would be required.

An alternative to reducing NOx emissions through reductions in fuel consumption is to remove NOx from vehicle exhaust through the use of catalytic converters. However, the continued effectiveness of these devices requires inspection and maintenance, and existing vehicle inspection programs have recently been subject to criticism for failure to provide consumers with incentives to maintain vehicles to minimize emissions (Hubbard, T. 1997, 1998).

For stationary sources, emissions from fossil fuel consumption can be reduced by reducing output (e.g., reducing the amount of electricity generated), or by switching to alternative fuels (e.g., nuclear or renewable sources such as hydroelectric power). To avoid shortages, reductions in electricity output would have to be accompanied by reductions in demand, either through price increases or other energy conservation measures. As with gasoline demand, the effectiveness of these programs depends on how responsive consumers are to electricity price increases and incentives for conservation (Silk and Joutz 1997; Wirl 1997). Alternatively, emissions can be reduced through the use of pollution control equipment such as flue-gas desulfurization equipment (scrubbers).

Since there are a number of different ways in which stationary or point sources of NOx can be reduced, cost-effective policies must have the flexibility to allow firms to achieve reductions with the least cost. This type of flexibility is not provided when regulations mandate the installation of certain pollution control devices (e.g., scrubbers). As a result, technology standards of this type do not achieve emission reductions at least cost. Fullerton et al. (1997) estimated that the cost of compliance under a “forced scrubbing” policy is almost five times the minimum that is possible under the Clean Air Act Amendments. Increased flexibility can be provided through the use of emission taxes, performance standards, or tradable permits (Baumol and Oates 1988; Burtrow 1996; see related discussion in Chapter 8). However, in designing flexible policies, the impact of other market distortions, such as imperfect competition or public utility regulation, must be considered. Failure to account for these distortions can result in flexible policies that are actually less economically efficient than more rigid regulations (Besanko 1987; Fullerton et al. 1997).

To date, policies designed to reduce NOx emissions have stemmed not from concerns about excess nutrient loadings to waterbodies, but rather from the other environmental impacts of NOx emissions. For example, NOx is a precursor to the formation of ground level ozone or photo-

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

chemical smog (NRC 1991a; U.S. Congress 1991). Ozone is formed when nitrogen oxides and volatile hydrocarbons react in the presence of sunlight. In addition, NOx is thought to be a contributor to acid rain (NRC 1986). Because of concerns about the health effects of ozone, considerable attention has been focused on efforts to reduce NOx emissions. While not designed specifically to reduce nutrient loadings to waterbodies, these efforts can be expected to have eutrophication-related benefits as well.

Concerns about the transboundary nature of ground level ozone led in 1995 to the formation of the Ozone Transport Assessment Group, with representatives of 37 eastern states, the District of Columbia, Environmental Protection Agency (EPA), and stakeholder groups. The Ozone Transport Assessment Group recommended the need for further NOx reductions to reduce ozone, and, in response, EPA finalized the NOx State Implementation Plan Call in 1998. This regulation limits summer NOx emissions for 22 states and the District of Columbia, and requires states to amend their State Implementation Plans to ensure that NOx budgets are met. As part of this, EPA advocated the adoption of a nitrogen trading program. EPA also noted the potential need for Federal Implementation Plans if states fail to meet their obligations under the State Implementation Plan provisions. The 1990 Clean Air Act Amendments required additional NOx control as well. Under the Amendments, both existing and new or modified sources are required to meet certain technology standards, which differ depending on whether the facility is located in an area that meets the current ozone standards. As noted above (Chapter 8), in the absence of other market distortions, technology standards are generally not cost-effective policies, since they do not allow firms flexibility to meet emission reduction goals in a least cost way. In addition, since these regulations target summer emissions, their impact on atmospheric deposition of nitrogen is limited to that period. Efforts to control emissions on a year-round basis are necessary for eutrophication-reduction benefits, particularly because of time delays between when nitrogen is deposited onto a watershed and when it is exported downstream to estuaries.

EPA has also sought further reductions in NOx emissions from new or reconstructed sources. In September of 1998, EPA was forced to finalize a standard for fossil-fuel fired utilities and industrial boilers for which construction or modification was begun after July 9, 1997. EPA projects that this standard will reduce NOx emissions from new sources by approximately 42 percent (EPA 1999c).

Federal initiatives have also had a significant impact on motor vehicle emissions of NOx. The effect comes through regulations relating both to fuel economy and to tailpipe emissions. As noted above, the Corporate Average Fuel Economy program was created to establish vehicle manufacturers’ compliance with fuel economy standards set by Congress in

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

1975 (EPA 1991c). Manufacturers’ cars and light trucks must meet minimum miles per gallon standards or face monetary damages from the Department of Transportation (see Section 508 of the Motor Vehicle Information and Cost Savings Act). The Corporate Average Fuel Economy values are sales-weighted averages of fuel economy test results. In addition, motor vehicle emissions standards (i.e., limits on allowable grams of emissions per mile) are set by the Clean Air Act. The current standard for NOx for cars is 0.4 grams per mile (EPA 1994), with a higher standard for light duty trucks. EPA’s Tier 2 Report to Congress found the need for more stringent standards in order to meet and maintain the National Ambient Air Quality Standards for both ozone and particulate matter (EPA 1998a).

In summary, atmospheric sources of nitrogen constitute a significant (in some cases, the major) source of nutrient loadings to many estuaries. There are a number of federal and regional initiatives currently under way that are designed to reduce emissions of NOx from both stationary and mobile sources. The impetus for these policies has come primarily from concerns about the contribution of NOx to other pollution problems, such as ground level ozone and acid rain. Nonetheless, to the extent that these policies are effective in reducing NOx emissions, they will reduce eutrophication as well. This additional benefit of NOx emission reductions strengthens the case for stringent NOx control. However, controls that target only summer emissions will be less effective in reducing atmospheric deposition and eutrophication than year-round controls. A recognition of the importance of atmospheric deposition as a nitrogen source to coastal and other water bodies would provide a rationale for year-round controls.

URBAN SOURCES

Urban sources of nutrients can be significant in some watersheds and coastal water bodies. These urban sources, and particularly wastewater discharges, were thoroughly discussed in an earlier NRC report (NRC 1993a). Therefore, in this report we only briefly discuss the control of these discharges.

Urban Point Sources
Treated Municipal Waste

Standards for treated municipal wastewater set goals for biochemical oxygen demand and total suspended solids. In most cases, these goals are achieved through biologically-based secondary treatment processes.

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

However, the 1977 Clean Water Act recognized the argument made by coastal cities that these effluent standards might be too high for settings where ocean currents disperse pollutants and result in minimal oxygen depletion. For such coastal systems, nutrient releases are of much more significance than biological oxygen demand. Thus, Section 301(h) of the Clean Water Act established a waiver process by which municipalities could avoid constructing full secondary treatment facilities if, on a case-by-case basis, they could demonstrate compliance with a strict set of pollution control and environmental protection requirements (NRC 1993a). Some cities, such as San Diego, have been able to use the waiver process. Others, such as Boston, have not.

The goal of secondary treatment is primarily to reduce solids and organic oxygen demand (Table 9-4). Communities that have bans on phosphate detergents typically enjoy a reduction of approximately 32 and 39 percent on total phosphorus and orthophosphate concentrations, respectively, in domestic wastewater (WEF 1998). Biologically-based secondary treatment typically reduces total nitrogen by approximately 31 percent and total phosphorus by approximately 38 percent (NRC 1993a), although national survey data indicate a wide range may be observed in practice (zero to 63 percent and 10 to 66 percent, respectively, for total nitrogen and total phosphorus) (NRC 1993a). Hence, additional (tertiary) treatment for removal of nutrients may be required for nutrient control. Although less common, and rare in coastal areas, tertiary treatment is

TABLE 9-4

Constituent

Before Sedimentation

After Sedimentation

Biologically Treated

Total solids

800

680

530

Total volatile solids

440

340

220

Suspended solids

240

120

30

Volatile suspended solids

180

100

20

Biological oxygen demand

200

130

30

Ammonia nitrogen as nitrogen

15

15

24

Total nitrogen as nitrogen

35

30

26

Total nitrogen generation (kg/cap-yr)

3.4-5.0

 

 

Soluble phosphorus*

7

7

7

Total phosphorus*

10

9

8

*Before ban on phosphate detergents.

TABLE 9-4 Approximate composition of average domestic wastewater, mg l1 before and after sedimentation after biological treatment, showing relative reductions in components (Viessman and Hammer 1998).

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

implemented in many locations in the United States. This usually takes the form of additional phosphorus removal in freshwater systems and nitrogen removal for nitrogen-limited coastal systems.

As described in NRC (1993a), nitrogen removal may be accomplished by an extension of the conventional biological system to incorporate the biochemical processes of nitrification and denitrification. Nitrification is the oxidation of ammonia and organic nitrogen to nitrate nitrogen. The process is mediated by the activity of a specialized class of bacteria that can be grown in conventional activated sludge biological systems by extending the biological solids residence time resulting in more complete biodegradation of organic matter. Nitrogen removal is subsequently obtained by denitrification whereby the nitrate nitrogen is reduced to nitrogen gas and then released into the atmosphere.

Biological phosphorus removal can be accomplished through the selection of high phosphorus content microorganisms, resulting in a greater mass of phosphorus in the excess biological solids removed. Biological phosphorus removal systems are more capital cost-intensive and less operations and maintenance cost-intensive than alternative chemical phosphorus removal systems, and their efficiency can vary depending on a number of factors. Consequently, biological phosphorus removal systems typically incorporate some degree of chemical addition (usually for polishing). Additional physico-chemical mechanisms for nutrient removal are also summarized in NRC (1993a).

Depending on the process employed, up to 97 percent of total nitrogen and 99 percent of total phosphorus may be removed from the waste stream (Table 9-5). Biological treatment is more costly both from a capital and from an operational point of view, and is implemented only for water-quality limited water bodies for which municipal loadings constitute an important nutrient source (e.g., Tampa Bay for nitrogen, the Potomac Estuary for phosphorus, and the Chesapeake Bay for both). Effects on eutrophication can be dramatic, although as for most loading reduction practices, several years may be required for the effects to become evident.

Treated Industrial Waste

Industries that discharge directly to receiving waters are required to meet the same EPA National Pollutant Discharge Elimination System requirements as municipalities. Nitrogen concentrations vary widely depending on the industry (Table 9-6), with most of the nitrogen in the form of organic nitrogen (WEF 1998). The seafood industry, typically located in the coastal environment, can have high concentrations of total nitrogen in its waste stream. Phosphorus concentrations are too dependent upon the particular source to permit generalization in a table. Rela-

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

TABLE 9-5

 

Conventional Primary (%)

Chemically Enhanced Primary (CEPT) (%)

Conventional Biological Secondary Preceded by Conventional Primary (%)

Biological Secondary Preceded by CEPT (%)

Nutrient Removal Preceded by Conventional Biological Secondary and Conventional Primary (%)

Reverse Osmosis (%)

 

Low Dose

High Dose

Suspended Solids

as mg l−1 TSS

41-69

60-82

86-98

89-97

88-98

94

99

BOD

as mg I−1 BOD5

19-41

45-65

67-89

86-98

91-99

94

99

Nutrients

as mg l−1 TN

2-28

26-48

0-63

NA

NA

80-88

97

as mg l−1 TP

19-57

44-82

10-66

83-91

83-91

95-99

99

TABLE 9-5 Typical removal capability percentages for a range of wastewater treatment processes (NRC 1993a). NA = not available; BOD = biological oxygen demand; CEPT = chemically enhanced primary treatment.

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

TABLE 9-6

 

Total Nitrogen

Industry

Mean (mg/L)

Range (mg/L)

Meat Packing

 

52-115

Fish and Seafood

Catfish

34

21-51

Crab

100

62-147

Shrimp

222

168-276

Tuna

38

 

Combined Poultry

 

15-300

Fruit and Vegetable Processing

Apples

3.9

 

Citrus fruits

21

 

Potatoes

5.5

 

Winery Wastewater

20

5-40

Chemical Industries

NH3-N (mg/L)

1270

 

NO3-N (mg/L)

550

 

TABLE 9-6 Nitrogen concentrations in wastewater derived from a range of industries (WEF 1998).

tively few industries employ advanced waste treatment for nutrient removal. The focus at urban industries is often on pre-treatment for targeted pollutants, such as heavy metals or other toxic constituents. The wastewater is then sent to the publicly owned treatment works for further treatment, where tertiary nutrient removal may or may not occur.

Septic Tanks

Septic tanks for individual household treatment serve approximately 29 percent of the U.S. population (Novotny and Olem 1994) and often result in wastewater discharged directly to the groundwater system. Septic tanks in the riparian zone of a coastal waterbody (e.g., from homes along a beach) will discharge directly to the affected waterbody. Discharge from septic tank systems is commonly estimated as 280 liters per capita per day (l cap−1 day−1) with typical effluent concentrations of 40 to 80 mg l−1 for total nitrogen and 11-31 mg l−1 for total phosphorus (Novotny et al. 1989). Although a well-functioning septic system typically removes most organic pollutants and phosphorus, the ammonia is rapidly oxidized in the soil to nitrate-nitrogen that is not adsorbed by soils and readily moves into the groundwater (Novotny et al. 1989). Hence, septic

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

systems can contribute significant quantities of nitrate to riparian zones of coastal waters in addition to their contributions upstream in the watershed.

Improvements to septic tank design to provide for nitrification-denitrification can reduce nitrogen loadings. For instance, whereas conventional septic systems remove 10 to 45 percent of total nitrogen, anaerobic up-flow filters remove 40 to 75 percent, and recirculating sand filters remove 60 to 85 percent (EPA 1993a). These options typically involve a recirculation loop or tanks in series, and it is possible to retrofit conventional systems to improve denitrification performance. Other factors that affect the degree of nitrogen removal include temperature and the density of the soil in the septic tank fields.

Urban Diffuse Source Discharges

Urban diffuse nutrient sources include both runoff from streets and storm sewers and combined sewer overflows. Because of the enormous volume of runoff associated with rainfall, control of low concentrations of nutrients in stormwater runoff may lead to improvements in nutrient levels. In urban areas, overflows in older cities with combined sewer systems have the potential for large, concentrated loadings at overflow points. A mixture of stormwater and dry-weather sewage, combined sewage generally contains higher nutrient concentrations than does stormwater (Table 9-7). Hence, it is usually logical to control combined sewer overflows before urban stormwater, although both types of discharges are regulated under National Pollutant Discharge Elimination System regulations (stormwater currently only for cities of greater than 50,000 population).

Sources of nutrients in urban runoff include automobiles, atmospheric deposition (Chapter 5), erosion, deterioration of pavement and structures, fertilizer application, and miscellaneous wastes. Excessive fertilizer application can create especially high loads. For example, residential stormwater runoff is thought to contribute as much as 30 percent of total nitrogen loads to Sarasota Bay, Florida, largely related to excessive use of lawn fertilizers (Camp, Dresser, and McKee, Inc. 1992; Sarasota Bay National Estuary Program 1995).

A very large number of control options exist to help manage urban nonpoint source runoff (Schueler 1987; Camp et al. 1993; EPA 1993a; NRC 1993a; Urbonas and Stahre 1993; Horner et al. 1994; Novotny and Olem 1994; ASCE and WEF 1998), and their efficiency for nutrient removal varies widely. Passive treatment controls (typically structural options) include:

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

TABLE 9-7

 

 

 

Concentrations (mg/L)

 

 

Constituent

Reference

Source

Median (50th Percentile)

90th Percentile

Coefficient of Variation

TKN

a

Stormwater

1.50

3.30

0.50-1.00

NO2-N+NO3-N

a

Stormwater

0.68

1.75

0.50-1.00

Total N

a

Stormwater

2.20

5.00

0.50-1.00

TKN

b

Combined sewage

6.50

10.30

0.60

NH3-N (ammonia)

b

Combined sewage

1.90

3.90

0.80

NO2-N (nitrite)

b

Combined sewage

0.10

0.10

0.60

NO3-N (nitrate)

b

Combined sewage

1.00

4.50

0.50

Total N

b

Combined sewage

7.60

14.90

0.60

Soluble P

a

Stormwater

0.12

0.21

0.50-1.00

Total P

a

Stormwater

0.33

0.70

0.50-1.00

Ortho-P

b

Combined sewage

0.80

1.10

0.40

Total P

b

Combined sewage

2.40

7.90

0.70

TABLE 9-7 Nutrient characteristics of urban runoff and combined sewage. Definitions: TKN = Total Kjeldahl Nitrogen = organic-N + NH3-N. Total nitrogen = TKN + NO2-N + NO3-N. Coefficient of variation = standard deviation/mean. (a) is EPA 1983 and (b) is Driscoll and James 1987.

  • vegetated areas (filter strips, swales, riparian vegetation);

  • extended detention basins (dry between storm events);

  • wet ponds (continuously filled);

  • infiltration devices (ponds, trenches, swales, porous pavement);

  • filters (biofilters, compost filters, sand filters); and

  • constructed wetlands.

Pollutants in particulate or solid form are most amenable to treatment (e.g., nitrogen or phosphorus organic forms). For example, retention ponds (“wet ponds” with continual water storage) might remove 30 to 40 percent of total nitrogen and 50 to 60 percent of total phosphorus, with removal increasing as the dissolved forms of nitrogen and phosphorus

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

decrease (EPA 1983) (Table 9-8). Extended detention facilities dry out between storms and are not effective for removal of dissolved nutrients by biological mechanisms. However, such facilities can sometimes serve multi-purposes as recreational areas when dry. Design guidelines for storage and other passive treatment control devices are provided in references such as Schueler (1987), Camp et al. (1993), Urbonas and Stahre (1993), and American Society of Civil Engineers and Water Environment Federation (1998). Additional information may be found in Novotny and Olem (1994), EPA (1993b), Debo and Reese (1995), and Novotny (1995).

Caution should be exercised when comparing urban BMPs on the basis of removal efficiencies. It is often found that while influent quality varies considerably, effluent quality exhibits a much smaller range (Strecker et al. 1999). Thus, high removal efficiencies may result purely from the fact that influent concentrations are high. Hence, BMPs might be better characterized simply by effluent quality. Alternatives for determining urban BMP performance effectiveness, based on a review of the most complete data set currently available, are provided by Strecker et al. (1999).

Natural wetlands are protected waters by law in the United States and generally cannot be used for waste treatment, except sometimes for a “polishing” purpose. Nonetheless, they provide many functions that enhance water quality (NRC 1991b), including acting as a sink for phosphorus, and facilitating denitrification by converting nitrate to nitrogen gas. Their capacity for nutrient removal can be considerable (Mitsch and Gosselink 1986). Hence, protection of coastal wetlands and tidal exchange is an important water quality consideration for coastal waters. Many factors can act to impair the natural functions of wetlands, including the drainage of wetlands for additional cropland, overgrazing, construction of highways, channelization of an adjoining waterway, deposition of dredged material, and excavation for ports and marinas (EPA 1993a).

TABLE 9-8

Type of Pond

Total Suspended Sediments

Nitrogen

Phosphorus

Extended detention basins

70-80

0 (dissolved)

20-30 (total)

0 (dissolved)

20-50 (total)

Retention ponds

70-80

50-70 (dissolved)

30-40 (total)

50-70 (dissolved)

50-60 (total)

TABLE 9-8 Comparison of nutrient removal percentages from well-designed extended detention basins and retention ponds (EPA 1983).

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

Measures for protection include: acquisition, protective zoning, application of water quality standards to wetlands, education and training, inclusion in comprehensive watershed planning, and restoration. Restoration measures include: maintenance of a natural hydrologic regime, restoration of native plant species, reduction of nonpoint source or other pollutant inflows, and maintenance of historic wetlands sites (EPA 1993a).

Constructed wetlands function similarly to storage devices, and their nutrient removal effectiveness depends upon the characteristics of the inflow as well as hydraulic properties (e.g., avoidance of short-circuiting) and vegetation types (Schueler 1992; Strecker et al. 1992; Urbonas and Stahre 1993; Strecker 1996). Schueler (1992) indicates projected removal rates for total phosphorus and total nitrogen on the order of 40 to 60 percent and 20 to 30 percent, respectively. Actual monitoring of constructed wetland removal efficiencies yields a very large variability (e.g., from −4 percent to 62 percent for NH3 and −4 percent to 90 percent for total phosphorus) (Strecker et al. 1992; Urbonas and Stahre 1993; Strecker 1996). Nutrient removal efficiency depends strongly on the loading rate, percentage solid material, site conditions (such as soils), and hydraulic conditions that might lead to short-circuiting or scour—which might account for occasional negative removal efficiencies. Furthermore, Harper et al. (1988) point out that systems designed for removal of nutrients should avoid long detention times and stagnant conditions, both of which can decrease oxidation reduction potential and pH and reduce the efficiency of phosphorus removal. There is no clear advantage of constructed wetlands over storage ponds for nutrient control apart from the public appeal of wetland systems (Urbonas and Stahre 1993). Schueler (1992) presented extensive design guidelines for constructed wetlands.

Maintenance is a critical concern for all stormwater management facilities. When maintenance is poor, both quantity and quality control effectiveness can be greatly diminished. It is important that operation and maintenance costs be included during the planning and design of BMPs. Robustness of a design is also a factor (ASCE and WEF 1998). High robustness implies that when all the design parameters are correctly defined and quantified, the design has a high probability of performing as intended. For instance, wet retention ponds have a high robustness for removal of particulates and solids, but only a low to moderate robustness for removal of dissolved constituents (ASCE and WEF 1998). The robustness of extended detention basins and wetlands is moderate to high for particulates. Wetlands have a low-moderate robustness for removal of dissolved constituents while extended detention has none to low.

An additional number of structural controls exists for combined sewers, most of which are designed to store sewage during a storm for eventual treatment at the treatment plant or to divert only the cleanest

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

water to receiving waters during a storm event (WPCF 1989; Moffa 1990; EPA 1992, 1993b). The use of structural controls for combined sewer overflow management often involves significant costs when applied in dense, highly developed, older urban areas.

Most urban BMPs are designed to control parameters other than just nutrients, such as heavy metals, solids, and oxygen demanding constituents. Hence, their design will also be predicated upon removal of these other constituents, as well as for management of stormwater quantity.

A large number of nonstructural BMPs are available (ASCE and WEF 1998). In general, nonstructural BMPs emphasize source controls and “good housekeeping”. Many such options are routinely implemented as part of stormwater master plans in cities, although their effectiveness has not generally been quantified, especially for nutrient control. Examples include:

  • public education;

  • use of alternative products;

  • vehicle use reduction;

  • storm drain system signs (e.g., “dump no waste, drains to stream”);

  • spillage control;

  • control of illicit connections to storm sewers;

  • street cleaning and catchbasin cleaning;

  • general maintenance;

  • control of leaking sanitary sewers; and

  • land use controls.

Overall, post-construction monitoring data is lacking so there is little concrete evidence of the effectiveness of urban BMPs. Management practices are often implemented under the assumption that they will be effective in reducing the load of targeted pollutants, without any follow up on how well they actually perform. Hence, good design information is lacking. In response to the need to assemble and evaluate available effectiveness data, the American Society of Civil Engineers is conducting such a study for EPA (Strecker et al. 1999), due to be completed sometime in 2000 (Box 9-1). When finished, this study will provide a definitive statement about the effectiveness of urban BMPs.

OTHER MITIGATION OPTIONS

Regional Stormwater Control Facilities

Location as well as type of BMPs play an important role in control of nonpoint source runoff. For example, stormwater and combined sewer

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

BOX 9-1
National Stormwater Best Management Practices Database

In response to the need for a centralized, easy-to-use, scientifically-sound tool for assessing the appropriateness of stormwater runoff BMPs under various conditions, the Urban Water Resources Research Council of the American Society of Civil Engineers has entered into a cooperative agreement with the EPA to develop a National Stormwater BMP Database (http://www.bmpdatabase.org). The long-term goal of the project is to promote technical design improvements for BMPs and to better match their selection and design to the local stormwater problems being addressed. The database, which was released in late 1999, contains data from BMP evaluations conducted over the past 15 years (ASCE and EPA 1999). Database updates will be made available as additional BMP evaluation data are gathered.

overflow controls can be distributed at critical points throughout the watershed, such as at discharge locations. Another option is to collect nutrient-laden stormwater and control/treat it at a more centralized or downstream location. Such a regional facility may have advantages such as lower capital costs, reduced maintenance, and greater reliability (Stutler et al. 1995). Alternatively, a regional collection system may be better from the standpoint of the location of the receiving water discharge. For instance, the City of San Francisco collects combined sewage in large storage tanks placed along the Bay-side of the city. The combined sewage is then pumped across the dividing hills for treatment and discharge into the Pacific Ocean in the southwest corner of the city. In this way, combined sewer overflow loadings to San Francisco Bay are avoided, except for very high storm events.

Hydrologic/Hydraulic Alterations in the Watershed

The history of human development is one of encroachment upon wetlands and waterways, and loss of wetlands in coastal areas is substantial. An outstanding example is the Kissimmee River system of central Florida, which drains to Lake Okeechobee and ultimately, through the Everglades system to Florida Bay. Although not a coastal system, Lake Okeechobee has reacted to loss of upstream wetlands and attendant nutrient filtering with massive eutrophication problems since flood control facilities that straighten, narrow, and reduce the length of the river were built in the 1960s (Koebel 1995; SFWMD 1998; Koebel et al. 1999). The South Florida Water Management District is now working with the Corps

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

of Engineers to restore wetlands for purposes of phosphorus removal from the predominant inflow, the Kissimmee River. Restoration of the wetlands themselves, as well as enhancement of hydraulic connections, can provide a nutrient removal function that helps mitigate the overall trend of increased loadings from tributary watersheds and growing urban areas. Restoration of non-tidal wetlands as a management strategy has received much attention for the Mississippi Basin (NOAA 1999b), and is also a part of the Chesapeake Bay Program strategy.

Circulation Enhancement

Coastal developments, bridges, jetties, causeways, breakwaters, and flood control structures often lead to altered circulation patterns in an estuary. Reduced ocean exchange leads to lack of flushing, longer residence times, and more time for eutrophication processes to proceed. An extreme example is finger canals (Figure 9-4) that support extensive residential development, a pattern that has now been prohibited in most states. Finger canals lead to dead-ends and stagnant water, ripe for eutrophication and other pollution hazards. In many cases, circulation can be enhanced by tidal pumping promoted through new connectivity via culverts, pipes, and bridges. Small differences in tidal amplitude at multiple outlets, coupled with frictional resistance that depends on the flow direction, can create a net circulation through a looped system. Hence, where reduced flushing and increased residence time can contribute significantly to eutrophication problems, engineering alternatives may exist for mitigation through hydraulic controls. General guidance on flushing characteristics of estuaries and implications for mixing, residence times, and eutrophication potential can be found in references such as Officer (1976), McDowell and O’Connor (1977), Fischer et al. (1979), and Kjerfve (1988).

In Situ Biological Treatment Options

Eutrophication and other effects of nutrient over-enrichment in a waterbody are affected in part by the grazing activity of animals—both zooplankton and benthic filter feeders—on phytoplankton. The abundance of zooplankton that feed on phytoplankton is in part regulated by the abundance of zooplanktivorous fish, and these in turn are regulated in part by the abundance of higher predators (Carpenter et al. 1985). To some extent, nutrient problems in lakes can be managed by managing the populations of predatory fish, with the effect cascading down to zooplanktivorous fish, zooplankton, and then phytoplankton. The same principles apply to estuaries and coastal waters (Ingrid et al. 1996). However,

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

FIGURE 9-4 Finger canals in the Port Charlotte, Florida area, in 1974. Systems of canals with dead-ends have reduced circulation and flushing and can lead to accumulation of pollutants and nutrients, with resultant eutrophication problems (photo by W. Huber).

whereas lakes can be considered relatively closed systems with regard to fish populations, fish readily migrate between estuaries and coastal waters. While fishery practices in coastal areas may have impacts on nutrient enrichment in coastal areas, it would be exceedingly difficult to manage this through manipulations of fishery populations.

Benthic filter feeders such as oysters, mussels, and many species of clams can have a major influence on phytoplankton populations in coastal waters (Lucas et al. 1997; Meeuwig et al. 1998). In fact, it has been suggested that eutrophication of Chesapeake Bay is due in part to loss of oyster populations there: when oyster populations were high in the bay, they may have filtered the water as frequently as once per day on average, which would have been a significant control on phytoplankton abundance. Currently, oysters are believed to filter the water of Chesapeake Bay on average only once per year (Newell 1988). The data behind this

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

speculation are sparse, but the logic is sound, and such grazing activity currently is a major factor regulating primary production in San Francisco Bay (Lucas et al. 1998) and in many small estuaries in Prince Edward Island, Canada (Meeuwig et al. 1998). Manipulation of benthic filter feeding organisms deserves further study as a possible mechanism for partially managing nutrient loads in estuaries.

Control of Bloom Incidence through Nutrient Reductions

Options for control of harmful algal blooms (HABs) include prevention, control, and mitigation (Boesch et al. 1997) (Box 9-2). HAB algae, just like all plants, require certain major and minor nutrients for their nutrition. These can be supplied either naturally or through human activities, such as pollution. As described in Chapter 4, a strong case has been made in several areas of the world that increases in pollution are linked to increases in the frequency and abundance of red tides (e.g., Smayda 1990; Okaichi 1997). It follows that a reduction in pollution can sometimes lead to a decrease in HAB frequency or magnitude. It should be emphasized, however, that it is exceedingly difficult to predict with any certainty what the effect of pollution control strategies will be on HAB incidence, except in situations where the pollution loading is massive (e.g., in Tolo Harbour or the Inland Sea of Japan [Box 4-2]) where it is now clear that increasing pollution was associated with increasing algal biomass, and therefore with more red tides/HABs. Given the high pollution loads to many estuaries and coastal waters, there is little doubt that these inputs contribute to some of the harmful blooms that occur. What is not clear, however, is the nature of that linkage—how much, and in what specific ways, the pollution must change before the number of HABs will decrease to “acceptable” levels. What is needed from a management perspective is the development of quantitative relationships between nutrient loading parameters and HAB incidence, such as the relationship between nitrogen:phosphorus ratios and dinoflagellate abundance described by Hodgkiss and Ho (1997) for Tolo Harbour, Hong Kong. However, the validity of such a relationship needs to be evaluated more thoroughly and if found to be robust, expanded to include other watersheds and hydrographic systems before it can be used to justify major policy decisions on water quality options in any particular region.

In general, the argument can be made that to reduce HAB incidence in an area, strict pollution control regulations should be instituted. However, a reduction in pollution loading will not lead to a complete absence of red tides/HABs—it is likely to reduce red tides in general, but some toxic species that thrive in relatively clean waters may find the new conditions suitable for growth. Given these uncertainties, it is difficult to jus-

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

BOX 9-2
Can Harmful Algal Blooms be Controlled with a Natural Parasite?

Could naturally occurring parasites be tapped as a biological tool to help control harmful algal blooms? New evidence is emerging that this might be possible (Delgado 1999). During one red tide covered by a paralytic shellfish poison-producing dinoflagellate called Alexandreum catenella in Catalonia, Spain, scientists noticed that a decline in the bloom corresponded with the presence of unknown round cysts. Further work showed that these cysts infected the A. catenella cells. They named the new organisms “diablillo parasites” (a Spanish word related to devil) and conducted further research to understand how they attacked the algae. The new diablillo parasite develops rapidly, so hundreds of new parasites per infected host can grow in about the 48 hours it takes for the host to reach maturity. Additional work continues to see if the parasite could be used to control harmful algal blooms in the natural environment. One feature of the parasite is that it only infects motile cells, and not the quiet cell stages of the hosts, and this could limit its ability to totally destroy problem algae populations in natural settings. Scientists continue to work to culture the parasite on non-toxic and widespread dinoflagellate hosts, which might facilitate its use in different geographic areas.

tify major pollution reduction programs solely on the basis of an expected reduction in HABs. Instead, reductions of nutrient inputs into coastal waters should be rigorously pursued as a key element of general estuarine and coastal management. The potential benefits of reductions of nutrient loadings in terms of decreased frequency and severity of HABs should be one of several considerations driving pollution policy decisions in estuarine and coastal management programs, but it should not be the sole justification.

Marketable Permits

Prior to 1990, marketable permits played only a minor role in environmental policy design, but the 1990 Clean Air Act Amendments promoted the use of marketable permits for sulfur dioxide emissions and provided an impetus for increased attention to this policy instrument. There are now a number of trading programs in place. As noted earlier, EPA advocated the use of a tradable permit system for reductions in NOx emissions. In addition, several watersheds are experimenting with trading programs as a means of meeting water quality goals at lower cost. For example, the State of Connecticut estimates that trading will reduce the

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

state’s cost of meeting its target level of nitrogen removal by more than $200 million (CDEP 1998).

Although tradable permit systems have the potential to reduce the costs of achieving water quality goals, they have drawbacks that could limit their use. These include the administrative burden of operating a trading market (if it is publicly run) and the difficulty of establishing appropriate trading ratios when the environmental impact of a given discharge level varies by site.

NEXT STEPS FOR SOURCE REDUCTION

Much research has been conducted seeking agricultural, forest, and urban management practices that reduce the potential for nonpoint nutrient export. Yet we have not been successful at implementing cost-effective remedial measures in certain critical areas such as animal waste management. In most cases we know how to minimize nutrient export and input to coastal waters (the science is there), so that the major barriers to implementation now involve overcoming economic constraints, societal pressures, and political forces. New mechanisms to encourage implementation of BMPs, and remedial strategies in general, are necessary.

A critical component for facilitating widespread BMP implementation is by funding of cost-share programs and development of alliances among stakeholders. Stakeholder alliances encourage collaborative rather than adversarial relationships among affected groups.

There is a considerable scientific basis for reduction of nutrient releases from agriculture sources (e.g., enzyme adjustments for poultry and hogs to promote efficiency of phosphorus uptake; genetically-engineered corn to reduce unavailable phosphorus content). But there is a tendency on the part of farmers to over feed and urban dwellers to over fertilize—that is, to provide more nutrient supplements than are scientifically justified. Agricultural practices that reduce nutrient export must continually be communicated to end users in an effort to overcome the intuitive but false premise that “more is better.” Many approaches can help people manage fertilizer application. The most fundamental principle is to supply only the nitrogen and phosphorus needed to meet the needs of the current crop, and to apply them in synchrony with crop use.

Manure generated from confined animal feeding operations has a significant potential to discharge nutrients to receiving waters. Many options are available to mitigate this source. Entrepreneurial activities should be encouraged to take advantage of management practices that require more than just field-scale activities (e.g., transport of manure from one location to another).

Methods for managing nitrogen and phosphorus transport may differ

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

because nitrogen losses can occur from any location in a watershed via subsurface pathways, while phosphorus loss occurs most often in areas prone to surface runoff. Hence, remedial strategies for nitrogen may be applied to the whole watershed, whereas the most effective phosphorus strategy would be a combination of stringent measures at the most vulnerable sites to minimize loss of phosphorus in surface runoff with simple measures over the whole watershed to avoid excessive nutrient buildup, and thereby limit losses in subsurface flow. Extreme events must also be considered when designing phosphorus management strategies because one or two extremely high flows may be responsible for the bulk of annual phosphorus export.

There is a serious lack of post-implementation monitoring to assess the effectiveness and long-term viability of BMPs. Monitoring programs should be established to determine the long-term effectiveness of BMPs on nonpoint nitrogen and phosphorus reduction. A database of effective measures and design parameters should be maintained by appropriate federal agencies (e.g., EPA for urban areas and U.S. Department of Agriculture [USDA] for agricultural areas). The cost of implementing control measures is an important planning consideration, and databases of BMP effectiveness should also include relevant cost data. Economic data is also needed to help determine the economic benefits of management strategies and to see implementation costs in relation to the relative costs of different problems caused by nutrient over-enrichment.

The Clean Air Act may be as important as the Clean Water Act in protecting the nation’s coastal waters from nitrogen pollution. Air pollution policy for nitrogen control is driven mainly by concerns other than nutrient over-enrichment (e.g., smog and human health, ozone, acid rain, global warming), but addressing these concerns can yield some nutrient-related benefits. Thus the effects of nitrogen on coastal waters should be considered in the formulation of air pollution policy. While eutrophication reduction is an additional benefit of air pollution control, policymakers will need to recognize that year-round emission control is necessary to affect eutrophication, not just summer controls as are used to combat smog. Also, the full range of nitrogen emissions need attention, not just NOx, and thus ammonia-based scrubbers are inappropriate.

Although biologically-based secondary treatment of municipal wastewater is practiced at many U.S. cities and has some indirect nutrient benefits, point source discharges from publicly owned treatment works can still constitute a significant source of nutrients to coastal waters. In general, nutrient reduction strategies should address the least cost solutions first. Advanced waste treatment options of point sources for additional nutrient removal are often cheaper (on the basis of dollars per kilogram of nitrogen or phosphorus removed) than is control of nonpoint sources and

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
×

should be examined carefully when planning strategies for nutrient reduction.

The larger the tributary area to the coastal waters, the more important is source control in the control of coastal nutrient over-enrichment. However, managers have options beyond source control. For coastal waters with smaller tributary areas, mitigation strategies such as enhancement of coastal wetlands might be a possibility. Most nutrient management schemes rely on a combination of measures. In all cases, maintenance of natural systems, including water column biota and shellfish, is important. Economic incentives, such as tradable permits, have potential to be used to facilitate the design of comprehensive cost-effective management strategies.

Suggested Citation:"9 Source Reduction and Control." National Research Council. 2000. Clean Coastal Waters: Understanding and Reducing the Effects of Nutrient Pollution. Washington, DC: The National Academies Press. doi: 10.17226/9812.
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Environmental problems in coastal ecosystems can sometimes be attributed to excess nutrients flowing from upstream watersheds into estuarine settings. This nutrient over-enrichment can result in toxic algal blooms, shellfish poisoning, coral reef destruction, and other harmful outcomes. All U.S. coasts show signs of nutrient over-enrichment, and scientists predict worsening problems in the years ahead.

Clean Coastal Waters explains technical aspects of nutrient over-enrichment and proposes both immediate local action by coastal managers and a longer-term national strategy incorporating policy design, classification of affected sites, law and regulation, coordination, and communication.

Highlighting the Gulf of Mexico's "Dead Zone," the Pfiesteria outbreak in a tributary of Chesapeake Bay, and other cases, the book explains how nutrients work in the environment, why nitrogen is important, how enrichment turns into over-enrichment, and why some environments are especially susceptible. Economic as well as ecological impacts are examined.

In addressing abatement strategies, the committee discusses the importance of monitoring sites, developing useful models of over-enrichment, and setting water quality goals. The book also reviews voluntary programs, mandatory controls, tax incentives, and other policy options for reducing the flow of nutrients from agricultural operations and other sources.

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