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.
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-