Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 149
Wetlands: Characteristics and Boundaries 6 Especially Controversial Wetlands INTRODUCTION The wetlands and associated landscape features discussed in this chapter have been the subject of particular controversy because of their location, their unusual characteristics, or their regulatory status. They include permafrost wetlands, riparian ecosystems, isolated and headwater wetlands, especially shallow wetlands, agricultural wetlands, nonagricultural altered sites, and transitional zones. These areas are the source of many problems related to wetland regulation and delineation; their classification is particularly sensitive to changes in delineation procedures. PERMAFROST WETLANDS Permafrost is soil that has a temperature continuously below 32°F (0°c) for 2 years or more. This definition distinguishes permafrost from seasonal frost. The distribution of permafrost in the United States is restricted to Alaska and a few high alpine areas in the conterminous states. Except at latitudes and elevations so high that there is no summer thaw, permafrost is overlain by a zone of seasonal thaw called the active layer, which typically is 14-79 in. (25-200 cm) thick. Maximum depths of thaw are found where the Climate is warmest and the soils are driest; minimum depths of thaw are found in the coldest and wettest environments. North of the Brooks Range in Alaska, permafrost is generally continuous. In south-central and interior Alaska, permafrost is discontinuous, and it is generally
OCR for page 150
Wetlands: Characteristics and Boundaries found on north-facing slopes and poorly drained valley bottoms. The thickness of permafrost varies from almost 2,000 ft (600 m) in Northern Alaska to about 130 ft (40 m) or less in interior Alaska. The continuous permafrost areas of Alaska are mainly treeless tundra; discontinuous permafrost supports many plant communities, including forests. At the southern limits of permafrost and in low regions, thickening of the active layer can occur readily if the thermal regime changes. Not only a warmer climate, but also fire and clearing of surface-insulating vegetation, can result in thawing of permafrost. Because permafrost is relatively impermeable to water, any change in its proximity to the soil surface can cause hydrologic changes. Relevance of Permafrost to Wetland Formation Permafrost contributes to wetland formation by retarding the downward movement of soil water (Dingman, 1975; Hobbie, 1984). Water retained near the ground surface can saturate the active layer and thus lead to the formation of hydric soils and the growth of hydrophytic vegetation. The presence of permafrost alone, however, is not always sufficient to create a wetland. Wetland formation is most likely where the active layer is shallow, hydraulic gradients are low, and mineral soils have low permeabilities. Under such conditions, saturation to the surface can occur for significant portions of the warm season. Conversely, thick active layers, steep slopes, and coarse-grained soils act against wetland formation in permafrost environments. Permafrost wetlands are sometimes portrayed as uniform. Wetlands in permafrost environments vary, however, from brackish coastal marshes through shallow lakes and ponds to forests. Permafrost wetlands also occur on a variety of land forms ranging from flat coastal plains and river floodplains to steep north-facing slopes and alpine terrain. Soils in these areas can be mineral or organic, and the vegetation ranges from aquatic emergent to scrub-shrub and forest. Dynamics of Permafrost Wetlands Permafrost aggradation can create or restore wetland hydrology on forested sites. This process is especially important where permafrost is discontinuous. Aggradation can occur through primary succession on river floodplains as well as through postfire secondary succession on lowlands and on north-facing slopes of interior Alaska. Succession in these areas passes from hardwoods to spruce (Viereck, 1970; Foote, 1983). With succession, organic matter accumulates, especially in stands of white spruce (Picea glauca) and black spruce (P. mariana) with groundcover composed of feathermosses (Van Cleve et al., 1991). The accumulation of organic matter in turn affects the heat balance of the underlying soil. Dry peat reduces heat gain by the soil during summer, and frozen soil can accelerate winter heat loss because it has a high moisture content (Brown, 1963).
OCR for page 151
Wetlands: Characteristics and Boundaries As a result, mean soil temperature declines when organic matter accumulates during succession. A lower soil temperature reduces the mean rate of decomposition (Fox and Van Cleve, 1983), which contributes to further accumulation of organic matter, particularly in old stands of black spruce (Van Cleve et al., 1983). This process can produce permafrost in primary successional stands on floodplains over periods of 200 years (Viereck, 1970), or on upland sites in only 25-50 years after a fire (Dingman and Koutz, 1974; Van Cleve and Viereck, 1983). Rising permafrost tables increase saturation of the active layer and create or restore wetland hydrology on sites where lateral drainage is weak. With increasing soil moisture, forested sites of interior Alaska tend toward hydrophytic communities characterized by black spruce, ericaceous shrubs, and Sphagnum mosses. Such sites remain wetlands until floodplain processes, fire, or anthropogenic disturbances reinitiate succession. Treeless arctic wetlands share the dynamic nature of forested subarctic wetlands. On the Arctic Coastal Plain, for example, thermokarst lakes (thaw lakes) form, mature, drain, and reform (Carter et al., 1987). These cycles occur over several thousand years and cause lake basins to undergo vegetational succession after drainage (Billings and Peterson, 1980). Various phases of the thaw-lake cycle provide a variety of habitats for shorebirds and waterfowl (Bergman et al., 1977). Other processes include the formation of low-centered frost polygons by ice wedges and thermal erosion of these wedges to form high-centered polygons on the tundra surface (Walker et al., 1980). Microrelief associated with these changing geomorphic features causes a fine-grained mosaic of soils and vegetation to develop on the tundra surface and contributes to the wide variety of tundra wetlands. Disturbance of wetlands in the zone of discontinuous permafrost generally increases the thickness of the active layer. Increased thaw depth can temporarily eliminate wetland hydrology, as is the case after a fire (Van Cleve and Viereck, 1983) or after agricultural clearing (Ping, 1987), or it can increase the wetness of a site, as is common when melting of ground ice with consequent subsidence of the ground surface creates thaw ponds or lakes (Péwé, 1982). In contrast, wetlands in the continuous permafrost of the Arctic are less likely to lose wetland hydrologic characteristics after disturbance because the permafrost, which is both colder and more extensive in the Arctic, is less sensitive to changes in heat flux. Tundra wetlands show a variety of geobotanical features influenced by permafrost processes and span a moisture gradient from lakes to shrub-tussock tundra (Walker et al., 1980; Chapin and Shaver, 1985). Perturbation of wetlands at the drier end of this spectrum generally increases their seasonal depths of thaw and causes ground surfaces to subside, thus forming depressions through consolidation of fine-grained soils with high ice content (Lawson et al., 1978; Lawson, 1986). Depressions of this type in level terrain usually retain moisture, and often become wetlands.
OCR for page 152
Wetlands: Characteristics and Boundaries Regulation of Permafrost Wetlands Many proposals have been made to regulate permafrost wetlands differently from nonpermafrost wetlands. For example, the Food Security Act wetland definition excludes some permafrost wetlands of Alaska (Chapter 3), which has 174.7 million acres (70.8 million ha) of wetland (Hall et al., 1994). Permafrost is in part responsible for this large amount of wetland, although pleistocene glaciation and associated fluvial and lacustrine deposits contribute to Alaska's wetlands (Péwé, 1975). Alaska accounts for one-sixth of the total land area of United States, and it has about 63% of the nation's remaining wetlands (Hall et al., 1994). The regulatory treatment of permafrost wetlands is significant regionally, because of the abundance of wetlands in Alaska, and nationally, because so much of the nation's wetlands are in Alaska. Wetland formation by permafrost is influenced by latitude, topography, and climate, as are other mechanisms of wetland formation. Precipitation and evapotranspiration, for example, vary with latitude and climate in ways that affect many kinds of wetlands. Furthermore, studies of the National Wetlands Working Group (1988) in Canada show that permafrost wetlands have the same functions as other kinds of wetlands. To argue that saturated soils underlain by permafrost cannot be wetlands because they are a phenomenon of climate is akin to arguing that bottomland hardwood forests are not wetlands because they are a result of high river discharge. The sensitivity of permafrost wetlands to altered thermal regimes induced by anthropogenic disturbance or by fire also has been suggested as a reason for treating them as problem wetlands (Ping et al., 1992). Most wetlands are, however, similarly subject to loss or change by natural and anthropogenic forces. Because permafrost wetlands do not differ in their essential characteristics from other wetlands, separate regulatory treatment of them is not justifiable scientifically. Recommendations on permafrost wetlands can be found at the end of this chapter, numbers 1 to 3. RIPARIAN ECOSYSTEMS Land adjacent to a stream or river is often called a riparian zone or riparian ecosystem. The riparian zone is a characteristic association of substrate, flora, and fauna within the 100-year floodplain of a stream or, if a floodplain is absent, a zone hydrologically influenced by a stream or river (Hunt, 1988). Riparian ecosystems are maintained by high water tables and periodic flooding. Examples include bosques of the American Southwest, streamside communities along high-gradient streams of the Pacific Northwest and Rocky Mountains, gallery forests of prairie regions, cove forests of the eastern mountains, and wetlands and adjacent slopes that border streams of humid eastern states (Brinson et al., 1981). Riparian zones, which can be defined several ways, contain or adjoin riverine wetlands and share with them a multitude of functions including surface and
OCR for page 153
Wetlands: Characteristics and Boundaries subsurface water storage, sediment retention, nutrient and contaminant removal, and maintenance of habitat for plants and animals (Chapter 2). Support of Biodiversity Several studies document the importance of riparian ecosystems to regional biodiversity. Ohmart and Anderson (1986) conclude that the greatest densities of breeding birds in North America are found in riparian ecosystems, that more than 60% of the vertebrates in the add Southwest are obligately associated with this ecosystem, and that another 10-20% of the vertebrates are facultative users of streamside vegetation. Mosconi and Hutto (1982) report that in western Montana, 59% of the species of land birds use riparian ecosystems for breeding, and 36% breed only there. Cottonwood and mesquite forests are very high in species richness of migratory birds (Stromberg, 1993). Thomas et al. (1979) found that 299 of the 363 species of land vertebrates in the Great Basin of southeast Oregon depend directly on riparian habitats or use them more than any other habitat type. Current Regulation of Riparian Ecosystems Riparian ecosystems are among the nation's highly valued and threatened natural resources (Johnson and McCormick, 1979). Alteration of riparian ecosystems has been of special concern in the West. Alteration has accompanied regulated activities such as gravel mining, bridge crossings, and the creation of new dams and diversions, and such unregulated activities as reduction of surface discharge or lowering of water tables due to ground water pumping or surface water withdrawal. Other activities that can alter riparian zones include clearing of land for agricultural development, logging, or recreation (Stromberg, 1993). Degradation of riparian habitat has also resulted from the spread of exotic species such as saltcedar and Russian olive. In some areas, native riparian plant and animal species are greatly suppressed or have become locally extinct (Stromberg et al., 1991). Because of their proximity to flowing water, riparian ecosystems are Closely associated with the maintenance of the physical, chemical, and biological processes of streams. Although widely recognized as important to the goals of the Clean Water Act, riparian zones are not fully protected by it. Some parts of riparian ecosystems are regulated because they are located at an elevation below ordinary high-water, which qualifies them as waters of the United States, or because they conform to regulatory definitions of wetlands. Other parts of riparian ecosystems are unregulated because they do not satisfy any of the broadly-used definitions of wetlands and they lie outside the ordinary high-water mark. Unregulated riparian areas in add climatic regions such as the Southwest and the Great Basin include cottonwood-willow streamside forests as well as bosques on
OCR for page 154
Wetlands: Characteristics and Boundaries the higher portions of floodplains. These riparian ecosystems often include jurisdictional wetlands (Appendix B, Verde River case study). The overstory of arid zone riparian ecosystems is typically dominated by phreatophytes, plant species that rely on water drawn from points below the water table. Riparian phreatophytes of the West typically cannot live on uplands where the water table is inaccessible. Thus, whereas upland species can tolerate drought, riparian species avoid the effects of drought by use of shallow ground water near streams or rivers. Although ground water is close enough to the surface to support phreatophytes in arid zone riparian ecosystems, it is not close enough to sustain a hydrophyte-dominated wetland. Furthermore, full inundation might occur only during occasional floods at intervals of many years. Also, soils of arid riparian ecosystems generally lack hydric properties because organic matter seldom accumulates in sufficient quantities to cause the development of redoximorphic features and because saturation at or very near the surface is infrequent. Riparian ecosystems also can be found along headwater streams and annually inundated floodplains in humid regions such as the eastern United States and the Pacific Northwest. Significant proportions of these riparian zones often qualify as wetlands, but the uppermost portions typically do not. The upper zones of floodplains do flood periodically, but not often enough to qualify as wetlands. Even so, riparian zones outside wetland boundaries perform functions that are similar or complementary to those of wetlands. Even where the riparian zones of headwater streams are jurisdictional wetlands, however, protection is weak because of Nationwide Permit 26, through which significant alteration of headwater wetlands can occur (see following section on isolated and headwater wetlands). Since 1968, the National Flood Insurance Program has conditioned the availability of flood insurance on the adoption of local regulations designed to limit construction in the 100-year floodplain. Areas that receive flood disaster relief also must submit hazard mitigation plans for approval by the Federal Emergency Management Agency. These statutory programs are supplemented by Executive Order 11988, which directs federal agencies to avoid supporting development in floodplains if there is a practical alternative. Although federal policies are not oriented toward protection of the natural functions of floodplains, they have slowed the alteration of floodplains. Many state and local governments have supplemented the federal programs with even more restrictive regulations. Complementary programs that acknowledge the importance of riparian zones in hydrologic buffering and in the maintenance of water quality and biodiversity are warranted but have not yet been developed. Riparian zones may contain wetlands that meet the present regulatory definitions of wetland as well as the reference definition that is given in Chapter 3. Examples include floodplain depressions that are inundated every year or in most years, abandoned channel remnants that extend to contact with groundwater, or
OCR for page 155
Wetlands: Characteristics and Boundaries that accumulate considerable precipitation that causes them to be wet for extended intervals. In addition, however, riparian zones often contain substantial amounts of land that cannot be classified as wetland according to present regulatory definitions or the reference definition given in Chapter 3. For example, a broad definition of the riparian zone would correspond to the high-water mark of the hundred-year flood near a river channel. The uppermost portion of this zone would be inundated only once every hundred years on average, and even when inundated, it might not retain water very long. Thus this upper margin of the floodplain would not meet the requirements for recurrent, sustained inundation or saturation at or near the surface. Vegetation in this part of the riparian zone would not be predominantly hydrophytic, although the zone might contain some phreatophyte species dependent on a water table several feet below the surface of the substrate. The substrate would not show any physical or chemical evidence of repeated, sustained inundation. Thus riparian zones are not wholly contained within the set of ecosystems defined as wetlands by existing regulatory definitions or by the reference definition of Chapter 3. This conclusion does not imply that riparian zones are unimportant to the goals of the Clean Water Act, or that riparian zones are not critically threatened in much the same way that wetlands are threatened, but rather that extension of the definition of wetland to cover all riparian zones would unreasonably broaden the definition of wetland and undermine the specificity of criteria and indicators that have developed around wetland delineation. A recommendation from this section can be found at the end of this chapter, recommendation number 4. ISOLATED WETLANDS AND HEADWATERS As explained in Chapter 4, Nationwide Permit 26 affects isolated wetlands and headwaters, by authorizing the filling of relatively small areas if the permitted activity is consistent with CWA regulations. Most of the nationwide general permits refer to categories of activities, such as construction of aids to navigation, rather than to categories of wetlands. Unlike the other nationwide permits, Nationwide Permit 26 authorizes discharge to wetlands on the basis of their position in the drainage network, rather than on the basis of the activity itself. It permits filling of up to 1 acre (0.4 ha) with no review and 10 acres (4 ha) with minimal review in headwaters and isolated waters. Isolated waters, which include vernal pools, playas, potholes, and alpine wet meadows, are defined as the nontidal waters of the United States that are not a part of a surface tributary system to interstate or navigable waters of the United States and that are not adjacent to such tributary bodies of water (33 CFR 330.2). Even though such wetlands qualify for protection under Section 404 jurisdiction, Nationwide Permit 26 excludes some types of wetlands from individual permit requirements, except when overridden by the USACE division engineer. Nationwide Permit 26 has been controversial because of the cumulative wetland losses that can result through its
OCR for page 156
Wetlands: Characteristics and Boundaries application, and it is the cause of more litigation than any other nationwide permit (Strand, 1993). As indicated in Chapters 3 and 5, many functions of wetlands can be independent of isolation or adjacency. Even water quality functions might not be fully separate for isolated and other wetlands because of the ground water connections between isolated wetlands and surface waters. Special treatment of headwaters is also questionable, given that headwaters affect water quality downstream and perform many of the other functions of wetlands (Johnson and McCormick, 1979; Lowrance et al., 1984a, b; Peterjohn and Correll, 1984; Cooper and Gilliam, 1987; Cooper et al., 1987). The scientific basis for policies that attribute less importance to headwater areas and isolated wetlands than to other wetlands is weak. Small, shallow wetlands that are isolated from rivers are frequently important to waterfowl. For example, pintail draw a substantial proportion of their diet from the shallowest potholes (personal communication, 1994, Carter Johnson, South Dakota State University). Although these wetlands make up only 4% of the surface water in the pothole region, they support a large percentage of the total populations of several of the most abundant species such as mallards, gad-wall, bluewing teal, shoveler, and pintail (Kantrud et al., 1989b). Studies of the prairie potholes of the northern Plains states have shown why shallow potholes are especially important (Appendix B). Shallow potholes develop invertebrate populations earliest in the spring because they thaw earlier than do deeper potholes; invertebrates in turn provide critical early-season forage for the earliest waterfowl migrants of the Mississippi flyway. Similarly, for snowmelt-dependent depressional wetlands of the San Luis Valley of Colorado, in an area with 19,856 acres (8,039 ha) of wetlands, intermittently wet wetlands comprise the largest surface area (61%) and provide 81% of waterfowl food (personal communication, 1994, David Cooper, Colorado State University). A recommendation from this section can be found at the end of this chapter, recommendation number 5. ESPECIALLY SHALLOW OR INTERMITTENTLY FLOODED WETLANDS In some portions of the United States, including the arid West, annual rainfall is especially variable in total amount and in timing. Because wetlands in these areas may become completely dry for several years, the concept of average conditions can be difficult to apply. For example, Zedler (Bedford et al., 1992) showed that for San Diego, California, only 21 years out of 140 had total rainfall within 90-110% of the long-term average. Because wetlands are important in meeting CWA goals, then the wettest of wetlands might seem to be the areas most in need of protection. Landscape position and other factors are also important, however. For example, wetlands in
OCR for page 157
Wetlands: Characteristics and Boundaries zones that flood only intermittently could be among the most important for storing flood waters; their capacity to reduce peak discharge would be negligible if they were always full. It is sometimes difficult for the regulated public to understand how sites that are often dry can be classified as wetlands. Part of the reason, as explained in Chapters 2 and 5, is that intermittently flooded wetlands have a distinctive, water-dependent biota. Temporary wetlands support a variety of invertebrates, algae, or mosses that can persist over dry intervals as propagules (seeds, ephippia, spores). Propagules of these organisms are absent in uplands. Some upland plants and animals can colonize a wetland during prolonged dry periods, but the wetland biota will return with the water. For example, California's vernal pool fairy shrimp (Branchinecta sandiegoensis) can hatch within 48 hours and can complete its life cycle within 2 weeks (King et al., 1993; Simovich, 1993). Only about 15% of the eggs hatch at a time; if the first inundation period is short, a second wetting stimulates additional hatching. In this way, populations can be sustained even where inundation is brief and intermittent. During the long, dry summers, these same pools can be dry. They do not support extensive upland vegetation, however, because there is too much water for its establishment in the wet season and not enough in the dry season. The dependence of fish species on temporarily wet habitats is discussed by Finger and Stewart (1987), who document a decline in spring-spawning sunfishes of southeastern Missouri after the reduction of spring flooding. Seasonally flooded bottomlands greatly increase the feeding areas for fish, as has been shown for the Atchafalaya Basin, in Louisiana. Lambou (1990) noted that 54% of the 95 finfish species use wooded areas of the basin for reproduction arid 56% use them for feeding. The total harvest attributable to overflow areas was nearly 51,300 lbs/sq. mile (9,000 kg/km2) per year of finfish and nearly 400,000 lbs/sq. mile (70,000 kg/km2) per year of crawfish. Junk et al. (1989) report a strong relationship between the extent of accessible floodplain and fishery yields and production. During the rising floodwater period, fish take advantage of food and shelter in riparian wetlands. Shallow wetlands could be especially valuable in maintenance of water quality because of their high ratio of sediment surface relative to water volume. For example, wetlands in Minnesota are more effective in removing suspended solids, total phosphorus, and ammonia during high flows when waters cover more of the higher-elevation areas of the wetland, while nitrate removal is more effective during low flow (Johnston et al., 1990). Wetlands that are intermittently dry can retain wetland characteristics only if they are protected from physical alteration when dry. Delineation of intermittently dry wetlands can be justified by the same rationale as for other wetlands, and can follow the same methodology as delineation of other wetlands.
OCR for page 158
Wetlands: Characteristics and Boundaries AGRICULTURAL WETLANDS Agricultural wetlands are defined here as wetlands found on agricultural lands. Agricultural lands, in turn, are those that are intensively used and managed for food and fiber production and from which natural vegetation has been removed and cannot be used in making a wetland determination. Examples include cropland, hayland, and pasture composed of planted grasses and legumes; orchards; vineyards; and areas that support wetland crops such as cranberries, taro, watercress, and rice (NFSAM, 1994). Agricultural and silvicultural activities and associated lands were originally exempted from the permitting requirements of CWA Section 404. This created a conflict within the federal government in that the USACE and EPA were encouraging wetland conservation through the act, whereas the U.S. Department of Agriculture was encouraging wetland drainage projects with federal subsidies. This changed when Congress passed the FSA ''swampbuster'' provisions (Chapter 4). As a result of an executive decision by President Clinton in August 1993, the lead agency for delineating wetlands on all agricultural lands is now the Natural Resources Conservation Service (NRCS) of the U.S. Department of Agriculture (Chapter 4). NRCS is responsible for an estimated 20 million acres (8 million ha) of wetlands, or about 20% of the nation's remaining wetlands in the conterminous United States (Table 6.1). The cost to NRCS for carrying out these new responsibilities will be $15.6 million annually if intensively managed agricultural lands alone are delineated. If native grazing lands are included, the cost will be an additional $10.4 million per year (personal communication, 1994, Billy Teels, Wetlands Staff Leader, NRCS). The current and historical use of agricultural land, and especially the date of conversion to cropland, are important in determining whether a tract can be TABLE 6.1 Estimated Area of Wetlands for Which NRCS Is Responsible Under 1994 MOA Category Millions of Acres (ha) Farmed wetlands 7 (2.8) Wetlands fanned under natural conditions 3 (1.2) Farmed wetland pasture-hay 9 (3.6) Nonagricultural wetland inclusions within agricultural lands 1 (0.4) Total 20 (8) Source: Written response by Billy M. Teels, U.S. Natural Resources Conservation Service, June 22, 1994.
OCR for page 159
Wetlands: Characteristics and Boundaries TABLE 6.2. Agricultural Wetlands and Wetlands in Agricultural Settings as Defined by the NRCS Name Definition Wetland Meets wetland criteria under natural conditions and has typically not been manipulated by alteration of hydrology or vegetation. Can be used only to produce agricultural commodity if natural conditions prevail. Prior converted Drained, filled, or manipulated before Dec. 23, 1985, sufficient to make production possible, and an agricultural commodity was planted or produced at least once before Dec. 23, 1985. Farmed wetland Manipulated and planted before Dec. 23, 1985 but still meets wetland criteria, i.e., not converted prior to that date; can produce agricultural commodities without loss of benefits and existing drainage systems can be maintained. Farmed wetland pasture Manipulated and used for pasture or hayland before Dec. 23, 1985; management similar to farmed wetland. Converted wetland Drained, dredged, filled, or otherwise manipulated to make production of an agricultural commodity possible. Converted wetland for nonagricultural purpose Converted for purposes other than producing agricultural commodities (trees, vineyards, fish farms, cranberries, roads, building, waste management structures, livestock ponds, parking lots). Artificial wetland Nonwetland converted to wetland through human activities. considered for exemption under the swampbuster provisions. Table 6.2 lists some varieties of agricultural wetlands that are recognized by the National Food Security Act Manual, third edition. The switching point for history of these wetlands is Dec. 23, 1985, the date of FSA's enactment. Although implementation of the act is complicated, the basic concept is that wetlands that were drained or manipulated before that date can be maintained for agricultural production. Owners who drained or manipulated wetlands after that date are subject to federal penalties (Chapter 4). All four federal agencies that deal extensively with wetlands (NRCS, EPA, USACE, and the Fish and Wildlife Service [FWS]) are participating in a new effort to improve and standardize wetland identification and delineation on agricultural lands. One potential concern, however, is that agricultural wetlands will begin to diverge as separate from those regulated by USACE and EPA. This divergence could be fostered by maintenance of separate delineation manuals for agricultural and nonagricultural wetlands. Several major differences based on policy rather than science are already apparent (Chapters 4 and 5). Wetlands in the United States' are often found in agricultural settings. In fact, a significant proportion of the 117 million acres (46.8 million ha) of wetland loss in the lower 48 states since the 1780s (Dahl, 1990) can be attributed to the
OCR for page 160
Wetlands: Characteristics and Boundaries conversion of wetlands to agricultural use. Much of this conversion has occurred in the upper Midwest and in the lower Mississippi River Valley. Shaw and Fredine (1956) attributed a loss of 45 million acres (18.2 million ha) primarily to the Swamp Land Acts of the mid-nineteenth century (Chapter 3). In addition, more than 57 million acres (22.8 million ha) of wet farmland, including some wetlands, was drained under the terms of the U.S. Department of Agriculture's Agricultural Conservation Program between 1940 and 1977 (OTA, 1984). Between 1900 and 1990, except for the years of the Great Depression, there was a steady conversion of wet farmland to drained farmland (Gosselink and Maltby, 1990; Mitsch and Gosselink, 1993); an estimated 65% of this wet farmland was wetland (OTA, 1984). Between the 1950s and 1970s, most wetland conversions (87%) were caused by agricultural activity; from the 1970s to the 1980s, nearly 1.3 million acres (about 510,000 ha) or 54% of the conversion of palustrine wetland was caused by agricultural activity (Dahl and Johnson, 1991). As a result of wetlands protection legislation, especially FSA (Chapter 4), the loss rate has probably slowed, although few reliable data are available since the estimate by Dahl and Johnson. Although reduced in extent, wetlands that remain on farmed land are potentially subject to protection by CWA and FSA (Chapter 4). Some wetlands are now being used agriculturally without being converted. For example, depressional wetlands are sometimes allowed to flood and develop naturally in wet years or wet seasons, but are used for crops in dry years or during the dry season (Chapters 4 and 5; Appendix B , prairie pothole case study). Some wetlands also are being created and restored on former agricultural land through federal incentive programs to promote the removal of drainage systems, filling of drainage ditches, or the breaking of drainage tiles (NRC, 1992). FWS estimates that, as result of the conservation reserve program within FSA, about 90,000 acres (36,450 ha) of wetlands was restored from 1987 to 1990, much of it farmland. About 43,000 acres (17,400 ha) of wetlands was restored in the upper Midwest alone between 1987 and 1992 (Mitsch and Gosselink, 1993). In 1990, NRCS began to administer a wetlands reserve program that has acquired easements on agricultural lands that were formerly wetlands (Chapter 4). In fiscal year 1994, $67 million was authorized for the program and approximately 590,000 acres (23,900 ha) of land was offered by landowners for restoration. This is far in excess of the goal of 75,000 acres (30,300 ha) for 1994. Another 25,000 acres (10,100 ha) will be restored to wetland status through the Emergency Wetland Reserve Program for the Midwest flood area (personal communication, 1994, Billy Teels, Wetlands Staff Leader, NRCS). Agricultural wetlands are generally found in an extensively altered landscape where they can be particularly important for controlling water quality, preventing floods, and maintaining biodiversity. These wetlands are also of special interest because they are now being managed and protected under a dif-
OCR for page 161
Wetlands: Characteristics and Boundaries ferent set of definitions and rules and by a different federal agency than are most other wetlands (Chapters 3 and 4). Functions of Agricultural Wetlands Wetlands in agricultural settings have the same range of natural functions as do wetlands elsewhere. In addition, they often receive sediment, nitrate, phosphate, organic matter, and pesticides associated with the agricultural practices on adjacent lands. There has been considerable research on the ability of wetlands in agricultural settings to serve as sinks for fertilizers such as phosphate and nitrate (Peterjohn and Correll, 1984; Jacobs and Gilliam, 1985; Cooper et al., 1986, 1987; Mitsch, 1992, 1994) and a limited number of studies show the potential for wetlands to adsorb agricultural pesticides (Rodgers and Dunn, 1992). The water quality improvement function is often well developed in these systems, although pollutants can cause stress. Because many former wetlands were drained for crop production, the hydroperiods of wetlands that remain on or near agricultural lands might have been altered and floodwater retention functions diminished. Thus, although the wetlands in agricultural settings are potentially valuable for maintenance of water quality, they can be significantly disturbed and can show reduced functional capacity. van der Valk and Jolly (1992) present the argument that natural wetlands in rural settings should not be used as sinks for processing of nonpoint source pollutants because natural wetlands have been greatly reduced in agricultural settings and should therefore be preserved for their habitat and recreational values. Also, these wetlands in many cases already receive significant amounts of agricultural runoff. Differential Regulation of Agricultural Wetlands There are several major differences in the regulation of agricultural and nonagricultural wetlands. Wetland delineations for agricultural lands routinely are based on aerial photography and soil maps; seldom on field data (Chapter 8). Wetlands have different definitions in the National Food Security Act Manual (NFSAM, 1994) and in the USACE manuals (Chapter 4). The burden is with the federal government, through the NRCS, to prove that an agricultural area is a wetland. With nonagricultural delineations, the applicant is typically required to submit a delineation showing that there are no wetlands on a site to be developed. There is no threshold date for exemption of wetland conversions of nonagricultural lands through the 1987 Corps manual, as there is for agricultural lands. There is no binding regulatory classification of nonagricultural wetlands.
OCR for page 162
Wetlands: Characteristics and Boundaries Criteria for identifying agricultural and nonagricultural wetlands differ in some respects (Chapter 4). SITES ALTERED FOR NONAGRICULTURAL PURPOSES Altered sites are those that have been changed recently by anthropogenic or natural events to the extent that one or more indicators of wetland character are absent, obscured, or provide information that is not representative of current conditions. Such sites can retain their original character, either as wetlands or as uplands, or their character might have changed or be indiscernible by a standard field assessment. Much of the North American landscape has been subject to some degree of perturbation, but many disturbances do not change the character of wetland ecosystems. Altered sites are those at which disturbance has been recent enough and extensive enough that normal conditions are not readily apparent by the indicators of hydrology, substrate, and biota. Special methods could be required for the assessment of such sites for wetland determination and delineation. Types of Alterations Anthropogenic activities other than agriculture that alter substantial areas of wetlands include logging and silviculture, peat and mineral mining, construction of roads, construction of reservoirs, building of commercial and residential structures, dredging and disposal for maintenance of navigation, introduction of exotic plant and animal species, and numerous other physical and biological disturbances. These activities involve alteration of wetlands by: draining, dredging, or filling; structural modification of the hydrologic regime; removal or alteration of vegetation and wetland substrate; and discharge of pollutants (Mitsch and Gosselink, 1993). Natural events that affect the formation and status of wetlands include floods, erosion, alluvial or sediment deposition, earthquakes, landslides, fires, stream channel changes, wildlife activity, and plant succession. The results of such events include: draining or filling; modification of hydrologic regime through the creation or destruction of landscape features; destruction or introduction of vegetation components; and release or sequestering of nutrients. Although many changes can occur in altered wetlands, changes in vegetation, soils, and hydrology carry the greatest implications for the determination of jurisdiction or regulatory action. While the following alteration types are given primarily in terms of anthropogenic origins, some similar kinds of alterations can come about naturally as well: Complete removal of vegetation, which typically includes the use of biological indicators. The removal of vegetation can decrease water retention time,
OCR for page 163
Wetlands: Characteristics and Boundaries thus decreasing the duration of saturation, or decrease the amount of evapotranspiration, thus increasing the duration of saturation. Partial removal of vegetation, which can alter the outcome of vegetation assessments. Selective removal of specific components Coy overstory logging, burning of the herbaceous and shrub layers) also can cause hydrologic change. Herbicide treatment, which can remove specific vegetative components. Few herbicides are specific for hydrophytic species, but chemical specificity for herbaceous broadleaf plants, grasses, or woody vegetation can result in misleading results for plant surveys. Grazing or mowing, which can shift the composition of the plant community, often toward the xerophytic end of the spectrum. Planting or introduction of vegetation that can alter plant communities. Agricultural and silvicultural practices frequently result in total replacement of the natural plant community. Likewise, introduction or invasion by aggressive species can alter community composition. These actions also can influence the hydrology of a site. Soil disturbances and associated ramifications include the following: Soil removal, which can change the results of soil analysis or alter the relative water retention capacity of the substrate, thus either increasing or decreasing the degree of saturation and vegetation of a site. Soil disturbance, which can complicate the assessment of soil character. It can destroy or mask some indicators and, through time, can reduce the hydric character of a soil. Where subsurface clay layers limit drainage, soil disturbance may also alter the hydrology of the site. Covering of the soil, which results in the burial of soils that are relevant to delineation. It also can alter the hydrology of the site, usually by decreasing the likelihood of saturation. Hydrologic alterations and their associated ramifications include Increased drainage through ditching, dike removal, or tiling, which lowers water levels and shortens the duration of saturation. Water removal, which can reduce the likelihood of saturation. Water addition, which can result in higher water tables and greater amounts of saturation. Such changes can result in the formation of a wetland community through time; others can be ephemeral and of insufficient consequence to justify wetland status. Change in water retention, either through excavation or impediment to drainage, which can result in higher probability of saturation. Hydrologic alterations can originate at some distance from a site and might
OCR for page 164
Wetlands: Characteristics and Boundaries not be directly related to its management. For example, municipal withdrawal of water from an aquifer can reduce the wetland character of sites that are connected to the aquifer. Such sites can retain indicators, such as hydrophytic vegetation or hydric soils, that developed before the hydrologic change. Conversely, impoundment of water can maintain a high water table near an impoundment. Identification of Normal Conditions In the assessment of altered sites it is important to have information about normal conditions before the alteration, normal conditions after the alteration, the timing of the alteration, and the origin of the alteration. Generally, the assessment of normal conditions subsequent to alteration is done through standard wetland delineation procedures. There are some exceptions to this, however, in that one or more important indicators can be absent or significantly altered. The timing and origin of the alteration usually can be ascertained either from a landowner or from other persons. When the determination of normal conditions must be made at altered sites, special methods must sometimes be used in assessing normal vegetation, soils, and hydrology. Assessment of Altered Lands Evidence of normal vegetation can be derived from Review of aerial photographs. Both the National Wetlands Inventory (NWI) and NRCS maintain aerial photographs of wetlands. These can be useful in assessment of normal conditions. Local runoff or meteorologic data should be used in identifying seasons and years when normal conditions would be most likely observed. Study of adjacent similar areas. Analysis of unaltered reference areas can provide information on the normal vegetation at an altered site. Interviews. Landowners and other persons can provide useful information on the previous vegetation of an altered site. Remnants. Remnants of a plant community can provide sufficient information to support a delineation. Trees can frequently be identified by their stumps as well as by leaf and mast remnants. Buried vegetation can sometimes be excavated and identified. Review of NWI or NRCS maps. NWI maps provide basic descriptive information on vegetation. NRCS maps also provide some information about vegetation. Evidence of preexisting soils can be derived from
OCR for page 165
Wetlands: Characteristics and Boundaries Soil survey maps. Soil survey maps can provide useful information on soils, but care must be taken in interpreting them (Chapter 5). Soil samples. If the original soils have been buried, sampling pits will show the preexisting A horizon. Historic deposition, however, might have covered relict hydric soils that antedate CWA Section 404 enforcement. When the surface soils have been disturbed or removed, soil horizons immediately below the disturbed zone can be examined for indications of hydric character. Soils of adjacent areas. Soils tend to be of the same type in similar geomorphic positions on the landscape. When the preexisting soil has been removed or has otherwise been made unavailable for assessment, reference areas can be used to infer original soil types. Evidence of preexisting hydrology can be derived from Hydrologic models. As discussed in Chapters 5 and 8, hydrologic models can provide evidence of hydrology prior to alteration. Topographic maps. Sites in close proximity on the landscape will tend to exhibit similar hydrology. In such cases, review of topographic maps based on preexisting conditions can be of assistance in evaluating hydrology. This evidence can be particularly useful for floodplains, where the primary factor of importance is elevation (Appendix B, Steele Bayou case study). Aerial photographs. Aerial photographs can provide evidence of standing water, but they do not indicate saturation. Aerial photographs only rarely provide indications of duration of inundation, but the use of gauging or meteorologic data can increase the utility of these photographs. Also, NRCS currently uses evidence of stunted vegetation as an indicator of wetland hydrology. Such evidence can be used to infer prealteration conditions in conjunction with corroborative information, such as position in landscape and presence of hydric soils. Vegetation can be stunted as a result of several factors, however, and should not be considered definitive without supporting evidence. Limitations of assessment Methods for Altered Sites The assessment methods mentioned above are recommended by the 1989 interagency manual and the 1987 Corps: manual. The results are Subject to varying degrees of uncertainty, which can be reduced through the use of mutual kinds of evidence. which should be a priority for controversial cases. As is often true for standard delineations, the greatest uncertainty will likely be associated with the placement of the boundary line of a wetland. The establishment of the wetland boundary will involve professional judgment as well as technical analysis. A recommendation concerning altered lands can be found at the end of this chapter as recommendation number 11.
OCR for page 166
Wetlands: Characteristics and Boundaries TRANSITIONAL ZONES On gentle gradients, or where microtopography causes wetlands to be interspersed with uplands on fine scales, the wetland boundary can be difficult to locate (Chapters 2 and 5). The same is true of marginal sites where wetland status is questionable because evidence is weak or inconsistent. These transitional and marginal areas have stirred debate and criticism of current and past identification and delineation of wetlands. In these difficult cases, the evidence must be carefully weighed against the minimum essential characteristics of wetlands, namely: hydrologic features associated with flooding or saturation and the presence of organisms and physical and chemical features that reflect continuous or frequently recurring saturation or flooding. Evidence should be calibrated regionally for specific wetland types to facilitate more consistent delineation; reference wetlands are useful for this purpose. An approach that requires no conflicting evidence might have the effect of excluding some wetlands. In contrast, an approach that does not require strong evidence and that ignores conflicting evidence could include some uplands. For these reasons, the consequences of delineation procedures must be carefully considered on a regional basis. A recommendation concerning transitional zones is listed as recommendation number 11 at the end of this chapter. RECOMMENDATIONS Permafrost wetlands, which have structure and function similar to those of nonpermafrost wetlands, should be identified and delineated by the same principles as are other wetlands. A better scientific understanding of permafrost wetlands should be developed. The correlation of soils and hydrology as well as vegetation and hydrology should be studied for permafrost wetlands. Riparian zones perform many of the same functions as do wetlands, including maintenance of water quality, storage of floodwaters, and enhancement of biodiversity, especially in the western United States. Although they typically contain wetlands, riparian zones cannot be defined wholly as wetlands by any broad definition. If national policy extends to protection of riparian zones pursuant to the goals of the Clean Water Act, regulation must be achieved through legislation that recognizes the special attributes of these landscape features, and not by attempting to define them as wetlands. The scientific basis for special permitting of wetlands in headwaters or isolated wetlands is weak. Nationwide Permit 26 has been controversial because of the cumulative wetland losses that can result through its application. Conse-
OCR for page 167
Wetlands: Characteristics and Boundaries quently, Nationwide Permit 26 should be reviewed for validity in the context of the Clean Water Act and for consistency with other permitting practices. Especially shallow wetlands or wetlands that are only intermittently wet perform the same kinds of functions as other wetlands and can be delineated by the same procedures as those used for other wetlands. Wetlands on agricultural lands should not be regulated differently from other wetlands. These wetlands may have many of the same attributes as do other wetlands, including maintenance of water quality, and there is no scientific basis for delineating them under definitions or federal manuals different from those applicable to other wetlands. Wetlands in agricultural settings can enhance runoff water quality; the impairment of this function by agricultural practice should be considered when wetlands are proposed for agricultural use. When wetlands are to be constructed or restored using agricultural lands, it is preferable to locate such projects near natural wetlands. Restoration on agricultural lands should be encouraged whenever these practices can reduce impairment of the remaining natural wetlands on or near agricultural lands. Inference of wetland features that have been removed or changed by natural or anthropogenic means should be allowed as part of wetland delineation on altered lands. Federal manuals should instruct delineators on the valid use of inference for this purpose. Application of delineation methods should be tested on transitional and marginal lands in all regions.
Representative terms from entire chapter: