Applied Wetlands Science - Chapter 3

Kent, Donald M. “Evaluating Wetland Functions and Values” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 CHAPTER 3 Evaluating Wetland Functions and Values Donald M. Kent CONTENTS Functions and Values Aquatic and Wildlife Habitat Educational and Scientific Venue Elemental Transformation and Cycling Flood Flow Alteration Groundwater Recharge Particle Retention Production Export Raw Materials Recreation Soil Stabilization Evaluating Functions and Values Representative Evaluation Techniques Expert Opinion Wetland Evaluation Technique Rapid Assessment of Wetlands (RAW) Wetlands Integrated Monitoring Condition Index (WIMCI) Hydrogeomorphic Assessment (HGM) Habitat Evaluation Procedures (HEP) Virtual Reference Wetlands (VRW) Economic Valuation Economic Valuation Methodologies Direct Economic Valuation Indirect Economic Valuation ©2001 CRC Press LLC The Value of the World’s Ecosystem Services and Natural Capital References As do all ecosystems, wetlands have functions and values. Functions are pro-cesses that are inherent to a wetland. They derive from the wetland’s hydrological, geological, biological, and chemical characteristics. For example, groundwater recharge is a wetland function that occurs when water in the wetland, derived from precipitation, surface runoff, or both, infiltrates downward through permeable soils to the groundwater table. Wetland functions occur regardless of whether there are people present to benefit from these processes. Wetland values are functions that prove useful or are important to people. The aforementioned wetland functioning to recharge groundwater will possess a ground-water recharge value only if the recharged groundwater is used by local or regional populations. Values may be provided within the confines of the wetland, for example, recreation, or beyond the wetland boundaries, for example, flood protection. Another characteristic of wetland values is that they vary with time and circumstances. Again returning to the example of a groundwater recharge wetland, a downstream com-munity drawing drinking water from a surface impoundment does not view the wetland as valuable to its drinking water supply. Should the surface water supply diminish or become contaminated, and groundwater withdrawal become necessary, that wetland now takes on value. Clearly, wetland functions and values are inextricably linked. Values cannot be provided without there first being a function. Conversely, a function has no value until someone exploits that function. Recognizing the confounding nature of the relationship between wetland function and value, many functions and values have been attributed to wetlands (Amman et al., 1986; Mitsch and Gosselink, 1993; Adamus et al., 1987; Reimold, 1994; Brinson, 1995). Some of the commonly recognized functions and values of wetlands are listed in Table 1 and described briefly below. Table 1 Wetland Functions and Values Aquatic and wildlife habitat Educational and scientific venue Elemental transformation and cycling Flood flow alteration Groundwater recharge Particle retention Production export Raw materials Recreation Soil stabilization ©2001 CRC Press LLC FUNCTIONS AND VALUES Aquatic and Wildlife Habitat All wetlands, with the exception of those that have been severely degraded, provide habitat for wildlife. And wetlands with seasonal or permanent surface water support fish and other aquatic vertebrates and invertebrates. Many threatened and endangered species are associated with wetlands. The type and degree to which aquatic and wildlife habitat is provided is dependent upon local and landscape characteristics including water depth and permanence, vegetation type and cover, habitat size, and the nature of the surrounding environment (Forman and Godron, 1986; Kent, 1994). Educational and Scientific Venue Numerous public and private organizations exist for the purpose of educating people about the importance of wetlands. Educational topics include awareness, regulations and legislation, conservation and planning, and science and management (Drake and Vicario, 1994). Wetlands provide an opportunity for studying fundamen-tal biological and ecological principles including energy flow, biogeochemical cycling, population biology, and community structure. As well, wetlands are the focus of more specific studies related directly to inherent functions and values such as pollutant removal, habitat provision, and flood attenuation. Elemental Transformation and Cycling Wetlands serve as sinks, sources, or transformers of many inorganic and organic chemicals, including those of ecological and socioeconomic importance such as nitrogen and phosphorus, carbon, sulfur, iron, and manganese. Chemicals enter the wetland through hydrologic pathways such as precipitation, surface or groundwater, tidal exchange, or alternatively through biotic pathways including photosynthetic fixation of atmospheric carbon and bacterial fixation of nitrogen, respectively. Wet-lands export or lose chemicals by burying in the sediment, outflow in surface or groundwaters, denitrification, atmospheric loss of carbon dioxide, ammonia volatil-ization, or methane and sulfide release. While within the wetland, chemicals may become part of the litter, remineralized, translocated in plants, or transformed by changes in redox potential or biotic components. Flood Flow Alteration Wetlands have the potential for reducing downstream peak flows and delaying the timing of peak flows. Water from precipitation, overbank flow, overland flow, and subsurface flows may be detained in wetlands by depressions, plants, and debris, or as the result of the wetland slope. Alternatively, water may be retained in the wetland, infiltrate, and recharge surficial groundwater. The importance of wetlands ©2001 CRC Press LLC for reducing downstream flooding increases with an increase in wetland area, dis-tance the wetland is downstream, size of the flood, closeness to an upstream wetland, and the lack of other upstream storage areas (Ogawa and Male, 1983, 1986). Coastal wetlands also have the capacity to alter flood flows as well as reduce flood waveseverity. In this case, salt marshes and mangroveforests absorb the energy of coastal storms, thereby protecting inland areas. Groundwater Recharge Wetlands with pervious underlying soils recharge underlying materials, ground-water, or aquifers. Recharge is thought to occur primarily around the edge of wetlands, making groundwater recharge relatively more important in smaller wet-lands. As most wetlands are thought to haveimpervious underlying soils, the majority of wetlands may not exhibit this function and value (Larson, 1982; Carter and Novitzki, 1988). Particle Retention Wetlands trap and retain sediments, nutrients, and toxicants, primarily through physical processes. Reduction in water velocity causes sediments, and chemicals sorbed to sediments, to settle. Dissolved elements and compounds are retained with inorganic and organic particulates after sorption, complexation, precipitation, and chelation. In contrast to chemical transformation and cycling, incoming particles are subject to long-term accumulation or permanent loss from incoming water sources through burial in the sediments or uptake by vegetation. Production Export Some wetlands, especially those with high primary productivity, export dissolved and particulate organic carbon to downslope aquatic ecosystems. Plant material and other organic matter are leached, flushed, displaced, or eroded from the wetland, providing the basis for microbial and detrital food webs. Raw Materials Wetlands are a source of plants and animals that serve as raw materials for various domestic, commercial, and industrial activities. Forested wetlands, for exam-ple, bottomland hardwoods and cypress swamps, are a source of lumber. Lower quality timber and woody shrubs are used for the production of other wood products, paper pulp, or firewood. Marsh vegetation is used for food (e.g., rice), fodder, thatch for roofs, and other commodities. Wetland wildlife, fish, and shellfish are consumed as food, and wildlife skins are used for clothing and related items. Because of the extractive nature of this function and value, the provision of raw materials is likely to have serious impacts on other wetland functions and values. Sustainable practices can minimize these impacts. ©2001 CRC Press LLC ... - tailieumienphi.vn