Wetlands

Abstract

Wetlands have always influenced humans. Early civilizations first arose along the edges of rivers in the fertile soils of floodplains. Wetlands also produce many benefits for humans—along with fertile soils for agriculture, they provide food such as fish and water birds, and, of course, freshwater. Additionally, wetlands have other vital roles that are less obvious. They produce oxygen, store carbon, and process nitrogen. Since wetlands form at the interface of terrestrial and aquatic ecosystems, they possess features of both. They are often overlooked in standard books, since terrestrial ecologists focus on drier habitats, while limnologists focus on deep water. Shallow water, and seasonally flooded areas, fall comfortably into neither category. All wetlands share one causal factor: flooding. While wetlands may be highly variable in appearance and species composition, flooding produces distinctive soil processes and adaptations of the biota. Thus wetlands and water are inseparable. This treatment will first introduce you to some basic overviews that explain what a wetland is, what different kinds of wetlands exist, and some key processes that occur within them (General Guides and Introductions). Then we will turn to causal factors: flooding creates wetlands, so it receives a full section. Then we will consider how nutrient availability modifies wetlands. Other Casual Factors, such as salinity, competition, herbivory, and roads, are combined into a third section. Having provided this foundation, we will look at the global distributions (Geography of Wetlands). By this point, you will know what a wetland is, where they occur, and the main factors that affect their abundance and composition. We will then explore two more specialized topics. First, monographs are identified that apply to particular regions of the Earth (Regional Monographs). Second, we look at aquatic plants; they are a relatively small group with important implications for the understanding of wetlands as a whole (Aquatic Plants). We close with a section on conservation of wetlands. Two general obstacles must be met in coming to grips with the scientific literature in this field. First, much of the work on wetlands is scattered across ecological journals and may not even appear under key word searches for wetland; instead, material may appear under a term such as bog, fen, shoreline, lake, floodplain, pothole, playa, peatland, or mire (or a dozen other terms). Second, this discipline seems to have attracted a large number of conference symposia, the findings of which are recorded often in expensive books with a haphazard collection of papers, written by a haphazard collection of people, with no unifying theme whatsoever except that all deal with wet areas. Hence, the need is pressing for a few general principles to structure one’s knowledge. Here we focus on general causal factors and their relative importance.