How are wetlands linked ecologically and biogeochemically to other aquatic and terrestrial ecosystems?
Limnological research to answer such questions is critical in the quest to protect and manage the remnants of the valuable wetland resource in North America.
For millennia, humans have been modifying watersheds in ways other than by building dams and draining wetlands, often with adverse consequences for aquatic biota and water quality (Solbe, 1986; Harriman et al., 1994). Forests and grassland have been transformed to agricultural fields or urban pavements as societies have established themselves around water bodies; forest ecosystems have been replaced with tree plantations designed to meet human needs for timber. Studies by limnologists and their fellow water scientists have provided valuable insights about impacts of human development on water bodies. Examples of limnological work in this area include the following:
Effects of early agricultural and urban activities: Studies by limnologists have shown that even the earliest stages of agricultural and urban development caused changes in water quality. Fires built by native people significantly altered the landscape of North America (Lewis and Ferguson, 1988). Work by several limnologists has indicated that fire changes water quality, causing increases in runoff of water, nutrients, and mineral ions (Schindler et al., 1980; Bayley et al., 1992 a,b; MacDonald et al., 1993). Paleolimnological studies by Hutchinson et al. (1970) showed that construction of the Appian Way (Via Appia) by the Romans in the second century A.D. changed drainage patterns for Lago di Monterosi in Italy in such a way that the lake became eutrophic. Similarly, Frey (1955) showed that early agrarian societies in the catchment of Längsee, Austria, caused the lake to become meromictic (meaning the bottom waters no longer mix with the remainder of the lake) through land clearning and associated activities.
Changes in nutrient loads caused by land use: Limnological studies have shown that land-use changes alter the yield of nutrients from watersheds to lakes. For example, Dillon and Kirchner (1975) showed that the transformation of forested land into pasture causes a considerable increase in nutrient yields from catchments to lakes. Transformation to agricultural land causes still greater increases. Sorrano et al. (in press) showed that urbanization increases nutrient inputs and that in addition to land use, the proximity of modified land to stream edges is an important factor controlling nutrient inputs to Lake Mendota, Wisconsin.
Effects of forestry: Clearcut logging is well known to increase water yield and the transport of nutrients, sediments, and other substances to