Human Impacts on the Trophic Structure of Wetlands: the Florida Everglades as a Case Study

Coastal ecosystems have been significantly impacted by increased pressure of growing human populations and urbanization concentrated along coastlines. A couple of major impacts associated with urban growth include drainage of water levels in coastal wetlands and runoff to coastal communities from agriculture. The Florida Everglades is an example of a wetland ecosystem that has been severely altered by reclamation efforts, drainage, and agriculture. Wetlands are unique environments, serving as ecotones and being a source, sink, and transformer of chemical and biological material. The interactions between aquatic and terrestrial species in these ecosystems depend on biotic and abiotic processes. One main factor influencing changes to wetland trophic structure is the alteration of driving forces, especially in hydrology and nutrient enrichment. Since the beginning of the 20th century, major drainage efforts included construction of canals, levees, water conservation areas, and the Everglades Agricultural Area. Levels of phosphorus have increased and concentrated in particular ecosystem components, such as the flocculent detrital organic layer near soil at the bottom of the water column, periphyton, and within the soil. Along with alterations in the chemical components, there have been changes to hydrology. These two factors have resulted in conversion of sawgrass-dominated lands to cattails; altered the biomass and density of invertebrates and fishes; changed the biomass and population size of top predators; and resulted in the loss of important species of wading birds. Loss of periphyton assemblages have also been reported due to increased phosphorus levels. Over the last two decades, many projects and studies have been conducted to restore this environment, such as the Everglades Nutrient Removal Project and the Comprehensive Everglades Restoration Plan (Chimney and Goforth, 2006; Perry, 2008; reviewed by Reddy and Kadlec, 2006; Trexler and Goss, 2008). Wetlands are an important part of coastal environments and the loss of these ecosystems is severe. This capstone review paper describes how the Florida Everglades, a large unique wetland system in North America, changed during the 20th century due to human impacts