| Wetlands are capable of supporting diverse assemblages of plants and animals, and performing various ecosystem services (e.g., waterfowl production, flood mitigation). However, the capacity of a wetland to perform these functions is dependent upon its condition (i.e., ecosystem condition, integrity, or health). Wetland condition is affected and reflected by internal (within-system) biophysical features, and interactions among these features. To protect and effectively manage wetlands, it is essential that we identify reliable determinants and indicators of wetland condition. As a result of the inherent complexity of wetland ecosystem interactions, this knowledge is difficult to obtain. The objectives of this study were to measure biophysical features of prairie pothole wetlands in Iowa, identify determinants and indicators of wetland condition in the prairie pothole region (PPR) of Iowa, and develop a list of highly descriptive and cost effective variables useful for wetland condition management. Specifically, relationships among basin morphometry, trophic state, salt concentration, fish and tiger salamander abundance, and abundance and taxonomic diversity of plants and invertebrates were examined in 34 semipermanent and permanent wetlands. Correlation analysis, path analysis, and non-metric multidimensional scaling (nMDS) revealed variables that were key determinants and indicators of wetland condition, and provided insight into mechanisms by which wetland condition was affected. Results indicated that fish had strong adverse effects on wetland condition through both direct and indirect mechanisms. By increasing turbidity, fish indirectly reduced plant abundance, consequently reducing invertebrate densities and taxon richness. Results also suggest that fish reduced tiger salamander abundance primarily through direct mechanisms (e.g., predation). Additionally, fish abundance increased as a function of wetland depth. Therefore, deeper wetlands were more eutrophic, had reduced tiger salamander abundance, reduced abundance and diversity of plants and invertebrates, and were generally in poorer condition than shallower ecosystems. Management focused on eliminating fish is needed to improve wetland condition, and is necessary in part because watershed alterations have enabled increased fish abundance in PPR wetlands by increasing wetland depth. Fish biomass, turbidity, plant cover, tiger salamander biomass, and invertebrate taxon richness appear to be reliable and effective indicators of wetland condition in the Iowa PPR, and should be routinely measured to monitor wetland condition. |
