A spatial model of potential hydrologic connectivity between isolated wetlands and jurisdictional surface waters in a karst landscape

Background/Question/Methods

Geographically Isolated Wetlands (GIWs) provide ecosystem services similar to those provided by other types of wetlands, including biogeochemical nutrient processing, carbon sequestration, runoff containment, and water storage. Although GIWs were initially protected under the Clean Water Act, they are no longer federally regulated when connected to “navigable waters” by migratory bird presence alone. Thus, agricultural land use and urban development may lead to losses in functional ecosystem services provided by these wetlands and surrounding landscapes. Interest in determining significant hydrologic, biological, or chemical connections among GIWs and surface waters has emerged relative to jurisdictional criteria. Our objectives are to: (1) Create a GIS-connectivity model that identifies potential hydrologic flow paths in southwest Georgia; (2) Use this model to identify potential hydrologic connections among 30 mapped GIWs and surface waters; and (3) Evaluate this model using 200 potential GIWs identified by a previous study. 

Results/Conclusions

We examine GIWs within a 120-km² section of the karstic Dougherty Plain in southwest Georgia, an area with flat topography, few surface channels, and abundant sinks and surface depressions. Our model identifies areas of potential subsurface flow using flow accumulation, soil texture data, and deciduous forest from normalized difference vegetation index. These potential subsurface flow paths are used to connect other hydrographic features to more than half of 30 field-verified wetlands and 200 predicted wetlands. Our analysis indicates that some GIWs within the Dougherty Plain may be connected to streams via these subsurface flow paths. Preliminary soil assessments within the potential drainages connecting GIWs to surface waters indicate the presence of redoximorphic features and hydric soils in more than half of the drainages sampled. Remotely sensed soil moisture data are used to confirm these assessments. Potential flow paths identified by this study are used to determine optimal hydrologic monitoring sites during high water events for confirming the temporal components of biological, chemical and hydrologic connectivity. These data may provide a means for quantifying ecosystem services provided by GIWs in southwestern Georgia, including the ability to maintain the biological integrity of important upland ecosystems during dry conditions.