Rapid coastal development has led to loss/alteration of wetlands, streams, and headwater areas that buffer coastal waterways from pollution. The population of coastal counties along the Gulf of Mexico increased by 150% from 1960 – 2008, and is expected to continue rising. Headwater streams are particularly vulnerable to alteration and disappearance as a result of urban expansion and agriculture. This study aims to asses functioning of headwater slope wetlands: groundwater-fed forested wetlands that occur in headwater areas of first order streams and are abundant in the Alabama-Mississippi Coastal Plain. Headwater wetlands form a critical interface between terrestrial and aquatic environments and are extremely important in maintaining downstream flows, nutrient fluxes and regional biodiversity. However, headwater wetlands are less studied, especially in the Gulf Coastal Plain. To address this knowledge gap, three headwater wetlands along a gradient of urban modification in Baldwin County, AL were chosen for this study. The watershed model Soil and Watershed Assessment Tool (SWAT) was used to determine flow and nutrient loading into the headwater wetlands, and wetland model WetQual was used to simulate nutrient loads leaving the wetlands. SWAT and WetQual were calibrated using measured flow and nutrient data for these wetlands gathered during 2013-2014.
Modeling this system presents unique challenges pertinent to a low gradient coastal plain system including high water tables, significant groundwater interactions and dealing with very small watersheds (being headwater areas). Influences of degree of urbanization and proximity to coast were clearly discernible in the observed hydrology – the wetland with the highest degree of urbanization and farthest away from the coast had very flashy hydrology typical of an urban system with almost nonexistent baseflows, while wetlands closer to the coast had baseflows throughout. Hydrology in the intermediate wetland was mildly flashy in response to watershed urbanization, but characterized by high baseflows amplified by the presence of an upstream impounded lake. This study is significant for two reasons: (1) it expands our understanding of the impacts that urban modification has on hydrology and nutrient fluxes of headwater wetlands, and (2) it expounds on the many challenges that have to be met in order to model such complex systems.