Book Description

Located at the interface between uplands and surface water networks, headwater wetlands act as a natural filter to improve downstream water quality and play a critical role in maintaining the ecological integrity of downstream aquatic ecosystems. Vulnerable to development pressure, as well as indirect impacts from land use and climate change, the loss and alteration of headwater wetlands has been linked to the loss of biodiversity and regional water quality declines worldwide. The overall goal of this dissertation is to address some of the challenges associated with the management and conservation of headwater wetlands in the coastal plain of Virginia including: the identification of palustrine forested wetlands in flat coastal landscapes (Chapter II); and improved understanding of the impacts of land use (Chapter III) and climate change (Chapter IV) on the hydrologic regime of headwater wetlands. First, a simple model of wetland distribution was developed by characterizing the depth to groundwater using widely available geospatial data, including surface water features and a high-resolution digital elevation model. Comparison with the National Wetland Inventory (NWI) and targeted field validation indicated that this model provides an effective approach to identify palustrine forested wetlands often unmapped by NWI. Results from this study indicate that there may be at least 37% more wetland area than is currently mapped within the study area; and that in the future, modeling approaches should be used in addition to NWI mapping to better understand the full extent and distribution of wetlands in forested areas. The impacts of land use and climate change were then investigated through field studies of headwater wetland hydrology and community composition. Potential differences in headwater wetland hydrology were evaluated through an index of hydrophytic vegetation occurrence, the wetland prevalence index (PI). Changes in PI between sapling and canopy strata, with respect to local land use, indicated that decreased forest cover was associated with a shift in plant community composition, and that increasing road density was associated with a shift towards more upland type species, while increasing agricultural cover was associated with a shift towards more wetland type species. The effects of climate change, including rising temperatures and altered precipitation patterns were evaluated by developing an empirical model of water table depth for coastal headwater wetlands. Wetland water levels were simulated under current and potential future conditions to evaluate the impact of climate change on the hydrologic regime of headwater wetlands. Based on the model scenarios applied in this study, it appears that decreasing water availability may lead to drier conditions at headwater wetlands by the end of the 21st century, with a substantial decline in minimum water levels and a 3-10% decline in average annual percent saturation. Collectively, the results of this dissertation provide practical insights for improving the conservation and management of coastal headwater wetlands. Improved understanding of the extent and distribution of previously unmapped forested wetlands can improve the capacity to monitor wetland loss and degradation. Additionally, clarifying the influence of land use and climate on the hydrologic regime of these wetlands, can help improve the capacity to forecast and then mitigate potential future impacts to wetland hydrology.