Coastal plain wetlands occupy a critical landscape position at the intersection of terrestrial and aquatic and fresh and salt waters. Like all wetlands, coastal wetlands are disproportionately valuable in terms of services provided compared to the area they comprise including nutrient transformation, water purification, and flood control. Humans have drained wetlands throughout much of the southeastern coastal plain for agriculture and forestry, thus diminishing their capacity to provide critical ecosystem services such as nutrient and carbon sequestration. At the same time, fertilizer use and manure from intensive meat and poultry production have dramatically increased nutrient loading to coastal ecosystems. Increased loading and decreased retention of nutrients has caused eutrophication of downstream freshwater and coastal ecosystems, with the associated degradation in water quality and decline in coastal fisheries. Climate change may further exacerbate these trends: higher temperatures and increasingly sporadic precipitation may further diminish the spatial extent of perennially flooded wetlands and is already leading to seasonal salt water intrusion during drought. Predicting the likely ecosystem carbon and nutrient cycling of coastal plain freshwaters into a saltier and increasingly uncertain hydrologic future requires significant improvements to our current understanding of freshwater ecosystems. This proposal focuses strategically on two aspects of this problem: first, incorporating sulfur (~from sea salt) dynamics into our understanding of how microbes alter carbon and nutrient cycling and second, utilizing simulation modeling to mesh dynamic hydrology together with microbial biogeochemistry. Adaptive simulation modeling together with targeted empirical work will allow us to rapidly test and refine current models of wetland carbon and nutrient cycling and to formalize the emerging conceptual understanding of wetland biogeochemistry into a flexible, easily adjusted modeling framework.
The focal field site is a formerly ditched and drained agricultural field in North Carolina's coastal plain that was restored to riverine wetland hydrology in 2007, becoming the largest privately owned mitigation bank in the southeast. The site has very little topographic relief (-1 to +1 m elevation); experiences significant salt water intrusion via surface water mixing during summer droughts; and has wind tide driven hydrology that generates large gradients in sulfur concentrations in both time and space. The field site is representative of large areas of SE coastal plain agricultural landscapes that are being actively restored or abandoned. The economic and ecological "success" of this project will be closely watched by regulators and practitioners throughout the region. This research program will directly affect the potential for site owners to sell validated carbon and nutrient credits in emerging ecosystem service markets. Resulting research findings (together with their economic implications) will influence future patterns of mitigation and conservation investment throughout the southeastern coastal plain and will provide critical information that will facilitate climate adaptation planning throughout the region.
" project investigators have examined the effects of drought associated saltwater intrusion on freshwater wetland ecosystems. We anticipate that many of the low lying areas of the east coast of the United States will be subject to episodic exposure to saltwater, either as a result of storm surges or as a consequence of longer or more extreme droughts. Ultimately, many of these freshwater wetlands and managed agricultural landscapes will become saline as a result of sea level rise. Our work suggests that, without intervention, these former agricultural landscapes may emit substantial amounts of nitrous oxide and release large quantities of legacy fertilizer nitrogen to downstream waters. At the same time, exposure to marine salts is likely to prevent or suppress substantial methane release. Exposure to high salinities and high sulfide concentrations will eventually lead to substantial plant mortality, but high concentrations of iron in some wetlands will slow the pace of of this expected change by preventing buildup of sulfide, a potent phytotoxin. This project produced 4 masters students and supported 4 postdoctoral researchers who have now attained faculty positions. Grant supplements supported the training of a high school environmental science teacher and supported independent research for a faculty member from an undergraduate serving institution. Results from the project have been shared with resource management agencies, conservation organizations, and private landowners throughout coastal NC and early results of the project were reported in regional newspapers.
