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.
Our grant assessed the effects of periodic salt water inundation on coupled biogeochemical cycles in a coastal wetland. Our goal was to use the seasonal salt water inundation as a natural experiment to investigate how coastal wetlands may respond to impending sea level rise, which is difficult to study given the incremental changes over a long time scale. Together with other researchers studying this issue, we compiled over 300 published studies to understand the causes, consequences and extensiveness of the salinization of freshwater wetlands. We found that freshwater wetlands are undergoing salinization through many mechanisms, at an unprecedented rate and geographic scale. We also conducted experiments and collected samples from a freshwater wetland in coastal North Carolina, which undergoes periodic (seasonal) salt water intrusion. Our work at this site helped us understand that it is critical to quantify how salt water and soil minerals interact in order to predict how long it will take for coastal freshwater wetlands to "switch" from having predominantly freshwater to predominantly salt water characteristics. We also found that the plant and microbial communities in the wetland respond to the salt water intrusion at differing rates. Working with collaborators on our grant, we contributed data to building a model that links hydrology and chemistry - both of which will be critical factors for predicting the eventual switch of coastal wetlands. The information generated by our study will be used by the scientific community, particularly by groups working on issues related to understanding sea level rise. It will also be used more locally by our collaborators in North Carolina to better understand how their costal wetlands will respond to impending sea level rise. In addition to creating knowledge, these funds supported an early career female scientist, one female Master's student and four undergradute technicians (including two first generation female students). The Master's student is currently pursuing a Ph.D. in a similar topic, and two of the undergraduates intend to enroll in graduate school, indicating the training was valuable to their career preparation and professional development.
