Award: OCE-1635837

Coastal wetlands are among the most productive ecosystems on the earth and are recognized for their sequestration and storage of carbon for centuries to millennia within the soil. The top 1 meter of all soil contains almost twice the amount of carbon that is in the atmosphere. Wetlands, while only about 5% of the land area, store 1/3 of all soil carbon. Although many scientists focus on soil carbon near the surface, this research highlights the vast amount of soil carbon at depth in coastal wetlands. Understanding the amount and type of carbon stored in coastal wetland soils down as deep as 2 m is important because the combination of sea level rise, large storms (e.g., hurricanes), and wind driven waves are rapidly eroding many wetlands. We sought to quantify wetland erosion in coastal Louisiana, including the properties of the eroding soils (carbon, nitrogen, and phosphorous content) and their fate following submergence. Key findings from this project include: 1) The wetlands of Barataria Bay, LA are eroding at an average rate of 1.4 m per year, causing about 850 years of previously sequestered and stored soil carbon to break-apart and submerge into the coastal bay. 2) Based on comparative analysis of the properties of the eroded wetland soils and the sediments in the bay, the wetland soils are not being re-buried in the coastal zone, but rather are transported and transformed, including being broken-down by naturally occurring microbes. 3) Contrary to expectation, the mid-depths of soil (e.g., 50-100 cm) were the most carbon-rich and the most vulnerable to microbial break-down, which releases the stored soil carbon as carbon dioxide. 4) Bioavailable nitrogen and phosphorous was 7-11 times more abundant deep within the soil (e.g., 130-140 cm) when compared to the surface of the soil. These key findings suggest the erosion of large areas of coastal wetlands can serve as a climate change feedback where previously buried soil carbon is released into coastal water and the atmosphere as carbon dioxide, thus contributing to climate change. Moreover, the large amount of nitrogen and phosphorous stored in the eroding soils is also released into the coastal zone during wetland erosion and could contribute to Gulf of Mexico eutrophication and hypoxia. Additional knowledge gain through this research has advanced the understanding of the properties of deep organic coastal wetland soil deposits. For example, we show limited evidence that microbial processing of soil organic matter increases with age (depth), but rather the degradability and nutrient quality of the soil is more closely related to the history of the site, such as large shifts in water flow patterns and plant communities. We also differentiated coastal wetland loss caused by edge erosion for that caused by the formation of open water ponds in the interior of a wetland, referred to as ?peat collapse.? We posit that vegetation stress due to chronic or acute disturbance is a precursor to interior wetland loss, while edge erosion increases as the duration of wind-driven waves increases and undercuts unconsolidated soils beneath the root zone. Through this project, at least four graduate students were trained in cross-disciplinary science, as well as several undergraduate researchers. New teaching modules detailing the outcomes of the project were developed at two universities and more than 100 K-12 students were engaged in soil and wetland science through STEM Day activities and classroom visits. Last Modified: 03/29/2022 Submitted by: Lisa Chambers