Coastal wetlands filter water, buffer the coastline from storms, provide important habitat and are globally important for the storage of carbon. Carbon storage in wetland soils can be for the long-term and influences whether wetlands will persist during sea level rise by increasing a change in sediment elevation. Climate change and local freshwater management are increasing the movement of saltwater into coastal freshwater wetlands, altering the conditions of the wetlands and causing shifts in the types of vegetation growing there. In many tropical and subtropical coastal wetlands, mangroves are replacing grass-dominated marshes, with uncertain effects on the capability of soils to store carbon. This is especially true of coastal wetlands, because of their sensitivity to sea level rise. The goals of this study are to identify changes in the storage of carbon in wetland soils and releases to the atmosphere of the gases carbon dioxide and methane that occur as coastal wetland change from marshes dominated by grasses to mangrove forests. The research findings will provide valuable information for the conservation and restoration of the Florida Everglades locally as well as coastal wetlands throughout the world. Furthermore, the findings will provide a broader understanding of plant and soil interactions and ecosystem function in a changing world. The project will provide hands on scientific experience identifying and growing wetland plants and restoring urban coastal wetlands for local high school students during "Marsh Mangress", an outreach activity at Florida International University. This activity will also provide undergraduate students with laboratory and field experience at a majority minority institution. This research will utilize a vegetation gradient in 10,000 Islands National Wildlife Refuge in Naples, FL in which sea level rise and freshwater manipulation have driven vegetation change and mangrove encroachment, in order to understand how changing abiotic conditions and vegetation state change alter carbon storage through time. Changing carbon storage will be measured as current organic carbon stocks (above and belowground biomass, soil carbon content), inputs (root productivity, sediment surface accretion) and carbon losses (breakdown rates of organic carbon, gas flux measurements), past carbon sequestration rate (radiometric soil dating), and potential future rates of carbon loss (reciprocal transplant of organic matter to represent freshwater restoration or continuing saltwater intrusion). Specifically, the goals of this project are to: 1) Identify differences in carbon storage, accretion, and gas flux among wetlands dominated by brackish marsh, saltwater marsh, and mangrove-dominated vegetation communities. 2) Determine which abiotic and biotic mechanisms drive differences in soil carbon dynamics among wetland types. 3) Quantify the effect of time since mangrove establishment on soil carbon storage, accretion and gas flux by establishing a chronosequence of mangrove encroachment based on soil dating and historic aerial photography.