Carbon and Water Budgeting Along Upper Estuaries: Developing Linkages to Environmental Change

Science Center Objects

WARC Researchers are studying carbon, water, and nutrient cycling in upper estuarine wetlands.

Ecosystem carbon budget conceptual diagram

Conceptualization of components of the carbon (C) budget for upper estuarine tidal wetlands, including aboveground standing stocks (CAG), belowground standing stocks (CBG), C mass balance (Cin − Cout), soil C burial (CB), and lateral C fluxes (CI/E) along with a photographic series from our representative (a) Upper, (b) Middle, (c) Lower, and (d) Marsh sites. Photographs depict general habitat appearances as tidal freshwater forested wetlands transition to oligohaline marshes with salinity change from fresh water (<0.5 psu) to oligohaline marsh (0.5–5.0 psu) along the Waccamaw and Savannah Rivers. Rc = canopy respiration; RRMR = soil rhizomicrobial respiration (including decomposition); RRR = root respiration; OM = organic matter.

(Global Biogeochemical Cycles, v. 32, p. 817-839, 2018)

The Science Issue and Relevance: Upper estuarine wetlands along major rivers of the southeastern United States often transition from non-tidal/tidal freshwater forested wetlands to low salinity tidal marshes. Fluctuations in these boundaries have occurred for millennia, but rates of change have been altered by new processes (e.g., lower sedimentation, greater nutrients) associated with watershed disturbance over the past few centuries. These wetlands store large amounts of carbon (C) in wood, herbaceous vegetation, and soils, and it is important to understand not only the processes responsible for preserving C storage as watershed changes occur simultaneously, but also in how river management may be able to facilitate greater C sequestration in the future, especially on federal lands. Linking specific components of the C cycle among different upper estuarine wetland types with how those systems use water and nutrients is one way to understand this connection.

Methodologies for Addressing the Issue: For over 20 years, scientists have been studying soil and growth processes among different upper estuarine wetlands of the southeast. Sites along rivers in South Carolina and Georgia have been used to develop full ecosystem C budgets, and along with co-located nutrient flux and tree/stand water use studies (sap flow), we are beginning to understand how tightly connected processes are among coastal environments, such that small changes in delivery or flux of any component can disrupt ecosystem-scale processes to influence more rapid transition. Salinity influences can also restrict stand water use among coastal forested wetlands, and facilitate nutrient and C mineralization. Similar C budgets are being developed in Louisiana, and collaborations with a USGS science program in Virginia (Dr. Gregory B. Noe) have expanded project scope to four tidal rivers of the Chesapeake Bay.

Future Steps: We will continue to study C, water, and nutrient cycling in upper estuarine wetlands. We are actively developing a model of C and biogeochemical change (DeNitrification-DeComposition (DN-DC Model) Dr. Hongqing Wang, USGS) to apply to multiple upper estuaries that we are not currently studying and to ecosystem restoration scenarios that inform managers of their benefit. We are also expanding into new watersheds internationally through collaborations (Australia, New Zealand), and continue to communicate the important role upper estuaries can play in global “blue carbon” initiatives.