The South, Southeast and Mississippi River-Atchafalaya River Basin (MARB) U.S. terrestrial regions, in conjunction with the South Atlantic Bight (SAB) and the Gulf of Mexico (GOM), provide an excellent contrast in major factors driving terrestrial carbon storage and fluxes as well as differences in coastal carbon dynamics. Large population growth has occurred in the southern and southeastern regions in contrast to the Great Plains regions that comprise much of the MARB. These environments are also characterized by different land use and vegetation cover (cropland and grassland versus forest), thus providing a good basis for comparing different climate and land use scenarios. An overall decline in forest area in the U.S., particularly in the South and Southeast regions, is expected due to increased urbanization and population growth [Alig et al., 2010]. In addition, land use and management changes related to agricultural practices and water resource use are likely to alter biogeochemical dynamics in terrestrial ecosystems with potential impacts for greenhouse gas emission as well as downstream impacts on coastal environments [Searchinger et al., 2008].
A strength of our integrated terrestrial-coastal modeling approach is it scalability from relatively fine regional to basin-scale characterizations. The spatial extent of land-ocean systems necessitates a combination of macro-scale satellite observations and model-based approaches coupled with targeted ground-based site studies to adequately characterize relationships among climate forcing (e.g., wind and precipitation patterns, temperature, solar radiation, humidity, extreme weather events), land use/land cover and land practices, and transport of materials through watersheds and, ultimately, to coastal ocean. Supported by previous NASA funding, Tian and co-workers have used the Dynamic Land Ecosystem Model (DLEM) to assess the dynamic changes in terrestrial and riverine water, carbon and nitrogen fluxes from the MARB to the GOM during 1901-2010 as influenced by multiple environmental changes in climate, land cover and land management practices [Chen et al., 2012b; Liu et al., 2013; Tian et al., 2012a; Tian et al., 2012b; Xu et al., 2012; Zhang et al., 2012]. Model output from the DLEM has been validated [Liu et al., 2013] (Tao et al., in review) against datasets for runoff, nutrients, and sediment concentration and transport in the MARB which includes both USGS monitoring data and observations acquired from ship-based studies conducted in the northern GOM by our team (Cai and Lohrenz).
In this project, the DLEM model (see Supporting Work) [Tian et al., 2010a; Tian et al., 2011a; Tian et al., 2012b; Zhang et al., 2012] will be used to quantify terrestrial carbon storage and fluxes including characterization and quantification of soil and vegetative carbon biomass and land-atmosphere fluxes of CO2 and CH4 in the study land domain, and lateral fluxes of water, nutrients and organic and inorganic carbon from land to the GOM and the SAB. We have coupled the DLEM with the SABGOM marine ecosystem model to simulate and evaluate impacts of land use and climate changes on the riverine fluxes of water, carbon and nitrogen, on ecosystem processes and associated fluxes and exchanges of carbon in the northern Gulf of Mexico and southeastern U.S. coastal waters.