In recent decades, population density in the GA watersheds draining into the South Atlantic Bight has increased significantly. In the six GA counties with ocean access, population increased from 16 to 61 individuals/km2 between 1900 and 2005.

Population increase in coastal GA counties since 1900. Based on data from the U.S. Census Bureau

Nutrient export from the landscape to the coast is generally related to population density.

Relationship between population density and nitrogen loading to coastal waters

The two nutrients of most interest here are nitrogen (N) and phosphorus (P), the former typically being the limiting factor for primary production in coastal waters. Its addition can lead to increased primary production and enhances the potential for eutrophication (see section processes).

Relationship between dissolved inorganic nitrogen input and primary production

In addition to the nutrient delivery via surface waters, groundwater inputs to the coastal ocean may be significant: Though flowing much slower, high concentrations of dissolved nitrogen or phosphorus can lead to significant inputs. However, to date, relatively little is known on the processes occurring in the subsurface at the land-ocean interface, where two different - fresh and salty - water bodies meet. Here, we focus on this reaction zone.

Microorganisms mediate a significant fraction of nutrient turnover in the subsurface. Their main energy source is organic matter. Hence, we are studying settings with different amounts of reactive dissolved organic matter available. Such differences can, for example, reflect residential areas with leaking septic tanks.

The modeling efforts center on the analysis of such systems and are tightly linked to intense field campaigns in two distinct settings: One site is located on Sapelo Island, the other in the Satilla estuary. For more information see research conducted in the Joye lab, who collect data from a well field at a relatively pristine site at Moses Hammock (Schultz and Ruppel 2002), as well as in a setting impacted by septic systems at Dover Bluff.

Location of field sampling sites. Measurement transects are highlighted in red.

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