URBANIZATION IMPACT ON THE NATURE OF DISSOLVED ORGANIC CARBON IN COASTAL SOUTH CAROLINA

The carbon cycle has been put into stress due to climate change and land-use changes from agriculture, urbanization, and watershed modification. This study spotlighted dissolved organic carbon (DOC) by measuring concentrations in surface water and shallow groundwater in watersheds of the Charleston, South Carolina estuary. DOC is an indicator for the ecological health of a water system and is known to increase disinfection by-product formation potential during water treatment. We investigated the relationship between DOC concentration, DOC chemical structure, water salinity, and land use character of the watershed to understand how DOC may differ depending on those characteristics.

Water sampling from tidal creeks, rivers, and shallow groundwater was conducted during 2015. Sampled areas include the Francis Marion National Forest freshwater, the Filbin Creek watershed (a freshwater urban stream system in North Charleston, SC), the Ashley River (a brackish to saltwater estuary river), and the Charleston Harbor (saltwater). Filtered and acidified water samples were analyzed for DOC concentration using a total organic carbon (TOC) analyzer. Percent aromaticity, which is an estimate of the proportion of DOC derived from humic substances, was determined by quantifying samples on a UV-Visible Spectrophotometer followed by normalizing absorbance to determine specific absorbance (SUVA method). The SUVA value was compared to well-correlated C-NMR percent aromaticity data.

Preliminary results indicate that (i) salinity is showing to be inversely correlated with DOC values, (ii) higher DOC values are found in freshwater urban rather than forested systems, (iii) DOC in forested systems had significantly higher percent aromaticity, and (iv) salinity thus far does not appear to be a factor on percent aromaticity values. The study has provided a broad look at DOC concentrations and character in natural waters with varying salinity in coastal South Carolina. The main contributions thus far are the baseline data on DOC in different watersheds from the early spring to late fall. The final product of the research will be a GIS map to help visualize the DOC-surface water dynamics in coastal waters around the Charleston and ACE Basin estuaries. Ongoing work is looking at the source origin and the reactivity of DOC.