Geostatistical Modeling of the Spatial Distribution of Sediment Oxygen Demand Within a Coastal Plain Blackwater Watershed

Geoderma, Publication Acceptance Date: August 23, 2010

Todd, Jason; Lowrance, Robert; Goovaerts, Pierre; Vellidis, George; and Pringle, Catherine

“Blackwater streams of the Georgia Coastal Plain are often considered polluted due to chronically low DO levels. Previous research has shown that sediment oxygen demand (SOD, the amount of dissolved oxygen consumed by processes in the stream sediments) was significantly positively correlated with total organic carbon (TOC) within the stream sediments. SOD is probably a cause of lowered DO within these waters,. SOD measurements in the previous study were point measurements, making it difficult to characterize SOD values at the reach and watershed scale. However, the use of geostatistics allowed for the characterization and spatial depiction of SOD across the entire stream and floodplain in two study locations through its relationship with TOC. The results showed TOC to be spatially correlated at both experimental locations with the corresponding distribution and patchiness of SOD differing between the sites as a result of different hydrological regimes. The larger stream, with a larger, more persistent area of inundation, had higher average rates of oxygen demand both in terms of area-wide average and as a function of stream length when compared to the smaller stream. The mapping of floodplain soils on these watersheds showed that areas subject to flooding are larger per unit stream length along larger streams. The greater area per unit stream length in the larger streams demonstrates the importance of areas of these instream swamp areas in coastal blackwater streams and further illustrates their importance to oxygen dynamics on a watershed scale. Additionally, this research provides support for the hypothesis that many blackwater streams draining Georgia”s coastal plain are naturally low in DO as a result of elevated SOD.”