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United States Department of Agriculture

Agricultural Research Service

Research Project: LAND USE AND MANAGEMENT EFFECTS ON ENVIRONMENTAL PROCESSES AND HYDROLOGY IN COASTAL PLAIN WATERSHEDS

Location: Southeast Watershed Research

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

Authors
item Todd, Jason -
item Lowrance, Robert
item Goovaerts, Pierre -
item Vellidis, George -
item Pringle, Catherine -

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2010
Publication Date: October 15, 2010
Citation: Todd, J., Lowrance, R.R., Goovaerts, P., Vellidis, G., Pringle, C. 2010. Geostatistical Modeling of the Spatial Distribution of Sediment Oxygen Demand Within a Coastal Plain Blackwater Watershed. Geoderma. 159:53-61.

Interpretive Summary: 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.

Technical Abstract: Blackwater streams of the Georgia Coastal Plain are often listed as impaired due to chronically low DO levels. Previous research has shown that high sediment oxygen demand (SOD) values, a hypothesized cause of lowered DO within these waters, are significantly positively correlated with TOC within the stream sediments. 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 and SGS allowed for the characterization and spatial depiction of SOD across a reach 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 dissimilar hydrological regimes. The 5th order site, 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 3rd order site. While only measured at two experimental locations, the mapping of floodplain soils on the watershed scale showed that areas subject to inundation are common in this watershed and that these areas are more expansive per unit stream length in larger order streams. The greater area per unit stream length in the larger order streams demonstrates the importance of areas such as the 5th order experimental area. This study highlights the importance of 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.

Last Modified: 9/23/2014
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