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Title: High sediment oxygen demand within an in-stream swamp in Southern Georgia: Implications for low dissolved oxygen levels in coastal blackwater streams

Author
item TODD, JASON - Princeton University
item VELLIDIS, GEORGE - University Of Georgia
item Lowrance, Robert
item PRINGLE, CATHERINE - University Of Georgia

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2009
Publication Date: 12/15/2009
Citation: Todd, J., Vellidis, G., Lowrance, R.R., Pringle, C. 2009. High sediment oxygen demand within an in-stream swamp in Southern Georgia: Implications for low dissolved oxygen levels in coastal blackwater streams. Journal of the American Water Resources Association. 45:1493-1507.

Interpretive Summary: Blackwater streams are found throughout the Coastal Plain of the southeastern United States. The streams have blackwater because of the high levels of dissolved organic carbon and low levels of clay in the water. Blackwater streams generally have little slope from the top of the watershed to the bottom, have high summertime temperatures, and floodplains are generally flooded from winter to early spring. This flooding creates a multitude of in-stream floodplain swamps that play a vital role in overall water quality. Some of the blackwater streams have been listed as impaired (polluted) by the State of Georgia because they have low dissolved oxygen (DO). Low DO is harmful to aquatic life. A key influence on the DO levels within these floodplain swamps is sediment oxygen demand (SOD), which is the amount of oxygen that can be removed from overlying water oxygen consuming processes in the bottom sediments. We measured SOD in streams of the Little River Watershed near Tifton, GA. Results show SOD rates up to 18 times higher than values reported in the literature for southeastern sandy-bottomed streams and suggest that instream swamps are repositories of large amounts of organic matter and are thus areas of intense oxygen demand and a major factor in determining the oxygen balance of the watershed as a whole. These areas of intense oxygen demand in relatively unimpacted areas indicate that low DO concentrations may be a natural phenomenon. SOD rates were signigicantly correlated with a number of sediment parameters with soil organic carbon and total organic carbon being the best predictors of SOD rate. When developing water quality models, managers should pay closer attention to the influence of SOD as it plays a critical role in determining DO levels within in-stream swamps and the river system.

Technical Abstract: Blackwater streams are found throughout the Coastal Plain of the southeastern United States and are characterized by low gradients, high summertime temperatures, and extensive inundation of surrounding floodplains. Typically lasting from winter to early spring, the long inundation period creates a multitude of instream floodplain swamps that play a vital role in overall water quality. Over 90% of the blackwater streams lised as impaired on the Coastal Plain of Georgia are listed as being in violation of the State's dissolved oxygen (DO) standard. A key influence on the DO levels within these floodplain swamps is sediment oxygen demand (SOD), a critical and dominant sink for oxygen in many river systems that is often poorly investigated or roughly estimated in oxygen budgets. Results show SOD rates ranging from 0.491- 14.189gO2m-2d-1, up to 18 times higher than values reported for southeastern sandy-bottomed streams and suggest that instream swamps are repositories of large amounts of organic matter and are thus areas of intense oxygen demand and a major factor in determining the oxygen balance of the watershed as a whole. These areas of intense oxygen demand in relatively unimpacted areas indicate that low DO concentraions may be a natural phenomenon. SOD rates were significantly corrrelated with a number of sediment parameters with soil organic carbon and total organic carbon being the best predictors of SOD rate. When developing water quality models, managers should pay closer attention to the influence of SOD as it plays a critical role in determining DO levels within in-stream swamps and the river system.