Hydrologic Controls on Water Chemistry and Microbial Activity in a Small Coastal Plain Stream
Opsahl, Stephen P.
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Relationships between water chemistry, microbial activity, and hydrology were examined in Chickasawhatchee Creek, a small coastal plain stream in southwestern Georgia. Microbial activity in the creek was determined by measurement of water-column respiration rates and growth-limiting substrates through oxygen consumption experiments. Water chemistry parameters (nitrate-N, soluble reactive phosphate, dissolved organic and inorganic carbon, major cation species) were measured in order to evaluate introduction and removal of various compounds and to identify ground water contributions. Results indicated substantial differences in water chemistry between the upstream and downstream reaches that were related to streamflow variation. During low flow periods, the upper reach of the creek was regulated by surface runoff while groundwater inflow played a more important role in the lower reach. Conversely, during periods of high flow, surface water runoff dictated streamflow for the entire system. There is strong evidence that dissolved organic carbon (DOC) always served as the growth-limiting substrate, and that DOC concentrations varied based on dilution by low-DOC groundwater. However, there was no correlation between measurements of water-column respiration and dissolved organic carbon.