Benthic exchange of nutrients in Galveston Bay, Texas |
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| Authors: | Kent W Warnken Gary A Gill Peter H Santschi Lawrence L Griffin |
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| Institution: | (1) US. Geological Survey, 345 Middlefield Road Menlo Park, California 94025, USA;(2) US Geological Survey, 230 Collins Road Boise, ID 83702, USA;(3) Department of Geological Sciences, University of Southern California, 3651 Trousdale Parkway Los Angeles, CA 90089, USA;(4) US Geological Survey University of Washington, P.O. Box 355351 Seattle, WA 98195, USA |
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| Abstract: | Nutrient regeneration rates were determined at three sites increasing in distance from the Trinity River, the main freshwater
input source, to Galveston Bay, Texas, from 1994 through 1996. Diffusive fluxes generally agreed in direction with directly
measured benthic fluxes but underestimated the exchange of nutrients across the sediment-water interface. While the fluxes
of ammonium and phosphate were directed from the sediment into the overlying waters, the fluxes of silicate and chloride changed
in both magnitude and direction in response to changing Trinity River flow conditions. Oxygen fluxes showed benthic production
during both summer 1995 and winter 1996, while light-dark deployments showed production-consumption, respectively. Benthic
inputs of nutrients were higher at either the middle or outer Trinity Bay regions, most likely due to a higher quality and
quantity of the autochthonous organic matter deposited. This feature is consistent with and gives evidence for previously
observed non-conservative mixing behaviors reported for nutrients in this region of Galveston Bay. Calculated turnover times,
between 7 to 135 d for phosphate, 4 to 56 d for silicate, and 0.3 to 10 d for ammonium were significantly shorter than the
average Trinity Bay water residence time of 1.5 yr for the period September 1995 through October 1996. During periods of decreased
Trinity River flow and increased residence times, benthic inputs of ammonium and phosphate were 1 to 2 orders of magnitude
greater than Trinity River inputs and were the dominant input source of these nutrients to Trinity Bay. The sediments, a sink
for silicate when overlying water column concentrations of silicate were elevated, became a source of silicate to the overlying
waters of Trinity Bay under reduced flow, high salinity conditions. |
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