Benthic exchange of nutrients in Galveston Bay, Texas

Nutrient regeneration rates were determined at three sites increasing in di stance from the Trinity River, the main freshwater input source, to Galvest on Bay, Texas, from 1994 through 1996. Diffusive fluxes generally agreed in direction with directly measured benthic fluxes but underestimated the exc hange of nutrients across the sediment-water interface. While the fluxes of ammonium and phosphate were directed from the sediments 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 flu xes showed benthic production during both summer 1995 and winter 1996, whil e light-dark deployments showed production-consumption, respectively. Benth ic inputs of nutrients were higher at either the middle or outer Trinity Ba y regions, most likely due to a higher quality and quantity of the autochth onous organic matter deposited. This feature is consistent with and gives e vidence for previously observed non-conservative mixing behaviors reported for nutrients in this region of Galveston Bay. Calculated turnover times, b etween 7 to 135 d for phosphate, 4 to 56 d for silicate, and 0.3 to 10 d fo r ammonium were significantly shorter than the average Trinity Bay water re sidence time of 1.5 yr for the period September 1995 through October 1996. During periods of decreased Trinity River now 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 the se nutrients to Trinity Bay. The sediments, a sink for silicate when overly ing 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.