Sediment and benthic response to wastewater solids in a marine mesocosm

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Wastewater solids were added to a series of marine mesocosms at the Marine Ecosystem Research Laboratory (MERL), University of Rhode Island. There was a range of sludge addition simulating 1, 4, and 8 times the average nitrogen enrichment of Narragansett Bay. Three other mesocosms received inorganic nutrients at similar levels, and three mesocosms were maintained as controls. In systems receiving nutrients or sludge, primary production was initially increased. Respiration of the increased loading in the sludge treatment generally resulted in decreased dissolved oxygen concentrations. In the highest level of sludge treatment, the benthic respiration resulted in anoxic conditions in the fourth month of the experiment. The benthos seemed to be the area primarily affected by wastewater disposal. Species feeding at or near the sediment-water interface showed a strong positive density response to sludge addition because of the increase in available food. Based on the findings of this experiment and comparison with marine areas of wastewater disposal, the condition of the benthic community can be generally defined based on organic loading rates. Organic loading rates less than approximately 0.1 g/m2 · d C had little effect on the sediment community. Loading rates between 0.1 and 1.0 g/m2 · d C resulted in an enriched sediment community, while loading over 1.5 g/m2 · d C produced degraded conditions. The quantification of the relationship between organic loading and benthic response presented here can be useful in evaluating wastewater treatment and disposal options.

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Water Environment Research