DISSOLVED ORGANIC MATTER FLOCCULATION IN COASTAL STREAMS AND ITS EFFECTS ON WATER QUALITY

The formation of “dead zones”, or regions of low dissolved oxygen, in coastal ecosystems is attributed to excess nutrient runoff. However, recent studies suggest that the export of dissolved organic matter (DOM) from land to coastal waters can also deplete oxygen through the stimulation of bacterial growth. When terrestrially-derived DOM mixes with saline estuarine waters, flocculants of particulate organic matter are produced, providing potential habitat for bacteria to more readily access carbon and nutrients. We investigated the response of bacteria to flocculant production using fresh water from a stream draining a wetland and a stream draining a former agricultural field at Longwood’s Hull Springs Farm, Westmoreland County, VA. Laboratory experiments were conducted in air-tight bottles where salt was added to simulate the local salinity gradient, 0 - 13 PSU. Flocculant production and bacterial respiration were measured after a 7-day incubation in the dark. Flocculant production increased with increasing salinity, especially in the wetland stream. Bacterial respiration also increased with increasing salinity, likely related to increased flocculant production, and was highest in the wetland stream compared to the agricultural stream. These results suggest that the quantity and quality of DOM inputs to coastal ecosystems influence water quality, and consequently, ecosystem health.