WATER QUALITY IMPROVEMENT FROM TRANSPLANTED OYSTER (CRASSOSTREA VIRGINICA) BEDS IN SMALL TIDAL CREEKS

Benthic filter feeders, such as the oyster (Crassostrea virginica), are believed to improve water quality in estuarine environments through filtration of suspended solids and nutrients. In addition, the biogenic structure of oyster reef communities may alter hydrodynamic conditions, further facilitating the removal of particulate matter and increasing water quality. Currently, several large-scale rehabilitation projects are being conducted in Maryland and Virginia, and North Carolina has received over $300,000 in legislative funding for oyster restoration projects in association with water quality improvements. This study will examine the effects of a small-scale oyster restoration project on sediment loading, nutrient loading, and flow within a small tidal creek.

Two reefs (2m by 1.5m) have been established in Hewletts Creek, New Hanover County, North Carolina. Water samples are collected monthly above and below each reef on ebbing tides. These samples are used to determine concentrations of total suspended solids (TSS), ammonium, and chlorophyll a. Flow properties are also measured above, over, and below each reef with an electromagnetic current meter. Additional samples and flow measurements are taken for comparison at adjacent control sites without restored reefs.

Initial data show TSS concentrations ranging from 5 mg l-1 to 23 mg l-1 above restored reefs to 2 mg l-1 to 23 mg l-1 below restored reefs near the tidal creek mouth. At the upland sites, concentrations range from 5 mg l-1 to 40 mg l-1 above and 7 to 40 mg l-1 below the restored reefs. Prior to reef placement, the percent organic content of TSS ranged from 25% to 55% at all sites. Since reef placement in early fall, percent organic content has decreased slightly both above and below the reef. These preliminary data suggest that after three months, the oyster reef has not yet altered the sediment load significantly in this system. As the restored reef continues to grow, however, we expect to observe a decrease in downstream (below reef) turbidity and nutrient load.