Characterization of Nitrogen and Phosphorus Loads, Macroinvertebrate Communities and Habitat in the Non-tidal Portions of the St. Martins River

Niles L. Primrose

Chesapeake and Coastal Watershed Service

Watershed Restoration Division

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11 February, 2000                                                                             M99035NEP034

Executive Summary

The Chesapeake Bay Program has emphasized watershed management through the development of Tributary Strategies for major river basins. While the Coastal Bays are geographically smaller than the Chesapeake Bay, the challenges of non-point source pollution management are no less daunting. The St. Martins River watershed is the largest freshwater system in the coastal bays drainage, draining more than 20,000 acres. This prominence within the coastal bays drainage, plus some historical data from the area, made the St. Martins watershed an excellent location to begin the task of identifying non-point source problems. The completed assessment, in conjunction with input from local agricultural and planning officials, should result in identification of candidate areas for management activities such as BMP installation, channel restoration, and riparian reforestation or protection that will begin to address some of the non-point source issues in the watershed. Synoptic water chemistry samples were collected at 19 sites throughout the watershed. Weekly water samples were collected at Station 4(Buntings Br.) beginning 3 March and continuing through 2 September, 1999. Samples were analyzed by the Nutrient Analytical Services Laboratory at the University of Maryland's Chesapeake Biological Laboratory (CBL) for dissolved inorganic nitrogen (NO3, NO2, NH4), dissolved inorganic phosphorus (PO4), total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP). All analyses were conducted in accordance with U.S. Environmental Protection Agency (EPA) protocols. Stream discharge measurements were taken at the time of all water chemistry samples.Water chemistry samples collected weekly at Station 4 from early March through early September established a water chemistry baseline that allowed extrapolation of nutrient contributions from the other tributaries based on values obtained from the synoptic survey. Nutrient concentrations and loads were similar to those found in other agricultural watersheds on the Eastern Shore and piedmont. Three subwatersheds, unnamed tributary at St. Martins Neck Rd.(Sta.1), Buntings Branch (Stat.4), and Church Creek (Sta.15), stood out because of high nutrient concentrations (3.8 mg/L Total dissolved N) and/or loads (5300 kgs TN/6 mos.). Benthic macroinvertebrate communities were influenced by nutrient levels, having higher productivity in the more enriched streams. Current macroinvertebrate community metrics were comparable to historic data from the same streams and stations. The stream corridor assessment documented a variety of conditions within the watershed. Inadequate buffer was the most prevalent condition (24), and channel alteration were the next most numerous condition (11). Other conditions include barriers to fish passage, pipe outfalls and bank erosion. These conditions where spread relatively evenly throughout the watershed. Additional investigations within the unnamed tributary upstream of Station 1, and the Church Branch and Birch Branch watersheds would refine the targeting of areas that could respond favorably to management and/or restoration activities geared towards nutrient reduction and habitat improvement.

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