Nearshore Sediment Deposition Patterns Associated with a Subwatershed of Conesus Lake, NY

Sediment export and its associated phosphorus have been shown to be problematic in the Cottonwood Gully and similar watersheds of Conesus Lake, NY. The Cottonwood Gully watershed drains approximately 98 hectares that is approximately dominated by mixed row crop agriculture and dairy operations. A large macrophyte bed is located near the mouth of the stream and interacts with stream discharge and consequent sediment deposition. Sixty-five grab samples of the top 2.5 cm of sediment in an area defined by water depths ranging from 1 to 2 meters parallel to the coast were collected for particle size and chemical analyses. Results of particle size analyses show four distinct patterns on size distribution graphs. Median (D50) particle size, ranging from 19 to 395 microns, and D10 values, ranging from 2.9 to 77 microns were evaluated using the Mann-Whitney test. Samples were segregated into the four groups identified by size distribution graphs. All sets were determined to be statistically different at 95%. Furthermore, the spatial distribution of samples indicates that samples within the same groups are similarly located. This suggests the influence of the large macrophyte beds on sediment distribution and deposition patterns. Total P concentrations were also determined for a subset of 27 samples. Sediment concentrations of TP were found to range from approximately 190 mg/kg to 215 mg/kg, and do not appear to be correlated to particle size.