Sediment type percentages and grain size (GeoTIFF grid format) from surface grain size analysis of sediment grab samples, Long Island Sound mapping project Phase II

Sediment grab samples were taken in summer of 2017 and 2018 using a modified van Veen grab sampler. A sub-sample of the top two centimeters was taken and stored in a jar. Dried sub-samples samples were analyzed for grain size. First, the samples were treated with hydroperoxide to remove organic components. Then, the sample was passed through a series of standard sieves representing Phi sizes with the smallest being 64 µm. The content of each sieve was dried and weighed. If there was sufficient fine material (< 64 µm), this fine fraction was further analyzed using a Sedigraph system. The results of sieving and sedigraph analysis were combined and the percentages for gravel, sand, silt and clay were determined following the Wentworth scale. In addition, other statistics including mean, median, skewness and standard deviation were calculated using the USGS GSSTAT program. The results of the LDEO/Queens College grain size analysis were combined with data collected by the LISMARC group and analyzed by USGS. ArcGIS Pro empirical kriging was used to interpolate values for gravel, sand, silt, clay, and mud percentages as well as for mean grain size onto a 50 m raster. The interpolated raster was clipped to fit the extent of the phase 2 survey area. The final raster data files are in GeoTIFF grid format with UTM-18 N projection. Funding was provided by the Long Island Sound Mapping Fund administered cooperatively by the EPA Long Island Sound Study and the Connecticut Department of Energy and Environmental Protection (DEEP).