Shallow Water Benthic Mapping: West Side Manhattan and Brooklyn Waterfront
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New York State Department of Environmental Conservation 21 South Putt Corners Road New Paltz, NY 12561 Shallow water benthic mapping: West side Manhattan and Brooklyn waterfront !!!!! !!!!! !! October 28, 2015 27 GLEN ROAD, NORTH ENTRANCE CH2M HILL SANDY HOOK, CONNECTICUT 06482 22 CORTLANDT ST. 31ST FLOOR P.O. BOX 178, NEWTOWN, CT 06470 NEW YORK, NY 10007 (203) 270-8100, FAX (203) 364-0480 (720) 286-2000 www.e4sciences.com WWW.CH2M.COM Disclaimer All interpretations are opinions based on inferences from geophysical, biological and other measurements. We cannot, and do not, guarantee the accuracy or correctness of any interpretation. We shall not, except in the case of gross or willful negligence on our part, be liable or responsible for any loss, costs, damages or expenses incurred or sustained by anyone resulting from any interpretations made by any of our officers, agents or employees. i Executive Summary The New York State Department of Environmental Conservation (DEC) monitors the Hudson River Estuary. The New York City Department of Environmental Protection (DEP) has partnered with the DEC to map the shallow waters in the Hudson and East Rivers. The DEP assigned e4sciences (e4) to map the sediment strata, the shoreline structures, and the benthic infaunal communities on both the western shoreline of Manhattan and the northwestern shore of Brooklyn. e4 measured the bathymetry, sonar reflectivity, seismic reflectivity, sediment chemistry, grain size, infrastructure, and benthic organisms. e4 collected and analyzed sediment cores and grab samples to determine grain size distribution, benthic invertebrate faunal communities, and sediment chemistry. e4 collected and analyzed Sediment Profile Imagery (SPI) to determine fine-scale structures, infaunal activity, and water chemistry at the sediment-water interface and within the uppermost few (~21 cm) centimeters of sediment. e4 integrated geological, chemical, and biological data with additional mapping, acoustic and sub-bottom datasets to derive sediment accumulation rates and integrated bottom classifications in the harbor. e4 also integrated newly collected data and analyses with previous work conducted in the harbor. The current analysis included measures of change over time, to the extent that previous work spatially and analytically overlaps areas of investigation in this project. e4 developed detailed bathymetric, acoustic-reflectivity, benthic-organism, and acoustic- character maps of the shallow portions of the Upper Bay of New York Harbor. The area of investigation is divided into eight areas: 1. Bay Ridge Flats 2. Governors Island 3. Sunset Park waterfront 4. Brooklyn Bridge Park 5. Brooklyn Navy Yard 6. West Manhattan waterfront South (Harrison St. to 17th St.) 7. West Manhattan waterfront Middle (17th St. to 57th St.) 8. West Manhattan waterfront North (57th St. to 109th St.) The survey, SPI drop, and grab sample site results show that five areas – Bay Ridge Flats, Brooklyn Bridge Park, Sunset Park waterfront, West Manhattan waterfront South, and West Manhattan waterfront Middle – are overall healthy, lightly stressed1 ecosystems. They represent the breadth of diverse benthic ecosystems in NY Harbor. The other three areas – Governors Island, the Brooklyn Navy Yard, and West Manhattan waterfront North – are a mixture of healthy and stressed sites. Some of the more diverse and well-established communities live in the sandier environments with better circulation. Many of the healthier communities in the three areas with a mixture of healthy and stressed sites, were observed in the physically quiet regions with lower deposition, erosion, or disturbance2. e4 finds healthy communities in both fine and coarse-grained 1 e4 based our definition of stress on the work of Hale et al. (2007) who limited environmental stress to three measurable parameters: dissolved oxygen, salinity, and sediment composition. Because the Organism Sediment Index (OSI) captures two of these three parameters, we used OSI values to determine designations of stress level at each of our samples sites. More generally, environmental stress refers to physical, chemical, and biological forces on the productivity of species and on the development of ecosystems. When the exposure to environmental forces or stressors, such as pollution or pathogens, increases or decreases in intensity, ecological responses result (Rhoads and Germano, 1986). 2 e4 based the definition used for disturbance throughout this report on the previous work of Don Rhoads. By Rhoads’ definition, disturbance refers specifically to sediments that have been anthropogenically affected and captures both chemical contamination and physical manipulation (e.g. construction and dredging) of the harbor bottom. In e4’s modified definition, we account for sediment accumulation rate (volume/area/year) and include both, but distinguish between, natural and anthropogenic processes. We relate ii sediments: communities dominated by Stage I species in fine-grained sediments; communities dominated by Stage III species in coarse-grained sediments. Grain size is a controlling factor in determining the kind of benthic community observed, while physical disturbance relates most strongly to the apparent health, as indicated by the Organism Sediment Index (OSI), of the community. e4sciences compared the current results with data collected 10 or more years ago. Seasonal spring to fall variations notwithstanding, e4sciences observed that the western shorelines of Manhattan and Brooklyn are generally healthy and have been improving since 1993. Efforts to remove polluted silts, increase park areas (with corresponding reductions in boat traffic), and clean the water have begun to show measurable success. For example, on the southwest shore of Manhattan, our study showed that the benthic environment is less stressed compared to the conditions reported by Hale et al. (2007) with healthy sites observed further northward than previously reported. This is likely the consequence of New York City’s continued efforts to improve water quality with advanced sewage treatment programs and education of the public to encourage a higher quality, sustainable New York Harbor ecosystem that benefits the overall community. In addition, 400 water-acres in this area were designated the Hudson River Park and became part of the Hudson River Park Estuarine Sanctuary in 1998, which has reduced use of the shallows (less boat traffic) in this area and also contributed to increased benthic ecosystem health. The current results, when compared with data collected 10 or more years ago, indicate that the quality of the overall benthic habitat within open water areas such as Bay Ridge Flats and Governors Island remained stabilized with many Organism-Sediment Index (OSI) values greater than 6. We found pockets of low quality habitats in Brooklyn Navy Yard, at the mouth of the Gowanus Canal, within berthing slips of West Manhattan waterfront North, and in sediment traps around the shore of Governors Island and on the slopes of Bay Ridge Flats. These areas are active both from natural tidal forces and from sediment movement related to human use of the harbor. Many have been previously identified as stressed habitats. Analyses of the benthic communities show a strong association with sediment type, specifically grain size. Acoustic reflectivity in the orthosonographs, benchmarked by cores and grab samples, distinguishes the differences between the sandy environments and the silty environments. The more diverse and well-established communities live in the sandier environments with better circulation, corresponding to the highest observed OSI values. There are healthy communities in the siltier, finer-grained sediments, however these sites are more variable and, we hypothesize, more sensitive to sediment accumulation rates. The contour map of the black silt shows that such environments are generally restricted to the inner confines of the piers and the leeward sides of structures and outcrops, such as Governors Island. Sites with the highest rates of black silt and sediment accumulation (e.g. BNY14-02, BRF14-12) have low OSI scores. In Bay Ridge Flats, Brooklyn Bridge Park, some sites at Governors Island, Sunset Park waterfront, West Manhattan waterfront South, and West Manhattan waterfront Middle, infaunal amphipods, gastropods, and other sediment feeders represent equilibrium stage (Stage III) or successional end-stage species. e4 found shallow-dwelling bivalves (Mulinia lateralis, Tellina agilis), grazing gastropods (Illyanassa sp.), and a few species of tubicolous amphipods (Ampelisca sp.). Stage III assemblages include maldanid, nepthyd, and lumbrinerid polychaetes, nuculanid clams, and Molpadia tunicates. These areas have deeply oxygenated sediment surfaces where the apparent redox discontinuity (aRPD) commonly reaches depths of over 10 cm. chemical contamination with apparent redox potential discontinuity (aRPD), which is a proxy for soil oxygenation, cleanliness, and biotic irrigation. iii Opportunistic benthic organisms can be found in Sunset Park waterfront, Brooklyn Navy Yard, West Manhattan waterfront North, the southern tip of Governors Island, and the western and eastern sediment traps at Governors Island (GI14-04 and GI14-08). The opportunists are the initial species to occupy organically enriched habitat. In our SPI analyses, we observed small opportunistic tube-dwelling polychaetes or oligochaetes, identified as Stage I successional species. They are among the first macrofaunal components