Graphical Analysis

A cultural asset at the heart of New York City, the Hudson River Park harbors a large and diverse aquatic fauna making it an environmental sanctuary of substantial ecological importance. Our field sampling easily captured fish and benthic invertebrates in high numbers and broad diversity. Other field researchers (e.g., Duffy-Anderson et al. 2003, Woodhead et al. 1999) studying aquatic life in New York City have reported similar conclusions: large and species-rich fish communities are present with ecological and societal value. Despite the abundance and diversity of aquatic life in the Park, we found both the fish and invertebrate communities are dominated by inappropriate organisms for shoreline waters in a mesohaline section of an Northeastern US estuary. The Park and nearby waters of the harbor contain essentially all fish that would normally compose the proper mesohaline shoreline community. However, the current Park community is overwhelmingly dominated by a few species that primarily occupy open areas of coastal and estuary waters. Benthic invertebrates display a similar pattern: a large array of taxa documented in the Park with the most common taxa not indicative of a quality estuarine environment. While the invertebrate fauna is not overwhelmed by a few taxa as seen with fish, the most common organisms are known for their tolerance of pollution and abilities to colonize and persist in stressed environments. Our conclusions are not new because other field research (Woodhead et al. 1999, Iocco et al. 2000, Adams et al. 2003) with larger spatial scope reported similar assessments for the lower Hudson River and upper Hew York harbor. Our overall depiction of the Park fauna is a hopeful conclusion. The proper shoreline faunal elements are present suggesting that changes in the physical and chemical environment of the Park could shift community composition to a more appropriate mix of organisms.

This study was designed to identify impacts of dredging at one inter-pier site in the Hudson River Park. Without pre-impact data, we relied on a comparison of the dredged site with a series of seven undredged sites over a period of time adequate to detect biotic recovery. Differences among sites and the diminishing of any differences over time were the two lines of evidence sought to assess dredging impact. The dredged site was found to be deeper and slightly more saline than the other site and it was similar in thermal and oxygen characteristics. It terms of biological properties, our results do not indicate that the fish or invertebrate communities (abundance and diversity) at the dredged site differ from other undredged sites in the Park. During the two year study period, fish and invertebrate communities varied in abundance and diversity like the other sites, and much of the time the dredged site was within the margin of error of biotic measurements at other sites. One exception was benthic invertebrate abundance and diversity that was clearly below the other sites for the first few months of the study. This could reflect an initial impact to the invertebrates at the dredged site; an expected finding for dredged sites.

The nature of fish and invertebrate communities in the Hudson River Park make detection of dredging impacts difficult. The dominant fishes, which comprised a large majority of the community, are not sensitive to shoreline habitat conditions and their disruption. The common invertebrates are tolerant of environmental stress and appear to be influenced by large widespread factors such as sediment contaminants and seasonally poor quality of bottom waters. Dredging is known to impact aquatic life at the disturbed locations (Allen and Hardy 1980, Johnston 1981). However, effects such as reduced abundance and diversity of estuarine organisms are commonly localized and short term (Lewis et al. 2001) with recovery of pre-disturbance levels in 6 to 12 months (Conner and Simon 1979) and sometimes longer (Blanchard and Feder 2003). We observed some evidence for low abundance and diversity invertebrates at the dredged site in the first couple months of the study. Otherwise, we obtained no data indicating a lasting effect at the dredged site which distinguished this location from the other sites through the Park waterfront. Instead our results indicate why the anticipated impacts of dredging were not evident.

For the entire Discussion, please consult the Final Report section in REPORTING.