ABSTRACT

The U.S. Geological Survey (USGS), the New York State Department of Environmental Conservation (NYSDEC), and Cornell University carried out a cooperative 2-year study from the fall of 2004 through the fall of 2006 to characterize the potential effects of recreational-flow releases from Lake Abanakee on natural resources in the Indian and Hudson Rivers. Researchers gathered baseline information on hydrology, temperature, habitat, nearshore wetlands, and macroinvertebrate and fish communities and assessed the behavior and thermoregulation of stocked brown trout in study reaches from both rivers and from a control river. The effects of recreational-flow releases (releases) were assessed by comparing data from affected reaches with data from the same reaches during nonrelease days, control reaches in a nearby run-of-the-river system (the Cedar River), and one reach in the Hudson River upstream from the confluence with the Indian River.

A streamgage downstream from Lake Abanakee transmitted data by satellite from November 2004 to November 2006; these data were used as the basis for developing a rating curve that was used to estimate discharges for the study period. River habitat at most study reaches was delineated by using Global Positioning System and ArcMap software on a handheld computer, and wetlands were mapped by ground-based measurements of length, width, and areal density. River temperature in the Indian and Hudson Rivers was monitored continuously at eight sites during June through September of 2005 and 2006; temperature was mapped in 2005 by remote imaging made possible through collaboration with the Rochester Institute of Technology. Fish communities at all study reaches were surveyed and characterized through quantitative, nearshore electrofishing surveys. Macroinvertebrate communities in all study reaches were sampled using the traveling-kick method and characterized using standard indices. Radio telemetry was used to track the movement and persistence of stocked brown trout (implanted with temperature-sensitive transmitters) in the Indian and Hudson Rivers during the summer of 2005 and in all three rivers during the summer of 2006.

The releases had little effect on river temperatures, but increased discharges by about one order of magnitude. Regardless of the releases, river temperatures at all study sites commonly exceeded the threshold known to be stressful to brown trout. At most sites, mean and median water temperatures on release days were not significantly different, or slightly lower, than water temperatures on nonrelease days. Most differences were very small and, thus, were probably not biologically meaningful. The releases generally increased the total surface area of fast-water habitat (rapids, runs, and riffles) and decreased the total surface area of slow-water habitat (pools, glides, backwater areas, and side channels). The total surface areas of wetlands bordering the Indian River were substantially smaller than the surface areas bordering the Cedar River; however, no channel geomorphology or watershed soil and topographic data were assessed to determine whether the releases or other factors were mainly responsible for observed differences.

Results from surveys of resident biota indicate that the releases generally had a limited effect on fish and macroinvertebrate communities in the Indian River and had no effect on communities in the Hudson River. Compared to fish data from Cedar River control sites, the impoundment appeared to reduce total density, biomass, and richness in the Indian River at the first site downstream from Lake Abanakee, moderately reduce the indexes at the other two sites on the Indian River, and slightly reduce the indexes at the first Hudson River site downstream from the confluence with the Indian River. The densities of individual fish populations at all Indian River sites were also reduced, but related effects on fish populations in the Hudson River were less evident. Although statistical comparisons (and defensible conclusions) were not possible with the limited fishery data, the findings suggest that both the releases and the unique habitat (physical, chemical, and thermal features) of the lower Indian River are responsible, at least in part, for the character of the local fish populations and communities. The effects of both impoundments on macroinvertebrate communities in the Indian and Cedar Rivers were prominent and appear to overwhelm or mask possible effects related to the recreational releases. Compared to macroinvertebrate data from Cedar River control sites, the releases had small significant effects on macroinvertebrate assemblages and dominant species in the Indian River, and they occurred primarily downstream from the Lake Abanakee Dam. The macroinvertebrate communities at the Hudson River control site did not differ significantly from those at all other Hudson River sites and indicates that the effects of the impoundment and the releases did not extend much beyond its confluence with the Indian River.

The thermal-imaging and fish-telemetry results confirm that river temperatures in the Indian and Hudson study reaches were usually stressful to brown trout during the warm summer months. Few thermal refuges (defined as water at least 1°C cooler than the temperature in the main channel) were evident in both rivers during normal summer base flows, and use of these refuges by brown trout was typically low to moderate during 2005 and 2006. A few cold-water tributaries to the Hudson River provided limited areas of thermal refuges, but the releases from Lake Abanakee effectively eliminated these refuges by swamping them with warmer water. Multilevel-effect analyses indicate that the releases significantly reduced the ability of trout to thermoregulate themselves in the Indian and Hudson Rivers. The releases should ostensibly have only negligible effects on brown trout in the Indian and Hudson Rivers because few thermal refuges exist in both reaches, and relatively few study trout were found to exploit them. Trout movement was unaffected by the flow releases, but persistence of trout was low in the Indian and Hudson Rivers during 2005 and 2006 and higher in the Cedar River during 2006.

First posted May 6, 2011