Relations Among Benthic Invertebrate Communities, Environmental Conditions, and Land Use in Streams of the Hudson River Basin, New York, 1993

Karen R. Murray , Patrick J. Phillips , and Gretchen L. Rouse (U.S. Geological Survey, 425 Jordan Rd., Troy NY 12180)

A survey of benthic invertebrate communities and chemical and physical conditions in streams of the Hudson River Basin, New York, was conducted during 1993 as part of the U.S. Geological Survey's National Water-Quality Assessment Program, to describe relations between land use and invertebrate community structure. Invertebrate samples were collected by a kick technique in riffle zones of 29 streams during a low-flow period. A subsample of 100 specimens was picked from each sample and identified to the lowest practical taxonomic level. Data on physical-habitat conditions and water-column chemistry were collected during periods of low, medium, and high flow.

The total number of taxa collected (after resolution to lowest common taxonomic level) was 122. Taxa richness per site ranged from 9 to 33. An ordination (detrended canonical correspondence) analysis produced two major axes of variation in the invertebrate data. The first axis represented a shift from communities characterized by taxa such as midges (Chironomidae), leeches (Hirudinea), and snails (Gastropoda), which possess broad tolerance to physical and chemical conditions, toward communities characterized by taxa such as stoneflies (Plecoptera) and caddisflies (Trichoptera: e.g. Brachycentrus) which have narrow environmental tolerances. The chemical properties that were most strongly correlated with this axis were specific conductance and chloride concentration (r = -0.87). This gradient in major ion concentration, could be associated with differences among sites in land use and (or) natural geochemical conditions. The ordination's second axis represented a shift from communities characterized by mayflies, (Ephemeroptera), caddisflies, stoneflies, and other taxa with narrow environmental tolerances to communities characterized by silt- and organic- tolerant flatworms (Planorbidae) and tubificid worms (Tubificidae). The chemical constituents most strongly correlatedwith the second axis were fecal coliform (r = 0.61) and organic nitrogen plus ammonia (r = 0.52). This axis suggests a gradient of organic enrichment. Most of the highly urban sites were associated with tolerant taxa and high fecal coliform on this axis.

The overall ordination analysis produced four major groups of sites that could be distinguished primarily on the basis of watershed land use: (1) sites in watersheds with a high percentage of urban and (or) residential land (median = 52 percent of total watershed area) and high population density (median = 1,002 per square mile); (2) sites in watersheds with a high percentage of agricultural land (median = 53 percent of total area); (3) sites in watersheds with a low to moderate percentage of either agricultural or residential land (median = 22 percent of total area) and low population density (median = 41 per square mile); and (4) two sites in heavily or totally forested watersheds (forest land = 92 and 100 percent of total area) and extremely low population density (less than 1 per square mile). These patterns suggest that invertebrate communities in streams of the Hudson River Basin are affected by environmental factors associated with land use.

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