USE OF CHEMICAL, BIOLOGICAL, AND HYDROLOGIC DATA TO ASSESS WATER QUALITY IN CANAJOHARIE CREEK WATERSHED, NEW YORK

G. R. Wall* , (Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180), P. J. Phillips , (U.S. Geological Survey, 425 Jordan Rd., Troy, NY 12180), and B. Bode, (New York State Department of Environmental Conservation, 425 Jordan Rd., Troy, NY 12180)
Chemical, hydrologic, and biologic information was synthesized to assess surface-water quality in the Canajoharie Creek basin, a 60-mi2 agricultural watershed in upstate New York. Temporal and spatial patterns of silica and nitrate concentrations, and spatial patterns of chlorophyll-a concentrations in stream water, indicate a biological effect on nitrate concentrations and suggest that diatoms inversely affect nitrate and silica concentrations. Concentrations of dissolved nitrate and silica varied seasonally at the watershed outlet from April 1993 through September 1995; the highest concentrations (1.0 to 1.5 milligrams per liter and about 5.0 milligrams per liter, respectively) were measured from December through March, and the lowest concentrations (about 0.1 milligrams per liter, and 1.0 milligrams per liter respectively) were measured from May through November, when biological activity was high. Concentrations of both constituents decreased, and concentrations of chlorophyll-a in phytoplankton increased, downstream along the mainstem during base-flow conditions (June 1995).

Many of the spatial changes in stream chemistry parallel biological changes in invertebrate communities. Effects of agricultural inputs on invertebrate communities are evident along downstream reaches at sites for which relations among nitrate, silica, and chlorophyll-a con- centrations were observed. The invertebrate community near the head waters along the mainstem is characterized by taxa tolerant of siltation. Chemical and hydrologic data from this location suggest two natural (background) sources of siltation: (1) Judds Falls tributary contributes elevated concentrations of dissolved constituents that probably cause significant chemical precipitation in the mainstem, and (or) (2) a significant decrease in channel slope at the same location could result in increased sedimentation.

The water-quality assessment based on invertebrate communities did not always correspond to the assessment based on chemical data. For example, concentrations of atrazine (a common herbicide) increased downstream throughout the year along a 12-mile reach of mainstem (from 0.025 micrograms per liter upstream to 0.065 micrograms per liter downstream), but no significant decline in water quality was observed from the invertebrate community data. This apparent inconsistency could indicate that the downstream increase in atrazine concentration is too small to produce observable biologic effects, or that changes in community composition were present but not reflected in the water quality assessment.


Abstract published in American Geophysical Union 1996 Spring Meeting, EOS 77 (17) p. S117.

*Present address - U.S. Geological Survey, 425 Jordan Rd., Troy, NY 12180
US Geological Survey Back to the Hudson NAWQA Publications Page