PESTICIDE, DISSOLVED ORGANIC CARBON, AND NITRATE CONCENTRATIONS IN SURFACE WATERS OF THE CANAJOHARIE CREEK WATERSHED, NEW YORK, April 1994-July 1995.
Patrick J. Phillips (U.S. Geological Survey, 425 Jordan Road, Troy NY 12180) and Gary R. Wall* (Rensselaer Polytechnic Institute, Department of Earth and Environmental Sciences, West Hall, Troy NY 12180)
Analyses of surface-water samples collected in the Canajoharie Creek watershed from April 1994 through July 1995 indicate that the processes that control pesticide and nutrient concentrations vary with flow conditions and that shallow ground water is a significant source of these constituents under most flow conditions. Canajoharie Creek, a tributary to the Mohawk River drains 150 km2, of which more than 60 percent is agricultural land. The valley floor throughout much of the watershed is underlain by a 1- to 4-m-thick surficial aquifer, composed of late Pleistocene/Holocene fluvial sand and gravel that covered a post glacial-lake bottom. The land surface above the aquifer is permeable and extremely flat, and, thus, causes minimal overland flow. Water samples were collected along the Canajoharie Creek mainstem and from drainage ditches and tile drains in farmed areas within 1 km of the mainstem.
The highest pesticide concentrations (in excess of 2 ug/L for atrazine and cyanazine) in Canajoharie Creek occur during stormflows from June through August in association with elevated dissolved organic carbon (DOC) and nitrate concentrations. For example, the concentration of atrazine increased from 0.38 to 4.3 ug/L, that of DOC increased from 4 to 7.1 mg/L and that of nitrate as increased from <0.05 to 2.2 mg/L as the discharge at Canajoharie Creek increased from 0.15 to 2.5 cubic meters per second over a 7-day period in late June and early July 1994.
Samples collected in a synoptic survey under base-flow conditions were collected at six mainstem sites and at drainage ditches and tile drains within the Canajoharie Creek watershed in September 1994 and June 1995. Base-flow nitrate concentrations in the tile drains and drainage ditches exceeded those in the mainstem, suggesting that nitrate concentration should increase downstream, along the mainstem, but mainstem nitrate data show a downstream decrease in nitrate concentration from the headwaters to the mouth. A similar downstream decrease in silica and increase in DOC concentrations suggest that the decreasing nitrate concentration is attributable to uptake by algae in the mainstem channel.
Abstract published in American Geophysical Union 1995 Fall Meeting, EOS 76 (46), p. F195.
*Present address - U.S. Geological Survey, 425 Jordan Road, Troy NY 12180
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