Physical and chemical limnology of Ides Cove near Rochester, New York, 1970-1982

Water-Resources Investigations Report 92-4052

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Ides Cove is a small embayment on the western shore of Irondequoit Bay near Rochester, N.Y. In 1982, alum was applied to the cove to seal the bottom sediments and thereby decrease nutrient fluxes in an effort to assess the applicability of this technique to Irondequoit Bay. Published data were used to develop a baseline analysis of the chemical and physical limnology of Ides Cove prior to the alum treatment and to provide a basis for comparison and evaluation of post-treatment data. The baseline analysis also enables evaluation of trends in the nutrient status and mixing patterns in Ides Cove since the decrease of sewage inflows and use of road salt in the Irondequoit Bay and Ides Cove drainage basins during 1970-82. Data from 1970-72 and 1979-82 were used to construct partial and full-year depth profiles of several physical properties and chemical constituents of water in the cove; comparison of these profiles indicates a significant improvement in water quality between 1970 and 1982. The diversion of sewage out of the Irondequoit Creek drainage basin in the late 1970's resulted in an 80-percent decrease in total phosphate concentration and a 50- to 60-percent decrease in nitrogen (nitrate and ammonia) concentration in the cove. Indications of decreased primary productivity are associated with these lowered nutrient concentrations. Summer Secchi-disk transparency increased from 0.6 m (meters) in 1970-72 to 1.2 m in 1980-82; peak epilimnetic dissolved oxygen levels decreased from a range of 22 to 28 mg/L (milligrams per liter) to a range of 16 to 20 mg/L; and peak epilimnetic pH decreased from greater than 9.4 to between 8.8 and 9.0. The decrease in the use of road salt in the Irondequoit basin beginning in 1974 resulted in a decrease in chloride concentration and gradient (difference between the surface and bottom con- centration). The maximum annual chloride concentration in the epilimnion decreased from the 210-to-225-mg/L range in the spring of 1971-72 to the 140-to-l50-mg/L range in the spring of 1980-82, and the gradient between the hypolimnion and epilimnion during the spring decreased from the 80- to 160-mg/L range in 1971-72 to the O- to 90-mg/L range in 1980-82. Specific conductance values decreased similarly and indicate a comparable decrease in the density gradient from 1970-72 to 1980-82. The decrease in the density gradient resulted in an increase in the depth and duration of mixing in both the spring and fall of 1980-82, as illustrated by the profiles of physical properties, including temperature and specific conductance, and of chemical properties and constituents, including pH, alkalinity, dissolved oxygen, chloride, silica, and several species of nitrogen, phosphorus, and sulfur. These data indicate that Ides Cove, which was described as marginally meromictic in the early 1970's, had evolved by the early 1980's into a spring meromictic water body that underwent complete mixing in the fall and was approaching a consistent dimictic condition with spring and fall mixing. Thus, water quality and mixing patterns of the cove improved with the removal of sewage and the decrease in the use of road salt.

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USGS Numbered Series
Physical and chemical limnology of Ides Cove near Rochester, New York, 1970-1982
Series title:
Water-Resources Investigations Report
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U.S. Geological Survey ; U.S. Geological Survey, Books and Open-File Reports [distributor],
v, 45 p. :ill., map ;28 cm.