Water-quality assessment of the Middle Fork Anderson River watershed, Crawford and Perry counties, Indiana

Abstract

Surface-water quality in the watershed is generally good except for problem-causing concentrations of bacteria, dissolved oxygen, and phosphorus at some sites along the main stem during low flow and manganese at most sites year-round. Dissolved-solids concentration ranged from 76 to 248 milligrams per liter. Concentrations at sites upstream from reservoirs were greater than those at sites downstream during medium and low flows, but concentrations at sites upstream and downstream were similar during high flow. Calcium and bicarbonate ions were dominant at most sites during low flows, whereas these ions were codominant with magnesium and sulfate at most sites during high flows. Dissolved-oxygen concentration ranged from 2.1 to 11.6 milligrams per liter or from 21 to 124 percent of saturation. Low concentrations were associated with the main stem of the river during low flows when sluggish, pooled conditions prevailed. Concentrations of certain inorganic constituents (including nutrients) were as follows: Dissolved-manganese concentration ranged from 0.02 to 7.3 milligrams per liter. The concentrations were generally higher at sites downstream from reservoirs than at sites upstream and was greater than the problem-causing level 0.05 milligrams per liter at most sites. The high manganese concentrations are probably associated with organic acids in the streams. Dissolved-nitrate concentration (as nitrogen) ranged from 0.03 to 3.3 milligrams per liter, the highest concentrations occurring during winter and spring in drainage from areas of the most intense cultivation. Dissolved-phosphorus concentrations were typically 0.03 milligrams per liter or less, except at one site in September 1975, when the concentration was 0.12 milligrams per liter, and at three sites in July 1976, when concentrations were 0.12, 0.41, and 0.58 milligrams per liter. Chlorinated hydrocarbons were detected in bed material from two of the three sites sampled. Two micrograms or less per kilogram aldrin, DDT, DDD, DDE, dieldrin, and (or) chlordane and as much as 15 micrograms per kilogram PCB compounds were detected. Suspended-sediment concentration ranged from 1 to 148 milligrams per liter. Concentrations in two sites downstream from reservoirs were higher for medium and low flows and, despite large changes in flow, were considerably more consistent than the concentrations at two sites unaffected by reservoirs. Concentrations of fecal-coliform and fecal-streptococcal bacteria ranged from 5 to 9,900 and from 10 to 15,000 colonies per 100 milliliters, respectively. Source of high counts (more than 2,000 colonies per 100 milliliters) is probably livestock upstream from sampling sites. Diversity indices (genera level) 2.7 and 2.5 at the two sites sampled for benthic invertebrates indicate healthy biologic communities at both sites. Diversity indices (genera level) of the phytoplankton populations at seven sites ranged from 1.4 to 3.3. The phytoplankton populations were generally well balanced except for stressed communities at two mainstem sites during the September sampling.