Water-quality reconnaissance of the Larkin Creek watershed, Lee and St. Francis counties, Arkansas

A reconnaissance of the Larkin Creek watershed in Arkansas was made during April through September 1980 to assess the water quality of streams in the watershed. Streamflow was measured and water samples were collected three times during the study period. Samples of bottom material were collected in September. Concentrations of dissolved solids ranged from 45 to 391 milligrams per liter. Water hardness ranged from 31 milligrams per liter (soft) to 280 milligrams per liter (very hard). Fecal-coliform bacteria densities ranged from 40 to an estimated 540 colonies per 100 milliliters and may have exceeded the U.S. Environmental Protection Agency criterion for bathing waters. Total nitrogen concentrations ranged from 0.90 to 2.2 milligrams per liter. Total phosphorus concentrations often exceeded the State standard and ranged from 0.08 to 0.46 milligrams per liter. Low dissolved-oxygen concentrations (2.5 to 5.4 milligrams per liter at midday) were measured in Larkin Creek and a major tributary. Iron (290 to 9,800 micrograms per liter), manganese (60 to 3,100 micrograms per liter), and mercury (0.0 to 0.2 micrograms per liter) concentrations at times exceeded Environmental Protection Agency criteria for domestic use or freshwater aquatic life. High concentrations of toxaphene (20 to 170 micrograms per kilogram dry weight) were present in all bottom-material samples. In two water samples, concentrations of dieldrin (0.01 micrograms per liter) exceeded the Environmental Protection Agency criterion for freshwater aquatic life. Polychlorinated biphenyls, several insecticides, and several herbicides (including 2, 4, 5-T) were present in water or bottom-material samples. (USGS)