Water quality of Cedar Creek reservoir in northeast Texas, 1977 to 1984
Water in Cedar Creek Reservoir in northeast Texas had volume-weighted average concentrations of less than 140 milligrams per liter of dissolved solids, less than 30 milligrams per liter of dissolved sulfate, and less than 25 milligrams per liter of chloride between vh nuary 1977 and August 1984. The water was soft to moderately hard; the total hardness concentrations ranged from 55 to 75 milligrams per liter as calcium carbonate. Thermal stratification in Cedar Creek Reservoir usually begins in late winter or early spring and persists until late fall. Stratification or summer stagnation causes significant seasonal and areal variations in concentrations of dissolved oxygen, iron, manganese, total inorganic nitrogen, and total phosphorus. Oxygen used in the decay of organic matter is not replenished during summer stagnation, and water below depths of 30 feet usually contains less than 2 milligrams per liter of dissolved oxygen. Often, oxygen is nearly depleted near the bottom in the deepest areas of the reservoir, thus causing reducing conditions. Reducing conditions during summer stagnation result in the dissolution of iron and manganese in bottom sediments. At the deepest site (Ac) near Joe B. Hoggset Dam, dissolved iron concentrations in water near the bottom averaged 1,860 micrograms per liter and manganese concentrations averaged 3,170 micrograms per liter. The concentrations of dissolved iron and dissolved manganese averaged less than 120 micrograms per liter throughout the reservoir during winter and spring circulation and in water near the reservoir's surface during summer stagnation. Seasonal temperature and dissolved oxygen cycles cause the recycling of dissolved iron and manganese between the water and bottom sediments. However, no substantial accumulation of these constituents within the reservoir was detected during the study. Of 10 trace elements studied, barium and arsenic were the most commonly found in detectable concentrations. Of 22 water samples collected for traceelement analysis, 15 contained barium in concentrations ranging from 40 to 300 micrograms per liter, and 19 contained arsenic in concentrations ranging from 1 to 26 micrograms per liter. However, these concentrations are below the maximum contaminant Hmit for barium (1,000 micrograms per liter) and arsenic (50 micrograms per liter) in drinking water. The concentrations of total inorganic nitrogen, total nitrogen, and total phosphorus were largest during summer stagnation in water near the bottom at the deepest sites. At site Ac, the largest total phosphorus concentration was 5.3 milligrams per liter for a bottom sample. The maximum total inorganic nitrogen concentration for the same sample was 2.5 milligrams per liter. Water near the surface of Cedar Creek Reservoir during summer stagnation and throughout the reservoir during winter circulation had total phosphorus and total inorganic nitrogen concentrations of less than 0.1 milligram per liter. Total nitrogen concentrations near the surface ranged from 0.3 to 1.1 milligrams per liter from January 1980 to August 1984.