Water quality of Belton Lake, central Texas

Abstract

The concentrations of dissolved solids, chloride, and sulfate in Belton Lake on the Leon River in central Texas average about 240 milligrams per liter, 40 milligrams per liter, and 30 milligrams per liter, respectively. The water is hard or very hard, averaging 170 milligrams per liter as calcium carbonate. The average concentrations of these constituents and hardness are least during late summer and early fall after periods of sustained high inflow. Thermal stratification begins to develop in Belton Lake in late February or early March. The water usually is stratified into three fairly distinct layers by early June, and stratification usually persists until September or October. Thermal stratification and seasonal variations in the concentrations of dissolved constituents in inflow result in stratification of the principal dissolved constituents. Dissolved solids in water at the surface of deep sites during summer differ from those at the bottom by about 40 milligrams per liter. Thermal stratification also results in significant seasonal and areal variations in dissolved oxygen, dissolved iron, dissolved manganese, total inorganic nitrogen, and total phosphorus. Oxygen used in the oxidation of dead organisms and other organic material near the bottom of the lake is not replaced during periods of summer stagnation. Consequently, water below depths of 35 to 40 feet (10.7 to 12.2 meters) usually contains less than 1.0 milligram per liter of dissolved oxygen during these periods. Water near the surface at most sites in the lake throughout the year usually contains less than 30 micrograms per liter of dissolved iron and 20 micrograms per liter of dissolved manganese. Reducing conditions during periods of summer stagnation result in tile dissolution of iron and manganese from the sediments in deep areas of the lake. The concentrations of both constituents are greatest near the bottom at site Ac, a deep site near Belton Dam. Iron concentrations at this site during the summer have ranged from 0 to 600 micrograms per liter and have averaged about 290 micrograms per liter; manganese concentrations have ranged from 0 to 540 micrograms per liter and have averaged about 320 micrograms per liter. Concentrations of total inorganic nitrogen and total phosphorus are greatest at deep sites during periods of summer stagnation when decay of aquatic organisms and chemical reduction of bottom sediments release the constituents to the water. The concentrations of total inorganic nitrogen and total phosphorus in the bottom stratum of water at site A c during the summer average about 0.75 milligram per liter of nitrogen and 0.10 milligram per liter of phosphorus. The concentrations of these constituents in the surface stratum at site A C during the summer average about 0.02 milligram per liter of nitrogen and 0.01 milligram per liter of phosphorus. The maximum concentrations of chlorinated hydrocarbon insecticides or their degradation products detected in bottom sediments collected from the lake during four lake surveys included 1.1 micrograms per kilogram of DDT, 3.0 micrograms per kilogram of DDD, 11 micrograms per kilogram of DDE, and 2 micrograms per kilogram of chlordane.