The effect of temperature on sulfate release from Pearl River sediments in South China

Abstract

Sulfate (SO42−) has received attention as means of monitoring water quality and pollution. However, the SO42− content of rivers, lakes, and reservoirs varies significantly by season, so environmental factors such as temperature can affect it. An experiment was conducted with a series of aerobic and anaerobic tanks containing Pearl River sediments and distilled water to assess the release of SO42− from sediments under controlled conditions. “Black-odor river” refers to near anoxic conditions in the water column and foul odors emanating from affected rivers in southeastern China. These river systems typical have sediments containing ammonia (NH3), hydrogen sulfide (H2S), and organic sulfide compounds in excess, and precipitates of sulfide (S2−), with ferrous (Fe2+) or manganese (Mn2+). SO42− concentration was measured at various depths in pore water and in the water column while controlling temperature and dissolved oxygen (DO) concentrations. Interpolation of study results revealed that SO42− content was highest between temperatures of 20 °C and 25 °C. The relationship between SO42− concentration, which varied with temperature and time, was fit using a linearized Michaelis-Menten function (R2 = 0.69). The release of SO42− to the water column was accelerated during the experiment (for temperatures higher than 20 °C), and led to higher SO42− content in the water column than in pore water. The maximum concentration of SO42− within the sediment occurred at a temperature of 20 °C. Comparing aerated and non-aerated tanks at 20 °C, we found that O2 restricted SO42− content in the water column; DO could, in turn, also be controlled by temperature. Fe2+ and Mn2+ had a negative correlation with SO42−.