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

Sulfate (SO₄^2-) has received attention as means of monitoring water quality and pollution. However, the SO₄^2- 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 SO₄^2- 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 (S^2-), with ferrous (Fe²⁺) or manganese (Mn²⁺). SO₄^2- 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 SO₄^2- content was highest between temperatures of 20 °C and 25 °C. The relationship between SO₄^2- concentration, which varied with temperature and time, was fit using a linearized Michaelis-Menten function (R² = 0.69). The release of SO₄^2- to the water column was accelerated during the experiment (for temperatures higher than 20 °C), and led to higher SO₄^2- content in the water column than in pore water. The maximum concentration of SO₄^2- within the sediment occurred at a temperature of 20 °C. Comparing aerated and non-aerated tanks at 20 °C, we found that O₂ restricted SO₄^2- content in the water column; DO could, in turn, also be controlled by temperature. Fe²⁺ and Mn²⁺ had a negative correlation with SO₄^2-.