Sulphur isotope mass balance of dissolved sulphate ion in a freshwater dam reservoir

We show that sulphur isotopic composition can be a useful tool to discriminate between various sources of sulphate and a tool for better understanding of the sulphur cycling and mass balance. Our investigations, carried out in a dam reservoir, demonstrate differences in sulphur biogeochemistry between different seasons, caused by recharge water supply in spring and intensive sulphate reduction in summer. In the riverine-affected part of the reservoir δ³⁴S(SO₄ ²⁻) varied from 4.7 to 5.9‰ in spring, and from 4.1 to 4.6‰ in summer. In the lacustrine-affected part δ³⁴S(SO₄²⁻) varied from 4.0 to 5.0‰ in spring, and from 4.5 to 5.4‰ in summer. Diurnal variations of δ³⁴S(SO₄ ²⁻) were negligible as compared to seasonal variations.