Abstract: Damming on the rivers has important effects on biogeochemical cycles of carbon,nitrogen and sulfur. To clarify the responses of C and S elements under the influence of cascade reservoirs, four representative cascade reservoirs in Jialing River were selected as the research objects. Samples of inflow, outflow, and stratified water in four cascade reservoirs were collected in winter (January) and summer (July) of 2016. Dissolved inorganic carbon (DIC) concentration, SO₄^2- concentration and isotopic compositions of δ¹³C_DIC and δ³⁴S were analyzed. The results showed that: (1) Water chemistry was mainly controlled by carbonic acid balance. At the same time, H₂SO₄, derived from pyrite and atmospheric SO₂ oxidation, was widely involved in regional carbonate weathering; (2) DIC was mainly affected by soil CO₂ and carbonate. SO₄^2- was mainly controlled by precipitation and pyrite oxidation process; (3) Significant correlations (P<0.05) existed among paired characters of reservoir water DIC concentration, SO₄^2- concentration, δ³⁴S value and δ¹³C_DIC value, indicating that the spatial and temporal dynamics of C and S elements in reservoir were affected by similar processes (physical, chemical, and biological). After intercepting of the dam, the river water environment and nutrient cycle had undergone great changes. The use of C and S double isotopes can effectively track the limnetic evolution of reservoirs.

Key words: pollution degree, leaf surface morphology, PM₂₅ adsorption amount, water-soluble ionic characteristics