Sulfur isotope composition characters of Wujiang river water in Guizhou province

The sulfur isotopic (δ³⁴S-SO₄^2-) composition of the water in Wujiang river and its catchment area was measured during high-flow period.The average SO₄^2- concentration is 0.48 mmol/L.The river water δ³⁴S values range from -11.5‰ to 8.3‰,whereas the δ³⁴S values of mainstream show only a narrow range and exhibit negative values from -6.7‰ to -3.9‰.The isotopic composition of surface water allows distinguishing the contribution due to the weathering rock and atmospheric precipitation,and the spatial variation in δ³⁴S over the catchment area is obvious.The average SO₄^2- concentration is higher in the upper part of the river than in the lower regions,while the average δ³⁴S value is lower.The upper river shows a three end 2 member mixing between rainwater SO₄^2-,SO₄^2- from oxidation of pyrite in coal and the sulfide deposits.In the lower reaches,the samples lie mainly on the isotopic mixing trend between the evaporitic SO₄^2- and rainwater SO₄^2-,the contribution of SO₄^2- from oxidation of pyrite is less.The SO₄^2- export flux of Wujiang river is 172×10¹⁰ g/a,of which the high-flow period export flux accounts for 80%.the relative contributions from the oxidation of pyrite in coal,the oxidation of sulfides deposits,the rainwater SO₄^2- and the evaporitic SO₄^2- are 50%,25%,20% and 5%,respectively.The erosion rate of carbonate by sulfuric acid is 35.1 t/km²/a (17.5 mm/ka) and the consumption rate reducing CO₂ is 3.66×10⁵ mol/km²/a approximately.