Minning River Sulfate Source Identification And Microbial Transformation-Based On Sulfur And Oxygen Isotopes

Identification of the the source of sulfate and geochemical activities of sulfate is an important prerequisite for environmental remediation.Stable isotope compositions of dissolved sulfate and have been widely used to track sulfate sources and relevant geochemical process,which is necessary to adequately understand the sulfur cycle,and fate of toxic heavy metals.In this study,Hengshi River located at the Dabaoshan Minning area was investigated.Dabaoshan minning area was near the largest poly-metallic sulfide mine of Guangdong Province in southern China.Surface water and sediment samples were collected from the Hengshi River at different seasons?January,August and November of 2016?.Phsical and chemical characters of arearal rivers,heavy metals distributions,mineralogy characteristics of sediments,sulfur distributions in water and sediments,and the isotopes compositions(?³⁴S and?¹⁸O)of dissolved sulfate were investigated,in order to identify the sources of dissolved sulfate and elucidate the geochemical and minning activities'influences on concentrations and isotopic compositions of dissolve SO₄^2-along the Hengshi River.In addition,we studied the sulfate reduction characteristics using the native mixed bacteria collected from sediments near Shangba Village in August,2016.Main results were as follows:?1?The Hengshi River was seriouslypolluted by the AMD from the impoundment before the operation of sewage treatment plant.Water at S1-S7 were acidic?pH<4?and had high levels of ORP?+192mV⁴50mV?,indicated that the water were in a strong oxidation state.In the mud impoundment,concentrations of cations were excessive and the abundances rank was Fe>Zn>Cu.Concentrations of cations decreased with increased distance from the headwater region.The operation of sewage treatment plant had positive effects on AMD's remediation.Due to the sewage treatment plant built in S2,pH of S3 raised rapidly accompanied by the decrease of cations.?2?The oxidation of pyrite by Fe???produced amounts of SO₄^2-which enriched the ³²S and ¹⁶O.The?³⁴S value was similar to the?³⁴S value of pyrite in Dabaoshan mining area.The isotopic composition of SO₄^2-in the upperstream?S1^S7?had little change,however,the values of?³⁴S and?¹⁸O in the downstream?S8^S11?increased gradually along the river.The average concentration of SO₄^2-in rivers not contaminated by AMD is low,but?³⁴S value is relatively high.Although the mineralization,injection of tributaries,atmospheric precipitation,and domestic sewage discharge will reduce the concentration of SO₄^2-ions in rivers,they have little effect on the?³⁴S and?¹⁸O values.The?³⁴S and?¹⁸O of the downstream?S8^S11?increased,probably due to the reduction of microorganisms.Rayleigh fractionation model showed that the enrichment factors of the S and O isotopes were between-0.431‰^-0.725‰and-1.141‰^-1.442‰,respectively.?3?The microbial composition in sediments of S8 mainly included:Acinetobacter,Paludibacter and Geobacter.The amount of sulfate reducing bacteria is small,but under certain conditions,microorganisms can reduce sulfate.When Fe³⁺and SO₄^2-are both electron acceptors,the reduction of iron takes precedence over sulfate reduction.The presence of SO₄^2-has no significant effect on the reduction of Fe³⁺,but the reduction of Fe³⁺promotes the reduction of SO₄^2-.When the concentration of Fe³⁺is 10 mM,all SO₄^2-can be reduced.The change of microbial community is obviously related to the reduction process in the system.In the iron reduction stage,with the consumption of electron donors,Anaeromusa,Acinetobacter and Bacteroides are the main dominant bacteria.In the sulfur reduction stage,SRB ?Desulfobulbus,Desulfosporosinus and Desulfovibrio?remained the dominant bacteria.