Perturbing Effects of HNO3 On Carbonate Weathering in an Premontane Agricultural Region,an Example from the Upper Reaches of the Qingshui River
Carbonate rocks represent the largest carbon reservoir on Earth.A quantitative evaluation of the effects of HNO3 on the car-bonate weathering in the agricultural piedmont region is crucial for understanding the global carbon cycle.In July 2022,samples were collected from 13 monitoring points in the Qingshui River agricultural piedmont region.Hydrochemical and isotopic indicators(δ2H-H2O、δ18O-H2O、δ15N-NO3-and δ18O-NO3-)were analyzed.The MixSIAR model was employed to identify the primary sources of NO3-in river water,while hydrogeochemical evidence was utilized to elucidate the key biogeochemical processes controlling NO3-lev-els.The results indicated that the water in this agricultural piedmont region of the upper reaches of the Qingshui River was typically weakly alkaline,with a chemical composition categorized as HCO3-Ca·Mg type,and the ion composition of the water was primarily influenced by the combined dissolution of calcite and dolomite.The MixSIAR model results revealed that the contribution ratios of pollution sources were as follows:atmospheric deposition(0.18％±0.06％)＜NO3--synthetic fertilizer(0.40％±0.11％)＜soil organic nitrogen(9.30％±4.50％)＜NH4+-synthetic fertilizer(16.10％±9.00％)＜manure & domestic sewage(74.00％±13.00％).Approxi-mately 99.4％of riverine NO3-contents were derived from NH4+-containing pollutants.The HNO3 from microbial nitrification was in-volved in the weathering process of carbonate rocks.The participation of HNO3 in agricultural piedmont region accounted for 22.80％±6.80％of Ca2++Mg2+and 18.10％±7.50％of HCO3-in the river water,while reducing the carbon sink flux of carbonate weathering by 22.80％±6.80％.This may potentially exacerbate the water hardness and increase the NO3-pollution risk.
NETL
NSTL
万方数据
