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Determining nitrogen fate by hydrological pathways and impact on carbonate weathering in an agricultural karst watershed

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International Soil and Water Conservation Research 2023年第2期11卷 327-338页

作者： Zhuo Hao Yang Gao Yang Yang Qingwen Zhang Agricultural Clean Watershed Research Group Institute of Environment and Sustainable Development in AgricultureCAASBeijing100081China Key Laboratory of Ecosystem Network Observation and Modeling Institute of Geographic Sciences and Natural Resources ResearchCAsBejing10011 China Sierra Nevada Research Institute University of CalifomiaMercedCA95344USA

Identifying the nitrogen(N)fate is complicated and a great challenge in karst watersheds because of the co-existence of natural pools and anthropogenic sources.The objective of the study was to use stable isotopic composition of dual-isotope(δ^(15)NNitrate and δ^(18)O_(Nitrate))and LOADEST model approaches to trace N sources,pathways in karst watershed.The study was conducted in the Houzhai watershed,which is a typical agricultural karst watershed from July 2016 to August 2018,to reveal the N fate and the coupled carbon(C)-N processes occurring in the riverine-watershed with agricultural activities.We found that the wet deposition of total nitrogen(TN)flux was 33.50 kg hm^(-2)·a^(-1)and dissolved nitrogen(DN)flux was 21.66 kg hm^(-2)·a^(-1).The DN runoff loss was 2.10×10^(5)kg·a^(-1)and the loss of DN during the wet season accounted for 95.4%over a year.In the wet season,NO_(3)^(-)-N daily efflux was 977.62±516.66 kg ha^(-1)·day^(-1)and 248.77±57.83 kg ha^(-1)·day^(-1)in the dry season.The NH_(4)^(+)-N efflux was 29.17±10.50 kg ha^(-1)·day^(-1)and 4.42±3.07 kg ha^(-1)·day^(-1)in the wet and dry seasons,respectively.The main form output load of N was NO_(3)^(-)-N which was more than 30 times as much as NH_(4)^(+)-N output loss.The NO_(3)^(-)N caused by rainfall contributed11.82%-53.61%to the export load.Nitrate from soil contributed over 94%of the N to Houzhai river caused by N leaching.In addition,manure and farmland soil were the main sources of groundwater in the Houzhai watersheds,the contribution rates were 25.9%and 22.5%.The chemical N fertilizers affected carbonate weathering strongly,and the HCO_(3)^(-) flux caused by nitrifi-cation due to N fertilizers application in soil accounted for 23.5%of the entire watershed.This study suggested that carbonate weathering may be influenced by nitrogen nitrification in the karst watershed.

关键词： Karst Agricultural watershed hydrological pathway Nitrogen Carbonate weathering

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