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Temporal and Spatial Variation of Nitrate Sources in the Chishui River Watershed based on Isotope Approach (Vol.47, No.6, Tot No.332) TEXT SIZE: A A A

REN Yimeng1, YUE Fujun1, XU Sen1, CHEN Sainan1, WANG Zhongjun2, LI Siliang1

(1.Insititute of Surface-Earth System Science, Tianjin University, Tianjin 300072;
2. Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081)

Abstract: The Chishui river watershed is an important water conservation area of the Yangtze River Basin with very high economic values, its ecological service function and water environment quality such have attracted more and more public attentions. To understand water quality of this watershed, the nitrate pollution resulted from human activities was studied from the perspectives of sources and transformation processes of nitrate using approaches of stable isotopes (15N, 18O) in nitrate and land uses during wet season and dry season. Nitrate concentrations showed significant spatial and temporal heterogeneity, nitrate concentrations were higher in wet season than in dry season and higher in karst areas than in non-karst areas. The seasonal variations of dual isotopes of nitrate in the mainstream and tributaries were different, for example, the variation of N isotope compositions was small in tributary samples and big in mainstream samples during wet seasons, but the scenario was reversed during dry seasons. The data of land use and dual nitrate isotopes suggested that nitrate sources of tributaries varied and depended largely on the land use, while nitrate sources of the mainstream were mixtures of tributaries contributions. During dry seasons, nitrate in tributaries derived mainly from soil organic nitrogen and showed obvious signals of anthropology activities since the tributaries located mostly in developed areas. To manage the nitrogen pollution in the Chishui river watershed, more attentions on the upper and middle stream where the karst landscape widely spreads should be paid. Meanwhile, the controlling of point sources in the downstream of the Chishui river watershed is also important.

Key words: nitrate; nitrogen and oxygen isotope; nitrogen sources; land use; Chishui River Watershed

EARTH AND ENVIRONMENT Vol.47, No.6, Tot No.332, 2019, Page 820-828

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