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Nitrate source apportionment using a combined dual isotope, chemical and bacterial property, and Bayesian model approach in river systems
Author(s) -
Xia Yongqiu,
Li Yuefei,
Zhang Xinyu,
Yan Xiaoyuan
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003447
Subject(s) - environmental science , effluent , denitrification , nitrate , dry season , agriculture , isotope analysis , sewage , fertilizer , hydrology (agriculture) , watershed , manure , wet season , apportionment , environmental engineering , environmental chemistry , nitrogen , ecology , chemistry , biology , geotechnical engineering , organic chemistry , machine learning , computer science , law , political science , engineering
Nitrate (NO 3 − ) pollution is a serious problem worldwide, particularly in countries with intensive agricultural and population activities. Previous studies have used δ 15 N‐NO 3 − and δ 18 O‐NO 3 − to determine the NO 3 − sources in rivers. However, this approach is subject to substantial uncertainties and limitations because of the numerous NO 3 − sources, the wide isotopic ranges, and the existing isotopic fractionations. In this study, we outline a combined procedure for improving the determination of NO 3 − sources in a paddy agriculture‐urban gradient watershed in eastern China. First, the main sources of NO 3 − in the Qinhuai River were examined by the dual‐isotope biplot approach, in which we narrowed the isotope ranges using site‐specific isotopic results. Next, the bacterial groups and chemical properties of the river water were analyzed to verify these sources. Finally, we introduced a Bayesian model to apportion the spatiotemporal variations of the NO 3 − sources. Denitrification was first incorporated into the Bayesian model because denitrification plays an important role in the nitrogen pathway. The results showed that fertilizer contributed large amounts of NO 3 − to the surface water in traditional agricultural regions, whereas manure effluents were the dominant NO 3 − source in intensified agricultural regions, especially during the wet seasons. Sewage effluents were important in all three land uses and exhibited great differences between the dry season and the wet season. This combined analysis quantitatively delineates the proportion of NO 3 − sources from paddy agriculture to urban river water for both dry and wet seasons and incorporates isotopic fractionation and uncertainties in the source compositions.