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Spatial distribution of nitrate sources of rivers in the Lake Biwa watershed, Japan: Controlling factors revealed by nitrogen and oxygen isotope values
Author(s) -
Ohte Nobuhito,
Tayasu Ichiro,
Kohzu Ayato,
Yoshimizu Chikage,
Osaka Ken'ichi,
Makabe Akiko,
Koba Keisuke,
Yoshida Naohiro,
Nagata Toshi
Publication year - 2010
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2009wr007871
Subject(s) - environmental science , watershed , hydrology (agriculture) , drainage basin , spatial distribution , precipitation , nitrate , structural basin , population , ecology , geology , geography , geomorphology , remote sensing , geotechnical engineering , machine learning , computer science , biology , cartography , demography , sociology , meteorology
To clarify the pathways and origins of dissolved nitrate (NO 3 − ) in rivers flowing into Lake Biwa, Japan, three types of coordinated surveys of concentrations and isotope compositions of NO 3 − were conducted: (1) synoptic river sampling of 32 representative inflow rivers, (2) two rivers in catchments with different land uses, and (3) headwater catchment samplings. The data set used in this paper is the first comprehensive collection of isotopic composition of NO 3 − in rivers of a large‐scale basin in Asia. While the NO 3 − spatial concentration pattern showed significant seasonal variation, the spatial pattern of the δ 15 N of dissolved NO 3 − was more consistent throughout the year. The was significantly positively correlated with the population density of each catchment. A mass balance model assuming the and the flow rate of sewage effluent was developed. The model simulated the relationship between the population density and the reasonably well, suggesting that the dominant source contributing to the increase in was the sewage effluent. The spatiotemporal distribution of suggested the possibility of the addition of atmospherically derived NO 3 − through precipitation and was indicated by the hydrological pathways for NO 3 − exports in different land uses. In forest‐dominated catchments with natural drainage systems, a slightly elevated δ 18 O NO3 signal remained in the stream water even during base flow conditions. This study demonstrated that multiscale, multi‐isotopic investigation is a promising strategy for describing the spatial distribution of NO 3 − sources synoptically and is useful for evaluating the influences of land use change.