Using δ¹⁵N- and δ¹⁸O-Values To Identify Nitrate Sources in Karst Ground Water, Guiyang, Southwest China

Abstract

Nitrate pollution of the karstic groundwater is an increasingly serious problem with the development of Guiyang, the capital city of Guizhou Province, southwest China. The higher content of NO3- in groundwater compared to surface water during both summer and winter seasons indicates that the karstic groundwater system cannot easily recover once contaminated with nitrate. In order to assess the sources and conversion of nitrate in the groundwater of Guiyang, we analyzed the major ions, delta(15)N-NH4+, delta(15)N-NO3-, and delta(18)O-NO3- in surface and groundwater samples collected during both summer and winter seasons. The results show that nitrate is the major dominant species of nitrogen in most water samples and there is a big variation of nitrate sources in groundwater between winter and summer season, due to fast response of groundwater to rain or surface water in the karst area. Combined with information on NO3- /Cl-, the variations of the isotope values of nitrate in the groundwater show a mixing process of multiple sources of nitrate, especially in the summer season. Chemical fertilizer and nitrification of nitrogen-containing organic materials contribute nitrate to suburban groundwater, while the sewage effluents and denitrification mainly control the nitrate distribution in urban groundwater.

Impact of different fertilizers on carbonate weathering in a typical karst area, Southwest China: a field column experiment

“…A monsoonal climate often results in high precipitation during summer, with much less during winter, although the humidity is often high throughout most of the year (Han and Jin, 1996). Agriculture is a major land use in order to produce the vegetables and foods in the suburbs of Guiyang (Liu et al, 2006). The consumption of chemical fertilizer increased from 150 kg ha −1 in 1980 to 190 kg ha −1 in 2013 (GBS, 2014).…”

Nitrogen pollution and source identification of urban ecosystem surface water in Beijing

“…Cl -is a good indicator of sewage impacts because it is not subject to physical, chemical, and biologic processes [43] and as such, the NO -…”

Identifying organic matter provenance in sediments using isotopic ratios in an urban river

“…Even so, phytoplankton was not an important contributor for sedimentary OM because of the relatively low contents of suspended materials in river water (<15 mg L -1 ) in most sampling sites. The δ 15 N values of soil OM sampled at Guiyang, reported by Liu et al (2006), averaged +5.7 ± 2.0‰. OM in surface soils (0-20 cm) of Huaxi (HX) has atomic C/N ratios between 9.3 and 19.5, and δ 13 C values between -26.4‰ and -22.3‰ (Zhu, 2006).…”

“…OM in surface soils (0-20 cm) of Huaxi (HX) has atomic C/N ratios between 9.3 and 19.5, and δ 13 C values between -26.4‰ and -22.3‰ (Zhu, 2006). Although soil OM has a similar characteristic to that of SOM (Liu et al, 2006), most of it was accepted by effluent channels and then enter the river. So soil OM was only a component of OM in effluents.…”