Quantitative identification of nitrate sources using stable isotopes in
a drinking water source watershed of Eastern China
Abstract
The quantitative identification of nitrate sources is of great
significance for the control of non-point source pollution and the
comprehensive management of water resources in watersheds. δ
15N-NO 3 - and δ
18O-NO 3 - isotopes
combined with the Bayesian isotope mixing model were widely used as
effective methods to identify nitrogen sources. In this study, a total
of 60 surface water samples and 82 groundwater samples were collected in
study area from November 2021 to October 2022, and atmospheric
deposition (AD), chemical nitrogen fertilizer (NF), soil nitrogen (SN),
and manure and sewage (M&S) were determined as the potential nitrate
sources. Source identification by SIAR indicated that in November 2021
the M&S was the main contributor of nitrate to surface water (mean
38.1%), while NF was the main contributor to groundwater (mean 39.8%).
In April 2022, NF contributed the most to surface water (38.3%), while
groundwater mainly originated from SN (29.4%) and MS (29.8%). The
uncertainty analysis showed that the greatest uncertainties were in SN
and NF, followed by M&S and AD. Sensitivity analysis showed that the
changes in the nitrate isotopic composition of M&S had the greatest
effect on the results for δ 15N, whereas only the mean
values of oxygen isotope values of AD had a greater effect on the
results for δ 18O. The sensitivity analysis results
can optimize the sampling scheme and improve the accuracy of the model
predictions. Additionally, the contributions of soil nitrogen and
nitrogen fertilizer to nitrate in surface water and groundwater reached
58% and 64%, respectively. Therefore, optimizing fertilizer and
irrigation management is necessary to improve nitrogen use efficiency in
watershed management.