Anthropogenic impacts and quantitative sources of nitrate in a rural-urban canal using a combined PMF, δ15N/δ18O-NO3-, and MixSIAR approach.

Nitrate (NO3-) pollution in irrigation canals is of great concern because it threatens canal water use; however, little is known about it at present. Herein, a combination of positive matrix factorization (PMF), isotope tracers, and Mixing Stable Isotope Analysis in R (MixSIAR) was developed to identify anthropogenic impacts and quantitative sources of NO3- in a rural-urban canal in China. The NO3- concentration (0.99-1.93 mg/L) of canal water increased along the flow direction and was higher than the internationally recognized eutrophication risk value in autumn and spring. The inputs of the Fuhe River, NH4+ fertilizer, soil nitrogen, manure & sewage, and rainfall were the main driving factors of canal water NO3- based on principal component analysis and PMF, which was supported by evidence from δ15N/δ18O-NO3-. According to the chemical and isotopic analyses, nitrogen transformation was weak, highlighting the potential of δ15N/δ18O-NO3- to trace NO3- sources in canal water. The MixSIAR and PMF results with a <15% divergence emphasized the predominance of the Fuhe River (contributing >50%) and anthropogenic impacts (NH4+ fertilizer plus manure & sewage, >37%) on NO3- in the entire canal, reflecting the effectiveness of the model analysis. According to the MixSIAR model, (1) higher NO3- concentration in canal water was caused by the general enhancement of human activities in spring and (2) NO3- source contributions were associated with land-use patterns. The high contributions of NH4+ fertilizer and manure & sewage showed inverse spatial variations, suggesting the necessity of reducing excessive fertilizer use in the agricultural area and controlling blind wastewater release in the urban area. These findings provide valuable insights into NO3- dynamics and fate for sustainable management of canal water resources. Nevertheless, long-term chemical and isotopic monitoring with alternative modeling should be strengthened for the accurate evaluation of canal NO3- pollution in future studies.

Pollution source identification of nitrogen and phosphorus in the lower West Main Canal, the Ganfu Plain irrigation district (South China).

The degradation of surface water quality has been a widespread concern around the world. However, irrigation canal water does not attract much attention although it is important to agriculture and population. In this study, a 5-year water quality monitoring of surface water was conducted in the lower West Main Canal of the Ganfu Plain irrigation district to identify the levels and pollution sources of nitrogen and phosphorus.Over 75% of samples had total phosphorus (TP) concentrations of > 0.02 mg/L, and all samples had total nitrogen (TN) concentrations of > 0.2 mg/L, indicating a risk of eutrophication. The concentrations of NO3--N and NH4+-N averagely occupied 57% and 18% of TN, respectively. PCA analysis showed that phosphorus and nitrogen in canal water were associated with meteorological factors, urban life and surface runoff, agricultural cultivation, livestock-poultry breeding, and water-sediment interaction in the wet season, whereas they were affected by meteorological factors, industrial effluent, urban domestic sewage, and livestock-poultry breeding in the dry season. Absolute principal component score-multiple linear regression (APCS-MLR) model results revealed that (1) agricultural cultivation plus livestock-poultry breeding contributed 43.2% of TP in canal water in the wet season, while livestock-poultry breeding contributed 52.9% in the dry season, and (2) domestic sewage plus surface runoff contributed 29.4% of TN in the wet season, while livestock-poultry breeding contributed 45.9% in the dry season. The unidentified sources had significant contributions of > 20% for almost all variables. So further investigations are required for determining unidentified sources, and anthropogenic pollution control is imperative for canal water quality protection.

Strontium isotopic and hydrochemical characteristics of shallow groundwater and lake water in the Badain Jaran Desert, North China.

Shallow groundwater and lake water are the dominant water resources in the Badain Jaran Desert. There are still controversial hypotheses related to the origin of groundwater in this desert. Few studies have been conducted to explore the Sr provenance of these waters and assess the water-rock interactions using a Sr isotope approach until now. In this text, the Sr isotope data of waters in the hinterland of the Badain Jaran Desert and neighbouring areas are reported. The waters in the Badain Jaran Desert have few links to its surrounding rivers, but could be influenced by the precipitation in the Yabulai Mountains. The 87Sr/86Sr ratio changes constantly, while the Sr2+ concentration of shallow groundwater gradually decreases from Yabulai to the desert hinterland to Gurinai-Guaizihu. Combined with hydrochemical data and hydrodynamic conditions, these results show that the dissolved Sr of waters in the desert hinterland is controlled by the Yabulai precipitation and catchment weathering. They further show that the desert shallow groundwater Sr originates mainly from the Yabulai precipitation (> 94 %), while whole-rock weathering contributes little (< 6 %), as calculated using isotope mass balance equations. Relative Sr contributions to lakes from shallow groundwater and catchment weathering are calculated to be 92.5 and 7.5 %, respectively.

Major ion chemistry of a representative river in South-central China: Runoff effects and controlling mechanisms.

The Gan River is a large tributary of the Yangtze River in Jiangxi Province, South-central China. Hydrochemical data for this river were analyzed for the period 1958-2016. Ca2+, Na+ + K+, HCO3-, and SO42- were dominant in river water, and pH and total dissolved solids (TDS) varied from 6.0 to 8.8 and 15.7 to 141 mg/L, respectively. The chemical composition of river water was different between the two periods 1958-1979 and 1980-2016. Monthly yields of all ions were positively correlated with river runoff. Monthly yields of SO42-, NO3-, and Cl- were more positively correlated with river runoff before 1980, indicating non-point sources, while multiple sources were indicated after 1980. Sea salt-sourced Cl- comprised less than 19% of the total Cl- in river water. Weathering of basin rocks with sulfuric acid reflected strengthening of anthropogenic activities after 1980. This was reflected by increases in Cl-/(Na+ + Cl-) and SO42-/(Na+ + Cl-) with gross domestic production, population, coal consumption, fertilizer use, and wastewater discharge. Although water quality in the Gan River makes the water acceptable for drinking according to the World Health Organization standards, increases in Cl- and NO3- concentrations after 1980 are of some concern.