Assessment of sources and fate of nitrate in shallow groundwater of an agricultural area by using a multi-tracer approach

Abstract

Nitrate isotopic values are often used as a tool to understand sources of contamination in order to effectively manage groundwater quality. However, recent literature describes that biogeochemical reactions may modify these values. Therefore, data interpretation is difficult and often vague. We provide a discussion on this topic and complement the study using halides as comparative tracers assessing an aquifer underneath a sub-humid to humid region in NE Mexico. Hydrogeological information and stable water isotopes indicate that active groundwater recharge occurs in the 8000km(2) study area under present-day climatic and hydrologic conditions. Nitrate isotopes and halide ratios indicate a diverse mix of nitrate sources and transformations. Nitrate sources include organic waste and wastewater, synthetic fertilizers and soil processes. Animal manure and sewage from septic tanks were the causes of groundwater nitrate pollution within orchards and vegetable agriculture. Dairy activities within a radius of 1,000 m from a sampling point significantly contributed to nitrate pollution. Leachates from septic tanks caused nitrate pollution in residential areas. Soil nitrogen and animal waste were the sources of nitrate in groundwater under shrubland and grassland. Partial denitrification processes helped to attenuate nitrate concentration underneath agricultural lands and grassland, especially during summer months.

Contamination of Nitrate in Groundwater and Evaluation of Health Risk in Bachok, Kelantan: A Cross-Sectional Study

“…In the non-agriculture area, 35 wells had nitrate values exceeded 10 mg L −1 standard. This possibly due to factors of atmospheric deposition, discharge from septic tanks and leaking sewers which also can contribute to the high concentration of nitrate (Pastén-Zapata et al, 2014). Besides, soil characteristics and hydrogeologic variables such as depth of well, depth below the water table, aggregated thickness of clay above the well screen and thickness of clay in the unsaturated and saturated zones were also considered potential factors influence nitrate contamination in the study area Kuo et al, 2007;Khademikia et al, 2013).…”

“…The nitrate level in the agricultural area has exceeded the Malaysia NDWQS (10 mg L −1 NO 3 -N). The natural levels of nitrate in groundwater are usually less than 3 mg L −1 NO 3 -N and nitrate concentration exceeding the threshold of 3 mg L −1 NO 3 -N is considered as contaminated due to human activities (the so-called human affected value) (Babiker et al, 2004;Pastén-Zapata et al, 2014). The maximum acceptable levels of nitrate in drinking water is set at value 10 mg L −1 NO 3 -N according to Malaysia NDWQS.…”

Evaluating Temporal and Spatial Variation in Nitrogen Sources along the Lower Reach of Fenhe River (Shanxi Province, China) Using Stable Isotope and Hydrochemical Tracers

“…Total nitrogen (TN) is defined as the total amount of DIN and dissolved organic nitrogen (DON) in water. The TN concentration is one of the important indices to measure water quality [37]. In this study, the TN concentration in the IR was 26 ± 1.6 mg/L in the rainy season and 24.4 ± 3.0 mg/L in the dry season, while the TN concentration in the UR was the highest among the three regions, with mean values of 23.9 ± 3.1 mg/L in the rainy season and 28.6 ± 3.2 mg/L in the dry season, which means that the river water in this region is extremely polluted.…”

Sources and fate of nitrate in groundwater at agricultural operations overlying glacial sediments

“…In agricultural areas, multiple sources of NO3 -are common and could include precipitation, soil NO3 -, inorganic fertilizer, manure, and septic waste (Komor and Anderson, 1993;Liu et al, 2006;Pastén-Zapata et al, 2014;Clague et al, 2015;Xu et al, 2015). While source identification is theoretically possible using δ 15 NNO3 and δ 18 ONO3 (particularly with a dual-isotope approach), in practice this can be difficult due to geologic heterogeneity, overlapping source values, and the complexity of biologically mediated reactions 30 (Aravena et al, 1993;Wassenaar, 1995;Mengis et al, 2001;Choi et al, 2003;Granger et al, 2008;Vavilin and Rytov, 2015;Xu et al, 2015).…”