Stable Isotopes of Water and Nitrate for the Identification of Groundwater Flowpaths: A Review

Abstract

Nitrate contamination in stream water and groundwater is a serious environmental problem that arises in areas of high agricultural activities or high population density. It is therefore important to identify the source and flowpath of nitrate in water bodies. In recent decades, the dual isotope analysis (δ15N and δ18O) of nitrate has been widely applied to track contamination sources by taking advantage of the difference in nitrogen and oxygen isotope ratios for different sources. However, transformation processes of nitrogen compounds can change the isotopic composition of nitrate due to the various redox processes in the environment, which often makes it difficult to identify contaminant sources. To compensate for this, the stable water isotope of the H2O itself can be used to interpret the complex hydrological and hydrochemical processes for the movement of nitrate contaminants. Therefore, the present study aims at understanding the fundamental background of stable water and nitrate isotope analysis, including isotope fractionation, analytical methods such as nitrate concentration from samples, instrumentation, and the typical ranges of δ15N and δ18O from various nitrate sources. In addition, we discuss hydrograph separation using the oxygen and hydrogen isotopes of water in combination with the nitrogen and oxygen isotopes of nitrate to understand the relative contributions of precipitation and groundwater to stream water. This study will assist in understanding the groundwater flowpaths as well as tracking the sources of nitrate contamination using the stable isotope analysis in combination with nitrate and water.

Geochemical Characteristics of Alluvial Aquifer in the Varaždin Region

“…However, the highest concentrations in groundwater are usually from natural sources Another indicator of anthropogenic influence is high nitrate concentration (Figure 11). Usually, the sources of nitrate are fertilizers, organic and mineral [44][45][46]. Although agricultural production is dominant in the research area, there has been a decrease in agricultural surfaces and the application of fertilizers in the past 10-15 years, followed by an increase in the urban area by 12% [47].…”

Response of Nitrate Processing to Bio-labile Dissolved Organic Matter Supply Under Variable Oxygen Conditions in a Sandy Beach Seepage Face

“…The indiscriminate use of fertilizers, manure and waste sludge in land together with industrial spillages has led to the widespread accumulation of nitrate (NO 3 − ) in coastal groundwater on a global scale (Rivett et al, 2008). Coupled with the transport of groundwater from aquifers to coastal oceans driven by hydraulic gradients, a significant portion of land-derived NO 3 − reaches permeable coastal sediments in subterranean estuaries (STEs; defined as the underground mixing zone between continental groundwater and infiltrating seawater; Moore, 1999) prior to discharge to the coast (Jung et al, 2020;Ibánhez et al, 2021a). High groundwater-borne NO 3 − loadings frequently trigger a series of negative feedbacks on coastal ecosystems such as blooms of toxic phytoplankton, accumulation of organic matter, and oxygen depletion (Troccoli-Ghinaglia et al, 2010;Amato et al, 2016;Rocha et al, 2016).…”

Using Si, Al and Fe as Tracers for Source Apportionment of Air Pollutants in Lake Baikal Snowpack

“…Changes in organic tracer values may also occur during the sampling process [40][41][42] or due to physicochemical [43,44] or biological [45] fractionation. Stable isotopes of light elements are more conservative than those of PAHs; however, they also can be biased due to mixing of element sources and biological fractionation [46][47][48][49][50][51]. The most reliable results are obtained using lead isotope ratios as source tracers [52][53][54][55], as the Pb isotope ratio does not change in industrial or environmental processing, and retains its characteristic value from its source ore [56].…”