Deciphering Natural and Anthropogenic Nitrate Sources and Fate in Arid Region Groundwater
Recently, the subsoils of ephemeral stream floodplains in the northern Chihuahuan Desert were discovered to contain large naturally occurring NO3- reservoirs (~38,000 kg NO3-N/ha). These reservoirs may be mobilized through land use change or natural stream channel migration. This makes differentiating between anthropogenic and natural groundwater NO3- sources challenging in arid regions. In this paper, I investigate the fate and sources of NO3- in an area with multiple anthropogenic NO3- sources and natural reservoirs of NO3- in ephemeral stream floodplains. To differentiate sources, this study uses a large suite of geochemical tools including nitrogen, oxygen, and carbon stable isotopes, carbon-14 (14C), tritium ( 3H), dissolved gas concentrations, major ion chemistry, and contaminants of emerging concern (COEC) such as pharmaceuticals, artificial sweeteners, and organic wastewater indicators. Based on elemental ratios and isotope analyses, at sites with very high NO3- concentrations (>25 mg/L NO3-N) NO3- is sourced from naturally occurring subsoil NO3- deposits. Nitrogen isotope results indicate that denitrification is fairly limited in the field area. As such, both anthropogenic and natural NO3- in groundwater will likely persist into the future. Neotame, a relatively recently approved (2002) artificial sweetener known to break down rapidly in the environment, was used to identify locations of very recent (<15 ybp) or ongoing wastewater influxes to the aquifer. Due to the ubiquity of COEC in groundwater even at 3H dead sites, this study shows that COEC are often more useful indicators of recent recharge than traditional geochemical tracers. Based on a synthesis of geochemical analyses, NO3- sources were classified as being largely from anthropogenic (62%), ephemeral stream floodplain subsoil NO3- (16%), background (12%), and unknown (10%). This work provides a template for future studies seeking to differentiate between multiple and potentially mixed natural and anthropogenic NO3- sources to groundwater
Year of publication: |
[2022]
|
---|---|
Authors: | Linhoff, Benjamin |
Publisher: |
[S.l.] : SSRN |
Subject: | Grundwasser | Groundwater |
Saved in:
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