Abstract
An unusually high concentration of nitrate (NO3) ranging between 291 and 6790 mg/L (as N) was observed during a review of solute data for brine samples from the inland Sabkha Matti. A multi-tracer approach considering water chemistry, stable nitrate isotopes (δ15N and δ18O), and the radioactive isotope of hydrogen (tritium, 3H) was utilized to evaluate the nitrate sources and transformation in this hydrogeological setting. The results suggested that the source of the high nitrate levels is related to a leakage from a manure/septic system near the proximal eastern edge of the Sabkha. Moreover, the impact of Sabkha’s characteristics on biological denitrifications was evaluated in this study. The results suggest that denitrification was not a major process in Sabkha Matti. Several factors may contribute to the limitation of denitrification on the brine samples including high dissolved oxygen contents, high salinity and chloride.
Highlights
Concentrations of oxygenated nitrogen species are typically low in geologic brines [1]
Determining the source of this nitrate can play a key role in understanding the process by which Sabkha Matti system was developed, and to better enhance the development of a hydrological budget analysis for the Sabkha, which would be the subject for a future study
The vast majority of these fluvial sediments were accumulated during the Holocene [8], in a paleo-deltaic depositional environment formed by the ~140 m rises of the Gulf in the last 10,000 years, combined with a huge source of continental fluvial sediments derived from a large drainage basin
Summary
Concentrations of oxygenated nitrogen species are typically low in geologic brines [1]. Groundwater can be enriched with nitrate concentrations by several natural and anthropogenic activities These include atmospheric deposition, bacterial production, mineral fertilisation, leaking septic systems, animal manure, and leakage if the sabkha have contact with adjacent aquifers that have high nitrate contents [3]. A dual isotope approach involving the isotopic composition of nitrogen (δ15N) and oxygen (δ18O) of nitrate has been proposed when there is a difficulty in differentiating numerous nitrate sources based solely on δ15N [5, 6]. The high nitrate concentration of the shallow aquifer system in Sabkha Matti was investigated using a multi-tracer approach considering water chemistry, stable nitrate isotopes (δ15N and δ18O) and the radioactive isotope of hydrogen (3H).
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