Source, Transport, and Fate of Nitrate in Shallow Groundwater in the Eastern Niger Delta

Overview

Journal Environ Sci Pollut Res Int

Publisher Springer

Specialties Environmental Health
Toxicology

Date 2024 Nov 20

PMID 39565481

Authors

Dogo Lawrence Aleku

Kirstin Dahnke

Thomas Pichler

Affiliations

Soon will be listed here.

Abstract

The eastern Niger Delta region in Nigeria is a hotspot for reactive nitrogen pollution due to extensive animal husbandry, pit latrine usage, and agricultural practices. Despite the high level of human activity, the sources and processes affecting nitrogen in groundwater remain understudied. Groundwater nitrate (NO) concentrations are highly variable, with some areas recording values well above the safe drinking water threshold of 50 mg/L. This is particularly true near municipal sewage systems. Elevated nitrite (NO) and ammonium (NH) concentrations were also detected in the study area. Sewage analysis revealed NO concentrations ranging from 1 to 145 mg/L, NO from 0.2 to 2 mg/L, and notably high NH concentrations. A comparison of major ions indicated that 71%, 90%, 87%, and 92% of groundwater samples surpassed reference site levels for calcium (Ca), sodium (Na), potassium (K), and chloride (Cl), respectively, pointing to sewage as a likely source of contamination. The NO/Cl ratios at several sites suggested that most groundwater NO originates from human waste. Stable isotope analysis of NO showed a general enrichment in N and, in some cases, a depletion in O, indicating that the NO originates from sewage-derived NH nitrification. Although denitrification, a process that reduces NO, is present, the high dissolved oxygen (DO) and NO levels in the groundwater suggest that denitrification is insufficient to fully mitigate NO pollution. Consequently, there is a risk of NO leaching from shallow aquifers into the Niger Delta's surface waters and ultimately into the coastal ocean.

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