Nitrogen Speciation in Regolith Aquifers at Enugu, Southeastern Nigeria
DOI:
https://doi.org/10.58885/ijees.v8i1.16.eoKeywords:
Groundwater contamination, Nitrogen cycle, Nitrate pollution, Regolith aquifers, Shallow groundwater, Subsurface hydrogeochemistry, Groundwater quality, Eutrophication Microbial contamination, Anthropogenic pollution.Abstract
This study investigates nitrogen speciation in groundwater across multiple locations in Enugu, Southeastern Nigeria, using Eh-pH diagrams to interpret dominant microbial processes influencing nitrogen transformations. A total of 30 groundwater samples from multiple locations such as Centenary, 9th mile, Ologo, Trans-Ekulu, New-artizan and Amechi were studied. Eh and pH were determined using the Standard Hydrogen Electrode and a pH meter respectively. Water samples from urban hand dug wells and streams were analyzed for redox potential and pH, and their positions were plotted against thermodynamic stability fields of nitrate (NO₃⁻), ammonium (NH₄⁺), ammonia (NH₃), and nitrogen gas (N₂) using geochemist work bench software. The results reveal that most groundwater samples fall within the NH₄⁺ and N₂ stability fields, indicating that ammonification and denitrification are the predominant nitrogen transformation pathways. Nitrification was largely absent due to low oxygen levels, with no samples falling within the NO₃⁻ stability field. Sites like New Artisan Stream and several wells in the Amechi and Trans-Ekulu areas exhibited strong denitrification signatures, facilitated by bacteria such as Pseudomonas sp., Geobacter sp., and Bacillus sp. On the other hand, samples from the 9th Mile and Premier Layout areas showed evidence of ammonification under reducing conditions, with high NH₄⁺ concentrations pointing to organic matter decomposition and limited oxygen availability. These microbial-mediated nitrogen processes have critical implications for groundwater quality, particularly with respect to nitrate attenuation and potential ammonia toxicity. The findings magnify the importance of redox conditions in shaping nitrogen dynamics in tropical groundwater systems and highlight the need for integrated water quality management in the face of increasing anthropogenic impact.
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