The Variation in Groundwater Microbial Communities in an Unconfined Aquifer Contaminated by Multiple Nitrogen Contamination Sources

Justin G Morrissy,Nicholas D Crosbie,Simon Aquilina,Mallavarapu Megharaj,Aravind Surapaneni,Matthew J Currell,Daniel Hirth,Andrew S Ball,Suzie M Reichman,William Rajendram

doi:10.3390/w14040613

Abstract

Aquifers provide integral freshwater resources and host ecosystems of largely uncharacterized, truncated endemic microorganisms. In recent history, many aquifers have become increasingly contaminated from various anthropogenic sources. To better understand the impacts of nitrogen contamination on native groundwater ecosystems, 16S rRNA sequencing of the groundwater microbial communities was carried out. Samples were taken from an aquifer known to be contaminated with nitrogen from multiple sources, including fertilizers and wastewater treatment plant effluents. In total, two primary contaminants were identified: NH4+ (<0.1–3.7–26 mg L−1 NH4+ min-median-max), and NO3− (<0.01–18–150 mg L−1 NO3− min-median-max). These contaminants were found to be associated with a decrease/increase in microbial species richness within affected groundwater for NH4+/NO3−, respectively. Important phyla were identified, including Proteobacteria, which had the highest abundance within samples unaffected by NH4+ (36–81% NH4+ unaffected, 4–33% NH4+ affected), and Planctomycetes (0.05–10% NH4+ unaffected, 43–72% NH4+ affected), which had the highest abundance within the NH4+ affected samples, likely due to its ability to perform anaerobic ammonia oxidation (ANAMMOX). Planctomycetes were identified as a potential indicator for the presence of NH4+ contamination. The analysis and characterization of sequencing data alongside physicochemical data showed potential to increase the depth of our understanding of contaminant behavior and fate within a contaminated aquifer using this type of data and analysis.

Highlights

Aquifers serve various ecosystem functions, and are immeasurably important as resources providing potable water for humans and animals alike [1]
The main nitrogen groundwater plume was centered around the wastewater treatment plant (WWTP); due to the up-gradient intensive agriculture and down-gradient cattle grazing paddocks, the normal background concentration of nitrogen, and the extent of influence from the WWTP versus other sources, was difficult to determine
The primary contaminant of concern originating from both the diffuse source upstream market gardens (MG) and within the WWTP was nitrogen, in the form of nitrate (NO3 − )

Summary

Introduction

Aquifers serve various ecosystem functions, and are immeasurably important as resources providing potable water for humans and animals alike [1]. They constitute a vast and poorly characterized reservoir of biological diversity, with numerous undescribed and endemic species, with significant ecological value and potential application, for example groundwater bioremediation [2,3,4]. Filtration and storage of water rank highly among the groundwater aquifers’ ecosystem functions Both the substrate (that isolates aquifers from the surface and constitutes the solid matrix) and the endemic ecosystems that reside within, between, and upon this substrate are integral to the effective filtration of the groundwater [3]. There has been very little characterization of the effects of contamination on the microbes that reside within the groundwater itself

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