Microbial Evaluation of Groundwater and its Implications on Redox Condition of a Multi-Layer Sedimentary Aquifer System

Abstract

A synoptic microbial assessment of groundwater has been carried to describe the groundwater quality and its geochemical environment in the Pondicherry region located in the southeast part of India. Spatial and vertical variability in dissolved oxygen (DO) and chemical species clearly explain that regional geological settings associated with human pressure are controlling the groundwater quality in this region. Results show that the abundance of bacteria is positively related to DO, total organic carbon (TOC) and inversely related to well depth, whereas sulphate reducing bacteria (SRB) present at some locations do not show any systematic trend with the above parameters. About half of the measured groundwater samples showed presence of E. coli. Some suboxic deep aquifers (DO≤2 mg/L) showed presence of E.coli which are not commonly observed. SRB are found mostly in deeper Tertiary and Cretaceous aquifers reflecting presence of reducing conditions. The rapid accumulation of organic matter associated with heterotrophic conditions has increased the prevalence of redox sensitive SRB in coastal zones of Pondicherry region. Reducing conditions in deeper aquifers of Cretaceous and Tertiary formations and availability of Marcasite in these formations may lead to possible arsenic contamination in groundwater. Climate change induced sea level rise and human pollution may exacerbate the nutrient and microbial pollution in this coastal region, and this warrants a detailed investigation so that proper protection strategies for sustainable management of the groundwater resources along the Indian coastal zone can be proposed.

Wells provide a distorted view of life in the aquifer: implications for sampling, monitoring and assessment of groundwater ecosystems

“…There are many protocols for sampling aquifers in order to characterise the biota. Some protocols require wells to be purged by the removal of predefined volumes of water2122 or until constant water quality conditions are achieved23 while others do not require purging1324.…”

Physicochemical and Microbiological Quality of Shallow Groundwater in Lomé, Togo

“…Mazari-Hiriart et al (2000) used groundwater bacterial indicators and pathogens and the relationship between water quality and diarrheal disease rates in Mexico City (Mexico) to suggest ways to improve the potential of environmental health indicators (EHI) by framing epidemiological data and the use of GIS. Viable counts, fecal coliforms, Vibrio cholera, total streptococci, sulfate-reducing bacteria, and Escherichia coli allowed indicating vulnerable zones to water quality deterioration in Tamil Nadu and Pondicherry coastal aquifers, South India (Keesari et al, 2015;Vasudevan et al, 2020). In the deeper part of these aquifers, sulfate-reducing bacteria's predominance supported the hypothesis of reducing conditions that may lead to possible arsenic contamination in groundwater (Keesari et al, 2015).…”

“…These results show a significant variation in groundwater mineralization, probably due to local processes. Very low to brackish TDS values were also found in groundwater from aquifers in large coastal cities worldwide (Keesari et al, 2015;Shi et al, 2018;Vasudevan et al, 2020).…”

“…tests (Gibrilla et al, 2011;Keesari et al, 2015). Therefore, testing was done for groups of thermotolerant coliforms and sulfite-reducing anaerobes that discriminate fecal contamination and total mesophilic flora to estimate sanitation and hygiene failure conditions around sampling points.…”

“…The use of cased large diameter wells instead of boreholes at some water sale points can explain the result obtained. Fecal contamination can reach the deeper zone of the aquifer system due to hydrogeological conditions, inadequate borehole construction and maintenance, and the insufficient depth of protective soil layers above the groundwater table (Pitkänen et al, 2011;Llopis-González et al, 2014;Keesari et al, 2015). Based on the three microbiological indicators used, about 65% of groundwater samples did not comply with the drinking water guidelines for human consumption.…”