Assessment of spatio-temporal variation in microbial quality of groundwater for irrigation and drinking water: A case study in Santa Lucia canton, Ecuador

The community of Paipayales is placed in the Santa Lucia Canton of Guayas Province, Ecuador. The residents rely mainly on well water for irrigation of their agricultural products, as well as for consumption. This study aimed to evaluate the temporal and spatial variation in microbial quality among different wells in Paipayales. Addi-tionally, the research aimed to identify potential sources of contamination by assessing the association between groundwater microbial sources and land use patterns. The microbiological and physicochemical quality of 26 water wells were studied across 16 months. Samples were taken at the end of dry season in November 2018 (ED), beginning of dry season June 2019 (BD), and rainy season February 2020 (RS). Overall, the mean values of all studied microorganisms were found to be lowest in ED, followed by BD and RS. Fecal indicators microorganisms displayed less variability compared to heterotrophic aerobic bacteria, and Pseudomonas, all of which showed significant differences between years (p < 0.01). No significant difference was found between microorganisms and well characteristics. Out of the analyzed E. coli strains, seven (16.66%) exhibited resistance to at least one antibiotic, and two strains were found to be multiresistant. These findings indicate the influence of activities such as rice cultivation and animal husbandry near the wells, as well as the absence of proper sanitation facilities in their vicinity. Turbidity increased from 2018 to 2020, while pH, temperature, and salinity showed minimal variation across all years, with only a few samples displaying correlation. Most wells met the Ecuadorian guidelines for drinking water after disinfection, with only one sample failing to meet the irrigation standards. The results suggest that microbial communities in groundwater aquifers are primarily influenced by external factors, notably anthropogenic activities related to agriculture and urbanization in the area.