Chemical and microbiological indicators to assess the impact of agricultural activities on groundwater in the Pampean agro-ecosystem

Abstract

The aim of this research is to demonstrate the usefulness of chemical and microbiological indicators for analyzing the impact of agricultural activities on groundwater in different hydrogeological and land-use situations. The study area is a typical agro-ecosystem of the fluvio-aeolian plain of Córdoba (Argentina). The main chemical constituents and bacterial indicators were determined. Antibiotic resistance was also analyzed using standard methods. The structural framework of the area controls the hydrodynamics of the unconfined aquifer. Thus, regional and local flows control the natural geochemistry of the groundwater: highly developed waters are found in the Lower Block (LB) and fresh waters in the local recharge area Upper Block (UB). The multivariate analysis allowed us to observe that the values of NO3 and the counts of total and thermos-tolerant coliform bacteria in wells adjacent to punctual contamination sites are higher than those of diffuse contamination environments. There are sites in the agricultural zone belonging to the LB that showed an intermediate number of total and faecal coliform bacteria, but no development of E. coli. Thermo-tolerant coliforms are considered an acceptable index of faecal contamination, but less reliable than E. coli. The observed antibiotic resistance profiles of E. coli and their relationship with land use showed that the source of faecal contamination in water is mainly from animal residues.