Evaluation of geochemical processes and nitrate contamination pathways in Vailapally watershed, Telangana, India: a stable isotope perspective

Present research work is carried out to identify the sources of nitrate (NO3-) contamination in groundwater of Vailapally and its surrounding areas of Nalgonda district, Telangana having mixed agri-rural set up by means of geochemical perspectives. Altogether Twenty seven (27) groundwater samples are collected from borewell/hand pump covering both agricultural as well as rural residential areas. Analytical results reveal that maximum nitrate contamination (263 mg/L) is restricted to rural areas whereas, most of agricultural areas have nitrate concentration below the WHO permissible limit of 45 mg/L. Presence of significant (p < 0.01) positive correlations between EC, TDS, Cl- and SO42- with nitrate signify the unlined domestic sewage and sanitary system of the residential areas as the source of contaminant. Elevated concentration of lead (Pb) and mercury (Hg) and their affinity towards NO3- are found to be regulated by some anthropogenic sources like inorganic fertilizer, animal manure or sewage. Maximum NO3- concentration is also corroborated to minimum C/N ratio (0.32). Isotopic signature further pinpoints that both animal waste and organic soil nitrogen are the major contributor of nitrate in the groundwater of Vailapally watershed.