The use of hydrogeochemical analyses and multivariate statistics for the characterization of groundwater resources in a complex aquifer system. A case study in Amyros River basin, Thessaly, central Greece

摘要

The present study investigates the hydrogeochemical regime of a complex aquifer system in a highly cultivated area of Thessaly, central Greece. To do so, totally forty (40) groundwater samples were collected for three aquifer units with diverse geological and hydrogeological attributes and analyzed for 77 parameters. Data processing was accomplished with the joint use of classic hydrogeochemical techniques including major ion molar ratios and graphical interpretation, as well as multivariate statistical methods including R-mode factor (FA) and hierarchical cluster analysis (HCA). Results showed that major ion hydrogeochemistry is characterized by the prevalence of calcium (median = 81 mg/L) and bicarbonates (median = 308 mg/L) in the following descending order of concentrations for cations Ca2+ > Mg2+ > Na+ > K+ and anions HCO3- > NO3- > SO42- > Cl-, respectively. Nitrate values are elevated (median = 23 mg/L), especially in the porous quaternary aquifer, indicating the ongoing agricultural impact from the excessive use of nitrogen fertilizers and manure. The results of multivariate statistics highlighted four factors that chiefly control 81.4 % of overall hydrogeochemistry, related with both geogenic and anthropogenic impacts. The geogenic impact is mainly attributed to the geological substrate and secondarily to the ongoing geochemical (redox) conditions which in turn enrich or deplete groundwater solution with different ions; anthropogenic impact is mainly related with the extensive agricultural practices which favor nitrate enrichment and salinization due to irrigation water return flow.