ORIGINAL ARTICLE 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 Evangelos Tziritis 1 • Konstantinos Skordas 2 • Akindynos Kelepertsis 3 Received: 6 September 2015 / Accepted: 24 October 2015 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract The present study investigates the hydrogeo- chemical 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 hydrogeo- chemical 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 (me- dian = 308 mg/L) in the following descending order of concentrations for cations Ca 2? [ Mg 2? [ Na ? [ K ? and anions HCO 3 - [ NO 3 - [ SO 4 2- [ Cl - , respectively. Nitrate values are elevated (median = 23 mg/L), especially in the porous quaternary aquifer, indicating the ongoing agricul- tural impact from the excessive use of nitrogen fertilizers and manure. The results of multivariate statistics high- lighted 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. Keywords Hydrogeochemistry Á Groundwater quality Á Major ion molar ratios Á Multivariate statistics Á Thessaly Introduction Groundwater constitutes a vital water resource recognized for its paramount importance; it represents an important link of the hydrological cycle through the maintenance of wetlands and river flows, having significant environmental and aesthetical value. Moreover, groundwater resources are related with direct or indirect processes, like, e.g., irriga- tion, drinking water supplies, etc., being closely related with the economic prosperity of an area. Hence, assessment of groundwater quality and the understanding of hydro- geochemical signatures is critical to ensure environmental sustainability and development. Groundwater chemistry is chiefly influenced by the characteristics of the catchment area; several natural (geo- genic) factors like climatic conditions, bedrock geology and soil properties control its chemical constituents, fate and transport. In addition, man-driven activities and land use are crucial for water flow and its overall quality status. The hydrogeochemical characteristics depend on the chemistry of rock-forming minerals (e.g., carbonate, sulfide, silicate, etc.) and on the physical process of erosion that creates favorable conditions for mineral dissolution. As a result, groundwater is enriched in ions, metals or metalloids, & Evangelos Tziritis tziritis@gmail.com 1 Soil and Water Resources Institute, Hellenic Agricultural Organization ‘‘Demeter’’, Sindos Industrial Zone, 57400 Sindos, Greece 2 Department of Ichthyology and Aquatic Environment, School of Agricultural Sciences, University of Thessaly, Fitokou street, 38446 Volos, Greece 3 Faculty of Geology and Geoenvironment, School of Scince, University of Athens, Panepistimiopolis, Zographou, 157 84 Athens, Greece 123 Environ Earth Sci (2016)75:339 DOI 10.1007/s12665-015-5204-y