Groundwater Deterioration: The Simultaneous Effects of Intense Agricultural Activity and Heavy Metals in Soil

Groundwater deterioration due to agricultural activity is mainly attributed to intense fertilization, groundwater overpumping and seawater intrusion being more pronounced in coastal areas. Irrigation return water is one of the main sources of aquifers enrichment and it is expected to become the main source due to the simultaneous reduction of the amount/frequency of precipitation for many areas in Greece and the Mediterranean. The reduction of groundwater quantity and the simultaneous deterioration due to enhanced concentrations of fertilizer residues, such as nitrates, is well documented. Moreover, heavy metals of both anthropogenic and natural origin may be present in soils where agricultural activity takes place. As a result, groundwater is enriched in soluble species of heavy metals and this enrichment is a serious problem added on top of the above mentioned problems of groundwater deterioration. The relationship between heavy metals mobilization from soils to groundwater and the content of irrigation return water in solutes that influence the generation rates and mobility of heavy metals soluble species are discussed in this work. Data from groundwater samples taken in Psachna, Evia, a region characterized by elevated geogenic Cr in soils and intense agricultural activity, are presented. Two aspects of the problem are discussed: 1. The intense use of ammonium fertilizers: The pH reduction from the nitrification of ammonium fertilizers may be a serious factor influencing Cr(III) mobility. 2. The role of the ionic strength of the water (enhanced concentrations of cations due to seawater intrusion in the aquifer) in the mobility of Cr(III) by mechanisms of cation exchange.