Combined use of geophysical methods and water information to assess human activities impacts on karst groundwater quality

Abstract

The presence of high vulnerable karstic systems in areas of intense human activities often results in the degradation of existing groundwater quality status. The water quality (WQ) protection and improvement, as required by the WFD (Water Framework Directive), depends on a correct prioritisation of the most relevant impact pollution sources to be identified within complex multi-stressor conditions. This paper presents a methodology that combines the use of hydrogeology, WQ and quantity data, and geophysical methods to access the human activities’ impacts upon the water cycle, focusing on the WQ of a karstic system. The procedure was applied to a section of the Portuguese karstic Querença-Silves aquifer, under FCT PROWATERMAN project PTDC/AAC-AMB/105061/2008 (http://www.lnec.pt/organizacao/dha/organizacao/dha/nas/estudos_id/PROWATERMAN). During this study an interpretation of the possible interconnections between pollutant sources, their pathways and local surface-groundwater connections was analysed, based on data obtained from field campaigns. As a result of this study, the most relevant recharge areas and the identification of influent sites of the local stream to the aquifer were acknowledged. The areal distribution of the diffuse pollution sources was verified in the monitoring points, especially those located in the near downstream of the larger farming plots. Pollution in this karst aquifer results from seepage through agricultural areas and infiltration in the influent points of the stream. This aspect of stream influence upon the aquifer means that pollution sources located upstream the area of the aquifer (e.g. WWTP (Wastewater Treatment Plant)) can contribute to the aquifer pollution.