Farming landscapes and presence of pesticides in surface waters: A GIS based on the correlation of land use cover surfaces and contaminants in the river Jucar, Spain

Trabajo presentado en NET-SCARCE International Conference, celebrada en Barcelona (España) del 15 al 16 de noviembre de 2016Farming might be the dominant land use/cover at large watershed scale in Mediterranean areas. To accomplish Water Frame Directive and efficient application of river basin management plans at river basin district levels a knowledge on indirect pressures (non point source pollution) due to agriculture human activities is required. Nonetheless, affording continuous and systematic assessment of river conditions is prohibitive requiring demanding approaches to identify potential source areas of incoming pollutants. The present work is based on the development of a combined methodology to identify and quantify farming chemicals in the entire Júcar river basin, a 22265 km2 Spanish Mediterranean watershed of which 54% is devoted to farming, either rainfed (44% of the river basin land) or irrigated (10%). The methodological framework consisted on the application of environmental forensic criteria associating laboratory analytical samples, cartographic analysis using Geographical Information Systems (GIS) and synthetic statistical analysis. Sampling consisted in the collection of 15 samples in surface waters distributed alongside the River Júcar and its two main tributaries (River Cabriel and Magro). After selective sample extraction, 50 pesticides were identified and quantified by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Geographical analysis were performed after geo-location of sampling points analytical results and integration in the GIS environment using CORINE land use-cover layers for the year 2012. Summary descriptive statistical analysis were further performed combining synthetic land use/cover information and pesticides results to determine correlation between dominant agricultural practices (irrigation and rainfed farming) and location of sampling points with regard to number of pollutants found, maximum and average pollutan concentration at each site. Out of 50 pesticides, 20 were identified and 18 presented concentrations higher than the Limits of Quantification in surface waters, with a large dispersion in concentrations: from 0.04 ng•L-1 (Terbuthylazine-2 Hydroxy) to 222.45 ng•L-1 (Imazalil). Statistical analyses reveals that there is a strong positive correlation between number of pollutants (R2 0.6), maximum concentration (0.71 R2) and mean concentrations (0.75 R2), whereas correlations are weaker and with negative trend when analysing the relationship between presence of pesticides in rainfed dominated areas.Peer reviewe