Assessment of hydrochemical trends in the highly anthropised Guadalhorce River basin (southern Spain) in terms of compliance with the European groundwater directive for 2015

One of the key aspects introduced by the European Water Framework Directive 2000/60/EC (WFD) and developed by Groundwater Directive 2006/118/EC was the need to analyse pollution trends in groundwater bodies in order to meet the environmental objectives set in Article 4 WFD. According to this Directive, the main goal of “good status” should be achieved by the year 2015, and having reached this horizon, now is a suitable time to assess the changes that have taken place with the progressive implementation of the WFD. An extensive database is available for the Guadalhorce River basin, and this was used not only to identify in groundwater but also to draw real conclusions with respect to the degree of success in meeting the targets established for this main deadline (2015) The geographic and climate context of the Guadalhorce basin has facilitated the development of a variety of economic activities, but the one affecting the largest surface area is agriculture (which is practised on over 50 % of the river basin). The main environmental impacts identified in the basin aquifers arise from the widespread use of fertilisers and manures, together with the input of sewage from population centres. In consequence, some of the groundwater bodies located in the basin have historically had very high nitrate concentrations, often exceeding 200 mg/L. In addition, return flows, the use of fertilisers and other pressures promote the entry of other pollutants into the groundwater, as well as the salinisation of the main aquifers in the basin. In order to assess the hydrochemical changes that have taken place since the entry into force of the WFD, we performed a detailed trends analysis, based on data from the official sampling networks. In some cases, over 35 years of water quality data are available, but these statistics also present significant limitations, due to some deficiencies in the design or management; thus, data are missing for many years, the results are subject to seasonality effects, there are gaps in the historical records obtained by the monitoring networks and other shortcomings. The results obtained were analysed with the non-parametric Mann-Kendall test and revealed a general upward trend of pollutants in the areas affected by major pressures. In this analysis, we evaluated not only the increase or decrease in pollutants but also the different processes detected and the sources of pollution within the basin area. Our evaluation shows that robust measures should be taken in order to prevent further major degradation of groundwater quality and to enable “good quality” status to be achieved in future extensions of the WFD.