Understanding effects of global change on water quantity and quality in river basins- The SCARCE Project

Abstract

The increasing anthropogenic manipulation of the hydrological cycle, as well as the exacerbation of climate change forcing, result in resource pressures that translate in even larger uncertainties in sensitive geographical areas. In particular, the Mediterranean region is undergoing severe alterations in water availability because of a decrease in the number of precipitation days but also in an increase of heavy rain events. An imbalance between water availability and its use is obvious in these water-thirsty regions, and clearly impacts the sustainability of water resources. The consequences are multiple, and include direct impacts on economic sectors that use and depend upon water availability, such as agriculture, tourism or industry. Ultimately, however, these consequences are the basis for a conflict between natural ecosystems and human needs, where ecosystems are those most challenged and their services remain at risk. The effects of water scarcity on river basins extend from its associated hydrological irregularity to the chemical quality of available water systems. Higher nutrient and pollutant concentrations are expected under lower water flows, both as an effect of direct human inflows as well as a simple effect of lower water dilution. This is especially relevant in many arid and semi-arid river systems, where flowing waters under scarcity mostly consists of treated sewage effluents. Wastewaters are being reused for drinking purposes and agriculture; some chemical compounds may eventually be transported from the waste water treatment plants (WWTPs) to river waters, and affect the chemical and biological quality of those waters. In these situations, potential water quality problems extend to the higher concentration of emerging pollutants, presence of pathogenic organisms, and multiple effects on the biota dwelling within the river systems. Biological communities respond to harsher environmental conditions imposed by scarcity with lower diversity, arrival of invasive species, as well as with lower efficiency of biological processes, some involving water quality as a return. The increased pressure on water resources will cause additional effects on aquatic ecosystems, in which the stress being produced by scarcity may sum up others physical or chemical stressors. Groundwater quality may be also affected by farming, or after leakage of industrial and domestic pollutants, making the use of these resources much more tenuous. This special issue is a collection of key articles presented at the 1st Annual Conference of the SCARCE-CONSOLIDER Responsible editor: Philippe Garrigues