Assessing effects of water abstraction on fish assemblages in Mediterranean streams

Abstract

Water abstraction strongly affects streams in arid and semiarid ecosystems, particularly where there is a Mediterranean climate. Excessive abstraction reduces the availability of water for human uses downstream and impairs the capacity of streams to support native biota. We investigated the flow regime and related variables in six river basins of the Iberian Peninsula and show that they have been strongly altered, with declining flows (autoregressive models) and groundwater levels during the 20th century. These streams had lower flows and more frequent droughts than predicted by the official hydrological model used in this region. Three of these rivers were sometimes dry, whereas there were predicted by the model to be permanently flowing. Meanwhile, there has been no decrease in annual precipitation. We also investigated the fish assemblage of a stream in one of these river basins (Tordera) for 6 years and show that sites more affected by water abstraction display significant differences in four fish metrics (catch per unit effort, number of benthic species, number of intolerant species and proportional abundance of intolerant individuals) commonly used to assess the biotic condition of streams. We discuss the utility of these metrics in assessing impacts of water abstraction and point out the need for detailed characterisation of the natural flow regime (and hence drought events) prior to the application of biotic indices in streams severely affected by water abstraction. In particular, in cases of artificially dry streams, it is more appropriate for regulatory agencies to assign index scores that reflect biotic degradation than to assign 'missing' scores, as is presently customary in assessments of Iberian streamsThis study was financially supported by the Catalan Water Agency, Government of Catalonia and the Barcelona Provincial Council (‘Observatori de la Tordera’ to M. Boada), the Spanish Ministry of Education (CGL2006-11652-C02-01 ⁄BOS), the Banco Bilbao Vizcaya Argentaria Foundation (project GLOBRIO), and the Government of Catalonia (Catalan Government Distinction Award for University Research 2004 to EGB

Impacts of climate change on water resources in the Mediterranean Basin: a case study in Catalonia, Spain

“…Changes in ecological stream flow may affect species composition, biodiversity, productivity and life cycle of many aquatic species (Poff et al 2002). The observed stream flow reduction in the Tordera River during the 20th century caused by water abstraction has led to a reported reduction in fish population densities, the number of benthic species and the occurrence and abundance of intolerant species (Benejam et al 2010). Our results showed a strong increase by the end of the present century in the number of days per year with stream flow below the ecological flow.…”

Non-perennial Mediterranean rivers in Europe: Status, pressures, and challenges for research and management

“…Artificial intermittence may lead to a decline of freshwater species richness and abundances and to a loss of migratory pathways for many fish species . A major decline in native fish diversity has been already reported in many Iberian rivers, closely linked to unsustainable water management (Aparicio et al, 2000;Benejam et al, 2010;Clavero et al, 2010). Water management infrastructures and practices alter key hydrological processes that maintain riverine habitat diversity, longitudinal, lateral and vertical connectivity gradients, and good water quality conditions (Prat and Ward, 1994;Bunn and Arthington, 2002;Pringle, 2003).…”

“…This decrease favours the creation of disconnected pools and increases the number and extent of NPRS stretches (e.g. Benejam et al, 2010;Skoulikidis et al, 2011;Datry et al, 2014a).…”

“…Τhe natural seasonal dryness regime is exacerbated by human activities, and natural PRS are converted into NPRS (Datry et al, 2014a). These rivers and streams are considered "artificially dry" or "artificially intermittent" (Benejam et al, 2010;. On the other hand, natural NPRS may be transformed into PRS after receiving effluents from Wastewater Treatmennt Plants (WWTPs) or urban and industrial discharges (Hassan and Egozi, 2001).…”

Lifting the curtain on the freshwater mussel diversity of the Italian Peninsula and Croatian Adriatic coast

“…For example, the Mediterranean basins of southern Europe, with the exception of those of Iberia, are still understudied. This is particularly unfortunate, as these basins are of high conservation priority because of their high levels of endemism and the growing demand for water (for agricultural, industrial and domestic activities), which has already caused a decline and loss of endemic biodiversity in many freshwater ecosystems (Albrecht et al 2006;Benejam et al 2010).…”