Identifying physico-chemical indicators to assess the ecological quality of Mediterranean rivers in their dry-phase

Abstract

Temporary rivers, which support a dry phase, are abundant and expected to increase worldwide in the face of global change. The European Water Frame Directive still overlooks these ecosystems since information about a proper ecological assessment is scarce, especially during the complete absence of water. As a result, rivers that mostly run dry cannot be assessed yet. We aimed to examine the potential use of physico-chemical elements as suitable indicators during the dry phase of temporary rivers. We monitored 41 Mediterranean rivers (dry channel sediments and co-occurring riparian soils) previously categorized according to their level of anthropogenic impact by using both qualitative attributes at local scale (Mediterranean Reference Criteria) and by land use coverage at catchment scale. We examined common physico-chemical parameters used in monitoring programs (nutrients, electrical conductivity, pH), as well as organic matter and carbon, albeit measured in sediments and soils, to test whether they significantly changed across the monitored sites as impact level increased. Results from both approaches showed that leaching nitrate (NO3–) from dry-channel sediments and riparian zones increased significantly with the level of exposure of stressors in the study sites. High NO3– content, especially within sediments, seemed to respond to agriculture presence, which supports this parameter as a suitable indicator. However, natural variability linked to climate and geology of the study area hinders the reliability of the rest of parameters as robust indicators of the dry phase. We encourage more research across different regions to refine the physico-chemistry of dry phase to advance in properly assessing the ecological quality of temporary rivers.