An assessment of the relative impacts of key stressors on the hydrology of Greek river water bodies

The quantitative and qualitative status of a riverine ecosystem is mainly controlled by the characteristics of the catchment (topography, land use, and geological structure) and climatic factors (precipitation and temperature), both of which can be affected by anthropogenic activities. To quantify the impact of humanly imposed pressures on river discharge and to determine the dominant stressors that affect the hydrological regime of Greek rivers, two discharge datasets consisting of discharge/ichthyofauna and discharge/benthic macroinvertebrate measurements were employed, and 36 predictor variables were statistically elaborated. Impacted samplings were defined based on the classification of the corresponding biotic indices sensitive to hydrological alterations. The assessment indicated that the median discharge of impacted rivers was lower in relation to unimpacted conditions in all river types by up to 85% (R-M3), except for the case of R-M5 (temporary rivers), where discharge was higher by up to 46%. The most important variables affecting discharge values were the proximity of the dam upstream of the sampling site, the distance to source, the catchment area upstream, the presence of siliciclastic rocks upstream, annual precipitation, and the presence of artificial surfaces. Surprisingly, irrigated land area and water abstractions volume were not indicated as major driving variables affecting the hydrology of Greek rivers, possibly due to limitations of the current methodological approach. The development of a hydrological regime alteration index, specifically for Greek rivers, based on the deviation of the current state from the unimpacted conditions can be a valuable tool for the implementation of Water Framework Directive 2000/60 objectives concerning the hydromorphological quality of riverine ecosystems.

Automated summary

The quantitative and qualitative status of a riverine ecosystem is primarily determined by the characteristics of the catchment and climatic factors, both of which can be influenced by human activities. This study aimed to assess the impact of human pressures on river discharge and identify the dominant stressors affecting the hydrological regime of Greek rivers. The results revealed that the median discharge of impacted rivers was significantly lower compared to unimpacted conditions in most river types, except for temporary rivers. The proximity of dams, distance to source, catchment area upstream, presence of siliciclastic rocks, annual precipitation, and presence of artificial surfaces were identified as the most important variables affecting discharge values. Surprisingly, irrigated land area and water abstractions volume were not found to be major driving variables for the hydrology of Greek rivers.