Abstract
The Water Framework Directive (WFD) requires European countries to achieve a good ecological status of surface water bodies and demands that River District Authorities define ecological flows consistently. Nevertheless, the relationship between ecological and hydrological indicators is not fully understood and not straightforward to apply because ecological and hydrological indicators are monitored by different institutions, with different timings and purposes. This work examines the correlation between a set of ecological indicators monitored by environmental agencies (STAR-ICMi, LIMeco, IBMR, and TDI) and water levels with assigned durations monitored by the hydrologic service in Tuscany (central Italy). Reference water levels are derived from stage-duration curves obtained by the statistical analysis of daily levels in the same year of ecological sampling. The two datasets are paired through a geospatial association for the same river reach and the correlation is measured through Pearson’s r. The results show poor correlation (r between −0.33 and −0.42) between ecological indicators and hydrologic variables, confirming the findings observed in other Italian catchments with different hydrologic regimes, climate, and anthropogenic pressures. Nevertheless, the negative correlations show a decreasing water quality with water depths, i.e., in the lower part of the catchments more affected by anthropogenic pressures. These findings suggests that the determination of ecological flows with a purely hydrological approach is not sufficient for achieving WFD objectives in the study area.
Highlights
The conservation of aquatic ecosystems in terms of quantity and quality is one of the sustainability challenges faced by many countries that exploit water resources for energy, agricultural, industrial, and domestic uses [1]
In the context of supporting the definition of ecological flows at the regional scale, this work aims at preliminarily analyzing the correlation between official ecological indicators, i.e., STAR_ICMi, LIMeco, diatom (TDI), and macrophytes (IBRM) and characteristics water levels derived from stage-duration curves for the river catchments in Tuscany, which have climatic conditions and anthropogenic pressures quite different from those examined in previous work
Most ecological monitoring sites are located in low order streams, i.e., in upper catchments or in flat areas hosting wetlands, whereas hydrometric stations are placed in the lower part of the catchments with the purpose of flood warning
Summary
The conservation of aquatic ecosystems in terms of quantity and quality is one of the sustainability challenges faced by many countries that exploit water resources for energy, agricultural, industrial, and domestic uses [1]. The achievement of good ecological status in natural surface water bodies is a key objective of the European Water Framework Directive (WFD) [2,3]. The WFD recognizes the critical role of water quantity and dynamics in supporting the quality of aquatic ecosystems and requires River Basin District Authorities to set out ecological flows for the river network as a part of the Water Management Plan. The relationship between ecological status indicators and flow parameters in a large Alpine catchment was recently studied and highlighted a poor correlation [18]. The study examined the STAR_ICMi index (STAndardisation of River classifications Intercalibration Common Metric index) [19], which is a macroinvertebrate-based index, officially adopted by the Italian legislation to classify the ecological status of river waters in the WFD framework. The index showed a low sensitivity to discharge in Alpine and perialpine rivers, which usually are affected by hydropower alterations but have low pollution [5,19,20,21,22,23]
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