Abstract
The Water Framework Directive (WFD) requires from member states to monitor hydromorphological features of rivers in order to assess their ecological quality. Thus, numerous hydromorphological assessment methods have been developed with most of them focusing on the dynamics of hydrology, geomorphology and riparian zone extent. Within the scope of this study, we assessed the hydromorphological features of 106 river reaches distributed among thirteen WFD River Basin Districts (RBDs) to identify the main drivers of hydromorphological perturbation at a national scale. The studied reaches reflect a wide range of natural variability as they include various types of watercourses extending from lowlands to mid-altitude and mountainous systems. We employed the River Habitat Survey (RHS), and we recorded hydromorphological features and modifications in both banks and the channel bed along 500 m for each reach. Then, the Habitat Modification Score (HMS) and the individual sub-scores that indicate the extent of specific modifications (e.g., bridges, fords, weirs, bank reprofiling, bank reinforcement, etc.) were calculated in order to a) assess the severity of the total artificial modification and b) to highlight the most common and severe causes of overall alteration. The results showed that alterations such as reprofiling and reinforcement of banks contributed the most to the total HMS followed by the presence of fords and bridges. Particularly, the bank alterations indicate a serious deterioration of the longitudinal profile of the reaches, while the occurrence of many fords and bridges is the main cause for perturbations that affect locally the stream cross-sectional profile. Overall, these results compile a first nationwide assessment of the hydromorphological status of Greek rivers in line with the WFD and set the basis for further research that will focus on the diversity of stream habitat features as a measure for the overall ecological quality.
Highlights
Riverine ecosystems of Europe are inarguably under threat of multiple stressors, with nutrient pollution and hydromorphological alteration being the most common and serious causes for ecological degradation [1,2,3]
Hydrology 2020, 7, 22 assessment methods initially required field surveys that evaluated the status of a given river reach by measuring and recording a series of characteristics associated with the naturalness of flow regime, riparian zone, river connectivity and others [5,6,7]
The introduction of Water Framework Directive (WFD) offered the opportunity to better understand the relationships between hydromorphology and ecology in European rivers [12], while at the same time dictated to all member states to monitor all community waters with the scope of establishing objectives to avert further status deterioration and to achieve a “Good Status” by 2021
Summary
Riverine ecosystems of Europe are inarguably under threat of multiple stressors, with nutrient pollution and hydromorphological alteration being the most common and serious causes for ecological degradation [1,2,3]. Numerous hydromorphological assessment methods have been developed, with most of them focusing on the dynamics of hydrology, geomorphology and riparian zones, in order to evaluate the severity and the extent of the hydromorphological degradation [4]. Hydrology 2020, 7, 22 assessment methods initially required field surveys that evaluated the status of a given river reach by measuring and recording a series of characteristics associated with the naturalness of flow regime, riparian zone, river connectivity and others [5,6,7]. Other assessment methods may combine field observations with remote sensing and GIS (Geographic Information Systems) tools to overcome some limitations such as the limited spatial scale and to provide assessments at a larger scale that might be more appropriate for capturing meaningful changes in the hydromorphology [8,9,10,11].
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