Ecological Status of Rivers and Streams in Saxony (Germany) According to the Water Framework Directive and Prospects of Improvement

Impact of hydrotechnical construction on aquatic ecosystems of the Kiliia branch of the Danube Delta

Resumption of shipping in the Bystryi branch in the Ukrainian part of the Danube Delta, one of the largest aquatic-wetland areas of Europe and the world, has made it necessary to control the anthropogenic impact on the neighboring water areas of the Danube Biosphere Reserve. The objective of the study was comparing the compositions and structure of phytoplankton, microphytobenthos, macrophytes, benthic invertebrates and ichthyofauna of the mouth area of the Bystryi branch with such communities of the mouths of the branches Vostochnyi, Tsyhanka and Starostambulskyi, which are situated in the protected zone and characterized by limited anthropogenic activity. We also determined the correspondence of the descriptors of biotic groups to the categories of the ecological status according to the Water Framework Directive of the EU. The studies were performed in the autumn and summer periods in 2020–2021. We recorded 367 species of animals and plants, the richest biodiversity was seen for the biota of the Bystryi branch – 250 species, and 180–231 species of hydrobionts were found in the undisturbed mouths. We determined 25.3% of shared species for the water areas, and therefore high values of similarity of the species compositions according to Bray-Curtis (47.5% to 81.5%). We determined no significant differences between the groups of the mouths of the examined branches according to most indicators of taxonomic and ecological structure. As the descriptors of ecological status, we chose assemblage indices of phytoplankton and microphytobenthos, which are based on ratios of biomass of functional groups of algae, and also the Macrophyte Biological Index for Rivers, saprobic index of Zelinka & Marvan and Biological Monitoring Working Party Index of Benthic Invertebrates and Representation of Species of Ichthyfauna according to vulnerability to actions of environmental factors. We determined that the range of descriptors of phytoplankton and microphytobenthos corresponded to the “high” ecological status category, such of macrophytes and benthic invertebrates to “good”, and such of ichthyofauna varied “high” to “good”. In general, all the mouth areas were characterized by “good” ecological status. Similarities of the species composition and the structure of biotic communities of the mouths of the studied branches of the delta indicate the absence of negative impact of the deepwater shipping on adjacent ecosystems, which may be related to the peculiarities of reactions of groups in the water areas with natural stress, as well as local impact of the hydrotechnical construction.

Nitrogen and Phosphorus Loads in Greek Rivers: Implications for Management in Compliance with the Water Framework Directive

Reduction of nutrient loadings is often prioritized among other management measures for improving the water quality of freshwaters within the catchment. However, urban point sources and agriculture still thrive as the main drivers of nitrogen and phosphorus pollution in European rivers. With this article we present a nationwide assessment of nitrogen and phosphorus loads that 18 large rivers in Greece receive with the purpose to assess variability among seasons, catchments, and river types and distinguish relationships between loads and land uses of the catchment. We employed an extensive dataset of 636 field measurements of nutrient concentrations and river discharges to calculate nitrogen and phosphorus loads. Descriptive statistics and a cluster analysis were conducted to identify commonalties and differences among catchments and seasons. In addition a network analysis was conducted and its modularity feature was used to detect commonalities among rivers and sampling sites with regard to their nutrient loads. A correlation analysis was used to identify major possible connections between types of land uses and nutrient loads. The results indicated that the rivers Alfeios, Strymonas, and Aliakmonas receive the highest inorganic nitrogen loads while the highest inorganic phosphorus loads were calculated for the rivers Strymonas, Aliakmonas, and Axios. Concerning the temporal variation of loads, inorganic nitrogen presented a peak on March and gradually declined until October when the dry period typically ends for most regions of Greece. Inorganic phosphorus loads had the highest average value in August and the lowest in October. Thus, our findings confirmed the presence of a typical seasonal variation in nitrogen loads that follows the seasonality in hydrology where high surface runoff during the wet months contribute to higher river discharges and higher nitrogen loads from the catchment. On the contrary, high phosphorus loads persisted during dry months that could be attributed to a dilution effect. Furthermore, the results imply a clear connection between agriculture and both nitrogen and phosphorus. Overall, this work presents extensive information on the nitrogen and phosphorus loads that major rivers in Greece receive that can largely aid water managers to adapt and revise basin management plans in accordance with agricultural management (e.g., which months farmers should reduce the use of fertilizers) with the purpose of meeting the environmental targets defined by the Water Framework Directive (WFD).

Water Quality and Hydromorphological Variability in Greek Rivers: A Nationwide Assessment with Implications for Management

European rivers are under ecological threat by a variety of stressors. Nutrient pollution, soil erosion, and alteration in hydrology are considered the most common problems that riverine ecosystems are facing today. Not surprisingly, river monitoring activities in Europe have been intensified during the last few years to fulfil the Water Framework Directive (WFD) requirements. With this article, we present a nationwide assessment of the water quality and hydromorphological variability in Greek Rivers based on the results of the national monitoring program under the WFD. Water quality and hydromorphological data from 352 sites belonging to 221 rivers were explored with principal component analysis (PCA) to identify main environmental gradients and the variables that contribute the most to the total variance. Nitrate, phosphate, ammonium and electrical conductivity were identified as the most important water chemistry parameters, and typical vector-based spatial data analysis was applied to map their spatial distribution at sub-basin scale. In addition, we conducted simple linear models between the aforementioned parameters and the share of land uses within the basin of each sampling site in order to identify significant relationships. Agriculture was the most important land use affecting the nitrate and electrical conductivity, while artificial surfaces were the best predictor for phosphate and ammonium. Concerning the hydromorphological variability, fine types of substrate and discharge were the variables with the highest contribution to the total variance. Overall, the results of this article can be used for the preliminary assessment of susceptible areas/rivers to high levels of nutrient pollution that can aid water managers to formulate recommendations for improvement of further monitoring activities. Furthermore, our findings implicate the need for enhancement of agri-environmental measures and reduction of point-source pollution in disturbed areas to avert the risk of further environmental degradation under the anticipated global change.