Exploring hydrological- and environmental indicators with their coupled consequences on ecosystem services relationships for the riparian zones of Danube River Basin

Riparian strips form a transition zone between terrestrial and freshwater ecosystems providing essential ecosystem services. Healthy strips are crucial for the stability and sustainability of ecological systems. Riparian zones have major environmental importance because these could be interpreted as collision zones of transporting pollutants (on both surface and subsurface) from the land to the freshwater. According to that riparian zones have irreplaceable effect on sediment- and nutrient mitigation and securing freshwater ecosystem biodiversity.

Despite their vital importance, the research community paid less attention on riparian strips. Policy-level regulation of land use and related pollutant emissions within strips is also lacks. As a result, degradation of riparian habitats is still increasing.

In this study, we determined of a critical delineation distance of riparian strip with the fixed buffer strip approach. This was based on the analyses of almost 5000 computed local groundwater – surface water gradients in four counties of the Danube River Basin. We evaluated the actual and historic land use conditions within the derived riparian strips. To establish and understand the motivations and cause-effect relationship behind the land use arrangement, we examined the vegetation biomass production inside and outside the defined zone. In addition, to gain a more accurate understanding of the water balance processes of the riparian strips, we performed three types of trend analysis on the groundwater well time series.

Based on our results, the distance from the watercourse influenced the historical trends of groundwater wells. We highlighted in our results, that the proportion of agricultural areas exceeds national level ratios concerning natural land cover types within the riparian strips. For most countries of the Danube River Basin, the agricultural land use category shows up to almost 10% increase within the riparian strips compared to outer zones regarding a crop yield indicator. This means, that within the riparian strips, areas with significant potential for provisioning services are primarily exploited, to the detriment of regulating services. This revealed conflict is also an opportunity that affects the feasibility of several European Union strategies (Water Framework Directive, Biodiversity Strategy until 2030), by pointing out potential restoration sites.