Suchergebnisse

The majority of studies on the ecological success of river restoration show improved morphological conditions, but a poor response of the biota. Because most river restoration projects are costly, a debate has started on the meaningfulness of such investments. Yet only a few studies have investigated the societal dimension of river restoration projects in detail. Therefore, the main aim of this study is to shed light on the social aspects of river restoration. Our empirical study consisted of two parts: (1) an explorative study conducted with 32 residents encountered at three restored river sections in Germany and (2) standardized telephone interviews with 760 residents living in the vicinity of 10 different restored river sections in three federal states. The survey covered questions including which activities local residents carry out at restored river sections, how they judge the nature experience, and how they perceive (negative) effects and costs. The restored river sections are perceived positively by > 80% of the respondents describing the respective section as near-natural and beautiful. In the view of the survey participants, both the ecosystem and residents profit highly from the restoration measure (> 90%), while the agricultural sector is not rated as a high profiteer (36%, multiple answers were possible). In full awareness of the costs of restoration projects (approximately 400,000 Euros per river km), 70% of the interviewees regard further restoration projects as useful and only 6% as not useful. The results show that river restorations are of great value and are held in high esteem by the population. Moreover, the interviewees considered the investments made by the public or sponsors to be predominantly useful. These results are highly valuable for water managers and politicians as the societal relevance of river restoration might be a key factor in the ongoing public and political discussion about river restoration.

Abstract
Background
Benthic invertebrate communities are an integral and longstanding component of stream biomonitoring. However, multiple stressors driven by global change threaten benthic invertebrate communities. In particular, climate warming is expected to disrupt freshwater ecosystems. While an increasing number of studies have shown changes in benthic invertebrate community composition in response to climate warming, the effect on stream assessments has rarely been investigated. As several community composition metrics are also used in stream assessments, we predicted that climate warming would worsen stream assessment results. Therefore, we used a comprehensive data set of 2865 benthic invertebrate samples taken between 2000 and 2014 from small central European low mountain streams. We examined the effects of changes in temperature on common community and stream assessment metrics. We used 31 metrics covering composition, richness, tolerance and function of communities, of which many are used in various stream assessment schemes.

Results
Against our expectations, we identified a decreasing air temperature trend of − 0.18 °C over 15 years. This trend was accompanied by significant changes in community composition, for example, increases in species richness and decreases in the community temperature index (CTI). Further, we identified slight concomitant improvements of various globally used stream quality assessment metrics, such as a decreasing saprobic index and an increasing BMWP.

Conclusions
While temperature increased by + 0.9 °C during the past 30 years (1985–2014), our 15-year study period (2000–2014) showed a decrease by − 0.18 °C. Therefore, we regard the concomitant improvement in several assessment metrics as a recovery from prior increasing temperatures. In turn, we assume that increases in water temperature will lead to opposite effects and therefore cause declining assessment results. Water managers should be aware of this linkage that in turn could provide a chance to mitigate the effects of global warming by, for example, planting trees along the rivers and the removal of artificial barriers to increase current velocity to minimize a warming effect.

Abstract
Background
Recent studies indicate a partial recovery of European stream macroinvertebrate diversity. However, the key determinants shaping the overall community trends are only partly explored, owing to insufficient long-term environmental data collected in parallel with community responses. We investigate long-term trends in stream macroinvertebrate communities (i.e., taxonomic and trait composition and metrics), and explore their relationships to diverse environmental drivers (i.e., land-use, runoff, water temperature, and in-stream chemicals). We use macroinvertebrate data collected annually in spring and summer between 2007 and 2021 at four sampling sites within the Rhine-Main-Observatory Long-Term Ecological Research site. These sampling sites encompass a gradient from less-disturbed to disturbed conditions.

Results
Over time, shifts in taxonomic and trait composition and metrics indicated an improvement in environmental conditions. Long-term trends of biological trait metrics mirrored those for taxonomic metrics; for example, increases over time in taxonomic richness were paralleled by increases in functional richness and functional dispersion. Meanwhile, trends of ecological trait metrics were particularly driven by changes in environmental drivers. Land-use, water temperature, and runoff explained around 20% of the overall variance in long-term trends of macroinvertebrate communities. Water temperature and land-use played relatively equal roles in shaping taxonomic and trait composition and metric responses in spring, while water temperature emerged as the most influential driver in summer. However, when incorporating long-term chemical data as a more direct measurement of changes in land-use, the overall variance explained in macroinvertebrate community trends increased to c.a. 50% in both seasons.

Conclusions
Examining more relevant driver variables beyond land-use and climate improves insights into why biodiversity exhibits long-term trends. We call for an increase in initiatives to link biodiversity monitoring with parallel sampling of relevant environmental drivers.