Abstract
BackgroundBenthic 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.ResultsAgainst 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.ConclusionsWhile 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.
Highlights
Benthic invertebrate communities are an integral and longstanding component of stream biomonitoring
In respect to stream quality metrics, the Saprobic Index (SI) displayed a decrease of − 3.0% (− 0.002 ± 0.001 year−1, generalized linear mixed models (GLMMs):p < 0.05), while the Multi-Metric Index (MMI) (29.3%; 0.019 ± 0.004 year−1; GLMM: p < 0.05), BMWP score (19.8%; 1.3 ± 0.05 year−1; GLMM: p < 0.05) and Number of taxa (23.0%; 0.016 ± 0.25 year−1; GLMM: p < 0.05) increased significantly (Fig. 1; Table 1)
To accurately assess stressors that affect the quality of freshwater ecosystems, ideally assessment metrics display the effect of the respective stressor
Summary
Benthic invertebrate communities are an integral and longstanding component of stream biomonitoring. In recent decades, accelerated warming rates have resulted in changes in terrestrial [20, 21] and freshwater community compositions [55], as well as species range shifts towards higher elevated areas and towards the poles [62, 73]. For benthic stream invertebrate communities, such spatial and temporal community shifts to meet their species-specific temperature preferences have been described [32] and will likely continue in the future [23]. This is especially true for (low) mountain streams, which are considered biological hotspots as they serve as refugia for cold-adapted and specialized species [39], and are disproportionally affected by temperature changes [62]
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