Projected effects of Climate-change-induced flow alterations on stream macroinvertebrate abundances.

Karan Kakouei,Sami Domisch,Jochem Kail,Katie S Irving,Sonja C Jähnig,Jens Kiesel

doi:10.1002/ece3.3907

Abstract

Global change has the potential to affect river flow conditions which are fundamental determinants of physical habitats. Predictions of the effects of flow alterations on aquatic biota have mostly been assessed based on species ecological traits (e.g., current preferences), which are difficult to link to quantitative discharge data. Alternatively, we used empirically derived predictive relationships for species’ response to flow to assess the effect of flow alterations due to climate change in two contrasting central European river catchments. Predictive relationships were set up for 294 individual species based on (1) abundance data from 223 sampling sites in the Kinzig lower‐mountainous catchment and 67 sites in the Treene lowland catchment, and (2) flow conditions at these sites described by five flow metrics quantifying the duration, frequency, magnitude, timing and rate of flow events using present‐day gauging data. Species’ abundances were predicted for three periods: (1) baseline (1998–2017), (2) horizon 2050 (2046–2065) and (3) horizon 2090 (2080–2099) based on these empirical relationships and using high‐resolution modeled discharge data for the present and future climate conditions. We compared the differences in predicted abundances among periods for individual species at each site, where the percent change served as a proxy to assess the potential species responses to flow alterations. Climate change was predicted to most strongly affect the low‐flow conditions, leading to decreased abundances of species up to −42%. Finally combining the response of all species over all metrics indicated increasing overall species assemblage responses in 98% of the studied river reaches in both projected horizons and were significantly larger in the lower‐mountainous Kinzig compared to the lowland Treene catchment. Such quantitative analyses of freshwater taxa responses to flow alterations provide valuable tools for predicting potential climate‐change impacts on species abundances and can be applied to any stressor, species, or region.

Highlights

River biota depend on a range of environmental variables, including natural habitat conditions as well as stressors
Assessing the quantitative impact of possible flow alterations on species response (SR) yielded several key findings: (1) Climate change was predicted to strongly decrease the low flows in both studied catchments; (2) the predicted increases and decreases in species abundances were not proportional to changes in flow metrics; and (3) predictions showed that species would experience decreased and increased abundances with regard to flow alterations detected by five IHA metrics in both the lowland and lower-mountainous region
The species assemblage responses were predicted to increase at most sampling sites for most IHA metrics, which resulted in increasing overall species assemblage responses (OSARs) in all Kinzig and 98% of Treene river reaches

Summary

| INTRODUCTION

River biota depend on a range of environmental variables, including natural habitat conditions as well as stressors. While the effects of a variety of environmental variables and stressors such as land-use, climate, and substrate conditions on riverine species are well understood (Miserendino et al, 2011; Schröder et al, 2013), the relationship between riverine species’ abundances and river flow is less often explored (Kuemmerlen et al, 2014, 2015; Pyne & Poff, 2017), it has been widely stated that flow (i.e., discharge) is one of the key habitat variables in river ecosystems (Arthington, Bunn, Poff, & Naiman, 2006; Dewson, James, & Death, 2007; Domisch et al, 2017; Poff et al, 1997). Discharge data have been used to empirically derive quantitative flow preferences for macroinvertebrates (Kakouei, Kiesel, Kail, Pusch, & Jähnig, 2017) These flow preferences reveal species response (SR) along the range of flow conditions. In which regard do the climate change-induced changes in discharge (different flow conditions according to IHA metrics) have varying effects on stream macroinvertebrates’ abundances? How do possible climate-change impacts on species’ abundances, mediated through flow, differ between the two catchments?

| METHODS

Findings

| DISCUSSION