MARS Experiments: Peak Flows in Alpine Rivers

The Hytech experimental channels in Austria. Image: Christian Feld

The MARS project is carrying out seven long-term experiments across Europe to study how river and lake ecosystems respond to multiple stresses.  Last week, we profiled the experiments on Peak Flows in Nordic Rivers which are being carried out near Trondheim in Norway.  This week, we introduce the work of a team led by researchers at the University of Natural Resources and Life Sciences (BOKU) in Vienna, Austria on ‘Peak Flows in Alpine Rivers’.

As in the experiments in Norway, the BOKU research team in Austria are interested in understanding the effect of extremely high water flows on the freshwater environment.  Here, the team are seeking to understand the effect of sudden releases of water from hydropower plants (or ‘hydropeaks’) on the ecology of Alpine rivers, specifically in fish, insects and algae communities.

Researchers electrofishing. Image: Christian Feld

Hydropower has become big business in the Alps, generating renewable energy using the force of rivers flowing strongly down steep mountain sides.  However, this approach to ‘green’ energy production brings a range of potentially harmful effects on freshwater life – affecting the flow speed and amount, the water temperature and the physical characteristics of the river (its ‘morphology’) amongst others.   These potentially harmful stresses on the freshwater environment are strongest where there is no compensation reservoir to buffer flow fluctuations from  hydropower releases.

It is estimated that around 800km of Austrian rivers are significantly affected by hydropower developments.  However, the effects of hydropeaking on freshwater environments are not fully understood.  As a result, the BOKU team are using a two experimental channels at the HyTEC (Hydromorphological and Temperature Experimental Channels) facility in Lunz am See, Austria to carry out research on the topic.

Mesocosms on the experimental channels. Image: Lisa Schülting

The changes in water amount, speed and temperature associated with a ‘hydropeak’ release from a hydropower plant can be replicated on the experimental channels, which are 40 metres long and 6 metres wide.  The channels are fed by an outflow from Lake Lunz, which provides nutrient poor water which is common in mountain stream environments.

Different temperatures of water can be taken from different outflows: one on the lake’s surface for warmer water during summer, and one at 10m depth for cooler water.

The effects of hydropeaking on the freshwater environment are being explored in these experiments by using three key freshwater groups: fish, represented by larvae and juveniles of the European grayling and brown trout;  macroinvertebrates (or aquatic insects), which are collected from a nearby stream; and benthic algae that grows on the bottom of the stream bed.

The experiments seek to understand how far the fish and macroinvertebrates are forced out of their normal habitat by high flows (termed ‘drift’ by the researchers), and whether this causes them to become stranded (for example, on a gravel bar) as water levels quickly recede.  The influence of gravel bar morphology, time of day and water temperature on this stranding risk will be investigated, along with rates of (re)colonisation of habitats by the different species after the hydropeak.  The fish behaviour will be observed directly and through video analysis, and the fish will be safely released back into the wild after the experiments are finished.

Benthic algae are an important part of the food web in nutrient-poor mountain streams.  These experiments will examine how the colonisation, photosynthesis rate and diversity of benthic algae communities is affected by daily hydropeaking.  Researchers will also studying how rates of leaf decomposition – a process which releases nutrients into the water and encourage algal growth – vary with hydropeaking.

Caddis flies (Allogamus auricollis) on the stream bed. Image: Wolfram Graf

During a hydropeak event, there are changes not only to the water’s flow but also to its temperature.  The experiments will examine how different species of macroinvertebrates are affected separately by each of the multiple stresses: temperature, flow speed and time of day.  Understanding how different macroinvertebrates respond to different stresses will allow the researchers to identify indicator species, which can potentially be monitored in the future to assess the wider health of an ecosystem in response to a hydropeak.

The results of this exciting work will potentially allow for better informed environmental planning and policy decisions and impact assessments for hydropower developments on Alpine mountain streams.  As with all the MARS experiments, we’ll keep you updated with the results.

Research team:

Lisa Schülting, Wolfram Graf, Elisabeth Bondar-Kunze, Thomas Hein, Stefan Auer, Bernhard Zeiringer, Stefan Schmutz and Rafaela Schinegger.

Contact: stefan.auer@boku.ac.at