Assessing the impact of a downscaled climate change simulation on the fish fauna in an Inner-Alpine River

Abstract

This study assesses the impact of a changing climate on fish fauna by comparing the past mean state of fish assemblage to a possible future mean state. It is based on (1) local scale observations along an Inner-Alpine river called Mur, (2) an IPCC emission scenario (IS92a), implemented by atmosphere-ocean global circulation model (AOGCM) ECHAM4/OPYC3, and (3) a model-chain that links climate research to hydrobiology. The Mur River is still in a near-natural condition and water temperature in summer is the most important aquatic ecological constraint for fish distribution. The methodological strategy is (1) to use downscaled air temperature and precipitation scenarios for the first half of the twenty-first century, (2) to establish a model that simulates water temperature by means of air temperature and flow rate in order to generate water temperature scenarios, and (3) to evaluate the impact on fish communities using an ecological model that is driven by water temperature. This methodology links the response of fish fauna to an IPCC emission scenario and is to our knowledge an unprecedented approach. The downscaled IS92a scenarios show increased mean air temperatures during the whole year and increased precipitation totals during summer, but reduced totals for the rest of the annual cycle. These changes result in scenarios of increased water temperatures, an altered annual cycle of flow rate, and, in turn, a 70 m displacement in elevation of fish communities towards the river's head. This would enhance stress on species that rely on low water temperatures and coerce cyprinid species into advancing against retreating salmonids. Hyporhithral river sectors would turn into epipotamal sectors. Grayling (Thymallus thymallus) and Danube salmon (Hucho hucho), presently characteristic for the Mur River, would be superceded by other species. Native brown trout (Salmo trutta), already now under pressure of competition, may be at risk of losing its habitat in favour of invaders like the exotic rainbow trout (Oncorhynchus mykiss), which are better adapted to higher water temperatures. Projected changes in fish communities suggest an adverse influence on salmonid sport fishing and a loss in its high economic value.

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

“…; Hari et al 2006). Rising air temperature is reflected in coherent rise in water temperatures (up to +1.1°C) in streams both in the lowlands and in the foothills of the Alps, but the changes are less obvious in alpine streams influenced by glaciers and/or hydropower stations (Hari et al 2006;Matulla et al 2007). Rising water temperature has shifted the thermal habitat for fish communities upwards up to 130 m (Hari et al 2006;Matulla et al 2007) and might affect fish health and reproduction (see discussion below).…”

The influence of riparian vegetation shading on water temperature during low flow conditions in a medium sized river

“…Stream water temperature is an important and limiting parameter for a number of organisms such as fish or aquatic invertebrates (Broadmeadow and Nisbet, 2004;Matulla et al, 2007;Rahel and Olden, 2008;Logez and Pont, 2013;Pletterbauer et al, 2014). It results from the multiple processes, which influence the gains and losses of thermal energy in streambeds, depending on the amount of stream discharge, topography and atmospheric conditions along the river course (Caissie, 2006).…”

Simulation modeling of phytoplankton dynamics in a large eutrophic river, Hungary — Danubian Phytoplankton Growth Model (DPGM)

“…Other models are devoted to answer related questions of certain water bodies (e.g. Matulla et al 2007;Hartman et al 2006;Peeters et al 2007), which can be of great use, but also their methodology can be adapted to other questions or habitats. Complex ecosystem models (e.g.…”