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

Abstract

Background, aim, and scope Catch decline of freshwater fish has been recorded in several countries. Among the possible causes, habitat change is discussed. This article focuses on potentially increased levels of fine sediments going to rivers and their effects on gravel-spawning brown trout. Indications of increased erosion rates are evident from land-use change in agriculture, changes in forest management practices, and from climate change. The latter induces an increase in air and river water temperatures, reduction in permafrost, changes in snow dynamics and an increase in heavy rain events. As a result, an increase in river sediment is likely. Suspended sediment may affect fish health and behaviour directly. Furthermore, sediment loads may clog gravel beds impeding fish such as brown trout from spawning and reducing recruitment rates. To assess the potential impact on fine sediments, knowledge of brown trout reproductive needs and the effects of sediment on brown trout health were evaluated. Approach We critically reviewed the literature and included results from ongoing studies to answer the following questions, focusing on recent decades and rivers in alpine countries.-Have climate change and land-use change increased erosion and sediment loads in rivers? -Do we have indications of an increase in riverbed clogging?-Are there indications of direct or indirect effects on brown trout from increased suspended sediment concentrations in rivers or from an increase in riverbed clogging?Results Rising air temperatures have led to more intensive precipitation in winter months, earlier snow melt in spring, and rising snow lines and hence to increased erosion. Intensification of land use has supported erosion in lowland and prealpine areas in the second half of the twentieth century. In the Alps, however, reforestation of abandoned land at high altitudes might reduce the erosion risk while intensification on the lower, more easily accessible slopes increases erosion risk. Data from laboratory experiments show that suspended sediments affect the health and behaviour of fish when available in high amounts. Point measurements in large rivers indicate no common lethal threat and suspended sediment is rarely measured continuously in small rivers. However, effects on fish can be expected under environmentally relevant conditions. River bed clogging impairs the reproductive performance of gravel-spawning fish. Discussion Overall, higher erosion and increased levels of fine sediment going into rivers are expected in future. Additionally, sediment loads in rivers are suspected to have considerably impaired gravel bed structure and brown trout spawning is impeded. Timing of discharge is put forward and is now more likely to affect brown trout spawning than in previous decades. Conclusions Reports on riverbed clogging from changes in erosion and fine sediment deposition patterns, caused by climate change and land-use change are rare. This review identifies both a risk of increases in climate erosive forces and fine sedi...

An attempt to estimate tolerable soil erosion rates by matching soil formation with denudation in Alpine grasslands

“…Generally, the combined effects of climate and changing land use have been predicted to increase future soil erosion in Alpine regions (Frei et al 2007). A rising snowline, intensified precipitation during the winter and strong leaching effects with no or sparse vegetation cover in late autumn and early spring could result in an increase in erosion especially in the Northern (mainly North-Western) Alps (Fuhrer et al 2006;Scheurer et al 2009). However, other models predict increased erosion susceptibility more on the southern part of the Alps (Bosco et al 2009).…”

Impact of climate change on freshwater ecosystems: a global-scale analysis of ecologically relevant river flow alterations

“…Long-term average annual discharge will not change significantly. Consequences of these changes of the Danube river flow regime due to climate change may include disruption of spawning, with decreased reproduction and recruitment, decreased oxygen concentrations in the summer and alteration of floodplain vegetation, decreases in young fish and other effects of decreased duration of floodplain inundation (Scheurer et al, 2009;Poff and Zimmerman, 2010).…”

“…Kundczewicz et al (2007) reviewed some publications that deal with the impacts of climate change induced river flow alterations on freshwater ecosystems, discussing decreased habitat availability due to decreased ice-jam flooding, impacts of lower water column depth on spawning of salmon, and impacts of reduced runoff on breeding grounds for water birds. In a review on the impact of climate and land use change on Alpine brown trout, Scheurer et al (2009) concluded that climate change induced increases of river discharge and sediment loads in winter and early spring could be especially harmful for brown trout reproduction and development of young life stages. Erwin (2009) reflected on the challenges to wetland conservation and restoration under climate change, pointing out the need to reduce non-climate stressors, including monitoring, in particular of invasive species that are favored by climate change.…”

Measurement of spatial and temporal fine sediment dynamics in a small river

“…Studies for the Alps, pre-Alps and the hilly regions of the Swiss Plateau are rare. This includes small rivers, which are habitats for gravel spawning fish (Scheurer et al, 2009).…”

“…The results of those empirical studies of fine sediment infiltration rates are difficult to generalize mostly due to different measurement methodologies (Sear et al, 2008). Hence, there is a need to compare methodologies as well as data on sediment input and riverbed clogging to achieve a better comparability of results from different studies and to increase knowledge on the interaction between fine sediment dynamics and fine sediment infiltration and accumulation (Scheurer et al, 2009). The aim of this study was to (i) compare results obtained by different methods used to capture temporal and spatial dynamics of suspended sediment and fine sediment infiltration and accumulation, (ii) test their suitability for a river in the Swiss Plateau, (iii) compare the results with hydrological data, and (iv) compare the results with literature data.…”