Alpine Waters

The elements of the water balance, namely precipitation, runoff, evapotranspiration, and storage change, their interaction and special attributes in the mountains are presented using the example of the European Alps, with particular reference to Switzerland. Strong differentiation in the alpine climate over time and space exerts a significant influence on the water cycle. This chapter therefore discusses each of the elements of the water balance with particular reference to the influence of mountains and their measurement, as well as the spatial differentiation characteristics. The analysis of the water balance is accompanied by a discussion on the attributes and differences at different altitudes and in different climatic regions. Finally, the importance of alpine water resources for water supplies in the adjacent lowlands is examined.

Alpine regions have been and will be responding sensitively to global climate change compared to other European regions. This chapter analyses past and future changes in the climate of the Alps and its consequences on the elements of the water cycle. One obvious consequence is the melting of European glaciers by more than 65% since the end of the Little Ice Age in 1850. As a result of temperature increase hydrological regimes are changing. How will climate and water balance change in the future? Scenario results for the European Alps and in more detail for the Swiss Alps are discussed. Consequences in inner Alpine valleys are less precipitation in summer and hence more droughts.

In mountainous regions water often constitutes the dominant – and even in many cases the only – useful natural resource. Therefore, water is used for various purposes, especially for the production of hydropower, for water supplies, irrigation, and artificial snow making. The use of water resources and other human interventions, for example structural control and the correction of water courses, may result in fundamental quantitative changes in the natural water cycle or in the natural runoff characteristics on varying time scales. These interventions also significantly influence a wide range of other physical, chemical, and morphological parameters of rivers and streams.

In the future changes in runoff patterns forced by climate change as well as a growing demand for water for various applications in mountainous regions must be assumed. As a consequence, the strain on natural water supplies in alpine regions will be much stronger, especially at the local level. As mountains play an important role as water towers for the lowlands, this may also impact the water supply in the surrounding regions.

Average concentrations of dissolved nutrients (NO₃, DRP, K) in the large alpine rivers Rhine, Rhône, Ticino, and Inn, and in small alpine streams and glacier streams, are low compared to those in midland rivers. Concentrations of NO₃ in the large rivers clearly exceed background concentrations. In spite of limited anthropogenic activities in alpine catchments, DRP concentrations in large rivers exhibited a downward trend over the last 30 years. Time series of NO₃ concentrations were first increasing and then leveled off. Export coefficients of NO₃ and DRP in alpine streams fall in the range of those estimated for nonagricultural lands and forests on the Swiss Plateau.

The chemical weathering rate of rock-forming minerals in alpine catchments is about 165 ± 45 g m⁻² y⁻¹, corresponding to an ablation rate of about 0.06 mm y⁻¹. Rates are dominated by the reaction of carbonate-containing rocks with CO₂ and the dissolution of anhydrite, whereas the weathering of silicate minerals contributes little. Total chemical weathering rates are in the same range as the export rate of fine sediments, as part of physical weathering products. In this respect, alpine rivers differ distinctly from lowland running waters. Long-term observations also revealed small changes in concentrations and loads of geochemical constituents. An increase in water temperature may be one driver for these changes, although other factors also play a role.

Trend analyses of the key parameters involved in acidification processes measured in 20 Alpine lakes during the period 1980–2004 revealed significant decreasing sulphate (15 out of 20) and increasing alkalinity trends (14 out of 20) in most studied lakes, while trends for base cations and nitrate were small and mostly insignificant. The average increase in alkalinity between 1980 and 2004 was 0.012 meq l⁻¹. Today two lakes out of 20 are still acidic (alkalinity < 0 meq l⁻¹), 13 are sensitive to acidification (0 meq l⁻¹ < alkalinity < 0.05 meq l⁻¹) and five have low alkalinities but are not at risk (0.05 meq l⁻¹ < alkalinity < 0.2 meq l⁻¹). Differently, in the 1980s four lakes were acidic, 14 were sensitive to acidification and two had low alkalinities. During the same time period the pH increased on average by 0.3 units.

Because of accelerated dissolution of aluminium minerals a pH value below 6 can become critical for the biology of lakes. Compared to seven lakes in the 1980s today only three lakes out of 20 exhibit an average pH below 6. A comparison between the populations of macroinvertebrates in lakes with different acidity showed that at average lake pH’s below 6 the population of macroinvertebrate changes. The taxa richness and the EPT index (= number of families of the order Ephemeroptera, Plecoptera, Trichoptera) decreases and acid-sensitive species disappear.

Alpine glaciers are natural archives of past precipitation. At high elevations where melting is negligible and precipitation occurs as snow throughout the year the manifold information contained in the annual snow layers is well preserved. This information is accessed by ice core drilling and analyses. The stable isotope composition of water and the chemical impurities in the ice allow reconstructing past climate conditions and air pollution. The time period covered by suitable glaciers in the Alps depends on accumulation rate and glacier thickness and varies from a few hundred to more than 10,000 years. Concentration records of various trace species demonstrate the impact of anthropogenic emissions on the impurity content of snow. They show a generally consistent picture of a vastly altered atmospheric composition due to anthropogenic activities. Compared to rain samples from the vicinity of Zurich, concentrations of chemical impurities in Alpine ice are lower by a factor of 3–4, reflecting the different vertical and horizontal distance to the emission sources.

Organic chemicals that are sufficiently persistent are capable of undergoing long-range transport and travel great distances from their sources through the atmosphere. Those organic chemicals that are more efficiently scavenged from the atmosphere in alpine environments than in the surrounding areas can become enriched in mountains, i.e. are found in higher than background concentrations at higher altitudes. This is confirmed by measurements in snow and glacial ice as well as in the waters and aquatic and lotic biota of mountains. Those organic contaminants that exhibit increasing concentrations with elevation are often also those expected to exhibit bioaccumulation and biomagnification, i.e. to achieve higher concentrations at higher trophic levels. As the effects of long-term exposure to many of these chemicals is not yet understood, and as they are – or are structurally related to – known toxins, the presence of higher-than-background concentrations of certain POCs in alpine environments is of considerable concern.

We review the different water sources of alpine streams, namely snowmelt, glacial meltwater, and groundwater. Alpine water sources have different physicochemical properties, with their relative contributions determining habitat characteristics of receiving streams. High spatio-temporal variability of water source contributions makes rivers in alpine glacierized basins distinct from other lotic systems. The timing and volume of bulk (snow and ice) meltwater production, along with inputs of groundwater generate distinct patterns of stream discharge, water temperature, suspended sediment, hydrochemistry and channel stability over annual, seasonal and diurnal time-scales. These temporal changes in water sources are sensitive to anthropogenic pressures including climate change, water resource allocations, and contaminants which will ultimately influence water quality and habitat suitability for biotic communities. Heterogeneity of the physicochemical environment creates a spatial and temporal mosaic of stream habitats related to differences in water source contributions, and hydrological connectivity. Hydrochemical characteristics are strongly influenced by seasonal snowmelt, and the development of glacier drainage systems. River ice is a particular feature of alpine streams, creating unique environmental conditions that strongly affect the flora and fauna, both directly, and indirectly through changes in their environment. The extent, nature and duration of river ice varies widely across alpine areas. We outline the characteristic longitudinal patterns in benthic macroinvertebrate communities downstream from these water sources created by this physical template.

Electricity generation from hydropower is responsible for a large part of the human impacts on water resources in the Alps. Attempts at finding an encompassing mitigation approach to these impacts are often confronted with high levels of societal conflict. Therefore, an integrative approach has to consider both ecological and political/social aspects of this economic activity. In the following, we will present an integrative mitigation approach that was developed as an eco-label for electricity in Switzerland. This label was developed and implemented in the early 2000s and has meanwhile been accepted as an environmental standard for hydropower operation in many other countries. The chapter emphasizes the interdisciplinary competencies needed as well as the potential benefits of an integrative approach to the problem.

The management of dams serves many purposes and goals all over the globe, and has important consequences for the downstream rivers and lakes. Among the more than 50,000 so-called large dams, the biggest are located in alpine regions. As a result, the water residence time in heavily dammed alpine valleys typically increased from a few days to several weeks, hydrological regimes shifted seasonally and sediment transport often decreased to half of its natural value. The occurrence of high flows responsible for most particle transport is reduced and particles are trapped behind the dams. These changes modify particle concentrations and particle size distributions, thermal regimes and water quality in downstream waters. As a result, downstream rivers and pre-alpine lakes often experience significant alterations in particle, carbon and nutrient cycling. Also described are common mitigation measures that are often applied in newly-planned damming management.

Hydropower use and settlement development adversely affected Alpine rivers and streams. The majority of Swiss and Austrian electricity is produced by hydropower plants, which impact the natural flow regime of running waters. In addition, channelization impairs the river morphology.

The resulting changes (alterations of the natural flow regime, lack of hydrological connectivity, deficits in morphology) significantly affect the ecology of rivers and streams, and cause major deficits. Restoration of hydrological connectivity and ecomorphological integrity is an urgent need for Alpine streams. The “Rhone-Thur” project developed guidelines for planning river restoration and formulated ten basic elements for carrying out successful projects. Inclusion of a reference system, baseline monitoring and a clear definition of project objectives are important steps at the beginning. The project scale and ecological improvements are also specified. Each successful project has to deal with the socio-economic aspects and include the stakeholders in an early project phase. Prediction of restoration measures and the alternative possibilities are helpful processes. After implementation, the core of each project is the evaluation of success and outcome. Comparison of appropriate indicator values before and after the restoration helps to classify the project objectives into different success categories: from failure to great success. However, great success is difficult to achieve and it is important to understand the outcome. Generally, river morphology recovers more quickly after restoration than biological communities (fishes) do. The degree of connectivity to intact neighborhood communities and the size of the restoration area influence the success of the restoration project. Possible restoration sites should therefore be prioritized within the watershed, and sites close to intact habitat with existing source populations provide higher success expectations. For Alpine ecosystems the restoration of a dynamic hydrological regime is a major task and a challenge for the future. This is mainly true for stream reaches with residual flow and river segments with hydropeaking problems.

The Middle Mountains in the Himalayas contain some of the most intensively used watersheds in mountain regions of the world. As shown in this case study increased climatic variability is leading to widespread shortages of drinking and irrigation water and land stability, accelerated erosion, sediment transport and flooding are the main issues during storm events. Conservation farming to prevent soil erosion is a major challenge particularly on sloping agriculture. Degraded areas are the main source of sediments and rehabilitation efforts that focus on using nitrogen-fixing fodder trees, planted in hedgerows on sloping terrain, are proving to be an effective adaptation technique. Water harvesting and storage in ponds and cisterns during the monsoon season is another effective adaptation technique that enables the production of food via low-cost drip irrigation during the dry season. Reducing the land use intensification and population pressure on the marginal lands in the headwaters of these watersheds is likely to be the most effective coping methods in view of increased climatic variability.