Degradation and recovery of mountain watersheds: the Jizera Mountains, Czech Republic

J. Keek and Z. Hoická

Josef Keek is Associate Professor
in the Department of Hydrology,
Czech Technical University, Prague,
Czech Republic.

Zuzana Hoická is Lecturer in the
Department of Hydrobiology,
Charles University, Prague, Czech
Republic.

Watershed management practices help improve water quality altered by effects of airborne pollution and inappropriate forestry practices.

Degraded sites in the "Black Triangle" region of the Czech Republic

In the 1970s and 1980s, the watersheds of the Jizera Mountains in northern Bohemia, Czech Republic, declined as a consequence of acid atmospheric deposition (mainly sulphate from lignite combustion) and inappropriate forestry practices. Although the headwater area was a protected area, ecologically oriented watershed management was not realized until the 1990s. Soil erosion and sediment runoff resulted in deterioration of the water quality in watercourses and reservoirs. Low pH values and high content of toxic metals in the surface waters led to extinction of fish and reduced populations of other aquatic life.

Restoration of mountain watersheds in the Jizera Mountains began in the 1990s with the political and economic changes in Eastern Europe. The atmospheric deposition of sulphate decreased, and nature protection and landscape restoration became more prominent issues (Keek, 1994; Grennfelt et al., 1995; Haigh and Keek, 2000).

This article describes how water quality has recovered in the past decade through a combination of decreased air pollution and watershed management practices including harvesting of spruce stands (reducing leaf area) and liming of both the reservoir and the watershed. Mean annual pH values have increased and aluminium concentrations have dropped, making possible the successful reintroduction of fish. A return to traditional forestry practices (skidding the timber using horses or cables, respecting riparian zones, seasonal skidding and manual reforestation) has contributed to the stabilization of mountain watersheds.

SITE CHARACTERISTICS

The Jizera Mountains region (350 km², latitude 50^o40' to 50^o52', longitude 15^o08' to 15^o24', humid temperate zone) is part of the so-called "Black Triangle", the epicentre of acid atmospheric deposition in Europe. Forest cover in this region is 83 percent. The native tree species are common beech (Fagus sylvatica), Norway spruce (Picea abies) and common silver fir (Abies alba). The region includes a 200 km² plateau above 800 m elevation (the highest peak is 1 124 m) with gentle slopes, almost completely forested. Significant changes in species composition occurred here during the twentieth century, with spruce plantations (covering 90 percent of mountain forests) dominating.

Mean annual precipitation increases with elevation from 800 to 1 600 mm (the highest precipitation in the Czech Republic), while the mean annual air temperature decreases from 8^o to 4^oC as the elevation rises from 300 to 900 m above sea level. In the high plateau (above 800 m), the snow cover usually lasts from the beginning of November to the end of April; the average maximum depth of the snowpack is 120 cm. The bedrock (granite) and shallow podzolic soils are extremely sensitive to acidification. Surface runoff is dominant; groundwater occurs only in shallow subsurface layers. Between 1902 and 1909 (after catastrophic floods in 1897), five water reservoirs were constructed in the Jizera Mountains to protect the lowland cities and villages. The drinking-water supply system was built after the 1960s.

In 1956, the government established the Protected Landscape Region of the Jizera Mountains to preserve the unique natural elements of the region. To support an important role in water and soil conservation, the Protected Headwater Area of the Jizera Mountains was proclaimed by government decree in 1978. Unfortunately, the proposal for ecologically oriented watershed management (including limits on forest clear-cutting) was not realized.

DAMAGE TO WATERSHEDS IN THE 1980s

In the 1980s, watersheds covered by spruce stands, particularly in the high plateau, were damaged significantly as a consequence of acid atmospheric deposition (from lignite combustion) and inappropriate forestry practices: development of spruce plantations of lower stability (e.g. more sensitive to environmental stresses such as climate, wind, air pollution and acid deposition, insect epidemics), extensive clear-cut harvesting using heavy mechanization and ineffective control of insect epidemics. Reforestation was unsuccessful, mainly because of strong competition from the invasive grass Calamagrostis villosa.

Stresses on the watersheds in the Jizera Mountains: dieback of spruce plantations and extensive clear-cutting in the watershed of the Sous reservoir, 1991

 - J. KEEK

Impact of inappropriate forestry practices

About 100 km² (50 percent of the high plateau) was harvested in the 1980s. The applied clear-cutting technology (particularly skidding timber using heavy tractors) compacted about 10 percent of the soil surface. As a result, the infiltration capacity of soils dropped from 150 to 40 mm per hour. The development of a network of skid roads and the lengthening of periodic stream channels led to intensive soil erosion and sediment runoff, which led in turn to deterioration of water quality in watercourses and reservoirs.

The density of skid roads and the related drainage network in the high plateau of the mountains increased from 1.3 to 4.7 km per square kilometre. The surface runoff, which occurred only in skid roads, therefore increased from 52 to 68 percent. Thus the retention capacity of watersheds declined. Soil erosion intensified from 0.01 to 1.34 mm, and sediment runoff increased from 8 to 30 percent of the eroded soil volume.

Soil erosion in skid roads of the Jizerka catchment (1993) - which led to degradation of water quality in watercourses and reservoirs

 - J. KEEK

Acid atmospheric deposition

The acid atmospheric load measured in the open field peaked in the late 1980s (Figure 1).

1
Mean annual content of SO₂ in the air, Jizera Mountains, 1972-1993
Note: Jizerka, altitude 860 m, located in the eastern plateau; Bedrichov, altitude 760 m, in the central plateau; Hejnice, altitude 400 m, on the north rim of the mountains.

Sulphate was 45 percent and nitrate 16 percent of the total atmospheric deposition. Subsequently, SO₂ concentration in the air decreased as a result of the reduced output of coal power stations in central Europe, particularly in eastern Germany. The acid atmospheric load in the open field in the 1990s was about 40 percent of the 1987 level. However, the atmospheric load of sulphur observed under vegetation, particularly in spruce forests, was still much higher than in the open (Table 1). Under the forest canopy, the deposition of sulphur decreases with defoliation of spruce stands and with the occurrence of deciduous trees.

DECLINE OF WATERCOURSES AND RESERVOIRS

Since 1982, a long-term hydrological investigation to monitor the ecological effects of the acid deposition and the forestry practices has been conducted in:

• the experimental basin Jizerka (100 ha, elevation 860 to 980 m), to study the effects of clear-cutting of mature spruce stands;
• the control basin Oldrichov (23 ha, elevation 400 to 620 m), to study the hydrology and biochemistry of a mature beech forest;
• watersheds of three drinking-water reservoirs: Bedrichov, Sous and Josefuv Dul (Table 2).

The results indicated that water quality in watercourses and reservoirs of the Jizera Mountains had declined significantly in the 1970s and 1980s: pH values dropped to between 4 and 5 (Table 3); the content of aluminium increased to 1 to 2 mg per litre, with a high level of toxic forms of aluminium (free Al³⁺ as well as inorganic aluminium complexes); and benthic fauna was reduced. In the reservoirs Bedrichov, Sous and Josefuv Dul, the extinction of fish was documented, and both zooplankton and phytoplankton (algae) were drastically reduced (Stuchlik et al., 1997). The species composition of phytoplankton in the reservoirs (few taxa, dominated by Dinophyceae, mainly Peridinium sp.) reflects the acidity of the water. Zooplankton was scarce; the prevailing organisms were rotifers (Brachionus sericus and Keratella valga) and crustaceans (Ceriodaphnia quadrangula and Cyclopidae spp). Seasonal changes in the water chemistry (episodic acidification after snowmelt or rainstorms) were relatively high (Figure 2).

2
Seasonal pH changes in the Bedrichov reservoir, 1995

RECOVERY OF WATER QUALITY THROUGH WATERSHED MANAGEMENT

In surface waters, the first signs of recovery were observed in the late 1980s as a result of reduction in the leaf area of spruce plantations and the consequent reduction in acid deposition under the canopy. In the Jizerka experimental catchment, the clear-cut of mature spruce stands and reforestation with spruce seedlings decreased the leaf area index from 18.5 (mature spruce forests) to a seasonal maximum of 2.7 (spruce seedlings and grass) and increased the annual water yield by 108 mm (872 mm observed in the period 1991 to 2000 versus 764 mm calculated for the period 1981 to 1985, when the catchment was still covered by mature spruce plantations). Consequently, the long-term annual evapotranspiration dropped from 543 mm (mature spruce stand) to 355 mm (reforested stand with spruce seedlings and grass).

After the clear-cutting of spruce stands, signs of recovery were found in the water chemistry of streams in the Jizerka catchment (Figure 3): mean annual pH values increased from 4.0 to 5.3, concentrations of sulphate decreased from 13 to 6 mg per litre, and concentrations of nitrate decreased from 6 to 4 mg per litre.

3
Stream-water chemistry related to the clear-cut of mature spruce stands, Jizerka catchment, 1982-2000

Since the 1990s traditional environmentally friendly forest-harvesting practices have been adopted: limited clear-cut (small coupe size), skidding of timber by horses and cables, seasonal skidding and respecting of riparian buffer zones. Effective control of rills - small erosion channels - depends on the succession of plants related to the depth, slope and length of rills. Almost 90 percent of the rills have stabilized naturally.

Use of native species

Native deep-rooting tree species (beech, fir) can improve ecosystem stability by including subsoil horizons in the cycling of nutrients, minimizing leaching of nutrients and supporting stabilization of slopes (including wind-cast susceptibility). Semi-natural beech forests (native forests managed by selective cut mainly to support natural regrowth) are more acid resistant than spruce plantations and grow naturally on steep slopes in the Jizera Mountains. They have an essential role for soil stability, conservation of the forest microclimate and the hydrological regime. In beech forests, deposition of acidic substances under the canopy is lower - 30 percent that of comparable spruce stands (Table 1). Therefore, forest stands with composition resembling the historical structure (Table 4) could contribute to long-term control of acidification.

Liming for increased alkalinity

Since 1998, the Sous reservoir has been limed annually after the snowmelt (air application of calcite powder, about 10 to 12 g per cubic metre, particle size of less than 0.2 mm) to raise pH and thus detoxify the water. Liming has significantly increased the alkalinity of the reservoir water, as was also shown in Scandinavian countries in the 1980s (Brocksen and Wisniewski, 1988). Liming, however, supports seasonal fluctuation in pH of the reservoir water (Figure 4) and results in drastic changes in the water chemistry which can introduce unpredictable changes in both phytoplankton and zooplankton productivity in the reservoir (a topic currently under study).

Semi-natural beech forests (shown here in the watershed of the Raspenava reservoir) promote soil stability with their deep roots and are more acid resistant than spruce plantations

 - J. KEEK

4
Seasonal pH changes in the Sous reservoir influenced by liming, 1999

REINTRODUCTION OF FISH

Since the 1950s, the surface waters of the high plateau of the Jizera Mountains had been without fish as a result of the extremely acidified environment and the related high content of toxic metals.

Long-term monitoring of the effects on water quality and biota in reservoirs and watercourses related to processes in the watersheds was begun in 1991; 20 main stream channels and six reservoirs were sampled regularly. The transparency, conductivity, pH and content of dissolved oxygen were measured in situ. Laboratory tests included analyses of pH, conductivity, alkalinity, cation and anion concentration, concentration of total phosphorus and dissolved organic carbon. Phytoplankton and zooplankton were identified and counted in preserved samples.

The improvement in the physical and chemical parameters of the waters observed in the early 1990s made it possible to consider reintroduction of fish.

In 1991, brook char (Salvelinus fontinalis, also known as brook trout, the most acid-tolerant species) and brown trout (Salmo trutta morpha fario) were experimentally reintroduced to the Bedrichov reservoir and its inlets. An inventory of fish populations in the stream channels was done after snowmelt (May), in the summer (July) and in the period of reproduction (October). Fish were inventoried through electrofishing (catching the fish using electric shocks, and returning the fish to the streams after inventory) in transects 30 to 60 m long in stream channels. The char were able to survive and reproduce; a sufficient amount of food and well-proportioned age structure and individual growth in the population were observed in the following years. The individuals of brown trout evidently starved and did not reproduce.

In 1996, the Sous reservoir and its inflows were stocked with 30 000 fingerlings of brook char. This population also survived successfully. However, the concentrations of aluminium and heavy metals in the muscles and liver of the fish still exceed the hygienic limit (Table 5). These high concentrations derive from the extremely high content of aluminium and heavy metals in the food eaten by the fish, mainly benthic Ephemeroptera (mayflies) and Trichoptera (caddisflies, Hydropsyche sp. dominating).

In 1999-2000, the fish reintroduction continued in the Josefuv Dul reservoir. To increase the resistance of the new population, the fingerlings used for restocking were produced in the cold water of a strongly acidified stream.

The survival of fish in surface waters of the high plateau of the Jizera Mountains seems to be limited by episodic drops in pH values and by the level of toxic forms of aluminium (free Al³⁺ as well as inorganic aluminium complexes). Significant mobilization of toxic aluminium occurs when the pH of the water is approximately 5.3 or lower. Based on fish survival, 300 µg per litre is considered the critical value for aluminium toxicity. In surface waters, both of these limits are still exceeded during the snowmelt and rainstorms.

Monitoring of effects on water quality included measurements of pH, conductivity and dissolved oxygen in situ (Bedrichov reservoir, March 1995)

 - J. KEEK

Electrofishing to inventory fish populations in tributaries of the Bedrichov reservoir, August 1996

 - J. KEEK

DISCUSSION AND CONCLUSIONS

The predominantly coniferous forests in many mountainous regions of central Europe are in a phase of change in response to a changing environment (Teller, Mathy and Jeffers, 1992). In the 1980s, watersheds in the Jizera Mountains were stressed by extreme acid atmospheric deposition, dieback of spruce plantations and injurious commercial forestry practices. The forests of the Jizera Mountains are among the most sensitive ecosystems in Europe: slow weathering bedrock and shallow podzolic soils with a very shallow pool of basic cations have low buffering capacity to cope with acid deposition.

The recent improvement of surface water quality in the Jizera Mountains is a consequence of both decrease in air pollution and reduction of leaf area (as well as the roughness of the canopy) by the clear-cutting of spruce stands, and partially also a result of the liming of both reservoirs and watersheds. The pH values of the water have increased from between 4 and 5 to between 5 and 6; the aluminium concentrations have dropped from between 1 and 2 mg per litre to between 0.2 and 0.5 mg per litre; and brook char (Salvelinus fontinalis) has been successfully reintroduced in headwater reservoirs.

Liming has demonstrably increased the alkalinity of reservoir water. However, a drastic change in water chemistry can start unpredictable changes in both phytoplankton and zooplankton productivity in reservoirs, creating problems in water treatment. Liming of watersheds as a means of mitigating soil acidity also bears many risks on sites with excess mineralization.

A successful revitalization of headwater catchments should be sustainable without additional intervention (Haigh and Keek, 2000). The critical atmospheric acidity load in the forests of the Jizera Mountains (500 to 700 acid equivalents per hectare per year) is still exceeded by about 50 percent (RIVM, 1993).

In a long-term perspective, the water quality might be improved by planting stands with nearly native composition (deciduous or mixed forests with lower leaf area and surface roughness in comparison with spruce plantations). Natural deep-rooting tree species (beech, fir) can also improve the ecosystem stability, by including subsoil horizons in the cycling of nutrients, minimizing leaching of nutrients and stabilizing slopes. The management of mountain watersheds should include traditional environmentally friendly forestry practices: clear-cutting limits, advance planting, skidding of timber by horses or cables, seasonal skidding, manual reforestation. Respecting riparian zones is essential for the stabilization of mountain watersheds. 

Bibliography

Brocksen, R.W. & Wisniewski, J., eds. 1988. Restoration of aquatic and terrestrial systems. Dordrecht, the Netherlands, Kluwer Academic Publishers.

Grennfelt, P., Rodhe, H., Thörnelöf, E. & Wisniewski, J., eds. 1995. Acid reign '95? Dordrecht, the Netherlands, Kluwer Academic Publishers.

Haigh, M.J. & Keek, J., eds. 2000. Environmental reconstruction in headwater areas. Dordrecht, the Netherlands, Kluwer Academic Publishers.

Keek, J. 1994. Effects of acid atmospheric deposition on mountain watersheds in central Europe. In Colloque Forêt de Montagne - La forêt dans l'espace montagnard: Vers un nouvel équilibre? p. 24-29. Grenoble, France, Association des Ingénieurs et Cadres de l'Environ-nement et de la Forêt (AICEF)/Syndicat National des Ingénieurs et Cadres de l'Environnement et de la Forêt (SNICEF).

Stuchlík, E., Hoická, Z., Prchalová, M., Keek, J. & Barica, J. 1997. Hydro-biological investigation of three acidified reservoirs in the Jizera Mountains, the Czech Republic, during the summer stratification. Can. Tech. Rep. Fish. Aquat. Sci. 2155: 56-64.

RIVM. 1993. Calculation and mapping of critical loads in Europe: status report 1993. Bilthoven, the Netherlands, National Institute of Public Health and the Environment.

Teller, A., Mathy, P. & Jeffers, J.N.R., eds. 1992. Response of forest ecosystems to environmental changes. London, Elsevier Science Publishers.