J. Křeček and Z. Hořická
Josef Křeček is Associate Professor in the Department of Hydrology, Czech Technical University, Prague, Czech Republic.
Zuzana Hořická is Lecturer in the Department of Hydrobiology, Charles University, Prague, Czech Republic.
Forests and forestry practices in mountain watersheds can moderate
the effects of acid rain on water quality – essential for human health.
Jizera Mountains region
Water is essential for human health and development. Access to safe water is a basic human right and a component of effective policy for health protection. Water resource management is an
integral aspect of the management of water quality. Prevention of microbial and chemical contamination of source water is the first hurdle in preventing water contamination of public health concern. Pollution in the catchment will influence water quality downstream. Therefore, the influence of land use on water quality should be assessed as part of water resource management (WHO, 2004).
On a global scale, headwaters – the small streams that are the sources of a river in its highest reaches – are strongly related to environmental security and human opportunities to live in a healthy environment. In the water cycle, the headwater environment is the recharge area. Adverse changes in headwater systems can have an impact over a large area which may include distant downstream regions (Křeček and Haigh, 2006).
The water protection role of forests is central in the “Black Triangle” area on the borders of the Czech Republic, the former German Democratic Republic and Poland (Figure 1). This area acquired its name because of its extreme air pollution caused by rapid industrialization after the Second World War. Many air pollutants (sulphur dioxide, particulates, carbon monoxide) have been more closely controlled over the past two decades and their impact has been reduced (Grennfelt et al., 1995). However, in Europe there is a striking contrast between environmental pollution levels in the east and in the west.
In addition to causing or exacerbating respiratory diseases, the air pollution in the Black Triangle, especially sulphur dioxide and nitrogen oxides, resulted in acid rain – meaning any wet deposition (rain, sleet, snow or fog drip) that has become more acidic than normal rain (i.e. pH <5.5). Acid rain is harmful to both forest and aquatic ecosystems. Acid rain that seeps into the ground can dissolve nutrients such as magnesium and calcium and can cause aluminium to be released into the soil. Forest stands located at higher elevations are at greater risk because they are exposed to acidic clouds and fog, which contain greater amounts of acid than rain or snow and strip nutrients from leaves or needles. The loss of nutrients makes it easier for diseases, insects and cold weather to damage forests. The reduced quality of water and soil also affects human health.
This article, based on research carried out by the authors since 1982, describes the effects of acid atmospheric deposition, and the role of forestry practices in moderating these effects, in the
Jizera Mountains of the Czech Republic. Acidification in this area, which began in the early 1950s and peaked in the mid-1980s, resulted in large-scale dieback (40 to 80 percent) of spruce stands, a decrease in pH of surface waters and decline of life in streams and reservoirs. Since 1990, however, some recovery has been observed.
The headwaters of the Jizera Mountains in the Czech Republic have 83 percent forest cover. The region’s bedrock (granite) and shallow podzolic soils are extremely sensitive to acidification. Direct runoff (particularly fast subsurface flow) is the dominant source of water; groundwater bodies occur only in shallow subsurface layers.
|Semi-natural beech stands at the north rim of the Jizera Mountains|
In the reservoirs of the Jizera Mountains, low pH, low hardness and high aluminium content were observed in the 1980s.
No health-based guideline value has been proposed for the pH of water. However, pH is one of the most important operational water quality parameters. National guidelines for drinking water quality often suggest that optimum pH is in the range 6.5 to 8.5 (WHO, 2004). Thus, not only acidification, but also high alkalinization (which is related to extreme mineralization) affects
drinking-water quality. Very low or very high pH may also affect recreational users, with negative impacts on the skin and eyes (WHO, 2003). Without pollution and subsequent acid rain, most lakes and streams would have a pH level close to 6.5 (Nordic Council of Ministers, 1988). Acid rain in the Jizera Mountains, however, caused many lakes and streams to have much lower pH levels in the 1980s, around 4 to 5.
Hardness refers to concentrations of dissolved calcium and, to a lesser extent, magnesium in water. Low hardness (up to 10 mg of calcium and magnesium per litre), related to the low pH, was also observed in the area. Soft water with less than about 100 mg per litre has a low buffering capacity and may be more corrosive to water pipes. Epidemiological studies have shown a statistically significant inverse relationship between hardness of drinking-water and cardiovascular disease (WHO, 2004) – in other words, low calcium and magnesium content in drinking-water is related to higher rates of heart disease. There is some indication that very soft water may have an adverse effect on human mineral balance.
Aluminium released into the soil eventually ends up in lakes and streams. The aluminium content of the surface waters in the area in the 1980s was 1 to 2 mg per litre. The established limit of aluminium in drinking-water is 0.1 mg per litre for large treatment facilities, and 0.2 mg per litre for small facilities (WHO, 2004). Although aluminium is widespread in foods, drinking-water and many antacid medications, there is some indication that when ingested orally in concentrations exceeding hygienic limits (i.e. 30 mg of aluminium per kilogram of fish meat, or 0.2 mg of aluminium per litre of drinking-water) it is toxic to humans. It has been hypothesized that aluminium exposure is a risk factor for the development or acceleration of Alzheimer’s disease in humans (WHO, 2004).
The elevated acidity and aluminium levels not only posed risks to human health, but were also deadly to aquatic wildlife, including phytoplankton, mayflies, rainbow trout, smallmouth bass, frogs, spotted salamanders, crayfish and other creatures that are part of the food web. This problem was observed to be much worse during events of episodic acidification from heavy downpours of rain or initial snowmelt (Křeček and Hořická, 2001).
Mean monthly concentration of sulphur dioxide at the Jizerka reservoir, 1987 and 1997
The native tree species in the Jizera Mountains are common beech (Fagus sylvatica), Norway spruce (Picea abies) and common silver fir (Abies alba). However, following the introduction of clear-cutting in the upper mountain plateaus in the seventeenth century (provoked by the development of glass manufacturing), the forests were severely reduced in the eighteenth and nineteenth centuries. In the second half of the nineteenth century Norway spruce was planted for commercial reasons, and by the twentieth century spruce plantations made up 90 percent of the forests in the Jizera Mountains. Nursery practices were established with seeds imported from regions of Europe with a different climate, so the pure spruce plantations had poor ecological stability.
Within a forest stand, the atmospheric deposition of sulphur rises with canopy density (leaf area), height and roughness (the turbulence of the air mass above the canopy). Thus, the effects of acidification were found to be worse in spruce stands.
Beech stands have a lower canopy area, particularly in the dormant season when the concentration of sulphur dioxide in the atmosphere is highest (Figure 2).
Furthermore, native beech stands are more resistant to acidification problems. Their annual shedding of leaves helps them to suffer less than coniferous species which keep their needles for many years and thus accumulate more toxic substances.
Soils in beech stands have higher capacity to buffer acidification because of deeper root systems and higher nutrient content. Therefore, the stream water at a beech stand was found to be twice as hard (i.e. its calcium and magnesium content was twice as high) as that at a spruce site.
Thus the commercial support for converting native mixed stands into spruce plantations over the past two centuries contributed to the degradation of forest health and water quality.
Gradual recovery of mean annual pH in three reservoirs in the Jizera Mountains (Bedrichov, Sous and Josefuv Dul)
From 1984 to 1990, forest harvesting at Jizerka (clear-cut of mature spruce stands and skidding timber by wheeled tractors) also contributed to soil erosion and sedimentation, as well as to contamination of water by humic acids from related drainage of peat soils. On the catchment scale, the annual erosion of soil, which was 0.01 mm between 1981 and 1984, intensified to 1.34 mm between 1984 and 1990. Sediment runoff increased from 8 to 30 percent of the eroded soil volume.
From field observation, negligible sheet erosion occurred in both forest plots (mature spruce stands) and clear-cut plots (invasive grass). However, the significant loss of soil was related to the length of erosion rills produced by the harvest of timber. Forest harvesting can be prevented from causing soil erosion, sedimentation and contamination of surface waters through the use of environmentally safe forest harvesting practices such as skidding timber by horses or cables and respecting riparian buffer zones.
Mean pH in stream water at two reservoirs, Jizerka (influenced by clear-cutting of spruce plantations) and Oldrichov (semi-natural beech stands), in relation to air pollution by sulphur dioxide
In the Jizerka catchment a recent recovery in water quality has been observed, including an increase in mean annual pH values to 5 to 6 (Figure 3) and a drop in aluminium concentrations to 0.2 to 0.5 mg per litre. The improvement can be explained in large part by decreased sulphur dioxide pollution in the air (following the Sulphur Protocol of European countries, and observed in the field since 1990), and also by the annual liming of selected reservoirs after snowmelt to improve the drinking-water treatment.
However, it has also been attributed to significantly reduced leaf area index (from 18 to 3.5) resulting from clear-cutting of spruce stands between 1984 and 1990 (Figure 4) and decreased atmospheric deposition at cleared stands.
With the recovery of some physical and chemical parameters in surface waters, it has been possible to reintroduce fish, which had been extinct since the 1980s. Brook char (Salvelinus fontinalis, an acid-tolerant species) and brown trout (Salmo trutta morpha fario) were reintroduced in reservoir inlets in the 1990s. The char survived and reproduced, while the individuals of brown trout evidently starved and did not reproduce. However, because the char feed primarily on benthic Ephemeroptera (mayflies) and Trichoptera (caddisflies, Hydropsyche spp. dominating) containing extremely high values of aluminium, mercury, cadmium and lead, the concentration of aluminium and heavy metals in the fish tissues still exceeds national health limits.
|Introducing deciduous trees into spruce stands in the Jizera Mountains|
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 a small buffering capacity with respect to the actual acid deposition. In the 1980s, watersheds in this area were stressed by extreme acidification which brought parameters of pH, hardness and aluminium to levels incompatible with good health. The recent improvement in surface water quality seems to be a consequence of a combination of decreased air pollution, liming and reduced canopy density (leaf area and roughness) caused by clear-cutting of spruce stands. Although the recovery is reflected in the successful reintroduction of brook char in headwater reservoirs, the high content of pollutants in the fish (exceeding health standards) and benthic organisms reflects a still degraded environment.
The higher water quality observed in semi-natural beech forests results particularly from the limited acid deposition in the dormant season and the higher buffer capacity of beech stands.
Thus, in a long-term perspective, water quality might be improved by planting deciduous or mixed stands with lower leaf area and surface roughness, which can decrease the atmospheric deposition and increase buffering capacity in comparison with spruce plantations. Such planting is now being carried out, particularly in the upper mountain plateau, but it is too early to judge what influence it may have on water quality.
In addition, the management of mountain watersheds should include traditional environment-friendly forestry practices (clear-cutting limits, skidding of timber by horses or cables, seasonal skidding and respect for riparian buffer zones) to avoid soil erosion, sedimentation and contamination of water.
These recommendations might be generalized to other forested mountain regions affected by acid atmospheric deposition, particularly in regions of Central Europe with a similar history of forestry development.
Grennfelt, P., Rodhe, H., Thornelof, E. & Wisniewski, J., eds. 1995. Acid Reign ‘95? Proceedings from the 5th International Conference on Acidic Deposition, Göteborg, Sweden, 26–30 June 1995. Dordrecht, Netherlands, Kluwer Academic Publishers.
Křeček, J. & Haigh, M.J., eds. 2006. Environmental role of wetlands in headwaters. Dordrecht, Netherlands, Springer.
Křeček, J. & Hořická, J. 2001. Degradation and recovery of mountain watersheds: the Jizera Mountains, Czech Republic. Unasylva, 52(207): 43–49.
Nordic Council of Ministers. 1988. Surface water acidification in the ECE region. Copenhagen, Denmark.
World Health Organization (WHO). 2003. Guidelines for safe recreational water environments: coastal and fresh waters. Geneva, Switzerland.
WHO. 2004. Guidelines for drinking water quality (third edition). Geneva, Switzerland.