Atle Hindar

Recovery from Acidification in European Surface Waters: A View to the Future

Abstract There is now overwhelming documentation of large-scale chemical recovery from surface water acidification in Europe, but to date there has been little documentation of biological recovery. Modelling studies based on current emission reduction plans in Europe indicate that there will be further chemical recovery. The uncertainties in these scenarios mainly relate to the future behavior of nitrogen in the ecosystem and the effects of climate change. Four major climate-related confounding factors that may influence the chemical and biological recovery process are: i) increased frequency and severity of sea-salt episodes; ii) increased frequency and severity of drought; iii) in-creased turnover of organic carbon; iv) increased mineralization of nitrogen. International cooperative work to abate acidification has so far been very successful, but there is still a long way to go, and many potential setbacks. It is essential that future development of water chemistry and aquatic biota in acidified waterbodies continue to be monitored in relation to further emission reductions of S and N and future effects of climate change.

Extreme acidification in small catchments in southwestern Norway associated with a sea salt episode

During heavy storm events in January 1993 in the coastal areas of south-western Norway, a sea salt episode created extreme acidification in the afforested Svela catchment. Stream-water chloride increased sharply to eight times the normal concentration and the non-marine Na concentration was calculated to −208 μeq L−1. Negative values indicate that Na was retained in the soil profile. By ion-exchange processes this was largely compensated by an increase in stream-concentrations of Al and H+. Concentrations of inorganic monomeric Al increased from about 20 to 200 μeq L−1 and pH decreased from 4.90 to 4.45. Due to the low pH and the dramatic increase in inorganic monomeric Al the water toxicity for aquatic organisms increased. Acidification associated with the storm was also observed in a forested and a non-forested catchment, but never reached the levels of the afforested catchment. The extra vulnerability of afforested catchments may be due to their ability to intercept larger amounts of sea salts than areas less dominated by dense tree stands. Although both pH and Al went back to normal levels for the area after 3–4 months the Na/Cl-relationship in cumulated transport values indicated a longlasting effect (> 2 years) on the soil profile. Reloading the soil profile with Al and H+ back to prestorm values will affect the catchments ability to mobilize these ions during future sea salt episodes. More frequent episodes will probably result in less acid and Al-rich stream-water during the episodes than documented here due to incomplete reacidification of the soils.

Effects of Regional Reductions in Sulphur Deposition on the Chemical and Biological Recovery of Lakes within Killarney Park, Ontario, Canada

The lakes in KillarneyProvincial Park, located 40–60 km southwest ofSudbury, Ontario, were some of the first lakesin North America to be acidified by atmosphericpollutants. Acidification affected thousandsof fish and invertebrate populations in dozensof lakes. Since the 1970s, water quality hasimproved in response to atmospheric pollutionreductions and some lakes have alreadyrecovered to approximately their pre-industrialpH levels, as inferred from diatom microfossilsin lake sediments. Since the 1970s, fishspecies richness has not changed substantially,but zooplankton species richness has increasedin acidified lakes. The critical sulphur load,the amount of SO2-derived acid depositionthat can occur while still maintaining suitable water quality, was estimated to beexceeded in 38% of the park area in 1997. Depending on which of four possible NorthAmerican emission control scenarios (CLR =currently legislated reduction; CLR + 25%; CLR+ 50%; CLR + 75%) is achieved by 2010, theprojected critical loads will be exceeded inabout 0-30% of the park area in the future. There are many factors that can affectbiological recovery rates of damaged lakes, butit is expected that biological recovery willlag considerably behind observed chemicalrecovery rates.

WHOLE-CATCHMENT LIMING AT TJØNNSTROND, NORWAY: AN 11-YEAR RECORD

In June 1983 a whole-catchment liming experiment was conducted at Tjønnstrond, southernmost Norway, to test the utility of terrestrial liming as a technique to restore fish populations in remote lakes with short water-retention times. Tjønnstrond consists of 2 small ponds of 3.0 and 1.5 ha in area which drain a 25-ha catchment. The area is located at about 650–700 meters above sea-level in sparse and unproductive forests of spruce, pine and birch with abundant peatlands. A dose of 3 ton/ha of powdered limestone were spread by helicopter to the terrestrial area. No limestone was added to the ponds themselves. The ponds were subsequently stocked with brown and brook trout.Liming caused large and immediate changes in surface water chemistry; pH increased from 4.5 to 7.0, Ca increased from 40 to 200μeq/L, ANC increased from −30 to +70μeq/L, and reactive-Al decreased from about 10 to 3μmol/L. During the subsequent 11 years the chemical composition of runoff has decreased gradually back towards the acidic pre-treatment situation. The major trends in concentrations of runoff Ca, ANC, pH, Al and NO3 in runoff are all well simulated by the acidification model MAGIC. Neither the measured data nor the MAGIC simulations indicate significant changes in any other major ion as a result of liming.The soils at Tjønnstrond in 1992 contained significantly higher amounts of exchangeable Ca relative to those at the untreated reference catchment Storgama. In 1992 about 75% of the added Ca remains in the soil as exchangeable Ca, 15% has been lost in runoff, and 10% is unaccounted for.The whole-catchment liming experiment at Tjønnstrond clearly demonstrates that this liming technique produces a long-term stable and favourable water quality for fish. Brown trout in both ponds in 1994 have good condition factors, which indicate that the fish are not stressed by marginal water quality due to re-acidification. The water quality is still adequate after 11 years and >20 water renewals. Concentrations of H+ and inorganic Al have gradually increased and approach levels toxic to trout, but the toxicity of these are offset by the continued elevated Ca concentrations. Reduced sulphate deposition during the last 4 years (1990–94) has also helped to slow and even reverse the rate of reacidification. The experiment at Tjønnstrond demonstrates that for this type of upland, remote terrain typical of large areas of southern Norway, terrestrial liming offers a suitable mitigation technique for treating acidified surface waters with short retention times.

Liming of lakes, rivers and catchments in Norway

Despite a slight reduction in the level of acidic deposition in Norway, acidification of lakes and rivers continues. The Norwegian Liming Project (1979–84) demonstrated that lime treatment can be an effective measure against acidification of watercourses given appropriate adaptation to local conditions. Liming in Norway is difficult because of (1) large amounts of precipitation, (2) short retention time of lakes, and (3) episodic changes in water chemistry. In 1988 NOK 14 mill. has been allocated to operational liming and research. We report here on chemical and biological responses from lime treatment of a lake, a river and a catchment. Lake Store Hovvatn was limed in 1981 and successfully stocked with brown trout. Before reliming in 1987, fish growth had ceased, but increased post liming. The River Audna has been continuously limed since 1985. Sea trout fisheries have improved, and the stocking of Atlantic salmon smolts at the mouth of the river in 1986 has already resulted in the return of spawners. Liming of the entire terrestrial catchment to the pond Tjønnstrond in 1983 by helicopter was also successful; stocked brown trout have survived to the present.

Extreme acidification of a lake in southern Norway caused by weathering of sulphide-containing bedrock

In 1986 Lake Langedalstjenn in southern Norway was a weakly acidified lake with a pH of 5.2–5.6, and an average concentration of SO4 of 330 μeq L−1. The total Al concentration varied between 10 and 20 μeq L−1 (expressed as Al3+). The lake supported populations of brown trout and perch and had supplied about 100 people with drinking water until the late 1980s. During 1986–1989, a dramatic change in the water chemistry occurred because of blasting of and weathering of sulphidic gneisses in the watershed. The oxidation of sulphide to sulphate (sulphuric acid) caused an increase in the SO4 concentration of the draining stream of up to ≈ 4800 μeq L−1. Weathering and/or cation exchange of Ca and Mg neutralized approximately 52% of the protons from the sulphuric acid production, while about 46% were consumed by mobilization of aluminium and iron. Nevertheless, about 2% of the hydrogen ions from the sulfuric acid were still present, which resulted in a stream pH of 4.0. In the lake, the pH was 4.4, and the concentrations of all major cations and anions were significantly lower than in the heavily affected stream. Mixing of the stream water with lake water, formation of aluminium-sulphate complexes and coprecipitation of Ca may explain the resulting concentrations of major ions in the lake.

Liming Acidic Waters in Norway: National Policy and Research and Development

Since 1983, the Norwegian environmental authorities have given financial support to operational liming and research following recommendation given by the Norwegian Liming Project (1979–1984). Liming all acid waters in Norway would require an annual expenditure exceeding NOK (Norwegian Kroner) 300 × 106. The funding level for 1988 is NOK 14 × 106 and will probably increase to NOK 30 mill. by 1990, including NOK 1 to 3 mill. for research and development. Priority is given to lakes and rivers whose fishing is open to the public, and to save or restore valuable fish populations. Local support in the form of voluntary labor is a condition for financial aid. Two salmon rivers are currently included in the program. T h e Norwegian Institute for Water Research (NIVA) plays an important role in liming research and development in Norway. The aims of this research are twofold: to document the chemical and biological response to neutralization and liming, and to improve liming strategy to obtain cost efficient liming activities.

Incomplete mixing of limed water and acidic runoff restricts recruitment of lake spawning brown trout in Hovvatn, southern Norway

Repeated liming of Hovvatn during the 1981–1995 period assured successful reintroduction of lake spawning brown trout, Salmo trutta. Poor natural recruitment to the population was associated with low survival during early life stages (before hatching) as shown by the 0.5, 3.5, 0.9 and 1.0% of live embryos found in natural redds during the 1992–1995 period, respectively. The low survival was most likely caused by the combination of shallow spawning areas (<2.0 m) and acidic runoff (pH 4.0–4.8) which overlayed the limed part of the water body during the ice covered period. It is therefore concluded that this type of episodic acidification poses a major threat to lake spawning salmonids, and that it can retard or inhibit biotic recovery towards preacidified conditions expected as a result of liming. Addition of limestone gravel (8–32 mm) onto spawning grounds was an efficient alternative liming strategy as 33–36% live embryos were found in this substrate. Conversely, the trout actively avoided additions of shellsand, a behaviour most likely caused by the small particle size of shellsand (3–7 mm) relative to natural spawning gravel.

Counteractions Against Acidification in Forests Ecosystems. Effects on stream water quality after dolomite application to forest soil in Gjerstad, Norway

The deposition of strong acids is one of many threats to forest ecosystems and viable forestry. Several counteractions against acidification have been launched, e.g. changes in forestry management and the introduction of chemicals. The inter-institutional programme “Counteractions Against Acidification in Forest Ecosystems” was established in 1993 to evaluate existing knowledge and run experimental and fullscale field experiments. A total of 240 metric tons of coarse dolomite powder was spread by helicopter in September 1994 on 84 ha forest catchment dominated by pine (Pinus sylvestris) and Norway spruce (Picea abies). Potential desirable and undesirable effects after this carbonate application may be less pronounced than recorded at other sites due to the relatively moderate dose (3 tons ha−1). Pre-liming stream water quality (mean values for May 1993-September 1994) was as follows: pH 4.8; Ca 1.13 mg L−1; reactive Al (RAl) 248 μg L−1; inorganic monomeric Al (Al) 72 μg L−1. The reference station was slightly higher in Ca and slightly lower in both RAl and Al. Dolomite application resulted in a significant increase in pH to 5.7 as mean value for the post-liming period (September 1994-April 1995). Both Ca and Mg increased significantly after liming, and both RAl and Al, declined significantly. The rapid detoxification of stream-water may be explained by dissolution of dolomite particles in both streams and catchment, a resulting pH increase and change in Al species composition. Retention of Al in the catchment probably explains the reduction in RAl. No increase in NO3, total N, total P or TOC was recorded the first seven months.

Management of Headwaters in Acidified Areas along the West Coast of Norway

Management of headwaters aims at achieving good ecological status, and global, European and local options exist for improving the quality of acidified waters along the west coast of Norway. Norwegian headwaters are often considered clean as they are situated in areas far from or up-stream of large pollution sources. However, long-range transported air pollution has impacted surface waters in southern Norway for decades, and the resulting acidification and die-back of thousands of fish populations are widely known.