Surface water acidification in the UK; current status,recent trends and future predictions

Data collected at 22 lake and stream sites under the UK Acid Waters Monitoring Network, established in 1988, are assessed. Non-marine sulphate concentrations in surface waters largely reflect the sulphur deposition gradient across the country. Time series analysis indicates an increase in non-marine sulphate concentrations at sites in SW Scotland, the Lake District and in Wales. No similar trends have been detected in deposition data for the same period. Predictions of water chemistry response at each site to the new UNECE sulphur protocol have been made using a long-term, dynamic acidification model (MAGIC). The results indicate that the agreed emissions reductions will lead to recovery at many sites over a 15–20 year timescale but will have little effect at the most impacted sites, within the next 15 years.     

The use of zooplankton in a biomonitoring program to detect lake acidification and recovery

A detailed review of the zooplankton literature found strong evidence that lake acidification consistently causes declines in crustacean and rotifer species richness, the relative abundance of cyclopoids and daphnids, and the relative abundance of 16 particular zooplankton species. Five species were found to consistently increase as lake pH declines. Inconsistent effects were observed on crustacean biomass and mean organism size. Biomonitoring response variables recommended to detect incipient community changes include the relative abundance of pH sensitive species, overall crustacean and rotifer community composition plotted in abundance ordination space, crustacean and rotifer species richness, and the relative abundance of acid tolerant species. If acidification effects have been detected using the above response variables, then more detailed monitoring to understand the functional characteristics of affected systems (e.g. crustacean biomass, rotifer biomass and/or overall community size spectra) is appropriate. A lake selection procedure is recommended to maximize the number of systems containing sensitive species, and ensure a set of reference systems whose acidity is unlikely to change significantly.     

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 1980's. 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.     

Groundwater acidification at Birkenes,southern Norway: Comparing trends of chemical composition of precipitation,throughfall, soilwater and groundwater

Chemical time trends for precipitation, throughfall, and soilwater (1986–1992), and groundwater (1980–1993) at Birkenes, southern Norway, are compared to gain insights into possible causes for the recent increase in groundwater acidification there. Precipitation and throughfall trends do not show evidence for an increase in anthropogenic acids (e.g. sulphate), but seasalt deposition (e.g. chloride) has been marginally greater in 1990–1992 than in most previous years on record. Soilwater composition partly indicates increasing acidification in recent years (pH, Al and ANC), but hardness and sulphate content are decreasing. Soilwater ANC became negative in 1989, revealing a lasting deficit in its potential to buffer acidity. Groundwater shows clear signs of intensifying acidification (pH, Al, ANC, hardness and sulphate), and this may result partly from climatic conditions (mild winters, seasalt episodes) and partly from the deterioration of an acid buffering system within the soil cover. Acidification via sulphate deposition certainly is not a direct cause. The declining hardness of soilwater suggests that the ion-exchange buffer in the soil may have ceased to function properly. The necessity for obtaining long-term time-series of water chemistry is underscored by this study.     

Chrysophyte scales in lake sediments provide evidence of recent acidification in two Quebec (Canada) lakes

Several lake surveys have indicated that many lakes in Quebec are sensitive to acidification, but no historical data are available to provide conclusive evidence of lake acidification. Paleolimnological studies can provide such evidence. Chrysophycean algal microfossils were analyzed from the sediments of Lake Bonneville and Lake Truite Rouge in Quebec. The chrysophyte flora in the study lakes was stable until 40 yr ago, but since then the taxa characteristic of acidic or slightly acidic waters increased in abundance. The study provides evidence of recent lake acidification in Quebec.     

Regional monitoring of lake acidification in Finland

The primary objective of this monitoring is to detect long-term Long-Range Transboundary Air Pollution (LRTAP) induced changes in the water quality of small lakes, throughout Finland, with low conductivity. The monitored lakes (n=171, sampled every autumn since 1990 and in 1987) have a smaller watershed (usually headwater or seepage lakes), a larger lake/catchment ratio, and lower base cation concentrations, alkalinity and pH than Finnish lakes on average. The monitoring network provides background data for air pollution dose/response studies, critical load calculations and for the modelling of acidification scenarios. The declining sulphate deposition seems to be reflected in small headwater lakes all over southern and central Finland as a lowering of the sulphate concentration in the waters. Nitrate concentrations in these lakes have been typically low in the autumn. The base cation concentration is not generally declining, as it is in deposition in many areas. The sulphate concentration in lakes has declined more than base cations. Hydrologically, the recent years have been quite variable because of varying annual precipitation. The variation in alkalinity and pH in typical Finnish lakes is dependent on the content of humic material derived from catchments. The monitoring period is too short to reveal consistent trends in major ion chemistry. However, signs of improvement in recent years can be seen; in comparing 1993 to 1987, years with similar organic acidity and base cations, it seems that the sulphate decline in lakes monitored is compensated by a significant rise in both alkalinity and pH.     

Gårdsjön Project: lake acidification,chemistry in catchment runoff,lake liming and microcatchment manipulations

The Gårdsjön Project is an ecosystem approach in studying acid deposition and its effects on terrestrial parts and lakes within a catchment. The study is an attempt to quantify the processes causing the acidification as well as an analyses of the chemical and biological conditions before liming of the lake and manipulations in microcatchments. This paper gives a brief overview of some studies already performed and recently started experiments within the project, such as lake liming, lime application on land, forest fertilization, clearcutting and applications of acid and neutral sulphate on land.     

Relations between lake acidification and sulfate deposition in Northern Minnesota,Wisconsin, and Michigan

From a level of 1 kg ha^?1yr^?1 in north central Minnesota, emission-related wet SO₄ deposition increases across northern Wisconsin and northern Michigan to about 18 kg ha^?1yr^?1 in south central Michigan. Samples taken from 82 clearwater (low color) lakes across this region in the summer of 1984 showed a pattern of acidification in proportion to deposition. We found a linear increase in the difference between alkalinity and Ca+Mg and in lake SO₄ concentration with increasing deposition. We developed a simple equation to predict the emission-related SO₄ deposition levels that will cause the alkalinity of sensitive clear-water lakes to go to zero.     

Sulfur constituents of sediments and their relationship to lake acidification

Sulfate is a major component of acid precipitation in the Northeastern United States. Transformations and fluxes of S may be important indices of the effect of acidification on limnetic systems. Sulfur constiuents and respiration rates were compared in sediments among Oneida, Deer and South Lakes in New York which exhibit a range of buffering capacity and pH from high to low, respectively. Total S in Deer and South was higher near their major inlets. Sulfide was highest in Oneida sediment, which had a lower redox potential (Eh). Ester sulfate was a major portion of the S in the three lakes. Oxygen consumption was highest in Oneida and lowest in South sediments. The low ester sulfate and an elevated C/N ratio of South sediment may indicate that acidification inhibits decomposition     

The uncertainty in forecasting trends of forest soil acidification

A Regional Soil Acidification Model (RESAM) has been developed to gain insight in long-term impacts of deposition scenarios on forest soils in The Netherlands. Model predictions of such large-scale environmental effects of acid deposition require extrapolation of site specific data to large geographical regions. The major aim of this study is to quantify the uncertainty in model response to a given deposition scenario, due to uncertainty and spatial variability in data. Furthermore, the uncertainty analysis was performed to determine which additional data will most likely improve the reliability of predictions. An efficient Monte Carlo technique was used in combination with regression analysis. The analysis was restricted to one forest soil ecosystem: a leptic podzol with Douglas fir, subject to a reducing deposition scenario. The investigated output variables were pH, Al/Ca ratio and NH₄/K ratio in the root zone, which are generally used as indicators of forest soil acidification and of potential forest damage. Statistical analyses showed that in most cases the relation between the parameters and model output can be satisfactorily described by a linear regression model. The uncertainty contribution of various parameters depends on the considered output variable, soil compartment and time. The uncertainty, as measured by the coefficient of variation, appears to be high for the NH₄/K and Al/Ca ratios, whereas it was relatively low for the pH. Results show that the uncertainty in the depositions of SO_x, NO_x, and NH_x in a receptor area and the uncertainty in the parameters and variables determining the nitrogen and aluminium dynamics contribute most to the resulting uncertainty of the considered model output.     

Experimental studies and modelling of enhanced acidification and recovery

During the last three decades the experimental manipulations of whole ecosystems have been shown to be a useful and widely used tool for investigation of the effects of air pollution, air pollution reduction strategies and management practices on the health and productivity of forests and the acidification of catchments and fresh waters. Generally the aims have been to investigate the impact of a continued or increased load of air pollutants on the ecosystems, and the possibilities of reversing the acidifying effects by soil amelioration, addition of buffer acting substances or by removal of the air pollutants. Along with the field experiments, models have been developed to predict future effects and dynamics in the ecosystems under different air pollution scenarios. The present paper gives an overview of experimental field manipulation studies and examples of results obtained with the acidification model MAGIC. All the acidification recovery studies performed so far have shown that a reduced input of S to the ecosystem immediately from the first year resulted in reduced output, although the expected parallel reduction in output of Al and H⁺ did not occur until some years later, or not at all. The MAGIC model generally predicts the results of both acidification and liming field experiments very well, apart from minor discrepancies in year-to-year variability around the observed trends. Several experimental studies have confirmed that reduced input of acidity or increased input of base cations caused no or only slight changes in the pH in the soil. The buffer processes of the soil may cause the effects to be restricted to the very top soil layer, unless the manipulations were very strong. It is concluded that experimental field studies have increased our understanding of the complexity of the ecosystem and highlighted the need for studies integrating field and laboratory work.     

Terrestrial liming as a tool to mitigate acidification of woods lake,NY

The Soil Liming Model (SLiM) has been used to simulate lake and stream water quality response to different strategies for the application of limestone to subcatchment soils in the Woods Lake, NY watershed. Simulations using doses of 3, 10, or 30 t ha⁻¹ forecast that a dose in excess of 10 t ha⁻¹ must be applied to discharge areas in order to sufficiently improve water quality in the lake. At 3 t ha⁻¹ inlet stream water quality could support fish populations. As expected, treatment effectiveness is strongly influenced by subcatchment hydrologic flow paths. Where shallow flow predominates, soil liming provides a more effective tool for lake water quality improvement. In subcatchments drained primarily by ground water, the effect of liming on water quality is less pronounced albeit of longer duration. Based upon the results of these model simulations, the authors compare results of conventional lake liming to simulated watershed treatment predictions.     

Simulated mobilization of metals from sediments in response to lake acidification

The regeneratable forms of pollutant metals in lake sediments were estimated using different chemical extractants and the effects of lake acidification on the mobilization of such metal fractions studied in laboratory microcosm. The release of each metal was found to increase exponentially below a threshold pH value, which was about 4.0 for Cu, Ni, Zn, Cd and Fe. The data suggest that a large percentage of pollutant metals are mobile as determined by chemical extraction techniques and long-term release experiments.     

Empirical models for lake acidification in the upper Great Lakes Region

A large data base on inland lakes in the Upper Great Lakes Region (UGLR) was used to evaluate assumptions and relationships of empirical acidification models. Improved methods to calculate background alkalinity and background SO₄ ^2? are reported; SO₄ ^2? enrichment factors indicate that terrestrial SO₄ ^2? sources and watershed or lake sinks must be considered for site-specific background SO₄ ^2? estimates. Significant relationships were found between lake acidification estimated as change in SO₄ ^2? and precipitation acidity but not between changes in lake alkalinity and precipitation acidity in this lightly impacted region.     

Controlled experimental acidification of lake sediments and resulting trace metal behavior

Severe stream water acidification occurs at higher altitudes (> 600 m a.s.l.) in the Western Harz mountains in Northern Germany. Since 1986 an interdisciplinary research team has followed the fate of pollutants in the 50 km² catchment of an important drinking water reservoir (Lake Söse). An acidification experiment has estimated the role of the remobilization of selected elements from the lake sediments via acidification. Aquaria were used to monitor the effects of a stepwise acidification (from the natural pH of 6.5 to 5.0, 4.0 and 3.0) of the water column over a reconstituted sediment layer. The sediment chemistry has been analyzed before and after the acidification by XRF. The water chemistry was sampled at time intervals and analyzed by ICP-MS. With a pH drop from 6.5 to 3.0, many elements increase in concentration in the water of the acidified basins. Enrichment factors were: Al (5000), Ba (10), Cd (220), Co (800), Cu (170), Ni (90), Pb (5000), and Zn (400). This corresponds fairly well with the field data. Al, Cd, Fe, Mn, and Pb exceed German drinking water limits at pH 4.0. The combined high concentrations (μg L^?1) of Al (1000–2600), Cd (2–4), Cu (4–7), Pb (30–60), and Zn (100–300) in the water column of the acidified streams are not only toxic for fish but also for many other aquatic organisms. Chemical changes in the sediment are not significant within the experimental setup.     

Influence of pollution and acidification on metal concentrations in Finnish Lapland lake sediments

Fifteen Finnish Lapland lakes have been investigated to study pollution levels and possible acidification effects on nickel (Ni), copper (Cu), cobalt (Co), zinc (Zn), cadmium (Cd), lead (Pb), manganese (Mn), iron (Fe), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and aluminium (Al) concentrations in sediments. Four lakes have average water pH lower than 6.0 and alkalinity lower than 0.050 meq/1. Contamination factor (C_f, ratio of metal concentrations in the uppermost to the deepest layers for a given lake sediment core) of Pb is high, particularly for acidic and acidifying lakes (C_f=5.2–10.4). Ni, Cu, Co, Zn and Cd concentrations increase insignificantly towards sediment surface of some lakes (with a neutral pH) with the rare exception. The influence of passible lake acidification consists of decreasing Cu, Cd, Al, Zn concentrations and organic material contents (loss on ignition) towards the sediment surface. The buffer capacity index (BCI), determined as the ratio of the sum of alkaline and alkaline-earth metals (K, Na, Ca, Mg) to Al, is lower for acidic lakes (from 0.12 to 0.36), whereas for the other lakes the BCI values are higher (from 0.42 to 1.34). Thus, BCI-values, decreased contents of Al, Cd, Zn and Cu, as well as organic matter contents (OMC in the upper lake sediment suggest acidification of freshwater environments.     

The PIRLA project (paleoecological investigation of recent lake acidification): Preliminary results for the Adirondacks,New England,N. Great Lakes states,and N. Florida

The PIRLA project is an interdisciplinary paleoecological study designed to provide reconstructions of the recent acidification histories of a representative set of lakes in four acid-sensitive regions in North America. We are trying to determine if lakes in the study regions have acidified, and if so, to what extent, over what time period and why. Sediment cores from 5 to 15 lakes in each region are being analyzed for several characteristics. Diatoms and chrysophytes are being used to reconstruct lakewater pH. Results for three Adirondack lakes with current pH of 4.8 to 5.0 indicate a decrease in pH beginning in the 1930's–1950's. Increased atmospheric deposition of strong acids appears to be the primary factor responsible for the pH decline. Two lakes (pH 4.4 and 4.7) in New England show clear evidence of acidification probably due to acidic deposition. Preliminary reconstructions for two lakes in Michigan (pH 4.4 and 5.6), one in Wisconsin (pH 5.3), and one in Minnesota (pH 6.8) suggest no recent pH decrease. For, the one Florida lake (pH 4.4) analyzed, inferred pH decreases by about 0.5 unit, beginning in the 1950s; the cause has not been determined.     

Evaluating macroinvertebrate responses to recovery from acidification in small lakes in Ontario,Canada

The biomonitoring program of Environment Canada examines food chains in small Ontario lakes to interpret ecological responses of waterfowl and their foods to changing acid deposition. Macroinvertebrates and fish were sampled in three acid-sensitive regions: Muskoka (1991; N=20), Algoma (1992; N=20), and Sudbury (1994; N=22). Small lakes (<11 ha;=" important=" breeding=" habitat=" for=" waterfowl)=" were=" chosen=" to=" cover=" the=" range=" of=" ph=" in=" each=" region,=" and=" include=" those=" with=" and=" without=" fish.=" in=" all=" regions,=" macroinvertebrate=" taxonomic=" richness=" (particularly=" nekton=" and=" benthos)=" was=" greater=" in=" fishless=" lakes=" compared=" to=" lakes=" with=" fish.=" among=" fishless=" lakes,=" taxonomic=" richness=" (especially=" benthos)=" was=" positively=" correlated=" with=" ph,=" although=" regional=" differences=" were=" evident.=" previous=" studies=" near=" sudbury=" have=" shown=" that=" several=" benthic=" groups=" have=" distribution=" and=" abundance=" patterns=" with=" respect=" to=" ph=" (trichoptera,=" ephemeroptera,=" hirudinea,=" amphipoda,=" and=" gastropoda).=" those=" patterns=" continue=" near=" sudbury,=" and=" were=" also=" strongly=" apparent=" in=" algoma.=" in=" all=" regions,=" the=" number=" of=" acid-sensitive=" taxa=" per=" lake=" is=" related=" to=" ph,=" and=" should=" increase=" as=" lakes=" recover=" from=" acidification.=" however,=" predicting=" macroinvertebrate=" responses=" to=" recovery=" must=" consider=" concurrent=" effects=" of=" fish,=" as=" they=" are=" a=" dominant=" factor=" structuring=" these=">