Surface Water Acidification Research Articles

Coal Tailings Reclamation Practices: Soil Cover Variances - The Ayrshire Alternative

Reclamation of potentially acid producing coal processing waste generally requires 4 feet (1.2 m) of soil cover to comply with most state and federal requirements (Surface Mining Control and Reclamation Act of 1977 (PL 95 87)). Soil cover variances for acid coal slurry (tailings) have included alkaline amendments (agricultural limestone) and reduced soil cover depths. Direct seeding of alkaline amended coal tailings substrates has been demonstrated on more than 1,800 acres throughout the midwest since the late 1970's. Slurry reclamation practices have included upland cool season grasses and legumes, warm season native prairie grasses, and emergent and open water wetlands. Direct seeded slurry demonstrations implemented by the Cooperative Wildlife Research Laboratory SIUC during the 1980's and 1990's have received regulatory approval (bond release), as well as state and national (OSM) reclamation awards. Reclamation monitoring has documented vegetative cover, water quality, and substrate geochemistry through the period up to bond release. This annual monitoring has established a > 25-year database supporting the principles and practices of acid coal tailings reclamation. A recent soil cover variance at the Amax Ayrshire Mine (southwest Indiana) incorporated the principles of pyrite aging and weathering, and incremental limestone amendment to establish warm season grasses and shallow water wetlands on a ~170 acre (70 ha) acid producing slurry basin. Pre-treatment (1995) and posttreatment (1996 1999, 2003) substrate monitoring identified differential pyrite oxidation in unsaturated surface, and saturated subsurface profiles within the Ayrshire slurry basin. Agricultural limestone amendment (~100 150 tons/ac (225 335 Mg/ha)) has restored and maintained a favorable (alkaline) acid-base balance for seven years since the initial (1995) application. Warm season grass establishment provided > 87% aerial coverage in the direct seeded upland zones. Pretreatment acid (pH 2.6) surface water quality in the shallow wetland zone has been restored to post-treatment alkaline (pH 7.8) conditions. Additional

The significance of the North Atlantic Oscillation (NAO) for sea-salt episodes and acidification-related effects in Norwegian rivers.

Acidification of Norwegian surface waters, as indicated by elevated concentrations of sulfate and a corresponding reduction in acid neutralizing capacity and pH, is a result of emission and subsequent deposition of sulfur and nitrogen compounds. Episodic sea-salt deposition during severe weather conditions may increase the effects of acidification by mobilizing more toxic aluminum during such episodes. Changes in climatic conditions may increase the frequency and strength of storms along the coast thus interacting with acidification effects on chemistry and biota. We found that the North Atlantic Oscillation (NAO) is linked to sea-salt deposition and sea-salt induced water chemistry effects in five rivers. Particularly, toxic levels of aluminum in all rivers were significantly correlated with higher NAO index values. Further, temporal trends were studied by comparing tendencies for selected statistical indices (i.e. frequency distributions) with time. The selected indices exhibited strong correlations between the NAO index, sea-salt deposition and river data such as chloride, pH and inorganic monomeric aluminum, pointing at the influence of North Atlantic climate variability on water chemistry and water toxicity. The potentially toxic effects of sea-salt deposition in rivers seem to be reduced as the acidification is reduced. This suggests that sea-salt episodes have to increase in strength in order to give the same potential negative biological effects in the future, if acid deposition is further reduced. More extreme winter precipitation events have been predicted in the northwest of Europe as a result of climate change. If this change will be associated with more severe sea-salt episodes is yet unknown.

Predicting recovery of acidified freshwaters in Europe and Canada: an introduction

Abstract. Abstract: The RECOVER: 2010 project was designed to assess the current and future anthropogenic pressures on sensitive European freshwater ecosystems. This pan–European assessment utilised a standardised predictive modelling approach to evaluate the degree of compliance with respect to the restoration of acidified waters by 2016, as specified under the EU Water Framework Directive (WFD), and evaluated the environmental benefits of proposed UN-ECE protocols on emissions control. Between 1970 and 2000, observations and model simulations show a significant decline in acidic surface water in all regions of Europe. This demonstrated the success of policies aimed at reducing emission of acidifying compounds. The nature and extent of future regional recovery from acidification is, however, dependent upon the historical pattern of deposition, regional ecosystem characteristics and the role of confounding factors, which may delay the onset of recovery or the magnitude of response. Model predictions to 2010 and beyond emphasise the continued benefit of currently proposed reductions, as reflected by the degree of recovery of freshwater ecosystems. A key component was to link such hydrochemical recovery with ecological response, and the project aimed to evaluate this against current WFD criteria of “good status" and “reference conditions". The RECOVER: 2010 project research has also played a major role in defining the dynamic modelling outputs which will be required to support the review of the Gothenburg Protocol within the work of the UN-ECE CLRTAP Working Group on Effects (WGE), and model outputs have been made available to a range of national agencies throughout Europe. Keyword: recovery, acidification, modelling, policy, good status, reference conditions

A modelling assessment of acidification and recovery of European surface waters

Abstract. The increase in emission of sulphur oxides and nitrogen (both oxidised and reduced forms) since the mid-1800s caused a severe decline in pH and ANC in acid-sensitive surface waters across Europe. Since c.1980, these emissions have declined and trends towards recovery from acidification have been widely observed in time-series of water chemistry data. In this paper, the MAGIC model was applied to 10 regions (the SMART model to one) in Europe to address the question of future recovery under the most recently agreed emission protocols (the 1999 Gothenburg Protocol). The models were calibrated using best available data and driven using S and N deposition sequences for Europe derived from EMEP data. The wide extent and the severity of water acidification in 1980 in many regions were illustrated by model simulations which showed significant deterioration in ANC away from the pre-acidification conditions. The simulations also captured the recovery to 2000 in response to the existing emission reductions. Predictions to 2016 indicated further significant recovery towards pre-acidification chemistry in all regions except Central England (S Pennines), S Alps, S Norway and S Sweden. In these areas it is clear that further emission reductions will be required and that the recovery of surface waters will take several decades as soils slowly replenish their depleted base cation pools. Chemical recovery may not, however, ensure biological recovery and further reductions may also be required to enable these waters to achieve the "good ecological status" as required by the EU Water Framework Directive. Keywords: Europe, acid-sensitive, waters, predictions, recovery, protocols

Modelling reversibility of central European mountain lakes from acidification: Part II – the Tatra Mountains

Abstract. A dynamic, process-based model of surface water acidification, MAGIC7, has been applied to four representative alpine lakes in the Tatra Mountains (Slovakia and Poland). The model was calibrated for a set of 12 to 22-year experimental records of lake water composition. Surface water and soil chemistry were reconstructed from 1860 to 2002 and forecast to 2050 based on the reduction in sulphur and nitrogen emissions presupposed by the Gothenburg Protocol. Relatively small changes in the soil C:N ratios were not sufficient to simulate observed changes in NO3‾ concentrations, so an alternative empirical approach of changes in terrestrial N uptake was applied. Measured sulphate sorption isotherms did not allow calibration of the pattern of sulphate response in the lakes, indicating that other mechanisms of S release were also important. The lake water chemistry exhibited significant changes during both the acidification advance (1860 to 1980s) and retreat (1980s to 2010). An increase in lake water concentrations of strong acid anions (SAA; 104–149 μeq l–1) was balanced by a decline in HCO3‾ (13–62 μeq l–1) and an increase in base cations (BC; 42–72 μeq l–1), H+ (0-18 μeq l–1), and Alin+ (0–26 μeq l–1). The carbonate buffering system was depleted in three lakes. In contrast, lake water concentrations of SAA, BC, H+, and Alin+ decreased by 57–82, 28–42, 0–11, and 0–22 μeq l–1, respectively, the carbonate buffering system was re-established, and HCO3‾ increased by 1–21 μeq l–1 during the chemical reversal from atmospheric acidification (by 2000). The MAGIC7 model forecasts a slight continuation in this reversal for the next decade and new steady-state conditions thereafter. Gran alkalinity should come back to 1950s levels (0–71 μeq l–1) in all lakes after 2010. Partial recovery of the soil pool of exchangeable base cations can be expected in one catchment, while only conservation of the current conditions is predicted for three lakes. Even though the pre-industrial alkalinity values of 16–80 μeq l–1 will not be reached due to the insufficient recovery of soil quality, the ongoing chemical improvement of water should be sufficient for biological recovery of most alpine lakes in the Tatra Mountains. Keywords: MAGIC, atmospheric deposition, sulphate, nitrate, base cations, aluminium, alkalinity, pH

A kinetic study of the oxidation of arsenopyrite in acidic solutions: implications for the environment

Arsenopyrite is an important component of many ore deposits and dissolves in the O2-rich, acidic surface waters that are commonly found in the vicinity of active mines, releasing As, Fe and S to the environment. However, despite the potentially serious effect of this pollution on the human and animal population, the rate at which such oxidation occurs is poorly known. Kinetic experiments were therefore conducted in a mixed flow reactor to investigate the oxidation of arsenopyrite in Fe2(SO4)3 solutions (pH=l.8) having a concentration of l×l0−2 to 1 ×l0−5 mol kg−1 at temperatures of 45, 35, 25 and 15 °C. The results of these experiments show that the rate of oxidation of arsenopyrite increases with increasing concentration of dissolved Fe2(SO4)3 and temperature. They also show that As released during the oxidation of arsenopyrite has the form As(III), and that the rate of conversion of As(III) to As(V) is relatively low, although it tends to increase with increasing concentration of dissolved Fe2(SO4)3 and temperature. In the presence of Cl−, oxidation of arsenopyrite is accelerated, as is the conversion of As(III) to As(V). These findings indicate that exploitation of arsenopyrite-bearing ores will cause contamination of groundwaters by As at levels sufficient to have a major negative effect on the health of humans and animals.

A Review of Liming Options for Afforested Catchments in Ireland

Afforested catchments with acid bedrock are particularly susceptible to surface-water acidification. Liming has been used throughout Europe and North America as a means of mitigating the adverse effects of increased acidity of surface waters. One of the principal aims of liming is to increase alkalinity and pH to ensure suitable conditions for fish survival, in particular salmonids. This review examines the range of available liming methods in detail with specific emphasis on their potential use in afforested catchments in Ireland. The most promising method is the stream doser system because the dose rate can be varied automatically in response to changing stream conditions. Other methods worthy of further investigation include the spreading of lime on forest floors and the direct addition of limestone to stream beds. However, a better understanding of hydrological factors is required before a full assessment of terrestrial liming strategies can be made.

Cyanuric acid trace analysis by extractive methylation via phase-transfer catalysis and capillary gas chromatography coupled with flame thermoionic and mass-selective detection. Process parameter studies and kinetics.

A GC method using phase-transfer catalysis for the simultaneous derivatization, extraction, and preconcentration of the highly polar cyanuric acid (CYA) was developed. The method was based on the extractive N-methylation of the analyte of concern in two- and three-phase systems, whereby the 1,3,5-trimethyl-1,3,5-triazine-2,4,6-(1H,3H,5H)trione was formed. Subsequent detection was performed using flame thermoionic specific detection (FTD) and mass spectrometry (MS) selective-ion monitoring (SIM) using electron impact. The optimal experimental conditions related to pH, kind of catalyst and solvents, methyl iodide concentration, phase volumes, reaction time, temperature, and agitation were suitably established. Inter alia, the resulting method is highly sensitive, almost free from interferences, and was easily applied to the determination of cyanuric acid in swimming pool water, surface water, human urine, and simulated air filter samples. The minimal quantitable concentration was found to be less than 1 and 90 microg L(-1) using GC-MS-(SIM) and GC-FTD, respectively. The overall precision for the workup procedure did not exceed 3.6% (n = 6) for 5.0 microg L(-1) CYA-spiked urine and river water while the respective value for the same matrixes spiked at a concentration of 200 microg L(-1) was calculated to be in the range 1.9-4.0% (n = 6). The overall recovery from spiked samples was 98 +/- 5% for microgram per liter levels of CYA. A kinetic study conducted was helpful to get a better insight into the N-methylation reaction mechanism.

The role of secondary minerals in controlling the migration of arsenic and metals from high-sulfide wastes (Berikul gold mine, Siberia)

The role of secondary minerals in controlling the migration of As, Cu, Zn, Pb and Cd has been investigated in piles of high-sulfide waste at the Berikul Au mine, Kemerovo region, Russia. These wastes contain 40–45 wt.% sulfides and have been stored for approximately 50 a near the Mokry Berikul river. Sulfide oxidation generates acid pore solutions (pH=1.7) with high concentrations of SO 4 2− (190 g/l), Fe (57 g/l), As (22 g/l), Zn (2 g/l), Cu (0.4 g/l), Pb (0.04 g/l), and Cd (0.03 g/l). From these solutions, As is precipitated as amorphous non-stoichiometric Fe-sulfoarsenates in the lower horizons of the waste piles. During precipitation of the Fe-sulfoarsenates, the concentration of Fe in these phases decreases from 34 to 21 wt.%, that of As increases from 11 to 22 wt.%, while the S content remains approximately constant (5.4–5.8 wt.%). Arsenic is also accumulated in jarosite-beudantite solid solutions (up to 8.4 wt.% As), which occur as inclusions in the amorphous Fe-sulfoarsenates. In efflorescent crusts on the surface of the waste pile, As co-precipitates with the Fe(III) sulfates copiapite (0.27 wt.% As) and rhomboclase (0.87 wt.% As). Zinc and Cu are incorporated primarily into Fe(II) sulfates, i.e. melanterite in the interior of the waste pile, and rozenite in the efflorescent crust. The Zn mineral dietrichite is also formed at the surface of the waste pile as a result of evaporation of pore solutions, and is the only Fe(II) sulfate containing detectable amounts of As (0.64 wt.%). Lead is mainly co-precipitated with minerals of the jarosite group, where the Pb content may reach 4.3 wt.%. Co-precipitation of toxic elements with sulfates and sulfoarsenates of Fe is shown to be a significant mechanism in controlling the concentration of heavy metals in pore solutions of high-sulfide mine wastes. Precipitation of secondary phases causes the formation of a hardpan layer with low permeability at a depth of 1–1.5 m below the surface of the waste pile. Rainwater accumulates above the hardpan horizons and slowly drains along these aquicludes to the bottom of the pile. Most of the rainwater evaporates during infiltration. This leads to formation of the described efflorescent sulfate crusts. Dissolution of these crusts during the next rain storm produces highly acidic surface waters (pH=1.1) rich in SO 4 2− (30 g/l), Fe (18 g/l), As (0.24 g/l), Zn (0.12 g/l), Cu (0.04 g/l), Pb and Cd (0.002 g/l). During the warm ( t>0 °C) period of the year, which lasts about 7 months, these surface waters transport a total of a few tens of kilograms of As and Zn, several kilograms of Cu, and a few hundred grams of Pb and Cd from the waste pile into the Mokry Berikul river. As a result, the concentrations of these metals in the river water increase by an order of magnitude, thus reaching levels close to, or exceeding the maximum values permissible for drinking water.

Recovery from acidification in European surface waters: a view to the future.

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) increased 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.

Developing conceptual frameworks for the recovery of aquatic biota from acidification.

Surface water acidity is decreasing in large areas of Europe and North America in response to reductions in atmospheric S deposition, but the ecological responses to these water-quality improvements are uncertain. Biota are recovering in some lakes and rivers, as water quality improves, but they are not yet recovering in others. To make sense of these different responses, and to foster effective management of the acid rain problem, we need to understand 2 things: i) the sequence of ecological steps needed for biotic communities to recover; and ii) where and how to intervene in this process should recovery stall. Here our purpose is to develop conceptual frameworks to serve these 2 needs. In the first framework, the primarily ecological one, a decision tree highlights the sequence of processes necessary for ecological recovery, linking them with management tools and responses to bottlenecks in the process. These bottlenecks are inadequate water quality, an inadequate supply of colonists to permit establishment, and community-level impediments to recovery dynamics. A second, more management-oriented framework identifies where we can intervene to overcome these bottlenecks, and what research is needed to build the models to operationalize the framework. Our ability to assess the benefits of S emission reduction would be simplified if we had models to predict the rate and extent of ecological recovery from acidification. To build such models we must identify the ecological steps in the recovery process. The frameworks we present will advance us towards this goal.

Recovery of Crustacean Zooplankton Communities from Acidification in Killarney Park, Ontario, 1971–2000: pH 6 As a Recovery Goal

Despite reductions in atmospheric SO4(2-) deposition and resultant decreases in surface water acidity, widespread biological recovery from acidification has not yet been documented. Temporal trends in crustacean zooplankton species richness (number of species) and composition were examined between 1971-2000 in 46 Killarney Park lakes, Ontario, Canada, to assess the degree of biological recovery in lakes with significant water quality improvements, i.e. pH now > 6, compared to 2 other groups: i) lakes which never acidified; and ii) lakes which are still acidified (pH < 6). Time trends in species richness could not be distinguished among the 3 groups of lakes, nor did changes in species richness indicate recovery. In contrast, the zooplankton community composition of lakes in which the pH increased to above 6, as measured by a multivariate index of species abundances, changed from a "damaged" state to one typical of neutral lakes. Some recovery in composition was also documented for the acidic lakes. While still acidic, the pH levels of these lakes have risen. The extent and pace of recovery in Killarney Provincial Park bodes well for the future of other acidified regions in North America and Europe.

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

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

Assessment of the mobility of trace elements in acidic soils using soil and stream geochemical data

In the coastal areas of Finland and Sweden, widespread acid sulphate soil occurrences ( c. 4760 km 2 ), developed on artificially drained Holocene sulphide-bearing sediments, are causing serious environmental problems, such as acidification and metal contamination of surface waters, hydrobiological damage and elemental imbalance in crops. In this study, five acid sulphate soil profiles were geochemically characterized and compared with existing hydrogeochemical data in order to find evidence of the behaviour of a variety of trace elements in catchments affected by these soils. The results show that Cd, Co, Ni, Y and Zn are depleted in the acid sulphate soils and enriched in the recipient streams, whereas As, Ga, Mo, Nb, Pb, Sb, Sc, Ti and Zr are not depleted in detectable amounts in these soils and are not (or only weakly) enriched in the recipient streams. It is concluded that the former group is highly mobile in the acid sulphate soils and thus lost to adjacent drains in substantial amounts, whereas the latter group is moderately to highly immobile in these soils and is thus leached in background amounts only. The approach is possible to use in similar areas elsewhere, i.e. where oxidation and weathering of soils or overburden significantly affect the surface-water quality.

Role of soil freezing events in interannual patterns of stream chemistry at the Hubbard Brook Experimental Forest, New Hampshire.

Soil freezing is a disturbance of the below ground environment, potentially resulting in increased losses of NO3- and surface water acidification. Here, we report the effects of soil freezing on interannual variation in stream chemistry at the Hubbard Brook Experimental Forest, New Hampshire. Data from 1970 to 1997 of soil frost depth, snow cover, precipitation, air temperature, and stream discharge and chemistry were used in a stepwise linear regression model to select the variables that best predicted deviations of annual stream concentrations from 4-year running averages. Variables quantifying soil freezing severity were selected as significant predictors of short-term fluctuations in stream K+, NO3-, Ca2+, and Mg2+ concentrations from 1970 to 1989, explaining 59 and 47% of the short-term variability in K+ and NO3-, respectively. Fine-root mortality and disturbance of root-soil-microbe interactions, with subsequent effects on decomposition and nutrient uptake, likely contributed to the mobilization of K+ and NO3- to streamwater following severe soil freezing events. The relationship between soil freezing and stream chemistry, however, weakened during the period 1990-1997. Because soil freezing has had inconsistent effects on stream chemistry during the period 1970-1997, it is unclear whether future changes in the frequency, duration, and depth of soil freezing events as the result of changes in the snow cover regime under a warmer climate will have significant impacts on the losses of NO3- and nutrient-base cations from temperate northern ecosystems.

Isotope applications in environmental investigations part II: Groundwater age dating and recharge processes, and provenance of sulfur and methane

AbstractMeasurement of the isotopic composition of solids, solutes, gases, and water complement standard hydrogeological investigation techniques by providing information that may not otherwise be obtainable. Groundwater age estimates determined from the decay of radio‐isotopes or from groundwater concentrations of anthropogenic gases such as chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) are used to verify flow regimes and constrain or calibrate hydrologic flow models. Groundwater recharge rates are estimated by measuring the concentrations or activities of a variety of isotopes including 2H, 3H, 18O, and 36Cl. Excess sulfur causes salinization of water supplies and acidification of precipitation, surface water, and groundwater. The wide range of sulfur isotopic compositions exhibited by different sulfur species and sources allows the application of sulfur isotopes to trace sources and fate of sulfur in the environment. Methane is a ubiquitous gas that has economic value when located in extractable reservoirs. Methane is also a greenhouse gas and is a potential explosion and health hazard when it accumulates in buildings and water distribution systems. The carbon and hydrogen isotopic composition of methane can be used to determine the provenance of methane, distinguishing between thermogenic and biogenic sources. The addition of isotopic analyses to environmental investigations can be a cost‐effective means of resolving intractable issues. © 2003 Wiley Periodicals, Inc.

Hydroxyl radical production via the photo-Fenton reaction in the presence of fulvic acid.

The photo-Fenton reaction, the reaction of photoproduced Fe(II) with H2O2 to form the highly reactive hydroxyl radical (OH*), could be an important source of OH* in sunlit natural waters. To determine if the photo-Fenton reaction is significant in mildly acidic surface waters, we conducted experiments simulating conditions representative of natural freshwaters using solutions of standard fulvic acid and amorphous iron oxide at pH 6.0. A probe method measuring 14CO2 produced by the reaction of 14C-labeled formate with OH* was used to detect small OH* production rates without otherwise influencing the chemical reactions occurring in the experiments. Net H2O2 accumulation was simultaneously measured using an acridinium ester chemiluminescence method. Measured losses of H2O2 by reaction with Fe(II) in dark experiments produced approximately the expected quantities of OH*. The difference between H2O2 accumulation in the presence and absence of Fe(III) in fulvic acid solutions exposed to light was interpreted as the loss of H2O2 by reaction with photoproduced Fe(II), consistent with measured OH* production rates. The Fe ligand desferrioxamine mesylate eliminated both OH* production and H2O2 photoloss induced by Fe. Our results imply that when Fe is a major sink of H2O2, the photo-Fenton reaction is likely to be the most important source of OH*, leading to a significant sink of organic compounds in a wide variety of sunlit freshwaters.

Nitrogen Pollution in the Northeastern United States: Sources, Effects, and Management Options

Abstract The northeastern United States receives elevated inputs of anthropogenic nitrogen (N) largely from net imports of food and atmospheric deposition, with lesser inputs from fertilizer, net feed imports, and N fixation associated with leguminous crops. Ecological consequences of elevated N inputs to the Northeast include tropospheric ozone formation, ozone damage to plants, the alteration of forest N cycles, acidification of surface waters, and eutrophication in coastal waters. We used two models, PnET-BGC and WATERSN, to evaluate management strategies for reducing N inputs to forests and estuaries, respectively. Calculations with PnET-BGC suggest that aggressive reductions in N emissions alone will not result in marked improvements in the acid–base status of forest streams. WATERSN calculations showed that management scenarios targeting removal of N by wastewater treatment produce larger reductions in estuarine N loading than scenarios involving reductions in agricultural inputs or atmospheric emis...

The Impact of Conifer Harvesting on Stream Water Quality: A Case Study in Mid-Wales

A 12-year record of water quality data for runoff from a spruce forested hillslope with podzolic soils shows the impacts of conifer harvesting and replanting in relation to nitrate generation and its influence on surface water acidification. With felling, nitrate increases from a background of 18 μ Eq/l to about 50 μ Eq/l after 1 to 2 years and then declines to background levels over the next 1 to 2 years and to lower concentrations thereafter. This change is mirrored by an acidification process as manifest by a change in Gran alkalinity, acid neutralization capacity (ANC) and aluminium concentrations as well as pH. For example, Gran alkalinity and ANC, which start at negative concentrations prior to felling (about –20 and –50 μ Eq/l, respectively), become more negative (–30 and –100 μ Eq/l, respectively) at high nitrate concentrations. Correspondingly, pH decreases from about 4.7 to 4.5 and aluminium concentrations increase from about 14 to 16μ M. Subsequently, the acidification is reversed as nitrate concentrations decline and after five years post-felling the system has higher pH, Gran alkalinity and ANC together with lower aluminium concentrations than even before the felling took place (the post-felling values are about 4.9, -15μ Eq/l, –20μ Eq/l and 7 μ M/l, respectively).Other determinands show clear changes over time. For example, there is a marked increase in sodium and chloride prior to and around the time of felling (200 to 300 and 230 to 400 μ Eq/l, respectively), with a subsequent decline in concentration to pre-felling and to lower values of around 160 and 170 μ Eq/l, respectively, thereafter. This change is probably associated with abnormally high inputs of sea-salts from the atmosphere during the first quarter of the year of felling, and dilution thereafter, rather than a direct consequence of the felling activity itself: this change in sea salt loading has had an impact on stream acidity. Dissolved organic carbon and iron also change with concentrations increasing over time (60 to 200 and 1.0 to 1.5 μ M/l, respectively) and this mirrors a general pattern observed across the Plynlimon catchments irrespective of whether or not there has been felling activity.The implications of the findings are discussed in relations to environmental management and hydrochemical processes.

The biogeochemistry of two forested catchments in the Black Forest and the eastern Ore Mountains (Germany)

The biogeochemical input-output fluxes of two forested catchments with contrasting levels of atmospheric deposition were investigated in Germany. This paper focuses on the effects of recent changes in atmospheric inputs on the chemical composition in the soil solution and stream. The catchment 'Schluchsee' (Black Forest; SW Germany) is characterized by relatively low atmospheric inputs whereas 'Rotherdbach' (Ore Mountains; E Germany) received significant amounts of acid deposition (mainly originating from SO2 emissions) until recent years. Both sites reveal decreases in H+ and S deposition during the 1990s. This pattern is typical when compared to trends in Europe. In response to the reduced S deposition, soil solution and streamwater SO42− concentrations decreased significantly. A net release of SO42− (output > input) was observed at both sites due to the release of S previously stored in the soil. The level of N deposition was more or less constant at both sites. At Schluchsee, NO3− concentration in streamwater remained more or less unchanged, whereas a decrease at Rotherdbach was observed. A recovery from acidification was found in seepage water as indicated by increasing acid neutralizing capacity (ANC). Streamwater ANC increased only in the permanently acidified Rotherdbach. No change of ANC was observed in the Schluchsee stream, which was characterized by episodic acidification during high-flow conditions. Nevertheless, the key factor controlling the recovery from surface water acidification was the type, amount and distribution of stored S pools in the ecosystem. Thus, time series analysis of long-term data of input-output chemistry can be a valuable instrument in order to improve the understanding of linked terrestrial-aquatic systems and give useful clues for modeling efforts.