Surface Water Acidification Research Articles

Occurrence and fate of the human pharmaceutical metabolite ritalinic acid in the aquatic system

To investigate the occurrence and fate of ritalinic acid – the main human metabolite of the psychostimulant drug methylphenidate – in the aquatic environment, a HPLC–electrospray–MS/MS method for the quantification of ritalinic acid in wastewater, surface water and bank filtrate was developed. Carbamazepine known as very stable in the aquatic environment was analyzed as anthropogenic marker in parallel. Furthermore, the removal of ritalinic acid was studied in a sewage treatment plant using an activated sludge system during a field study and in lab-scale plants. In good agreement between lab-scale and field studies a low removal rate of 13% and 23%, respectively, was determined. As a consequence, the concentration of ritalinic acid in the wastewater effluents were in the range of <50–170 ng L −1 which corresponds to a mean specific load per capita of 17.7 μg d −1. Ritalinic acid has further been detected in German rivers at concentrations of 4–23 ng L −1 and in bank filtrate samples in 100–850 m distance from the river up to 5 ng L −1 demonstrating the widespread occurrence of this stable metabolite in the aquatic environment. A comparison to available sales data shows that a significant amount of methylphenidate applied can be found in waters as ritalinic acid.

An enigmatic mortality event in the only population of the Critically Endangered Cameroonian frog Xenopus longipes

Contemporary global declines and mortality events in amphibian populations have been often attributed to infectious disease and climate change, separately and in combination. We report on an enigmatic mortality event in the only known population of the Critically Endangered frog species Xenopus longipes. This aquatic and biologically distinctive species is restricted to Lake Oku, a high-elevation crater lake on Mt. Oku in Cameroon. Neither a quantitative PCR-based screen nor histopathological analysis revealed the presence of the chytrid fungus Batrachochytrium dendrobatidis, which is believed to be responsible for many declines and mortality events in amphibian populations around the world. Histopathology revealed widespread epidermal hyperplasia and multifocal saprolegniasis suggesting that the animals have been exposed to a source of skin irritation. These sources might include acidified surface waters, perhaps derived from inorganic fertilisers or other human-related pollutants, or to local geological processes distinctive of the Cameroonian Volcanic Line. Currently, the causes underlying this mortality event remain obscure.

Monosulfidic black ooze accumulations in sediments of the Geographe Bay area, Western Australia

Mobilisation of sedimentary monosulfidic black ooze (MBO) may result in rapid deoxygenation and acidification of surface waters, and release of potentially toxic metals. This study examines the extent and nature of MBO accumulation in the Geographe Bay area, Western Australia. MBO accumulations were found to be widespread in benthic sediments of the Geographe Bay area with acid-volatile sulfide (AVS) contents as high as 320μmolg−1. The MBO materials often had unusually high dissolved sulfide (S−II) concentrations in their pore-waters (up to 610mgL−1) and elevated elemental sulfur (S0) contents (up to 51μmolg−1). Dissolved S−II is able to accumulate due to limited iron availability and S0 is largely its partial oxidation product. The availability of organic carbon and Fe limited MBO accumulation at many sites. A comparison of AVS and simultaneously extracted metal (SEM) concentrations has shown that metals are likely to be bound in sulfide complexes.

Modeling Future Acidification and Fish Populations in Norwegian Surface Waters

Despite great progress made in the past 25 years, acid deposition continues to cause widespread damage to the environment in Europe and eastern North America. Legislation to limit emissions of sulfur and nitrogen compounds in Europe is now under revision. The most recent protocol was based in part on the critical loads concept. The new protocol may also take into consideration the time delays between dose and response inherent in natural ecosystems. Policy decisions to reduce adverse effects on ecosystems entail a trade-off: quick response will require deeper cuts in emissions and thus higher costs, whereas lower costs with lesser cuts in emissions will give slower response. Acidification of lakes and damage to fish populations in Norway is used as an example. Under current legislation for emission reductions, surface waters will continue to slowly recover, but for many decades lakes in about 18% of Norway will continue to have water quality insufficient to support healthy populations of brown trout and other indicator organisms. Additional emission reductions can speed up the rate and degree of recovery.

Mercury and halogenated organic contaminants in river otters (Lontra canadensis) in New Jersey, USA

Liver samples collected from New Jersey river otters (Lontra canadensis) in 2005 and 2007 were tested for Hg, organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polybrominated diphenyl ethers (PBDEs). The highest mercury concentrations were found in otters living in the Pinelands region, where acidic soils and surface waters enhance Hg bioavailability. The highest individual Hg concentration was 19.8 µg/g wet weight, approximately 60% of the experimentally determined lethal threshold. Concentrations of OC pesticides were generally similar to those in otters from areas of Oregon and Washington close to agricultural and industrial sources. The geometric mean total PCB concentration (540 ng/g wet wt) was similar to the concentration in otters from the heavily populated and industrialized lower Columbia River in Oregon and Washington. Seven liver samples that were among the highest in terms of total PCBs were analyzed for PCDDs and PCDFs. Polychlorinated dibenzo-p-dioxins were detected in six of the samples at total concentrations ranging from 172 to 2,783 pg/g wet weight. Polychlorinated dibenzofurans were detected in three of the samples at total concentrations ranging from 1.50 to 2,719 pg/g wet weight. The geometric mean PBDE concentration was 10.6 ng/g wet weight, with a range of 0.82 to 436 ng/g wet weight. No statistically significant relationship was observed between liver contaminant concentrations and land use within an 8-km radius of the trapping location. Overall, the data suggest that contaminant concentrations are not high enough to adversely affect the overall otter population in New Jersey. However, contaminant-related effects on the health or reproductive success of individual otters in some areas are possible.

Occurrence and risk assessment of acidic pharmaceuticals in the Yellow River, Hai River and Liao River of north China

Pharmaceuticals in the aquatic environment have received great attentions from the general and scientific community due to their potential impacts on ecological and human health. We investigated the occurrence of twelve acidic pharmaceuticals and herbicides (salicylic acid, clofibric acid, ibuprofen, gemfibrozil, fenoprofen, naproxen, ketoprofen, mefenamic acid, tolfenamic acid, diclofenac, meclofenamic acid and indomethacin) in surface waters of the Yellow River, Hai River and Liao River in north China during the wet and dry seasons and assessed the potential risks to aquatic organisms posed by these acidic compounds. Seven acidic compounds were detected in the rivers, including five non-steroidal anti-inflammatory drugs (salicylic acid, ibuprofen, diclofenac, mefenamic acid and naproxen), and two blood lipid regulators (clofibric acid and gemfibrozil). The concentrations for acidic pharmaceuticals in the Yellow River and Liao River were in most cases higher in the dry season than in the wet season, but the concentrations of acidic compounds in the Hai River were generally higher in July than in November. High concentrations of these detected compounds in the Yellow River, Hai River and Liao River were found more frequently at those sites located in metropolitan areas, lower reaches or river confluences. Only diclofenac and ibuprofen were found to have medium to high risks in the three rivers based on the calculated risk quotients.

Determination of Perfluorinated Compounds in the Upper Mississippi River Basin

Despite ongoing efforts to develop robust analytical methods for the determination of perfluorinated compounds (PFCs) such as perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA) in surface water, comparatively little has been published on method performance, and the environmental distribution of these materials remains poorly described worldwide. In this study, an existing method was improved and applied in a large-scale evaluation of the Upper Mississippi River Basin, one of the largest watersheds in the world. Samples were collected in 2008 in an effort that involved multiple sample sites and collection teams, long-range transport, and storage of up to 4 weeks before analysis. Ninety-four percent of the resulting 177 samples had quantifiable PFC concentrations, with 80% of the individual target compounds below 10 ng/L. The most abundant PFCs were perfluorobutanoic acid (C4; 77% above the limit of quantitation, LOQ), perfluorooctanoic acid (C8; 73%), perfluorooctanesulfonate (PFOS; 71%), perfluorohexanoic acid (C6; 70%), and perfluoroheptanoic acid (C7; 69%), with the remaining target compounds occurring above the LOQ in less than 50% of the samples. The highest concentrations recorded include C4 at 458 ng/L, PFOS at 245 ng/L, and C8 at 125 ng/L, suggesting various point source inputs within the Basin.

Origin of acidic surface waters and the evolution of atmospheric chemistry on early Mars

Observations from in situ experiments and planetary orbiters have shown that the sedimentary rocks found at Meridiani Planum, Mars were formed in the presence of acidic surface waters. The water was thought to be brought to the surface by groundwater upwelling, and may represent the last vestiges of the widespread occurrence of liquid water on Mars. However, it is unclear why the surface waters were acidic. Here we use geochemical calculations, constrained by chemical and mineralogical data from the Mars Exploration Rover Opportunity, to show that Fe oxidation and the precipitation of oxidized iron (Fe^(3+)) minerals generate excess acid with respect to the amount of base anions available in the rocks present in outcrop. We suggest that subsurface waters of near-neutral pH and rich in Fe^(2+) were rapidly acidified as iron was oxidized on exposure to O_2 or photo-oxidized by ultraviolet radiation at the martian surface. Temporal variation in surface acidity would have been controlled by the availability of liquid water, and as such, low-pH fluids could be a natural consequence of the aridification of the martian surface. Finally, because iron oxidation at Meridiani would have generated large amounts of gaseous H_2, ultimately derived from the reduction of H_2O, we conclude that surface geochemical processes would have affected the redox state of the early martian atmosphere.

Soil piping and catchment response

AbstractOver the 40 years, since soil piping was first considered to be a potential factor in the hydrological response of catchments, research has revealed a considerable amount about its hydrological role and its geographical, climatic and pedological distribution. Piping has been shown to be a major factor supporting the hypothesis that subsurface flow can be a significant contributor to quickflow by field experiments ranging from the United Kingdom to Canada, India and China. This research has demonstrated that, at least in some areas, soil pipes may contribute up to nearly 50% of stormwater discharge. Piping processes therefore merit inclusion within rainfall–runoff simulation models, but this has yet to be achieved. Some progress has been made in modelling pipeflow itself, but integration within a catchment model presents major problems, not least in quantifying or parameterizing the nature and distribution of pipe networks. The wider environmental implications of soil piping are also only just beginning to be recognized. These range from the effects of changing residence times on water chemistry, especially on the acidification of surface waters, to the effects of hillslope drainage patterns on soil development and vegetation diversity. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Acid drainage at the inactive Santa Lucia mine, western Cuba: Natural attenuation of arsenic, barium and lead, and geochemical behavior of rare earth elements

Abstract A detailed geochemical study was conducted at the inactive Zn–Pb mine of Santa Lucia, in western Cuba. The studied mine-wastes are characterized by high total concentrations of potentially toxic elements (PTE), with average values of 17.4% Fe, 5.47% Ba, 2.27% Pb, 0.83% Zn, 1724 mg/kg As and 811 mg/kg Cu. Oxidation of sulfide minerals in mine-waste dumps and in the open pit produces acid mine effluents (pH = 2.5–2.6) enriched in dissolved SO 4 2 - (up to 6754 mg/L), Fe (up to 4620 mg/L) and Zn (up to 2090 mg/L). Low pH values (2.5–2.8) and high dissolved concentrations of the same PTE were found in surface waters, up to 1500 m downstream from the mine. Nevertheless, concentrations of As, Ba and Pb in acid mine effluents and impacted surface waters are relatively low: 0.01–0.3 mg/L As, 0.002–0.03 mg/L Ba and 0.3–4.3 mg/L Pb. Analysis by X-ray diffraction and electron microscopy revealed the occurrence of lead–bearing barite and beudantite and the more common solid phases, reported elsewhere in similar environments including Fe-oxyhydroxides, jarosite, anglesite and plumbojarosite. Because the reported solubilities for barite and beudantite are very low under acidic conditions, these minerals may serve as the most important control in the mobility of As, Ba and Pb. In contrast, Fe-oxyhydroxides are relatively soluble under acidic conditions and, therefore, they may have a less significant role in PTE on-site immobilization. Mine-wastes and stream sediments show a light REE (LREE) and middle REE (MREE) enrichment relative to heavy REE (HREE). In contrast, acid mine effluents and surface waters are enriched in HREE relative to LREE. These results suggest that the LREE released during the oxidation of sulfides are captured by secondary (weathering) minerals, while the MREE are removed from the altered rocks. The low concentrations of LREE in acid stream water suggest that these elements can be retained in the sediments more strongly than HREE and MREE. One possible explanation for the sharp decrease in dissolved LREE might be their retention by low-solubility secondary minerals such as anglesite, barite and jarosite.

Biological responses to liming in boreal lakes: an assessment using plankton, macroinvertebrate and fish communities

1. Biological responses to liming of acidified surface waters are equivocal and limit the overall assessment of food web responses. In this study, we analysed community structure in limed, acidified and circumneutral lakes, based on the analyses of phytoplankton, zooplankton, macroinvertebrates (littoral, sublittoral, profundal) and fish between 2000 and 2004. We also studied associations between functional feeding groups in food webs. 2. Most univariate metrics of structure and function revealed similar community attributes among lake types, suggesting that community responses to natural recovery from acidification and liming management converge with those observed in circumneutral lakes. These trends were less clear in the multivariate analyses which showed significant community differences among lake types. For phytoplankton, these patterns were partly mediated by the invasive raphidophycean flagellate Gonyostomum semen. 3. The associations between functional feeding groups indicated less connectivity and food web complexity in limed lakes relative to the other lake types. We speculate that repeated lime applications comprise frequent pulse disturbances which offset the establishment of stable trophic relationships in the food webs of limed lakes. 4. Synthesis and applications. The limited structural and functional food web similarity among lake types supports the argument that liming constitutes an ecosystem-level disturbance. Managers should be aware of the ecosystem impacts of altered disturbance regimes when designing their management schemes because this can influence the success of restoration programmes. Furthermore, the lack of recovery, mediated in part by species invasions, suggests that impacts derived from global change are likely to lead to novel environmental situations. This calls for adaptive management strategies where managers are challenged to tackle multiple forms of anthropogenic stress simultaneously.

The present is the key to the past, but what does the future hold for the recovery of surface waters from acidification?

Analogue matching was used to identify close modern water quality analogues for a set of 59 acid-sensitive lakes in the Galloway region of south-west Scotland. Modern analogues were identified that closely matched the pre-disturbance conditions of these lakes using simulated water quality parameters from the MAGIC (Model of Acidification of Groundwater in Catchments) model for key years from 1860 to 2100. The lakes were matched with hydrochemical samples from a large spatial data set in the UK. For the majority of the 59 lakes, several close modern analogues were identified from the training set for specified years. The close modern analogues for the reference year (1860) were predominantly located in north-west Scotland, an area of low acid deposition and high-status water quality. A clear recovery in the regional surface water acid neutralising capacity (ANC) was simulated by MAGIC in 2015 compared to the situation in 1970 at the height of acid emissions. Predicted trends in surface water chemistry from present day to 2015 indicate some improvement in water quality with c. 23 ± 0.97% recovery towards pre-acidification (1860) ANC for the region. Output from the MAGIC model was used with the analogue technique to investigate the combined influence of future changes in deposition and climate on biogeochemical processes and water quality at the Round Loch of Glenhead (RLGH). Our results demonstrate that pre-acidification restoration targets will not be achieved by simply reducing acid deposition, and climate change will further confound the beneficial effects of deposition reductions. Results for 2015 and beyond show that modern analogues for these periods were predominantly concentrated in North Wales, with some in north-west Scotland, Galloway and the Lake District. Evidence from model simulations and modern analogues indicate that more stringent measures to further reduce acid deposition and combat climate change in the future are necessary if the majority of lakes in the Galloway region are to be restored to their pre-acidification target chemistry. The identified analogues for selected periods may be used to study wider ecological conditions to better define reference conditions and future recovery trajectories. That modern analogues were identified for the simulated chemistry in 2100 at RLGH suggests that unprecedented chemical conditions are unlikely to be observed as a result of future climate change.

Acidification Remediation Alternatives: Exploring the Temporal Dimension with Cost Benefit Analysis

Acidification of soils and surface waters caused by acid deposition is still a major problem in southern Scandinavia, despite clear signs of recovery. Besides emission control, liming of lakes, streams, and wetlands is currently used to ameliorate acidification in Sweden. An alternative strategy is forest soil liming to restore the acidified upland soils from which much acidified runoff originates. This cost-benefit analysis compared these liming strategies with a special emphasis on the time perspective for expected benefits. Benefits transfer was used to estimate use values for sport ffishing and nonuse values in terms of existence values. The results show that large-scale forest soil liming is not socioeconomically profitable, while lake liming is, if it is done efficiently-in other words, if only acidified surface waters are treated. The beguiling logic of "solving" an environmental problem at its source (soils), rather than continuing to treat the symptoms (surface waters), is thus misleading.

Comparison of different critical load approaches for assessing streamwater acid-sensitivity to broadleaf woodland expansion

Due to its potential adverse effects on freshwater acidification, risk assessments of the impacts of forest expansion on surface waters are required. The critical load methodology is the standard way of assessing these risks and the two most widely used models are the Steady-State Water Chemistry (SSWC) and First-order Acidity Balance (FAB) models. In the UK the recommended risk assessment procedure for assessing the impact of forest expansion on freshwater acidification uses the SSWC model, whilst the FAB model is used for guiding emission policy. This study compared the two models for assessing the sensitivity of streamwater to acidification in 14 catchments with different proportions of broadleaf woodland cover in acid-sensitive areas in the UK. Both models predicted the exceedance of streamwater critical loads in the same catchments, but the magnitudes of exceedance varied due to the different treatment of nitrogen processes. The FAB model failed to account for high nitrogen leaching to streamwater, attributed to nitrogen deposition and/or fixation of nitrogen by alder trees in some study catchments, while both models underestimated the influence of high seasalt deposition. Critical load exceedance in most catchments was not sensitive to the use of different acid neutralising capacity thresholds or runoff estimates, probably due to the large difference between critical load values and acidic deposition loadings. However, the assessments were more sensitive to differences in calculation procedure in catchments where nitrogen deposition was similar to the availability of base cations from weathering and/or where critical load exceedance values were < 1 keq H + ha − 1 yr − 1 . Critical load exceedance values from both models agreed with assessments of acid-sensitivity based on indicator macroinvertebrates sampled from the study catchments. Thus the methodology currently used in the UK appears to be robust for assessing the risk of broadleaf woodland expansion on surface water acidification and ecological status.

Decreasing pH trend estimated from 25-yr time series of carbonate parameters in the western North Pacific

We estimated long-term trends of ocean acidification in surface waters in latitudinal zones from 3°N to 33°N along the repeat hydrographic line at 137°E in the western North Pacific Ocean. Estimates were based on the observational records of oceanic CO2 partial pressure and related surface properties over the last two decades. The computed pH time series both for 25 yr in winter (late January.early February) and for 21 yr in summer (June.July) exhibited significant decreasing trends in the extensive subtropical to equatorial zones, with interannual variations that were larger in summer. The calculated rates of pH decrease ranged from 0.0015 to 0.0021 yr-1 (average, 0.0018 ± 0.0002 yr-1) in winter and from 0.0008 to 0.0019 yr-1 (average, 0.0013 ) 0.0005 yr-1) in summer. The thermodynamic effects of rising sea surface temperature (SST) accounted for up to 44% (average, 15%) of the trend of pH decrease in the subtropical region in winter, whereas a trend of decreasing SST slowed the pH decrease in the northern subtropical region (around 25°N) in summer. We used the results from recent trends to evaluate future possible thermodynamic changes in the upper ocean carbonate system.

Determination of EDTA in Dairy Wastewater and Adjacent Surface Water

An HPLC-UV analytical method was developed to determine ethylenediaminetetraacetic acid (EDTA) in dairy wastewater and surface water. The optimizing separation was achieved by reversed-phase ion-pair liquid chromatography on a C18 column using methanol as mobile phase solvent, tetrabutylammonium bromide as the ion-pair reagent in pH 3.3 formate buffer solution at a flow rate of 0.9 mL min -1 with a UV detector at 265 nm. No interference of Ca, Mg or NO3 - was detected. Method performance was evaluated in terms of linearity, repeatability and reproducibility. The method detection limit was 5 µg L -1 . The contents of EDTA in dairy effluents were 72 ~ 261 µg L -1 at a large dairy site. A change of EDTA concentration was observed downstream of the dairy effluent discharge, but this was well under the predicted no effect concentration for aquatic ecosystem. Keywords—Dairy wastewater, EDTA, HPLC, surface water. I. INTRODUCTION LEANING of equipment for production plants is a key process in the dairy industry to ensure safe products with high quality. It has been demonstrated (1) that using synergic effects of single components in chemical mixtures, for instance adding an effective complexing agent, is more likely to achieve an improved cleansing result with lower concentration compared to aqueous solutions merely containing the basic component of sodium hydroxide. The main function of complexing agents in a cleaning solution is to prevent precipitation of calcium, magnesium and heavy metal salts, which can cause deposits to appear on both the cleaning equipment and the plant to be cleaned (2). At present, ethylenediaminetetraacetic acid (EDTA) is the cheapest and most suitable complexing compound for many technical purposes, and is used in large quantities (3). In the New Zealand dairy industry, EDTA has been used as a cleaning additive to improve the cleansing efficiency during the clean-in-place (CIP) procedure. Nearly all applications eventually result in the release of EDTA to the aquatic environment (2), (3). In the late 1980s, the environmental impacts of EDTA were scrutinized in Europe, as EDTA occurred at a higher concentration in surface waters than any other identified anthropogenic organic compounds that may

Changes of the plankton community composition during chemical neutralisation of the Bockwitz pit lake

Lake Bockwitz, a pit lake in a former lignite open-cast mine south of Leipzig (Germany), was neutralised (from pH 2.65 to pH 7.1) by addition of soda ash (14,620 t) from 2004 to 2007. The additions had to be continued due to ongoing inflows of acid ground and surface water. This paper reports on the changes in the plankton community accompanying the neutralisation. At the beginning, the community composition and biomass was comparable to other acidic pit lakes, i.e. the pigmented flagellates Chlamydomonas and Ochromonas dominated the autotrophs, and ciliates and rotifers were the top predators. The biomass was small (maximum 2 mg fresh weight per litre) and decreased until the end of 2008. With increasing pH, the autotrophic community became more diverse, whereby diatoms, chrysophyceans and blue greens contributed significantly to biomass. Although neutral pH conditions were achieved in autumn 2007, picocyanobacteria were not present until the end of 2008. In addition, crustaceans were under-represented in terms of biomass and diversity. Daphnids were not found. We attributed this to short-term changes of the ionic composition of the water and to the limited time available for non-acido-tolerant organisms to colonise the system.

Erratum to: Prediction of the thermodynamic properties of metal–arsenate and metal–arsenite aqueous complexes to high temperatures and pressures and some geological consequences

The standard thermodynamic properties at 25°C, 1 bar (ΔG f o , ΔH f o , S o, C P o , V o, ω) and the coefficients of the revised Helgeson–Kirkham–Flowers equations of state were evaluated for several aqueous complexes formed by dissolved metals and either arsenate or arsenite ions. The guidelines of Shock and Helgeson (Geochim Cosmochim Acta 52:2009–2036, 1988) and Sverjensky et al. (Geochim Cosmochim Acta 61:1359–1412, 1997) were followed and corroborated with alternative approaches, whenever possible. The SUPCRT92 computer code was used to generate the log K of the destruction reactions of these metal–arsenate and metal–arsenite aqueous complexes at pressures and temperatures required by the EQ3/6 software package, version 7.2b. Apart from the AlAsO 4 o and FeAsO 4 o complexes, our log K at 25°C, 1 bar are in fair agreement with those of Whiting (MS Thesis, Colorado School of Mines, Golden, CO, 1992). Moreover, the equilibrium constants evaluated in this study are in good to fair agreement with those determined experimentally for the Ca–dihydroarsenate and Ca–hydroarsenate complexes at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) and for Fe(III)–hydroarsenate complex at 25°C (Raposo et al., J Sol Chem 35:79–94, 2006), whereas the disagreement with the log K measured for the Ca–arsenate complex at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) might be due to uncertainties in this measured value. The implications of aqueous complexing between dissolved metals and arsenate/arsenite ions were investigated for seawater, high-temperature geothermal liquids and acid mine drainage and aqueous solutions deriving from mixing of acid mine waters and surface waters.

Alkalinity and acidity cycling and fluxes in an intermediate fen peatland in northern Ontario

Peatlands are important to global carbon (C) sequestration and surface water acid–base status, both of which are affected by peatland alkalinity and acidity cycling. Relationships among sulfate (SO4 2−), nitrate (NO3 −), organic acids (OA−), base cations (i.e., Ca2+, Mg2+, K+, and Na+), proton (H+) acidity, and bicarbonate (HCO3 −) alkalinity were investigated in an intermediate fen peatland in northern Ontario during 2004 (an average precipitation year) and 2005 (a dry summer). Potential evapotranspiration was higher and the water table, groundwater input from the uplands, and runoff were lower during 2005. Net inputs of base cations, HCO3 −, SO4 2−, and OA−, and to a lesser degree NO3 −, were lower during the drier year, mainly due to lower groundwater transfer to the fen. Fen porewater HCO3 − concentration and net output were also lower in the drier year, whereas Ca2+, Mg2+, and SO4 2− concentrations and net output were higher. During the climatically average year, N immobilization, carbonic acid (H2CO3) dissociation, and OA dissociation were equally important H+-producing reactions. Peat cation exchange accounted for 50% of the H+ sink, while SO4 2− reduction and denitrification accounted for an additional 20 and 25% of the H+ sink, respectively. During the dry year, S oxidation accounted for 55% of the H+ net production, while that for H2CO3 dissociation was 70% lower than that during the climatically average year. Peat cation exchange consumed three times the acidity, and accounted for 92% of the H+ consumption during the dry year compared to the climatically average year. This was consistent with a three-fold higher net base cation export from the fen during the dry year. Based on the study results, a conceptual model was developed that describes the role of acidity formation and its implications to intermediate fen acidification.

Comparing pre-industrial and post-limed diatom communities in Swedish lakes, with implications for defining realistic management targets

In the 1960s and 1970s, acidification was identified as a major environmental problem in Scandinavia, Great Britain and North America. In Sweden, a liming program was launched in order to counteract the effects of acidification on surface waters. More than 30 years after large-scale liming began, there is still debate about whether liming actually achieves its goals, i.e., to prevent acidification in acid-sensitive surface waters and to restore natural conditions in acidified waters. We used Detrended Correspondence Analysis (DCA) and analogue matching of diatom assemblages in surface sediment samples (recent conditions) from 31 limed lakes and pre-industrial samples from 291 reference lakes to help answer the question as to whether the Swedish liming program achieves its goals. Diatoms are important primary producers in lakes and established indicator organisms for lake-water quality. First we compared pre-industrial with post-limed diatom communities to address the question whether liming causes unnatural conditions, i.e., diatom communities that have not previously occurred in Swedish lakes. Second, we addressed the issue of what is a realistic condition to use as a reference (natural condition) or a target in management programs. We found that the diatom communities in limed lakes were not different from the communities in the reference lakes. Most of the limed lakes had one or more analogues within the reference data set and many of them had at least one within-lake analogue. Hence, liming does not create unique diatom communities in lakes. Based on this and previous paleolimnological studies in Swedish lakes we suggest a conceptual model integrating the natural lake condition, the historical human impact, and the recent and contemporary human impact, when defining realistic targets in management programs.