Acid Rain Deposition Research Articles

The recovery of river chemistry from acid rain in the Mississippi River basin amid intensifying anthropogenic activities and climate change

Acid rain has degraded the environmental health of many regions worldwide since the Industrial Revolution. Signatures of river chemistry recovery from acid rain since the Clean Air Act and similar legislation have been reported extensively in small streams but are often subdued or masked in large rivers by complex, co-occurring drivers. Here we assess the recovery of river chemistry from acid rain deposition in the Mississippi River Basin (MRB), the largest river basin in North America. We combine analysis of temporal trends of acid rain indicator solutes with Bayesian statistical models to assess the large-scale recovery from acid rain and characterize effects of anthropogenic activities. We found evidence of river chemistry recovery from acid rain; however, the effects of other anthropogenic activities, including fertilizer application and road salting, and changing climate, are likely intensifying. Trends of pH, alkalinity and SO4 export suggest acid rain recovery at large in the MRB, with stronger evidence of recovery in the historically afflicted eastern region of the basin. The concentrations of acid rain indicators generally correlate positively to NO3 and Cl, indicating that N-fertilizer application may have significantly increased weathering, and possibly acidification, and road salt application likely increased cation loss from catchments and contributed to SO4 export. Temperature correlates positively with solute concentrations, possibly through respiration-driven weathering or evaporation. The concentrations of acid rain indicators correlate negatively and most strongly to discharge, indicating discharge as a predominant driver and that lower discharge during droughts can elevate concentrations of riverine solutes in a changing climate. Using long-term data, this study represents a rare, comprehensive assessment of the recovery from acid rain in a large river basin, taking into consideration the entangled effects of multiple human activities and climate change. Our results highlight the ever-present need for adaptive environmental management in a constantly changing world.

Catchment properties as predictors of greenhouse gas concentrations across a gradient of boreal lakes

Boreal lakes are the most abundant lakes on Earth. Changes in acid rain deposition, climate, and catchment land use have increased lateral fluxes of terrestrial dissolved organic matter (DOM), resulting in a widespread browning of boreal freshwaters. This browning affects the aqueous communities and ecosystem processes, and boost emissions of the greenhouse gases (GHG) CH4, CO2, and N2O. In this study, we predicted biotic saturation of GHGs in boreal lakes by using a set of chemical, hydrological, climate, and land use parameters. For this purpose, concentrations of GHGs and nutrients (organic C, -P, and -N) were determined in surface water samples from 73 lakes in south-eastern Norway covering wide ranges in DOM and nutrient concentrations, as well as catchment properties and land use. The spatial variation in saturation of each GHG is related to explanatory variables. Catchment characteristics (hydrological and climate parameters) such as lake size and summer precipitation, as well as NDVI, were key determinants when fitting GAM models for CH4 and CO2 saturation (explaining 71 and 54%, respectively), while summer precipitation and land use data were the best predictors for the N2O saturation, explaining almost 50% of deviance. Our results suggest that lake size, precipitation, and terrestrial primary production in the watershed control the saturation of GHG in boreal lakes. These predictions based on the 73-lake dataset was validated against an independent dataset from 46 lakes in the same region. Together, this provides an improved understanding of drivers and spatial variation in GHG saturation in boreal lakes across wide gradients of lake and catchment properties. The assessment highlights the need to incorporate multiple explanatory parameters in prediction models of GHGs for extrapolation across the boreal biome.

Photochemical Aging of Atmospheric Fine Particles as a Potential Source for Gas-Phase Hydrogen Peroxide.

Atmospheric hydrogen peroxide (H2O2), as an important oxidant, plays a key role in atmospheric sulfate formation, affecting the global radiation budget and causing acid rain deposition. The disproportionation reactions of hydroperoxyl radicals (HO2) in both gas and aqueous phases have long been considered as dominant sources for atmospheric H2O2. However, these known sources cannot explain the significant formation of H2O2 in polluted areas under the conditions of high NO levels and low ambient relative humidity (RH). Here, we show that under relatively dry conditions during daytime, atmospheric fine particles directly produce abundant gas-phase H2O2. The formation of H2O2 is verified to be by a reaction between the particle surface -OH group and HO2 radicals formed by photooxidation of chromophoric dissolved organic matters (CDOMs), which is slightly influenced by the presence of high NO levels but remarkably accelerated by water vapor and O2. In contrast to aqueous-phase chemistry, transition metal ions (TMIs) are found to significantly suppress H2O2 formation from the atmospheric fine particles. The H2O2 formed from relatively dry particles can be directly involved in in situ SO2 oxidation, leading to sulfate formation. As CDOMs are ubiquitous in atmospheric fine particles, their daytime photochemistry is expected to play important roles in formation of H2O2 and sulfate worldwide.

Morphological, Physiological and Photophysiological Responses of Critically Endangered Acer catalpifolium to Acid Stress.

Acid rain deposition (AR) has long-lasting implications for the community stability and biodiversity conservation in southwest China. Acer catalpifolium is a critically endangered species in the rain zone of Western China where AR occurs frequently. To understand the effects of AR on the morphology and physiology of A. catalpifolium, we conducted an acid stress simulation experiment for 1.5 years. The morphological, physiological, and photosynthetic responses of A. catalpifolium to the acidity, composition, and deposition pattern of acid stress was observed. The results showed that simulated acid stress can promote the growth of A. catalpifolium via the soil application mode. The growth improvement of A. catalpifolium under nitric-balanced acid rain via the soil application mode was greater than that of sulfuric-dominated acid rain via the soil application mode. On the contrary, the growth of A. catalpifolium was significantly inhibited by acid stress and the inhibition increased with the acidity of acid stress applied via leaf spraying. The inhibitory impacts of nitric-balanced acid rain via the leaf spraying of A. catalpifolium were greater than that of sulfur-dominant acid rain via leaf spraying. The observations presented in this work can be utilized for considering potential population restoration plans for A. catalpifolium, as well as the forests in southwest China.

A review on the direct effect of particulate atmospheric pollution on materials and its mitigation for sustainable cities and societies.

Particulate matter (PM) has gained significant attention due to the increasing concerns related to their effects on human health. Although several reviews have shed light on the effect of PM on human health, their critical adverse effect on material's structure and sustainability was almost neglected. The current study is an attempt to fill this gap related to PM impact on structural materials under the overall consideration of sustainability. More specifically, this review highlights the existing knowledge by providing an overview on PM classification, composition, and sources in different locations around the world. Then, it focuses on PM soiling of surfaces such as solar panels due to an increasing need to mitigate the impact of soiling on reducing photovoltaic (PV) power output and financial competitiveness in dusty regions. This topic is of critical importance for sustainable deployment of solar energy in arid and desert areas around the world to help in reducing their impact on overall climate change and life quality. In addition, this review summarizes climate change phenomena driven by the increase of PM concentration in air such as radiative forcing and acid rain deposition due to their impact on human health, visibility and biodiversity. To this end, this work highlights the role of process management, choice of fuel, the implementation of clean technologies and urban vegetation as some possible sustainable mitigation policies to control PM pollution in cities and urban regions. This research is designed to conduct a comprehensive narrative literature review which targets broad spectrum of readers and new researchers in the field. Moreover, it provides a critical analysis highlighting the need to fill main research gaps in this domain. The findings of this review paper show that PM pollution imposes severe adverse impacts on materials, structures and climate which directly affect the sustainability of urban cities. The advantages of this review include the value of the extensive works that elaborate on the negative impacts of PM atmospheric pollution towards high level of public awareness, management flexibility, stakeholder's involvements, and collaboration between academy, research, and industry to mitigate PM impact on materials and human welfare.

Acid Rain Deposition Modulates Photosynthesis, Enzymatic and Non-enzymatic Antioxidant Activities in Tomato

Acid rain is one of the serious environmental issues causing morphological and physiological changes in plants. However, the impact of acid rain to vegetable crops remains indescribable. This study explored the effects of two pH levels of simulated acid rain (SAR) on photosynthesis and activity of different enzymatic and non-enzymatic key antioxidant compounds compared with control in two different tomato cultivars. With the increasing levels of acidity of SAR, decreased significantly the plant growth, chlorophyll, carotenoids, soluble protein and soluble sugar contents in leaves of both tomato cultivars but decreased percentages were more in Red Rain than Micro-Tom cultivar of tomato. Different enzymatic antioxidant key compounds accumulation was the maximum at pH 3.5 and degraded at pH 2.5 of SAR treatment for both tomato cultivars. In contrast, the growth of hydrogen peroxide (H2O2), malondialdehyde (MDA) and proline content was increased by SAR treatment which depends on the level of pH value of SAR. In addition, marked increase in phenolic, flavonoid and reducing antioxidant activity was found at pH 3.5 followed by pH 2.5 of SAR and control in both tomato cultivars. Our findings suggested that the tomato seedlings produced more reactive oxygen species (ROS) scavenging enzymatic and non-enzymatic antioxidant compounds to SAR stress at 3.5 pH level. Meanwhile, the inhibition of growth as well as photosynthesis of tomato seedlings and the severity of oxidative damage were found at pH 2.5 of SAR which might be depend on the types of cultivar.

Catchment-wide weathering and erosion rates of mafic, ultramafic, and granitic rock from cosmogenic meteoric 10Be/9Be ratios

Quantifying rates of weathering and erosion of mafic rocks is essential for estimating changes to the oceans alkalinity budget that plays a significant role in regulating atmospheric CO2 levels. In this study, we present catchment-wide rates of weathering, erosion, and denudation measured with cosmogenic nuclides in mafic and ultramafic rock. We use the ratio of the meteoric cosmogenic nuclide 10Be, deposited from the atmosphere onto the weathering zone, to stable 9Be, a trace metal released by silicate weathering. We tested this approach in stream sediment and water from three upland forested catchments in the north-west Czech Republic. The catchments are underlain by felsic (granite), mafic (amphibolite) and ultramafic (serpentinite) lithologies. Due to acid rain deposition in the 20th century, the waters in the granite catchment exhibit acidic pH, whereas waters in the mafic catchments exhibit neutral to alkaline pH values due to their acid buffering capability. The atmospheric depositional 10Be flux is estimated to be balanced with the streams’ dissolved and particulate meteoric 10Be export flux to within a factor of two. We suggest a correlation method to derive bedrock Be concentrations, required as an input parameter, which are highly heterogeneous in these small catchments.Derived Earth surface metrics comprise (1) Denudation rates calculated from the 10Be/9Be ratio of the “reactive” Be (meaning sorbed to mineral surfaces) range between 110 and 185 t km−2 y−1 (40 and 70 mm ky−1). These rates are similar to denudation rates we obtained from in situ-cosmogenic 10Be in quartz minerals present in the bedrock or in quartz veins in the felsic and the mafic catchment. (2) The degree of weathering, calculated from the fraction of 9Be released from primary minerals as a new proxy, is about 40–50% in the mafic catchments, and 10% in the granitic catchment. Lastly, (3) erosion rates were calculated from 10Be concentrations in river sediment and corrected for sorting and dissolved loss. These amount to 50% of denudation rates from 10Be/9Be in the mafic and ultramafic catchments, the remainder being mass loss in the dissolved form by weathering. In contrast, erosion comprises most of the mass loss in the granitic catchment.These first results are encouraging, given that we find overall good agreement between in situ and meteoric cosmogenic methods, that our denudation rates are in the range of those published for middle European river catchments, and that degrees of weathering are as expected for these diverse lithologies. This method allows quantifying rates of erosion and weathering in mafic rock over the time scale of weathering that are, unlike in situ cosmogenic 10Be, independent from the presence of quartz. 10Be/9Be therefore offers to quantify Earth surface processes in a wide range of landscapes underlain by mafic rock – rates that are of high importance for exploring climate-weathering feedbacks but that have been inaccessible to date.

Acid deposition and assessment of its critical load for the environmental health of waterbodies in a subtropical watershed, China

Atmospheric acidic deposition in subtropical watersheds poses an environmental risk of causing acidification of aquatic ecosystems. In this study, we evaluated the frequency of acid deposition in a subtropical forest ecosystem and the associated critical loads of acidity for a sensitive aquatic ecosystem. We found that out of 132 rainfall events, 33(25%) were acidic rainfall occurrences. Estimated wet acid deposition (2282.78 eq·ha−1·yr−1), consistent with SO42− and NH4+ deposition, was high in spring and summer and low in autumn and winter. Waterbodies surrounded by mixed wood and citrus orchard experience severe acidification, mostly from S deposition because acidic deposition exceeds the corresponding critical loads of acidity. Modifications that take acid rain deposition into consideration are needed for land-use and agricultural management strategies to improve the environmental health of waterbodies in subtropical watersheds.

Effect of Biochar in Cadmium Availability and Soil Biological Activity in an Anthrosol Following Acid Rain Deposition and Aging

Acidic deposition is a worldwide problem that often leads to the increase in soil available heavy metals. Liming and biochar can both raise soil pH and immobilize heavy metals. An experiment was conducted in the laboratory to study the effects of acidic deposition on soil Cd mobility and soil biological activity in a soil polluted with Cd. Biochar, prepared from poultry litter biochar (PLB) or eucalyptus biochar (EB) was added at a rate of 3 %. Liming controls, bringing the soil to the same pH as that attained with biochar, were also used. The experimental results showed a higher risk of Cd leaching and impaired biological properties under simulated acid rain. Biochar addition resulted in a reduction in the risk of leaching and in improved biological properties and could provide benefits over liming for the management of soil polluted with heavy metals, especially in areas affected by acidic deposition.

Trans-disciplinarity required in understanding, predicting and dealing with water eutrophication

Eutrophication remains a challenge for water quality, and leaching of phosphorus (P) from agriculture remains usually the determining factor as point source emissions of sewage are mainly under control. The Morsa watershed, southeast of Oslo, is a case in point. In spite of abatement actions during the past 20 years, the total concentration of P in the lake has decreased less than expected, causing growing frustration and scepticism among farmers. Hydro-biochemical interactions between phosphate (PO4) and calcium, aluminium and iron in soil and water have produced unexpected results. Decline in acid rain deposition over Norway has reduced the leaching of aluminium into water. This has caused a loss of an important fixation and removal of P by sorption to precipitating aluminium oxy-hydroxides. The combination of more precipitation and higher winter temperatures causes more flushing of P from surface soil horizons. Furthermore, water-logged soil loses much of its ability to hold PO4 in that iron is reduced, thereby allowing more P to escape. Farmers proved to have good agronomical knowledge and are taking part in an active network for spreading of agricultural practices. Reducing the amount of P in fertilizers was accepted fairly easily, whereas minimal autumn tillage has been a much harder task to implement. Therefore, just applying economic incentives will not do; developing basic environmental literacy with an ability to understand feedback loops and rebound effects is necessary. Following this, interaction between science and stakeholders is required, calling for trans-disciplinary research and trans-disciplinary processes.

Temporal trends of Al, Fe, Cu, Mn and Zn concentrations in streams draining agricultural catchments of the south-eastern Norway

In Norway, water quality of small streams draining agricultural catchments has been monitored since 1993 by the Agricultural and Environmental Monitoring Program. This article attempted to examine the concentration levels, temporal dynamics and long-term trends (1993–2009 and 1996–2009) of Al, Fe, Cu, Mn and Zn in streams draining the catchment areas of Skuterud (4.5 km2) and Mørdre (6.8 km2), located in south-east Norway. In the Mørdre stream, Al, Fe, Cu, Mn and Zn all showed statistically significant downward trends (p<0.05), whilst in the Skuterud stream only Al and Fe showed statistically downward significance (p<0.05). The general declining trends of metal concentrations are most likely associated with reduction of acid rain deposition in southern Norway. In spite of this declining trends, over the 14–17 years of monitoring mean monthly concentrations of total Al (2.0–3.2 mg L−1), Fe (1.3–2.5 mg L−1) and Cu (8.9–26.1 µg L−1) in Skuterud and Mørdre streams, respectively exceeded the limits of the Norwegian Water Framework Directives, whereas the concentrations of Mn (22.3–40.8 µg L−1) and Zn (13.1–99.4 µg L−1) fell within the range of desired limits. Of the total water samples analysed from Skuterud (n=370) and Mørdre streams (n=255), nearly 80–84%, 70–87% and 79–96% were above the desired limits for Al (0.2 mg L−1), Fe (0.3 mg L−1) and Cu (3 µg L−1), respectively. In 2011, water analysis from drainage of forest soils (in Skuterud catchment) measured total Al: 0.42–0.79 mg L−1 and total Fe: 0.84–1.0 mg L−1 which were two to three folds greater than the desired limits. In general, weak correlations between runoff and concentrations of the metals in the streams were noted. Future research should focus on identifying the sources of Al, Fe and Cu and management interventions of elevated metal inputs to Skuterud and Mørdre streams.

Cloud pattern and water relations in Picea rubens and Abies fraseri, southern Appalachian Mountains, USA

The spruce-fir [Picea rubens Sarg.-Abies fraseri (Pursh) Poir.] forests of the southern Appalachian Mountains are considered refugial, endangered communities that exist on only seven mountaintop areas in Virginia and North Carolina, USA. These relict forests continue to be threatened by stress factors such as logging, acid rain deposition, attacks from invasive insects, and climate change. It has been suggested that these communities have persisted because of frequent cloudiness and periods of cloud immersion (fog), although few studies have examined corresponding effects on microclimate and tree ecophysiology. Incident sunlight (PPFD), air temperature, vapor pressure deficit (VPD), and xylem water potentials were measured throughout the summer growing season in Mount Mitchell State Park, NC (35°45′53″N, 82°15′54″W), along with continuous camera recordings of the forest canopy and accompanying cloud conditions. Approximately 60% of all summer days had at least 2h of cloud immersion with the large majority (80.3%) of immersion events occurring during morning hours. Cloud-immersed days had the greatest reduction in cumulative daily PPFD compared to clear days (11.09molm−2day−1 vs. 38.03molm−2day−1, respectively), as well as substantially reduced mean VPD (0.98kPa vs. 1.81kPa) but only slightly lower mean air temperatures (14.5°C vs. 14.9°C, respectively). Moreover, xylem water potential (Ψ) increased significantly (∼0.2MPa; values) from morning to afternoon on cloud-immersed days. In contrast, clear days showed no afternoon recovery in Ψ, but a continued decrease during the afternoon. Juvenile Ψ was more responsive to daily cloud regime compared to adult Ψ and had a strong negative correlation with vapor pressure deficit. When all measurement days were sorted by the cloud pattern of the previous day, there was a strong response in juveniles trees, i.e. Ψ increased following previous afternoon cloud-immersion. Juveniles of both species also had greater seasonal decreases in Ψ than adults (P. rubens, adult: 0.05MPa, juvenile: 0.13MPa; A. fraseri, adult: 0.06MPa, juvenile: 0.20Mpa). For climate change models that predict a higher cloud base (resulting in less immersion) and dryer conditions, the water relations of Abies fraseri and Picea rubens could be substantially and negatively influenced.

Different responses of two Mosla species to potassium limitation in relation to acid rain deposition

The increasingly serious problem of acid rain is leading to increased potassium (K) loss from soils, and in our field investigation, we found that even congenerically relative Mosla species show different tolerance to K-deficiency. A hydroponic study was conducted on the growth of two Mosla species and their morphological, physiological and stoichiometric traits in response to limited (0.35 mmol K/L), normal (3.25 mmol K/L) and excessive (6.50 mmol K/L) K concentrations. Mosla hangchowensis is an endangered plant, whereas Mosla dianthera a widespread weed. In the case of M. hangchowensis, in comparison with normal K concentration, K-limitation induced a significant reduction in net photosynthetic rate (P(n)), soluble protein content, and superoxide dismutase (SOD) activity, but an increase in malondialdehyde (MDA) concentration. However, leaf mass ratio (LMR) and root mass ratio (RMR) were changed little by K-limitation. In contrast, for M. dianthera, K-limitation had little effect on P(n), soluble protein content, SOD activity, and MDA concentration, but increased LMR and RMR. Critical values of N (nitrogen):K and K:P (phosphorus) ratios in the shoots indicated that limitation in acquiring K occurred under K-limited conditions for M. hangchowensis but not for M. dianthera. We found that low K content in natural habitats was a restrictive factor in the growth and distribution of M. hangchowensis, and soil K-deficiency caused by acid rain worsened the situation of M. hangchowensis, while M. dianthera could well acclimate to the increasing K-deficiency. We suggest that controlling the acid rain and applying K fertilizers may be an effective way to rescue the endangered M. hangchowensis.

Sensors for Environmental Compliance of Diesel Engines

Nitrogen oxides generated from the combustion of fossil fuels contribute to ground level ozone formation and acid rain deposition. To minimize emissions the robust sensor technologies required. Solid-state electrochemical NOx and NH3 sensors evaluated in this study showed significant cross-interference issues. In contrast, the semiconductor nanowires of Cu and Pb Pthtalocyanine and CdS thin films functionalized with Fe and Mn Porphyrines (Ph) exhibited negligible cross-interferences. The computational molecular modeling was utilized to analyze equilibrium structures and binding energies of O2, CO, NO, NH3, and these were shown to control the selectivity. The FePh exhibited the highest selectivity for NO (-190 kJ/mol), while MnPh was most selective to NH3 (-46.7 kJ/mol). The binding energies of gas molecules to the hybrid Ph-CdS system were approximately 30 kJ/mol greater than binding to the Ph alone. Therefore, the semiconductor surface buried under the Ph layer enhanced sensitivity, but it did not alter the selectivity.

Effect of aluminum chloride and dietary phytase on relative ammonia losses from swine manure1

Ammonia (NH3) losses from swine manure contribute to odor problems, decrease animal productivity, and increase the risk of acid rain deposition. This study was conducted to determine whether aluminum chloride (AlCl3) or dietary manipulation with phytase could decrease relative NH3 losses from swine manure. Twenty-four pens of nursery pigs were used in two trials, and the pigs were fed normal or phytase-supplemented (500 IU/kg) diets. Aluminum chloride was added to manure pits (1.9 x 1.2 x 0.5 m) under each pen at 0, 0.25, 0.50, or 0.75% (vol:vol) of final manure volume. Manure pH and NH3 losses (measured by relative NH3 flux) were determined twice weekly. The addition of AlCl3 at 0.75% decreased (P < 0.05) manure pH from 7.48 to 6.69. Phytase decreased (P < 0.05) manure pH to 7.07 compared with 7.12 in the normal diet manure. Aluminum chloride administered at 0.75% without phytase reduced (P < 0.05) relative NH3 losses 52% for the entire 6-wk period. Relative NH3 losses were decreased (P < 0.05) from 109 mg of NH3/(m2 x h) in pens containing pigs fed the normal diet without AlCl3 to 81 mg of NH3/(m2 x h) in pens housing pigs administered the phytase diet, a 26% reduction. When the phytase diet and 0.75% AlCl3 additions were used in combination, relative NH3 losses were reduced (P < 0.05) by 60% compared with pens of pigs fed the control diet without AlCl3. Decreases in manure pH were likely responsible for the observed reduction in NH3 losses. Multiple regression was performed with relative rates of NH3 losses as the dependent variable and rate of AlCl3 addition, diet, and manure pH as independent variables. The model was tested using a stepwise regression (P < 0.001), and results indicated that the most important factors determining NH3 losses were manure pH and diet. However, the contribution of AlCl3 cannot be discounted. When manure pH was regressed against AlCl3 and dietary phytase, AlCl3 levels accounted for 64% of the variation in manure pH (P < 0.001). Dietary manipulation with phytase and application of AlCl3 to manure are promising management practices for the reduction of NH3 from swine facilities.

Estimating Mean Willingness To Pay From Dichotomous Choice Contingent Valuation Studies

Methods for estimating mean willingness to pay for some environmental goal are reviewed. Logistic regression analysis of data from dichotomous choice contingent valuation studies often models the willingness-to-pay curve poorly. We develop solutions to this problem. We also show how to model responses as a function of several covariates, and how to model the case in which a proportion of respondents is not willing to pay anything. Analytic and bootstrap methods for quantifying precision are developed. We illustrate the methods by using an example in which biodiversity losses due to acid rain deposition in Scotland are valued.

A CONTINGENT VALUATION STUDY OF UNCERTAIN ENVIRONMENTAL GAINS

AbstractAcid deposition in a present and future cause of biodiversity losses in vulnerable upland areas of Scotland important for nature conservation. However, the exact nature of damages under the status quo, and both the timing and extent of recovery of upland ecosystems if deposition is reduced, are subject to uncertainty. this uncertainty complicates damages cost estimation. In this paper, we have explored the use of CVM to measure the willingness to pay (WTP) of the Scottish population for uncertain recovery/damage scenarios from reduced acid rain deposition. An optimally‐designed referendum format was used utilising the distribution of open‐ended bids from a pilot study to determine bid amounts and sampling size for each bid amount. Eight explanatory variables, including future damage level were selected in a non‐linear step‐wise regression analysis. Average household WTP for abatement of acid rain was £247 and £351 per year when faced with low and high future damage levels respectively. Recovery level and recovery time did not significantly influence WTP. When faced with risky outcomes regarding future damage and recovery level, respondent were found to be risk averse to both environmental gains and losses.

Acidification, Buffering, and Salt Effects in the Unsaturated Zone of a Sandy Aquifer, Klosterhede, Denmark

Acidification of groundwater in a noncalcareous sandy aquifer at Klosterhede, Denmark, is the result of acid rain deposition. In the 4‐ to 5‐m‐thick unsaturated zone the pH ranges from 4.2 to 4.9 with Al concentrations of up to 0.8 mmol L−1. The groundwater at the top of the saturated zone still has a pH below 5. Deposition of sea salt affects the solute profiles, and its importance varies both spatially from the forest margin to the inner part of the forest and temporally through seasonal variations in infiltration and dry deposition. As a result, pulses of high solute concentrations travel downward through the unsaturated zone. The cation exchange capacity (CEC) of the sediments ranges between 0.2 and 1 meq 100 g−1, and in the acidified zone, base saturation is around 17%. The pore waters are close to equilibrium with gibbsite, supersaturated for kaolinite, and strongly undersaturated for other silicateminerals. Mass balance calculations on increases in dissolved silica over depth suggest that the buffering effect of silicate weathering is small. Buffering processes and solute transport were modeled with the code PHREEQM. Simulation of pre–acid rain weathering indicates that this process operates on a timescale of thousands of years, yielding minimum pH values near 5.2 and a base saturation of greater than 70%. The present leaching of Al3+ rich acid water from the soil yields acidification rates of 7 and 10 cm yr−1 for weathering of a naturally weathered and a pristine profile, respectively. Simulation of infiltration of sea‐salt pulses indicates that the cation distribution quickly becomes attenuated by the exchanger composition. However, due to coupling of gibbsite equilibrium with ion exchange processes, downward traveling pulses with high solute concentrations will cause pH variations throughout the unsaturated zone by precipitation and dissolution of gibbsite. Accordingly, the general acidification pattern at Klosterhede is overprinted by salts effects in a complicated fashion.

CH 4 production, oxidation and emission in a U.K. ombrotrophic peat bog: Influence of SO 42− from acid rain

Factors influencing the rates of production and emission of CH 4, CH 4 oxidation and rates of SO 4 2− reduction, were measured in the peat of an ombrotrophic bog in New Galloway, Scotland. Vertical concentration profiles of CH 4 and O 2 showed that the water table essentially represented the oxic-anoxic boundary in the peat. This boundary was usually at the surface in the case of peat-bog hollows, but up to 20 cm of oxic peat occurred above the water table in peat-bog hummocks. Penetration of O 2 into the peat increased under illumination when photosynthesis was active, but decreased in the dark. Emission of CH 4 from the peat surface was faster from peat-bog hollows than from hummocks, where most CH 4 was reoxidized before emission. CH 4 emission rates also varied seasonally, being greatest during summer. For most of the year the amount of organic C oxidized to CO 2 by SO 4 2− reduction by anaerobic bacteria exceeded that being transformed to CH 4 by methanogenic bacteria, except during summer when SO 4 2− reduction became SO 4 2− limited. Laboratory experiments showed that the addition of SO 4 2− to peat inhibited CH 4 formation, confirming that there was competitive inhibition of CH 4 formation by active SO 4 2− reduction, as demonstrated in other environments. The degree of acid rain deposition of SO 4 2− onto peat bogs may therefore be extremely important in regulating the production and emission of CH 4 from peat. CH 4 formation was most active in the strata of peat 5–15 cm below the water table, although actual rates of CH 4 formation were slower in the peat beneath hummocks than that below hollows. In contrast, CH 4 oxidation occurred nearer the peat surface (only 3–7 cm below the water table) where the methanotrophic bacteria could intercept vertically migrating CH 4. Surprisingly, the peak for CH 4 oxidation potential occurred at about 5 cm below the water table, in peat which was apparently anoxic. This may reflect either a transiently oxic peat environment, in which aerobic CH 4-oxidizing bacteria persisted, or the presence of a community of facultatively anaerobic CH 4-oxidizing bacteria which, in anoxic conditions, metabolized substrates other than CH 4. There was no evidence of anaerobic CH 4 oxidation.

Influence of acid rain and ozone on soil heavy metals under loblolly pine trees: A field study

A field growth chamber study was conducted to determine the effects of ozone and simulated acid rain (SAR) on soil heavy metals. Loblolly pine (Pinus taeda L.), grown in open-top chambers, was exposed to three concentrations of ozone (charcoal filtered air with 0.026 µL O3 L-1, and two non-filtered treatments in which ozone concentrations were 0.074 µL L-1 and 0.147 µL L-1, respectively) and two levels of SAR (pH 3.5 and 5.2). Ozone was applied for 12 h d-1 for 9 months and acid rain deposition was 125 mm event-1. After 9 months exposure, soil pH, organic matter and DTPA-extractable heavy metals (Cd, Pb, Zn, Mn, Fe, Cu) were determined on soil samples collected from exposed chambers at two depths (0–15 cm and 15–30 cm). Simulated acid rain decreased the original soil pH. The concentrations of Cd, Pb and Mn at SAR pH 3.5 were significantly higher than at SAR pH 5.2. Ozone did not affect Zn, Fe and Cu, but a significant interaction between pH and O3 on Mn, Pb and Cd was observed. Due to the poor drainage capacity of this soil, leaching of heavy metals was not observed.