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To evaluate the sustainability of biomass plantations, effects on soil organic carbon (SOC) need to be quantified. Miscanthus × giganteus is increasingly used as a bioenergy plant, and it has been hypothesized that, after conversion from cropland, Miscanthus cropping increases SOC storage, whereas conversion from grassland to Miscanthus provides, on average, no sequestration. All field studies hitherto were carried out on mineral soils with topsoil SOC contents of below 3.3%. Here, we analyze in the temperate zone of Switzerland five sites that have been cultivated with Miscanthus for 19–24 years and of which four sites are higher in topsoil SOC content (4.7%–16.2%) and storage (188–262 t SOC) than any previously studied Miscanthus plantation in Europe. We used the difference in carbon isotopic signature between C4 (Miscanthus) and neighboring plots with C3 vegetation (grassland) to quantify the accumulation of new SOC from Miscanthus down to 0.75 m. Annual C4‐C accumulation rates were 1.66 (standard error ± 0.14) t C4‐C ha−1 year−1 (range: 1.26–2.01) in the upper 0.3 m of soil and 1.96 (±0.18) t C4‐C ha−1 year−1 (1.40–2.38) in 0–0.75 m. Average rates for 0–0.3 m were higher than those of mineral soils (n = 37) published previously (0.96 [±0.10] t C4‐C ha−1 year−1). However, high rates of C4‐C accumulation were also reported previously for some mineral soils. Nevertheless, the one mineral soil in our study did not reveal a systematically different accumulation of Miscanthus‐derived carbon compared with the four carbon‐rich soils. We therefore conclude that soils rich in organic matter do not show a different C4‐C accumulation pattern as compared with mineral soils. However, their C4‐C accumulation rates are at the upper end of the data ensemble. Our results further underpin that conversion to Miscanthus, despite C4‐C accumulation, provides no means to increase soil carbon stocks relative to grassland management.

Understanding the sorption kinetics of Hg2+ is the key to predicting its reactivity in soils which is indispensable for environmental risk assessment. The temporal change in the solubility of 196Hg2+ spikes (6 mg kg−1) added to a range of soils with different properties was investigated and modelled. The sorption of 196Hg2+ displayed a biphasic pattern with a rapid initial (short-term) phase followed by a slower (time-dependent) one. The overall reaction rate constants ranged from 0.003 to 4.9 h−1 and were significantly correlated (r = 0.94) to soil organic carbon (SOC). Elovich and Spherical Diffusion expressions compellingly fitted the observed 196Hg2+ sorption kinetics highlighting their flexibility to describe reactions occurring over multiple phases and wide timeframes. A parameterized Elovich model from soil variables indicated that the short-term sorption is solely controlled by SOC while the time-dependent sorption appeared independent of SOC and decreased at higher pH values and Al(OH)3 and MnO2 concentrations. This is consistent with a rapid chemical reaction of Hg2+ with soil organic matter (SOM) which is followed by a noticeably slower phase likely occurring through physical pathways e.g. pore diffusion of Hg2+ into spherical soil aggregates and progressive incorporation of soluble organic-Hg into solid phase. The model lines predicted that in soils with >4% SOC, Hg2+ is removed from soil solution over seconds to minutes; however, in soils with

From a carbon sequestration perspective, peatland restoration projects could be considered successful when net primary productivity exceeds decomposition, resulting in net peat growth in the ecosystem. To demonstrate the effectiveness of peatland restoration projects with a carbon storage aim, analytical techniques are needed that can distinguish between natural/restored ecosystems undergoing (or transitioning to) net peat growth and degraded ecosystems experiencing increased rates of aerobic decomposition (carbon loss). Molecular analysis techniques able to relate changes in organic matter (OM) chemical composition to changes in degradation status occurring on the mechanistic level are especially needed.This study combined a molecular biomarker and chemical compound class approach to conduct a depth-based molecular comparison of natural (ON) and drained (OD) ombrotrophic peatland sites in Lakkasuo Finland. To explore how changes in hydrology impacted peat OM chemical composition, the relative abundance of various molecular biomarkers (Sphagnum marker p-isopropenylphenol, lignin vascular plant markers) and chemical compound classes (phenolics, polysaccharides, aromatics, N-containing compounds, lipids) was determined with depth from three replicate cores per site using pyrolysis gas chromatography tandem mass spectrometry (Py-GCMS). Py-GCMS results were compared with onsite vegetative assemblages and bulk elemental analysis conducted on the same cores. ON and OD were matched by age using radiocarbon dating at three depths per core.For OD relative to ON, significant reductions in average relative percent abundance were observed for p-isopropenylphenol, phenolics and polysaccharides, and corresponding increases in abundance were observed for lignin, aromatics, N-containing compounds, and lipid sterols. Differences in compound classes between sites were greatest in the drainage-affected upper acrotelm, and diminished with depth. Samples consistently below the depth of the water table (>20 cm) followed similar trends in both ON and OD, suggesting that deeper horizons remained unaffected by the onsite drainage activities. An increasing trend in the relative abundance of lignin-derived compounds was observed with depth - particularly in ON. As the plant macrofossil assessment did not suggest previous dominance of vascular plants, this trend was considered evidence for preservation of lignin in anaerobic conditions in organic soils. Overall, these findings indicate that differences in chemical composition between the two sites can be directly correlated to OM transformation occurring on a mechanistic level, and that observed shifts in chemical composition reflect the effect of altered hydrology in peatland ecosystems.

Constructed wetlands (CWs) are engineered systems for treating wastewater by sequestering nutrients and contaminants. Our aim was to assess the main phosphorus (P) binding states in operating CWs to assess P saturation and indications on P recycling potential of filter materials, which might be necessary under future peak P scenarios. The investigated vertical flow CWs (operation time up to 16 years) are based on either fluviatile (Fluv) sand or zeolite‐ (Ze‐LS) and clinopyroxene (Cl‐LS)‐dominated lava sand. Organic and inorganic P accumulated in all CWs independent of filter materials and showed a considerable increase with operation time. Concentrations of P decreased sharply with depth in the Fluv‐CWs compared to only a slight decrease in the lava sand CWs, with P concentrations of deeper horizons approximating the relatively P enriched original lava sand substrates. Orthophosphate was the dominant pool in all CWs, while the sum of organic fractions ranged between 11% and 33%. Sequential extraction indicated that P was mainly associated with Fe and Al (hydr)oxides for Fluv‐CWs and Ze‐LS‐CWs, while Ca and Mg bound mineral phosphates dominated in Cl‐LS‐CWs. Oxalate extractions pointed to a clear dominance of P fractions associated with poorly crystalline Fe‐ and Al‐(oxy)hydroxides. Solution 31P NMR analyses revealed that inositol hexakisphosphates were a major pool of organic P in surface layers of CWs, which increased with operation time. With a maximum of 0.5% P content, filter sands do not appear to be a suitable fertilizer for direct application to agricultural fields. The dominance of inorganic, poorly crystalline P species point to potentially high desorption capacity which might be investigated further, to assess recycling potential of P or usage of filter materials as soil amendments with relatively high plant available P. The latter might become feasible and economically attractive under future P scarcity. Simultaneously, P saturation indexes (DPS) did not indicate an imminent P saturation of filters, since P accumulation was not restricted by binding to Al and Fe minerals., Hydrological Processes, 35 (2), ISSN:0885-6087, ISSN:1099-1085

Drainage for agriculture has turned peatlands from a net sink to a net source of carbon (C). In order to reduce the environmental footprint of agricultural peatland drainage, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland. To explore the effect of mineral soil coverage on soil C loss and the source of CO2 from peatland drained for agriculture, we utilized the radiocarbon signature (F14C) of soil C and emitted CO2 in the field. The experiment, located in the Swiss Rhine Valley, was carried out on two adjacent drained organic soils, either without mineral soil cover (reference 'Ref'), or covered with mineral soil (thickness ~ 40 cm) (coverage 'Cov') 13 years ago. Drainage already commenced 130 years ago and the site was managed as meadow since the 1970ies. Drainage induced 41-75 kg C m-2 loss, which is equivalent to annual C loss rates of 0.49-0.58 kg C m-2 yr-1 and 0.31-0.63 kg C m-2 yr-1 for Cov and Ref, respectively. Mineral soil coverage had no significant effect on the amount of heterotrophic respiration, however, at Cov, the radiocarbon signature of heterotrophic CO2 was significantly (p

Soil phosphorus (P) loss from agricultural systems will limit food and feed production in the future. Here, we combine spatially distributed global soil erosion estimates (only considering sheet and rill erosion by water) with spatially distributed global P content for cropland soils to assess global soil P loss. The world’s soils are currently being depleted in P in spite of high chemical fertilizer input. Africa (not being able to afford the high costs of chemical fertilizer) as well as South America (due to non-efficient organic P management) and Eastern Europe (for a combination of the two previous reasons) have the highest P depletion rates. In a future world, with an assumed absolute shortage of mineral P fertilizer, agricultural soils worldwide will be depleted by between 4–19 kg ha−1 yr−1, with average losses of P due to erosion by water contributing over 50% of total P losses., Phosphorus is an essential nutrient critical for agriculture, but because it is non-renewable its future availability is threatened. Here the authors show that across the globe most nations have net losses of phosphorus, with soil erosion as the major route of loss in Europe, Africa and South America.

10 páginas. 1 figuras.- 2 tablas.- 134 referencias., To track changes in organic matter (OM) in peat soils, analytical techniques are needed that effectively characterize their chemical components. Pyrolysis-gas chromatography/mass spectrometry is a useful method for obtaining a chemical "fingerprint" of OM. To obtain representative fingerprints, the pyrolysis process should be highly reproducible and representative of the original sample; however, these key indicators for successful volatilization are underreported in the literature. We investigated the influence of instrumental parameters (temperatures, heating rates, sample mass), original organic C and nitrogen (N) content, and instrument type ("slow" vs "flash"), on volatilization of different peat samples by monitoring sample mass loss and changes in organic C and N content before and after pyrolysis. Average percent C by mass volatilized ("C pyrolysis efficiency") across all pyrolysis experiments conducted (mass, instrument types, and settings) was 47.8 +/- 1.8%. Sample mass was not a major driver; however, instrument temperatures, heating rate, and original N content had a significant influence on pyrolysis efficiency. N pyrolysis efficiency occurred at significantly higher rates (56.7-75.8%) than C pyrolysis efficiency (45.1-51.6%). N pyrolysis efficiency was also negatively influenced by decreasing concentrations of original sample N, suggesting that N-containing compounds may undergo preferential volatilization in high pyrolysis temperatures. Our data suggest that C pyrolysis efficiency is relatively insensitive to instrumental parameters; whereas when seeking to identify N-containing compounds, appropriate temperatures and heating rates must be chosen. These results provide an expected range for pyrolysis efficiency as a reference for peat samples analyzed with this technique., This work was supported by the Consejo Superior de Investigaciones Científicas [RYC2014-16338]; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung [200021_169556].

Application of compound-specific isotope analysis (CSIA) in sediment fingerprinting source apportionment studies is becoming more frequent, as it can potentially provide robust land-use-based source attribution of suspended sediments in freshwater and marine systems. Isotopic tracers such as δ13C values of vegetation-derived organic compounds are considered to be suitable for the CSIA-based fingerprinting method. However, a rigorous evaluation of tracer conservativeness in terms of the stability of isotopic signature during detachment and transport of soil during erosion is essential for the suitability of the method. With the aim to identify potential fractionation and shifts in tracer signature during early degradation of organic matter in surface soils, we measured concentrations and δ13C values of long-chain fatty acids and n-alkanes from fresh plant biomass (as vegetation is a direct source of these compounds to the soils), degraded organic horizon (O horizon), and mineral soil (A horizon) from various forest types with different humus forms (five sites). The bulk δ13C values showed continuous 13C enrichment through the degradation stages from fresh plant material to the O and A horizons, ranging between 3.5 ‰ and 5.6 ‰. Compound-specific δ13C values showed a general 13C enrichment for both long-chain fatty acids (up to 5 ‰) and n-alkanes (up to 3.9 ‰) from fresh plant biomass to the O horizon overlying the A horizon. However, only slight or no further changes occurred from the O to the A horizon. We also compared compound-specific δ13C values between two soil particle size classes ( mm and  µm) from four sites and found no significant differences of tracer values between them, with even less fractionation for the long-chain n-alkanes within the soil particle fractions. This points to the conclusion that sampling and analysing bulk soil material might be valid for the isotopic tracer applications. We further conclude that our results support the suitability of studied isotopic tracers as a representative source soil signature in the CSIA-based sediment source attribution, as they demonstrated necessary stability in the plant–soil system during organic matter degradation.

Global nuclear weapon testing and the Chernobyl accident have released large amounts of radionuclides into the environment. However, to date, the spatial patterns of these fallout sources remain poorly constrained. Fallout radionuclides (137Cs, 239Pu, 240Pu) were measured in soil samples (n = 160) collected at flat, undisturbed grasslands in Western Europe in the framework of a harmonised European soil survey. We show that both fallout sources left a specific radionuclide imprint in European soils. Accordingly, we used plutonium to quantify contributions of global versus Chernobyl fallout to 137Cs found in European soils. Spatial prediction models allowed for a first assessment of the global versus Chernobyl fallout pattern across national boundaries. Understanding the magnitude of these fallout sources is crucial not only to establish a baseline in case of future radionuclide fallout but also to define a baseline for geomorphological reconstructions of soil redistribution due to soil erosion processes.

Ongoing peatland degradation calls for an efficient method to indicate peatland hydrology and the success of restoration effort. In previous studies we found specific depth patterns of 13C and 15N depending on peatland hydrology (drained, rewetted or natural), but were unable to find an explanation of these patterns. As degradation is mostly connected to drainage we assumed an increase of microbial activity. This microbial activity should then be imprinted in stable isotope signatures (15N, 13C) due to differences in microorganism communities, their metabolic pathways and nutrient sources. We aimed to find a link between our investigated isotope depth patterns to microbial community composition. Therefore, we conducted a phospholipid fatty acid (PLFAs) analysis. As a marker for bacteria we used PLFAs i-C15:0 and a-C-15:0 as well as the C18:2,9c as a marker for fungi. We studied two nutrient poor peatlands in Northern Europe: Lakkasuo (Central Finland) and Degerö Stormyr (Northern Sweden). At all locations cores were taken from adjacent drained (or rewetted) and natural sites. At Lakkasuo drained site, we found a high humification index (HI, after van Post), shown by less plant residuals and a high amount of matrix. For Degerö Stormyr the picture looks different. Above the drained horizon (high HI) peat was light, with a smaller amount of matrix and lots of plant residuals (low HI), like it was also seen in the natural cores. At the drained (and rewetted) sites we found distinct peaks in microbial PLFA concentrations, which correlate to the stable isotope peaks ("turning point”) we found before. At the 15N turning point, in the center of the drained horizon, overall microbial-derived PLFA abundance is also the highest. Furthermore, the overall microbial-derived PLFA abundance is positively correlated with 15N values (r2=0.5). Fungi-derived PLFAs are negatively correlated (r2=0.4) to 13C. Fungi-derived PLFAs showed the highest amount at the uppermost part of the drained horizon and low amounts in the waterlogged conditions below the drained horizon, whereas 13C showed lowest values at the surface and high values below the drained horizon. Our results suggest, that fungi dominate microbial metabolism in the upper, aerobic peat horizon. Downwards the drained horizon conditions slowly switch to oxygen limitation. Thus, fungal-derived PLFAs decrease whereas bacterial-derived PLFAs are increasing. The highest diversity of microbial-derived PLFAs is indicated by the 15N turning point. Below this point, oxygen is increasingly limited and concentrations of all microbial-derived PLFAs are decreasing down to the 13C turning point and the onset of the permanently waterlogged, anaerobic horizon. Cores from rewetted peatlands show no depth trend of 15N values above the formerly drained horizon and a low amount of microbial-derived PLFAs. Hence, we conclude that stable isotope values reflect microbial metabolism processes, which differ between drained, rewetted and natural peatlands. Additionally, stable isotope patterns reflect a switch in the predominant communities from fungi to bacteria within a drained horizon. Summing up, the PLFA analysis approved that stable isotope measurements can serve as a cost and work efficient monitoring tool for peatland history as well as peatland restoration success.

Peatlands are a major source of methylmercury that contaminates downstream aquatic food webs. The large store of mercury (Hg) in peatlands could be a source of Hg for over a century even if deposition is dramatically reduced. However, the reliability of Hg mass balances can be questioned due to missing long-term land-atmosphere flux measurements. We used a novel micrometeorological system for continuous measurement of Hg peatland-atmosphere exchange to derive the first annual Hg budget for a peatland. The evasion of Hg (9.4 µg m−2 yr−1) over the course of a year was seven times greater than stream Hg export, and over two times greater than wet bulk deposition to the boreal peatland. Measurements of dissolved gaseous Hg in the peat pore water also indicate Hg evasion. The net efflux may result from recent declines in atmospheric Hg concentrations that have turned the peatland from a net sink into a source of atmospheric Hg. This net Hg loss suggests that open boreal peatlands and downstream ecosystems can recover more rapidly from past atmospheric Hg deposition than previously assumed. This has important implications for future levels of methylmercury in boreal freshwater fish and the estimation of historical Hg accumulation rates from peat profiles.

Pyrogenic carbon (PyC) derives from incomplete combustion of organic matter and is ubiquitous in terrestrial and aquatic systems. Most PyC is inherently more stable against decomposition than plant residues, and PyC therefore forms an important component of the global carbon (C) cycle. During the Holocene, about 436 Pg organic C accumulated in northern peatlands, and we hypothesize that PyC may contribute substantially to that C stock. We studied 70 samples from 19 intact and degraded European peatland sites and analyzed their PyC content by 13C nuclear magnetic resonance spectroscopy and molecular modeling and peat age and accumulation by radiocarbon dating. Classification of a peatland as either intact or degraded was based on the comparison between apparent and expected long-term C accumulation rates. On average, PyC amounted for 13·5% of soil C across sites, and accounted for up to 50% at single sites. The amount of PyC increased significantly with peat age. Degraded peatlands had lost approximately 56 kg C m�2, half of their former C stock. However, degraded peat had higher PyC contents than intact one. Selective enrichment of PyC during both peat build-up and decomposition seems to be an important factor fostering PyC accumulation. Assignment of our results to peatlands of the northern hemisphere, stratified by age, revealed an estimated PyC stock of 62 (±22) Pg. Our estimate indicates a substantial and hitherto unquantified contribution of northern peatlands to global PyC storage. © 2017 The Authors. Land Degradation & Development Published by John Wiley & Sons Ltd.

The Minamata Convention entered into force in 2017 with the aim to phase-out the use of mercury (Hg) in manufacturing processes such as the chlor-alkali or vinyl chloride monomer production. However, past industrial use of Hg had already resulted in extensive soil pollution, which poses a potential environmental threat. We investigated the emission of gaseous elemental mercury (Hg0) from Hg polluted soils in settlement areas in the canton of Valais, Switzerland, and its impact on local air Hg concentrations. Most soil Hg was found as soil matrix-bound divalent Hg (HgII). Elemental mercury (Hg0) was undetectable in soils, yet we observed substantial Hg0 emission (20–1392 ng m−2 h−1) from 27 soil plots contaminated with Hg (0.2–390 mg Hg kg−1). The emissions of Hg0 were calculated for 1274 parcels covering an area of 8.6 km2 of which 12% exceeded the Swiss soil remediation threshold of 2 mg Hg kg−1. The annual Hg0 emission from this area was approximately 6 kg a−1, which is almost 1% of the total atmospheric Hg emissions in Switzerland based on emission inventory estimates. Our results show a higher abundance of Hg resistance genes (merA) in soil microbial communities with increasing soil Hg concentrations, indicating that biotic reduction of HgII is likely an important pathway to form volatile Hg0 in these soils. The total soil Hg pool in the top 20 cm of the investigated area was 4288 kg; hence, if not remediated, these contaminated soils remain a long-term source of atmospheric Hg, which is prone to long-range atmospheric transport.

The agricultural use of peatlands usually requires drainage, thereby transforming these organic soils from a net carbon sink into a net source. The Seeland region of Switzerland is characterised by fens that have been intensively used for agriculture for 150 years. Our site is a degraded fen with a remaining peat layer of 60 cm that had been used as cropland until 2009. In connection to a nature protection project it has been managed as extensive permanent grassland since then. The net ecosystem carbon balance (NECB) was determined for two years (2015-2016). For this purpose, the net ecosystem exchange of CO2 (NEE) and CH4 fluxes were measured by eddy covariance, and the carbon removed by harvest was quantified. Our degraded fen site was found to be a net carbon source of 477±73g C m−2 yr -1 and 434±51 g C m-2 yr−1 in 2015 and 2016, respectively. Annual CH4 emissions were marginal in both years with 0.4±0.8 g CH4-C m−2 yr -1 (2015) and 0.7±0.7 g CH4-C m−2 yr -1 (2016). In contrast to NECB, the NEE was considerably higher in 2015 than in 2016 (308±71 g C m−2 yr -1 vs 117±39 g C m−2 yr -1). The year 2015 was characterised by partial flooding of the grassland, followed by a dry and hot summer leading to lower CO2 uptake due to reduced growth, which was reflected in lower harvest compared to 2016. Thus, the short-term plant-induced carbon fluxes were altered, whereas total soil carbon loss remained rather constant. This was verified by an intra site comparison between the flooded and non-flooded part in 2015. Our results indicate that the soil carbon loss of this highly degraded peatland with a shallow peat layer is relatively moderate and hardly influenced by interannual weather variations.

The reversal of freshwater acidification in the low mountain ranges of Germany is of public, political and scientific concern, because these regions are near natural ecosystems and function as an important drinking water supply. The aim of this study was to evaluate the status and trends of acidification reversal after two decades of reduced anthropogenic deposition in selected freshwaters of the low mountain ranges in the Harz, the Fichtelgebirge, the Bavarian Forest, the Spessart and the Black Forest. In response to decreased sulphate deposition, seven out of nine streams investigated had significantly decreasing sulphate concentrations (all trends were calculated with the Seasonal Kendall Test). The decrease in sulphate concentration was only minor, however, due to the release of previously stored soil sulphur. No increase was found in pH and acid neutralising capacity (defined by Reuss and Johnson, 1986). Aluminum concentrations in the streams did not decrease. Thus, no major acidification reversal can currently be noted in spite of two decades of decreased acid deposition. Nevertheless, the first signs of improvement in water quality were detected as there was a decrease in the level and frequency of extreme values of pH, acid neutralising capacity and aluminium concentrations in streams. With respect to nitrogen, no change was determined for either nitrate or ammonium concentrations in precipitation or stream water. Base cation fluxes indicate increasing net loss of base cations from all ecosystems investigated, which could be interpreted as an increase in soil acidification. The latter was due to a combination of continued high anion leaching and significant reduction of base cation deposition. No major improvement was noted in biological recovery, however, initial signs of recovery were detectable as there was re-occurrence of some single macroinvertebrate species which were formerly extinct. The results of this study have important implications for water authorities, forest managers and policy makers: the delay in acidification reversal suggests a need for ongoing intensive amelioration of waters, a careful selection of management tools to guarantee sustainable management of forests and the reduction of nitrogen deposition to prevent further acidification of soils and waters. Keywords: freshwater, acidification reversal, drinking water supply, forested catchments, Germany

Following the decline in sulphur deposition in Europe, sulphate dynamics of catchments and the reversibility of anthropogenic acidification of soils and freshwaters became of major interest. Long-term trends in sulphate concentrations and fluxes in precipitation/throughfall and freshwaters of 20 European catchments were analysed to evaluate catchment response to decreasing sulphate deposition. Sulphate deposition in the catchments studied declined by 38-82% during the last decade. Sulphate concentrations in all freshwaters decreased significantly, but acidification reversal was clearly delayed in the German streams. In Scandinavian streams and Czech/Slovakian lakes sulphate concentrations responded quickly to decreased input. Sulphate fluxes in run-off showed no clear trend in Germany and Italy but decreased in Scandinavia, the Czech Republic and Slovakia. The decrease, however, was less than the decline in input fluxes. While long-term sulphate output fluxes from catchments were generally correlated to input fluxes, most catchments started a net release of sulphate during the early 1990s. Release of stored sulphate leads to a delay of acidification reversal and can be caused by four major processes. Desorption and excess mineralisation were regarded as the most important for the catchments investigated, while oxidation and weathering were of lesser importance for the long-term release of sulphate. Input from weathering has to be considered for the Italian catchments. Sulphate fluxes in German catchments, with deeply weathered soils and high soil storage capacity, responded more slowly to decreased deposition than catchments in Scandinavia and the Czech Republic/Slovakia, which have thin soils and relatively small sulphate storage. For predictions of acidification reversal, soil characteristics, sulphur pools and their dynamics have to be evaluated in future research. Keywords: acidification reversal, sulphur, sulphate release, Europe, catchments, deposition, lake, stream

The fate of anthropogenic emissions of mercury (Hg) to the atmosphere is influenced by the exchange of elemental Hg with the earth surface. This exchange holds the key to a better understanding of Hg cycling from local to global scales, which has been difficult to quantify. To advance research about land–atmosphere Hg interactions, we developed a dual-inlet, single detector relaxed eddy accumulation (REA) system. REA is an established technique for measuring turbulent fluxes of trace gases and aerosol particles in the atmospheric surface layer. Accurate determination of gaseous elemental mercury (GEM) fluxes has proven difficult due to technical challenges presented by extremely small concentration differences (typically

The accurate estimation of soil mercury lability is crucial for risk assessment. In comparison to chemical fractionation and speciation, isotopic dilution (ID) offers precise definition of labile mercury fractions while maintaining the natural equilibrium. We developed and applied an ID protocol with Hg-199 to estimate the soil mercury (Hg) isotopically exchangeable (labile) pool or HgE using a range of industrially contaminated soils in Switzerland. The measured HgE values were consistent for the same soil against different spike levels (50, 100, and 200% of native Hg-199), indicating that the spiked and soil isotopes achieved required dynamic equilibrium at the soil-water interface. Total soil Hg (THg; mg kg(-1)) was the best predictor of HgE (mg kg(-1)) and %HgE and accounted for 96 and 63% of the variance, respectively. Nonetheless, despite the wide range of THg values (0.37-310 mg kg(-1)) in the studied soils, Hg lability spanned a narrow range (similar to 12-25% of THg), highlighting the large capacity of soils to sequester Hg in a very stable form. The "exchangeable pool" of Hg extracted by CH3COONH4 and MgCl2 (

This study highlights the accumulation and speciation of vanadium in Chinese cabbage (Brassica rapa L.) in relation to the speciation of soil vanadium with pot experiments at 122-622mgVkg(-1) by spiking NH4VO3. Cabbage planting decreased the bioavailable and residual vanadium based on sequential extraction, leading to enrichment of oxalate-extractable vanadium in soils. The biomass production increased with increasing concentrations of soil vanadium from 122 to 372mgVkg(-1), probably due to the increasing nitrogen availability and low vanadium availability in our soils with a consequent low vanadium toxicity. Although the concentrations of root vanadium (14.4-24.9mgVkg(-1)) related positively with soil vanadium, the bio-dilution alleviated the increase of leaf vanadium (2.1-2.7mgVkg(-1)). The predominance of vanadium(IV) in leaves (∼60-80% of total vanadium) indicates bio-reduction of vanadium in Chinese cabbage, since the mobile vanadium in oxic soils was usually pentavalent. Approximately 15-20% of the leaf vanadium was associated with recalcitrant leaf tissues. The majority of leaf vanadium was water and ethanol extractable, which is considered mobile and may cause more toxic effects on Chinese cabbage.

We investigated the evasion of TGM (total gaseous mercury) from experimental plots on a boreal peatland that had been exposed for 15 years to different combinations of atmospheric sulfur (S) and nitrogen (N) deposition as well as greenhouse treatments simulating climate change. Shaded dynamic flux chamber measurements during the summer in 2009 showed emission of TGM to the atmosphere from most of the treated plots (0.7 ± 0.94 ng m–2 h–1). However, TGM exchange rates were significantly lower, occasionally indicating Hg uptake, on plots subjected to S addition at rates of 20 kg ha–1 year–1. Enhanced nitrogen deposition and greenhouse treatment had no significant effect on TGM fluxes. We hypothesize that the lower Hg evasion from the sulfur-treated plots is related to either earlier Hg evasion or Hg binding to S in organic matter, making Hg less susceptible to volatilization and more prone to transport in runoff.

Soil erosion can alter the storage of carbon (C) and other biogeochemical properties in both eroding and depositional soils. Little is yet known about soil microbial responses to erosion-induced changes in the quantity and quality of organic matter in mountain grasslands. To examine biogeochemical and microbiological responses to soil erosion, we compared the concentrations and stable isotope ratios of C and N, and microbial properties in eroding upslope (oxic), and depositional downslope (oxic) and wetland soils among three grasslands in the Swiss Alps. Compared to the reference site (Moos), the eroding upslope soils (Laui and Bielen) tended to have lower N concentrations and δ15N. The depositional wetland soils had higher δ13C and lower δ15N and C and N concentrations compared to the reference wetland, reflecting the influence of dry, oxic soils from eroding slopes. The depositional wetland soils had lower water-extractable organic C (WEOC) concentrations and optical intensities (UV absorbance and humic- and protein-like fluorescence) compared to the reference wetland. The activity of soil enzymes was positively related to most of the measured parameters indicative of organic matter quantity (e.g., %C and %N) and quality (e.g., WEOC and protein-like fluorescence), exhibiting significantly lower values in the sheet erosion-affected wetland (Bielen) than at the other sites. 16S rRNA gene copy numbers in the wetland were smaller than in the upland soil at all sites and greatest at Laui among three sites, indicating a potential alteration of the microbial community by the deposited oxic soils and attached microbial cells. The results suggest that soils deposited from the eroding slopes can slow down organic matter decomposition in the depositional wetland soils through decreases in the availability of labile organic matter and enzyme activity. Further research is required to elucidate erosion-induced changes in the activity and abundance of wetland microbial communities.

Since decades, drop-freezing instruments have contributed to a better understanding of biological ice nucleation and its likely implications on cloud and precipitation development. Yet, current instruments have limitations. Drops analysed on a cold stage are subject to evaporation and potential contamination. The use of closed tubes provides a partial solution to these problems, but freezing events are still difficult to be clearly detected. Here, we present a new apparatus where freezing in closed tubes is detected automatically by a change in light transmission upon ice development, caused by the formation of air bubbles and crystal facets that scatter light. Risks of contamination and introduction of biases linked to detecting the freezing temperature of a sample are then minimized. To illustrate the performance of the new apparatus we show initial results of two assays with snow samples. In one, we repeatedly analysed the sample (208 tubes) over the course of a month with storage at +4 °C, during which evidence for biological ice nucleation activity emerged through an increase in the number of ice nucleators active around −4 °C. In the second assay, we indicate the possibility to increasingly isolate a single ice nucleator from a precipitation sample, potentially determining the nature of a particle responsible for a nucleation activity measured directly in the sample. These two seminal approaches highlight the relevance of this handy apparatus to provide new points of view in biological ice nucleation research.

This study combines two unprecedentedly high resolution (250 × 250 m) maps of soil erosion (inter-rill and rill processes) and soil organic carbon to calculate a global estimate of erosion-induced organic carbon (C) displacement. The results indicate a gross C displacement by soil erosion of 2.5-0.3+0.5 Pg C/year. The greatest share of displaced C (64%) comes from seminatural lands and forests. This suggests that lateral C transfer from erosion in noncroplands may play a more important role than previously assumed.

RATIONALE Natural abundance δ15N values in soil samples analysed by isotope ratio mass spectrometry (IRMS) are often used to confirm a perturbation after it has been indicated by other parameters. We propose a concept of how δ15N values may a priori indicate a perturbation. METHODS We analysed the δ15N values and C:N ratios of 102 soil samples from five regions in northern Eurasia by using an elemental analyser coupled to an isotope ratio mass spectrometer. RESULTS Unperturbed samples ranged in δ15N values from –4.8 to 9.7 ‰ and in C:N ratio from 6.4 to 48.1. The δ15N values were linearly proportional to the inverse of the square root of the C:N ratio (R2 = 0.79). At any particular C:N ratio, 94 % of the δ15N values of the unperturbed samples were within ±2.4 ‰, but 72 % of perturbed samples had values outside this range. CONCLUSIONS The δ15N natural abundance values, when related to the C:N ratios, may readily indicate perturbation of soil N cycling prior to other, more demanding investigations into related processes and extend the current use of IRMS in ecosystem research. Copyright © 2013 John Wiley & Sons, Ltd.

The impact of fire on the nitrogen (N) cycle of natural ecosystems is arguable. Here we report and interpret an observation from boreal ecosystems in the Lena River basin, Sakha Republic (Yakutia), Russian Federation. Different types of permafrost soil (0–30 cm depth) were sampled along transects (60–150 m length) from the forest edge towards the centre of four separate thermokarst depressions under grassland. The average values of δ15N were remarkably similar within three transects, but differed systematically between them. Three findings point towards fire being the cause of the observed pattern. First, the spatial extent of systematic differences in soil δ15N coincides with the extent of typical fire scars in the region. Second, soil enrichment in 15N is larger in the proximity of settlements, where fire is generally more frequent than in more remote places. Third, there is a significant positive correlation between δ15N values and the ratio of black C to total N. These findings point towards fire having a marked impact on soil δ15N and, accordingly, on the N cycle of this cold and dry ecosystem. Copyright © 2011 John Wiley & Sons, Ltd.

This study aimed to gain insight into the generation and fate of dissolved organic carbon (DOC) in organic layers. In a Free Air CO2 Enrichment Experiment at the alpine treeline, we estimated the contribution of C-13-depleted recent plant C to DOC of mor-type organic layers. In an additional laboratory soil column study with 40 leaching cycles, we traced the fate of C-13-labelled litter-DOC (22 and 45 mg l(-1)) in intact Oa horizons at 2 and 15 degrees C. Results of the field study showed that DOC in the Oa horizon at 5 cm depth contained only 20 +/- 3% of less than six-year-old C, indicating minor contributions of throughfall, root exudates, and fresh litter to leached DOC. In the soil column experiment, there was a sustained DOC leaching from native soil organic matter. Less than 10% of totally added litter-DOC was leached despite a rapid breakthrough of a bromide tracer (50 +/- 7% within two days). Biodegradation contributed only partly to the DOC removal with 18-30% of added litter-DOC being mineralized in the Oa horizons at 2 and 15 degrees C, respectively. This was substantially less than the potential 70%-biodegradability of the litter-DOC itself, which indicates a stabilization of litter-DOC in the Oa horizon. In summary, our results give evidence on an apparent 'exchange' of DOC in thick organic layers with litter-DOC being retained and 'replaced' by 'older' DOC leached from the large pool of indigenous soil organic matter. (C) 2009 Elsevier Ltd. All rights reserved.

Analyses of soil organic carbon (SOC) content and stable carbon isotope signatures (delta C-13) Of Soils were assessed for their suitability to detect early stage soil erosion. We investigated the soils in the alpine Urseren Valley (southern central Switzerland) which are highly impacted by soil erosion. Hill slope transects from uplands (cambisols) to adjacent wetlands (histosols and histic to mollic gleysols) differing in their intensity of visible soil erosion, and reference wetlands without erosion influence were sampled. Carbon isotopic signature and SOC content of soil depth profiles were determined. A close correlation of delta C-13 and carbon content (r < 0.80) is found for upland soils not affected by soil erosion, indicating that depth profiles of delta C-13 of these upland soils mainly reflect decomposition of SOC. Long-term disturbance of an upland soil is indicated by decreasing correlation of delta C-13 and SOC W 0.80) which goes in parallel with increasing (visible) damage at the site. Early stage soil erosion in hill slope transects from uplands to adjacent wetlands is documented as an intermediate delta C-13 value (-27.5 parts per thousand) for affected wetland soil horizons (0-12cm) between upland (aerobic metabolism, relatively heavier delta C-13 of -26.6 parts per thousand) and wetland isotopic signatures (anaerobic metabolism, relatively lighter delta C-13 of -28.6 parts per thousand). Carbon isotopic signature and SOC content are found to be sensitive indicators of short- and long-term soil erosion processes. Copyright (C) 2009 John Wiley & Sons, Ltd.

The stable oxygen isotope signature (delta O-18) of soil is expected to be the result of a mixture of components within the soil with varying delta O-18 signatures. Thus, the delta O-18 of soils should provide information about the soil's substrate, especially about the relative contribution of organic matter versus minerals. As there is no standard method available for measuring soil delta O-18, the method for the measurement of single components using a high-temperature conversion elemental analyser (TC/EA) was adapted. We measured in standard materials (IAEA 601, IAEA 602, Merck cellulose) and soils (organic and mineral soils) in order to determine a suitable pyrolysis temperature for soil analysis. We consider a pyrolysis temperature suitable when the yield of signal intensity (intensity of mass 28 per 100 mu g) is at a maximum and the acquired raw delta O-18 signature is constant for the standard materials used and when the quartz signal from the soil is still negligible. After testing several substances within the temperature range of 1075 to 1375 degrees C we decided to use a pyrolysis temperature of 1325 degrees C for further measurements. For the Urseren Valley we have found a sequence of increasing delta O-18 signatures from phyllosilicates to upland soils, wetland soils and vegetation. Our measurements show that the delta O-18 values of upland soil samples differ significantly from wetland soil samples. The latter can be related to the changing mixing ratio of the mineral and organic constituents of the soil. For wetlands affected by soil erosion, we have found intermediate delta O-18 signatures which lie between typical signatures for upland and wetland sites and give evidence for the input of upland soil material through erosion. Copyright (C) 2008 John Wiley & Sons, Ltd.

The exchange of gaseous elemental mercury (GEM) over a sub-alpine grassland in central Switzerland was measured over a full year. Seasonal and diurnal variability were measured with two micrometeorological techniques: the aerodynamic method and the modified Bowen ratio method. With these two methods mean deposition rates of 4.3 and 1.7 ng m - 2 h - 1 were calculated throughout the vegetation period. As no significant GEM exchange occurred under snow covered conditions the mean annual deposition fluxes reached 2.9 and 1.1 ng m - 2 h - 1 , respectively. A fair weather period in October 2005 was selected to specifically study diurnal patterns of GEM exchange. During this time vertical day-time GEM gradients averaged 0.01 ng m - 4 and night-time gradients 0.07 ng m - 4 , but no clear diurnal pattern of the GEM fluxes was observed. The measured gradients were very small, which entailed considerable uncertainties in the calculated GEM fluxes. However, the observed exchange pattern is verified by the agreement of the applied methods regarding the direction of the flux and the pronounced seasonal trends. Complementary measurements of total mercury in precipitation during three rain events revealed that dry deposition of GEM would account for 67% of a total annual input of 0.26 g ha - 1 and would therefore constitute a major deposition pathway.

It is known that in wetland soils and soils contaminated with mercury (Hg), direct biotic reduction of Hg 2+ to Hg° leads to Hg° emissions to the atmosphere. In terrestrial soils, numerous factors have been reported that control Hg0 emissions, but it is still unclear if biotic processes are also important. In this study, microbiological activity of Cambisol monoliths from a subalpine grassland with Hg concentrations of approx. 100 ng g -1 were manipulated in laboratory incubation experiments. Elemental Hg emissions were recorded together with CO 2 emission rates as proxy for microbiological respiration. Emissions of Hg° increased from approx. 5 ng m -2 h -1 up to 130 ng m -2 h -1 with stimulated biological activity (glucose addition, increase in temperature) and decreased with inhibited activity (chloroform fumigation, autoclaving, drying). Similar patterns with evasion rates of >90 ng m -2 h -1 were observed after dried soils were remoistened again. Our results indicated that processes leading to Hg° emissions from uncontaminated terrestrial soils are at least partly controlled by biotic processes. However, it is still uncertain if Hg° emission is caused directly by biotic reduction of Hg 2+ or indirectly by abiotic reduction, induced by products of microbiological degradation, e.g., humic acids.

Life on earth drives a continuous exchange of carbon between soils and the atmosphere. Some forms of soil carbon, or organic matter, are more stable and have a longer residence time in soil than others. Relative differences in stability have often been derived from shifts in δ13C (which is bound to a vegetation change from C3 to C4 type) or through 14C-dating (which is bound to small sample numbers because of high measurement costs). Here, we propose a new concept based on the increase in δ15N and the decrease in C:N ratio with increasing stability. We tested the concept on grasslands at different elevations in the Swiss Alps. Depending on elevation and soil depth, it predicted mineral-associated organic carbon to be 3 to 73 times more stable than particulate organic carbon. Analysis of 14C-ages generally endorsed these predictions.

The impact of 60 a of SO2 emissions from a Ni-Cu plant in the Kola Peninsula (Russia) on soil S contents was assessed in podzols under pine forests. Sulphate desorption and the possible delay of acidification reversal was investigated, because the plant will be reconstructed in 2006 with an expected emission reduction of 90%. Sites were sampled along a pollution gradient in the prevailing wind direction from 1 to 66 km. The investigated podzols stored S mostly in the organic form. The concentrations of total and organic S in soil organic horizons tended to be higher near the smelter but were only weakly correlated with S deposition. No relationship between distance to smelter and S contents was found for the mineral horizons. Sulphate content and desorption behavior were highly variable due to natural variations of texture and extractable Al and Fe contents of the soils. The lack of a clear strong trend with distance from the smelter except in the organic layer indicated that long range transport and diffuse input of SO4 played a major role rather than point source impact. It was concluded that biological turnover is most likely the regulating process in these soils and thus low to medium release of SO4 is expected under decreasing deposition scenarios because organic S was the dominant fraction of total S in all soils. (c) 2007 Elsevier Ltd. All rights reserved.

An attempt is made to synthesize the occurrence of inorganic and organic arsenic compounds and the factors affecting their concentration and speciation during production of wine and beer. The arsenic concentration is generally low in wines and beers (mostly

Biogeochemistry and regulation of redox processes in wetlands and especially their source sink functions regarding sulfur, nitrogen, iron, and alkalinity are still poorly understood and become increasingly important in a world of global change. We investigated three forested wetlands within the Lehstenbach catchment (Fichtelgebirge, Northeastern Bavaria, Germany) differing in their degree of water saturation, vegetation, and availability of iron with stable sulfur analysis as well as geochemical analysis (iron, nitrate, sulfate, and oxygen contents in soil solutions and groundwater). Results indicated considerable nitrate, sulfate, and iron reduction rates bound to high spatial and temporal heterogeneity at all three sites. Sites differed significantly regarding their oxygen saturation and their dynamics of sulfur and iron reduction. The sequential reduction chain did not seem an applicable concept to describe redox dynamics at micro-(cm(2)) or mesoscale (m(2)) because of (1) high small-scale heterogeneity and (2) an absence of clear relationships between redox indicative parameters. The latter might be caused by redox processes occurring simultaneously at the investigated spatial and temporal scales. However, a tendency toward exclusive relationships between oxygen and iron, nitrate and iron, and delta S-34 with oxygen, nitrate, and sulfate indicated that the sequential reduction chain might be a suitable modeling concept for macroscale (km(2)) investigations with large sample numbers.

Wetlands are considered to be the biggest unknowns regarding the influence of global climate change on element dynamics, so knowledge of processes and conditions controlling sink and source functions of redox processes is crucial. The aim of this study was to investigate the sink/source function of nitrate, Fe, sulfate reduction and methanogenesis of an upland and a lowland fen within a boreal spruce catchment, southern Germany. We used suction cups and anaerobic dialysis chambers for soil solution sampling, FeS probes for the determination of S oxidation potential and stability of anoxic conditions and analysis of the soil solid phase (contents of C, S and Fe species). Both fens had high rates of nitrate reduction and potentially high rates of CH4 production. The upper few cm of all profiles were oxic with low CH4 concentrations, suggesting low CH4 emission rates from the soil, though emission by vascular plants cannot be excluded. Sulfate and Fe reduction processes differed significantly in the fens. The upland fen was characterized by relatively stable anoxic conditions, low Fe contents but high contents of organic S and low C/S ratios. We concluded that the upland fen is an effective sink for sulfate with long-term S storage. In contrast, the lowland fen was characterized by alternating oxidation-reduction cycles with high Fe contents, lower contents of organic S and higher C/S ratios. Thus, even though low sulfate and high Fe concentrations in soil solutions indicated high reduction rates in the lowland fen, long-term storage of S is not likely in this fen. Differences in biogeochemical processes between sites are most likely not associated with hydrology but rather with the role of vascular plants. (c) 2005 Elsevier Ltd. All rights reserved.

To assess the concern over declining base cation levels in forest soils caused by acid deposition, input-output budgets (1990s average) for sulphate (SO(4)), inorganic nitrogen (NO(3)-N; NH(4)-N), calcium (Ca), magnesium (Mg) and potassium (K) were synthesised for 21 forested catchments from 17 regions in Canada, the United States and Europe. Trend analysis was conducted on monthly ion concentrations in deposition and runoff when more than 9 years of data were available (14 regions, 17 sites). Annual average SO(4) deposition during the 1990s ranged between 7.3 and 28.4 kg ha(-1) per year, and inorganic nitrogen (N) deposition was between 2.8 and 13.8 kg ha(-1) per year, of which 41-67% was nitrate (NO(3)-N). Over the period of record, SO(4) concentration in deposition decreased in 13/14 (13 out of 14 total) regions and SO(4) in runoff decreased at 14/17 catchments. In contrast, NO(3)-N concentrations in deposition decreased in only 1/14 regions, while NH(4)-N concentration patterns varied; increasing at 3/14 regions and decreasing at 2/14 regions. Nitrate concentrations in runoff decreased at 4/17 catchments and increased at only 1 site, whereas runoff levels of NH(4)-N increased at 5/17 catchments. Decreasing trends in deposition were also recorded for Ca, Mg, and K at many of the catchments and on an equivalent basis, accounted for up to 131% (median 22%) of the decrease in acid anion deposition. Base cation concentrations in streams generally declined over time, with significant decreases in Ca, Mg and K occurring at 8, 9 and 7 of 17 sites respectively, which accounted for up to 133% (median 48%) of the decrease in acid anion concentration. Sulphate export exceeded input at 18/21 catchments, likely due to dry deposition and/or internal sources. The majority of N in deposition (31-100%; median 94%) was retained in the catchments, although there was a tendency for greater NO(3)-N leaching at sites receiving higher (7 kg ha(-1) per year) bulk inorganic N deposition. Mass balance calculations show that export of Ca and Mg in runoff exceeds input at all 21 catchments, but K export only exceeds input at 16/21 sites. Estimates of base cation weathering were available for 18 sites. When included in the mass balance calculation, Ca, Mg and K exports exceeded inputs at 14, 10 and 2 sites respectively. Annual Ca and Mg losses represent appreciable proportions of the current exchangeable soil Ca and Mg pools, although losses at some of the sites likely occur from weathering reactions beneath the rooting zone and there is considerable uncertainty associated with mineral weathering estimates. Critical loads for sulphur (S) and N, using a critical base cation to aluminium ratio of 10 in soil solution, are currently exceeded at 7 of the 18 sites with base cation weathering estimates. Despite reductions in SO(4) and H(+) deposition, mass balance estimates indicate that acid deposition continues to acidify soils in many regions with losses of Ca and Mg of primary concern.

Monitoring programs of ion concentrations and fluxes in semi-natural ecosystems are confronted with the task to gain as much information as possible with simultaneously minimizing costs and efforts. The aim of this study was (i) to assess how much of the heterogeneity of solution concentrations is lost because of temporal integration of measurements and (ii) to estimate the error in ion fluxes due to temporal integration. High resolution measurements (daily interval) of ion concentrations (sulfate, nitrate, chloride, pH and EC) in throughfall, soil solutions and runoff at the catchment Lehstenbach (Fichtelgebirge, Northeast Bavaria, Germany) were compared over a two year period with the reference monitoring program (biweekly measurement interval). Evaluation of the maximum temporal heterogeneity of ion concentrations in throughfall, soil solution and runoff (expressed as minimum, maximum, median and 25–75% percentile) did not result in an overall higher heterogeneity of the high resolution measurements compared to the reference program. The calculation of runoff fluxes from the reference data (biweekly concentration) resulted in significant errors of up to 25% for time periods < 1 year (high resolution data was considered the "true" value and set as 100%). However, errors became minor (< 10%) if longer time periods were considered. The suitability of different interpolation methods to up-scale biweekly concentration data for the calculation of runoff fluxes was evaluated in this study. We concluded for the monitoring programs at the Lehstenbach catchment that a biweekly measurement interval seemed to be suitable to capture the heterogeneity of ion concentrations and fluxes (and thus temporal trends). In comparison, high resolution measurements with a daily measurement interval were higher in cost, work and time resources and had a relatively low information gain. While the introduced methods are applicable in all monitoring programs, conclusions on temporal resolution of measurements are most likely not valid for systems where ion concentrations have a low autocorrelation length (e.g., agricultural or urban systems with nitrate or pesticide treatment; tropical systems with extreme temperature or hydrological events).

A synthesis of the biogeochemistry of S was done during 34 yr (1964-1965 to 1997-1998) in reference and human-manipulated forest ecosystems of the Hubbard Brook Experimental Forest (HBEF), NH. There have been significant declines in concentration (0.44 mol/liter-yr) and input (5.44 mol/ha-yr) of SO4 in atmospheric bulk wet deposition, and in concentration (0.64 mol/liter-yr) an d output (3.74 mol/ha-yr) of SO4 in stream water of the HBEF since 1964. These changes are strongly correlated with concurrent decreases in emissions of SO2 from the source area for the HBEF. The con- centration and input of SO4 in bulk deposition ranged from a low of 13.1 mol/liter (1983-1984) and 211 mol/ha-yr (1997-1998) to a high of 34.7 mol/liter (1965-1966) and 479 mol/ha-yr (1967-1968), with a long-term mean of 23.9 mol/liter and 336 mol/ha-yr during 1964-1965 to 1997-1998. Despite recent declines in concentrations, SO4 is the dominant anion in both bulk deposition and stream water at HBEF. Dry deposition is difficult to measure, especially in mountainous terrain, but was estimated at 21% of bulk deposition. Thus, average total atmospheric deposition was 491 and 323 mol/ha-yr during 1964-1969 and 1993-1998, respectively. Based on the long-term 34 S pattern associated with anthro- pogenic emissions, SO4 deposition at HBEF is influenced by numerous SO2 sources, but biogenic sources appear to be small. Annual throughfall plus stemflow in 1993-1994 was estimated at 346 mol SO4 /ha. Aboveground litterfall, for the watershed-ecosystem averaged about 180 mol S/ha-yr, with highest inputs (190 mol S/ha-yr) in the lower elevation, more deciduous forest zone. Weathering release was calculated at a maximum of 50 mol S/ha-yr. The concentration and output of SO4 in stream water ranged from a low of 42.3 mol/liter (1996-1997) and 309 mol/ha-yr (1964-1965), to a high of 66.1 mol/liter (1970-1971) and 849 mol/ha-yr (1973-1974), with a long-term mean of 55.5 mol/liter and 496 mol/ha-yr during the 34 yrs of study. Gross outputs of SO4 in stream water consistently exceeded inputs in bulk deposition and were positively and significantly related to annual precipitation and streamflow. The relation between gross SO4 output and annual streamflow changed with time as atmo- spheric inputs declined. In contrast to the pattern for bulk deposition concentration, there was no sea- sonal pattern for stream SO4 concentration. Nevertheless, stream outputs of SO4 were highly sea- sonal, peaking during spring snowmelt, and producing a monthly cross-over pattern where net hydro- logic flux (NHF) is positive during summer and negative during the remainder of the year. No significant elevational pattern in streamwater SO4 concentration was observed. Mean annual, volume-weighted

International audience; Water quality data for 56 long-term monitoring sites in eight European countries are used to assess freshwater responses to reductions in acid deposition at a large spatial scale. In a consistent analysis of trends from 1980 onwards, the majority of surface waters (38 of 56) showed significant (p ?0.05) decreasing trends in pollution-derived sulphate. Only two sites showed a significant increase. Nitrate, on the other hand, had a much weaker and more varied pattern, with no significant trend at 35 of 56 sites, decreases at some sites in Scandinavia and Central Europe, and increases at some sites in Italy and the UK. The general reduction in surface water acid anion concentrations has led to increases in acid neutralising capacity (significant at 27 of 56 sites) but has also been offset in part by decreases in base cations, particularly calcium (significant at 26 of 56 sites), indicating that much of the improvement in runoff quality to date has been the result of decreasing ionic strength. Increases in acid neutralising capacity have been accompanied by increases in pH and decreases in aluminium, although fewer trends were significant (pH 19 of 56, aluminium 13 of 53). Increases in pH appear to have been limited in some areas by rising concentrations of organic acids. Within a general trend towards recovery, some inter-regional variation is evident, with recovery strongest in the Czech Republic and Slovakia, moderate in Scandinavia and the United Kingdom, and apparently weakest in Germany. Keywords: acidification, recovery, European trends, sulphate, nitrate, acid neutralising capacity

Anthropogenic S emissions have been declining in eastern North America since the early 1970s. Declines in atmospheric S deposition have resulted in decreases in concentrations and fluxes of SO4 2− in precipitation and drainage waters. Recent S mass balance studies have shown that the outflow of SO4 2− in drainage waters greatly exceeds current S inputs from atmospheric deposition. Identifying the S source(s) which contribute(s) to the discrepancy in watershed S budgets is a major concern to scientists and policy makers because of the need to better understand the rate and spatial extent of recovery from acidic deposition. Results from S mass balances combined with model calculations and isotopic analyses of SO4 2− in precipitation and drainage waters at the Hubbard Brook Experimental Forest (HBEF) suggest that this discrepancy cannot be explained by either underestimates of dry deposited S or desorption of previously stored SO4 2−. Isotopic results suggest that the excess S may be at least partially derived from net mineralization of organic S as well as the weathering of S-bearing minerals.

Because of the deleterious effects of acid rain and the need to predict reversibility of acidification, various scientific tools such as modeling, stable isotopes and flux/budget calculations have been used in biogeochemical sulfur (S) research. The aim of this study was to evaluate consistencies and discrepancies between these different tools. While modeling has been seemingly successful in predicting S dynamics in soil solution and stream water by considering inorganic sulfate sorption and desorption only, stable S isotopes indicate that biological S turnover plays a crucial role for the sulfate released to soil solution and stream water. A comparison of budget calculations with soil S pools reveals that inorganic sulfate sorption and desorption are the controlling processes as long as deposition is high (> 15 kg S ha-1yr-1) and soils have a high sulfate sorption capacity. This explains the successful model predictions of the last two decades. However, for soils with low sulfate sorption capacity and under low sulfate deposition, organic S seems to be a significant source for stream water sulfate and has to be considered in future modeling.

To predict reversibility of soil and water acidification under conditions of decreasing S-input into forested ecosystems, the amount of reversibly bound SO42- in the soil as well as its desorption behavior must be considered. This study investigated variability of sulfate isotherms and their spatial scaling. The Langmuir isotherm parameters in two forested catchments (one deciduous, one coniferous stand) and their spatial distribution at two different scales (site and catchment scale) were investigated. The soil samples (250 cm(3)) were taken in a systematic grid with spatial distances ranging from 20 x 20 m to 300 X 300 m, Isotherm parameters, soil pH, dithionite- and oxalate-extractable iron and aluminum, crystalline iron oxide, and ent were determined. Significant relationships were found between sulfate sorption isotherm parameters and soil chemical properties for each site. It would be useful to be able to replace the experimental determination of isotherm parameters with the less costly measurements of soil chemical properties such as pH, Al- and Fe-oxides, and C-org content of the soils. Regression analysis, however, resulted in different parameters for each site. Thus, at sites where this relation is unknown, isotherms have to be determined via soil extraction procedures and cannot be predicted by soil chemical properties. To determine the average isotherms with an accuracy of +/- 0.2 mu mol g(-1) SO42- (sorb), a sample size of 55 for the site scale and up to 106 for the catchment scale is required. The semivariance of the isotherm parameters revealed no spatial patterns. The influence of isothenll variability on the prediction of SO42--fluxes with seepage was investigated using the chemical equilibrium model MAGIC. Forecast accuracy depends on proper consideration of the variability of sulfate sorption in a catchment.

The decrease in anthropogenic deposition, namely SO42- and SO2, in European forest ecosystems during the last 20 years has raised questions concerning the recovery of forest ecosystems. The aim of this study was to evaluate if the long term data of element concentrations at the Fichtelgebirge (NE-Bavaria, Germany) monitoring site indicates a relationship between the nutrient content of needles and the state of soil solution acidity. The soil at the site is very acidic and has relatively small pools of exchangeable Ca and Mg. The trees show medium to severe nutrient deficiency symptoms such as needle loss and needle yellowing. The Ca and Mg concentrations in throughfall decreased significantly during the last 12 years parallel to the significant decline in the throughfall of H+ and SO42- concentrations. Soil solution concentrations of SO42-, Ca and Mg generally decreased while the pH value remained stable. Aluminum concentrations decreased slightly, but only at a depth of 90 cm. Simultaneously a decrease in the molar Ca/Al and Mg/Al ratios in the soil solution was observed. Ca and Mg contents in the spruce needles decreased, emphasizing the relevance of soil solution changes for tree nutrition. The reasons for the delay in ecosystem recovery are due to a combination of the following two factors: (1) the continued high concentrations of NO3— and SO42— in the soil solution leading to high Al concentrations and low pH values and, (2) the decreased rates of Ca and Mg deposition cause a correlated decrease in the concentration of Ca and Mg in the soil solution, since little Ca and Mg is present in the soil's exchangeable cation pools. It is our conclusion that detrimental soil conditions with respect to Mg and Ca nutrition as well as to Al stress are not easily reversed by the decreasing deposition of H+ and SO42—. Thus, forest management is still confronted with the necessity of frequent liming to counteract the nutrient depletion in soils and subsequent nutrient deficiencies in trees.

The forest floor represents the major source of dissolved organic carbon (DOC) and nitrogen (DON) in forest soils. The release mechanisms of DOC and DON from forest floors and their environmental controls as well as the dynamics of concentrations and fluxes are still poorly understood. We investigated the effect of drying and rewetting on the release of DOC and DON from a Norway spruce forest floor. Undisturbed soil columns of 17 cm diameter and 15-20 cm height were taken with 7 replicates from the forest floor of a mature Norway spruce (Picea abies [L.] Karst.) site and established at 10 degreesC in the laboratory. Columns were exposed to different periods of drying (3, 5, 10, 20 days). Each drying period was followed by a rewetting for 5 days at an irrigation rate of 10 mm d(-1) with a natural throughfall solution. The percolates from the forest floor were collected daily and analyzed for DOC, total N, NH4, NO3, pH, electrical conductivity and major ions. Drying for 10 and 20 days decreased the water content of the Oi horizon from 280% dry weight to about 30%. The water content of the Oe and the Oa horizon only changed from about 300% to 200%. The fluxes of DOC from the forest floor were moderately effected by drying and rewetting with an increase after 3 and 5 days of drying, but a decrease after 10 and 20 days. On the contrary, the drying for 10 and 20 days resulted in a drastic increase of the DON fluxes and a subsequent decrease of the DOC/DON ratios in the forest floor percolates from about 50 to 3.3. These results suggest that the mechanisms for DOC release in forest floors differ from those for DON and that drying and rewetting cause temporal variations in the DOC/DON ratios in forest floor percolates.

The mitigating effect of decreasing anthropogenic SO4 deposition on acidified soils and waters can be delayed by the release of previously stored soil SO4. We investigated SO4 pools and desorption in the weathered substrata (0.5-10 m depth) of a forested catchment on granite to quantify the importance of these layers to SO4 dynamics. Solid-phase materials from 10 boreholes to a maximum depth of 10 m were analyzed for water- and phosphate-extractable SO4, SO4 desorption, cation-exchange capacity (CEC), pH, and dithionite- and oxalate-extractable Fe (Fe-d and Fe-o) and Al (Al-d and Al-0). Seven of the investigated boreholes were used to monitor water table depth and to obtain samples for measurement of solution SO4 concentrations. The storage of phosphate-extractable SO4 in the weathered substrata was estimated at 90 kmol ha(-1), of which approximate to 50 kmol ha(-1) were water soluble, Sulfate pools and their desorption behavior were highly variable, which could partly be explained by the variation of pH and extractable Fe and Al contents of the samples, Sulfate concentrations in groundwater were dependent on the depth of groundwater table and corresponded with the depth gradients of solid-phase SO4. The SO4 pools of the substrata were apparently regulating solution concentrations. Thus, groundwater acidification in such aquifers will not be easily reversed by decreasing SO4 deposition because of the release of previously stored SO4.

Sulfur deposition in the northeastern U.S. has been decreasing since the 1970s and there has been a concomitant decrease in the SO42− lost from drainage waters from forest catchments of this region. It has been established previously that the SO42− lost from drainage waters exceeds SO42− inputs in bulk precipitation, but the cause for this imbalance has not been resolved. The use of stable S isotopes and the availability of archived bulk precipitation and stream water samples at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire provided a unique opportunity to evaluate potential sources and sinks of S by analyzing the long-term patterns (1966–1994) of the δ34S values of SO42−. In bulk precipitation adjacent to the Ecosystem Laboratory and near Watershed 6 the δ34S values were greater (mean: 4.5 and 4.2l, respectively) and showed more variation (variance: 0.49 and 0.30) than stream samples from Watersheds 5 (W5) and 6 (W6) (mean: 3.2 and 3.7j; variance: 0.09 and 0.08, respectively). These results are consistent with other studies in forest catchments that have combined results for mass balances with stable S isotopes. These results indicate that for those sites, including the HBEF, where atmospheric inputs are ≤10 kg S ha−1 yr−1, most of the deposited SO42− cycles through the biomass before it is released to stream water. Results from W5, which had a whole-tree harvest in 1983–1984 showed that adsorption/desorption processes play an important role in regulating net SO42− retention for this watershed-ecosystem. Although the isotopic results suggest the importance of S mineralization, conclusive evidence that there is net mineralization has not yet been shown. However, S mass balances and the isotopic result are consistent with the mineralization of organic S being a major contributor to the SO42− in stream waters at the HBEF.

Current climatic conditions and the occurrence of discontinuous and sporadic permafrost in the Alps result in a low turnover rate and therefore accumulation of organic matter (OM) in soils. Alpine soils are thus highly sensitive to global warming that potentially promotes the mineralisation of soil organic matter (SOM). This process might increase the release of CO2 to the atmosphere. Our aim was to investigate the potential effect of permafrost thawing by the analysis of the physical–chemical soil properties of permafrost versus non-permafrost sites. Specifically, we i) quantified the SOM stocks at such sites, ii) characterised SOM and its physical and chemical fractions and iii) estimated the age range of the bulk soil and stable C-fraction (radiocarbon dating). In south-eastern Switzerland, two areas above the timberline and one below the timberline (where isolated permafrost was verified) were investigated in detail. At each site, the experimental set-up consisted in the comparison of nearby soils that were either influenced or not by permafrost. The C-stocks (down to the C horizon or rock surface) did not show a significant difference between permafrost and non-permafrost soils and were in the same range of 10–15 kg/m2 in alpine (grassland) and subalpine (forest) sites. Above the timberline, the bulk SOM showed a distinct higher age at permafrost sites compared to non-permafrost sites. This higher age was even more evident in the stable C-fraction (resistant to an H2O2 treatment), where ages of up to 11 ky in permafrost soils were recorded. The highest age obtained in the stable C-fraction in non-permafrost soils was around 4 ky. Consequently, climatic conditions and the occurrence of discontinuous permafrost resulted in a very low turnover rate of SOM. At the subalpine site, the difference between permafrost and non-permafrost sites was less. At both sites (alpine and subalpine), DRIFT (Diffuse Reflection Infrared Fourier Transform) was used to determine the functional groups in the bulk soil and in the stable C-fraction. In general, the stable C-fraction had a different composition compared to the bulk SOM at non-permafrost sites; this was mostly not the case at the permafrost sites. This confirms that different decomposition processes occur between permafrost and non-permafrost sites. Furthermore, permafrost sites accumulated more the low-density physical fractions of SOM that are potentially easily degradable. The obtained results suggest that a warmer climate may not necessarily lead to an increased CO2 release from SOM-degradation in permafrost soils compared to non-permafrost soils. High-alpine soils and OM furthermore integrate a multi-facetted response to the past and ongoing surrounding conditions. The melting of permafrost will most likely enhance vegetation growth, which to a certain degree will probably compensate for carbon losses on the long-term.

In a forested catchment in the Fichtelgebirge mountains (NE-Bavaria, Germany) the long term SO(4) (2-) budget (average 1988-1994) indicated that about 40% of the input with throughfall (16.8 kg SO(4) (2-) S·ha(-1)·yr(-1)) was retained in the catchment. In order to identify processes acting as potential SO(4) (2-) sinks, δ(34)S values of SO(4) (2-) in soil solutions and runoff were measured between May and November 1994. δ(34)S values of the runoff and the fen were higher (5.8‰) than the δ(34)S values of the soil solution of the oxic soils in the terrestrial area (3.9‰). Because there is no lithogenic S source within the catchment, it can be assumed that SO(4) (2-) deposition is the only S source in the catchment. Thus the results were interpreted as a result of SO(4) (2-) reduction within the catchment, because the uptake of (32)S is favoured during the dissimilatory SO(4) (2-) reduction and (34)S is consequently enriched in the soil solution. To estimate the amount of SO(4) (2-) reduced isotopic fractionation factors between - 9‰ and -46‰ were considered, resulting in SO(4) (2-) reduction rates of 1.8-9.3 kg SO(4) (2)-S·ha(-1)yr(-1). It was concluded that besides dissimilatory SO(4) (2-) reduction another sink exists in the catchment (e.g. SO(4) (2-) sorption in deep soil layers).

A variety of different methods have been used for the determination of inorganic soil SO42- in the past, which makes it difficult to compare SO42- contents of soils. Sulfate was extracted with the four commonly used extraction solutions 0.5 M NaHCO3, 0.02 M NaH2PO4, 0.1 M NaCl and H2O from A-, Bw- and Bs-horizons of six acid forest soils. 5 g of field moist soil were percolated with a flow rate of 5 ml/h and percolations were repeated as long as SO42- was detectable in the percolate (< 0.5 mg SO4 . l-1). NaCl and NaHCO3 extracted highest amounts of total inorganic SO42- in A-horizons, but NaHCO3 caused analytical problems. NaHCO3 and NaH2PO4 yielded highest amounts in B-horizons. With the exception of Bs-horizons more than 70% of the total inorganic SO42- was H2O-soluble. Thus, if H2O-soluble SO42- is defined as reversibly bound, the greater part of the inorganic SO42- fraction can potentially be released, if SO42- deposition decreases.