Permafrost thaw causes large carbon loss in boreal peatlands while changes to peat quality are limited.

Rapid, ongoing permafrost thaw of peatlands in the discontinuous permafrost zone is exposing a globally significant store of soil carbon (C) to microbial processes. Mineralization and release of this peat C to the atmosphere as greenhouse gases is a potentially important feedback to climate change. Here we investigated the effects of permafrost thaw on peat C at a peatland complex in western Canada. We collected 15 complete peat cores (between 2.7 and 4.5 m deep) along four chronosequences, from elevated permafrost peat plateaus to saturated thermokarst bogs that thawed up to 600 years ago. The peat cores were analysed for peat C storage and peat quality, as indicated by decomposition proxies (FTIR and C/N ratios) and potential decomposability using a 200-day aerobic laboratory incubation. Our results suggest net C loss following thaw, with average total peat C stocks decreasing by ~19.3 ± 7.2 kg C m-2 over <600 years (~13% loss). Average post-thaw accumulation of new peat at the surface over the same period was ~13.1 ± 2.5 kg C m-2 . We estimate ~19% (±5.8%) of deep peat (>40 cm below surface) C is lost following thaw (average 26 ± 7.9 kg C m-2 over <600 years). Our FTIR analysis shows peat below the thaw transition in thermokarst bogs is slightly more decomposed than peat of a similar type and age in permafrost plateaus, but we found no significant changes to the quality or lability of deeper peat across the chronosequences. Our incubation results also showed no increase in C mineralization of deep peat across the chronosequences. While these limited changes in peat quality in deeper peat following permafrost thaw highlight uncertainty in the exact mechanisms and processes for C loss, our analysis of peat C stocks shows large C losses following permafrost thaw in peatlands in western Canada.

Control of carbon and nitrogen accumulation by vegetation in pristine bogs of southern Patagonia.

Peatlands are long-term sinks of carbon (C) and nitrogen (N) that are exposed to anthropogenic pressure. This has often induced a vegetation shift from peat mosses towards increasing presence of vascular plants. However, the impact of this vegetation shift on the sink function of peatlands remains unclear. To address this research gap, we studied C and N accumulation in a Patagonian cushion bog where a shift to the predominance of vascular cushion plants is a natural phenomenon since millennia. For comparison, long-term accumulation and decomposition patterns in a pristine Patagonian Sphagnum bog were studied. Thereto, we determined recent and long-term rates of C and N accumulation, their within-site variability, and studied plant-macrofossils. These results were related to decomposition indicators (C/N ratio, humification index, stable isotopes) of the bog types. Despite differences in decomposition indicators, long-term rates of C accumulation were of similar magnitude in the Sphagnum (21.9 g C m-2 yr-1) and in the cushion bog (22.2 g C m-2 yr-1). N accumulation was significantly lower in the Sphagnum bog (0.35 g N m-2 yr-1) compared to the surprisingly high accumulation in the cushion bog (0.55 g N m-2 yr-1). Tephra depositions in the cushion bog about 1600 cal. Years ago presumably triggered the vegetation shift towards dominance of cushion plants by a fertilization effect. C accumulation rates during past decades in the upper decimeters of peat were four times higher in the cushion bog (245 g C m-2 yr-1) compared to the Sphagnum bog (64 g C m-2 yr-1), but substantially decreased since the appearance of cushion plants. High decomposition rates as indicated by decomposition indicators thus apparently offset the higher productivity of cushion plants in the long term. While cushion bogs appear to be effective N sinks, their C sink function may therefore be equal to Sphagnum bogs.

Impact of Morphine Treatment on Infarct Size and Reperfusion Injury in Acute Reperfused ST-Elevation Myocardial Infarction.

Current evidence regarding the effect of intravenous morphine administration on reperfusion injury and/or cardioprotection in patients with myocardial infarction is conflicting. The aim of this study was to evaluate the impact of morphine administration, on infarct size and reperfusion injury assessed by cardiac magnetic resonance imaging (CMR) in a large multicenter ST-elevation myocardial infarction (STEMI) population. In total, 734 STEMI patients reperfused by primary percutaneous coronary intervention <12 h after symptom onset underwent CMR imaging at eight centers for assessment of myocardial damage. Intravenous morphine administration was recorded in all patients. CMR was completed within one week after infarction using a standardized protocol. The clinical endpoint of the study was the occurrence of major adverse cardiac events (MACE) within 12 months after infarction. Intravenous morphine was administered in 61.8% (n = 454) of all patients. There were no differences in infarct size (17%LV, interquartile range [IQR] 8-25%LV versus 16%LV, IQR 8-26%LV, p = 0.67) and microvascular obstruction (p = 0.92) in patients with versus without morphine administration. In the subgroup of patients with early reperfusion within 120 min and reduced flow of the infarcted vessel (TIMI-flow ≤2 before PCI) morphine administration resulted in significantly smaller infarcts (12%LV, IQR 12-19 versus 19%LV, IQR 10-29, p = 0.035) and reduced microvascular obstruction (p = 0.003). Morphine administration had no effect on hard clinical endpoints (log-rank test p = 0.74) and was not an independent predictor of clinical outcome in Cox regression analysis. In our large multicenter CMR study, morphine administration did not have a negative effect on myocardial damage or clinical prognosis in acute reperfused STEMI. In patients, presenting early ( ≤120 min) morphine may have a cardioprotective effect as reflected by smaller infarcts; but this finding has to be assessed in further well-designed clinical studies.

A 1-year greenhouse gas budget of a peatland exposed to long-term nutrient infiltration and altered hydrology: high carbon uptake and methane emission.

Long-term increased nutrient influx into normally nutrient-limited peatlands in combination with altered hydrological conditions may threaten a peatland's carbon storage function and affect its greenhouse gas (GHG) budget. However, in situ studies on the effects of long-term altered conditions on peatland functioning and GHG budgets are scarce. We thus quantified GHG fluxes in a peatland exposed to enhanced water level fluctuations and long-term nutrient infiltration in Ontario, Canada, via eddy-covariance and flux chamber measurements. The peatland was a prominent sink of - 680 ± 202 g carbon dioxide (CO2) and a source of 22 ± 8 g methane (CH4) m-2 year-1, resulting in a negative radiative forcing of - 80 g CO2 eq. m-2 y-1. During the growing season CH4 fluxes were constantly high (0.1 g m-2 s-1). Further, on three dates, we measured nitrous oxide (N2O) fluxes and observed a small flux of 2.2 mg m-2 day-1 occurring during the thawing period. Taking the studied ecosystem as a model system for other peatlands exposed to long-term increased nutrient infiltration and enhanced water level fluctuations, our data suggest that such peatlands can maintain their carbon storage function and CO2 sequestration may outweigh emissions of CH4.

Controls on iron(II) fluxes into waterways impacted by acid mine drainage: A Damköhler analysis of groundwater seepage and iron kinetics.

When acidic groundwater flows into an aquatic system the sediment water interface (SWI) acts as a transition zone between the groundwater and lake water, and often exhibits strong physical and biogeochemical gradients. The fate of groundwater-borne solutes, such as Fe(II), is determined by the balance between the exposure time during transport across the SWI and the reaction time within the SWI, however the relative role of groundwater seepage rates and iron kinetics on acidity generation in lakes is unknown. Porewater seepage velocities, porewater chemical profiles, and limnological data were collected across multiple field campaigns over the last two decades, in acid Mine Lake 77, in Lusatia, Germany. This rare data set was analyzed using a Damköhler approach that compares exposure and reactions timescales, to determine that Fe(II) would typically be transported with little reaction across the SWI, spatially separating it from sediment-processes that produce alkalinity and providing a source of acidity to the lake. This Damköhler analysis further showed that remediation should be focused on reducing groundwater seepage velocities and enhancing exposure times. Strategic planting of submerged benthic macroalgae would slow groundwater inflows, as well as oxygenating overlying waters and supplying organic matter to the sediments. A similar Damköhler analysis could be used to assess the fate of any groundwater-borne reactive chemicals (e.g. phosphorus) into lakes and streams.

Occurrence and fate of colloids and colloid-associated metals in a mining-impacted agricultural soil upon prolonged flooding.

Colloids formed during soil flooding can potentially facilitate the mobilization of metal contaminants. Here, laboratory batch incubations with a contaminated soil were performed to monitor temporal changes in the porewater dynamics of metals, the morphology and composition of colloids, and the speciation of colloids-associated metals during 30 days of flooding. The concentrations of colloidal and dissolved metals increased initially and peaked at a certain time, but then decreased with the on-going sulfate reduction. The combined analysis of spectrometric, spectroscopic, and size-fractionation results revealed that the dynamics of Cu were dominated by microbe-associated colloids and were mediated largely by Cu(0) biomineralization and subsequent sulfidation, while the microbe-associated and freely dispersed colloids were equally relevant for governing the dynamics of Cd and Pb. Mobilization of Zn, on the other hand, was dominated by its dissolved form, probably due to the low thermodynamic stability of Zn-sulfide. Additionally, adsorption via organic functional groups was another mechanism for metal incorporation into colloids. We also provided direct spectroscopic evidence for the formation and persistence of dispersed heterocolloids consisting of CuxS and CdS during flooding. Our findings suggest that colloids-induced metal mobilization should be considered in assessing bioavailability and risks of metals in contaminated soils upon flooding.

Effects of extreme experimental drought and rewetting on CO2 and CH4 exchange in mesocosms of 14 European peatlands with different nitrogen and sulfur deposition.

The quantitative impact of intense drought and rewetting on gas exchange in ombrotrophic bogs is still uncertain. In particular, we lack studies investigating multitudes of sites with different soil properties and nitrogen (N) and sulfur (S) deposition under consistent environmental conditions. We explored the timing and magnitude of change in CO2 (Respiration, Gross Primary Production - GPP, and Net Exchange - NE) and CH4 fluxes during an initial wet, a prolonged dry (~100 days), and a subsequent wet period (~230 days) at 12 °C in 14 Sphagnum peat mesocosms collected in hollows from bogs in the UK, Ireland, Poland, and Slovakia. The relationship of N and S deposition with GPP, respiration, and CH4 exchange was investigated. Nitrogen deposition increased CO2 fluxes and GPP more than respiration, at least up to about 15 kg N ha(-1)  yr(-1) . All mesocosms became CO2 sources during drying and most of them when the entire annual period was considered. Response of GPP to drying was faster than that of respiration and contributed more to the change in NE; the effect was persistent and few sites recovered "predry" GPP by the end of the wet phase. Respiration was higher during the dry phase, but did not keep increasing as WT kept falling and peaked within the initial 33 days of drying; the change was larger when differences in humification with depth were small. CH4 fluxes strongly peaked during early drought and water table decline. After rewetting, methanogenesis recovered faster in dense peats, but CH4 fluxes remained low for several months, especially in peats with higher inorganic reduced sulfur content, where sulfate was generated and methanogenesis remained suppressed. Based on a range of European sites, the results support the idea that N and S deposition and intense drought can substantially affect greenhouse gas exchange on the annual scale.

How suitable are peat cores to study historical deposition of PAHs?

Ombrotrophic peat bogs are natural archives of atmospheric pollution, their depth profiles can be used to study the deposition chronology of harmful contaminants. Prerequisites for deriving historical deposition rates from the peat archive are that contaminants are persistent and immobile in the peat and that the applied dating technique is accurate. To examine these requirements and the accuracy of peat archives for polycyclic aromatic hydrocarbons (PAHs) 12 peat profiles were sampled in 4 bogs in Ontario, Canada, as well as surface peat in one bog. Additionally we carried out laboratory incubations; no degradation occurred over a 3-year period in these experiments. The standard deviations of PAH concentrations in surface samples and of PAH inventories in whole cores was approximately 30%, and concentrations in surface peat were on average 50% higher in hollows than in hummocks. No indications for mobility of PAHs were observed in peat. Temporal deposition trends inferred from peat cores were generally in agreement with trends derived from a sediment core sampled close by but deposition rates to the sediment were substantially higher. A major source of uncertainty was the rather coarse vertical sampling resolution of 5 cm which introduced substantial uncertainty in the dating of the individual segments. This caused variations of the deposition rates up to 70% per PAH between three replicate cores, and it also impedes the identification of deposition peaks. Overall, we conclude that peat cores are suitable archives for inferring atmospheric deposition trends, but due to their relatively low temporal resolution short-term events may not be identified and the development of sampling methods that allow a higher vertical resolution would greatly improve the performance of the method. The analysis of more than one core per site is suggested to provide a realistic estimate of the historic deposition and total inventories.

Experimental burial inhibits methanogenesis and anaerobic decomposition in water-saturated peats.

A mechanistic understanding of carbon (C) sequestration and methane (CH(4)) production is of great interest due to the importance of these processes for the global C budget. Here we demonstrate experimentally, by means of column experiments, that burial of water saturated, anoxic bog peat leads to inactivation of anaerobic respiration and methanogenesis. This effect can be related to the slowness of diffusive transport of solutes and evolving energetic constraints on anaerobic respiration. Burial lowered decomposition constants in homogenized peat sand mixtures from about 10(-5) to 10(-7) yr(-1), which is considerably slower than previously assumed, and methanogenesis slowed down in a similar manner. The latter effect could be related to acetoclastic methanogenesis approaching a minimum energy quantum of -25 kJ mol(-1) (CH(4)). Given the robustness of hydraulic properties that locate the oxic-anoxic boundary near the peatland surface and constrain solute transport deeper into the peat, this effect has likely been critical for building the peatland C store and will continue supporting long-term C sequestration in northern peatlands even under moderately changing climatic conditions.

Energetic constraints on H2-dependent terminal electron accepting processes in anoxic environments: a review of observations and model approaches.

Microbially mediated terminal electron accepting processes (TEAPs) to a large extent control the fate of redox reactive elements and associated reactions in anoxic soils, sediments, and aquifers. This review focuses on thermodynamic controls and regulation of H2-dependent TEAPs, case studies illustrating this concept, and the quantitative description of thermodynamic controls in modeling. Other electron transfer processes are considered where appropriate. The work reviewed shows that thermodynamics and microbial kinetics are connected near thermodynamic equilibrium. Free energy thresholds for terminal respiration are physiologically based and often near -20 kJ mol(-1), depending on the mechanism of ATP generation; more positive free energy values have been reported under "starvation conditions" for methanogenesis and lower values for TEAPs that provide more energy. H2-dependent methanogenesis and sulfate reduction are under direct thermodynamic control in soils and sediments and generally approach theoretical minimum energy thresholds. If H2 concentrations are lowered by thermodynamically more potent TEAPs, these processes are inhibited. This principle is also valid for TEAPS providing more free energy, such as denitrification and arsenate reduction, but electron donor concentration cannot be lowered so that the processes reach theoretical energy thresholds. Thermodynamics and kinetics have been integrated by combining traditional descriptions of microbial kinetics with the equilibrium constant K and reaction quotient Q of a process, taking into account process-specific threshold energies. This approach is dynamically evolving toward a general concept of microbially driven electron transfer in anoxic environments and has been used successfully in applications ranging from bioreactor regulation to groundwater and sediment biogeochemistry.

Effects of short-term drying and irrigation on electron flow in mesocosms of a northern bog and an alpine fen.

Methane emissions and element mobility in wetlands are controlled by soil moisture and redox conditions. We manipulated soil moisture by weekly drying and irrigation of mesocosms of peat from a bog and iron and sulfur rich fen. Water table changed more strongly in the decomposed fen peat ( approximately 11 cm) than in the fibric bog peat ( approximately 5 cm), where impacts on redox processes were larger due to larger change in air filled porosity. Methanogenesis was partly decoupled from acetogenesis and acetate accumulated up to 5.6 mmol L(-1) in the fen peat after sulfate was depleted. Irrigation and drying led to rapid redox-cycles with sulfate, hydrogen sulfide, nitrate, and methane being produced and consumed on the scale of days, contributing substantially to the total electron flow and suggesting short-term resilience of the microbial community to intermittent aeration. Anaerobic CO2 production was partly balanced by methanogenesis (0-34%), acetate fermentation (0-86%), and sulfate reduction (1-30%) in the bog peat. In the fen peat unknown electron acceptors and aerenchymatic oxygen influx apparently drove respiration. The results suggest that regular rainfall and subsequent drying may lead to local oxidation-reduction cycles that substantially influence electron flow in electron acceptor poor wetlands.

Groundwater derived arsenic in high carbonate wetland soils: sources, sinks, and mobility.

Wetlands and organic soils have been recognized as important sinks for arsenic in the environment, yet sources and immobilization mechanisms of As are often unclear. To begin rectifying this deficiency, we investigated As retention and binding mechanisms at a degraded, minerotrophic wetland site in contact with groundwater rich in As and Fe. Arsenic occurred in high dissolved concentrations of up to 467 microg L(-1) in the groundwater, but dropped to values below 10 microg L(-1) towards the surface. The solid phase As content instead was high in the topsoil with up to 3400 mg kg(-1) and decreased with depth to 15 mg kg(-1). A similar pattern was observed with respect to Fe. Amorphous and crystalline iron precipitates were the main sorbents for arsenic in the soil horizons according to results from wet chemical sequential extractions. Arsenic was apparently not associated with inorganic carbon phases, but a substantial portion of up to 31% of As(tot) could be mobilized by dispersion of soil organic matter. Ratios of dissolved As(III)/As(V) decreased from the deeper As(III) dominated groundwater to the As(V) dominated soil porewaters, where As was apparently immobilized in its oxidized form. Concentrations of the organic species DMA and MMA were negligible. According to the results of simple one-dimensional estimates the vertical arsenic transport from the source in the groundwater to the topsoil was slow given an extrapolation of current conditions. These results suggest that As accumulation started before the beginning of drainage in the now degraded peatland soils and the degradation and mass loss of organic matter under oxic conditions caused the very high As concentrations found in the topsoil horizon today.

Hydrogen thresholds and steady-state concentrations associated with microbial arsenate respiration.

H2 thresholds for microbial respiration of arsenate (As(V)) were investigated in a pure culture of Sulfurospirillum arsenophilum. H2 was consumed to threshold concentrations of 0.03-0.09 nmol/L with As(V) as terminal electron acceptor, allowing for a Gibbs free-energy yield of 36-41 kJ per mol of reaction. These thresholds are among the lowest measured for anaerobic respirers and fall into the range of denitrifiers or Fe(III)-reducers. In sediments from an arsenic-contaminated aquifer in the Red River flood plain, Vietnam, H2 levels decreased to 0.4-2 nmol/L when As(V) was added under anoxic conditions. When As-(V) was depleted, H2 concentrations rebounded by a factor of 10, a level similar to that observed in arsenic-free controls. The sediment-associated microbial population completely reduced millimolar levels of As(V) to arsenite (As-(III)) within a few days. The rate of As(V)-reduction was essentially the same in sediments amended with a pure culture of S. arsenophilum. These findings together with a review of observed H2 threshold and steady-state values suggest that microbial As(V)-respirers have a competitive advantage over several other anaerobic respirers through their ability to thrive at low H2 levels.

Electron transfer capacities and reaction kinetics of peat dissolved organic matter.

Information about electron-transfer reactions of dissolved organic matter (DOM) is lacking. We determined electron acceptor and donor capacities (EAC and EDC) of a peat humic acid and an untreated peat DOM by electrochemical reduction and reduction with metallic Zn and H2S (EAC), and by oxidation with complexed ferric iron (EDC) at pH 6.5. DOC concentrations (10-100 mg L(-1)) and pH values (4.5-8) were varied in selected experiments. EAC reached up to 6.2 mequiv x (g C)(-1) and EDC reached up to 1.52 mequiv-(g C)(-1). EDC decreased with pH and conversion of chelated to colloidal iron, and the electron-transfer capacity (ETC) was controlled by the redox potential Eh of the reactant (ETC = 1.016x Eh - 0.138; R(2) = 0.87; p = 0.05). The kinetics could be adequately described by pseudo first-order rate laws, one or two DOM pools, and time constants ranging from 2.1 x 10(-3) d-1 to 1.9 x 10(-2) d(-1) for the fast pool. Reactions were completed after 24-160 h depending on the redox couple applied. The results indicate that DOM may act as a redox buffer over electrochemical potentials ranging from -0.9 to +1.0 V.

A review of acidity generation and consumption in acidic coal mine lakes and their watersheds.

Lakes developing in former coal mine pits are often characterized by high concentrations of sulfate and iron and low pH. The review focuses on the causes for and fate of acidity in these lakes and their watersheds. Acidification is primarily caused by the generation of ferrous iron bearing and mineralized groundwater, transport through the groundwater-surface water interface, and subsequent iron oxidation and precipitation. Rates of acidity generation in mine tailings and dumps, and surface water are often similar (1 to >10 mol m(-2) yr(-1)). Weathering processes, however, often suffice to buffer groundwaters to only moderately acidic or neutral pH, depending on the suite of minerals present. In mine lakes, the acidity balance is further influenced by proton release from transformation of metastable iron hydroxysulfate minerals to goethite, and proton and ferrous iron sequestration by burial of iron sulfides and carbonates in sediments. These processes mostly cannot compensate acidity loading from the watershed, though. A master variable for almost all processes is the pH: rates of pyrite oxidation, ferrous iron oxidation, mineral dissolution, iron precipitation, iron hydroxide transformation, and iron and sulfate reduction are strongly pH dependent. While the principle mechanism of acidity generation and consumption and several controls are mostly understood, this cannot be said about the fate of acidity on larger spatial and temporal scales. Little is also known about critical loads and the internal regulation of biogeochemical iron, sulfur, and carbon cycling in acidic mine lakes.

Experimentally altered groundwater inflow remobilizes acidity from sediments of an iron rich and acidic lake.

To study the impact of changes in groundwater flow and chemistry on acidity export from sediments in acid mine drainage (AMD) polluted lakes, a column experiment was carried out. Schwertmannite rich sediment was subjected to three different flow rates (0, 5, and 20 L m(-2) a(-1)), two percolate chemistries (1/1 mmol L(-1) vs 10/15 mmol L(-1) sulfate/ferrous iron, pH 5), and DOC input (approximately 2.5 mmol C L(-1)). Percolation induced acidity export in all percolated treatments (8.8-40.4 mol m(-2) a(-1)) by accelerated proton generation from schwertmannite transformation (18.0-35.9 mol m(-2) a(-1)) and ferrous iron release (3.8-11.6 mol m(-2) a(-1)) from the sediment matrix. Mobilization increased with flow rate and decreased with sulfate and iron concentrations. Unspecifically bound ferrous iron contents increased within the sediment (up to 40.5 mol m(-2) a(-1)) when iron concentrations in the percolate were high. Reduced sulfur species formed following raises in pH, but acidity consumption through this process (0.3-6.6 mol m(-2) a(-1)) and the formation of carbonates (0.11-0.45 mol m(-2) a(-1)) remained small. The study thus suggests that increases in groundwater inflow remobilize acidity from AMD polluted sediments.

Mobilization of arsenic by dissolved organic matter from iron oxides, soils and sediments.

The arsenic contamination of aquifers has been linked to the input of dissolved organic matter (DOM). In light of this suggestion, the aim of this study was to quantify chemical effects of DOM on desorption and redox transformations of arsenic bound to synthetic iron oxide and natural samples from different geochemical environments (soils, shallow aquifer, lake sediment). In batch experiments, solutions containing 25-50 mg/L of two different types of DOM (purified peat humic acid and DOM from a peat drainage) were used as extractants in comparison to inorganic solutions. DOM solution was able to mobilize arsenic from all solid phases. Mobilization from iron oxides (maximum: 53.3%) was larger than from natural samples (maximum: 2.9%). The mobilization effect of extractants decreased in the order HCl>NaH2PO4>DOM>NaNO3. DOM solutions, therefore, mainly targeted weakly sorbed arsenic. Mobilization was complete within 24-36 h and DOM was sorbed during incubation indicating competition for sorption sites. The same patterns were observed for different DOM types and concentrations. Addition of DOM lead to (a) enhanced reduction (maximum 7.8%) and oxidation (6.4%) of arsenic in aqueous solution and (b) the appearance of arsenite in aqueous phase of soil samples (5.5%). As the primary mechanism for the arsenic release from solid phases we identified the competition between arsenic and organic anions for sorption sites, whereas redox reactions were probably of minor importance. The results of this study demonstrate that sorption of DOM has a strong potential to mobilize arsenic from soils and sediments.

The fate of experimentally deposited nitrogen in mesocosms from two Canadian peatlands.

In large regions of Europe and North America, peatlands have been exposed to elevated rates of atmospheric nitrogen (N) deposition. We investigated the fate of experimentally added N (NH(4)(15)NO3) at two different N loads (1.2 and 4.7 g N m(-2) yr(-1)) and water tables (1 and 32 cm) in intact cores from two peatlands, located in Central and Eastern Canada. The sites receive an estimated total N load of 0.6 g m(-2) a(-1) and 1.5 g m(-2) yr(-1), excluding nitrogen fixation. In all treatments, experimentally added nitrate (NO(3-)) was fully (96-99%) and ammonium (NH(4+)) mostly (81-97%) retained by the plant cover, mainly consisting of Sphagnum mosses, or in the unsaturated zone below. However, on average only 48% of the (15)N were recovered from the plant cover, and substantial amounts were found in depth layers of 2-6 cm (21-46%) and 8-12 cm (1.4-10.8%) below the moss surface. The amount of (15)N retained also significantly decreased with a lower water table from 56+/-9% to 40+/-10%. These findings document a substantial mobility of N, particularly during water table drawdown. Analysis of (15)N by a sequential diffusion procedure revealed a transfer of (15)N from NO(3-) into NH(4+) and dissolved organic N (DON), but the contents of (15)N in these pools accounted for less than 1% of the total N, natural background subtracted. The mass flux of dissolved (15)N into the peat was small compared to the total mass flux of (15)N. The accumulation of (15)N in the bulk peat must have been caused by a mechanism that was not investigated, possibly by transport of particulate organic N.

Long-term change of polycyclic aromatic hydrocarbon deposition to peatlands of eastern Canada.

To date, studies about historic PAH (polycyclic aromatic hydrocarbons) deposition at a regional scale have rarely been published. To address this research gap, we sampled 17 ombrotrophic peatlands across eastern Canada. The peat cores from hollows were dated with 210Pb for the period of about 1850-2000 and analyzed fortheir PAH concentration, so PAH deposition could be reconstructed. Peat samples were extracted by accelerated solvent extraction (ASE). The extracts were purified by column chromatography with aluminum oxide and silica gel. PAH were measured by gas chromatography-tandem mass spectrometry (GC-MS/MS). Overall reconstructed deposition rates of sigma-11 PAH ranged from 4 to 1432 microg m(-2) year(-1). Three different long-term trends in PAH deposition could be distinguished: sites with two separated periods of maximum PAH deposition, sites with one period of maximum PAH deposition, and sites with no clearly separated period of maximum PAH deposition. Increasing PAH depositions were caused by rapid industrialization accompanied by extensive use of fossil fuels; decreasing PAH depositions were caused by substitution of these fuels and movements of PAH emitting industry to different regions. At all sites either phenanthrene (20-60%) or benzo[b+k]fluoranthene (10-40%) was the predominant PAH. Detailed analysis of three bogs suggested that combustion of coal and vehicle exhausts mainly contributed to the peat PAH burden. The temporal trends of PAH deposition indicated that increases in the PAH deposition rates followed the industrial development in Canada, particularly in the periods 1880-1910 and 1940-1960. Recent abatement efforts were reflected in decreased PAH deposition rates to about 15% of the maximum.