R. Kelman Wieder

Boreal Peatland Ecosystems

1 Peatlands and the Boreal Forest 2 Functional Characteristics and Indicators of Boreal Peatlands 3 The Postglacial Development of Boreal Peatlands 4 The Role of Sphagnum in Peatland Development and Persistence 5 Peatland Fauna 6 The Role of Fungi in Boreal Peatlands 7 Decomposition in Boreal Peatlands 8 Primary Production in Boreal Peatlands 9 Carbon in Boreal Peatlands 10 The Nitrogen Cycle in Boreal Peatlands 11 Phosphorus in Boreal Peatlands 12 Sulfur Cycling in Boreal Peatlands: From Acid Rain to Global Climate Change 13 The Hydrology of Boreal Peatlands 14 Modeling Ecosystem Processes and Peat Accumulation in Boreal Peatlands 15 Forestry and BorealPeatlands 16 Disturbance in Boreal Peatlands 17 Restoration of Degraded Peatlands 18 Boreal Peatland Ecosystems: Our Carbon Heritage

Production of methane and carbon dioxide in peatland ecosystems across North America: Effects of temperature, aeration, and organic chemistry of peat

Peat soil from 12 northern peatlands, spanning broad gradients in mean annual temperature (MAT), mean annual precipitation (MAP), and plant species composition, was incubated in vitro at differing temperature (2, 12, 22°C), aeration (anoxic, oxic), and with or without added glucose to evaluate controls on potential production of CH4 and CO2 (and CH4 consumption). Methane production and CH4 consumption (at 12°C) were significantly higher in open (nonforested) than forested peatlands, and varied as a function of MAT at each site, with maximum CH4 production (>450 nmol g‐1 d‐1) and minimum CH4 consumption (‐0.03 h‐1 g‐1) at intermediate MAT (i.e., CH4 production <200 nmol g‐1 d‐1 and CH4 consumption ‐0.06 h‐1 g‐1 at lower and higher MAT). Differences in lignin chemistry of the peat helped explain the variation in CH4 cycling: Added glucose stimulated CH4 production, but only in lignin‐rich peat. Carbon dioxide production (10–60 μmol g‐1 d‐1 at 12°C) showed a strong negative relationship with MAT and with the...

Tropical Forest Litter Dynamics and Dry Season Irrigation on Barro Colorado Island, Panama

Moisture seasonality may control forest floor decomposition rates in tropical forest. We used a mass balance model and 5 yr (December 1986 through December 1990) of weekly litterfall and monthly forest floor mass measurements from control and dry season irrigated plots to test this hypothesis on Barro Colorado Island, Panama. Litterfall and forest floor mass were greater in the dry season that in the wet season. Irrigation affected neither the timing nor the quantity of litterfall. In contrast, dry season irrigation reduced forest floor mass throughout the year, not just during the dry season. Forest floor decomposition during the dry season was enhanced by irrigation. During the dry season, net decomposition (in grams per square metre per day) and exponential decay coefficients (per day) averaged 48 and 42% greater, respectively, in irrigated plots than in controls plots. As a consequence, seasonal differences in decomposition rates were more pronounced in the control plots than in the irrigated plots. Net decomposition rates, for examples, a averaged 105 and 22% greater during the wet season than during the dry season on control and irrigated plots, respectively. Net decomposition was positively correlated with rainfall in the control plots, but not in the irrigated plots. These results support the hypothesis that moisture seasonality controls forest floor decomposition in tropical moist forests.

Control of carbon mineralization to CH4 and CO2 in anaerobic, Sphagnum-derived peat from Big Run Bog, West Virginia

The mineralization of organic carbon to CH4 and CO2 inSphagnum-derived peat from Big Run Bog, West Virginia, was measured at 4 times in the year (February, May, September, and November) using anaerobic, peat-slurry incubations. Rates of both CH4 production and CO2 production changed seasonally in surface peat (0–25 cm depth), but were the same on each collection date in deep peat (30–45 cm depth). Methane production in surface peat ranged from 0.2 to 18.8 μmol mol(C)−1 hr−1 (or 0.07 to 10.4 μg(CH4) g−1 hr−1) between the February and September collections, respectively, and was approximately 1 μmol mol(C)−1 hr−1 in deep peat. Carbon dioxide production in surface peat ranged from 3.2 to 20 μmol mol(C)−1 hr−1 (or 4.8 to 30.3 μg(CO2) g−1 hr−1) between the February and September collections, respectively, and was about 4 μmol mol(C)−1 hr−1 in deep peat. In surface peat, temperature the master variable controlling the seasonal pattern in CO2 production, but the rate of CH4 production still had the lowest values in the February collection even when the peat was incubated at 19°C. The addition of glucose, acetate, and H2 to the peat-slurry did not stimulate CH4 production in surface peat, indicating that CH4 production in the winter was limited by factors other than glucose degradation products. The low rate of carbon mineralization in deep peat was due, in part, to poor chemical quality of the peat, because adding glucose and hydrogen directly stimulated CH4 production, and CO2 production to a lesser extent. Acetate was utilized in the peat by methanogens, but became a toxin at low pH values. The addition of SO42− to the peat-slurry inhibited CH4 production in surface peat, as expected, but surprisingly increased carbon mineralization through CH4 production in deep peat. Carbon mineralization under anaerobic conditions is of sufficient magnitude to have a major influence on peat accumulation and helps to explain the thin (< 2 m deep), old (> 13,000 yr) peat deposit found in Big Run Bog.

DATING RECENT PEAT DEPOSITS

Dating recent peat deposits (i.e., past } 300 yrs of peat accumulation) has emerged as an important yet challenging task for estimating rates of organic matter accumulation and atmospheric pollutant deposition in peatlands. Due to their ombrotrophic nature and the tendency for Sphagnum-derived peat to have high cation exchange capacity, peatlands are ideal archives of atmospheric pollution. However, efforts to establish depth-age relationships in peats are complicated by the difficulty of dating deposits reliably. Assumptions underlying the techniques available for dating peat deposits often are poorly understood and generally untested. We outline the approaches used to establish depth-age relationships in peat chronologies, including brief descriptions of the theory, assumptions, methodology, and logistics of each technique. We include both continuous dating methods (i.e., methods based on 14C, 210Pb, constant bulk density, acidinsoluble ash, moss increment, pollen density) and chrono-stratigraphic markers (i.e., fallout isotopes from the Chernobyl accident and nuclear weapons testing, pollen stratigraphies, isothermal remanence magnetism, charcoal particles, spherical carbonaceous particles, PAHs, PCBs, DDT, toxaphene) that can be measured in peat and correlated temporally with known historical events. We also describe the relatively new radiocarbon application of wiggle matching and use hypothetical data to highlight the potential of this developing technique for dating recent peat. Until the uncertainty associated with each of these dating approaches is clarified, we recommend employing multiple techniques to allow for corroboration between different methods.

A survey of constructed wetlands for acid coal mine drainage treatment in the Eastern United States

The oxidation of pyritic minerals, exposed to oxygen and water during the mining of coal, results in the formation of acid mine drainage (AMD), which is characterized by low pH and high concentrations of dissolved sulfate, iron, and other metals. Federal and State regulations require that discharges from coal surface mines meet water quality criteria. Toward that end, chemical treatment of AMD, usually with soda ash briquettes, lime, limestone, or sodium hydroxide, is effective but expensive. Recently, man-made wetlands have been proposed as a low-cost, low-maintenance alternative to chemical treatment of AMD. To assess the status of man-made wetland treatment of AMD in the eastern U.S., a survey was conducted by the U.S. Office of Surface Mining, Reclamation, and Enforcement. As of May 1988, 142 wetlands had been constructed for AMD treatment. In 50% of the constructed wetlands, treatment efficiencies (reductions in concentration) for H+, acidity, Fe, Al, Mn, and SO42 of at least 68, 67, 81, 48, 34, and 8%, respectively, were obtained. However, over 11% of the constructed wetlands yielded greater concentrations in the effluent from the wetland than were present in the influent AMD for one or more of these 6 chemical parameters. Treatment efficiency generally was not correlated with design criteria (e.g., area of wetland, depth of the organic substrate in the wetland, AMD flow rate, metal loading rates). Also, treatment efficiency was generally not affected by either the type of organic substrate used in wetland construction or the addition of lime and/or fertilizer to the constructed wetland. The effectiveness of wetland treatment of AMD is not only extremely variable, but also presently not predictable.

Mobility of Pb in Sphagnum-derived peat

One important assumption in applying210Pb-dating is that atmospherically deposited Pb is immobilized in the peat or sediment column. This assumption has been challenged widely, but has never been evaluated experimentally. We evaluated Pb mobility and the chemical forms in which Pb is stabilized in peat profiles by adding either soluble or particulate Pb to intact peat cores that were maintained under different water level regimes (permanently high, permanently low, fluctuating between high and low) and were subjected to simulated precipitation over a five month period. By analyzing the behavior of stable Pb we made inferences about the expected behavior of210Pb. Results indicate that added soluble Pb2+ was retained in the peat through physiochemical binding to organic matter, and as such Pb2+ was largely immobile in peat even under conditions of a fluctuating water table. Added particulate Pb was largely (most likely by physical entrapment), but not completely, immobilized in peat. In none of the water table treatments was there evidence to support mobility of Pb by alternating formation and oxidation of Sulfides, or by any other mechanism. The binding of Pb2+ with organic matter at the peat surface, and the absence of Pb mobility lend credence to210Pb-dating ofSphagnum-dominated peat deposits, which are over 90% organic matter throughout, and have high cation exchange capacities.

RESPONSE OF ANAEROBIC CARBON MINERALIZATION RATES TO SULFATE AMENDMENTS IN A BOREAL PEATLAND

A small body of research suggests that dissimilatory sulfate reduction can affect the carbon balance of peatlands, yet this has not been tested widely, despite the fact that peatlands contain approximately one-third of the global soil carbon pool. Here we evaluate the role of dissimilatory sulfate reduction in a site that receives low atmospheric sulfur deposition. We hypothesized that, in peatlands receiving low sulfate inputs, methane production should dominate anaerobic carbon mineralization. We further hypothesized that with sulfate amendments, anaerobic carbon mineralization could show an overall increase if terminal carbon mineralization in unamended peat is limited by an inadequate supply of electron acceptors. To test these hypotheses, we delineated six 1-m2 plots in an ombrotrophic, boreal peatland in central Alberta, Canada (Bleak Lake Bog), which receives <2 mmol S·m−2·yr−1. Three of the plots were amended with sulfate (78 mmol S·m−2·yr−1). We measured anaerobic rates of sulfate reduction, CH4 production, and CO2 production. In opposition to our hypotheses, sulfate amendments did not increase rates of sulfate reduction, increase CO2 production, or decrease CH4 production over a 2-yr period, but did increase both sulfate pool sizes and residence times. Despite low rates of sulfate reduction compared to other freshwater wetlands, daily average sulfate reduction (1.7 mmol/m2) exceeded regional annual inputs of atmospheric sulfate deposition (1.6 mmol/m2). Between 77% and 99% of reduced sulfate was incorporated into the carbon-bonded sulfur pool, which turns over slowly. The slow turnover rate and comparatively low sulfate reduction rates may be related to the low iron content of the bog peat. Additionally, sulfate reduction initially was sulfate limited in the control plots, but with sulfur amendments, the sulfate limitation was removed; sulfate reduction appeared to be limited by some other factor, possibly labile carbon. Dissimilatory sulfate reduction was more important to total anaerobic carbon mineralization than methane production, although neither process dominated overall anaerobic carbon mineralization (<2% of total). Fermentation appeared to be the dominant anaerobic carbon mineralization pathway at Bleak Lake Bog, yet the mechanisms of how this process affects the carbon balance of peatlands has never been evaluated. Overall, our results suggest that, in at least the short term, soil carbon turnover in peatlands will not be enhanced by increased atmospheric sulfur deposition. If we want to understand the controlling factors on soil carbon storage in sites like Bleak Lake Bog, we should begin to examine anaerobic carbon mineralization via fermentation pathways. Corresponding Editor: J. M. Melack

PAST, PRESENT, AND FUTURE PEATLAND CARBON BALANCE: AN EMPIRICAL MODEL BASED ON 210Pb‐DATED CORES

Boreal and subarctic peatlands today represent a large global carbon (C) reservoir. Existing models that describe organic matter accumulation in peatlands over thousands of years are inadequate for predicting short-term responses to changing climate. This paper develops a new, empirically based model that estimates net primary production (NPP) and depth-dependent decay rates (exponential decay k values) of near-surface peat. Application of the model to three sites in boreal Alberta indicates that today the sites are net sinks for atmospheric C at rates of 34–52 g C·m−2·yr−1. Even without climate change, within 80–160 years, these sites will attain steady-state conditions with no further net C accumulation. Climate change scenarios in which NPP or k values are allowed to change gradually and linearly (at 0.1% per year) affect net C sequestration. Any scenario of decreasing NPP or increasing k values results in the peatlands switching from net sinks to net sources of atmospheric C within the next 20–62 year...

ALKALINITY GENERATION BY Fe(III) REDUCTION VERSUS SULFATE REDUCTION IN WETLANDS CONSTRUCTED FOR ACID MINE DRAINAGE TREATMENT

Despite the widespread use of wetlands for acid mine drainage (AMD) treatment, alkalinity generating mechanisms in wetlands and their abiotic and biotic controls are poorly understood. While both dissimilatory sulfate reduction and Fe(III) reduction are alkalinity-generating mechanisms, only the former has been considered as important in wetlands constructed for AMD treatment. This study was conducted to determine the extent to which Fe(III) reduction occurs and the extent to which sulfate reduction versus Fe(III) reduction contributes to alkalinity generation in 5 wetlands constructed with different organic substrates (Sphagnum peat with limestone and fertilizer, Sphagnum peat, sawdust, straw/ manure, mushroom compost) that had been exposed to the same quality and quantity of AMD for 18–22 months. These substrates had Fe oxyhydroxide concentrations of 250–810 μmol Fe g−1 dry substrate. Flasks containing 100 g of wet substrate along with either 150 mL of wetland water or 130 mL of wetland water and 20 mL of 37 % formalin were incubated at 4 °C in January and 25 °C in May. On days 0, 2, 4, 8, 12 and 16, the slurry mixtures were analyzed for concentrations of H+, Fe2+ and SO42−. The bulk of the evidence indicates that for all except the mushroom compost wetland, especially at 25 °C, biologically-mediated Fe(II) reduction occurred and generated alkalinity. However, in none of the wetlands, regardless of incubation temperature, was there evidence to support net biological sulfate reduction or its attendant alkalinity generation. Sulfate reduction and concurrent Fe(III) oxyhydroxide accumulation may be important in the initial stages of wetland treatment of AMD, both contributing to effective Fe retention. However, as Fe(III) oxyhydroxides accumulate over time, Fe(III) reduction could lead not only to decreased Fe retention, but also to the potential net release of Fe from the wetland.