More evidence that anaerobic oxidation of methane is prevalent in soils: Is it time to upgrade our biogeochemical models?

Estimating future fluxes of CH₄ between land and atmosphere requires well-conceived process-based biogeochemical models. Current models do not represent the anaerobic oxidation of methane (AOM) in land surface soils, in spite of increasing evidence that this process is widespread. Our objective was to determine whether AOM, or potential AOM, commonly occurs in 20 hydromorphic soils spanning a wide range of chemical properties. Bulk soil samples were collected under shallow water near the shoreline of 15 recently drained fish ponds in southern Bohemia (Czech Republic), as well as from below the water table at 3 peatland locations in northeast Scotland and 2 acid sulfate soils on the southern coast of Finland. Each soil slurry was incubated under both oxic and anoxic conditions, with or without the addition of alternative electron acceptors (SO₄²⁻ and NO₃⁻) or H₂PO₄⁻. Here, “oxic” and “anoxic” conditions refer to anoxic soil respectively incubated in a headspace containing air or argon. Using the isotope dilution method, we determined the gross production and oxidation rates of CH₄ after 2 days incubation under oxic headspace conditions, and after 2, 21 and 60 days incubation under anoxic conditions. Large differences in net CH₄ fluxes were observed between soil types and between incubation conditions. AOM was detected in each of the 20 bulk soil samples, which spanned >6 pH units and 2 orders of magnitude in organic C content. Significant positive relationships were found between AOM and gross CH₄ production rates under anoxic conditions, resulting in AOM rates that were sometimes higher than CH₄ oxidation rates under oxic headspace conditions. There was no relationship between net and gross CH₄ production rates, such that 2 soil types could display similar low net rates, yet conceal very large differences in gross rates. The effects of alternative electron acceptors on AOM were idiosyncratic and resulted in no net trend. We did find, however, a negative effect of SO₄²⁻ and H₂PO₄⁻ on gross CH₄ production rates under anoxic and oxic conditions respectively. Under oxic headspace conditions, CH₄ oxidation was related to soil organic C content. Taken collectively, our results suggest that AOM, or potential AOM, is prevalent over a wide range of soil types, that AOM may contribute substantially to CH₄ oxidation in soils, and that AOM in soils should be integrated to current process-based CH₄ cycling models.     

Above- and belowground biomass measurements in an unthinned stand of Sitka spruce (<Emphasis Type="Italic">Picea sitchensis</Emphasis> (Bong) Carr.)

Reporting carbon (C) stocks in tree biomass (above- and belowground) to the United Nations Framework Convention on Climate Change (UNFCCC) should be transparent and verifiable. The development of nationally specific data is considered ‘good practice’ to assist in meeting these reporting requirements. From this study, biomass functions were developed for estimating above- and belowground C stock in a 19-year-old stand of Sitka spruce (Picea sitchensis (Bong) Carr.). Our estimates were then tested against current default values used for reporting in Ireland and literature equations. Ten trees were destructively sampled to develop aboveground and tree component biomass equations. The roots were excavated and a root:shoot (R) ratio developed to estimate belowground biomass. Application of the total aboveground biomass function yielded a C stock estimate for the stand of 74 tonnes C ha⁻¹, with an uncertainty of 7%. The R ratio was determined to be 0.23, with an uncertainty of 10%. The C stock estimate of the belowground biomass component was then calculated to be 17 tonnes C ha⁻¹, with an uncertainty of 12%. The equivalent C stock estimate from the biomass expansion factor (BEF) method, applying Ireland’s currently reported default values for BEF (inclusive of belowground biomass), wood density and C concentration and methods for estimating volume, was found to be 60 tonnes C ha⁻¹, with an uncertainty of 26%. We found that volume tables, currently used for determining merchantable timber volume in Irish forestry conditions, underestimated volume since they did not extend to the yield of the forest under investigation. Mean stock values for belowground biomass compared well with that generated using published models.     

Emissions of CO2, CH4 and N2O from Southern European peatlands

Peatlands play an important role in emissions of the greenhouse gases CO₂, CH₄ and N₂O, which are produced during mineralization of the peat organic matter. To examine the influence of soil type (fen, bog soil) and environmental factors (temperature, groundwater level), emission of CO₂, CH₄ and N₂O and soil temperature and groundwater level were measured weekly or biweekly in loco over a one-year period at four sites located in Ljubljana Marsh, Slovenia using the static chamber technique. The study involved two fen and two bog soils differing in organic carbon and nitrogen content, pH, bulk density, water holding capacity and groundwater level. The lowest CO₂ fluxes occurred during the winter, fluxes of N₂O were highest during summer and early spring (February, March) and fluxes of CH₄ were highest during autumn. The temporal variation in CO₂ fluxes could be explained by seasonal temperature variations, whereas CH₄ and N₂O fluxes could be correlated to groundwater level and soil carbon content. The experimental sites were net sources of measured greenhouse gases except for the drained bog site, which was a net sink of CH₄. The mean fluxes of CO₂ ranged between 139 mg m⁻² h⁻¹ in the undrained bog and 206 mg m⁻² h⁻¹ in the drained fen; mean fluxes of CH₄ were between −0.04 mg m⁻² h⁻¹ in the drained bog and 0.05 mg m⁻² h⁻¹ in the drained fen; and mean fluxes of N₂O were between 0.43 mg m⁻² h⁻¹ in the drained fen and 1.03 mg m⁻² h⁻¹ in the drained bog. These results indicate that the examined peatlands emit similar amounts of CO₂ and CH₄ to peatlands in Central and Northern Europe and significantly higher amounts of N₂O.     

Recycled iron phosphate as a fertilizer raw material for tree stands on drained boreal peatlands

Fertilization of drained peatland forests with easily soluble or slow-release apatite fertilizers can increase phosphorus (P) export to water courses, especially when the soil is low in aluminum (Al) and iron (Fe) hydroxides and oxides. Application of Al and Fe together with P increases P adsorption to the soil and decreases the risk of leaching. The aim of this study was to investigate the use of recycled iron phosphate (rFePO₄) as forest fertilizer raw material from environmental and forest production perspectives. Trial fertilizers with different mixtures of rFePO₄ and Russian Kola apatite (Kap) were applied on 15 mini-catchments (area 100 m²), where the discharge at the outlet was collected, sampled and analyzed throughout the about 4-year measurement period. The foliage P content and height growth of the trees on the mini-catchments were measured. The biomass growth of the extramatrical mycorrhizal mycelia (EMM) was studied with a separate in-growth mesh bag experiment conducted on the same site. The results indicated no increase in phosphorus export to surface waters after application of rFePO₄ and 25/75 and 50/50 mixtures of rFePO₄ and Kap. In contrast to earlier studies showing a relatively high P export with different types of apatite fertilizers, the Kap fertilizer showed only minor phosphorus export. The height growth measurements and needle analyses of the juvenile Scots pine stands indicated poor P availability from pure rFePO₄, but the P availability from the 50/50 and 25/75 mixtures of rFePO₄ and Kap was similar to pure Kap. The mixtures of Kap and rFePO₄ enhanced the EMM biomass by 2- to 3-fold, whereas Kap and rFePO₄ alone, and high P availability (superphosphate) had no significant effect compared to non-P controls. The increase in EMM biomass as induced by concurrent application of Kap and rFePO₄ was not clearly reflected in tree growth and P acquisition. However, longer follow-up studies than in this one may be needed in order to verify the effect of increased EMM biomass on mycorrhizal mycelia mediated nutrient uptake and tree growth.     

Using plant community uniqueness and floristic quality assessment in management decision-making in an urban park setting

With the densification of cities, it is imperative to identify urban ecosystems that should be protected or restored. We aimed to determine the conservation and restoration needs in a large urban park (1,35 km²) in Quebec City (Canada), based on site history, current species richness, floristic uniqueness, and floristic quality assessment of its diverse ecosystems: forest, swamp, wooded peatland, open peatland, and marsh. We evaluated the cover of all vascular species in 70 plots (400 m²) and assessed 18 environmental variables. We found that forest and swamp plots were the richest while peatland plots were the poorest, with marsh plots showing intermediate values. Ecological uniqueness (LCBD) was not correlated with richness (ρ = 0.17; p > 0.05), with marsh and peatland plots showing the highest and lowest uniqueness, respectively. With a regression tree, we identified canopy openness as the most influential variable explaining plot uniqueness across all ecosystems, especially in the peatland, indicating that future recreational development should be avoided in open ecosystems. By plotting ecological uniqueness (LCBD) with tolerance to disturbance (Mean C) values, we identified areas that could benefit from conservation or restoration, and areas that could sustain future development for recreational use. For each area, floristic composition, site characteristics, and past land-use history were investigated further to identify appropriate actions. The open peatland was identified as the main conservation priority, but actions will be needed to limit rapid tree encroachment. Three marshes were identified as areas that would floristically benefit from restoration actions. Still, since they also act as natural retention basins hosting species adapted to the soil conditions, we suggested monitoring the expansion of exotic and invasive species. Approaches developed and lessons learned from this project will serve as guidelines for municipalities aiming to implement a restoration and management plan in urban parks.     

Indirect regulation of heterotrophic peat soil respiration by water level via microbial community structure and temperature sensitivity

Northern peatlands contain a considerable share of the terrestrial carbon (C) pool, which climate change will likely affect in the future. The magnitude of this effect, however, remains uncertain, due mainly to difficulties in predicting decomposition rates in the old peat layers. We studied the effects of water level depth (WL) and soil temperature on heterotrophic soil respiration originating from peat decomposition (R_PD) in six drained peatlands using a chamber technique. The microbial community structure was determined through PLFA. Within the studied sites, temperature appeared to be the main driver of R_PD. However, our results indicate that there exist mechanisms related to lower WL conditions that can tone down the effect of temperature on R_PD. These mechanisms were described with a mathematical model that included the optimum WL response of R_PD and the effect of average WL conditions on the temperature sensitivity of R_PD. The following implications were apparent from the model parameterisation: (1) The instantaneous effect of WL on R_PD followed a Gaussian form; the optimum WL for R_PD was 61 cm. The tolerance of R_PD to the WL, however, was rather broad, indicating that the overall effect of WL was relatively weak. (2) The temperature sensitivity of R_PD depended on the average WL of the plot: plots with a high average WL showed higher temperature sensitivity than did those under drier conditions. This variation in temperature sensitivity of R_PD correlated with microbial community structure. Thus, moisture stress in the surface peat layer or, alternatively, the lowered temperature sensitivity of R_PD in low water level conditions via microbial community structure and biomass may restrict R_PD. We conclude that a warmer future climate may raise R_PD in drained peatlands only if the subsequent decrease in the moisture of the surface peat layers is minor and, thus, conditions remain favourable for decomposition.     

我国泥炭地生态功能及其保护恢复策略

中国泥炭地分布面积广,储量大,泥炭类型多种多样,具有重要的生态功能和利用价值。但目前由于人类的不合理开发利用,使泥炭资源受到严重破坏,泥炭地面临严重的生态和环境问题。在系统生态学原理指导下,运用生态建设方法,开展泥炭资源的合理利用,泥炭地水资源的科学管理研究,积极恢复退化的泥炭地植被,控制农业生产活动,确定合理的泥炭地开发模式。     

Drainage Ditches Facilitate Frog Movements in a Hostile Landscape

Ditches are common in landscapes influenced by agricultural, forestry, and peat mining activities, and their value as corridors remains unassessed. Pond-breeding amphibians can encounter hostile environments when moving between breeding, summering, or hibernation sites, and are likely to benefit from the presence of ditches in the landscape. Within a system consisting of ditch networks in bogs mined for peat in eastern New Brunswick, Canada, I quantified the breeding, survival, and movements of green frogs (Rana clamitans melanota) in drainage ditches and also surveyed peat fields. Frogs rarely ventured on peat fields and most individuals frequented drainage ditches containing water, particularly in late summer. Though frogs did not breed in ditches, their survival rate in ditches was high (88%). Ditches did not hinder frog movements, as frogs moved independently of the current. Results indicate that drainage ditches containing water enable some movements between habitats isolated by peat mining, in contrast to peat surfaces, and suggest they function as amphibian movement corridors. Thus, such drainage ditches may mitigate the effects of peat extraction on amphibian populations. At the very least, these structures provide an alternative to hostile peat surfaces. This study highlights that small-scale corridors are potentially valuable in population dynamics.     

Regional significance of peatlands for avifaunal diversity in southern Québec

Altough peatlands in southern Québec are facing increasing pressure, neither specific nor substantial protection measures have been implemented, partly due to a lack of information on this ecosystem. We determined the contribution of peatlands to bird regional diversity by measuring the difference between peatland and associated regional avifaunas. We sampled 112 peatlands located along the Saint Lawrence River during one breeding season. We used data on regional nesting bird assemblages from the Québec breeding bird atlas. Peatland bird species contrasted increasingly with regional avifauna from north to south or from undisturbed to managed landscapes. Of the 17 bird species found significantly more often in peatlands than in surroundings, some preferred peatlands in the whole study area and others preferred peatlands only in particular regions. Peatland avifaunas within regions were more similar to each other than to their regional avifauna, and differences between regions probably reflected changes in peatland physiognomy. We conclude that peatlands contribute to enrich local and regional avian diversity, particularly in the lowlands of the Saint Lawrence River, where industrial pressure on peatlands is highest.     

Influence of water table levels on CO2 emissions in a Colorado subalpine fen: an in situ microcosm study

We quantified the relationship between water table position and CO₂ emissions by manipulating water table levels for two summers in microcosms installed in a Colorado subalpine fen. Water levels were manipulated in the microcosms by either adding water or removing water and ranged from +10 cm above the soil surface to 40 cm below the soil surface, with ambient water levels in the fen averaging +3 and +2 cm above the soil surface during 1998 and 1999, respectively. Microcosm installation had no significant effect on CO₂ efflux; the 2 year means of natural and reference CO₂ efflux were 205.4 and 213.9 mg CO₂-C m⁻² h⁻¹, respectively (p=0.80). Mean CO₂ emissions were lowest at the highest water tables (water +6 to +10 cm above the soil surface), averaging 133.8 mg CO₂-C m⁻² h⁻¹, increased to 231.3 mg CO₂-C m⁻² h⁻¹ when the water table was +1 to +5 cm above the soil surface and doubled to 453.7 mg CO₂-C m⁻² h⁻¹, when the water table was 0-5 cm below the soil surface. However, further lowering of the water table had little additional effect on CO₂ emissions, which averaged 470.3 and 401.1 mg CO₂-C m⁻² h⁻¹ when the water table was 6-10 cm, and 11-40 cm beneath the soil surface, respectively. The large increase in CO₂ emissions as we experimentally lowered the water table beneath the soil surface, coupled with no increase in CO₂ emissions as we furthered lowered water tables beneath the soil surface, suggest the presence of an easily oxidized labile carbon pool near the soil surface.