Effect of vegetation removal and water table drawdown on the non-methane biogenic volatile organic compound emissions in boreal peatland microcosms

Biogenic volatile organic compound (BVOC) emissions are important in the global atmospheric chemistry and their feedbacks to global warming are uncertain. Global warming is expected to trigger vegetation changes and water table drawdown in boreal peatlands, such changes have only been investigated on isoprene emission but never on other BVOCs. We aimed at distinguishing the BVOCs released from vascular plants, mosses and peat in hummocks (dry microsites) and hollows (wet microsites) of boreal peatland microcosms maintained in growth chambers. We also assessed the effect of water table drawdown (?20 cm) on the BVOC emissions in hollow microcosms. BVOC emissions were measured from peat samples underneath the moss surface after the 7-week-long experiment to investigate whether the potential effects of vegetation and water table drawdown were shown. BVOCs were sampled using a conventional chamber method, collected on adsorbent and analyzed with GC–MS. In hummock microcosms, vascular plants increased the monoterpene emissions compared with the treatment where all above-ground vegetation was removed while no effect was detected on the sesquiterpenes, other reactive VOCs (ORVOCs) and other VOCs. Peat layer from underneath the surface with intact vegetation had the highest sesquiterpene emissions. In hollow microcosms, intact vegetation had the highest sesquiterpene emissions. Water table drawdown decreased monoterpene and other VOC emissions. Specific compounds could be closely associated to the natural/lowered water tables. Peat layer from underneath the surface of hollows with intact vegetation had the highest emissions of monoterpenes, sesquiterpenes and ORVOCs whereas water table drawdown decreased those emissions. The results suggest that global warming would change the BVOC emission mixtures from boreal peatlands following changes in vegetation composition and water table drawdown.     

Contribution of winter to the annual CH4 emission from a eutrophied boreal lake

The springtime methane (CH4) emission from a small, eutrophied boreal lake was assessed during the winter ice-cover by measurement of gas ebullition and CH4 accumulation in the water column in association with the development of oxygen depletion after ice formation. The winter CH4 production was estimated to result in a loss of 3.6-7.9 g CH4 m(-2) from the lake to the atmosphere during the short period of ice melt. This could account for 22-48% of the annual CH4 emission from the pelagic zone of the lake. The contribution of winter to the annual CH4 release can be similar or even higher in seasonally ice-covered northern aquatic ecosystems than in northern terrestrial wetlands, thus winter must be considered in any studies into the aquatic CH4 emissions. The trophic state and wintertime oxygen conditions, linked to the changes in land-use in the catchments and climate, are important factors controlling the springtime lake CH4 emissions.     

A synthesis of the impacts of ditch network maintenance on the quantity and quality of runoff from drained boreal peatland forests

Drained peatlands are an important source of forest biomass in boreal regions and ditch network maintenance (DNM) operations may be needed to restore the drainage functions of ditches. By reviewing the available literature, as well as utilizing an existing hydrological model and analyzing the characteristics of eroded sediments, we assessed the impacts of DNM on runoff and exports of suspended solids (SS), dissolved organic carbon (DOC), nitrogen (N), and phosphorus (P). In general, DNM had minor impact on runoff and dissolved N and P, and it decreased rather than increased DOC exports. To increase the understanding of the hydrochemical impacts of DNM, future research should focus on the characteristics of SS and particulate nutrient exports. A major gap in knowledge is also the very limited regional representativeness of the available studies. High erosion risk in the ditches reaching the mineral soil below peat should be acknowledged when planning mitigation measures.     

Contribution of dissolved sulfates and sulfites in hydrogen sulfide emission from stagnant water bodies in Sri Lanka

Accumulation of sulfur-containing compounds and their bacterial mediated reductions have led to the emission of pungent odors from stagnant water bodies. This study is focused on the contribution of inorganic sulfur compounds in the emission of hydrogen sulfide. The measured dissolved oxygen levels have demonstrated good negative correlations with the dissolved sulfide levels implying the oxygen deficiency is the key for the reduction of sulfate ion and sulfite ion to sulfide ion. Particularly, the dissolved molar fractions of sulfide from the total dissolved sulfur compounds (sulfates, sulfites and sulfides) have a very good correlation with the dissolved oxygen for the stagnant water bodies except the artificially aerated prawn farms. For the stagnant water bodies with significant correlations, linear regressions are reported for them to be utilized in estimating one component of the regression from the measurement of the other. The measured data were further utilized to estimate the levels of hydrogen sulfide gas. The pH of the water bodies has confined much of the dissolved sulfides in the form of bisulfide ion and they can be easily escaped to the atmosphere upon acidification due to industrial discharges and/or acidic precipitations. The estimated levels of hydrogen sulfide just above the water surface were plotted for the most polluted stagnant water body in Sri Lanka for the pH range of 5-10 and temperature range of 25-35 degrees C.     

Methane efflux from littoral vegetation stands of southern boreal lakes: An upscaled regional estimate

We studied the role of vegetated littoral area in the efflux of methane (CH₄) in a southern boreal landscape (1600 km²), in Finland, covered by 619 lakes. A regression model was constructed to describe the relationship between lake area or lake shoreline length and total macrophyte or total emergent macrophyte coverage. Phragmites australis and Equisetum fluviatile were by far the most widely distributed emergent macrophytes in the area with a proportion of 40% of all zone-forming macrophytes. The zone-forming floating-leaved species Nuphar lutea, Potamogeton natans and Sparganium spp. covered 44% of all vegetated littoral areas. The strong temperature dependence of the emission rates was taken into consideration in the emission estimations for P. australis and E. fluviatile. The regional efflux, estimated for the growing seasons 1998–2002, varied between 0.8×10⁵ and 1.1×10⁵ kg CH₄ and between 1.6×10⁵ and 2.4×10⁵ kg CH₄, respectively. The emissions from the stands of floating-leaved species were negligible compared to the emissions from stands of P. australis and E. fluviatile. This indicates that species specific emission rates and areal coverage of the dominating species, as well as ambient temperature, should all be carefully considered when estimating the total regional emissions of CH₄ from lake littorals. The natural open ombrogenous bogs and minerogenous fens in the study region covered a 2.5-fold larger area than P. australis and E. fluviatile littoral, but their emissions were estimated to be only 78% of the emissions of P. australis and E. fluviatile, indicating that vegetated lake littoral is an important natural CH₄ source in the region.     

Measured isoprene emission rates of plants in California landscapes: comparison to estimates from taxonomic relationships

Isoprene emission rates of 64 plant species found in California's urban and natural landscapes were measured using a dynamic flow-through chamber enclosure technique. Species were selected to provide data for previously unmeasured species and to test estimates of isoprene emission rates based upon taxonomic relationships developed for compilation of biogenic emission inventories as proposed by Benjamin et al. (1996, Atmospheric Environment 30, 1437–1452). Branch-level isoprene emission rates ranged from undetectable for 47 species, to 54 μg g⁻¹ h⁻¹ for Quercus kelloggii, California black oak. Isoprene emission rate estimates based on taxonomy agreed well with our measurements for species within the same genus, with the exception of the Quercus genus for which a wide range of isoprene emission rates have been reported. As expected, family-level estimates based on taxonomy showed greater deviation from our measured values than did genus-based estimates. The data developed in the present study support use of a taxonomic predictive methodology, especially if previous measurements within specific families, sub-families, and genera are extensive, and the results of such assignment are treated with proper caution. A taxonomic approach may be most useful where plant species in natural and urban landscapes are numerous, such as in California, where no experimental measurements are available for thousands of species.     

Contribution of isoprene to formaldehyde and ozone formation based on its oxidation products measurement in Beijing,China

The atmospheric mixing ratios of methacrolein (MACR) and methyl vinyl ketone (MVK), the two specific products from isoprene oxidation in the atmosphere, were measured in Beijing from March to November, 2006. Distinct amounts of MACR and MVK were detected during vegetable growing seasons from April to October with ambient levels of 0.11–0.67 ppbv and 0.19–1.36 ppbv, respectively. The reacted isoprene and its ozone formation potentials (OFPs) in Beijing were evaluated in the range of 0.49–3.46 ppbv and 6.4–44.7 ppbv, respectively, from April to October. OFP of the reacted isoprene accounted for 10.6–23.6% of the total OFPs of VOCs (including carbonyls and isoprene) and 6.38–29.9% of the photo-chemically produced ozone. The maximum OFP of the original emitted isoprene prior to its photo-oxidation was calculated as 56.0 ppbv in August. The contribution from the reacted isoprene in Beijing to HCHO formation was also estimated to be in the range of 0.35–2.45 ppbv from April to October, which accounted for 4.6–11.5% of ambient HCHO.     

Phytase-Fe3O4 nanoparticles-loaded microcosms of silica for catalytic remediation of phytate-phosphorous from eutrophic water bodies

Agriculture P management practices elevate the level of inorganic phosphates in soil that results in phosphorous (P) seepage into water-bodies. This is one of the key factors that have accelerated the menace of eutrophication. Phytic acid (phytate)-P-rich plant metabolite is infamous for its anti-nutrient activity and regularly oozing in to environment though discharge of mono-gastric animals. That has amplified the magnitudes of eutrophication. In this work, for catalysis of phytate-P, the metal-organic framework fabricated towards metal oxides (Fe₃O₄) and phytase in highly ordered microcosms of silica was employed. The synthesized framework was characterized through transmission electron microscopy (TEM) and nitrogen isotherm analysis. Average pore diameter of synthesized bisect oval shaped structures was measured around ≈200 nm. Herein, phytase and Fe₃O₄ nanoparticles were loaded to the cavities of microcosms through glutaraldehyde-mediated crosslinking. Whereas Fe₃O₄ nanoparticles act as nano-absorbents that adsorb P liberated from phytase-mediated catalysis of phytate. Kinetic analysis of free and loaded phytase has shown relatively small reduction in catalytic efficiency. These loaded microcosms have removed 60–80% of phytate-phosphate. The optimized process has reduced the growth of photoautotrophs by 50%. Additionally the magnet-assisted separation of loaded microcosms eased the reapplication of loaded microcosms tested for six independent instances. The primary studies conducted to evaluate the geno-toxicity of loaded microcosms have not shown any harmful effect on the process like cell division and seed germination. The efficacy of this method has evaluated towards on-field testing in Changa (Gujarat, India) lake.

     

Importance of water level management for peatland outflow water quality in the face of climate change and drought

Environmental Science and Pollution Research - The impact of different climate scenarios, drought, and water level management on the outflow water quality of peatlands has been investigated. A...     

Biogenic fluxes of halomethanes from Irish peatland ecosystems

Irish peatland ecosystems have been shown to be important sources of low molecular weight halocarbons. Emission of CH₃Br, CH₃Cl, CH₃I and CHCl₃ was recorded from all peatland sites monitored, with minor flux of other halocarbons at certain sites. Fluxes were found to be highly linked to incident light, with strong diurnal cycles recorded at all open peatland sites. Estimates of halomethane emissions, particularly from coastal peatland and conifer plantation forest floor sites, suggests that these ecosystems may make a significant contribution to the global budgets of several important halocarbons. Global annual fluxes of 4.7 (0.1–151.9), 0.9 (0.1–3.3), 5.5 (0.9–43.4), and 1.4 (0.1–12.8) Gg yr⁻¹ for CHCl₃, CH₃Br, CH₃Cl, and CH₃I, respectively, were determined for peatland ecosystems.     

Removal of pyrene from contaminated sediments by mangrove microcosms

The potential of mangrove wetland systems to remove pyrene from surface- or bottom-contaminated sediments was investigated by microcosm studies. The performance of two mangrove plant species, Kandelia candel and Bruguiera gymnorrhiza in pyrene removal was also compared. During the six-months experimental period, the growth of both species in the surface-contaminated microcosms was not significantly different from that in the bottom-contaminated ones, and was comparable to the control (without any pyrene contamination). At the end of six-months treatment, pyrene concentrations in contaminated sediments declined from an initial 3 microg g(-1) to less than 0.4 microg g(-1), indicating that pyrene was successfully removed by mangrove microcosms. Around 96.4% and 92.8% pyrene in microcosms planted with K. candel were removed from the surface- and bottom-contaminated sediments, respectively. The removal percentages were slightly lower in microcosms planted with B. gymnorrhiza. Significant accumulation of pyrene in roots was only found in microcosms having bottom-contaminated sediments, and pyrene concentrations were 3.05 microg g(-1) and 4.50 microg g(-1) in roots of K. candel and B. gymnorrhiza, respectively. These values were much higher than that in control microcosms (without pyrene contamination, root pyrene concentrations were 0.27 microg g(-1) for K. candel and 0.34 microg g(-1) for B. gymnorrhiza) and in microcosms with contaminated sediments placed at the surface layer. Nevertheless, the overall contribution of root accumulation and plant uptake to the removal of pyrene from contaminated sediments was insignificant.     

水位波动带氮素迁移转化规律

为考察水位波动对非饱和-饱和土层中氮素迁移转化的影响,设计土柱实验装置Ⅰ和Ⅱ分别模拟水位稳定与波动两种情景,测定一个水位波动周期内地下水中NO₃^--N、NO₂^--N和NH₄⁺-N浓度变化情况。结果表明,柱Ⅱ水位第1次下降柱内1^#,2^#,3^#,4^#采样点NO₃^--N浓度均增大,增幅分别为6.5%、14.9%、15.33%和19.8%。水位上升时结果相反,分别降低17.3%、26.15%、50.29%和44.61%。第2次水位下降至初始位置4个采样点NO₃^--N浓度再次增大,幅度分别为7.1%、10.6%、13.89%和7.76%。铵态氮呈相反趋势不同程度的变化。水位波动柱Ⅱ连通水槽内总氮量增加显著高于柱I水槽,即水位波动有利于波动带地下水中氮素垂向迁移,加重波动带以下地下水硝酸盐污染。因此,水位波动对氮素迁移转化的影响不容忽视。     

Density of foliage mass and area in the boreal forest cover in Finland,with applications to the estimation of monoterpene and isoprene emissions

The distribution of the density of foliage mass and area in forest canopies throughout Finland (60–70°N) were determined on the basis of the permanent sample plots used in the Finnish National Forest Inventory. These parameters were linked to the long-term monthly mean air temperatures for 1961–1990, which had been converted to hourly temperature and radiation values with the help of a weather simulator in order to calculate the spatial distribution of mean yearly emissions of monoterpene and isoprene over Finland. The mean total density of foliage mass in southern Finland (60°⩽latitude<65°N) was around 500 g m⁻², equivalent to 4–5 m² of total foliage area per m² of land area. In northern Finland (65°⩽latitude<70°N), the maximum values remained below 200–300 g m⁻², or 2–3 m² m⁻². The highest values were achieved in forests dominated by mature Norway spruces. The higher temperatures and longer growing season in southern Finland led to greater emissions than in the rest of the country. Total annual emissions of monoterpene were 1070 kg km⁻² yr⁻¹ in southern Finland and 460 kg km⁻² yr⁻¹ in the north, and those of isoprene from Norway spruce canopies 150 and 40 kg km⁻² yr⁻¹, respectively.     

A land use database and examples of biogenic isoprene emission estimates for the state of Texas, USA

Using data from a variety of sources, land use and vegetation in Texas were mapped with a spatial resolution of approximately 1 km. Over 600 classifications were used to characterize the land use and land cover throughout the state and field surveys were performed to assign leaf biomass densities, by species, to the land cover classifications. The total leaf biomass densities associated with these land use classifications ranged from 0 to 556 g/m², with the highest assigned total and oak leaf biomass densities located in central and eastern Texas. The land cover data were used as input to a biogenic emissions model, GLOBEIS2. Estimates of biogenic emissions of isoprene based on GLOBEIS2 and the new land cover data showed significant differences when compared to biogenic isoprene emissions estimated using previous land cover data and emission estimation procedures. For example, for one typical domain in eastern Texas, total daily isoprene emissions increased by 38% with the new modeling tools. These results may ultimately affect the way in which ozone and other photochemical pollutants are modeled and evaluated in the state of Texas.     

Episodic release of methane bubbles from peatland during spring thaw

Methane (CH(4)) flux into the atmosphere during spring thaw was investigated in a small ombrotrophic peatland (141 degrees 48'E, 43 degrees 19'N, Japan) using the conventional chamber method. More than 50 chamber deployments on top of the snow cover were carried out and continued for more than 165h until the surface snow and underlying ice cover on top of the peat layer had thawed completely. Methane emissions were almost absent in the presence of snow cover. At the very moment the surface ice cover thawed, a large CH(4) flush (>10mgCH(4)m(-2)h(-1)) was recorded, which was on the same order of magnitude as episodic ebullition previously observed in the high-summer. Gas bubbles trapped in the ice layer on top of the waterlogged peat were preliminarily analyzed for the volumetric percentage in the total ice volume and their gas species compositions. Results showed that the bubbles occupied about 3.2% volume and that the mixing ratio of CH(4) in the bubbles was about 20%. The abundance of the bubble-form CH(4) was sufficient to explain the observed episodic CH(4) release during the thaw. Results of this study show that CH(4) emissions during the thaw season have great temporal variability; emission occurs as an episodic release of bubble-form CH(4) stored in the frozen layer. The results also imply the possibility that gas-phase CH(4) plays an important role, not only during the growing season but also in cold-season CH(4) dynamics in northern peatlands.     

低温环境中乙醇汽油和普通汽油的冷凝水与污染物排放

对低温环境中乙醇汽油和普通汽油的冷凝水、CO、HC、NOx和CO2排放特性进行了研究,并对5种排放物的形成机理和排放趋势进行了分析。ECE工况(-20、-10和0 ℃)和怠速工况(-30、-20、-10和0 ℃)下,乙醇汽油和普通汽油的冷凝水排放量主要受含氢量、车辆构造和外界环境的共同影响。ECE工况中冷凝水的总体排放趋势是随着温度降低而增加,乙醇汽油的总排水量持平或略低于普通汽油。-10 ℃时乙醇汽油的高含氧量能促进燃烧速度和燃烧效率,减少CO和HC排放,增加NOx排放;0 ℃时低温环境和乙醇的高汽化潜热会影响可燃混合气形成和燃烧速度,降低缸壁温度,增加CO和HC排放。     

The flux of isoprene from a willow coppice plantation and the effect on local air quality

Isoprene fluxes from a Salix viminalis (willow) plantation in western Sweden were measured using the relaxed eddy accumulation (REA) technique. Fluxes of up to 0.23 μg m⁻² s⁻¹ could be observed. A standard emission factor at 303 K and a PAR flux of 1000 μ mol m⁻² s⁻¹ was estimated to 0.98 μg m⁻² s⁻¹ by using the G93 algorithm. The chemistry of an air parcel passing over a willow coppice plantation was investigated utilising a Lagrangian box model in which the measured isoprene fluxes were used as input data. Dispersion after the field was accounted for by a procedure based on the Gaussian plume model. The calculations indicate that, in most cases, the isoprene emissions have a small effect on the local air quality.     

Remediation of NAPL below the water table by steam-induced heat conduction

Previous experimental studies have shown that NAPL will be removed when it is contacted by steam. However, in full-scale operations, steam may not contact the NAPL directly and this is the situation addressed in this study. A two-dimensional intermediate scale sand box experiment was performed where an organic contaminant was emplaced below the water table at the interface between a coarse and a fine sand layer. Steam was injected above the water table and after an initial heating period the contaminant was recovered at the outlet. The experiment was successfully modeled using the numerical code T2VOC and the dominant removal mechanism was identified to be heat conduction induced boiling of the separate phase contaminant. Subsequent numerical modeling showed that this mechanism was insensitive to the porous medium properties and that it could be evaluated by considering only one-dimensional heat conduction.     

Model evidence for a significant source of secondary organic aerosol from isoprene

We investigate how a recently suggested pathway for production of secondary organic aerosol (SOA) affects the consistency of simulated organic aerosol (OA) mass in a global three-dimensional model of oxidant-aerosol chemistry (GEOS-Chem) versus surface measurements from the interagency monitoring of protected visual environments (IMPROVE) network. Simulations in which isoprene oxidation products contribute to SOA formation, with a yield of 2.0% by mass reduce a model bias versus measured OA surface mass concentrations. The resultant increase in simulated OA mass concentrations during summer of 0.6–1.0 μg m⁻³ in the southeastern United States reduces the regional RMSE to 0.88 μg m⁻³ from 1.26 μg m⁻³. Spring and fall biases are also reduced, with little change in winter when isoprene emissions are negligible.