Methane dynamics across wetland plant species

We examined patterns of methane flux, plant biomass, and microbial methanogenic populations in nine wetland plant species. Methane dynamics varied across plant functional groupings, with patterns distinctive among forbs, clonal dominants, and tussock/clump-forming graminoids. Carex stricta and Scirpus atrovirens showed the highest emissions (31.7 and 20.6 mg CH₄-C m⁻² h⁻¹), followed by other tussock- or clump-forming graminoids that averaged 11.0 mg CH₄-C m⁻² h⁻¹ (Scirpus cyperinus, Glyceria striata, and Juncus effusus). The clonal dominants (Phalaris arundinacea and Typha angustifolia) had the lowest methane emissions (1.3 and 3.4 mg CH₄-C m⁻² h⁻¹) of all seven graminoid species, and the forbs (Mimulus ringens and Verbena hastata) emitted no detectable methane flux from their leaves. In general, methane emissions decreased with greater plant biomass. Terminal restriction fragment analysis (T-RFLP) of archaeal 16S rRNA revealed that the structure of the soil methanogen communities isolated from plant rhizospheres had no effect on methane flux. The relative proportions of the different terminal fragments were not correlated with either methane emissions or plant biomass. Methanogen populations from J. effusus soils were dominated by acetoclastic archaea of the Methanosarcinaceae and Methanosaetaceae families, while all other graminoid soils were colonized primarily by hydrogenotrophic archaea of the Methanobacteriaceae family. The results indicate that plant functional groups and plant biomass are useful in predicting methane flux differences across plant species, while soil methanogen community structure showed no distinguishable patterns.     

潮汐作用对黄河三角洲盐沼湿地甲烷排放的影响

盐沼湿地作为陆海交互作用的过渡带是CH₄重要的自然来源。潮汐活动通过影响CH₄的产生、氧化和传输驱动了湿地CH₄间歇性、周期性的排放。利用涡度相关和微气象监测技术,对黄河三角洲一个盐地碱蓬生态系统CH₄通量、环境因子和水文要素（潮汐）进行了长期连续监测分析了该生态系统生长季CH₄排放的季节动态及潮汐作用对CH₄排放的影响。结果表明：生长季该生态系统是CH₄的排放源,排放日均值为0.063 mg m^-2 h^-1,（范围为-0.36-0.57 mg m^-2 h^-1）。潮汐淹水阶段和落潮后湿润阶段表现为CH₄的显著源。此外我们发现,短期潮汐活动引起土壤干湿状况的变化促进了CH₄脉冲式的排放,因此未来气候变化下温度升高和降雨季节分配引起的土壤干湿变化将会对该区域CH₄排放甚至碳循环产生积极影响。     

Dynamics of gaseous nitrogen and carbon fluxes in riparian alder forests

We studied greenhouse gas (GHG) fluxes in two differently loaded riparian Alnus incana-dominated forests in agricultural landscapes of southern Estonia: a 33-year-old stand in Porijõgi, in which the uphill agricultural activities had been abandoned since the middle of the 1990s, and a 50-year-old stand in Viiratsi, which still receives polluted lateral flow from uphill fields fertilized with pig slurry. In Porijõgi, closed-chamber based sampling lasted from October 2001 to October 2009, whereas in Viiratsi the sampling period was from November 2003 to October 2009. Both temporal and spatial variations in all GHG gas fluxes were remarkable. Local differences in GHG fluxes between micro-sites (“Edge”, “Dry” and “Wet” in Porijõgi, and “Wet”, “Slope” and “Dry” in Viiratsi) were sometimes greater than those between sites. Median values of GHG fluxes from both sites over the whole study period and all microsites did not differ significantly, being 45 and 42 mg CO₂-C m⁻² h⁻¹, 8 and 0.5 μg CH₄-C m⁻² h⁻¹, 1.0 and 2.1 mg N₂-N m⁻² h⁻¹, and 5 and 9 μg N₂O-N m⁻² h⁻¹, in Porijõgi and Viiratsi, respectively. The N₂:N₂O ratio in Viiratsi (40-1200) was lower than in Porijõgi (10-7600). The median values-based estimation of the Global Warming Potential of CH₄ and N₂O was 19 and 185 kg CO₂ equivalents (eq) ha⁻¹ yr⁻¹ in Porijõgi and −14 and 336 kg CO₂ eq ha⁻¹ yr⁻¹ in Viiratsi, respectively. A significant Spearman rank correlation was found between the mean monthly air temperature and CO₂, CH₄ and N₂ fluxes in Porijõgi, and N₂O flux in Viiratsi, and between the monthly precipitation and CH₄ fluxes in both study sites. Higher groundwater level significantly increases CH₄ emission and decreases CO₂ and N₂O emission, whereas higher soil temperature significantly increases N₂O, CH₄ and N₂ emission values. In Porijõgi, GHG emissions did not display any discernable trend, whereas in Viiratsi a significant increase in CO₂, N₂, and N₂O emissions has been found. This may be a result of the age of the grey alder stand, but may also be caused by the long-term nutrient load of this riparian alder stand, which indicates a need for the management of similar heavily loaded riparian alder stands.     

Methane in sulfate-rich and sulfate-poor wetland sediments

Wetlands of northern Belize provide a unique opportunity to study methane production and emissions from marshes dominated by identical species (Typha domingensis, Cladium jamaicense) and genus (Eleocharis spp.), but differing substantially in the amount of sulfates present in the sediments. Some marshes occur on limestone marls rich in gypsum (CaSO₄) while others are underlain by alluvial sands poor in sulfates. Concentrations of methane and sulfates in the sediment interstitial water are one or more orders of magnitude different for these two geological substrata averaging 139.2 and 14.9 M of CH₄, and 0.08 and 11.53 mM of SO₄ ^–2 2 on alluvial sands and limestone respectively. The amount of methane found in the internal atmosphere of plants from alluvial sands is significantly higher (6.3 M) than in plants from limestone (0.19 M). The average methane emissions measured in wetlands located on alluvial sands were 25.2 mg m^–2 h^–1 while emissions from marshes on limestone were only 2.4 mg m^–2 h^–1. These values extrapolated for the entire year and the respective wetland areas resulted in the estimate of total CH4 emissions from northern Belize of 0.066 Tg per year.     

Improvement of methane biofiltration by the addition of non-ionic surfactants to biofilters packed with inert materials

The effect of non-ionic surfactants on the biofiltration of methane (CH₄) was analyzed. Two biofilters (BF) treating CH₄ were operated for one year at fixed CH₄ concentration of 4.8 g m⁻³ and air flow rate of 0.25 m⁻³ h⁻¹. Three polyoxyethylenes (Brijs), and 3 mono polyoxyethylenesorbitans (Tweens) were added to the nutrient solution at a concentration of 0.5% (w/w). Without surfactant, CH₄ conversion had an average level of 35%, with Brijs the CH₄ conversion varied between 38% and 46%, and with Tweens between 43% and 48%. The non-ionic surfactants decreased the biomass accumulation in the packed bed due to their detergent character. Biofilters were operated in a range of nitrogen concentration in the nutrient solution from 0.5 to 2 gN L⁻¹ using Tween 20 at a concentration of 0.5% (w/w). The EC_max observed in this study, 45 g m⁻³ h⁻¹, occurred when the nitrogen concentration was 1 gN L⁻¹.     

Seasonal and spatial variations of methane emissions from coastal marshes in the northern Yellow River estuary, China

Aims and methods

To evaluate the seasonal and spatial variations of methane (CH₄) emissions and understand the controlling factors, we measured CH₄ fluxes and their environmental variables for the first time by a static chamber technique in high Suaeda salsa marsh (HSM), middle S. salsa marsh (MSM), low S. salsa marsh (LSM) and bare flat (BF) in the northern Yellow River estuary throughout a year.

Results

CH₄ emissions from coastal marsh varied throughout different times of the day and significant differences were observed in some sampling periods (p?<?0.05). Over all sampling periods, CH₄ fluxes averaged between ?0.392 mgCH₄ m^?2?h^?1 and 0.495 mgCH₄ m^?2?h^?1, and emissions occurred during spring (0.008 mgCH₄ m^?2?h^?1) and autumn (0.068 mgCH₄ m^?2?h^?1) while sinks were observed during summer (?0.110 mgCH₄ m^?2?h^?1) and winter (?0.009 mgCH₄ m^?2?h^?1). CH₄ fluxes from the four marshes were not significantly different (p?>?0.05), and emissions occurred in LSM (0.026 mgCH₄ m^?2?h^?1) and BF (0.055 mgCH₄ m^?2?h^?1) while sinks were observed in HSM (?0.035 mgCH₄ m^?2?h^?1) and MSM (?0.022 mgCH₄ m^?2?h^?1). The annual average CH₄ flux from the intertidal zone was 0.002 mgCH₄ m^?2?h^?1, indicating that coastal marsh acted as a weak CH₄ source. Temporal variations of CH₄ emission were related to the interactions of abiotic factors (temperatures, soil moisture and salinity) and the variations of limited C and mineral N in sediments, while spatial variations were mainly affected by the vegetation composition at spatial scale.

Conclusions

This study observed a large spatial variation of CH₄ fluxes across the coastal marsh of the Yellow River estuary (CV?=?7856.25 %), suggesting that the need to increase the spatial replicates at fine scales before the regional CH₄ budget was evaluated precisely. With increasing exogenous nitrogen loading to the Yellow River estuary, the magnitude of CH₄ emission might be enhanced, which should also be paid more attentions as the annual CH₄ inventory was assessed accurately.     

Methane emissions from a full-scale A/A/O wastewater treatment plant

Methane (CH₄) emissions from a full-scale anaerobic/anoxic/oxic (A/A/O) wastewater treatment plant (WWTP) (Jinan, China) were investigated during spring and summer of 2010. Results showed that the major emission sources of CH₄ performed the following descending order: anaerobic tanks, oxic tanks, aerated grit chambers and sludge concentration tanks. The total annual fluxes of CH₄ emissions from the Jinan WWTP were 1.69 × 10⁴ kg yr⁻¹, with the emission factors of per capita emissions of 11.3 g CH₄ person⁻¹ yr⁻¹ and flow-based emissions of 1.55 × 10⁻⁴ g CH₄ (L of wastewater)⁻¹. The estimated source strength of methane for all WWTPs in China was 6.2 Gg yr⁻¹ (1 Gg = 10⁹ g). The most significant factors influencing methane emissions were dissolved oxygen concentration in aerated grit chamber and oxic tank and water temperature in high density settler tanks.     

Phosphorus release from sediments in a treatment wetland: Contrast between DET and EPC0 methodologies

Wetlands are capable of reducing nutrient loadings to receiving water bodies, and hence many artificial wetlands have been constructed for wastewater nutrient removal. In this study, diffusive equilibrium in thin films (DETs) and equilibrium phosphorus concentration (EPC₀) analysis were used to examine the role of sediment as a nutrient source or sink in a constructed treatment wetland in summer. The effect of dredging on sediment-water nutrient exchange was also studied. Soluble reactive phosphorus (SRP), ammonium (NH₄⁺) and sulphate (SO₄²⁻) concentration profiles were measured by DET across the sediment-water interface (SWI) in both a settling pond and iris reed bed within the wetland. The SRP concentrations in the sediment pore-waters of the settling pond were extremely high (up to 29,500 μg l⁻¹) near the SWI. This is over an order of magnitude higher than the levels found in the water column, which in turn are over an order of magnitude higher than environmental levels proposed to limit eutrophication in rivers. The profiles demonstrated an average net release of SRP and NH₄⁺ from the settling pond sediment to the overlying water of 58 mg m⁻² d⁻¹ (±32 mg m⁻² d⁻¹ (1 sd)) and 16 mg m⁻² d⁻¹ (±25 mg m⁻² d⁻¹ (1 sd)), respectively. The DET SO₄²⁻ concentration profiles revealed that the sediment was anoxic within 2 cm of the SWI. Dredging of the reed bed made no significant difference to the P release characteristics across the SWI. The EPC₀s were much lower than the SRP concentration of the overlying water, indicating that the sediment had the potential to act as a phosphate sink. The apparent contradiction of the DET and EPC₀ results is attributed to the fact that DET measurements are made in situ, where as EPC₀ measurements are ex situ. These results show that substantial releases of P can occur from wetland sediments, and also highlight the need for caution when interpreting ex situ EPC₀ analytical results.     

Migration and retention of dissolved iron in three mesocosm wetlands

Three mesocosm wetlands (250 cm × 100 cm × 100 cm) with different wetland plants (Calamgrostis angustifolia, CA, Carex lasiocarpa, CL, and C. angustifolia/C. lasiocarpa mixture, AL, respectively) and hydrologic regimes were set to test migration and retention of exogenous dissolved iron ((NH₄)₂Fe(SO₄)₂of 40 mg Fe(II) L⁻¹) in the Sanjiang Plain Wetland in northeast China. The experiment was designed as two stages: open migration period (OMP) for 1.5 d and close retention period (CRP) for 28.5 d. Based on the outflow Fe(II) concentration during the OMP, retention efficiencies (RE) and iron retention fluxes adjusted by area (RF_ad) in the three mesocosm wetlands were calculated, and the migration of iron were modeled using the first-order kinetic model. Outflow pH decreased gradually from a weak alkaline condition to a weak acid condition during the OMP, and then increased during the CRP, while outflow Eh and DO decreased during the experiment. The three mesocosm wetlands had considerable RE ranging from 75% to 98%, with the averaged RF_ad of 4.31 ± 0.17, 4.20 ± 0.16, and 4.37 ± 0.13 g m⁻² h⁻¹ for CA, CL, and AL, respectively. The reduction conditions in the mesocosm wetlands developed after 4 d or 12 d and the former retained iron during the OMP became mobile and discharged primarily in the form of Fe(III). The first-order kinetic model could simulate the outflow concentration of dissolved iron during the OMP (R² = 0.91, 0.69, and 0.68 for CA, CL, and AL, respectively), while the outflow dissolved iron during the CMP was difficult to model because the changed pH and Eh conditions in the mesocosm wetlands cause the former precipitated iron to be mobile after several days.     

Nongrowing season methane emissions–a significant component of annual emissions across northern ecosystems

Wetlands are the single largest natural source of atmospheric methane (CH₄), a greenhouse gas, and occur extensively in the northern hemisphere. Large discrepancies remain between “bottom‐up” and “top‐down” estimates of northern CH₄ emissions. To explore whether these discrepancies are due to poor representation of nongrowing season CH₄ emissions, we synthesized nongrowing season and annual CH₄ flux measurements from temperate, boreal, and tundra wetlands and uplands. Median nongrowing season wetland emissions ranged from 0.9 g/m² in bogs to 5.2 g/m² in marshes and were dependent on moisture, vegetation, and permafrost. Annual wetland emissions ranged from 0.9 g m^?2 year^?1 in tundra bogs to 78 g m^?2 year^?1 in temperate marshes. Uplands varied from CH₄ sinks to CH₄ sources with a median annual flux of 0.0 ± 0.2 g m^?2 year^?1. The measured fraction of annual CH₄ emissions during the nongrowing season (observed: 13% to 47%) was significantly larger than that was predicted by two process‐based model ensembles, especially between 40° and 60°N (modeled: 4% to 17%). Constraining the model ensembles with the measured nongrowing fraction increased total nongrowing season and annual CH₄ emissions. Using this constraint, the modeled nongrowing season wetland CH₄ flux from >40° north was 6.1 ± 1.5 Tg/year, three times greater than the nongrowing season emissions of the unconstrained model ensemble. The annual wetland CH₄ flux was 37 ± 7 Tg/year from the data‐constrained model ensemble, 25% larger than the unconstrained ensemble. Considering nongrowing season processes is critical for accurately estimating CH₄ emissions from high‐latitude ecosystems, and necessary for constraining the role of wetland emissions in a warming climate.     

Assessing constructed wetland functional success using diel changes in dissolved oxygen, pH, and temperature in submerged, emergent, and open-water habitats in the Beaver Creek Wetlands Complex, Kentucky (USA)

We assessed the functional success of restored wetlands by determining if the patterns in dissolved oxygen (DO), temperature, and pH were similar to those conditions observed in natural wetlands. The Beaver Creek Wetlands Complex consists of dozens of marshes and ponds built in a former Licking River floodplain, in the hills of east Kentucky, USA. In natural wetland ecosystems, aquatic primary production is highest in emergent and submerged vegetations zones; where daybreak dissolved oxygen (DO) is often near zero, and DO may rise to well over 100% saturation past mid-day. Open-water areas, dominated by phytoplankton, have less dramatic diel DO fluctuations—often without pre-dawn anoxia. Compared to open water, temperatures fluctuate less dramatically in vascular vegetation, due to shading and suppression of wind and waves. Measurements of ecosystem metabolism (diel changes in DO and pH) in three aquatic habitats of the constructed wetlands (emergent vegetation, submerged vegetation, open water) were compared to these natural ideals. In Beaver Creek Wetlands, water temperature patterns were not as dramatic as in natural habitats, nor did they did follow a similar trend. Waters in emergent vegetation (29.5 °C) were warmest; submerged vegetation coolest (26.5 °C); open-water intermediate (27.4 °C). Diel DO and pH patterns were not similar to natural habitats. Highest net primary production (NPP) and gross primary production (GPP) were measured in emergent vegetation waters (mean GPP = 7.58 g m⁻² d⁻¹); lowest in submerged vegetation (mean GPP = 5.48 g m⁻² d⁻¹); and intermediate in open-water (mean GPP = 6.95 g m⁻²d⁻¹). Diel pH changes were greatest in the highly productive emergent waters (median maximum daily difference of 0.36), and not as pronounced in submerged vegetation and open-water (median maximum change = 0.16 and 0.22, respectively). Water-column respiration was generally about double NPP. Like natural ecosystems, near anoxic DO concentrations were consistently measured in emergent and submerged plants before dawn; whereas open-water zones were generally >4 mg l⁻¹. These restored wetland systems may need more time to be functionally equivalent to natural marshes.     

Chlorobenzene removal efficiencies and removal processes in a pilot-scale constructed wetland treating contaminated groundwater

Low-chlorinated benzenes (CBs) are widespread groundwater contaminants and often threaten to contaminate surface waters. Constructed wetlands (CWs) in river floodplains are a promising technology for protecting sensitive surface water bodies from the impact of CBs. The efficiency and seasonal variability of monochlorobenzene (MCB), 1,4-dichlorobenzene (1,4-DCB) and 1,2-dichlorobenzene (1,2-DCB) removal, the impact of planting, and gaseous MCB emissions from the filter surface were investigated over the course of 1 year in both a vegetated pilot-scale CW and an unplanted reference plot (UR). Annual mean concentration decreases of MCB and 1,4-DCB were observed; however, annual mean 1,2-DCB removal was seen only in the upper filter layer. Planting (Phragmites australis) had a statistically significant beneficial effect on removal. The CB removal efficiency in the CW generally decreased with depth, and seasonal variations of removal were evident, with less concentration decrease during summer. Load removal efficiencies of 59-65% (262-358 mg m⁻² d⁻¹) for MCB, 59-69% (4.0-5.1 mg m⁻² d⁻¹) for 1,4-DCB and 29-42% (0.6-2.1 mg m⁻² d⁻¹) for 1,2-DCB were observed in June and July. Volatilization of MCB from the filter surface accounted for 2-4% of the total amount removed. Simple cover layers of organic materials on the filter surface were suitable for MCB emission reduction. Model calculations were carried out to estimate the MCB removal potential attributable to microbial degradation, volatilisation, and plant uptake in the CW and UR. Microbial degradation was the dominating process. The observed positive impact of plants on MCB removal was caused by improved oxygen supply (due to root oxygen release into the rhizosphere and enhanced water table fluctuations), and direct plant uptake.     

Emission of Methane and Nitrous Oxide by Australian Mangrove Ecosystems

Abstract: The fluxes of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O) were measured in mangrove wetlands in Queensland, Australia, using the closed chamber technique. Large differences in the fluxes of both gases from different study sites were observed, which presumably depended on differences in substrate availability. CH₄ emission rates were in the range of 20 to 350 μg m^‐2 h^‐1, whereas N₂O fluxes were lower, amounting to ‐ 2 to 14 μg m^‐2 h^‐1. In general, the field sites with high substrate availability showed higher emissions than sites with poor nutrient supply. This assumption is supported by the observation of dramatically increased N₂O emissions (150 ‐ 400 μg m^‐2 h^‐1) if study sites were artificially fertilised with additional N. As expected, N fertilisation did not alter CH₄ fluxes during the period of investigation. In the present study, it was confirmed that the mangrove vegetation may play a role as a transport path for CH₄ and N₂O by facilitating diffusion out of the soil. Prop roots from Rhizophora stylosa emitted CH₄ and N₂O at rates of 2.6 and 3.3 μg m^‐2 root surface h^‐1, respectively, whereas the soil of this stand acted as a sink for CH₄. As a consequence, the ecosystem as a whole could constitute a CH₄ source despite CH₄ uptake by the soil. In contrast to prop roots, the presence of pneumatophores in Avicennia marina led to a significant increase in CH₄ emissions from mangrove soils, but did not enhance N₂O emissions. These findings indicate that mangrove ecosystems may be considered a significant source of N₂O and that anthropogenic nutrient input into these ecosystems will lead to enhanced source strengths. For an up‐scaling of greenhouse gas emissions from mangrove forests to a global scale, more information is needed, particularly on the significance of vegetation.     

Fluxes of nitrous oxide and methane on an abandoned peat extraction site: Effect of reed canary grass cultivation

Drained organic soils are among the most risky soil types as far as their greenhouse gas emissions are considered. Reed canary grass (RCG) is a potential bioenergy crop in the boreal region, but the atmospheric impact of its cultivation is unknown. The fluxes of N₂O and CH₄ were measured from an abandoned peat extraction site (an organic soil) cultivated with RCG using static chamber and snow gradient techniques. The fluxes were measured also at an adjacent site which is under active peat extraction and it is devoid of any vegetation (BP site). The 4-year average annual N₂O emissions were low being 0.1 and 0.01 g N₂O m⁻² a⁻¹ at the RCG and BP sites, respectively. The corresponding mean annual CH₄ emissions from the RCG and BP sites were also low (0.4 g and 0.9 g CH₄ m⁻² a⁻¹). These results highlight for the first time that there are organic soils where cultivation of perennial bioenergy crops is possible with low N₂O and CH₄ emissions.     

Rates, controls and potential adverse effects of nitrate removal in a denitrification bed

Denitrification beds are a simple approach for removing nitrate (NO₃⁻) from a range of point sources prior to discharge into receiving waters. These beds are large containers filled with woodchips that act as an energy source for microorganisms to convert NO₃⁻ to nitrogen (N) gases (N₂O, N₂) through denitrification. This study investigated the biological mechanism of NO₃⁻ removal, its controlling factors and its adverse effects in a large denitrification bed (176 m × 5 m × 1.5 m) receiving effluent with a high NO₃⁻ concentration (>100 g N m⁻³) from a hydroponic glasshouse (Karaka, Auckland, New Zealand). Samples of woodchips and water were collected from 12 sites along the bed every two months for one year, along with measurements of gas fluxes from the bed surface. Denitrifying enzyme activity (DEA), factors limiting denitrification (availability of carbon, dissolved organic carbon (DOC), dissolved oxygen (DO), temperature, pH, and concentrations of NO₃⁻, nitrite (NO₂⁻) and sulfide (S²⁻)), greenhouse gas (GHG) production - as nitrous oxide (N₂O), methane (CH₄), carbon dioxide (CO₂) - and carbon (C) loss were determined. NO₃⁻-N concentration declined along the bed with total NO₃⁻-N removal rates of 10.1 kg N d⁻¹ for the whole bed or 7.6 g N m⁻³ d⁻¹. NO₃⁻-N removal rates increased with temperature (Q₁₀ = 2.0). In laboratory incubations, denitrification was always limited by C availability rather than by NO₃⁻. DO levels were above 0.5 mg L⁻¹ at the inlet but did not limit NO₃⁻-N removal. pH increased steadily from about 6 to 7 along the length of the bed. Dissolved inorganic carbon (C-CO₂) increased in average about 27.8 mg L⁻¹, whereas DOC decreased slightly by about 0.2 mg L⁻¹ along the length of the bed. The bed surface emitted on average 78.58 μg m⁻² min⁻¹ N₂O-N (reflecting 1% of the removed NO₃⁻-N), 0.238 μg m⁻² min⁻¹ CH₄ and 12.6 mg m⁻² min⁻¹ CO₂. Dissolved N₂O-N increased along the length of the bed and the bed released on average 362 g dissolved N₂O-N per day coupled with N₂O emission at the surface about 4.3% of the removed NO₃⁻-N as N₂O. Mechanisms to reduce the production of this GHG need to be investigated if denitrification beds are commonly used. Dissolved CH₄ concentrations showed no trends along the length of the bed, ranging from 5.28 μg L⁻¹ to 34.24 μg L⁻¹. Sulfate (SO₄²⁻) concentrations declined along the length of the bed on three of six samplings; however, declines in SO₄²⁻ did not appear to be due to SO₄²⁻ reduction because S²⁻ concentrations were generally undetectable. Ammonium (NH₄⁺) (range: <0.0007 mg L⁻¹ to 2.12 mg L⁻¹) and NO₂⁻ concentrations (range: 0.0018 mg L⁻¹ to 0.95 mg L⁻¹) were always very low suggesting that anammox was an unlikely mechanism for NO₃⁻ removal in the bed. C longevity was calculated from surface emission rates of CO₂ and release of dissolved carbon (DC) and suggested that there would be ample C available to support denitrification for up to 39 years.This study showed that denitrification beds can be an efficient tool for reducing high NO₃⁻ concentrations in effluents but did produce some GHGs. Over the course of a year NO₃⁻ removal rates were always limited by C and temperature and not by NO₃⁻ or DO concentration.     

Spatial and Seasonal CH4 Flux in the Littoral Zone of Miyun Reservoir near Beijing: The Effects of Water Level and Its Fluctuation

Wetlands, and especially their littoral zones, are considered to be CH₄ emissions hotspots. The recent creation of reservoirs has caused a rapid increase in the area of the world’s littoral zones. To investigate the effects of water depth and water level fluctuation on CH₄ fluxes, and how these are coupled with vegetation and nutrients, we used static closed chamber and gas chromatography techniques to measure CH₄ fluxes in the littoral zone of a large reservoir near Beijing, China, from November 2011 to October 2012. We found that CH₄ flux decreased significantly along a transect from open water to dry land, from 3.1 mg m⁻² h⁻¹ at the deep water site to approximately 1.3 mg m⁻² h⁻¹ at the shallow water site, and less than 0.01 mg m⁻² h⁻¹ in the non-flooded area. Water level influenced CH₄ flux by affecting soil properties including soil redox potential, soil carbon and nitrogen, and bulk density. The largest emission of all was from the seasonally flooded site after a flooding event (up to 21.1 mg m⁻² h⁻¹), which may have been caused by vegetation decomposition. Submerged sites had greater emissions, while the driest site had lower emissions. Immediately after the monthly measurements had been made, we removed the aboveground vegetation to enable an assessment of the gas transportation per unit of biomass. Removal of biomass decreased emissions by up to 53%. These results indicated the dominant effect of water depth on CH₄ flux through effects of soil conditions, plant species composition and distribution. This study suggests that temporally flooded wetlands, including littoral zones, contribute significantly to the global CH₄ burden. However, the current challenge is to capture their spatial extent and temporal variation in the fluxes.     

A synthesis of methane emissions from shallow vegetated coastal ecosystems

Vegetated coastal ecosystems (VCEs; i.e., mangroves, salt marshes, and seagrasses) play a critical role in global carbon (C) cycling, storing 10× more C than temperate forests. Methane (CH₄), a potent greenhouse gas, can form in the sediments of these ecosystems. Currently, CH₄ emissions are a missing component of VCE C budgets. This review summarizes 97 studies describing CH₄ fluxes from mangrove, salt marsh, and seagrass ecosystems and discusses factors controlling CH₄ flux in these systems. CH₄ fluxes from these ecosystems were highly variable yet they all act as net methane sources (median, range; mangrove: 279.17, ?67.33 to 72,867.83; salt marsh: 224.44, ?92.60 to 94,129.68; seagrass: 64.80, 1.25–401.50 µmol CH₄ m^?2 day^?1). Together CH₄ emissions from mangrove, salt marsh, and seagrass ecosystems are about 0.33–0.39 Tmol CH₄‐C/year—an addition that increases the current global marine CH₄ budget by more than 60%. The majority (~45%) of this increase is driven by mangrove CH₄ fluxes. While organic matter content and quality were commonly reported in individual studies as the most important environmental factors driving CH₄ flux, they were not significant predictors of CH₄ flux when data were combined across studies. Salinity was negatively correlated with CH₄ emissions from salt marshes, but not seagrasses and mangroves. Thus the available data suggest that other environmental drivers are important for predicting CH₄ emissions in vegetated coastal systems. Finally, we examine stressor effects on CH₄ emissions from VCEs and we hypothesize that future changes in temperature and other anthropogenic activites (e.g., nitrogen loading) will likely increase CH₄ emissions from these ecosystems. Overall, this review highlights the current and growing importance of VCEs in the global marine CH₄ budget.     

基于过程模型的青藏高原湿地甲烷排放格局评估

甲烷(CH₄)是大气中最丰富的碳氢化合物,是仅次于二氧化碳(CO₂)的温室气体。湿地是甲烷的重要来源,在全球碳循环中发挥着重要作用,其排放的甲烷占所有天然甲烷排放源的70%,占全球甲烷排放总量的24.8%。青藏高原平均海拔4000 m以上,占有中国约三分之一的湿地。近几十年来,由于全球气候变暖和降水增加,该地区甲烷排放率和湿地面积都发生着巨大变化,因此,青藏高原湿地CH₄排放的长期变化在很大程度上仍存在较大的不确定性。利用TRIPLEX-GHG模型模拟了青藏高原湿地1978—2008年CH₄排放的动态特征,研究结果表明:(1)1978—2008年青藏高原湿地CH₄排放速率呈逐渐增加趋势。(2)青藏高原大多数湿地区域CH₄排放速率为0—6.13 g CH₄ m^-2 a^-1;东北部分湿地区域CH₄排放速率为6.14—20.19 g CH₄ m^...     

Potential for methane production from anaerobic co-digestion of swine manure with winery wastewater

This work examines the methane production potential for the anaerobic co-digestion of swine manure (SM) with winery wastewater (WW). Batch and semi-continuous experiments were carried out under mesophilic conditions. Batch experiments revealed that the highest specific methane yield was 348 mL CH₄ g⁻¹ COD added, obtained at 85.4% of WW and 0.7 g COD g⁻¹ VS. Specific methane yield from SM alone was 27 mL CH₄ g⁻¹ COD added d⁻¹. Furthermore, specific methane yields were 49, 87 and 107 mL CH₄ g⁻¹ COD added d⁻¹ for the reactors co-digesting mixtures with 10% WW, 25% WW and 40% WW, respectively. Co-digestion with 40% WW improved the removal efficiencies up to 52% (TCOD), 132% (SCOD) and 61% (VSS) compared to SM alone. These results suggest that methane can be produced very efficiently by the co-digestion of swine manure with winery wastewater.     

Effects of eutrophic water flooding on nitrate concentrations in mine wastes

Salt marshes near urban, industrial and mining areas are often affected both by heavy metals and by eutrophic water. The aim of this study was to assess and evaluate the main processes involved in the decrease of nitrate concentration in pore water of mine wastes flooded with eutrophic water, considering the presence or absence of plant rhizhosphere. Basic (pH ∼ 7.8) carbonated loam mine wastes and free-carbonated acidic (pH ∼ 6.2) sandy-loam mine wastes were collected from polluted coastal salt marshes of SE Spain which regularly receive nutrient-enriched water. The wastes were put in pots and flooded for 15 weeks with eutrophic water (dissolved organic carbon ∼26 mg L⁻¹, PO₄³⁻ ∼23 mg L⁻¹, NO₃⁻ ∼180 mg L⁻¹). Three treatments were assayed for each type of waste: pots with Sarcocornia fruticosa, pots with Phragmites australis and unvegetated pots. Soluble organic carbon, nitrate, soluble Cd, Pb and Zn, pH and Eh were monitored. But the 2nd day of flooding, nitrate concentrations had decreased between 70% and 90% (equivalent to 1.01-1.12 g N-NO₃⁻ m⁻² day⁻¹) with respect to the content in the water used for flooding, except in unvegetated pots with acidic wastes. Denitrification was the main mechanism associated with the removal of nitrate. The role of vegetation in improving the rhizospheric environment was relevant in the acidic wastes because higher sand content, lower pH and higher soluble metal concentrations might strongly hinder microbial activity Hence, revegetation of salt marshes polluted by acidic sandy mining wastes might improve the capacity of this type of environment to act as a green filter against excessive nitrate contents flowing through them.