Monoterpene emissions and carbonyl compound air concentrations during the blooming period of rape (Brassica napus)

An increasing percentage of agricultural land in Germany is used for oil seed plants. Hence, rape has become an important agricultural plant (in Saxony 1998: 12% of the farmland) in the recent years. During flowering of rape along with intensive radiation and high temperatures, a higher production and emission of biogenic VOC was observed. The emissions of terpenes were determined and more importantly, high concentrations of organic carbonyl compounds were observed during this field experiment. All measurements of interest have been carried out during two selected days with optimal weather conditions. It is found that the origin or the mechanism of formation of different group of compounds had strong influence on the day to day variation of their concentrations. The emission flux of terpenes from flowering rape plants was determined to be 16–32 μg h⁻¹ m⁻² (30–60 ng h⁻¹ per g dry plant––540–1080 ng h⁻¹ per plant), in total. Limonene, -thujene and sabinene were the most important compounds (about 60% of total terpenes). For limonene and sabinene reference emission rates (M_S) and temperature coefficients were determined: β_limonene=0.108 K⁻¹ and M_S=14.57 μg h⁻¹ m⁻²; β_sabinene=0.095 K⁻¹ and M_S=5.39 μg h⁻¹ m⁻².

The detected carbonyl compound concentrations were unexpectedly high (maximum formaldehyde concentration was 18.1 ppbv and 3.4 ppbv for butyraldehyde) for an open field. Possible reasons for these concentrations are the combination of primary emission from the plants induced by high temperature and high ozone stress, the secondary formation from biogenically and advected anthropogenically emitted VOC at high radiation intensities and furthered by the low wind speeds at this time.     

Decomposition of chlorinated dioxins, odourous compounds and NOx from MSW incineraton plant by oxidizing catalyst

An experiment was carried out to decompose chlorinated dioxins (PCDDs, PCDFs) Chlorobenzenes, NOx and odourous compounds (H₂S, CH₄S, C₂H₆S₂, C₈H₈, C₂H₆S, C₂H₄O, NH₃) simultaneously using a catalyst in the MSW incineration plant. The experiments were conducted at temperatures from 200°C to 400°C and from 3000h⁻¹ to 6000h⁻¹ at space velocity. A catalyst containing V₂O₅ and WO₃ on the basis of TiO₂ is used, an oxidizing catalyst of the honeycomb type. The average decomposition efficiencis were 95%, 98%, 92% for PCDDs(48CDDs), PCDFs(48CDFs) and Chlorobenzenes(36CLBs) at a reaction temperature of 350°C and a space velocity of 3000h⁻¹, more than 90% for NOx at a reactiont temperature of 300°C and more than 80% for odourous compounds at the reaction temperature of 300°C and a space velocity of 6000h⁻¹. All those compounds were decomposed successfully with increasing contact time and surface. The rate-determing step was the chemical reaction of catalyst surface.     

Biodegradation kinetics and toxicity of vegetable oil triacylglycerols under aerobic conditions

The aerobic biodegradation of five triacylglycerols (TAGs), three liquids [triolein (OOO), trilinolein (LLL), and trilinolenin (LnLnLn)] and two solids [tripalmitin (PPP) and tristearin (SSS)] was studied in water. Respirometry tests were designed and conducted to determine the biochemical oxygen demand (BOD) parameters of the compounds. In the case of the solid lipids, the degradation process was limited by their extremely non-polar nature. When added to water, PPP and SSS formed irregular clumps or gumballs, not a fine and uniform suspension required for the lipase activity. After 30 days, appreciable mineralization was not achieved; therefore, first-order biodegradation coefficients could not be determined. The bioavailability of the liquid TAGs was restricted due to the presence of double bonds in the fatty acids (FAs). An autoxidation process occurred in the allylic chains, resulting in the production of hydroperoxides. These compounds polymerized and became non-biodegradable. Nevertheless, the non-oxidized fractions were readily mineralized, and BOD rate constants were estimated by non-linear regression: LLL (k = 0.0061 h⁻¹) and LnLnLn (k = 0.0071 h⁻¹) were degraded more rapidly than OOO (k = 0.0025 h⁻¹). Lipids strongly partitioned to the biomass and, therefore, Microtox^® toxicity was not observed in the water column. However, EC₅₀ values (<15% sample volume) were measured in the solid phase.     

Methane fluxes from tundra soils and snowpack in the maritime Antarctic

Methane fluxes were measured from three exposed tundra sites and four snowpack sites on the Fildes Peninsula in the maritime Antarctic in the summertime of 2002. The average fluxes at two normal tundra sites were −15.3 μg m⁻² h⁻¹ and −14.3 μg m⁻² h⁻¹, respectively. The fluxes from tundra site with fresh penguin dropping addition showed positive values with the average of 36.1 μg m⁻² h⁻¹, suggesting that the deposition of fresh droppings greatly enhanced CH₄ emissions from the poor Antarctic tundra during penguin breeding periods. The summertime variation in CH₄ flux was correlated with surface ground temperature and the precipitation. The correlation between the flux and PT₀, which is the product of the precipitation and surface ground temperature, was quite strong. The diurnal cycle of CH₄ flux from the tundra soils was not obtained due to local fluky weather conditions. The fluxes through four snowpack sites were also obtained by the vertical CH₄ concentration gradient and their average fluxes were −46.5 μg m⁻² h⁻¹, −28.2 μg m⁻² h⁻¹, −46.4 μg m⁻² h⁻¹ and −17.9 μg m⁻² h⁻¹, respectively, indicating that tundra soils under snowpack also consume atmospheric CH₄ in the maritime Antarctic; therefore these fluxes could constitute an important part of the annual CH₄ budget for Antarctic tundra ecosystem.     

Laboratory shake flask batch tests can predict field biodegradation of aniline in the Rhine

The aim of this study was to compare degradation rates of aniline in laboratory shake flask simulation tests with field rates in the river Rhine. The combined events of a low flow situation in the Rhine and residual aniline concentrations in the effluent from the BASF treatment plant in Ludwigshafen temporarily higher than normal, made it possible to monitor aniline at trace concentrations in the river water downstream the wastewater outlet by means of a sensitive GC headspace analytical method. Aniline was analyzed along a downstream gradient and the dilution along the gradient was calculated from measurements of conductivity, sulfate and a non-readily biodegradable substance, 1,4-dioxane. Compensating dilution, field first-order degradation rate constants downstream the discharge of BASF were estimated at 1.8 day⁻¹ for two different dates with water temperatures of 21.9 and 14.7 °C, respectively. This field rate estimate was compared with results from 38 laboratory shake flask batch tests with Rhine water which averaged 1.5 day⁻¹ at 15 °C and 2.0 day⁻¹ at 20 °C. These results indicate that laboratory shake flask batch tests with low concentrations of test substance can be good predictors of degradation rates in natural water bodies––at least as ascertained here for short duration tests with readily degradable compounds among which aniline is a commonly used reference.     

Isoprene emission from tropical trees in Okinawa Island, Japan

This study surveyed isoprene emission from 42 indigenous and exotic tropical trees in subtropic Okinawa, Japan. Of the 42 trees studied, 4 emitted isoprene at a rate in excess of 20 μg g⁻¹ h⁻¹, and 28 showed the rates of 1–10 μg g⁻¹ h⁻¹. The remainder emitted less than 1 μg g⁻¹ h⁻¹. The majority of trees in this study may therefore fall within the lower emitting species. However, species in Moraceae that is indigenous in Okinawa emitted isoprene at relatively higher rates with an average of 14.2 μg g⁻¹ h⁻¹. The highest emission rate of 107.1 μg g⁻¹ h⁻¹ for Ficus virgata yielded the area basis rate of 47.4 nmol m⁻² s⁻¹, which is almost equivalent to the rate of high emitting species. Furthermore, a linear relationship between light intensity and isoprene emission was noted with Ficus virgata up to 1700 μmol m⁻² s⁻¹. These findings may show the potential importance of subtropical areas as sources of isoprene to the atmosphere.     

Continuous time random walk model better describes the tailing of atrazine transport in soil

Contaminant transport in soils is complicated and involves some physical and chemical nonequilibrium processes. In this research, the soil column displacement experiments of Cl⁻ and atrazine under different flow velocities were carried out. The data sets of Cl⁻ transport in sandy loam fitted to the convection dispersion equation (CDE) and the two-region model (TRM) indicated that the effects of physical nonequilibrium process produced by immobile water on the breakthrough curves (BTCs) of Cl⁻ and atrazine transport through the repacking soil columns were negligible. The two-site model (TSM) and the continuous time random walk (CTRW) were also used to fit atrazine transport behavior at the flow rate of 19.86 cm h⁻¹. The CTRW convincingly captured the full evolution of atrazine BTC in the soil column, especially for the part of long tailing. However, the TSM failed to characterize the tailing of atrazine BTC in the soil column. The calculated fraction of equilibrium sorption sites, F, ranging from 0.78 to 0.80 for all flow rates suggested the contribution of nonequilibrium sorption sites to the asymmetry of atrazine BTCs. Furthermore, the data sets for the flow rates of 6.68 cm h⁻¹ and 32.81 cm h⁻¹ were predicted by the TSM and the CTRW. As to the flow rate of 6.68 cm h⁻¹, the CTRW predicted the entire BTC of atrazine transport better than the TSM did. For the flow rate of 32.81 cm h⁻¹, the CTRW characterized the late part of the tail better, while the TSM failed to predict the tailings of atrazine BTC.     

Release flux of mercury from different environmental surfaces in Chongqing, China

An investigation was conducted to estimate mercury emission to the atmosphere from different environmental surfaces and to assess its contribution to the local mercury budget in Chongqing, China. Mercury flux was measured using dynamic flux chamber (DFC) at six soil sites of three different areas (mercury polluted area, farmland and woodland) and four water surfaces from August 2003 to April 2004. The mercury emission fluxes were 3.5 ± 1.2–8.4 ± 2.5 ng m⁻² h⁻¹ for three shaded forest sites, 85.8 ± 32.4 ng m⁻² h⁻¹ for farming field, 12.3 ± 9.8–733.8 ± 255 ng m⁻² h⁻¹ for grassland sites, and 5.9 ± 12.6–618.6 ± 339 ng m⁻² h⁻¹ for water surfaces. Mercury exchange fluxes were generally higher from air/water surfaces than from air/soil surfaces. The mercury negative fluxes were found in tow soil sites at overcast days (mean = −6.4 ± 1.5 ng m⁻² h⁻¹). The diurnal and seasonal variations of mercury flux were observed in all sites. The mercury emission responded positively to the solar radiation, but negatively to the relative humidity. The mercury flux from air/soil surfaces was significantly correlated with soil temperature, which was well described by an Arrhenius-type expression with activation energy of 31.1 kcal mol⁻¹. The annual mercury emission to the atmosphere from land surface is about 1.787 t of mercury in Chongqing.     

Octyl and nonylphenol ethoxylates and carboxylates in wastewater and sediments by liquid chromatography/tandem mass spectrometry

This work presents an LC–MS–MS-based method for the quantitation of nonylphenol ethoxylates (NPEOs) and octylphenol ethoxylates (OPEOs) in water, sediment, and suspended particulate matter, and three of their carboxylated derivatives in water. The alkylphenol ethoxylates (APEOs) were analyzed using isotope dilution mass spectrometry with [¹³C₆]-labeled analogues, whereas the carboxylated derivatives were determined by external standard quantitation followed by confirmation using standard additions. The method was used to study APEO’s behavior in a wastewater treatment plant (WWTP), where total dissolved NP0-16EO concentration was reduced by approximately 99% from influent (390 μg l⁻¹) to final effluent (4 μg l⁻¹), and total OP0-5EO concentration decreased by 94% from 3.1 to 0.2 μg l⁻¹. In contrast, the carboxylated derivatives were formed during the process with NP0-1EC concentrations increasing from 1.4 to 24 μg l⁻¹. Short-chain APEOs were present in higher proportions in particulate matter, presumably due to greater affinity for solids compared to the long-chain homologues. NP (0.49 μg l⁻¹) and NP0-1EC (4.8 μg l⁻¹) were the only APEO-related compounds detected in a surface water sample from a WWTP-impacted estuary; implying that 90% of the mass was in the form of carboxylated derivatives. Sediment analysis showed nonylphenol to be the single most abundant compound in sediments from the Baltimore Harbor area, where differences in homologue distribution suggested the presence of treated effluent in some of the sites and non-treated sources in the rest.     

Nitrous oxide emissions from tundra soil and snowpack in the maritime Antarctic

The nitrous oxide emissions were measured at three tundra sites and one snowpack on the Fildes Peninsula in the maritime Antarctic in the summertime of 2002. The average fluxes at two normal tundra sites were 1.1 ± 2.2 and 0.6 ± 1.7 μg N₂O m⁻² h⁻¹, respectively. The average flux from tundra soil site with penguin dropping addition was 3.7 ± 2.0 μg N₂O m⁻² h⁻¹, 3–6 times those from the normal tundra soils, suggesting that the deposition of fresh droppings enhanced N₂O emissions during penguin breeding period. The summer precipitation had an important effect on N₂O emissions; the flux decreased when heavy precipitation occurred. The diurnal cycle of the N₂O fluxes from Antarctic tundra soils was not obtained due to local fluky weather conditions. The N₂O fluxes through four snowpack sites were obtained by the vertical N₂O concentration gradient and their average fluxes were 0.94, 1.36, 0.81 and 0.85 μg N₂O m⁻² h⁻¹, respectively. The tundra soils under snowpack emitted N₂O in the maritime Antarctic and increased local atmospheric N₂O concentrations; therefore these fluxes could constitute an important part of the annual N₂O budget for Antarctic tundra ecosystem.     

The impact of vegetation on sedimentary organic matter composition and PAH desorption

Relationships between sedimentary organic matter (SOM) composition and PAH desorption behavior were determined for vegetated and non-vegetated refinery distillate waste sediments. Sediments were fractionated into size, density, and humin fractions and analyzed for their organic matter content. Bulk sediment and humin fractions differed more in organic matter composition than size/density fractions. Vegetated humin and bulk sediments contained more polar organic carbon, black carbon, and modern (plant) carbon than non-vegetated sediment fractions. Desorption kinetics of phenanthrene, pyrene, chrysene, and C₃-phenanthrene/anthracenes from humin and bulk sediments were investigated using Tenax^® beads and a two-compartment, first-order kinetic model. PAH desorption from distillate waste sediments appeared to be controlled by the slow desorbing fractions of sediment; rate constants were similar to literature values for k_slow and k_{very slow}. After several decades of plant colonization and growth (Phragmites australis), vegetated sediment fractions more extensively desorbed PAHs and had faster desorption kinetics than non-vegetated sediment fractions.     

Slow desorption of PCBs and chlorobenzenes from soils and sediments: relations with sorbent and sorbate characteristics

The kinetics of slow desorption were studied for four soils and four sediments with widely varying characteristics [organic carbon (OC) content 0.5-50%, organic matter (OM) aromatic content (7-37%)] for three chlorobenzenes and five polychlorinated biphenyls (PCBs). Slowly and very slowly desorbing fractions ranged from 1 to 50% (slow) and 3 to 40% (very slow) of the total amount sorbed, and were observed for all compounds and all soils and sediments. In spite of the wide variations in sorbate K(OW) (factor 1000) and sorbent characteristics, the rate constants of slow (k(slow), around 10(-3) h(-1)) and very slow (k(very slow), 10(-5)-10(-4) h(-1)) desorption appeared to be rather constant among the sorbates and sorbents (both within a factor of 5). There was a good correlation (r(2) above 0.9) between the distribution over the slow, very slow and rapid sediment fractions and log K(OC), indicating that sorbate hydrophobicity may be important for this distribution. No correlation could be found between sorbent characteristics [OC, N, and O in the organic matter, polarity index C/(N+O), OC aromaticity as determined by CP-MAS (13)C-NMR] and slow desorption parameters (slowly/very slowly desorbing fractions+corresponding rate constants). The absence of (1) a correlation between k(slow) and k(very slow), respectively, and OC content, and (2) the narrow range of k(slow) and k(very slow) values, indicates that intra-OM diffusion is not the mechanism of slow or very slow desorption, because on the basis of this mechanism it would be expected that increasing OC content would lead to longer diffusion pathlengths and, consequently, to smaller rate constants. In addition, it was tested whether differential scanning calorimetry would reveal a glass transition in the soils/sediments. In spite of the sensitivity of the equipment used (changes in heat flow in the micro-Watt range were measurable), a glass transition was not observed. This means that activation enthalpies of slow desorption can be calculated from desorption measurements at various temperatures. In the present study these values ranged from 60 to 100 kJ/mol among the various soils and sediments studied.     

The role of humic substances in chromium sorption onto natural organic matter (peat)

To elucidate mechanisms of Cr³⁺ sorption onto the unaltered solid natural organic matter, the comparative studies of this ion binding from a solution at pH 4.0 onto three selected particle size fractions: 2000–1000 μm, 630–200 μm and 63–20 μm of markedly different HS content and structure, separated by a wet sieving from an overall sample of peat (Brushwood Peat Humus) were carried out. Comparable patterns of COOH groups and CEC_t confirmed that for cation exchange capacity were responsible mainly cations connected with COO⁻ functional groups. It was though found that aliphatic acids in the solid state did not take part in Cr³⁺ binding, thus the finest studied fraction 63–20 μm of the highest contents of functional groups showed the lowest sorption capacity for Cr³⁺, while similar patterns of sorbed Cr³⁺, soluble HS content and base CEC₀ indicated that these parameters were directly interrelated. The base ion exchange processes determined by CEC₀ (with Ca²⁺ as a predominant exchangeable cation) appeared to be not the major mechanisms responsible for Cr³⁺ sorption. For this metal, strong binding to insoluble large molecular weight organic pool two- to threefold prevailed over the ion exchange processes. Very low acid desorption indicated generally low mobility of Cr³⁺-organic compounds.     

Short-term toxicity of pyraclofos used as a blackfly larvicide on non-target aquatic fauna in a tropical environment

Among the many larvicides tested for the control of s.l. larvae, the vector of human onchocerciasis in West Africa, pyraclofos proved to be 100% effective at 100 μg × L⁻¹ for 10 min in river, with a carry of 20 km at 100 m³ × sec⁻¹. Tests were then performed both in laboratory and field conditions to evaluate its toxicity on the non-target aquatic fauna. In experimental short-term gutter tests, the detachment of the total benthic insects was 35% at 100 μg × L⁻¹ for 10 min against 17% for temephos at the same dose and 59% for chlorphoxim at 50μg × L⁻¹ for 10 min. , and were the most affected organisms. The treatment of a river resulted in a considerable detachment of the same taxonomic groups, plus Orthocladiinae. On the other hand, investigations conducted in tanks showed that the 24-hr LC₅₀ for is 150 μg × L⁻¹ and that for 170 μg × L⁻¹, values which are not very different from the operational dose of the larvicide (100 μg × L⁻¹ for 10 min.). Nevertheless, in a river, no fish mortality was recorded. Based on fish LC₅₀ and drift of benthic insects, pyraclofos at 100 μg × L⁻¹ was judged to be less toxic to aquatic fauna in the short term than permethrin and carbosulfan.     

Temperature effects on chlorinated-benzene sorption to hydrophobic surfaces

Sorption and desorption of chlorinated benzenes were investigated in a series of column experiments using porous silica that had phenyl groups bonded to the surface; the mass-fraction organic carbon was 0.016. Both sorption and desorption curves were asymmetrical, but they were mirror images of each other for most experiments, indicating good sorption reversibility. The resulting breakthrough curves were fit to an advection-dispersion mathematical model, with sorption as a first-order, reversible reaction. Significantly greater tailing in the chlorinated-benzene breakthrough curves versus the salt-tracer ones was evidence of slow sorption and desorption. ΔH° values for di-, tri- and tetra-chlorobenzene were 13–21 kJ mol₋₁, indicative of strong van der Waals binding. Despite these small values, slow desorption was attributed to slow binding and release rather than diffusion through the bonded organic phase. Desorption rates decreased in going from di- to tri- to tetra- to penta-chlorobenzene. This decrease was significantly more than the decrease in molecular-diffusion coefficients in the same series, suggesting a chemical rather than a physical rate control. There was less difference in sorption rates through the series, suggesting an inverse relation between partition coefficient and desorption rate. ΔG° values were −17 to −23 kJ mol⁻¹, giving TΔS° values of about 4 kJ mol⁻¹. Thus enthalpic contributions to sorption appear to be of greater importance than entropic contributions.     

Screening 31 endocrine-disrupting pesticides in water and surface sediment samples from Beijing Guanting reservoir

For screening 31 potential or suspected endocrine-disrupting pesticides in water and surface sediments, a multiresidue analysis method based on gas chromatography with electron capture detection (GC/ECD) was developed. Solid phase extraction (SPE) technology with Oasis^® HLB cartridge was also applied in sample extraction. The relevant mean recoveries were 70–103% and 71–103% for water and sediment, respectively. Relative standard deviations (RSD) are 2.0–7.0%, 4.0–8.0% for water and sediment, respectively. Thirty one pesticides (-HCH, β-HCH, γ-HCH, δ-HCH, hexachlorobenzene (HCB), aldrin, heptachlor, endosulfan I & II, p,p′-DDD, o,p′-DDT, p,p′-DDT, p,p′-DDE, endrin aldehyde, endosulfan sulphate, methoxychlor, hepachlor epoxide, -chlordane, γ-chlordane, dieldrin, endrin, dicofol, acetochlor, alachlor, metolachlor, chlorpyriphos, nitrofen, trifluralin, cypermethrin, fenvalerate, deltamethrin) in water and surface sediment samples from Beijing Guanting reservoir were analyzed. Concentrations of pesticides ranged from 7.59 to 36.0 ng g⁻¹ on a dry wt. basis for sediment samples, from 279.3 to 2740 ng l⁻¹ for pore waters and from 48.8 to 890 ng l⁻¹ for water samples, respectively, with a mean concentration of 10.7 ng g⁻¹ in sediment, 735 ng l⁻¹ in pore water and 295 ng l⁻¹ in water, respectively. The data obtained provides information on the levels and sources of endocrine-disrupting pesticides in Guanting reservoir. These results underscore the need to improved environmental protection measures in order to reduce the exposure of the population and aquatic biota to these endocrine-disrupting compounds.     

Concentrations of chlorine, bromine and iodine in Japanese rivers

Concentrations of halogens (Cl, Br and I) in 30 Japanese rivers were measured by ion chromatography and inductively coupled plasma mass spectrometry to understand their behavior in the terrestrial environment. Concentrations of Cl, Br and I in each river, obtained at 10 sampling points from the upper stream to the river mouth, tended to increase near the river mouth. The ranges of geometric means of Cl, Br and I in each river were 1.0–19.4 mg l⁻¹, 2.5–67.9 μg l⁻¹, and 0.18–8.34 μg l⁻¹, respectively. To compare halogen behavior, the concentration ratios, Br/Cl and I/Cl, were calculated. The Br/Cl range was (2.3–7.8) × 10⁻³ (geometric mean: 3.74 × 10⁻³), and it was nearly constant except for the Yoneshiro river. It was estimated that 60–80% of total Br in the middle to lower parts of this river was the excess Br. The Br chemical form in all the rivers is generally considered to be Br⁻. The I/Cl ratios had different trends in rivers flowing into the Japan Sea and Pacific Ocean, possibly due to the different geological features in the river catchments.     

Effects of black carbon and montmorillonite clay on multiphasic hexachlorobenzene desorption from sediments

The desorption kinetics of hexachlorobenzene (HCB) in four freshly spiked artificial sediments were determined using a polymeric adsorbent Tenax-mediated desorption. The sediments included a standard sediment (SS) prepared as per Organisation for Economic Cooperation and Development 218 guidelines and three derived artificial sediments prepared by supplementing the SS sediment with various levels of black carbon (lamp black soot) and/or montmorillonite clay. The desorption kinetics exhibited biphasic behavior, i.e., a fast desorbing fraction followed by a slow desorbing fraction. The addition of either lamp black soot or montmorillonite clay resulted in the reduction of the fast desorbing fraction (Ffast) of HCB in three derived sediments compared with SS sediment. Both black carbon and montmorillonite clay treatment effects on the fast desorbing fraction were statistically significant for the four artificial sediments. The black carbon treatment (i.e., addition of 0.5% wt/wt lamp black soot) effect was an average reduction of Ffast by approximately 11%, whereas the montmorillonite treatment (i.e., addition of 15% wt/wt montmorillonite clay) effect was an average reduction of Ffast by approximately 17%. The presence of soot black carbon particles reduced the desorption rate of HCB in sediments since black carbon exhibits very high sorption capacity and extremely slow diffusion rate compared with those of the natural organic matter in sediment.     

Cold season CH4, CO2 and N2O fluxes from freshwater marshes in northeast China

Cold season (winter and thaw) CH₄, CO₂ and N₂O fluxes from freshwater marshes (47°35′N, 133°31′E, Northeast China) were measured, using the static chamber method. The mean CH₄ and CO₂ fluxes from Carex lasiocarpa (Cl) were 0.5 ± 0.19 and 6.23 ± 1.36 mg C m⁻² h⁻¹, respectively, and those from Deyeuxia angustifoli (Da) were 0.18 ± 0.15 and 5.22 ± 2.48 mg C m⁻² h⁻¹, respectively in winter. There was no significant difference between Cl and Da (p > 0.05). The contributions of winter CH₄ fluxes were about 5.5% and 3% in the Cl and Da, respectively. Marshes are an important potential N₂O sink in winter season in northeast China. During thaw, the CH₄ and CO₂ emissions rapidly increased, 4.5–6 times of winter emissions. Wetland became a source of N₂O. Cold season gases flux from northern wetlands play an important role in the seasonal gas exchange.     

Relationship between the loading rate of inorganic mercury to aquatic ecosystems and dissolved gaseous mercury production and evasion

The purpose of our study was to test the hypothesis that dissolved gaseous mercury (DGM) production and evasion is directly proportional to the loading rate of inorganic mercury [Hg(II)] to aquatic ecosystems. We simulated different rates of atmospheric mercury deposition in 10-m diameter mesocosms in a boreal lake by adding multiple additions of Hg(II) enriched with a stable mercury isotope (²⁰²Hg). We measured DGM concentrations in surface waters and estimated evasion rates using the thin-film gas exchange model and mass transfer coefficients derived from sulfur hexafluoride (SF₆) additions. The additions of Hg(II) stimulated DGM production, indicating that newly added Hg(II) was highly reactive. Concentrations of DGM derived from the experimental Hg(II) additions (“spike DGM”) were directly proportional to the rate of Hg(II) loading to the mesocosms. Spike DGM concentrations averaged 0.15, 0.48 and 0.94 ng l⁻¹ in mesocosms loaded at 7.1, 14.2, and 35.5 μg Hg m⁻² yr⁻¹, respectively. The evasion rates of spike DGM from these mesocosms averaged 4.2, 17.2, and 22.3 ng m⁻² h⁻¹, respectively. The percentage of Hg(II) added to the mesocosms that was lost to the atmosphere was substantial (33–59% over 8 weeks) and was unrelated to the rate of Hg(II) loading. We conclude that changes in atmospheric mercury deposition to aquatic ecosystems will not change the relative proportion of mercury recycled to the atmosphere.