Mekonnen-Hoekstra-2010-waterfootprint-wheat

4．USER INTERFACE 用户界面Controller Display 控制显示器The 5000 Controller default normal operation screen is shown in Figure 4-1. The first three lines of the display are fully user-programmable. Live moisture concentration and system values such as cell temperature, pressure, and flow rate can be displayed. The fourth line displays system messages and alarm / error information only. Refer to Display Flags and Labels in Chapter 5 for more information on changing the format of the controller display. 5000控制器默认的通常操作界面如图4-1所示。

显示屏前三行用户是可完全设计（编程）的。

实时潮湿度和系统数值，比如单元温度，压力，流动速度都可以显示出来。

第四行只显示系统信息和警报/错误信息。

关于控制显示器变换格式的更多信息请参照第5章控制显示器显示标记和标签。

Figure 4-1. Typical operation screen (system message will vary) 典型操作界面（系统信息不同）System Security and Passwords 系统的安全性和密码The 5000 Controller has four system security levels: Levels 0, 1, 2 and Level 3.You must enter a password before you can access certain menus and system values. Factory default passwords are listed later in this section.5000控制器有四层系统安全性：0，1，2层和3层。

ORIGINAL PAPERCarbon Storage and Fluxes within Freshwater Wetlands:a Critical ReviewBirol Kayranli &Miklas Scholz &Atif Mustafa &Åsa HedmarkReceived:10February 2009/Accepted:4September 2009/Published online:9December 2009#Society of Wetland Scientists 2009Abstract We critically review recent literature on carbon storage and fluxes within natural and constructed freshwa-ter wetlands,and specifically address concerns of readers working in applied science and engineering.Our purpose is to review and assess the distribution and conversion of carbon in the water environment,particularly within wetland systems.A key aim is to assess if wetlands are carbon sinks or sources.Carbon sequestration and fluxes in natural and constructed wetlands located around the world has been assessed.All facets of carbon (solid and gaseous forms)have been covered.We draw conclusions based on these studies.Findings indicate that wetlands can be both sources and sinks of carbon,depending on their age,operation,and the environmental boundary conditions such as location and climate.Suggestions for further research needs in the area of carbon storage in wetland sediments are outlined to facilitate the understanding of the processes of carbon storage and removal and also the factors that influence them.Keywords Carbon dioxide .Constructed wetland .Global warming .Greenhouse gases .Methane .PeatlandIntroductionWetlands and ProcessesWetlands are areas of water saturated soil,and include small lakes,floodplains,and marshes.Wetlands only cover a small proportion of the earth ’s land surface (approximate-ly between 2%and 6%,depending on definitions),but contain a large proportion of the world ’s carbon (approx-imately 15×1014kg)stored in terrestrial soil reservoirs (Schlesinger 1991;Amthor et al.1998;Whitting and Chanton 2001).Wetlands play an important role in carbon cycling because they represent 15%of the terrestrial organic matter losses to the oceans (Hedges et al.1997;Stern et al.2007).Among all terrestrial ecosystems,they have the highest carbon density.Furthermore,wetlands are a diffuse source of humic substances for some receiving freshwater systems (Stern et al.2007).Decomposition within wetlands is a complicated process as it involves aerobic and anaerobic anic matter decomposition is often incomplete under anaerobic conditions.The lack of oxygen is therefore the main factor determining plant detritus turnover.Consequently,plant remains coming from the inflow,the wetland biomass,and/or from the vegetation growing along the wetland margins accumulate within the wetland system,and different decomposition stages can be identified (Gorham et al.1998;Collins and Kuehl 2001;Holden 2005).A net retention of organic matter and plant detritus can be observed in most wetlands (Mitsch and Gosselink 2007).Organic matter accumulation in wetland sediments dependsB.Kayranli :M.Scholz (*):A.Mustafa Institute for Infrastructure and Environment,School of Engineering,The University of Edinburgh,William Rankine Building,The King ’s Buildings,Edinburgh EH93JL Scotland,UK e-mail:m.scholz@Å.HedmarkSwedish University of Agricultural Sciences,Department of Forest Products,Box 7008,75007Uppsala,Sweden Å.HedmarkAir Policy Unit,Corporate Office,Scottish Environment Protection Agency,Erskine Court,Castle Business Park,Stirling FK94TR Scotland,UKWetlands (2010)30:111–124DOI10.1007/s13157-009-0003-4on the ratio between inputs(organic matter produced in situ and ex situ)and outputs.The latter may be due to the decomposition under waterlogged conditions,erosion due to high precipitation,and soil disturbance in general (Gorham et al.1998).Since1980,treatment wetland systems have gained popularity,and have been applied successfully for the treatment of numerous waste streams(Kadlec et al.2000; Haberl et al.2003;Zhang et al.2005;Vymazal2007)and runoff from urban areas(Scholz2006),farm yards(Carty et al.2008),and log yards(Hedmark and Scholz2008).The concept of constructed wetlands applied for the purification of wastewaters has received growing interest because most of these systems are easy to use,require only little maintenance and have low construction costs(Machate et al.1997).Dissolved organic matter is a very important water quality parameter associated with the performance of treatment wetland systems.Some microorganisms includ-ing bacteria use dissolved organic matter as an energy source for processes such as denitrification.However,too high levels of dissolved organic matter can prevent light penetration within the water column(Pinney et al.2000;Li et al.2008).The treatment efficiencies of wetlands vary depending on climate,vegetation,microorganism commu-nities,and type of wetland system(Waddington et al.1996; Schlesinger1997;Joabsson et al.1999;Trettin and Jurgensen2003;Whalen2005;Picek et al.2007;Ström and Christensen2007;Weishampel et al.2009).Scientists have carried out detailed investigations concerning wetland biochemistry and hydrology.Neverthe-less,there is no commonly accepted agreement if wetlands are actually carbon sources or sinks.There is disagreement in the interpretation of variables,reactions and the impact of environmental conditions on carbon storage and release. Therefore,recommendations on how to adapt policies and planning processes to enhance carbon storage vary parisons of carbon storage and flux data vary greatly as a function of region and climate.Global WarmingGlobal warming mitigation is becoming increasingly important as the effects of climate change are becoming apparent around the world.Depending predominantly on the meteorological and hydrological conditions,wetlands can absorb carbon dioxide from the atmosphere and capture it within the sediment,and may therefore be greenhouse gas sinks.The high productivity,high water table,and low decomposition rate associated with wetlands lead to carbon storage within the soil,sediment,and detritus (Whitting and Chanton2001).The process of locking carbon dioxide away from the atmosphere is called carbon sequestration.On the other hand,wetlands are considered to be greenhouse gas sources,particularly with respect to the emission of methane gas to the atmosphere.Methane has a much higher global warming potential than carbon dioxide, and contributes to the atmospheric sorption of infrared radiation and subsequent warming(Carroll and Crill1997; Whitting and Chanton2001;Zhang et al.2005).Minimiz-ing methane fluxes from created and restored wetlands should therefore be a vital aim in combating climate change.Improved design,construction,and operation of wetlands used for treatment and conservation purposes should therefore help to mitigate global warming by reducing the release of greenhouse gases and enhancing carbon storage at the same time.Purpose and Review MethodOur critical review focuses on the assessment of the key processes determining carbon removal,sequestration,and fluxes within wetlands.It has specifically been written for applied scientists and engineers working world-wide,and complements other more ecology-based papers such as Bridgham et al.(2006)focusing on Northern America.The aims of the key sections are:&To discuss carbon turnover and removal processes within wetlands.&To highlight processes where wetlands can be described as carbon sources or carbon sinks.&To discuss the effect of global warming on wetlands.The authors undertook a comprehensive literature search predominantly with the help of the literature data base ISI Web of Knowledge,version4.6(). Grey literature and reports were also assessed,but an attempt was made to find the same information in more easily accessible journal papers.Carbon Turnover and Removal MechanismsCarbon TurnoverThe major components of the carbon cycle within a wetland are illustrated in Fig.1.Various reactions utilizing carbon take place within wetlands.The key processes are respira-tion in the aerobic zone,fermentation,methanogenesis,and sulfate,iron,and nitrate reduction in the anaerobic zone. Organic matter typically contains between45%and50% carbon.Wetlands contain large amounts of dissolved organic matter,promoting microbial activity(Bano et al. 1997;Zweifel1999).Bacterial oxidation of dissolved organic carbon subsequently results in mineralization,which is a process where organic matter is converted to inorganic substances (Hensel et al.1999).Respiration is the biological conversion of carbohydrates to carbon dioxide,and fermentation is the conversion of carbohydrates to chemical compounds such as lactic acid,or ethanol and carbon dioxide.In a wetland,organic carbon is converted into compounds including carbon dioxide and methane and/or stored in plants,dead plant matter,micro-organisms,or peat.A significant part of the biochemical oxygen demand may be particle-bound and,therefore,suscep-tible to removal by particulate settling (Kadlec et al.2000).Carbon ComponentsWetlands contain five main carbon reservoirs:plant biomass carbon,particulate organic carbon,dissolved organic carbon,microbial biomass carbon,and gaseous end products such as carbon dioxide and methane (Fig.1).The latter four are present in water,detritus,and soil (Kadlec and Knight 1996).Wynn and Liehr (2001)outlined a carbon cycle comprising the following key components:plant biomass,standing dead plants,particulate organic carbon,dissolved organic carbon,and refractory carbon (i.e.resistant carbon,which would retain its strength at high temperatures).These carbon reservoirs can be used in the description of carbon cycles.Active biomass may comprise wetland plants and periphyton (microorganisms and detritus attached to sub-merged surfaces),and contributes to the transformation of inorganic carbon such as carbon dioxide to organic carbon through photosynthesis.The productivity of wetlands varies due to the time of year,geographic location,nutrient status,and type of vegetation.Particulate organic carbon consists of decaying plant matter,microbial cells,particulate influent,and particulate organic substances found on thesoil surface.Dissolved organic carbon comprises dissolved biochemical oxygen demand and other carbon components in solution.While dissolved organic carbon typically represents <1%of the total organic carbon in soil,it represents approximately 90%of the total organic carbon in surface waters (Kadlec and Knight 1996;Wynn and Liehr 2001;Reddy and Delaune 2008).Microbial biomass carbon occurs in heterotrophic micro-floral catabolic activities,transforming organic carbon (energy reserve of the ecosys-tem)back to inorganic carbon,and mineralizing particulate organic carbon and dissolved organic carbon (D ’Angelo and Reddy 1999;Picek et al.2007).The turnover of active biomass happens relatively quickly,usually in the order of days,while the corresponding turnover of soil organic matter takes decades.Soil microbial biomass can be regarded as a significant carbon sink.Carbon Removal MechanismsCarbon processing in the wetland environment is complex,and the various decomposition reactions take place in different horizons;e.g.respiration and methane oxidation occur in the aerobic zones while methanogenesis occurs in anaerobic zones (Knight and Wallace 2008).However,the highest rates of decomposition are found closest to the wetland surface where there is an elevated input of fresh litter and recently synthesized labile organic matter (Sherry et al.1998).The organic matter content within wetland systems is impacted by processes such as biodegradation,photochemical oxidation,sedimentation,volatilization,and sorption.Some of these mechanisms provide natural organic matter accumu-lation via microbial and/or vegetative decay (Burgoon et al.1995;Reddy and D ’Angelo 1997;Stottmeister et al.2003;Carbon outputParticulate anddissolved carbon inputFig.1Schematic diagram showing the major components of the carbon cycleQuanrud et al.2004;Li et al.2008).Moreover,the accumulation of organic matter is a potential energy source for microbial communities(Turcq et al.2002;Reddy and Delaune2008).Dissolved organic matter degradation is expected to occur via heterotrophic uptake by aerobic and anaerobic bacteria,and degradation by ultra-violet light.Several authors have reported on dissolved organic matter trans-formations in algae(Kragh and Søndergaard2004),forest vegetation(Li et al.2008),Typha spp.wetland plant material(Pinney et al.2000),microbial groups(Ibekwe et al.2003;Li et al.2008),and soils(Qualls and Haines 1992).Dissolved organic matter from plant exudates appears more dominant during warm months with active plant growth(Pinney et al.2000).Organic matter accumulates when primary productivity is faster than the corresponding decomposition rate,leading to a net accumulation of organic matter(Mitsch and Gosselink 2007).Due to slow organic matter decomposition rates,strata are built up and compressed to form different soil layers. Organic matter from inflow and wetland plants is accumulat-ed,decomposed,and subsequently buried in the system.This results in a shift from aerobic to anaerobic processes due to lack of oxygen in the wetland sediment,which drastically reduces decomposition rates(Holden2005).It is also believed that some parameters such as temperature,organic matter quality,residence time of organic matter in the water column,vegetation pattern,wetland maturity,sedimentation rate,sediment texture,and sediment reworking impact on the organic matter decomposition within the water body and the organic matter compositions(Bormann et al.1995;van der Peijl and Verhoeven1999;Barber et al.2001;Savage and Davidson2001;Turcq et al.2002;Yu et al.2002;Lafleur et al.2005;Wolf and Wagner2005;Shepherd et al.2007; Yurova and Lankreijer2007).Furthermore,organic matter compositions consist of labile and resistant fractions within the soil profile.Many of the labile compounds are accumulated on the sediment surface and decomposed within a few months(Schlesinger1997;Wolf and Wagner2005).Wetlands have aerobic and anaerobic interfaces in water, soil,and the accumulated organic matter(Scholz et al. 2007).Gaseous end products are formed under anaerobic and aerobic conditions.Under anaerobic conditions,carbon dioxide and methane are formed through the decomposition of organic matter.In comparison,under aerobic conditions, only carbon dioxide is formed.Previous researchers (Kadlec and Knight1996;Scholz2006;Mitsch and Gosselink2007)pointed out that the aerobic respiration in wetland systems is far more effective with respect to organic matter degradation than anaerobic processes such as fermentation and methanogenesis.The dissolved organic carbon cycle depends on the cycling and bioavailability of phosphorus and nitrogen (Craft and Richardson1998)as well as on the bioavailabil-ity and transport of metals(V oelker and Kogut2001; Tipping and Center2002).Microbial death is generally assumed to only contribute to particulate organic matter and not to dissolved organic matter,because most bacteria in wetlands are associated with plant litter and soil organic matter.When the growing season reaches its end,approximately15%of the plant carbon disappears due to leaching and physical degradation in temperate climates(Kadlec and Knight1996).The remainder degrades over approximately one year,and predominantly becomes particulate carbon(Johnston1991;Wynn and Liehr2001).Are Wetlands Carbon Sources or Sinks?Wetlands as Carbon SourcesThe important greenhouse gases carbon dioxide,methane, and nitrous oxide can be released from natural and constructed wetlands(Le Mer and Roger2001;Whitting and Chanton2001;Malmer et al.2005;Liikanen et al. 2006;Mander et al.2008).Processes such as denitrification and methane production are dependent on the oxygen status of soil and sediment.Anoxic soils and sediments produce methane,while well-drained soils act as a sink for atmospheric methane due to methane oxidation(Hanson and Hanson1996).Table1summarizes an overview of methane fluxes within wetlands located in different countries.The water table level of wetlands not only influences the amount of methane emitted to the atmosphere,but also the removal of methane from the atmosphere.For example,Harris et al. (1982)determined that peat from the Great Dismal Swamp contributes to the removal of atmospheric methane when the water table level is below the surface of peat during dry periods.In contrast,when peat is well saturated with water, it becomes an important methane source.Furthermore, Augustin et al.(1998)conclude that lowering the ground-water table of minerotrophic fens in the northeast of Germany increases the release of nitrous oxide and the reduction of methane.Relatively high methane emissions could be observed when the groundwater table was high and soil temperatures were higher than12°C.They also point out that these fens release approximately between0.6 and9.0mg CH4-C m−2h−1(Table1).Natural wetlands emit approximately 1.45×1011kg CH4-C yr−1to the atmosphere.This equates to about25% of the total emissions from all anthropogenic and natural sources.Wetland methane flux rates are commonly 10−6kg m−2d−1and represent the net effects of microbial production and consumption(Whalen2005).The studies carried out so far have demonstrated that constructed and restored wetlands also have high nitrous oxide(Fey et al.1999;Xue et al.1999;Johansson et al. 2003;Mander et al.2005;Stadmark and Leonardson2005; Teiter and Mander2005;Liikanen et al.2006;Picek et al. 2007)and methane(Schipper and Reddy1994;Tanner et al.1997;Cao et al.1998;Tuittila et al.2000;Johansson et al.2004;Mander et al.2005;Teiter and Mander2005; Altor and Mitsch2006;Liikanen et al.2006;Picek et al. 2007)emissions.However,data are highly variable due to different design and operations,and more importantly as a result of system locations in different climates.The methane emissions from vegetated constructed treatment wetlands can be similar to those from productive natural wetlands.Methanogenesis can be an important decomposi-tion process in constructed wetlands treating organic wastewaters.For example,a flux of approximately between 28and278mg CH4-C m−2h−1(Table1)has been reported for pilot-scale constructed wetlands(Tanner et al.1997).Brix et al.(2001)reported that in wetlands dominated by Phragmites australis,the primary productivity is high and approximately50%of the net primary production is respired to carbon dioxide and methane in the sediment. In the growing season,the process of methanogenesis is primarily limited by organic matter availability while at other times temperature is the most important factor.Similarly to natural wetlands,rice paddies have been identified as one of the important sources of atmospheric methane.The majority of studies reporting on methane emissions from wetlands have been conducted in natural ecosystems or heavily managed rice paddies(Cao et al.1998; Crutzen1995).Cao et al.(1998)estimated that the globalTable1Overview of methane-carbon(CH4-C)fluxes from different types of wetlandsType of Wetland Location CH4-C flux(mg CH4-C m-2h-1)ReferenceRiparian marsh wetlands USA(Ohio)~3.5(growing season)Altor and Mitsch(2006) Swamp forest and marsh USA(Louisiana) 6.08–38Alford et al.(1997)Wet meadow tundra USA(Alaska)0.66–17.75Bartlett et al.(1992) Forested swamps and marshes USA 3.99Bartlett and Harris(1993) Peatlands Northern USA 5.48Armentano and Menges(1986) Peatlands USA(Florida)25.68Armentano and Menges(1986) Peatlands Central Canada 2.79±0.27Turetsky et al.2002 Peatlands Central Canada0–14.84Moore and Roulet(1995) Bogs and rich fens Canada(Manitoba)0.91–9.95Bellisario et al.(1999) Fens,bogs,ponds and palsa Canada(Northwest Territories)-0.054–10.62Liblik et al.1997 Minerotrophic fens Northeast Germany0.6–9.0Augustin et al.(1998)Free water surface wetland Eastern China130Tai et al.(2002)Free water surface wetland Germany 1.0–35.3Wild et al.(2002) Subsurface,free surface,overlandand groundwater flow wetlandsEstonia,Finland,Norway,and Poland-1.3–1,583Søvik et al.(2006)Planted horizontal subsurface flowconstructed wetlandsCzech Republic(South Bohemia)0–93Picek et al.(2007)Horizontal sub-surface flowplanted soil filterSouthern Estonia 1.7–528Mander et al.(2005)Vertical sub-surface flow plantedsoil filterSouthern Estonia16.4Mander et al.(2005)Horizontal subsurface flowconstructed wetlandsEstonia0.0091–371.83Mander et al.(2008)Pilot-scale constructed wetlands New Zealand27.6–278Tanner et al.(1997) Wetlands(continuously flooded)Northeast China(Sanjiang)0.5±0.19Zhang et al.(2005) Wetlands(seasonally flooded)Northeast China(Sanjiang)0.18±0.15Zhang et al.(2005)Naturally flooded forests andfloating grass matsBrazil(Amazon floodplain)8–92Bartlett et al.(1988)Temporarily flooded meadow, mire bank,lacustrine sedge fen, and reed marshes Finland(Lake Heposelkäin Liperi;Lake Mekrijärvi in Ilomantsi)-0.2–6Juutinen et al.(2001)Sub-arctic wetland Sweden0.2–36.1Ström and Christensen(2007) Bog and forested swamp UK(North Wales)-0.006–3.14Kang and Freeman(2002)annual methane emission from wetlands is1.45×1011kg of which0.92×1011kg comes from natural wetlands and0.53×1011kg from rice paddies.A limited number of studies consider carbon dioxide fluxes from constructed wetlands(Mander et al.2005; Liikanen et al.2006).Many authors report that carbon dioxide emissions increase with increasing temperature and are higher under drained than flooded conditions(Bridgham and Richardson1992;Moore and Dalva1993;Moore and Dalva1997;Price and Waddington2000;Scanlon and Moore2000;Waddington et al.2001).Deep wetlands generally capture carbon dioxide from and release methane to the atmosphere(Whitting and Chanton2001).The combination of these two fluxes determines whether these countervailing processes make a wetland system an overall contributor to the greenhouse effect.The ratio of methane release to carbon dioxide consumption determines the carbon exchange balance with the atmosphere for any wetland ecosystem.A better understanding of the critical processes regulat-ing greenhouse gases associated with wetlands such as freezing-thawing cycles and pulsing hydrological regimes are important to assess carbon dioxide,methane,and nitrous oxide fluxes.The production and consumption of greenhouse gases are partly regulated by microbial pro-cesses,which in turn are influenced by soil moisture and temperature.Nitrification and denitrification are the key processes that produce nitrous oxide.However,nitrous oxide production in frozen soils is more likely to be regulated by denitrification(Mørkved et al.2006;Öquist et al.2007). Van Bochove et al.(2001)highlighted that nitrous oxide fluxes are high in winter because of sudden release of stored nitrous oxide.Maljanen et al.(2007)reported that nitrous oxide and carbon dioxide accumulated in the soil during winter and were released swiftly during thawing in spring.During winter,methane concentrations in the soil remained lower than in the atmosphere,and subsequently increased as temperatures increased after thawing.Zhang et al.(2005)observed that during thawing,the methane and carbon dioxide emissions increased rapidly (4.5to6times of the winter emissions)for continuously flooded and seasonally flooded marshes.They estimated that a continuously flooded and a seasonally flooded wetland in Sanjiang(northeast China)released0.5±0.19and0.18±0.15mg CH4-C m−2h−1methane,respectively.In compar-ison,naturally flooded forests and floating grass mats in Brazil(Amazon floodplain)emitted between8and92mg CH4-C m−2h−1to the atmosphere(Bartlett et al.1988).Environmental parameters such as temperature,pH, depth of water table,planting regime(Waddington et al. 1996;Schlesinger1997;Trettin and Jurgensen2003;Whalen 2005;Inamori et al.2007;Picek et al.2007;Knoblauch et al. 2008),substrate type and quality(Bellisario et al.1999;Joabsson et al.1999;Ström et al.2003),and specialized microbes(Fischer and Pusch1999;Whalen2005;Buesing and Gessner2006;Picek et al.2007;Sleytr et al.2007; Ström and Christensen2007;Tietz et al.2008)impact on gas production and ultimately net methane emission rates. Furthermore,the methane exchange between wetland eco-systems and the atmosphere can be affected by the presence of plants because the convective flow process in plants facilitates a faster diffusion of gases through water,and particularly by the species composition of vascular plants. These plants affect important aspects of the methane dynamics such as production,consumption,and transport; for example,the root exudates are decomposed by microbes and transformed to methane and carbon dioxide(Zhu and Sikora1995;Joabsson and Christensen2001;Tanner2001; Picek et al.2007;Ström and Christensen2007).Walter and Heimann(2000)emphasize that most wetland plants root below the water table and that methane flux from the soil to the atmosphere takes place via aerenchyma in the vascular tissue of the plants.Further transport pathways are diffusion and bubble generation. Above the water table,methane is oxidized in the soil pores by methanotrophic bacteria.Landry et al.(2009)claim that constructed wetlands emit between2and10times more greenhouse gases than natural wetlands.This is likely due to high loading rates.They observed that methane was the most important greenhouse gas in unplanted wetland systems and that the presence of plants decreased methane fluxes but favored carbon dioxide production.Alford et al.(1997)estimated fluxes of between approx-imately6and38mg CH4-C m−2h−1for swamp forests and marshes near New Orleans,USA.Bartlett and Harris(1993) reported fluxes of approximately4mg CH4-C m-2h-1for forested swamps and marshes.Kang and Freeman(2002) reported that bog and forested swamps in North Wales(UK) emit up to approximately3mg CH4-C m-2h-1to the atmosphere(Table1).The relatively high data variability is likely due to different climatic regions.Hou et al.(2000)pointed out that the reduction of various oxidants in homogeneous soil suspensions occurs sequen-tially at corresponding soil redox potentials.The availability of soil oxidants such as oxygen and carbon dioxide used as electron acceptors for organic matter degradation contributes significantly to the soil microbiological processes.They found that emissions of methane were strongly correlated with changes in the soil redox potential.Significant methane emissions occurred only at soil redox potentials,which were lower than approximately-100mV.The water table level predominantly determines the presence of aerobic and anaerobic conditions occurring at different depths of wetlands.These conditions control the methanogenic and methanotrophic processes(Kelley et al.1995).Methanogenesis is a rigid anaerobic process,and it will be evoked during flooding periods,when the water table level rises.In contrast,with a decrease in flooding periods,methane production decreases.An inverse relation is observed for methane oxidation.Grünfeld and Brix(1999)compared vegetated organic sediments at different water table depths below the surface with vegetated inundated sediments.They found that due to the high water-holding capacity of organic sediments,rates of methanogenesis and methane emission in organic sedi-ments with a water table of8cm below the sediment surface were only slightly,but not statistically significantly different from rates in inundated sediments.Sandy sedi-ments with water tables of8cm below the sediment surface had very low methanogenic activity as compared with organic sediments.Methane can be transported to the atmosphere through pathways such as molecular diffusion,gas bubbling up (ebullition)from the sediments,and vascular plant stems (Walter and Heimann2000).King(1996)pointed out that the amount of methane oxidized did not correlate with the total potential methane fluxes from a wetland.Oxygen distribution and availability controls the rates of methane oxidation within wetlands.Moreover,oxygen penetration within peat varies from1to7mm,with some diurnal variation coupled to benthic photosynthesis.Moore and Dalva(1993)and Moore and Roulet(1993) reported that the mean position of the water table level is the best indicator of methane emissions.Apparently,a critical depth exists at which maximal emissions occur.It has been determined that a water table depth greater than 18cm does not produce high emissions,since methane production(methanogenesis)decreases and its consumption increases(methanotrophy).However,when the depth of the water table is12cm below the surface of peat,or exceeds it,methane fluxes are high.Bubier et al.(1993)and Daulat and Clymo(1998)estimated that methane emitted to the atmosphere from experimental digs is between5and60 times higher than that produced in hillocks(small hills or mounds),due to the digs having a lower water table depth than the hillocks.Roulet et al.(1993)discovered that peatlands convert from a source to a sink of methane when the water table drops to25cm below the peat surface due to increased methane oxidation.Kelley et al.(1995)studied methane emissions across a tidally flooded riverbank in North Carolina,USA.Their study showed the highest methane fluxes when the water level was close to the surface,and the lowest fluxes at both high and low water table levels.Similarly,Smith et al.(2000)estimated that methane emissions stopped when the soil moisture content fell below approximately25%,as floodwaters receded in Venezuela’s Orinoco River floodplain.Glatze et al.(2004)pointed out that the highest rates of anaerobic methane production can be measured for samples close to the soil surface with fresh peat accumulation and a high water table.In contrast,the lowest rates were observed for samples from the subsurface of sites with a low water table.Anaerobic methane production was significantly positively correlated with aerobic and anaerobic carbon dioxide production.These production potentials show that drainage(Salm et al.2009),harvesting,and restoration change the ability of the peat profile to produce and emit carbon dioxide and methane.Wetlands as Carbon SinksPrevious world-wide studies relating to carbon storage within wetlands are summarized in Table2.The results indicate that wetlands are vital carbon sinks.The majority of studies on carbon sequestration within wetlands focus on sediment,soil,and living plant communities(Krogh et al. 2003;Brevik and Homburg2004;Bedard-Haughn et al. 2006;Euliss et al.2006;Alongi et al.2007).Freeman et al.(2001a,2004)pointed out that phenol oxidase is the main enzyme,which,by remaining inactive, keeps much of the worlds terrestrial wetland carbon locked up.Actinomyces(filamentous,mostly anaerobic micro-organisms of this genus),bacteria,and certain fungi areTable2Example of carbon accumulation in sediments of different wetland typesType of wetland Location Carbon accumulation(kg C m-2yr-1)ReferenceAgricultural field and riparian ecosystem USA(Maryland)0.16–0.22McCarty and Ritchie(2002) Coastal wetlands USA(California)0.033±0.0029Brevik and Homburg(2004) Prairie wetland Northcentral USA0.305Euliss et al.(2006)Boreal forests Canada(Ontario)0.003–0.01Trumbore and Harden(1997) Horizontal subsurface flow constructed wetlands Estonia 1.5–2.2Mander et al.(2008) Boreal peatlands Finland0.015–0.026Turunen et al.(2002) Temperate peatlands Finland0.01–0.046Turunen et al.(2002) Peatlands North America0.029Gorham(1991)。

Product data sheetPURA 10 Water BathPURA water baths stand for innovative, simple, and safe working in thelaboratory. All models (except PURA 4) come with an integrated drain screw for quick and clean draining of the baths. PURA water baths are flexible and can be easily transported through ergonomic side recessed grips. Non-slip rubber feet ensure a firm footing and more safety in the laboratory.Your advantages• Easy operation • Bright display• Mains switch is protected against spray water • Integrated protection against running dry • Integrated drain screw (except PURA 4)• No distracting elements in the bath • Platform included as standard • Integrated timer • Non-slip rubber feet• Ergonomic recessed gripsTechnical dataAvailable voltage versionsOrder No.9 550 510Available voltage versions:9 550 510.22100-115V/50-60Hz (Nema N5-15 Plug)9 550 510.33230V/50-60Hz (Schuko Plug - CEE 7/4Plug Type F)9 550 510.04230V/50-60Hz (UK Plug Type BS1363A)9 550 510.05230V/50-60Hz (CH Plug Type SEV 1011)9 550 510.33.chn230V/50-60Hz (CN Plug)BathBath tank Stainless steel Bath coveraccessory Usable bath opening cm (W x L / D)22 x 27 / 14CoolingCooling coilaccessoryOtherClassification Classification I (NFL)IP CodeIP 21ElectronicsTemperature display LED Temperature setting Keypad Electronic Timer hr:min00:01 ... 99:59WaterbathInsert capacity for test tube racks 13 mm ø pc.180Insert capacity for test tube racks 17 mm ø pc.120Dimension with bathcover cm (W x L x H)31 x 37 x 36Dimensions and volumesUsable immersion depth cm 14Weight kg7Dimensions cm (W × L × H)31 x 35 x 22Filling volume l1.4 ... 9.5Temperature valuesSetting the resolution of the temperature display °C0.1Working temperature range °C +18 ... +99.9Temperature stability °C ±0.15Ambient temperature °C5 ... 40Temperature display resolution °C0.1Performance values100-115V/50-60Hz (Nema N5-15 Plug)100V/50HzHeating capacity kW0.9100V/60HzHeating capacity kW0.9115V/50HzHeating capacity kW1.2115V/60HzHeating capacity kW1.2230V/50-60Hz (Schuko Plug - CEE 7/4 Plug Type F)230V/50HzHeating capacity kW1.2230V/60HzHeating capacity kW1.2230V/50-60Hz (UK Plug Type BS1363A)230V/50HzHeating capacity kW1.2230V/60HzHeating capacity kW1.2230V/50-60Hz (CH Plug Type SEV 1011)230V/50HzHeating capacity kW1.2230V/60HzHeating capacity kW1.2230V/50-60Hz (CN Plug)230V/50HzHeating capacity kW1.2230V/60HzHeating capacity kW1.2All BenefitsLess is more.Thanks to their design, PURA water baths require a minimum amount of water so thateven small sample containers stand safely.Lightweight.PURA water baths impress with their lowweight and can be flexibly used.Start. Stopp. Timer.PURA water baths offer an internal timer function. After expiration of the set time, a signal sounds and the device either continuesoperation or switches off.Tilting – no, thank you.The PURA water bath design is tiltproof. Non-slip rubber feet prevent slipping and carryinghandles simplify the transport.Easy cleaning.PURA does not incorporate any interfering functional elements. The smooth surfaces canbe cleaned quickly and without residue.Ease of use.The controls on the front side are easy to reach and use.Easy handling.A frontally integrated drain screw allows clean, safe, and effortless emptying of the baths. (notPURA 4)Brilliant.Very bright display makes it easy to read evenfrom a distance.100% Checked.100% testing. 100% quality. Each JULABOCirculator undergoes thorough quality testingbefore leaving the factory.Green technology.Development consistently appliedenvironmentally friendly materials andtechnologies.JULABO. Quality.Highest standards of quality for a long productlife.Quick start.Individual JULABO consultation andcomprehensive manuals at your disposal.Satisfied customers.11 subsidiaries and more than 100 partnersworldwide guarantee fast and qualifiedJULABO support.Services 24/7.Around the clock availability. You can findsuitable accessories, data sheets, manuals,case studies, and more at .。

co3o4表面水分解的限速步英文回答：The rate-limiting step for the surface water decomposition of Co3O4 is the dissociation of water molecules on the Co3O4 surface. This step involves breaking the O-H bonds in water molecules to form hydroxyl (OH) groups on the surface. The formation of hydroxyl groups isa necessary precursor for further reactions to occur.The dissociation of water molecules on the Co3O4surface is a complex process that involves the interactionof water molecules with Co3O4 surface sites. The water molecules adsorb onto the surface and undergo a series of reactions to form hydroxyl groups. These reactions can be influenced by factors such as temperature, pressure, andthe presence of other species on the surface.One possible mechanism for the dissociation of water molecules on the Co3O4 surface is the Eley-Rideal mechanism.In this mechanism, a water molecule collides with a surface oxygen atom and transfers one of its hydrogen atoms to the oxygen atom, forming a hydroxyl group. The remaining hydrogen atom can then react with another surface oxygen atom to form water.Another possible mechanism is the Langmuir-Hinshelwood mechanism, where water molecules adsorb onto the surfaceand react with surface oxygen atoms to form hydroxyl groups. This mechanism involves the formation of an activated complex, which is a high-energy intermediate state that facilitates the breaking of the O-H bond.To illustrate the rate-limiting step, let's consider an analogy. Imagine you are trying to make a sandwich. Therate-limiting step would be the process of spreading the mayonnaise onto the bread. This step is necessary for the sandwich to be completed, but it takes some time and effort to evenly spread the mayonnaise. Once the mayonnaise is spread, you can quickly add other ingredients and complete the sandwich.中文回答：Co3O4表面水分解的限速步骤是水分子在Co3O4表面的解离。