Article

Emissions of greenhouse gases from ponds constructed for nitrogen removal

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Abstract

Methane and carbon dioxide emission from three constructed ponds were monitored during an annual cycle. Water temperature was a good predictor of methane emission in all three ponds. In the most intensively studied pond, nitrate concentration in the bottom water could further explain the amount of methane emitted. When water temperature exceeded 15 °C between 1 and 54 mg, CH4 m−2 h−1 was emitted on all occasions, while at temperatures below 10 °C, less than 0.6 mg CH4 m−2 h−1 was emitted. The flux of carbon dioxide differed between the ponds and no consistent patterns were found. In a laboratory study at 20 °C, we showed that high, but naturally occurring, nitrate concentrations (8 and 16 mg NO3−–N l−1) constrained the production of methane compared to the treatment with no nitrate addition. Nitrous oxide production was positively correlated with nitrate concentration. Carbon dioxide production was highest at the highest nitrate concentration, which indicates that increased nitrate loading on ponds and wetlands will stimulate organic matter decomposition rates. Our conclusion is that these ponds constructed for nitrate removal emit greenhouse gases comparable to lakes in the temperate region.

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... Therefore the artificial control of C/N ratio in the CWs inlet wastewaters can determine a relatively high nutrient removal efficiency and, in the same time, a low GHG emission. Stadmark and Leonardson (2005), in a laboratory study at 20 • C, showed that nitrate addition to wastewaters at concentrations of 8 and 16 mg L −1 significantly inhibited CH 4 production, confirming the findings of Conrad (2002). The highest CO 2 production rate occurred at the highest nitrate concentration, which indicates that increased nitrate loading on ponds and wetlands stimulate OM decomposition rates disturbing the carbon balance (Paludan and Blicher-Mathiesen, 1996). ...
... N 2 O emissions from CWs are positively related to N load and in particular by nitrate concentration (Stadmark and Leonardson, 2005;Groh et al., 2015;Zhang et al., 2015). This result is in agree with Johansson et al. (2003) who also reported, during the summer season studies in FWS CW, a high atmospheric N 2 O consumption when the NO 3 − water concentrations were mostly low, due to bacteria communities that use this gas, very hydrosoluble, for their metabolism. ...
... de Klein and van der Werf (2014) measuring CH 4 emission in a FWS CW covered for 90% of its surface by P. australis (110 stems m −2 ) at two water temperatures, 15 and 24 • C, reported a gas emission respectively of 7.8 and 24.5 mg CH 4 m −2 h −1 . Stadmark and Leonardson (2005) in constructed ponds receiving wastewater with different loads of NO 3 − reported that water temperature was a good predictor of CH 4 emission in all three ponds with emissions between 1 and 54 mg CH 4 m −2 h −1 , when water temperature was higher than 15 • C, and less than 0.6 mg CH 4 m −2 h −1 when water temperature was below 10 • C. Significantly higher N 2 O emission during the summer season than during winter, due to a slowdown of the denitrification and nitrification processes at lower temperatures was found by Søvik et al. (2006). However Stadmark and Leonardson (2007) in a laboratory experiment using constructed pond sediments, collected at different times of the year, reported that N 2 O and CH 4 production was different when incubated at identical temperatures (13 • C or 20 • C) and NO 3 − concentrations indicating that there are other sediment characteristics that are important for GHGs production potential. ...
Article
Constructed wetlands (CWs) are natural-like systems for wastewater treatment capable to remove both pollutants and nutrients without additional energy demand. In these systems, gaseous compounds are released into the atmosphere through microbial processes. Among these gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the most dangerous because they act as greenhouse gases (GHGs) and are well known as contributory factors to cause global warming. In this paper we reviewed 224 scientific articles (from 1980 to 2016) from the literature in order to analyze the most important factors that drive the quantity and type of GHGs production and emission from different CWs systems. Wastewater flow and composition, hydroperiod, environmental conditions and plant presence and species used to vegetate CWs have been considered. CWs typologies influence GHGs fluxes with lower CH4 emissions from subsurface flow CWs than free water surface (FWS) ones and higher N2O emissions from vertical subsurface flow (VSSF) CWs than FWS ones. The inlet wastewater COD/N ratio of 5:1 has been found as the best ratio to obtain in the same time the lowest N2O emission and the highest nitrogen removal in FWS CWs. The inlet wastewater C/N ratio of 5:1 allows to obtain the lowest CO2 and CH4 emissions in VSSF CW treatment. Intermittent CWs bed wastewater loading decreases CH4 and promote CO2 and N2O emissions. Temperature is positively correlated with CO2, CH4 and N2O emissions and solar radiation with CO2 and CH4 emissions. GHGs flux is affected by plant presence and species, and it is influenced both by the phenology and density of vegetation. Plant presence significantly increases the CO2 emission respect to unvegetated condition in all CWs types, and increases N2O and CH4 emissions in VSSF CWs. Considering the HSSF CWs plant presence significantly reduce the CH4 emissions. Plant species richness effect on CH4 emission has been investigates in a limited number of papers with not unique results, probably due to the different plant species and number used by authors, which may have influenced the CWs microbial population and activity. Considering plant species Zizania latifolia determine significant higher CH4 and N2O emissions than Phragmites australis. No significant different CH4 and N2O emissions have been found between P. australis and Typha latifolia. Significant lower N2O emissions determine the T. angustifolia than P. australis. Although plant presence, in some case, increases CW GHG emissions respect to unvegetated situation, the vegetation fixes atmospheric carbon by photosynthesis; as a consequence CWs act, in most cases, as sink of CO2(eq).
... Wetlands have the tendency to build soil organic carbon during anaerobic periods, which could also be released as CO 2 during decomposition after wetland dry down (Mitsch and Gosselink, 2007). Methane production in wetlands generally follows the removal of nitrate from the water column because nitrate has been shown to have an inhibitory effect on methanogenesis (D' Angelo and Reddy, 1999;Stadmark and Leonardson, 2005;Laanbroek, 2010). It has been estimated that wetlands contribute between 20 and 25% of the world's total CH 4 emissions to the atmosphere, although there is considerable uncertainty regarding this value (Whalen, 2005;Schlesinger and Bernhardt, 2013). ...
... Both relationships were relatively weak, but high CH 4 fluxes were only measured when nitrate concentrations were near zero. This supports the observation that nitrate inhibits CH 4 production that has been found by a similar study (Stadmark and Leonardson, 2005). A concern with installing constructed wetlands to remove nitrate from tile lines is the release of N 2 O during denitrification. ...
... For the wetlands' CH 4 and N 2 O fluxes, surface water and soil temperature were important in inundated and terrestrial fluxes, respectively ( Fig. 5 and 6). Inundated CH 4 and N 2 O fluxes had a threshold at 18°C, similar to the 15°C value described by Stadmark and Leonardson (2005) for CH 4 . Any flux that occurred in water temperature below 18°C was limited when compared with fluxes that were emitted in water above 18°C. ...
Article
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Loss of nitrate from agricultural lands to surface waters is an important issue, especially in areas that are extensively tile drained. To reduce these losses, a wide range of in-field and edge-of-field practices have been proposed, including constructed wetlands. We re-evaluated constructed wetlands established in 1994 that were previously studied for their effectiveness in removing nitrate from tile drainage water. Along with this re-evaluation, we measured the production and flux of greenhouse gases (GHGs) (CO, NO, and CH). The tile inlets and outlets of two wetlands were monitored for flow and N during the 2012 and 2013 water years. In addition, seepage rates of water and nitrate under the berm and through the riparian buffer strip were measured. Greenhouse gas emissions from the wetlands were measured using floating chambers (inundated fluxes) or static chambers (terrestrial fluxes). During this 2-yr study, the wetlands removed 56% of the total inlet nitrate load, likely through denitrification in the wetland. Some additional removal of nitrate occurred in seepage water by the riparian buffer strip along each berm (6.1% of the total inlet load, for a total nitrate removal of 62%). The dominant GHG emitted from the wetlands was CO, which represented 75 and 96% of the total GHG emissions during the two water years. The flux of NO contributed between 3.7 and 13% of the total cumulative GHG flux. Emissions of NO were 3.2 and 1.3% of the total nitrate removed from wetlands A and B, respectively. These wetlands continue to remove nitrate at rates similar to those measured after construction, with relatively little GHG gas loss. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.
... Land-use change affects different soil properties such as microbial communities (Van Leeuwen et al, 2017), enzyme 64 activity (Niemi et al, 2005), soil water content (Grover et al, 2012), nutrient and terminal electron acceptor availability, and 65 inundation (Xu, Wong and Reef, 2020), all of which affect GHG emissions (Pouyat et al, 2007). These emissions are likely 66 to be highest in tropical conditions as temperature is one of the main drivers (Oertel et al, 2016). ...
... The GHG emissions from wetlands have an extensive range. For CO2 fluxes, they can range between −139 and 22,000 mg m -2 d -1 (Stadmark and Leonardson 2005;Morse et al. 2012), for CH4, from −1 to 418 mg m -2 d -1 (Allen et al. 325 2007;Mitsch et al 2013;Cabezas et al. 2018), and for N2O, from −0.3 to 3.9 mg m -2 d -1 (Hernandez and Mitsch 2006;Morse et al. 2012). The GHG fluxes measured in this study are within the lower end, with ranges from -1191 to 10, 970 mg m -2 d -1 for CO2, from −0.2 to 3.9 mg m -2 d -1 for CH4, and −0.2 to 2.8 mg m -2 d -1 for N2O. ...
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Tidal coastal wetlands are significant to the global carbon budgets through carbon sequestration and greenhouse gas (GHG; CO2, CH4 and N2O) emissions. The conversion of tidal coastal wetlands to agriculture land alters soil processes changing GHG emissions. The GHG emissions associated with land-use change are important for restoration strategies that rely upon financial incentives such as carbon credits. We measured GHG fluxes from mangroves, saltmarsh and freshwater tidal forest and their alternative agricultural lands including sugarcane and ponded pastures. We investigated seasonal variations between June 2018 and February 2020 in tropical. Australia. The wet ponded pasture had by far the highest CH4 emissions with 1,231 ± 386 mg m−2 d−1, which were 200-fold higher than any other land use. Agricultural lands were the most significant sources of N2O emissions with 55 ± 9 mg m−2 d−1 from dry ponded pasture (wet-hot period) and 11 ± 3 mg m−2 d−1 from sugar cane (hot-dry period), coinciding with fertilisation. The N2O fluxes from the tidal coastal wetlands ranged between −0.55 ± 0.23 and 2.76 ± 0.45 mg m−2 d−1 throughout the study period. The highest CO2 fluxes of 20 ± 1 g m−2 d−1 were from the dry ponded pasture during the wet-hot period, while the saltmarsh had the lowest CO2 fluxes having an uptake of −1.19 ± 0.08 g m−2 d−1 in the dry-hot period. Overall, agricultural lands had significantly higher total cumulative GHG emissions (CH4 + N2O) of 7142 to 56,124 CO2-eq kg ha−1 y−1 compared to those of any type of tidal coastal wetlands, which ranged between 144 and 884 CO2-eq kg ha−1 y−1. Converting agricultural land, particularly wet ponded pasture, to tidal coastal wetlands could provide large GHG mitigation gains and potential financial incentives.
... [67] Mangrove (Australia) −11-128 [68] Mangrove (Hong Kong) 15-21 10-1,374 0.032-0.534 [69] Mangrove ( Rice paddies (Vietnam) 0-75 0-0.132 [80] Rice paddies (China) 0-630 [81] Ponds (Sweden) 0. 75-40.50 * data were converted from electrical conductivity (EC). ...
... [67] Mangrove (Australia) −11-128 [68] Mangrove (Hong Kong) 15-21 10-1,374 0.032-0.534 [69] Mangrove ( [58,60,65,74,76,77,83], which is generally higher than in brackish marshes (−0.17-0.23 mg C m −2 h −1 ) [56], but lower than in tidal freshwater marshes (0.01-10.8 mg C m −2 h −1 ) [62,84] and freshwater ecosystems such as rice paddies (0-630 mg C m −2 h −1 ) [79,80,85] or ponds (0.75-40.5 mg C m −2 h −1 ) [81] ( Table 2). In addition, species in mangroves with pneumatophores had significantly lower CH 4 emission rates than in mangroves without pneumatophores because pneumatophores increase soil aeration [86]. ...
Article
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The mangrove forest provides various ecosystem services in tropical and subtropical regions. Many of these services are driven by the biogeochemical cycles of C and N, and soil is the major reservoir for these chemical elements. These cycles may be influenced by the changing climate. The high plant biomass in mangrove forests makes these forests an important sink for blue C storage. However, anaerobic soil conditions may also turn mangrove forests into an environmentally detrimental producer of greenhouse gases (such as CH4 and N2O), especially as air temperatures increase. In addition, the changing environmental factors associated with climate change may also influence the N cycles and change the patterns of N2 fixation, dissimilatory nitrate reduction to ammonium, and denitrification processes. This review summarizes the biogeochemical processes of C and N cycles in mangrove forest soils based on recently published studies, and how these processes may respond to climate change, with the aim of predicting the impacts of climate change on the mangrove forest ecosystem.
... Indeed, GHG fluxes range widely across wetland systems, reflecting these gradients. A cursory review of the literature indicates that CO 2 flux can range from −139 to 22,000 mg m −2 day −1 (Dinsmore et al. 2009;Morse et al. 2012;Stadmark and Leonardson 2005), CH 4 flux can range from −0.1 to 256 mg m −2 day −1 (Altor and Mitsch 2006;Dinsmore et al. 2009;Pulliam 1993;Waddington and Roulet 1996;Holm et al. 2016), and N 2 O flux can range from −0.3 to 3.9 mg m −2 day −1 (Dinsmore et al. 2009;Hernandez and Mitsch 2006;Morse et al. 2012). ...
... This study. The range of the fluxes represent mean -2 × SD to mean + 2 × SD 2. (Bartlett et al. 1987) 3. 4. (Morse et al. 2012) 5. (Pulliam 1993) 6. (Czobel et al. 2010) 7. (Dinsmore et al. 2009) 8. (Hernandez and Mitsch 2006) 9. (Stadmark and Leonardson 2005) Wetlands changes in salinity at the research site, possibly because SO 4 2− concentrations in the created marsh were high enough to suppress the CH 4 emissions along the entire gradient despite the variations in salinity. The average SO 4 2− concentration measured from the pore water samples was 14 mM, which was 3.5 times higher than the threshold value of 4 mM observed by Poffenbarger et al. (2011) to reduce porewater CH 4 concentrations. ...
Article
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Tidal marsh creation helps remediate global warming because tidal wetlands are especially proficient at sequestering carbon (C) in soils. However, greenhouse gas (GHG) losses can offset the climatic benefits gained from C storage depending on how these tidal marshes are constructed and managed. This study attempts to determine the GHG emissions from a 4–6 year old created brackish marsh, what environmental factors governed these emissions, and how the magnitude of the fluxes relates to other wetland ecosystems. The static flux chamber method was used to measure GHG fluxes across three distinct plant zones segregated by elevation. The major of soil GHG fluxes from the marsh were from CO2 (−48–192 mg C m-2 h-1), although it was near the lower end of values reported from other wetland types having lower salinities, and would mostly be offset by photosynthetic uptake in this created brackish marsh. Methane flux was also low (−0.33–0.86 mg C m-2 h-1), likely inhibited by the high soil SO42− and soil redox potentials poised above −150 mV in this in this created brackish marsh environment. Low N2O flux (−0.11–0.10 mg N m-2 h-1) was due to low soil NO3− and soil redox conditions favoring complete denitrification. GHG fluxes from this created brackish marsh were generally lower than those recorded from natural marshes, suggesting that C sequestration may not be offset by the radiative forcing from soil GHG emissions if projects are designed properly.
... Studies on the relationship between plant diversity and ecosystem functioning have found that plant species richness increases the nitrogen removal efficiency of CWs (Sun et al., 2013;Chang et al., 2014). However, the process of nitrate removal in CWs may promote methane emissions , as nitrate can constrain methane production by increasing redox potentials (Roy and Conrad, 1999;Stadmark and Leonardson, 2005). In addition, most studies have found a positive effect of plant biomass on CH 4 emission (Whiting and Chanton, 1993;Zhang et al., 2012) due to increased organic matter and gas transportation, while some others have reported either negative or no effect of plant biomass on CH 4 emission (Bouchard et al., 2007;Bhullar et al., 2013). ...
... In coarse sand microcosms, plant species richness improved nitrate and total nitrogen removal (Fig. 2), consistent with the findings in Zhang et al. (2012) and Sun et al. (2013). Studies on the effects of nitrate on CH 4 emission from wetlands have demonstrated that the removal of nitrate can promote methane emission because nitrate has an inhibitory effect on methanogenesis (Stadmark and Leonardson, 2005). However, no increase in CH 4 emission across the species richness was observed in our study (Fig. 2). ...
... Closed static flux chambers have been widely used for measuring greenhouse gas (GHG) emissions from aquatic ecosystems and wastewater treatment systems Johansson et al., 2004;Singh et al., 2005;Lambert and Fr echette, 2005;Stadmark and Leonardson, 2005;Søvik et al., 2006;Yacob et al., 2006;Søvik and Kløve, 2007;Mander et al., 2008). This technique is widely applied because it has a high degree of adaptability and sensitivity, and is easy to use to simultaneously measure CO 2 , CH 4 and N 2 O fluxes. ...
... CH 4 , CO 2 , and N 2 O in the AP). This is consistent with the use of this technique in other studies Johansson et al., 2004;Lambert and Fr echette, 2005;Singh et al., 2005;Stadmark and Leonardson, 2005;Liikanen et al., 2006;Yacob et al., 2006;Søvik and Kløve, 2007;Mander et al., 2008). However, in these studies the data analyses for gas concentration behaviour within the chamber headspace were not shown and besides nor was the reproducibility of the respective measurements reported. ...
Article
The closed static chamber technique is widely used to quantify greenhouse gases (GHG) i.e. CH4, CO2 and N2O from aquatic and wastewater treatment systems. However, chamber-measured fluxes over air–water interfaces appear to be subject to considerable uncertainty, depending on the chamber design, lack of air mixing in the chamber, concentration gradient changes during the deployment, and irregular eruptions of gas accumulated in the sediment. In this study, the closed static chamber technique was tested in an anaerobic pond operating under tropical conditions. The closed static chambers were found to be reliable to measure GHG, but an intrinsic limitation of using closed static chambers is that not all the data for gas concentrations measured within a chamber headspace can be used to estimate the flux due to gradient concentration curves with non-plausible and physical explanations. Based on the total data set, the percentage of curves accepted was 93.6, 87.2, and 73% for CH4, CO2 and N2O, respectively. The statistical analyses demonstrated that only considering linear regression was inappropriate (i.e. approximately 40% of the data for CH4, CO2 and N2O were best fitted to a non-linear regression) for the determination of GHG flux from stabilization ponds by the closed static chamber technique. In this work, it is clear that when R2adj-non-lin > R2adj-lin, the application of linear regression models is not recommended, as it leads to an underestimation of GHG fluxes by 10–50%. This suggests that adopting only or mostly linear regression models will affect the GHG inventories obtained by using closed static chambers. According to our results, the misuse of the usual R2 parameter and only the linear regression model to estimate the fluxes will lead to reporting erroneous information on the real contribution of GHG emissions from wastewater. Therefore, the R2adj and non-linear regression model analysis should be used to reduce the biases in flux estimation by the inappropriate application of only linear regression models.
... CH 4 production, oxidation, and emission (both diffusive and non-diffusive) in shallow aquatic systems are regulated by numerous factors, including water depth (Gorsky et al., 2019), the ratio of surface area to volume (Holgerson and Raymond, 2016), water temperature (Stadmark and Leonardson, 2005), sediment properties (Bodmer et al., 2020), system productivity (Delsontro et al., 2016), and vegetation (Bansal et al., 2020). The most overlooked processes affecting CH 4 dynamics are trophic and non-trophic interactions of methanogens and methanotrophs with benthic macroinvertebrates (Colina et al., 2021). ...
Article
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Small standing water emits a large amount of methane into the atmosphere. It has been found that chironomid larvae which dwell in sediment at their larval stage, reduce methane production and increase methane oxidation by enhancing oxygen transport into the sediment. Thus chironomids' presence may reduce methane emissions. We performed our study in twelve floodplain mesocosms to evaluate to what extent chironomids larvae influence methane cycle in aquatic systems. Six of the floodplain mesocosms were treated with mosquito biocide to reduce chironomids' abundance, whereas the six other floodplain mesocosms were not treated. We measured methane emissions, concentration, and oxidation in the twelve floodplains mesocosms during spring, summer, autumn, and winter. Our results show that the methane emissions in treated floodplain mesocosms with biocide are much higher than in non-treated floodplain mesocosms. We also observed large seasonal variations in methane emissions and methane concentrations. We suggest that the reduction in chironomids abundance promoted methane production in sediment due to a lack of oxygen transport. The findings suggest that by altering the chironomid abundance, mosquito biocide may affect methane biogeochemistry, highlighting the underappreciated role of invertebrates in biogeochemical cycling.
... Microbial communities are responsible for wetland effective nutrient cycling and ecological integrity [2] by removing nitrogen and metals, participating in sulfide oxidation, and driving carbon, nitrogen, and sulfur cycling [3]. In temperate regions, eutrophic wetlands are sources of N 2 O produced by denitrification under anoxic conditions [4] and high nitrate availability [5]. In these environments, archaea and bacteria-driven nitrifications release N 2 O below suboxic conditions [6]. ...
Article
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Urban wetlands are biodiversity reservoirs sustained by microbe-mediated processes. In tropical zones, wetland microbial dynamics remain poorly understood. Chemical parameters, heavy metal content, and microbiological community structure were investigated in surface sediments of the Santa Maria del Lago (SML) wetland in Bogota, Colombia. High-throughput sequencing was employed to generate RNAr 16S and nosZ gene sequence data with which bacteria, archaea, and nosZ-type denitrifier community composition and their phylogenetic relationships were investigated. A canonical correspondence analysis was conducted to determine the relationship between assessed environmental variables and microbial community composition. Results showed that the most abundant bacterial phyla were Proteobacteria, Acidobacteria (group GP18), and Aminicenantes; Archaea were represented by the taxa Methanomicrobia and Thermoprotei, and the nosZ community was dominated by Candidatus Competibacter denitrificans. A phylogenetic analysis revealed a high diversity of Operational Taxonomic Units (OTUs), according to 16S rRNA gene sequence data; however, the quantity and diversity of OTUs from the nosZ community were low compared to previous studies. High concentrations of ammonium, phosphorus, organic carbon, Pb, Fe, Zn, Cu, and Cd, were detected in sediments, but they were not strongly related to observed microbial community compositions. In conclusion, in the same polluted SML wetland sediments diverse bacteria and archaea communities were detected, although not nosZ-type denitrifiers.
... Wetlands and other conservation practices that facilitate anaerobic conditions and denitrification to reduce N fluxes from agricultural landscapes to downstream aquatic ecosystems have the potential to increase emissions of greenhouse gases by relying on practices that facilitate denitrification (Fennessy and Cronk 1997;Stadmark and Leonardson 2005;Hey et al. 2012). Nitrous oxide emission rates reported for wetlands in agricultural areas throughout the Midwest (Hernandez and Mitsch 2006;Gleason et al. 2009;Groh et al. 2015) ranged from 1.0 to 2.1 kg N 2 O-N ha -1 y -1 (figure 3; supplemental table 2) and were slightly higher in North Carolina (Morse et al. 2012) at 2.9 kg N 2 O-N ha -1 y -1 . ...
... In this study, both the fluxes of N 2 O and CH 4 strongly positively correlated with the sediment and water temperature. As previously documented, water temperature acts as a sensitive factor, which directly influences the rate of CH 4 flux and efficiency of transport through the water column [38][39][40]. Moreover, the fluctuating water temperature could also be accompanied by variations in the DO concentrations in water, which could affect the production of CH 4 [41]. ...
Article
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In pursuit of higher economic profits, an increasing number of conventional rice paddies are being converted into aquaculture ponds in Southeast China. Due to the lack of field observations, the greenhouse gas (GHG) emissions caused by this change are not clear. A parallel field experiment in Southeast China was performed to compare CH4 and N2O emissions from rice paddies and rice-paddy−converted freshwater crayfish−fish aquaculture ponds that had previously been rice paddies. The annual fluxes of CH4 and N2O fluxes from inland crayfish–fish aquaculture averaged 0.36 mg m−2 h−1 and 45.55 μg m−2 h−1, which amounted to 31.50 kg CH4 ha−1 and 3.99 kg N2O ha−1, respectively. Compared with traditional rice paddies, such conversions significantly reduced the emissions of CH4 and N2O emissions by 46.4% and 67.5%, respectively, but greatly increased the net ecosystem economic budget (NEEB) by 485%. The fluxes of both CH4 and N2O fluxes from aquaculture ponds were positively correlated with water/sediment temperature and dissolved organic carbon in the sediment, but were negatively correlated with the concentration of oxygen that is dissolved in the water. In addition, the emissions of CH4 and N2O were closely associated with the chemical oxygen demand of water and the content of N in the sediment, respectively. The results of this study suggest that converting rice paddies to freshwater crayfish−fish aquaculture ponds could cause a reduction in the impacts on the climate and result in greater economic benefits. There is an urgent need worldwide for more field studies on the emissions of CH4 and N2O emissions from aquaculture ponds, including more types of fish species and management practices. These results will help researchers to comprehensively evaluate whether such conversions of agricultural land use are ecologically and economically feasible.
... The N 2 O production starts at −20 • C and exponentially increases with temperature [76]. However, contradictory findings were also reported by Paudel et al. [55]. Paudel et al. observed that the N 2 O emissions from freshwater aquaculture systems significantly decreased with increased water temperature. ...
Article
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Inland water bodies (particularly ponds) emit a significant amount of greenhouse gases (GHGs), particularly methane (CH4), carbon dioxide (CO2), and a comparatively low amount of nitrous oxide (N2O) to the atmosphere. In recent decades, ponds (<10,000 m2) probably account for about 1/3rd of the global lake perimeter and are considered a hotspot of GHG emissions. High nutrients and waterlogged conditions provide an ideal environment for CH4 production and emission. The rate of emissions differs according to climatic regions and is influenced by several biotic and abiotic factors, such as temperature, nutrients (C, N, & P), pH, dissolved oxygen, sediments, water depth, etc. Moreover, micro and macro planktons play a significant role in CO2 and CH4 emissions from ponds systems. Generally, in freshwater bodies, the produced N2O diffuses in the water and is converted into N2 gas through different biological processes. There are several other factors and mechanisms which significantly affect the CH4 and CO2 emission rate from ponds and need a comprehensive evaluation. This study aims to develop a decisive understanding of GHG emissions mechanisms, processes, and methods of measurement from ponds. Key factors affecting the emissions rate will also be discussed. This review will be highly useful for the environmentalists, policymakers, and water resources planners and managers to take suitable mitigation measures in advance so that the climatic impact could be reduced in the future.
... In addition, compared to the fish aquaculture pond, a stronger dependence of CH4 fluxes on these parameters were found in the crab aquaculture system (Fig. S1). As previously documented, the high water temperature could stimulate the production of CH4 in sediment and enhance the ability of CH4 transport through the water column to the atmosphere, leading to higher CH4 emissions (Frei et al., 2007;Stadmark and Leonardson, 2005). Similar findings have been also reported by our previous studies at the same area (Liu et al., 2016;Wu et al., 2018b). ...
Article
Aquaculture ponds are of increasing worldwide concerns as critical sources of atmospheric methane (CH4) and nitrous oxide (N2O), but little is known about these gases emissions as affected by aquaculture species, stocking and water management in aquaculture ponds. Here, a two-year study was carried out to quantify CH4 and N2O emissions from freshwater crab and fish aquaculture ponds in subtropical China. We further explored how the microbial functional genes [CH4: mcrA and pmoA; N2O: archaeal and bacterial amoA (AOA + AOB), nirS, nirK, nosZ] may drive CH4 and N2O release in the crab aquaculture pond typically undergoing flooding-to-drainage alteration. Over the two-year period, annual CH4 and N2O fluxes averaged 0.95 mg m⁻² h⁻¹ and 20.94 μg m⁻² h⁻¹ in the fish aquaculture, and 0.78 mg m⁻² h⁻¹and 28.48 μg m⁻² h⁻¹ in the crab aquaculture, respectively. The direct N2O emission factors were estimated to be 0.77% and 0.36% of the total N input by feed or 1.59 g N2O-N kg⁻¹ and 1.06 g N2O-N kg⁻¹ aquaculture yield in the crab and fish ponds, respectively. Among three functional stocking areas, CH4 and N2O emissions were consistently the highest at the feeding area (FA) in the both aquaculture ponds, followed by at the undisturbed area (UA) and aerated area (AA). The shift in sediment soil moisture from waterlogging to drainage conditions significantly increased the abundance of AOB relative to AOA and pmoA, decreased those of denitrifying functional genes (nirS, nirK, nosZ) and mcrA, while did not alter the functional group ratio of nirS + nirK relative to nosZ. Our results highlight that a better understanding of CH4 and N2O emissions from aquaculture ponds requires taking into consideration of data sourced from more diverse aquaculture systems with different management patterns. In addition, a deep analysis of the microbial processes that drive CH4 and N2O production and consumption from aquaculture ponds remains to be addressed in future studies.
... Some studies report the relevance between temperature and CH 4 emissions from CWs Macdonald et al., 1998;Venkiteswaran and Schiff, 2005), which is exemplified by the optimum temperature for CH 4 oxidation being approximately 25 • C, but CH 4 can be oxidized at both extremely low (− 2 • C) and high (30 • C) temperatures (King and Adamsen, 1992;Sitaula et al., 1995). CH 4 emissions when the temperature exceeded 15 • C were 1.67 and 90 times higher than those below 10 • C (Stadmark and Leonardson, 2005). Changed months clearly affected methane for a variety of reasons (Søvik et al., 2006), and one of the most obvious consequences was temperature, which was in accord with the temperature trend in this study. ...
Article
This paper aims to investigate the methane emissions from typical urban and rural constructed wetlands (CWs) associated with methanogen diversity using Illumina sequencing in microcosms from five different CWs planted with Cyperus alternifolius L. The results show that the average CH 4 flux in summer in these five CWs was 0.33 gCH 4 m − 2 day − 1 , with a range of 0.01-1.52 g CH 4 m − 2 day − 1 ((GWP: global warming potential) = 0.28-42.72 kg CO 2eq m − 2 year − 1). Redundancy analysis (RDA) shows that methane fluxes were mostly impacted by local temperature (Y methane = 4.66 X temp-102.63, R 2 = 0.81), which is considered to be a key environmental factor. The dissolved oxygen of all CWs showed a significantly negative correlation with CH 4 emissions (R 2 = − 0.99, p = 0.01). Both the species richness index and species diversity index showed that Methanobacteria was the predominant class, with percentages ranging from 16.47% to 26.66% in the five CWs. The percentage of Methanomicrobia was 15.42-24.98% in the five CWs, and Methanococci was only found in the FengHuang constructed wetland. Other findings suggest that Methanomicrobiales in the Anlong Village constructed wetland was a dominant order and similar to a local paddy ecosystem in the Chengdu Plain.
... The mean daily diffusive flux of CH 4 from all waterbodies (41.3 mg CH 4 m -2 d -1 ) was similar to that from other artificial ditches and ponds in temperate zones (20-90 mg CH 4 m -2 d -1 , Stadmark & Leonardson, 2005, McPhillips & Walter, 2015, McPhillips et al., 2016, van Bergen et al., 2019, Audet et al., 2020. Considering that diffusive fluxes from subtropical zones are generally higher (50-350 mg CH 4 m -2 d -1 , Purvaja & Ramesh, 2001, Panneer Selvam et al., 2014, Gorsky et al., 2019, Ollivier et al., 2019a, and that we found a positive relationship between water temperature and CH 4 flux, it is likely that mean annual temperature is an important controller on the magnitude of CH 4 evasion. ...
Article
Inland waters play an active role in the global carbon cycle and emit large volumes of the greenhouse gases (GHGs) methane (CH4) and carbon dioxide (CO2). A considerable body of research has improved emissions estimates from lakes, reservoirs, and rivers but recent attention has been drawn to the importance of small, artificial waterbodies as poorly quantified but potentially important emission hotspots. Of particular interest are emissions from drainage ditches and constructed ponds. These waterbody types are prevalent in many landscapes and their cumulative surface areas can be substantial. Furthermore, GHG emissions from constructed waterbodies are anthropogenic in origin and form part of national emissions reporting, whereas emissions from natural water bodies do not (according to Intergovernmental Panel on Climate Change guidelines). Here, we present GHG data from two complementary studies covering a range of land uses. In the first, we measured emissions from nine ponds and seven ditches over a full year. Annual emissions varied considerably: 0.1 – 44.3 g CH4 m⁻² yr⁻¹ and -36 – 4421 g CO2 m⁻² yr⁻¹. In the second, we measured GHG concentrations in 96 ponds and 64 ditches across seven countries, covering subtropical, temperate and sub-arctic biomes. When CH4 emissions were converted to CO2 equivalents, 93% of waterbodies were GHG sources. In both studies, GHGs were positively related to nutrient status (C, N, P), and pond GHG concentrations were highest in smallest waterbodies. Ditch and pond emissions were larger per unit area when compared to equivalent natural systems (streams, natural ponds). We show that GHG emissions from natural systems should not be used as proxies for those from artificial waterbodies, and that artificial waterbodies have the potential to make a substantial but largely unquantified contribution to emissions from the Agriculture, Forestry and Other Land Use sector, and the global carbon cycle.
... Therefore, adding electron 32 donors to secondary effluent is an effective method to enhance denitrification and 33 improve the TN removal efficiency. 34 Electron donors can be divided into autotrophic electron donors (AEDs) and 35 heterotrophic electron donors (HEDs) according to the nutrient types that can be used 36 by microorganisms. They also can be divided into easily degradable electron donors 37 and slow-release electron donors according to the difficulty of microbial degradation. ...
Article
Electron donors have been widely used to improve denitrification performance. However, it is controversial which electron donor could be chosen. In this study, three electron donors were used to improve nitrogen removal from ecological floating beds (EFBs). The results showed that TN removal efficiency was 49–80%, 46–81%, and 45–79% in EFB-C (sodium acetate), EFB-S (sodium thiosulfate), EFB-Fe (iron scraps), respectively. Nitrification was limited in EFB-C and EFB-S while denitrification in EFB-Fe. The TN removal in the three EFBs were almost equivalent when HRT was 3 days. Lowest CH4 and N2O emissions were measured in EFB-Fe. Nitrifying and denitrifying bacteria were mainly concentrated in the root rhizospheres while iron cycle related and anammox bacteria were mainly concentrated on iron scraps surface. Heterotrophic denitrification and autotrophic denitrification were mainly attributed to TN removal in EFB-C and EFB-S, respectively. Autotrophic, heterotrophic denitrification and anammox contributed to TN removal in EFB-Fe.
... There have been many differences in the range of CH 4 emissions in different types of CWs seen in past research (Stadmark and Leonardson 2005;Søvik and Kløve 2007;Chiemchaisri et al. 2009;Soosaar et al. 2009;Pangala et al. 2010;Yan et al. 2012;Wang et al. 2013;Wu et al. 2017;Badiou et al. 2019). However, the CH 4 emissions of CWs are generally higher than those of natural wetlands. ...
Article
Full-text available
CH4 flux measured by a portable chamber using an infrared analyzer was compared with the flux by static chamber measurement for CW at 13 different sites from May 2012 to May 2017 in the Living Water Garden (LWG) in Chengdu, Sichuan Province, China, over 4 timescales (daily, monthly, seasonal, and annual). During the measurement period, a total of 1443 data were collected. CH4 fluxes were measured using the portable chamber method and the results showed that the annual mean and median CH4 flux values in the LWG were 17.4 mg m−2 h−1 and 6.2 mg m−2 h−1, respectively, ranging from − 19.7 to 98.0 mg m−2 h−1. Cumulative CH4 emissions for LWG ranged from − 0.17 to 0.86 kg m−2 year−1. Global warming potential (GWP, 25.7 kg CO2eq m−2 year−1) was at a high level, which means that the LWG was a source of CH4 emissions. Significant temporal variations on the 4 timescales were observed. And the asymmetry of measurement uncertainty of CH4 flux increases with the timescale. Although the total mean CH4 flux measured by the portable chamber method was 42.1% lower than that of the static chamber method, the temporal variation trends of CH4 flux were similar. The uncertainty of CH4 flux measured in portable chamber was more symmetrical than that in static chamber. These results suggest that the portable chamber method has considerable value as a long-term measurement method for CH4 flux temporal variations.
... Increased nutrient input to CWs increases the productivity of wetland ecosystems and the production of GHG. As CWs are designed to remove pollutants in an anaerobic/suboxic environment, they change the C and N biogeochemistry and contribute significantly to CH 4 and N 2 O emissions (Johansson, 2002, Johansson et al., 2003Mander et al., 2005Mander et al., , 2008Stadmark and Leonardson, 2005;Liikanen et al., 2006). Søvic et al. (2006) measured N 2 O, CH 4 , and CO 2 emissions in various CWs in different European countries, and suggested that the potential atmospheric impacts of CWs should be examined as their development is increasing globally. ...
Article
The removal efficiency of carbon (C) and nitrogen (N) in constructed wetlands (CWs) is very inconsistent and frequently does not reveal whether the removal processes are due to physical attenuation or whether the different species have been transformed to other reactive forms. Previous research on nutrient removal in CWs did not consider the dynamics of pollution swapping (the increase of one pollutant as a result of a measure introduced to reduce a different pollutant) driven by transformational processes within and around the system. This paper aims to address this knowledge gap by reviewing the biogeochemical dynamics and fate of C and N in CWs and their potential impact on the environment, and by presenting novel ways in which these knowledge gaps may be eliminated. Nutrient removal in CWs varies with the type of CW, vegetation, climate, season, geographical region, and management practices. Horizontal flow CWs tend to have good nitrate (NO − 3) removal, as they provide good conditions for denitrification, but cannot remove ammonium (NH + 4) due to limited ability to nitrify NH + 4. Vertical flow CWs have good NH + 4 removal, but their denitrification ability is low. Surface flow CWs decrease nitrous oxide (N 2 O) emissions but increase methane (CH 4) emissions; subsurface flow CWs increase N 2 O and carbon dioxide (CO 2) emissions, but decrease CH 4 emissions. Mixed species of vegetation perform better than monocultures in increasing C and N removal and decreasing greenhouse gas (GHG) emissions, but empirical evidence is still scarce. Lower hydraulic loadings with higher hydraulic retention times enhance nutrient removal, but more empirical evidence is required to determine an optimum design. A conceptual model highlighting the current state of knowledge is presented and experimental work that should be undertaken to address knowledge gaps across CWs, vegetation and wastewater types, hydraulic loading rates and regimes, and retention times, is suggested. We recommend that further research on process-based C and N removal and on the balancing of end products into reactive and benign forms is critical to the assessment of the environmental performance of CWs.
... Saline ponds: (Cameron et al. 2016), , (Chen et al. 2015), (Hai et al. 2013), (Strangmann et al. 2008), (Vasanth et al. 2016), . Freshwater and brackish ponds: (Baker-Blocker et al. 1977), (Casper et al. 2000), (Grinham 2018), (Hu et al. 2016), (Huang 2016), , (Merbach et al. 1996), , , (Stadmark & Leonardson 2005), (van Bergen 2015), (Singh et al. 2000), (Xiong et al. 2017), (Yang et al. 2017), (Zhu et al. 2016). Canals and ditches: (Best & Jacobs 1997), (Chamberlain et al. 2015), (Chistotin 2006;Chistotin et al. 2006), , (Harrison 2003), (Hendriks et al. 2007 ...
... Our calculated mean daily flux of 30.3 mg CH 4 Ám À2 Ád À1 is of the same magnitude as other literature values from temperate artificial ponds: for instance,~80 mg CH 4 Ám À2 Ád À1 for Swedish ❖ www.esajournals.org agricultural ponds (Stadmark and Leonardson 2005), and 88 mg CH 4 Ám À2 Ád À1 for wet stormwater basins in the United States (McPhillips and Walter 2015), as well as 80 mg CH 4 Ám À2 Ád À1 for urban streams draining U.S. stormwater ponds (Smith et al. 2017). Higher average fluxes have been recorded in tropical and sub-tropical ponds, for example, 287 mg CH 4 Ám À2 Ád À1 in India ) and 115-453 mg CH 4 Ám À2 Ád À1 in Australia (Grinham et al. 2018, Ollivier et al. 2018. ...
Article
Full-text available
Inland waters emit significant quantities of greenhouse gases (GHGs) such as methane (CH 4) and carbon dioxide (CO 2) to the atmosphere. On a global scale, these emissions are large enough that their contribution to climate change is now recognized by the Intergovernmental Panel on Climate Change. Much of the past focus on GHG emissions from inland waters has focused on lakes, reservoirs, and rivers, and the role of small, artificial waterbodies such as ponds has been overlooked. To investigate the spatial variation in GHG fluxes from artificial ponds, we conducted a synoptic survey of forty urban ponds in a Swedish city. We measured dissolved concentrations of CH 4 and CO 2 , and made complementary measurements of water chemistry. We found that CH 4 concentrations were greatest in high-nutrient ponds (mea-sured as total phosphorus and total organic carbon). For CO 2 , higher concentrations were associated with silicon and calcium, suggesting that groundwater inputs lead to elevated CO 2. When converted to diffusive GHG fluxes, mean emissions were 30.3 mg CH 4 Ám À2 Ád À1 and 752 mg CO 2 Ám À2 Ád À1. Although these fluxes are moderately high on an areal basis, upscaling them to all Swedish urban ponds gives an emission of 8336 t CO 2 eq/yr (AE1689) equivalent to 0.1% of Swedish agricultural GHG emissions. Artificial ponds could be important GHG sources in countries with larger proportions of urban land.
... An increase in temperature may stimulate methanogenesis and therefore increase CH 4 emissions (Therien and Morrison, 2005;Kellner et al., 2006;Sun et al., 2013;Treat et al., 2014). This result is also supported by previous studies (Xing et al., 2005) which demonstrated that the diffusive emission rate and transport efficiency of the CH 4 flux were influenced by temperature (Stadmark and Leonardson, 2005;Ma et al., 2013;Natchimuthu et al., 2014). Moreover, the fluctuating temperature causes variation in DO concentration, which may also affect CH 4 production (Yang et al., 2017). ...
... Both CH 4 and N 2 O fluxes were positively related to water temperature, while CH 4 fluxes had a more robust response (Fig. 3). As documented, the CH 4 flux rate and transport efficiency through the water columns were shown to be highly dependent on water temperature (Stadmark and Leonardson, 2005;Frei et al., 2007). On the contrary, a negative response of N 2 O fluxes to water temperature was found in a bench-scale intensive aquaculture system (Paudel et al., 2015), where no soils were included in such bench-scale intensive aquaculture systems, and only a narrow temperature range (15-24°C) was involved, which might have failed to reflect the actual inland aquaculture wetlands. ...
Article
Inland aquaculture ponds have been documented as important sources of atmospheric methane (CH4) and nitrous oxide (N2O), while their regional or global source strength remains unclear due to lack of direct flux measurements by covering more typical habitat-specific aquaculture environments. In this study, we compared the CH4 and N2O fluxes from rice paddies and nearby inland fish aquaculture wetlands that were converted from rice paddies in southeast China. Both CH4 and N2O fluxes were positively related to water temperature and sediment dissolved organic carbon, but negatively related to water dissolved oxygen concentration. More robust response of N2O fluxes to water mineral N was observed than to sediment mineral N. Annual CH4 and N2O fluxes from inland fish aquaculture averaged 0.51 mg m⁻² h⁻¹ and 54.78 μg m⁻² h⁻¹, amounting to 42.31 kg CH4 ha⁻¹ and 2.99 kg N2O-N ha⁻¹, respectively. The conversion of rice paddies to conventional fish aquaculture significantly reduced CH4 and N2O emissions by 23% and 66%, respectively. The emission factor for N2O was estimated to be 0.46% of total N input in the feed or 1.23 g N2O-N kg⁻¹ aquaculture production. The estimate of sustained-flux global warming potential of annual CH4 and N2O emissions and the net economic profit suggested that such conversion of rice paddies to inland fish aquaculture would help to reconcile the dilemma for simultaneously achieving both low climatic impacts and high economic benefits in China. More solid direct field measurements from inland aquaculture are in urgent need to direct the overall budget of national or global CH4 and N2O fluxes.
... In mangrove forests, CH 4 emission is 0.003-7.7 mg C m −2 h −1 [20][21][22], which is lower than that in other freshwater ecosystems such as rice paddies (4.3-16.4 mg C m −2 h −1 ) [58,59] and wet ponds (0.75-40.5 mg C m −2 h −1 ) [60]. This may be another reason why mostly type I methanotrophs were predominant in the fresh mangrove soils. ...
Article
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Methanotrophs are important microbial communities in coastal ecosystems. They reduce CH4 emission in situ, which is influenced by soil conditions. This study aimed to understand the differences in active aerobic methanotrophic communities in mangrove forest soils experiencing different inundation frequency, i.e., in soils from tidal mangroves, distributed at lower elevations, and from dwarf mangroves, distributed at higher elevations. Labeling of pmoA gene of active methanotrophs using DNA-based stable isotope probing (DNA-SIP) revealed that methanotrophic activity was higher in the dwarf mangrove soils than in the tidal mangrove soils, possibly because of the more aerobic soil conditions. Methanotrophs affiliated with the cluster deep-sea-5 belonging to type Ib methanotrophs were the most dominant methanotrophs in the fresh mangrove soils, whereas type II methanotrophs also appeared in the fresh dwarf mangrove soils. Furthermore, Methylobacter and Methylosarcina were the most important active methanotrophs in the dwarf mangrove soils, whereas Methylomonas and Methylosarcina were more active in the tidal mangrove soils. High-throughput sequencing of the 16S ribosomal RNA (rRNA) gene also confirmed similar differences in methanotrophic communities at the different locations. However, several unclassified methanotrophic bacteria were found by 16S rRNA MiSeq sequencing in both fresh and incubated mangrove soils, implying that methanotrophic communities in mangrove forests may significantly differ from the methanotrophic communities documented in previous studies. Overall, this study showed the feasibility of ¹³CH4 DNA-SIP to study the active methanotrophic communities in mangrove forest soils and revealed differences in the methanotrophic community structure between coastal mangrove forests experiencing different tide frequencies.
... Much of the NO 3 − entering wetlands and small headwater streams is likely to be transformed to the inert N 2 form (Hamilton 2015, Chapter 11 in this volume), albeit with some production and emission of N 2 O (Paludan and Blicher-Mathiesen 1996, Stadmark and Leonardson 2005, Beaulieu et al. 2011. Nitrate concentrations in headwater streams often limit denitrification (Inwood et al. 2005) and are the best predictor of N 2 O emissions rates from streams around KBS (Beaulieu et al. 2008). ...
... Further, across ecosystems, rates are correlated with nitrate levels, which can explain 70% of the observed variability, and inversely correlated with O 2 levels (Pina-Ochoa and Alvarez-Cobelas 2006). Stadmark and Leonardson (2005), measuring N 2 O emissions from shallow (<1.5 m) ponds constructed in southern Sweden for nitrogen retention/removal, indicated that N 2 O fluxes from the ponds were below their detection limit, but that N 2 O production in sediment and water incubations increased with increasing nitrate concentration. Liikanen et al. (2002) found a similar effect in incubations of shallow (4 m) and deep (8 m) sediments from a eutrophic or nutrient-rich lake in Finland. ...
Chapter
Both natural and anthropogenic sources produce N2O. The primary natural sources of N2O are upland soils under natural vegetation, oceans, coastal waters, riparian zones, estuaries, and rivers. Riparian zones, rivers, estuaries, and coastal waters are also impacted by anthropogenic activities from agriculture. The anthropogenic source is associated with leaching and export from agricultural soils. Natural sources accounts for 64% of global N2O emissions. Riparian zones have saturated conditions and microbially available C, which contribute to higher rates of production of N2O than dry land soils. The oceans are another major source of natural of N2O emissions to the atmosphere with production of N2O primarily occurring in the water column. Agriculture accounts for 67–80% of anthropogenic N2O emissions. The major anthropogenic sources from agriculture include organic and inorganic N added to as fertilizers, cultivation of legumes that fixes atmospheric N2 biologically. Other anthropogenic sources include industrial processes, biomass burning, and fossil fuel combustion. The current estimated global N2O emissions are estimated at 19.8 Tg N2O-N year−1, of which the anthropogenic emissions are 6.7 Tg N2O-N year−1. The prediction of future emissions depends on the changing human activities as well as on climate patterns that are shifting because of global climate change.
... Previous research has demonstrated that constructed wetlands contribute significantly to emissions of N 2 O, a significant greenhouse gas (Stadmark and Leonardson, 2005;Liikanen et al., 2006;Mander et al., 2008). Thus, this study focused on various forms of nitrogen in the liquid phase and gas phase and N 2 O fluxes emitted from the system were investigated as well (Fig. 6). ...
Article
Organic Carbon added to low ratio of carbon to nitrogen (C/N ratio) wastewater to enhance heterotrophic denitrification performance might lead to higher operating costs and secondary pollution. In this study, sodium thiosulfate (Na2S2O3) was applied as an electron donor for a gravel filter (one kind of constructed wetland) to investigate effects of hydraulic retention time (HRT) and water temperature on the nitrate removal efficiency. The results show that with an HRT of 12 h, the average total nitrogen (TN) removal efficiencies were 91% at 15-20 °C and 18% at 3-6 °C, respectively. When HRT increased to 24 h, the average TN removal increased accordingly to 41% at 3-6 °C, suggesting denitrification performance was improved by extended HRT at low water temperatures. Due to denitrification, 96% of added nitrate nitrogen (NO3(-)-N) was converted to nitrogen gas, with a mean flux of nitrous oxide (N2O) was 0.0268-0.1500 ug m(-2) h(-1), while 98.86% of thiosulfate was gradually converted to sulfate throughout the system. Thus, our results show that the sulfur driven autotrophic denitrification constructed wetland demonstrated an excellent removal efficiency of nitrate for wastewater treatment. The HRT and water temperature proved to be two influencing factors in this constructed wetland treatment system.
... Increased nutrient input to CWs increases the productivity of wetland ecosystems and the production of GHG. As CWs are designed to remove pollutants in an anaerobic/suboxic environment, they change the C and N biogeochemistry and contribute significantly to CH 4 and N 2 O emissions (Johansson, 2002, Johansson et al., 2003Mander et al., 2005Mander et al., , 2008Stadmark and Leonardson, 2005;Liikanen et al., 2006). Søvic et al. (2006) measured N 2 O, CH 4 , and CO 2 emissions in various CWs in different European countries, and suggested that the potential atmospheric impacts of CWs should be examined as their development is increasing globally. ...
Article
The removal efficiency of carbon (C) and nitrogen(N) in constructed wetlands (CWs) is very inconsistent andfrequently does not reveal whether the removal processes aredue to physical attenuation or whether the different specieshave been transformed to other reactive forms. Previous re-search on nutrient removal in CWs did not consider the dy-namics ofpollution swapping(the increase of one pollutantas a result of a measure introduced to reduce a different pollu-tant) driven by transformational processes within and aroundthe system. This paper aims to address this knowledge gap byreviewing the biogeochemical dynamics and fate of C and Nin CWs and their potential impact on the environment, and bypresenting novel ways in which these knowledge gaps maybe eliminated. Nutrient removal in CWs varies with the typeof CW, vegetation, climate, season, geographical region, andmanagement practices. Horizontal flow CWs tend to havegood nitrate (NO�3) removal, as they provide good conditionsfor denitrification, but cannot remove ammonium (NHC4) dueto limited ability to nitrify NHC4. Vertical flow CWs havegood NHC4removal, but their denitrification ability is low.Surface flow CWs decrease nitrous oxide (N2O) emissionsbut increase methane (CH4) emissions; subsurface flow CWsincrease N2O and carbon dioxide (CO2) emissions, but de-crease CH4emissions. Mixed species of vegetation performbetter than monocultures in increasing C and N removal anddecreasing greenhouse gas (GHG) emissions, but empiricalevidence is still scarce. Lower hydraulic loadings with higherhydraulic retention times enhance nutrient removal, but moreempirical evidence is required to determine an optimum de-sign. A conceptual model highlighting the current state ofknowledge is presented and experimental work that shouldbe undertaken to address knowledge gaps across CWs, veg-etation and wastewater types, hydraulic loading rates andregimes, and retention times, is suggested. We recommendthat further research on process-based C and N removal andon the balancing of end products into reactive and benignforms is critical to the assessment of the environmental per-formance of CWs. Carbon and nitrogen dynamics and greenhouse gas emissions in constructed wetlands treating wastewater: a review. Available from: https://www.researchgate.net/publication/290086292_Carbon_and_nitrogen_dynamics_and_greenhouse_gas_emissions_in_constructed_wetlands_treating_wastewater_a_review [accessed Jan 14, 2016].
... The water temperature constitutes a sensitive factor influencing CH 4 flux rate and transport efficiency through the water columns. 22,49 A stronger dependence of N 2 O fluxes on temperature during drainage period in inland aquaculture wetlands was similar to the results obtained in rice paddies, indicating that N 2 O fluxes were much higher and thus tended to be more temperature-dependent under drainage than under waterlogging conditions. 50 In contrast, Paudel et al. ...
Article
Aquaculture is an important source of atmospheric methane (CH4) and nitrous oxide (N2O), while few direct flux measurements are available for their regional and global source strength estimates. A parallel field experiment was performed to measure annual CH4 and N2O fluxes from rice paddies and rice paddy-converted inland crab-fish aquaculture wetlands in southeast China. Besides N2O fluxes dependent on water/sediment mineral N and CH4 fluxes related to water chemical oxygen demand, both CH4 and N2O fluxes from aquaculture were related to water/sediment temperature, sediment dissolved organic carbon, and water dissolved oxygen concentration. Annual CH4 and N2O fluxes from inland aquaculture averaged 0.37 mg m-2 h-1 and 48.1 μg m-2 h-1, yielding 32.57 kg ha-1 and 2.69 kg N2O-N ha-1, respectively. The conversion of rice paddies to aquaculture significantly reduced CH4 and N2O emissions by 48% and 56%, respectively. The emission factor for N2O was estimated to be 0.66% of total N input in the feed or 1.64 g N2O-N kg-1 aquaculture production in aquaculture. The conversion of rice paddies to inland aquaculture would benefit for reconciling greenhouse gas mitigation and agricultural income increase as far as global warming potentials and net ecosystem economic profits are of concomitant concern. Some agricultural practices such as better aeration and feeding, and fallow season dredging would help to lower CH4 and N2O emissions from inland aquaculture. More field measurements from inland aquaculture are highly needed to gain an insight into national and global accounting of CH4 and N2O emissions.
... NO is considered as a secondary greenhouse gas; it can promote photochemical formation of tropospheric ozone (O 3 ) (Scheer et al. 2009;Lan et al. 2013), which has higher global warming potential (GWP) than CO 2 (Zheng et al. 2000). Greenhouse gas emissions from CWs arouse concerns because high N 2 O fluxes were observed in wastewater treatment processes (Mander et al. 2014;Johansson et al. 2004;Stadmark and Leonardson 2005;Teiter and Mander 2005). The literature predominantly examines greenhouse gas emissions from CWs treating industrial and domestic wastewater Teiter and Mander 2005;Wu et al. 2009). ...
Article
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Nitric oxide (NO) and nitrous oxide (N2O) emitted from wetland systems contribute an important proportion to the global warming effect. In this study, four wetland microcosms vegetated with Myriophyllum elatinoides (WM), Alternanthera philoxeroides (WA), Eichhornia crassipes (WE), or without vegetation (NW) were compared to investigate the emissions of NO and N2O during nitrogen (N) removal process when treating swine wastewater. After 30-day incubation, TN removal rates of 96.4, 74.2, 97.2, and 47.3 % were observed for the WM, WA, WE, and NW microcosms, respectively. Yet, no significant difference was observed in WM and WE (p > 0.05). The average NO and N2O emissions in WE was significantly higher than those in WM, WA, and NW (p < 0.05). In addition, the emission of N2O in WE accounted for 2.10 % of initial TN load and 2.17 % of the total amount of TN removal, compared with less than 1 % in the other microcosms. These findings indicate that wetland vegetated with M. elatinoides may be an optimal system for swine wastewater treatment, based on its higher removal of N and lower emissions of NO and N2O.
... En el año 2005, midieron las emisiones de N 2 O, CO 2 y CH 4 en lagunas de estabilización para el tratamiento de aguas residuales domésticas [25]. En este estudio se observó que la temperatura del agua se relaciona directamente con las emisiones de gases de efecto invernadero. ...
... This effect should not dominate in the lagoons. On the contrary, methane emission has been observed in constructed wetland (Altor and Mitsch, 2006;Stadmark and Leonardson, 2005). It can be emitted by the sediments where anaerobic conditions can occur. ...
Article
Animal production increased regularly since some decades, in developed countries at first, and now in developing countries. Industrial systems have been developed to increase rapidly the productivity of animal farms and to supply the food consumed by the towns. They are efficient in terms of biosecurity and of feed conversion efficiency but they have severe environmental impacts such as the odor emissions, the ammonia or greenhouse gas emissions, or the water pollution. The sustainability of these systems depends on their ability to limit their impact on resource depletion and to limit their leakages so that the wild environment and the biodiversity can be preserved beside the producing areas. Expensive treatment systems can not be used because of economical reasons. Ecological engineering provides concepts that can help finding solutions more efficient economically and ecologically. Our work began with the starting up of a new system of animal production that associates a pig house with manure flushing and screening, a vermifilter, lagooning, and constructed wetlands. This system was designed to increases the recycling efficiency of water and to produce biomass for animal feed, fertilization, biogas, etc. The system combines high manure dilution, which allows a decrease in polluting emissions, to the reuse of water and nutrients. Water is reused for excretion flushing. The nutrients are either reused within the farm or exported. The needed surface is around 50 times less than for manure spreading. The fundamental objective of the present work was to improve the understanding of the system to define more precisely its advantages and its limits. The applied objective was to study if this new knowledge was useful to improve the design and the management of this system. Specific methods were developed to study from the process or from a systemic point of view a recycling system that was too large to be reproduced in a laboratory. They were applied to the gaseous emissions of the vermifilter and to the treatment efficiency of the combination of lagoons and constructed wetlands. The results show that an "optimal transfer" of liquid can be defined that will maximize the earthworm population (preferendum). Above this input the earthworms die because of anoxic conditions. When earthworm population is maximal, the ammonia and the greenhouse gases are minimized as related to the input flux. Therefore, the earthworm abundance can be used as a bioindicator of low energy and low emissions in manure transforming systems. The effect on gaseous emissions is mostly indirect, through the influence of earthworms on the structure of the organic layer, its free air space, transfer of organic particles and its microbial population. This "optimal transfer" between two successive levels also exists for the vegetation production of lagoons and constructed wetlands. If we compare "recycling" to "open" system, the water recycling will induces a change in the stoechiometry of nutrients, because of the various treatment efficiencies of elements: for example, potassium abatement rate is less than nitrogen abatement rate; this case induces an increase in potassium concentration in the water compared to nitrogen. Potassium concentration reaches a stable level when the retention by all subsystems corresponds to a mass decrease equivalent to the potassium excreted by the animals. This case shows that the stoechiometry of nutrients should change in agricultural systems with increased recycling efficiency. Calculating the mass balance of the system shows that ammonia and greenhouse gas emissions were low, regarding the nitrogen fluxes, and that the organic products (worm casts and sludge from lagoons) were the major contributors to the removal of nutrients. Recommendations for the design and management of systems that improve manure recycling are proposed, based on this knowledge. Our results were and can be further used for socio-economical purposes.
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In the modern era, due to urbanization, industrialization, and anthropogenic activities in the catchment, greenhouse gas (GHG; CO2, CH4, and N2O) emissions from freshwater ecosystems received scientific attention because of global warming and future climate impacts. A developing country like India contributes a huge share (4% of global) of GHGs from its freshwater ecosystems (e.g., rivers, lakes, reservoirs) to the atmosphere. This is the first comprehensive review dealing with the GHG emissions from Indian freshwater bodies. Literature reveals that the majority of GHG from India is emitted from its inland water with 19% of CH4 flux and 56% of CO2 flux. A large part of India’s Gross domestic product (GDP) is manipulated by its rivers. As a matter of fact, 117.8 Tg CO2 yr-1 of CO2 is released from its major riverine waters. The potential of GHG emission from Hydropower reservoirs varies between 11-52.9% (mainly CH4 and CO2) because of spatio-temporal variability in the GHG emissions. A significant contribution was also reported from urban lakes, wetlands and other Inland waters. Being a subtropical country, India is one of the GHG hotspots around the world having the highest ratio (GHG: GDP) of 1301.79. Although, a large portion of India’s freshwater has not been considered yet and needs to be accounted for précised regional carbon budgets. Therefore, in this review, GHG emissions from India’s freshwater bodies, drivers behind GHG emissions (e.g., pH, mean depth, dissolved oxygen, and nutrients), and long-term climatic risks are thoroughly reviewed. Besides, research gaps, future directions as well as mitigation measures are being suggested to provide useful insight into the carbon dynamics (sink/source) and control of GHG emissions.
Article
Freshwater aquaculture ponds constitute one of the important anthropogenic sources of atmospheric methane (CH4). Nevertheless, estimates of global CH4 emissions from freshwater aquaculture have large uncertainties due to a lack of data from different aquaculture types. Furthermore, despite that ebullition is a major pathway of CH4 in aquatic systems, the quantification of ebullitive CH4 fluxes from typical freshwater aquaculture ponds has been poorly represented. Here, field measurements of CH4 fluxes over two years were taken to quantify ebullitive CH4 fluxes from inland freshwater fish and crab aquaculture ponds in subtropical China. Ebullitive CH4 fluxes averaged 15.97 ± 1.57 and 11.22 ± 1.26 mg m⁻² d⁻¹ in the fish and crab ponds in the first experimental year, respectively, and were 22.86 ± 2.30 and 21.95 ± 2.19 mg m⁻² d⁻¹ in the second year. During aquaculture period, ebullition dominated the emission pathways of CH4, accounting for 83% and 98% of the total CH4 emissions in the fish and crab ponds, respectively. Ebullitive CH4 fluxes exhibited considerable spatial variations, with the lowest flux rates captured at the aeration area due to aerator-use in both the fish and crab ponds. Dissolved oxygen and dissolved organic carbon were the two primary factors that drove ebullitive CH4 fluxes in both aquaculture ponds. By incorporating global measurement data, we further assessed the CH4 mitigation potential of aerator use in freshwater aquaculture and revealed the dominant role of ebullition in this mitigation contribution. Together with the rice-based aquaculture, aerator use could reduce CH4 emissions from freshwater aquaculture ponds globally by 71% and in China by 63%.
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Studies on the flux measurements of methane (CH4) from wetlands of tropics are very meagre. Such data from this region would be valuable for generating the emission patterns at local/regional scale and would contribute to the global database. Investigations was done on measuring the daytime pattern of methane emissions during premonsoon, monsoon, and postmonsoon seasons from a tropical wetland system, namely the Vellayani lake located in the urbanized area of Thiruvananthapuram city in Southern India. The difference in the methane flux from the vegetated littoral zone and nonvegetated limnetic zone and the edaphic features controlling the production and emission of methane were also proposed to be studied. Methane emissions were measured using static chamber, and analyses were performed using gas chromatograph. The methane emissions recorded in monsoon season from vegetated littoral zone was significantly higher compared with pre- and postmonsoon seasons, indicating seasonal fluctuations in methane emission from the wetland system. CH4 efflux in the zone of emergent vegetation in the littoral zone was significantly higher than from the nonvegetated limnetic zone indicating the importance of vegetation in methane transport to the atmosphere. Positive correlation of CH4 efflux with edaphic factors like total organic carbon and total nitrogen showed that these factors largely determined the production and emission of methane. These results underlined the fact that the vegetated littoral zones of lake, especially the emergent plant zones were supersaturated with CH4 compared with nonvegetated zones, by facilitating the production of carbon for CH4 emission, and also enabled the release of CH4 by diffusion through the intercellular gas lacunas. The study arrives at the conclusion that the atmospheric CH4 emissions will be tilted by the growth of exotic species and may be the reason for enhancing the climate warming in local/regional environment and may be even important globally.
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Due to regular influx of organic matter and nutrients, waste stabilization ponds (WSPs) can release considerable quantities of greenhouse gases (GHGs). To investigate the spatiotemporal variations of GHG emissions from WSPs with a focus on the effects of sludge accumulation and distribution, we conducted a bathymetry survey and two sampling campaigns in Ucubamba WSP (Cuenca, Ecuador). The results indicated that spatial variation of GHG emissions was strongly dependent on sludge distribution. Thick sludge layers in aerated ponds and facultative ponds caused substantial CO2 and CH4 emissions which accounted for 21.3% and 78.7% of the total emissions from the plant. Conversely, the prevalence of anoxic conditions stimulated the N2O consumption via complete denitrification leading to a net uptake from the atmosphere, i.e. up to 1.4±0.2 mg-N m⁻² d⁻¹. Double emission rates of CO2 were found in the facultative and maturation ponds during the day compared to night-time emissions, indicating the important role of algal respiration, while no diel variation of the CH4 and N2O emissions was found. Despite the uptake of N2O, the total GHG emissions of the WSP was higher than constructed wetlands and conventional centralized wastewater treatment facilities. Hence, it is recommended that sludge management with proper desludging regulation should be included as an important mitigation measure to reduce the carbon footprint of pond treatment facilities.
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A study was conducted to evaluate the effect of three different organic manures and salinity levels on production of greenhouse gases (GHGs) and their interactive effects on growth and physiological parameters of common carp (Cyprinus carpio) in peri‐urban aquaculture tank system. The experiment had 3 × 3 factorial design with three types of organic manures, that is humic acid, FMGY (fermented boiled rice, molasses, groundnut oil cake and yeast) and cow dung tested in combination with three different salinity levels, that is 0.2, 2.5 and 5.0 g/L in triplicates. C. carpio fingerlings (average weight and length of 7 g and 7.15 cm respectively) were distributed to 27 number of 1000‐litre FRP tanks (nine treatments with triplicates) containing 10 fish per tank. Fish were maintained for an experimental period of 180 days with a diet containing 30% crude protein. GHG estimation was done on 120th, 150th and 180th days at 30‐day interval by collecting gaseous sample following floating chamber method. Lowest GHG emission (917.73) CO2 equivalent (mg m⁻² h⁻¹) was recorded in T3 treatment (humic acid + 5 g/L salinity). Highest fish growth was evident in T2 treatment (humic acid with 2.5 g/L salinity). GaSI and HSI were higher in treatment T2. Lowest stress parameters (plasma glucose and serum cortisol) were recorded in T4 treatment (FMGY with 0.2 g/L salinity). In terms of GHG emission, growth and bio‐indices in C. carpio tank rearing, humic acid is the best organic manure at less than 5 g/L water salinity.
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Despite covering a small portion of the earth’s surface, lakes and reservoirs offer enormous benefits to human society, environmental well-being, and economic welfare. Previous studies have provided insights into specific subjects, yet integrated perspectives on the development of the two waterbodies are missing. To this end, we conducted a bibliometric analysis as a systematic data gathering to perform a large-scale overview and assess global trends of their scientific publications. Moreover, a second goal is to differentiate their research hotspots and current challenges given the different nature of their origin and functionality. 147,811 publications from 1955 to 2019 were retrieved from the database of the Science Citation Index Expanded, and then, divided into four research lines, (1) design and operation; (2) environment and ecology; (3) sanitation and human health; (4) socioeconomics. Bibliometric indicators showed that the number of publications sustained a rapid growth, from 100 during the 1950s to around 7800 publications per year during the past few years. The United States and EU 28 have long been world leaders in lake and reservoir research yet China has tremendously boosted its publications within the past 20 years, advancing this nation to the new world leader in both categories in 2019. Taking a closer look at research hotspots, design and operation have been the main topics for reservoir research while environment and ecology topics are the hotspots in lakes-related studies. This reflected the intensive human interventions in reservoirs, whose major purposes are to supply hydropower energy, irrigation, water storage, and aquaculture. Conversely, the impacts of eutrophication, heavy metals, and climate change have become more severe with the increase of species extinction and biodiversity loss, leading to urgent needs for lake restoration. Both freshwater bodies show comparable attention on their roles in socioeconomics while much higher concerns about sanitation and human health have been paid in reservoirs compared to its counterpart. Clear obtained distinctions in the hotspots and challenges of lake and reservoir research can contribute to better decision support systems of the two waterbodies.
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This study used a self-developed a NDIR monitoring system to continuously monitor GHG emissions from a tidal constructed mangrove wetland at three typical habitats (mudflat, mangrove, and water surface) in four seasons. The NDIR monitoring system is able to explore the diurnal and seasonal variation of GHG emissions from the tidal constructed mangrove wetland and to estimate more precisely for the GHG emission based carbon budget of the wetland. The continuous monitoring technique is feasible and valuable for assessing the temporal variation of GHG uptake/emission to/from the wetland. Daytime CO2 emissions were always lower than those at nighttime due to photosynthesis process, while an opposite trend was observed for CH4 and N2O emissions. Seasonal variation of GHGs showed that the highest GHG emissions was observed in summer, and followed by fall, spring, and winter. For three typical habitats, mangrove emitted more amounts of GHGs than mudflat and water surface.
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Theaimofthisresearchwastoevaluatetheroleofconstructedwetland(CW)horizontalsub-surfaceflowpilotplantbedsvegetation,comparingfourperennialherbaceousplantspecieswithanunvegetatedbed,oncarbon dioxide(CO2)andmethane(CH4)emissions,andCO2(eq)budgets.TheresearchwasconductedfromApril1stto November30th in2012and2013inapilotplantlocatedinSanMichelediGanzaria(Sicily,Italy)thattreated urbanwastewaters,studyingPhragmitesaustralis(Cav.)Trin.exSteud.(commonreed),ArundodonaxL.(giant reed), Chrysopogon zizanioides (L.) Roberty (vetiver) and Miscanthus x giganteus Greef et Deu. (miscanthus). Resultsshowedagreaterabovegroundbiomassyieldinthesecondexperimentalyearthanthefirstoneforall speciesexceptvetiver,whichshoweda10.5%reduction.ConsideringCWsgasesemission,asignificantlyhigher CO2 emission (+52.5%) was monitored in 2013 than 2012 whereas CH4 had the opposite trend (−97.0%). Seasonsandplantspeciesinfluencedgasesemission.ThelowerCO2emission(medianvalue5.2gm−2d−1)was monitored during the spring seasons when instead was monitored the highest CH4 emission (median value 0.232gm−2d−1). Opposite CO2 and CH4 emissions were found in fall. A.donax, M. giganteus and P. australis determined significantly higher (2.9 times) CO2 emission than C. zizanioides and unvegetated bed. Vegetated bedsshowedapositiveCO2(eq)totalbalancewiththebestresultscalculatedforA.donaxwhereas,asexpected,it was negative for the unvegetated bed, with a cumulative CO2(eq) emission of 6.68kgm−2. Obtained results confirm the active and key role of plant species used in the CW systems and indicate A. donax as the most environmentallyfriendlyspeciestouseunderMediterraneanclimateconditions,followedbyP.australis.
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Stormwater ponds are ubiquitous features of developed landscapes of the eastern United States. Their design specifically controls the pace of water runoff from impervious cover of surrounding watersheds. Ponds accumulate organic matter that typically decomposes anaerobically in bottom sediments, and thus may be significant sources of greenhouse gases to the atmosphere (e.g., carbon dioxide (CO2), methane (CH4)). We sampled fifteen stormwater retention ponds in southeastern Virginia (USA) during summer 2018 to determine the diffusive emission of greenhouse gases with respect to measured environmental parameters. The equivalent CO2 (CO2e) flux from ponds ranged from 8.3 to 80 mmol m⁻² h⁻¹, with CH4 contributing 94%, CO2 6% and nitrous oxide less than 1% of the CO2e flux, on average. From linear mixed-effects modelling, diffusive flux of CO2 was inversely associated with pH. Maximum depth best explained diffusive flux of CH4, with surface area of secondary importance, i.e. CH4 flux was higher in smaller and more shallow ponds. With 300 stormwater ponds in the county where we conducted this study, we estimate that, during a 100-day warm season, these ponds emit 2.3 × 10⁹ ± 1.5 × 10⁹ SD g C as CO2e. As small, human-constructed ponds are becoming common features of urbanizing landscapes globally, results from this study suggest that, collectively, small ponds can contribute substantially to climate forcing. Better pond designs that reduce sediment methanogenesis, however, can mitigate the hypothesized potential disservice of GHG emissions from unvegetated stormwater retention ponds.
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Mitigation of agricultural nitrogen (N) loss via tile drains using woodchip-based subsurface constructed wetlands seems promising. However, the stochastic nature of drainage discharge and consequent temporal variations in hydraulic loading rates may result in the emission of the greenhouse gases (GHG) nitrous oxide (N2O) and methane (CH4) with potentially severe climatic effects that are not yet adequately studied. We investigated the influence of the direction of the convective transport on the net export of GHGs by measuring the two export paths of the gases (emitted and dissolved via the effluent) in six woodchip-based subsurface constructed wetlands with different hydraulic designs (horizontal and vertical up- and downward flow). Emissions ranged from −75.1 to 49.5 μg N2ON m⁻² h⁻¹ and from −0.28 to 720 mg CH4C m⁻² h⁻¹. Dissolved concentrations in the effluent ranged from 0 to 1108 μg N2ON L⁻¹ and from 4 to 8452 μg CH4C L⁻¹. Nitrous oxide emissions were negligible; thus, the main export path for N2O was as gas dissolved in the effluent. April and December were temporal hotspots for N2O production. High CH4 emissions and high dissolved concentrations were associated with the low hydraulic loading and high temperature occurring during the Danish summer. We found no effect of hydraulic design on the net export of N2O, whereas the ratio between CH4 emissions and net export in the form of dissolved CH4 via the effluent (the export ratio) was significantly affected. In conclusion, vertical downward flow lowered the export ratio of CH4 and may be the best hydraulic design, when conditions (i.e. low HLR) facilitate high CH4 production.
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Landscapes can be viewed as spatially heterogeneous areas encompassing terrestrial and aquatic domains. To date, most landscape carbon (C) fluxes have been estimated by accounting for terrestrial ecosystems, while aquatic ecosystems have been largely neglected. However, a robust assessment of C fluxes on the landscape scale requires the estimation of fluxes within and between both landscape components. Here, we compiled data from the literature on C fluxes across the air–water interface from various landscape components. We simulated C emissions and uptake for five different scenarios which represent a gradient of increasing spatial heterogeneity within a temperate young moraine landscape: (I) a homogeneous landscape with only cropland and large lakes; (II) separation of the terrestrial domain into cropland and forest; (III) further separation into cropland, forest, and grassland; (IV) additional division of the aquatic area into large lakes and peatlands; and (V) further separation of the aquatic area into large lakes, peatlands, running waters, and small water bodies These simulations suggest that C fluxes at the landscape scale might depend on spatial heterogeneity and landscape diversity, among other factors. When we consider spatial heterogeneity and diversity alone, small inland waters appear to play a pivotal and previously underestimated role in landscape greenhouse gas emissions that may be regarded as C hot spots. Approaches focusing on the landscape scale will also enable improved projections of ecosystems’ responses to perturbations, e.g., due to global change and anthropogenic activities, and evaluations of the specific role individual landscape components play in regional C fluxes. For further resources related to this article, please visit the WIREs website.
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Wetlands serve as sinks for carbon and nutrients but they are also a large source of greenhouse gases. Our objective was to quantify emissions of carbon dioxide (CO2) and methane (CH4) from three free water surface-flow constructed wetlands in the presence and absence of emergent herbaceous vegetation (Typha angustifolia L. and Typha latifolia L.) across a gradient of soil moisture. Measurements were collected on eight sampling dates during June and July, 2014. Similar to previous research, CO2 emissions were higher in vegetated plots, increasing from a median ± std. error of 242 ± 29 to 1612 ± 95 mg m−2 h−1. Emissions of CH4 were also significantly higher in vegetated plots, but the relative magnitude of the effect of plants varied among wetlands. Emissions of CH4 were highest from vegetated plots in the wetland with the highest soil moisture (4.4 ± 1.0 mg m−2 h−1). However, the largest effect of plants on methane emissions occurred in the wetland with intermediate soil moisture, with a 15-fold increase in CH4 emissions from 0.15 ± 0.90 to 2.4 ± 1.2 mg m−2 h−1. Design and management that consider the interactive effects of soil moisture and plants on CH4 emissions may help reduce the greenhouse gas footprint of constructed wetlands.
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In this study, nitrous oxide (N2O) emission was analyzed in a newly developed baffled subsurface constructed wetland. N2O was collected using a closed chamber. The effect of different loads and seasons was investigated and N2O emission rate within 24 h was obtained. In addition, variation of N2O flux along the flow direction was tested. The results indicated significant seasonal and diurnal variation. The peak of N2O emission occurred in September, which is 393.21μg/m2•d; the lowest value was in January, whichwas 84.291 iμg/m2•d. The maximum emission within a day was most likely occurred in the morning, whereas the minimum value was in the midnight. The nitrous oxide emission also varied obviously along the flow direction. The highest emission was observed at the inlet of the wetlands while lowest value was at outlet of the wetlands.
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Large dams may be substantial contributors to greenhouse gas emissions. Nitrous oxide (N2O) is the third most important greenhouse gas but studies on N2O emission from reservoirs are limited. We measured N2O emissions and environmental factors including atmospheric pressure, wind speed, air and soil/sediment temperature, biomass, soil water content and organic matter, total nitrogen, NH4+-N and NO3--N of soil, from the littoral zones of the Miyun Reservoir, near Beijing, China, in January, May, June, August, and October during 2009 and 2010. Using the static chamber method we investigated the seasonal and spatial variation, relating it to environmental factors. Spatial and temporal variations in N2O flux appeared to be influenced by several environmental factors, working singly or in conjunction, including soil water depth, soil nutrition, biomass, and wind speed. In winter and spring, high N2O emissions (up to 1.9 ± 0.6 mg N2O m-2 h-1) were recorded at both eulittoral and infralittoral zones, while the flux from the supralittoral zone was low during all the seasons (from -0.04 to 0.01 mg N2O m-2 h-1). This study suggests that the littoral zone is a substantial source of N2O. However, its spatiotemporal variation and environmental drivers are still not clear.
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Soil amendments have been proposed as a means to speed the development of plant and soil processes that contribute to water quality, habitat, and biodiversity functions in restored wetlands. However, because natural wetlands often act as significant methane sources, it remains unknown if amendments will also stimulate emissions of this greenhouse gas from restored wetlands. In this study, we investigated the potential trade-offs of incorporating soil amendments into wetland restoration methodology. We used controlled field-scale manipulations in four recently restored depressional freshwater wetlands in western New York, USA to investigate the impact that soils amended with organic materials have on water-quality functions and methane production in the first three years of development. Results showed that amendments, topsoil in particular, were effective for stimulating the development of a suite of biological (microbial biomass increased by 106% and respiration by 26%) and physicochemical (cation exchange capacity increased by 10%) soil properties indicative of water-quality functions. Furthermore, increases in microbial biomass and activity lasted for a significantly longer period of time (years instead of days) than studies examining less recalcitrant amendments. However, amended plots also had 20% times higher potential net methane production than control plots three years after restoration. Wetlands restoration projects are implemented to achieve a variety of goals, commonly including habitat provision, biodiversity, and water-quality functions, but also carbon sequestration, flood abatement, cultural heritage and livelihood preservation, recreation, education, and others. Projects should strive to achieve their specific goals while also evaluating the potential tradeoffs between wetland functions.
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Constructed wetlands (CWs) are widely used for wastewater treatment, but may also be sources of greenhouse gas (GHG). This study focuses on comparing the GHG emissions from a vertical flow constructed wetland (VFCW) and a horizontal flow constructed wetland (HFCW) in the city of Tianjin, China. Two methods are used in this paper to estimate the indirect and direct GHG emissions. It is found that the VFCW emits 0.09, 1.34, and 3.31 kg equivalent CO2 (CO2 Eq.) to remove 1.00 m3 wastewater, 1.00 kg COD, and 1.00 kg BOD in the studied life cycle, respectively, in contrast to 0.18, 2.10, and 5.42 kg CO2 Eq. for the HFCW. The results indicate that the adoption of VFCW is a more effective option with respect to GHG emissions when treating the same amount of pollutants. In addition, the operation phase which includes GHG emissions from water treatment process and energy consumption for pump dominates the GHG emissions. For different kinds of GHG from CWs, CO2 dominates the influence on climate change. The CH4 and N2O emissions should also deserve more attention due to their greater global warming potential. This paper further suggests that GHG emissions can be mitigated in the design, construction, and operation stages through some feasible measures. It would reduce GHG emissions in CWs by adopting hybrid CW system (e.g. HF–VF or VF–HF) or choosing suitable plant species which can mitigate GHG emissions. In addition, aeration could contribute to the control of GHG emissions from CWs.
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Static chamber measurements of N 2 O fluxes were taken during the 1998 and 1999 growth seasons in a Swedish constructed wetland receiving wastewater. The dominating plant species in different parts of the wetland were Lemna minor L ., Typha latifolia L . , Spirogyra sp . and Glyceria maxima (Hartm.) and Phalaris arundinacea (L.), respectively. There were large temporal and spatial variations in N 2 O fluxes, which ranged from consumption at –350 to emissions at 1791 μg N 2 O m −2 h −1 . The largest positive flux occurred in October 1999 and the lowest in the middle of July 1999. The average N 2 O flux for the two years was 130 μg N 2 O m −2 h −1 (SD = 220). No significant differences in N 2 O fluxes were found between the years, even though the two growing seasons differed considerably with respect to both air temperature and precipitation. 15% of the fluxes were negative, showing a consumption of N 2 O. Consumption occurred on a few occasions at most measurement sites and ranged from 1–350 μg N 2 O m −2 h −1 . 13–43% of the variation in N 2 O fluxes was explained by multiple linear regression analysis including principal components. Emission factors were calculated according to IPCC methods from the N 2 O fluxes in the constructed wetland. The calculated emission factors were always lower (0.02–0.27%) compared to the default factor provided by the IPCC (0.75%). Thus, direct application of the IPCC default factor may lead to overestimation of N 2 O fluxes from constructed wastewater-treating wetlands. DOI: 10.1034/j.1600-0889.2003.00034.x
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Methane emissions were measured over a 15-month interval for five lakes and five associated wetland sites in the Rockies of Colorado at elevations between 2800 and 3600 m. Three of the five lakes accumulated dissolved methane under ice; accumulation was as high as 53-fold above ice-free water column concentrations in the shallowest lake. The combination of high dissolved oxygen and low dissolved inorganic nitrogen concentrations within the water column during ice breakup suggests that methane emissions rather than methane oxidation led to the substantial loss of dissolved methane from the shallowest lake at the time of spring thaw. A pulsed release of methane to the atmosphere at the time of ice breakup within lakes may be widespread at high latitudes and may play a role in the observed increase in tropospheric methane concentrations in the northern hemisphere. During the ice-free season, the mean emission rate was 1.6 mmol m−2 d−1 over open water for the five lakes, but the mean was much higher (13 mmol m−2 d−1) over the Nuphar lutea beds located in one of the lakes. Open water emissions occurred primarily through diffusion rather than bubbling. For wetlands near the lakes, average lake emissions ranged from negligible to almost 6 mmol m−2 d−1; the average across all sites was 2.1 mmol m−2 d−1 during the warm season. There was no measurable emission during the winter months. Surface dissolved methane explains 40% of the variation in emissions from the open water sites; the combination of soil organic C content and soil temperature explains 40% of variation in emissions from the wetland sites. The data from the Southern Rockies and information that has accumulated on other lake types over the last 15 years indicate that lakes may be a larger source strength of methane than reported estimates.
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The number of emission measurements of methane (CH4) to the atmosphere has increased greatly in recent years, as recognition of its atmospheric chemical and radiative importance becomes widespread. In this report, we review progress on estimating and understanding both the magnitude of, and controls on, emissions of CH4 from natural wetlands. We also calculate global wetland CH4 emissions using this extensive flux data base and the wetland areas compiled and published by Matthews and Fung (1987). Tropical regions (20° N-30° S) were calculated to release 66 TgCH4/yr, 60% of the total wetland emission of 109 Tg/yr. Flux data from tropical wetlands, reported only within the last four years, are currently restricted in geographic coverage. Additional data from other regions will be required to confirm these calculated large emissions. Although emissions from subtropical and temperate wetlands (45° N-20° N and 30° S-50° S) were relatively low at 5 Tg/yr, the process-oriented focus of most of the research in this region suggests that work at these latitudes may serve as models to examine controls and possible uncertainties in estimating fluxes. These types of efforts are frequently not possible in more remote, globally significant wetlands. Northern wetlands (north of 45° N) were calculated to release a total of 38 TgCH4/yr (34% of total flux); 34 Tg/yr from wet soils and 4 Tg/yr from relatively dry tundra. These latitudes have been the focus of recent intensive research. Significant differences between the relatively large flux data bases accumulated in the two primary measurement areas, northern Minnesota and the Hudson Bay Lowlands of Canada, indicate that extrapolation from one wetland region to another may be subject to considerable error. Global emissions were also compared to fluxes calculated using the wetland areas published by Aselmann and Crutzen (1989) in an effort to assess uncertainties due to wetland area estimates. Further refinement of wetland CH4 emissions awaits flux measurements from large areas currently lacking data, particularly in the tropics and the Siberian Lowlands, more realistic assessments of seasonal active periods, and accurate, up-to-date habitat classification and measurement.
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The sources of methane and its flux to the troposphere from the Amazonian floodplain were investigated during the dry season of July and August 1985, using measurements of methane concentration gradients obtained aboard a houseboat laboratory anchored in Lago Calado, a stratified dendritic lake of about 6-sq km area located near the center of the Amazon Basin. Methane concentrations in the mixed layer of the lake were found to vary from 0.0001 to 0.0055 mM, with no consistent temporal trend. The measured methane flux from the surface of the open lake to the atmosphere averaged 27 mg CH4/sq m per day, consistent with the buildup in ambient methane in the nocturnal surface mixed layer of the troposphere. Ebullition contributed 70 percent to the average total flux. The source of methane to the lake and, ultimately, to the troposphere is the benthic sediments.
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Methane fluxes to the troposphere from the three principal habitats of the floodplain of the Amazon River main stem (open waters, emergent macrophyte beds, and flooded forests) were determined along a 1700-km reach of the river during the low-water period of the annual flood cycle (November-December 1988). Overall, emissions averaged 68 mg CH4/sq m per day and were significantly lower than similar emissions determined previously for the high-water period, 184 mg CH4/sq m per day (July-August 1986). This difference was due to significantly lower emissions from floating macrophyte environments. Low-water emissions from open waters and flooded forest areas were not significantly different than at high water. A monthly time series of methane emission from eight lakes located in the central Amazon basis showed similar results. The data were used to calculate a seasonally weighted annual emission to the troposphere from the Amazon River main stem floodplain of 5.1 Tg/yr, which indicates the importance of the area in global atmospheric chemistry.
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Previous methods of performing aquatic acetylene-reduction assays are described and several problems associated with them are discussed. A refinement of these older techniques is introduced and problems that it overcomes are also discussed. A depth profile of nitrogen fixation (C2H4 production), obtained by the refined technique, is shown for a fertilized Canadian Shield lake in the Experimental Lakes Area of northwestern Ontario.
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Agriculture plays a major role in the global fluxes of the greenhouse gases carbon dioxide, nitrous oxide, and methane. From 1991 to 1999, we measured gas fluxes and other sources of global warming potential (GWP) in cropped and nearby unmanaged ecosystems. Net GWP (grams of carbon dioxide equivalents per square meter per year) ranged from 110 in our conventional tillage systems to −211 in early successional communities. None of the annual cropping systems provided net mitigation, although soil carbon accumulation in no-till systems came closest to mitigating all other sources of GWP. In all but one ecosystem, nitrous oxide production was the single greatest source of GWP. In the late successional system, GWP was neutral because of significant methane oxidation. These results suggest additional opportunities for lessening the GWP of agronomic systems.
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Conceptual and numerical models of nitrogen cycling in temperate forests assume that nitrogen is lost from these ecosystems predominantly by way of inorganic forms, such as nitrate and ammonium ions. Of these, nitrate is thought to be particularly mobile, being responsible for nitrogen loss to deep soil and stream waters. But human activities-such as fossil fuel combustion, fertilizer production and land-use change-have substantially altered the nitrogen cycle over large regions, making it difficult to separate natural aspects of nitrogen cycling from those induced by human perturbations. Here we report stream chemistry data from 100 unpolluted primary forests in temperate South America. Although the sites exhibit a broad range of environmental factors that influence ecosystem nutrient cycles (such as climate, parent material, time of ecosystem development, topography and biotic diversity), we observed a remarkably consistent pattern of nitrogen loss across all forests. In contrast to findings from forests in polluted regions, streamwater nitrate concentrations are exceedingly low, such that nitrate to ammonium ratios were less than unity, and dissolved organic nitrogen is responsible for the majority of nitrogen losses from these forests. We therefore suggest that organic nitrogen losses should be considered in models of forest nutrient cycling, which could help to explain observations of nutrient limitation in temperate forest ecosystems.
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In many freshwater ecosystems, the contents of NO3- and SO4(2-) have increased, whereas O2 has been depleted due to the increased acid and nutrient loads. These changes may affect carbon turnover and the dynamics of the major greenhouse gases CO2, CH4, and N2O. We studied the effects of O2, NO3-, and SO4(2-) availability on carbon mineralization, and fluxes of CO2, CH4, and N2O in the sediments of hyper-eutrophic Lake Kevätön, Finland. Undisturbed sediment cores from the deep (9 m) and shallow (4 m) profundal were incubated in a laboratory microcosm with oxic and anoxic water flows with NO3- or SO4(2-) concentrations of 0, 30, 100, 300, and 2000 microM. The carbon mineralization rate (i.e., the sum of released CO2-C and CH4-C) was not affected by the oxidants. However, the oxidants did change the pathways of carbon degradation and the release of CH4. All of the oxidants depressed CH4 fluxes in the shallow profundal sediments, which had low organic matter content. In the deep profundal sediments rich in organic matter, the CH4 release was reduced by O2 but was not affected by SO4(2-) (the effect of NO3- was not studied). There was an increase in N2O release as the overlying water NO3- concentration increased. Anoxia and highly elevated NO3- concentrations, associated with eutrophication, increased drastically the global warming potential (GWP) of the sedimentary gases in contrast to the SO4(2-) load, which had only minor effects on the GWP.
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METHANE and nitrous oxide are long-lived, radiatively active trace gases that account for approximately 20% of the total anticipated atmospheric warming 1. The atmospheric concentrations of both gases have increased dramatically over the past few decades, and continue to increase at a rate of approximately 1.1 and 0.25% yr-1 for CH4 (ref. 2) and N2O (ref. 3) respectively. Increased biospheric production is generally suggested as the reason for the increases, but decreases in global sinks may also be important. It has been suggested, for example, that nitrogen fertilization may decrease the rate at which tropical 4,5 and temperate forest soils 6 take up methane from the atmosphere. Furthermore, the recent extensive changes in land management and cultivation could be contributing to the observed increases in both atmospheric CH4 and N2O, as has been suggested for tropical soils 7. Little information exists on CH4 uptake in temperate grasslands (which currently occupy approximately 8% of the Earth's surface), its relation to N2O production, or the effect of land management or cultivation 8,9. Here we report measurements of CH4 uptake and N2O emissions in native, nitrogen-fertilized and wheat-growing prairie soils from spring to late autumn, 1990. We found that nitrogen fertilization and cultivation can both decrease CH4 uptake and increase N2O production, thereby contributing to the increasing atmospheric concentrations of these gases.
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Sources of methane in Sweden emit about 3.0 Tg.yr⁻¹ to the atmosphere, corresponding to about 0.6% of the estimated global flux. Net flux, estimated by deducting amounts taken up by boreal forest soils could be about 10% lower. Wetlands are by far the largest source (2.2 Tg.yr⁻¹, 73% of total) followed in decreasing order by landfills (0.34 Tg.yr⁻¹, 11%), coastal areas and freshwater bodies (0.31 Tg.yr⁻¹, 10%) animal and manure (0.14 Tg.yr⁻¹, 5%) and combustion processes and leakage of natural gas (0.03 Tg.yr⁻¹, 1%). Man-made wetland disturbances associated with drainage have reduced methane emissions by about 0.29 Tg.yr⁻¹. -from Authors
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It is estimated that the Swedish emissions of N2O have approximately doubled due to anthropogenic activities. The natural production of N2O is dominated by emissions from forest soils. The most significant anthropogenic sources seem to be stationary combustion, traffic and fertilizer use. In order to formulate a rational strategy for decreasing the current level of emission the uncertainty ranges of known sources have to be narrowed, and possible additional sources have to be identified. -from Author
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Methane is considered to be a significant greenhouse gas. Methane is produced in soils as the end product of the anaerobic decomposition of organic matter. In the absence of oxygen, methane is very stable, but under aerobic conditions it is mineralized to carbon dioxide by methanotrophic bacteria. Soil methane emissions, primarily from natural wetlands, landfills and rice paddies, are estimated to represent about half of the annual global methane production. Oxidation of atmospheric methane by well-drained soils accounts for about 10% of the global methane sink. Whether a soil is a net source or sink for methane depends on the relative rates of methanogenic and methanotrophic activity. A number of factors including pH, Eh, temperature and moisture content influence methane transforming bacterial populations and soil fluxes. Several techniques are available for measuring methane fluxes. Flux estimation is complicated by spatial and temporal variability. Soil management can impact methane transformations. For example, landfilling of organic matter can result in significant methane emissions, whereas some cultural practices such as nitrogen fertilization inhibit methane oxidation by agricultural soils. Key words: Methane, methanogenesis, methane oxidation, soil, flux measurement
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In order to elucidate the mechanism of the inhibitory effect of nitrate and its denitrification intermediates nitrite, NO and N2O on methanogenesis in anoxic environments, we tested possible toxic effects of these N-compounds on the methanogenic bacteria Methanosarcina barkeri and Methanobacterium bryantii which are ubiquitous in methanogenic rice field soils. The different N-compounds inhibited H2-dependent methanogenesis by these bacteria to different extents. Nitrate showed the weakest inhibition of methanogenesis in both bacteria, followed by N2O and nitrite for Ms. barkeri, and nitrite and N2O for Mb. bryantii, respectively. In both bacteria, the strongest inhibition was caused by NO. Concentrations of 30 mM nitrate still enabled a CH4 production rate of 25-40% of that before the addition of the N-compound, whereas NO completely inhibited methanogenesis at concentrations ≤0.8-1.7 μM (equivalent to 50-100 Pa NO partial pressure). Removal of NO by replacing the atmosphere with H2/CO2 (8:2) resulted in resumption of methanogenesis only if the bacteria had been treated with NO concentrations ≤0.8 μM (50 Pa). Removal of N2O from the cultures resulted in resumption of methanogenesis if Mb. bryantii had been treated with ≤95 μM N2O (500 Pa) or Ms. barkeri with ≤950 μM N2O (5 kPa). These results show that the denitrification products of nitrate can inhibit CH4 production both reversibly and irreversibly depending on the type of methanogenic bacterium and the applied concentration of the N-compound. In a separate experiment with methanogenic rice field slurries addition of nitrate resulted in immediate inhibition of CH4 production. Nitrate was consumed resulting in the sequential accumulation of nitrite, NO and N2O which were subsequently utilized. Nitrite and N2O reached maximum concentrations that would have been inhibitory in the methanogenic bacterial cultures examined.
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ABSTRACT Static chamber measurements of N2O fluxes were taken during the 1998 and 1999 growth seasons in a Swedish constructed wetland receiving wastewater. The dominating plant species in different parts of the wetland were Lemna minor L., Typha latifolia L., Spirogyra sp. and Glyceria maxima (Hartm.) and Phalaris arundinacea (L.), respectively. There were large temporal and spatial variations in N2O fluxes, which ranged from consumption at –350 to emissions at 1791 g N2O m−2 h−1. The largest positive flux occurred in October 1999 and the lowest in the middle of July 1999. The average N2O flux for the two years was 130 g N2O m−2 h−1 (SD = 220). No significant differences in N2O fluxes were found between the years, even though the two growing seasons differed considerably with respect to both air temperature and precipitation. 15% of the fluxes were negative, showing a consumption of N2O. Consumption occurred on a few occasions at most measurement sites and ranged from 1–350 g N2O m−2 h−1. 13–43% of the variation in N2O fluxes was explained by multiple linear regression analysis including principal components. Emission factors were calculated according to IPCC methods from the N2O fluxes in the constructed wetland. The calculated emission factors were always lower (0.02–0.27%) compared to the default factor provided by the IPCC (0.75%). Thus, direct application of the IPCC default factor may lead to overestimation of N2O fluxes from constructed wastewater-treating wetlands.
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Methane, a radiatively active "greenhouse" gas, is emitted from lakes to the atmosphere throughout the open-water season. However, annual lake CH, emissions calculated solely from open-water measurements that exclude the time of spring ice melt may substantially underestimate the lake CH, source strength. We estimated potential spring CH4 emission at the time of ice melt for 19 lakes in northern Minnesota and Wisconsin. Lakes ranged in area from 2.7 to 57,300 ha and varied in littoral zone sediment type. Regression analyses indicated that lake area explained 38% of the variance in potential CH4 emission for relatively undisturbed lakes; as lake area increases potential CH4 emission per unit area decreases. Inclusion of a second term accounting for the presence or absence of soft organic-rich littoral-zone sediments explained 83% of the variance in potential spring CH, emission. Total estimated spring CH, emission for 1993 for all Minnesota lakes north of 45" with areas 14 ha was 1.5 x lo8 mol CH, assuming a 1 : 1 ratio of soft littoral sediment to hard littoral sediment lakes. Emission estimates ranged from 5.3 x lo7 mol assuming no lakes have soft organic-rich littoral sediments to 4.5 x lo8 mol assuming all lakes have soft organic-rich littoral sediments. This spring CH,, pulse may make up as much as 40% of the CH4 annually emitted to the atmosphere by small lakes.
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Methane emissions were measured during mid-smaller in four pilot-scale constructed wetlands that had treated dairy farm wastewaters for a period of 2 yr. Measurements were made at up and downstream sites in wetlands receiving low and high wastewater loadings (~26 and 45 mm d-1), both in the presence of wetland vegetation (Schoenoplectus validus). An automated flux chamber (enclosure area 0.25 m2) and gas circulation system, and associated sampling and chromatographic analysis system, were used to make measurements directly in the field. Median emissions ranged between 48 and 482 mg CH4 m-2 d-1, without discernible diurnal patterns. Upstream sites, closest to wastewater inflows, generally showed significantly higher (P < 0.05) emissions than downstream sites in the same wetland. Unvegetated sites tended to show higher emission rates than corresponding vegetated sites, with highest rates recorded at the highest loaded unvegetated site. Redox potentials in the surface 100 mm of the substratum at upstream sites, with and without vegetation, showed consistently more oxidized conditions in the presence of plants. This suggests that plant root-zone oxidation was acting to suppress methanogenesis and/or enhance methane oxidation in the vegetated wetlands. Emissions from the vegetated constructed wetlands were comparable with those reported for natural wetlands and inorganically fertilized rice paddies. Methane emissions were estimated to account for around 2 to 4% of wastewater C loadings to the vegetated wetlands and 7 to 8% of loadings to the unvegetated systems during the period of measurement.
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We studied the inhibitory mechanism of nitrate and its denitrification products (nitrite, NO, N2O) on the production of CH4 and the concentrations of reductants (H2, acetate, propionate, etc.) and oxidants (NO−3, NO−2, NO, N2O, Fe(III), SO2−4) in slurries of anoxic Italian rice soil. Addition of each of the N-compounds caused a complete but largely reversible inhibition of methanogenesis. Nitrate, nitrite and N2O significantly decreased the H2 partial pressure. With nitrate and N2O it decreased below the threshold of methanogens, thus not allowing exergonic production of methane (ΔG>0). Furthermore, significant production of the electron acceptors Fe(III) and/or sulfate was observed after addition of nitrate and N2O, probably due to the oxidation of reduced iron and sulfur species with nitrate and/or N2O as electron acceptors. Methanogenic activity did not resume until all electron acceptors were reduced and, as a consequence, H2 had reached the methanogenic threshold again. Thus competition for H2 with denitrifying bacteria, iron- and sulfate-reducing bacteria seemed to be one important factor for the inhibition of methanogenesis. Addition of rice straw to reduce competition for electron donors did not prevent inhibition of methanogenesis after addition of nitrate but decreased the inhibition period. Especially after addition of nitrite and NO, toxic effects may have been more important than competition. Although addition of nitrite or NO caused a decrease of the H2 concentration, exergonic methanogenesis from H2/CO2 was always possible (ΔG
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Methane emission to the atmosphere was studied in the deepest, central (pelagic) regions of one freshwater and three meromictic, alkaline saline lakes. The range of methane emissions was 0.004 to 2.916 mmol/sq m/hr (n=41). Outward flux was dominated by bubble ebullition only in the freshwater lake. Diffusive gas exchange was the sole mechanism of transfer in the meromictic lakes, and flux from these lakes was equivalent to or lower than that from the freshwater lake during its periods of ebullition. A comparison of measured flux with flux calculated using a model of gas exchange in Mono Lake suggested that floating chambers provide reasonable estimates of the magnitude of methane emissions from diffusion-dominated systems. 43 refs., 4 figs., 2 tabs.
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A laboratory perfusion system was used to investigate emissions of carbon dioxide, methane and nitrous oxide from an agricultural grassland soil flooded with nitrate-polluted sea water. Following inundation, the CO2-flux immediately declined by 92% and remained significantly lower than the control soil flux. The flooded soil acted mainly as a CH4 sink. N2O was produced from both the inundated and control systems, but fluxes tended to be significantly larger (up to 66-fold) from the flooded soil, where conditions favoured denitrification.
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Wetlands ameliorate nitrate pollution but have also been recognized as a source of the greenhouse gas nitrous oxide. Nitrate and N2O fluxes were studied in an experimental wetland in mid-Wales. Diversion of water inflows caused a 200% increase in nitrate release and a >95% decline in nitrous oxide emission over a 20-week period. The responses were attributed to the onset of drier (more aerobic) conditions causing (i) aerobic mineralization and nitrification of N-containing compounds that had previously been immobilized within the wetlands (releasing nitrate) and (ii) the absence of anaerobic denitrification (a potent mech anism for nitrate elimination and source of N2O), allowing NO3-N to leave the wetland. The responses were instantaneously reversible upon re-initiation of the nitrate inflow, indicating a close hydrological coupling between nitrate removal and nitrous oxide emission processes.
Article
In order to elucidate the mechanism of the inhibitory effect of nitrate and its denitrification intermediates nitrite, NO and N2O on methanogenesis in anoxic environments, we tested possible toxic effects of these N-compounds on the methanogenic bacteria Methanosarcina barkeri and Methanobacterium bryantii which are ubiquitous in methanogenic rice field soils. The different N-compounds inhibited H2-dependent methanogenesis by these bacteria to different extents. Nitrate showed the weakest inhibition of methanogenesis in both bacteria, followed by N2O and nitrite for Ms. barkeri, and nitrite and N2O for Mb. bryantii, respectively. In both bacteria, the strongest inhibition was caused by NO. Concentrations of 30 mM nitrate still enabled a CH4 production rate of 25–40% of that before the addition of the N-compound, whereas NO completely inhibited methanogenesis at concentrations ≥0.8–1.7 μM (equivalent to 50–100 Pa NO partial pressure). Removal of NO by replacing the atmosphere with H2/CO2 (8:2) resulted in resumption of methanogenesis only if the bacteria had been treated with NO concentrations ≤0.8 μM (50 Pa). Removal of N2O from the cultures resulted in resumption of methanogenesis if Mb. bryantii had been treated with ≤95 μM N2O (500 Pa) or Ms. barkeri with ≤950 μM N2O (5 kPa). These results show that the denitrification products of nitrate can inhibit CH4 production both reversibly and irreversibly depending on the type of methanogenic bacterium and the applied concentration of the N-compound. In a separate experiment with methanogenic rice field slurries addition of nitrate resulted in immediate inhibition of CH4 production. Nitrate was consumed resulting in the sequential accumulation of nitrite, NO and N2O which were subsequently utilized. Nitrite and N2O reached maximum concentrations that would have been inhibitory in the methanogenic bacterial cultures examined.
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The regulation of surface water pCO2 was studied in a set of 33 unproductive boreal lakes of different humic content, situated along a latitudinal gradient (57°N to 64°N) in Sweden. The lakes were sampled four times during one year, and analyzed on a wide variety of water chemistry parameters. With only one exception, all lakes were supersaturated with CO2 with respect to the atmosphere at all sampling occasions. pCO2 was closely related to the DOC concentration in lakes, which in turn was mainly regulated by catchment characteristics. This pattern was similar along the latitudinal gradient and at different seasons of the year, indicating that it is valid for a variety of climatic conditions within the boreal forest zone. We suggest that landscape characteristics determine the accumulation and subsequent supply of allochthonous organic matter from boreal catchments to lakes, which in turn results in boreal lakes becoming net sources of atmospheric CO2.
Article
We studied the export of inorganic carbon and nitrous oxide (N2O) from a Danish freshwater wetland. The wetland is situated in an agricultural catchment area and is recharged by groundwater enriched with nitrate (NO3 –) (1000 M). NO3 – in recharging groundwater was reduced (57.5 mol NO3 – m–2 yr–) within a narrow zone of the wetland. Congruently, the annual efflux of carbon dioxide (CO2) from the sediment was 19.1 mol C m–2 when estimated from monthly in situ measurements. In comparison the CO2 efflux was 4.8 mol C m–2 yr–1 further out in the wetland, where no NO3 – reduction occurred. Annual exports of inorganic carbon in groundwater and surface water was 78.4 mol C m–2 and 6.1 mol C m–2 at the two sites, respectively. N2O efflux from the sedimenst was detectable on five out of twelve sampling dates and was significantly (P < 0.0001) higher in the NO3 – reduction zone (0.35–9.40 mol m–2 h–1, range of monthly means) than in the zone without NO3 – reduction (0.21–0.41 mol m–2 h–1). No loss of dissolved N2O could be measured. Total annual export of N2O was not estimated. The reduction of oxygen (O2) in groundwater was minor throughout the wetland and did not exceed 0.2 mol 02 m–2yr–1. Sulfate (SO4 ––) was reduced in groundwater (2.1 mol SO4 –– m–2 yr–1) in the zone without NO3 – reduction. Although the NO3 – in our wetland can be reduced along several pathways our results strongly suggest that NO3 – loading of freshwater wetlands disturb the carbon balance of such areas, resulting in an accelerated loss of inorganic carbon in gaseous and dissolved forms.
Article
Slurries of anoxic paddy soil were either freshly prepared or were partially depleted in endogenous electron donors by prolonged incubation under anaerobic conditions. Endogenous NO 3 – was reduced within 4 h, followed by reduction of Fe3+ and SO 4 2– , and later by production of CH4. Addition of NO 3 – slightly inhibited the production of Fe2+ in the depleted but not in the fresh paddy soil. Inhibition was overcome by the addition of H2, acetate, or a mixture of fatty acids (and other compounds), indicating that these compounds served as electron donors for the bacteria reducing NO 3 – and/or ferric iron. Addition on NO 3 – also inhibited the reduction of SO 4 2– in the depleted paddy soil. This inhibition was only overcome by H2, but not by acetate or a mixture of compounds, indicating that H2 was the predominant electron donor for the bacteria involved in NO 3 – and/or SO 4 2– reduction. SO 4 2– reduction was also inhibited by exogenous Fe3+, but only in the depleted paddy soil. This inhibition was overcome by either H2, acetate, or a mixture of compounds, suggesting that they served as electron donors for reduction of Fe3+ and/or SO 4 2+ . CH4 production was inhibited by NO 3 – both in depleted and in fresh paddy soil. Fe3+ and SO 4 2– also inhibited methanogenesis, but the inhibition was stronger in the depleted than in the fresh paddy soil. Inhibition of CH4 production was paralleled by a decrease in the steady state concentration of H2 to a level which provided a free enthalpy of less than G=–17 kJ mol-1 CH4 compared to more than G=–32 kJ mol-1 CH4 in the control. The results indicate that in the presence of exogenous fe3+ or SO 4 2+ , methanogenic bacteria were outcompeted for H2 by bacteria reducing Fe3+ or SO 4 2+ .
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The fluxes of CH4 and CO2 to the atmosphere, and the relative contributions of ebullition and molecular diffusion, were determined for a small hypertrophic freshwater lake (Priest Pot, UK) over the period May to October 1997. The average total flux of CH4 and CO2 (estimated from 7 sites on the lake) was approximately 52 mmol m–2 d–1 and was apportioned 12 and 40 mmol m–2 d–1 toCH4 and CO2 respectively. Diffusion across the air-water interface accounted for the loss of 0.4and 40 mmol m–2 d–1 of CH4 and CO2 respectively whilst the corresponding figures for ebullition losses were 12.0 (CH4) and 0.23 (CO2) mmol m–2 d–1. Most CH4 (96%) was lost by ebullition, and most CO2 (99%) by diffusive processes. The ebullition of gas, measured at weekly intervals along a transect of the lake, showed high spatial and temporal variation. The CH4 content of the trapped gas varied between 44 and 88% (by volume) and was highest at the deepest points. Pulses of gas ebullition were detected during periods of rapidly falling barometric pressure. Therelevance of the measurements to global estimates ofcarbon emission from freshwaters are discussed.
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General design principles, landscape locations, and case studies of natural and constructed riverine wetlands for the control of nonpoint source (NPS) water pollution are presented. General design principles of wetland construction for NPS pollution control emphasize self-design and minimum maintenance systems, with an emphasis on function over form and biological form over rigid designs. These wetlands can be located as instream wetlands or as floodplain riparian wetlands, can be located as several wetlands in upstream reaches or fewer in downstream reaches of a watershed, and can be designed as terraced wetlands in steep terrain. Case studies of a natural riparian wetland in southern Illinois, an instream wetland in a downstream location in a northern Ohio watershed, and several constructed riparian wetlands in northeastern Illinois demonstrate a wide range of sediment and phosphorus retention, with greater efficiencies generally present in the constructed wetlands (63–96% retention of phosphorus) than in natural wetlands (4–10% retention of phosphorus). By itself, this could be misleading since the natural wetlands have much higher loading rates and actually retain an amount of nutrients comparable to constructed wetlands (1–4 g P m−2 year−1).
Article
Sequential reduction processes were studied in four oxic upland soils (cultivated, forest, savanna and desert soil) which were slurried and incubated under anoxic conditions. NO3−1 reduction began almost immediately and was followed by reduction of manganese(IV), sulfate and iron(III). The phases of reduction of Mn4+, SO42− and Fe3+ overlapped, with SO42− being depleted long before accumulation of Mn2+ and Fe2+ was finished. CH4 production and growth of methanogenic bacteria began when all the other reduction processes were finished. Radiotracer experiments showed that CH4 was produced from H2 (29–42%) and acetate. The respiratory index indicated that the acetate was predominantly degraded by methanogenic bacteria. The late onset of methanogenesis was not a consequence of limitation by the methanogenogenic precursors, since H2 and acetate were present long before the initiation of methanogenesis. Thermodynamic calculations showed that the concentrations of these substrates were always sufficient to allow exergonic production of CH4 at Gibbs free energies of ΔG < −30 kJ mol−1 CH4. However, exergonic production of acetate from was not possible. Propionate was also detected in the soil slurries. The redox potential in the soils decreased from > + 400 mV to final values of < − 150 mV, except in the forest soil where the redox potential stayed at + 50 mV. The onset of methanogenesis and of growth of methanogenic bacteria coincided with redox potentials between +70 and 0 mV, which is much higher than claimed in literature. We speculate that the redox-active substances in soil were the signal for methanogenic bacteria to initiate activity.
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The first direct evidence of a convective through-flow of gases in a grass is reported for Phragmites australis (Cav.) Trin. ex Steud. The flow appears to be initiated in living leafs sheaths and in the living nodal stomatal regions of the culm. The convected gases are transmitted via air spaces in the culm and underground rhizome, and are vented via old broken culms. The convection is particularly rapid in bright light and at low atmospheric humidities. Consequently, it should cause direct enhancement of rhizome aeration, and by increasing the oxygen regime at the root-shoot junction, cause a greater diffusion of oxygen intto the roots. Static pressure differentials up to 800 Pa and flow velocities of up to 800 mm min−1 per leafy shoot (flow rate, 960 × 10−6m3h−1) have been recorded in the field.The mechanism appears complex, but is probably based chiefly on humidity-induced Knudsen diffusion into the plant. In the light, humidity, temperature, stomatal and possibly photosynthetic factors are involved; at night, the convection is very much slower. The humidity-induced convection has been mimicked using membranes “sealing” humidified chambers.