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Abstract

Drained peatlands contribute to anthropic emissions of carbon dioxide (CO2), so a better understanding of the underlying processes and identification of mitigation options for agricultural peatlands are urgently required. Peatland soil properties vary greatly and, in combination with drainage, can affect emissions of CO2 both directly and indirectly. Drainage reduces soil water content but increases CO2 production, so it is important to find the optimum drainage level that minimises CO2 emissions without affecting agricultural use. Intact soil cores from nine different sites (topsoil, plus subsoil at four sites) were collected and brought into a controlled laboratory environment. Repeated measurements of CO2 fluxes were performed at increasing soil water suctions corresponding to different drainage levels. Physical and chemical properties of the soils were determined and compared with the CO2 emissions. The soil cores displayed different CO2 emission patterns with increasing soil water suction head. In some cores, emissions increased rapidly to a high level, while in others they remained at lower levels. At a soil water suction head of only 0.5 m of water, the average soil CO2 emissions had already reached a maximum. The soil cores represented peat soils with a wide range of soil properties, e.g. bulk density from 0.17 to 0.47 g cm-3 and total carbon from 26.3 to 43.5 %, but none of the properties measured was clearly correlated with CO2 emissions.

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... Three of the farms had vegetables and potatoes in their crop rotation (soils 2, 3, 4). The same eight topsoil and four subsoil samples were used in our previous study Norberg et al. (2018), where they were numbered differently (numbers in brackets); 1-3 (1-3), 4 (5), 5-8 (6-9). ...
... Detailed descriptions of field soil sampling and of the experimental set-up can be found in Norberg et al. (2018). In brief, intact soil cores were sampled in steel cylinders (Ø 7.2 cm, height 10 cm), at approximately 5-15 cm depth for topsoil samples and 20-50 cm depth for subsoil samples. ...
... Emissions of N 2 O and CH 4 were measured using a similar approach to that used for determination of CO 2 emissions in Norberg et al. (2018). Each soil sample cylinder was placed in a polypropylene jar (Ø 11 cm, height 12 cm) with air-tight screw lids equipped with two injection needles (Ø 0.8 mm, 40 mm long). ...
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Greenhouse gas emissions from drained agricultural peatlands contribute significantly to global warming. In a laboratory study using intact cores of peat soil from eight different sites in Sweden, factors controlling the emission of the greenhouse gases nitrous oxide (N2O) and methane (CH4) were examined. Soil properties, and the abundance of the total microbial community (16S rRNA gene abundance), and genes encoding for functions controlling N2O emissions (bacterial and archaeal amoA, nirS, nirK, nosZI, and nosZII) were analyzed and compared against measured greenhouse gas emissions. Emissions were measured at different drainage levels, i.e., higher soil water suction values, since drainage is an important factor controlling greenhouse gas emissions from peat soils. The results showed that N2O and CH4 emissions were generally low, except for N2O emissions at near water-saturated conditions, for which three soils displayed high values and large variations in fluxes. Relationships between N2O emissions and soil properties were mainly linked to soil pH, with higher emissions at lower pH. However, specific assemblages of nitrogen cycling guilds that included nosZII, typically present in non-denitrifying N2O reducers, were detected in soils with low N2O emissions. Overall, these results indicate that both pH and biotic controls determine net N2O fluxes.
... Average diurnal SR rates from 163C and 163 F decreased from April to September (Fig. 7), which can be explained by the following points: firstly, priming effects were caused by the early stage of soil exposure after submergence under water for a whole winter (Kuzyakov et al., 2000;Norberg et al., 2018;Pezzolla et al., 2019); meanwhile, water drainage increased microbial activity caused by increased aeration, which enhanced SR efflux (Silvola, 1986;Norberg et al., 2018;Mukumbuta et al., 2019). However, average diurnal SR rates decreased with the reduction of priming effects till September. ...
... Average diurnal SR rates from 163C and 163 F decreased from April to September (Fig. 7), which can be explained by the following points: firstly, priming effects were caused by the early stage of soil exposure after submergence under water for a whole winter (Kuzyakov et al., 2000;Norberg et al., 2018;Pezzolla et al., 2019); meanwhile, water drainage increased microbial activity caused by increased aeration, which enhanced SR efflux (Silvola, 1986;Norberg et al., 2018;Mukumbuta et al., 2019). However, average diurnal SR rates decreased with the reduction of priming effects till September. ...
... Soil & Tillage Research 197 (2020) 104522 increasing soil temperature. We also found that SR efflux was relatively higher on March 16 (Fig. 8) probably due to the priming effect after water level drop (Kuzyakov et al., 2000;Norberg et al., 2018;Pezzolla et al., 2019). From the end of March to the end of April, local farmers ploughed their croplands successively, which increased in SR efflux resulting from an increase in aeration due to tillage (Paustian et al., 2000;Buragienė et al., 2019;de Oliveira Silva et al., 2019). ...
Article
Soil respiration (SR) has been found to be highly influenced by land use and soil water regimes. However, the relative contribution of farming and dam-triggered flooding in influencing the SR of the riparian zone is poorly understood. The objectives of this study were to investigate the effects of land use and dam-triggered flooding intensity on SR in the riparian zone along the Three Gorges Reservoir (TGR), China, and to identify the main factors shaping the SR. At the Wuyang Bay of the Pengxi River, a tributary of the Yangtze River in the TGR, a series of SR field examinations in different land-use types and along elevation gradients in the riparian zone were carried out from March to September in 2018. During the study period, by analyzing SR in 177 m (elevation above sea level, the same as follows) unflooded site (UF), 173 m corn field (173C), 173 m paddy field (173 P), 168 m corn field (168C), 168 m paddy field (168 P), 168 m fallow grassland (168 F), 166 m fallow grassland (166 F), 163 m corn field (163C) and 163 m fallow grassland (163 F), significant differences in diurnal variations were found to be mainly affected by soil temperature (ST) at 10 cm depth, while seasonal variations were mainly regulated by ST and rainfall events (i.e. 10 cm depth soil water content). Importantly, croplands were found to contain higher soil organic carbon (SOC) but lower SR efflux and Q 10 values than those for non-cropping fields. The results imply that SR was strongly affected by land-use types rather than flooding intensity in the TGR riparian zone. Furthermore, this study highlights the significant impacts of tillage in stabilizing SOC and reducing SR efflux in the area that is highly influenced by hydrological regime shift. Finally, from the perspective of controlling the soil carbon dioxide emission, we suggest that local government should manage and guide farming activities in the riparian zone.
... Under such circumstances, the effects of soil physical parameters cannot be captured. However, there are some studies on GHG emissions that have incubated intact samples at different water contents, but the samples only came from one or two sites (Berglund and Berglund, 2011;Brouns et al., 2016;Kechavarzi et al., 2010;Norberg et al., 2018;van Lent et al., 2018) or GHG sampling only occurred sporadically (Berglund and Berglund, 2011;Norberg et al., 2018;van Lent et al., 2018). There is a lack of a systematic evaluation of hydrological and biogeochemical factors, such as peat type and nutrient availability, influencing GHG fluxes on a broader basis using intact samples. ...
... Under such circumstances, the effects of soil physical parameters cannot be captured. However, there are some studies on GHG emissions that have incubated intact samples at different water contents, but the samples only came from one or two sites (Berglund and Berglund, 2011;Brouns et al., 2016;Kechavarzi et al., 2010;Norberg et al., 2018;van Lent et al., 2018) or GHG sampling only occurred sporadically (Berglund and Berglund, 2011;Norberg et al., 2018;van Lent et al., 2018). There is a lack of a systematic evaluation of hydrological and biogeochemical factors, such as peat type and nutrient availability, influencing GHG fluxes on a broader basis using intact samples. ...
... The stepwise reduction of WFPS in the soil columns resulted in a parabolic response curve of CO 2 fluxes with an "optimum" WFPS at the suction step with maximal CO 2 fluxes (Fig. 4). This general shape is in accordance with results reported for both mineral soils (Linn and Doran, 1984;Moyano et al., 2012) and peat soils (Kechavarzi et al., 2010;Norberg et al., 2018;van Lent et al., 2018). Under water-saturated conditions, available oxygen limits microbial activity and CO 2 fluxes. ...
Article
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Drainage turns peatlands from natural carbon sinks into hotspots of greenhouse gas (GHG) emissions from soils due to alterations in hydrological and biogeochemical processes. As a consequence of drainage-induced mineralisation and anthropogenic sand addition, large areas of former peatlands under agricultural use have soil organic carbon (SOC) contents at the boundary between mineral and organic soils. Previous research has shown that the variability of GHG emissions increases with anthropogenic disturbance. However, how and whether sand addition affects GHG emissions remains a controversial issue. The aim of this long-term incubation experiment was to assess the influence of hydrological and biogeochemical soil properties on emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Strongly degraded peat with sand addition (peat-sand mixtures) and without sand addition (earthified peat) was systematically compared under different moisture conditions for fen and bog peat. Soil columns originating from both the topsoil and the subsoil of ten different peatlands under grassland use were investigated. Over a period of six months the almost saturated soil columns were drained stepwise via suction to −300 hPa. The CO2 fluxes were lowest at water-saturated and dry soil moisture conditions, resulting in a parabolic dependence of CO2 fluxes on the water-filled pore space (WFPS) peaking at 56–92% WFPS. The highest N2O fluxes were found at between 73 and 95% WFPS. Maximum CO2 fluxes were highest from topsoils, ranging from 21 to 77 mg C m−2 h−1, while the maximum CO2 fluxes from subsoils ranged from 3 to 14 mg C m−2 h−1. No systematic influence of peat type or sand addition on GHG emissions was found in topsoils, but CO2 fluxes from subsoils below peat-sand mixtures were higher than from subsoils below earthified peat. Maximum N2O fluxes were highly variable between sites and ranged from 18.5 to 234.9 and from 0.2 to 22.9 μg N m−2 h−1 for topsoils and subsoils, respectively. CH4 fluxes were negligible even under water-saturated conditions. The highest GHG emissions occurred at a WFPS that relates – under equilibrium conditions – to a water table of 20–60 cm below the surface in the field. High maximum CO2 and N2O fluxes were linked to high densities of plant-available phosphorus and potassium. The results of this study highlight that nutrient status plays a more important role in GHG emissions than peat type or sand addition, and do not support the idea of peat-sand mixtures as a mitigation option for GHG emissions.
... As they occupy the lowermost parts of the landscape (the borderline between land and water), organic soils play a very important role in the water, C and nutrient cycles (Joosten and Clarke, 2002;Rydin and Jeglum, 2006;Oleszczuk et al., 2008;Kimmel and Mander, 2010;Maljanen et al., 2010;Page and Baird, 2016;Kasimir et al., 2018;Norberg et al., 2018;Harris et al., 2022). The accumulation of organic matter (mainly in the form of plant remnants) in peatlands is a long-term process determined by climate, vegetation and the inundation processes that affect the edaphic factors in the catchment. ...
... This leads to the loss of a significant part of their C stock as dissolved organic carbon (DOC) via fluvial pathways . Although the labile organic fraction constitutes a small proportion of soil organic matter (SOM), it is one of the most mobile and bioavailable forms (Ghani et al., 2013;Kalisz et al., 2015;Cao et al., 2017;Norberg et al., 2018) and can be indicative of the processes that control SOM accumulation and stabilisation (Glina et al., 2016a;Bojko et al., 2017;Kalisz et al., 2021). Organic matter is an important soil constituent that provides a variety of functions that influence plant growth, greenhouse gases (GHGs) emissions, and the physical and chemical properties of the soil (Smólczyński and Orzechowski, 2010a;Heller and Zeitz, 2012;Lehmann and Kleber, 2015;Kalisz and Łachacz, 2023). ...
Article
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The Soil Science Society of Poland has selected organic soils (in Polish: gleby organiczne) as their Soil of the Year 2024. Organic soils consist of materials that contain ≥12% organic carbon (C), and include peat, gyttja and mud materials, as well as forest (leaf and woody debris) or meadow (grass debris) litter (≥20% organic C if saturated with water for <30 consecutive days a year). The specific properties of these soils, primarily the high organic C content, low bulk density and high porosity values, determine their disaggregation from mineral soils. In the 6th edition of the Polish Soil Classification (SGP 6), four main types of organic soils were distinguished: peat soils (in Polish: gleby torfowe), mursh soils (in Polish: gleby murszowe), limnic soils (in Polish: gleby limnowe) and folisols (in Polish: gleby ściółkowe). The estimated cover of organic soils in Poland ranges from 4 to 5% of the land surface, located mainly in closed depressions and river valleys; an exception are the folisols that mainly occur in mountain areas. Among organic soils, peat and mursh soils cover the largest area and are mainly used for agricultural purposes. Organic soils are considered the largest natural terrestrial reservoir of organic C, but disturbance to peatlands from climate change and human activities has impacted their C storage potential. In this review paper, we present (a) the concept of organic soils in Poland; (b) the classifi cation scheme for organic soils in Poland and their correlation with international classifi cation systems, such as the World Reference Base (WRB) and the NRCS Soil Taxonomy; (c) a review of the distribution, land use, threats and protection of organic soils in Poland; and (d) future research needs with regard to organic soils.
... This is primarily because the microclimate of the histosol surface changes, and in the root zone, depending on the species composition of the herbaceous vegetation, humification and CO 2 emission processes begin. This is also confirmed by research conducted in Sweden [31]. In grasslands older than 5 years, enough fallout begins to accumulate, and a sod horizon O is formed, which increases the protection level of histosol against mineralization (Figure 2, profiles 4, 7). ...
... The horizon O compensates for the lack of moisture that has occurred due to the reclamation of histosol. Moisture content, groundwater level and land use are important in reducing CO 2 emissions from histosols [31,32]. Histosol convention tillage is inseparable from the use of mineral fertilizers, which promote peat mineralization. ...
Article
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In the context of climate change, the questions of the sustainability of peat soil use are particularly relevant. The evaluation of changes in the properties of soils (including histosols) using chemical methods is expensive, thus, their application possibilities are limited. Analyzing the morphology of histosol profiles would provide effective spatial analysis opportunities for assessing the extent of their anthropogenic transformation and impact on climate change. The key diagnostic horizons and their sequences for the identification of the risk group are the main results of the study. The analysis included 12 soil profiles, whose morphological structure was characterized using the WRB 2022 system of master symbols and suffixes for soil profile horizon descriptions. The analyzed profiles were excavated in forested (relatively natural), agricultural (agrogenized) and peat mining (technogenized) areas. The insights of this article in the discussion are based on the chemical analyses (pH KCl, N, P and K, soil organic carbon, dissolved organic carbon, mobile humus substance, humic and fulvo acids, C:N ratio and humification degree) of three histosol profiles. The main discussion is based on the results of the morphological analysis of the profiles. The results of this research allowed for the identification of a different structure of the histosol profile. The upper part of the histosol profile, which consists of O–H(a,e,i) horizons, indicates its naturalness. The murshic horizon (Hap) is the classic top horizon of the agricultural histosol profile, which is most affected by mineralization. The technogenized histosols have a partially destroyed profile, which is represented by the Ahτ/Haτ or only Haτ horizons at the top. The morphology of the histosol profile and the identification of the relevant horizons (Hap, Haτ and Ahτ) indicate its risks and presuppose a usage optimization solution. The most dangerous in the context of sustainable land use principles and climate change is the murshic horizon (Hap), which is uncovered after removing the horizon O. The risks of sustainable use of histosol are caused by measures that promote its microbiological activity, which is the maintenance of a drained state and cultivation. In the context of GHG emissions and sustainable use, the most favorable means would be the formation of the horizon O by applying perennial plants. Rewetting should be applied to those histosols whose removal from the agricultural or mining balance would provide maximum ecological benefits.
... In turn, the decomposition of deeper soil layers is constrained by lower temperatures and the limited availability of oxygen. Study by Norberg et al. (2018) showed that at soil water suction corresponding to water table level of only from 0.5 m to 0.75 m, the average soil CO 2 emissions reaches a maximum in most peat soil types. The curved relationship between CO 2 emissions and GWL is crucial with respect of emission reduction efforts. ...
Article
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Optimizing the level of groundwater presents a viable strategy for mitigating the greenhouse gas (GHG) emissions associated with the cultivation of peatlands. This study investigated the impact of soil hydrological conditions on carbon dioxide (CO 2 ) and methane (CH 4 ) emissions. The CO 2 and CH 4 emissions from bare soil were continuously measured using an automated chamber system throughout the growing seasons from 2021 to 2023 at a boreal cultivated peat soil site. Annual CO 2 emissions from soil respiration averaged to 21,600 kg ha ⁻¹ (April-November) corresponding to carbon (C) loss of 5890 kg ha ⁻¹ . The CO 2 emissions were highly temperature dependent. Lowering the groundwater level (GWL) was found to increase the CO 2 emissions nearly linearly. The soil functioned as a CH 4 sink for the majority of the growing season, and the total sink corresponded to 27 and 20 kg ha ⁻¹ yr ⁻¹ CO 2 equivalent in 2022 and 2023, respectively. The CH 4 emissions occurred generally when soil water content (SWC) exceeded 0.6 m ³ m ⁻³ and when GWL was at the depth of less than 30 cm from soil surface. For optimal climate efficiency the mitigation measures must be implemented during the mid-growing season, and the water table should be brought close to the soil surface. Potentially, this can hamper the operation of machinery on the field and reduce the harvested yield. Thus, comprehensive cost-benefit analysis is necessary before adopting a raised water table level in large-scale crop production.
... Even though the field has been cultivated for at least 160 years, and the surface layer is highly decomposed (Table 1), the emissions still continue at a rate typical for cultivated peat soils. It has been shown that the CO 2 emissions of cultivated peat soils do not necessarily decrease with lowering carbon content (Norberg et al. 2018;Säurich et al. 2019), and CO 2 emissions from soils that have a lower carbon content than "real" peatlands can be as high as those from peat soils (Leiber-Sauheitl et al. 2014;Tiemeyer et al. 2016). The carbon content of our site is already relatively low, but the emissions might continue at a similar level as long as the majority of the two-metre peat layer is consumed. ...
Article
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The greenhouse gas (GHG) emissions of spring cereal monoculture under long-term conventional tillage (CT) and no-till (NT) treatment established in 2018 were measured in a peatland in Southwestern Finland during the period 2018–2021. Nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes were measured with chambers approximately every two weeks throughout the period under study. Net ecosystem exchange was measured during the growing seasons, and hourly ecosystem respiration (ER) and gross photosynthesis (GP) were modelled with empirical models. Across the whole period, annual emissions were 6.8 ± 1.2 and 5.7 ± 1.2 Mg CO2–C ha ⁻¹ yr⁻¹ (net ecosystem carbon balance), 8.8 ± 2.0 and 7.1 ± 2.0 kg N2O–N ha⁻¹ yr⁻¹, and − 0.43 ± 0.31 and − 0.40 ± 0.31 kg CH4-C ha⁻¹ yr⁻¹ for CT and NT, respectively. The global warming potential was lower in NT (p = 0.045), and it ranged from 26 to 34 Mg CO2 eq. ha⁻¹ yr⁻¹ in CT and from 19 to 31 Mg CO2 eq. ha⁻¹ yr⁻¹ in NT. The management effect on the rates of single GHGs was not consistent over the years. Higher GP was found in CT in 2019 and in NT in 2020. Differences in ER between treatments occurred mostly outside the growing season, especially after ploughing, but the annual rates did not differ statistically. NT reduced the N2O emissions by 31% compared to CT in 2020 (p = 0.044) while there were no differences between the treatments in other years. The results indicate that NT may have potential to reduce slightly CO2 and N2O emissions from cultivated peat soil, but the results originate from the first three years after a management change from CT to NT, and there is still a lack of long-term results on NT on cultivated peat soils.
... The gas concentration (ppm) was converted to mgGHG g soil − 1 h − 1 using the following equation ( Norberg et al., 2018 ): ...
Article
Rice production is an important sector of global agriculture, sustaining more than half of the world's population. However, rice production contributes significantly to global warming through increased emission of greenhouse gases (GHGs), primarily CH4, into the atmosphere. Therefore, this study examined countermeasures to reduce GHG emissions from paddy fields without affecting rice production. A column experiment was conducted to investigate the effects of soil macroporous structure and water management on GHG emissions from flooded alluvial clay soil (paddy soil). The soils were subjected to different management regimes: with and without artificial macropores, compost, and drainage treatment. Drainage was maintained at 6.5 mm d⁻¹ to ensure infiltration yet prevent excessive leakage from the paddy field. The measured parameters included GHG emissions, soil water content, redox potential, soil temperature, soil swelling, total carbon, total nitrogen, iron, and manganese. The results showed that the soil column with macropores and drainage had significantly lower CO2 and CH4 emissions than that without macropores and drainage. In addition, the soil level increment, and thus, the amount of gas (CH4) produced in the soil column with drainage were lower than that without drainage. The combination of drainage treatment and macropores might have effectively acted as a hydrodynamic gradient and a structure that promotes freshwater intrusion into deeper soil profiles, inhibiting absolute anaerobic methanogenic activity. The redox potential of the column with drainage and macropores was the highest. Moreover, CO2 and CH4 emissions were reduced at a relatively small drainage rate of 6.5 mm d⁻¹ by adding macropores to the soil. The findings confirmed that GHG emissions were effectively reduced by a porous soil structure at a low drainage rate. Macropore application also exhibited effectiveness at mitigating nutrient loss (TOC and TN) through the drainage. Therefore, low tillage before flooding would be preferable to conserve the macroporous structure. However, the results also highlight an adverse effect on mineral leaching (particularly Mn) through the column with macropores.
... Labile organic matter is a source of energy and organic nutrient forms, such as N and P readily accessible for soil microbiota [10,11]. Although the labile organic fraction constitutes a small proportion of SOM, it is one of the most mobile and bioavailable forms [8,[12][13][14][15] and can indicate processes that control SOM accumulation and stabilization [16,17]. ...
Article
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Large areas of peatlands, in addition to the effect of drainage, were subjected to erosional process and were silted. The objective of the study was to verify whether siltation of peatlands hampers mineralization of remaining peat and alters labile C, N, P and K. Total C and N were measured on a CN analyzer, and total P and K on an ICP spectrometer after microwave digestion. The labile fractions of C, N, P and K were extracted with hot water and measured on the CN analyzer and ICP spectrometer. We noted that labile C, N, P and K concentrations in silted topsoil were lower than the values reported in unsilted topsoil. Higher concentration of labile compounds in peats is a signal of higher biological activity and mineralization of organic matter. A TOC/TP < 300 and TOC/TN of approximately 8 in topsoil suggested diminished mineralization and supported our hypothesis that siltation hampered mineralization of organic matter. The TOC/TK ratio proved to be a fine indicator of the state of organic soils siltation, which enabled the separation of unsilted peats from silted topsoil (on the base of value of 177). It can be assumed that the mineralization of peat layers is hampered by the above lying silted topsoil, which is less biologically active, having less oxygen, and therefore conserving underlying peats against oxidation.
... Deionized water was added once a week to the paddy samples with drainage to compensate for the drained water. Because the gas concentration was expressed as ppm, the value was converted to µgCO 2 /CH 4 g soil −1 h −1 using the following equation (Norberg et al. 2018): ...
Article
The process of greenhouse gas (GHG) emission processes is substantially affected by soil factors. Here, an intensive experiment was conducted to observe the effects of pore structure and water management on agricultural soil GHG emissions, total soil carbon, and nitrogen. Masa and paddy soils were prepared with/without macropores and with/without compost application. The Masa soil was exposed to unsaturated/saturated conditions, whereas the paddy soil was exposed to flooded conditions with/without drainage. CO2 emission from the Masa soil with macropores was higher than that from the Masa soil without macropores due to enhanced gas emission pathway. Total carbon (TC) was relatively lower in the top soil than in the bottom soil under non-flooded conditions, indicating CO2 emission from the top soil. Contrarily, TC was relatively lower in the bottom soil than in the top soil under flooded conditions, showing CO2 and CH4 emission from the bottom soil. Furthermore, the paddy soil with macropores showed higher CO2 emission than the soil without macropores. However, CO2 and CH4 emissions were lower with drainage application than without drainage in soils when macropores and compost were applied. The CH4 concentration negatively correlated with the infiltration rate, indicating that fresh water or oxygen was available in the soils with macropores and drainage. The TC and TN concentrations were lower in the bottom soil than in the top soil, suggesting the development of reductive conditions in soils without drainage. The findings showed that macropores reduced reductive conditions, thereby lowering CH4 emission.
... Drainage peatlands can serve as hotspots for CO2 and N2O emissions from soils, minor sources of CH4 or even carbon sinks (Saurich, Tiemeyer, Dettmann, & Don, 2019). Drainage changes the biogeochemical and hydrological processes of peatlands and shifts peatland from being a carbon sink to a source (Norberg, Berglund, & Berglund, 2018;Tiemeyer et al., 2016). The magnitude of GHG emissions and microbial activity increases as soils become oxygenated (Chapuis-Lardy, Wrage, Metay, Chotte, & Bernoux, 2007;Oertel, Matschullat, Zurba, Zimmermann, & Erasmi, 2016). ...
Article
Alpine peatlands on the Qinghai‐Tibet Plateau are an important soil carbon pool and are extremely sensitive to global change. Duration of drainage and water table drawdown accelerate peatland degradation because the soil changes from an anaerobic to aerobic environment, and climate warming exacerbates this shift. The objective of the present study was to evaluate the effects of drainage on microbial characteristics and greenhouse gas (GHG) emissions, as well as identify the factors mediating those effects. This study also analyzed whether warming increases the variability of GHG emissions. Water table drawdown exerted greater influence on microbial communities than duration of drainage did. Water table drawdown significantly increased the relative abundances of Proteobacteria, Acidobacteria, Actinobacteria and Basidiomycota, and changes in soil microbiota correlated with differences in GHG emissions across three water table treatments. Longer drainage was associated with lower GHG emission; water table drawdown decreased emissions of CO2 and CH4, but increased emission of N2O. In addition, high temperature increased CO2 emission by 75% and N2O emission by 42%, without significantly affecting CH4 emission. Structural equation modeling showed that microbes, especially prokaryotes (r = 0.79, p < 0.05 for all), were the primary factor affecting GHG emissions from drained peatlands. Overall, this study indicates that the water table exerts a greater effect on GHG emissions than duration of drainage, and that warming increases variability of GHG emissions.
... In the case of samples from the drying experiment, water was added to 1.5 g of each replicate to adjust to a water content corresponding to 80% water-filled pore space (WFPS), which is the ratio of soil water content to soil porosity. The level of 80% was chosen as several studies have shown maximum carbon dioxide (CO 2 ) fluxes at a WFPS of around 80% Norberg et al., 2018;Säurich et al., 2019). The necessary amount of water was determined with: ...
Article
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Soil needs to be dried in order to determine water content, soil organic carbon content (SOC) and total nitrogen content (N). Water content is commonly measured using standard methods that involve drying temperatures of 105-110 • C. Recommended drying temperatures differ for the determination of SOC and N. However, at moderate drying temperatures, microbial activity might lead to organic matter mineralisation and nitrification, and thus to an underestimation of SOC and N. Furthermore, low drying temperatures might not dewater soils sufficiently to correctly determine water content or bulk density. Chemical processes such as thermal decomposition and volatilisation might occur at higher temperatures. This raises the question of whether the same sample can be used to determine water content, SOC and N. Further, the effect of drying, especially at different temperatures, on basal respiration of peat soils determined by incubation experiments is so far unknown. Effects of drying temperature might be especially severe for peat soils, which have high SOC and water contents. This study systematically evaluated the effect of different drying temperatures (20, 40, 60, 80 and 105 • C) on the determination of mass loss (proxy for water content), SOC and N over a wide range of 15 different peat soils comprising amorphous, Sphagnum and sedge peat substrate. The investigated peat soils had SOC contents ranging from approximately 16.8-52.5% with different degrees of decomposition. They were thus separated into two 'peat groups' (amorphous and weakly decomposed). In a subsequent investigation, an incubation experiment was carried out on a subset of five peat soils to investigate the pre-treatment effect of different drying temperatures on basal respiration. The results showed that amorphous samples should be dried at 105 • C to determine water content. The weakly decomposed peat soils in the study had reliable water contents for drying temperatures above 60 • C. For temperatures below 80 • C, the determined SOC and N were biased by residual water. This could be corrected for weakly decomposed samples, but for amorphous samples only for drying temperatures ≥60 • C. Thus, mineralisation of soil organic matter is likely to take place at lower drying temperatures which are not recommendable especially for amorphous peat prone to high mineralisation rates. This is supported by the results of the incubation experiment: The effect of peat type (amorphous topsoil vs. weakly decomposed subsoil) was greater than the effect of different drying temperatures, which nonetheless affected respiration rates. The differences between all five soils were consistent, irrespective of the drying temperature. Thus, incubation experiments might be possible using peat dried at moderate temperatures.
... A previous study on peat soils comparing the effect of different crops on N 2 O and CH 4 fluxes during the growing season found no difference in median seasonal emissions, but emissions differed widely between sites (Norberg et al., 2016a). This indicates that soil properties are a regulating factor (Norberg et al., 2018). Addition of N fertiliser generally increases soil N 2 O emissions if the weather is favourable (Butterbach-Bahl et al., 2013). ...
Article
Loss of organic matter from cultivated peat soils is a threat to farmers, due to the surface subsidence associated with organic matter loss, and to the atmosphere, due to CO2 and N2O emissions from the soil. In a three-year field experiment (2015–2017) on a drained, cultivated fen peat in southern Sweden, we tested whether reed canary grass (Phalaris arundinacea L.) and tall fescue (Festuca arundinacea Schreb.) perform better on peat soils than the commonly grown timothy grass (Phleum pratense L.), without increasing greenhouse gas emissions. In the experiment, we compared yield, nutrient uptake, penetration resistance and loss of organic matter measured as greenhouse gas emissions (CO2, N2O and CH4). Yield of timothy was significantly lower than that of reed canary grass and tall fescue in 2016, and lower than that of reed canary grass in 2017. Yield level increased over time, with total dry matter yield in 2017 of 11.7 Mg ha⁻¹ yr⁻¹ for timothy, 13.5 Mg ha⁻¹ yr⁻¹ for tall fescue and 14.3 Mg ha⁻¹ yr⁻¹ for reed canary grass. Total removal of all macronutrients in 2016 was higher in reed canary grass and tall fescue than in timothy. For nitrogen (N), reed canary grass removed a total of 173 kg N ha⁻¹ yr⁻¹, tall fescue 169 kg ha⁻¹ yr⁻¹ and timothy 121 kg ha⁻¹ yr⁻¹, while the fertilisation rate was only 50 kg N ha⁻¹. There were no differences in trafficability, measured as penetration resistance. Measurements of greenhouse gas emissions in the snow-free season in 2016 and 2017 using manual dark chambers (CO2, N2O and CH4) and in 2016 automatic dark chambers (CO2) revealed only small differences in CO2 emissions between the treatments. The N2O emissions were also low and CH4 emissions were very low and in general negative. The estimated carbon capture efficiency (ratio of C in aboveground biomass plus roots to emitted CO2-C measured by the automatic chambers) for the growing season (May–October) in 2016 was lowest for timothy (0.61) and higher for reed canary grass and tall fescue (0.70 and 0.70, respectively). Reed canary grass and tall fescue are thus promising alternatives to timothy on peat soils regarding yield, nutrient removal and carbon capture efficiency.
... Bei der höchsten Druckstufe betrug der WFPS 68 % in den Oberböden und 76 % in den Unterböden. Diese parabolische Abhängigkeit der Respirationsrate vom WFPS entspricht Ergebnissen anderer Studien mit mineralischen(Beare et al. 2009, Linn & Doran 1984, Moyano et al. 2012) und organischenBöden (Kechavarzi et al. 2010, Norberg et al. 2018, van Lent et al. 2018). Unter wassergesättigten Bedingungen ist der verfügbare Sauerstoff limitierend für die mikrobiologische Aktivität, während bei Wassergehalten unterhalb des WFPS-Optimums eine Limitierung durch mangelnde Wasserverfügbarkeit aufzutreten scheint. ...
Conference Paper
The utilization of biochar is often heralded as a salient approach to curtailing emissions and sequestering carbon. Agricultural and forestry soils have demonstrated its efficaciousness in reducing carbon emissions; however, the urban greening industry has yet to be thoroughly researched in this regard. To address this lacuna, the present study undertook the application of biochar to the soil of an urban green roof, with the aim of ascertaining its potential to mitigate carbon dioxide emissions. By studying the effects of applying BS-0%, BS-1%, BS-5%, and BS-10% biochar on green roof substrate, the study examined the carbon dioxide value over a period of 36 h encompassing both sunny and nocturnal environments. The results indicated that the addition of biochar to the soil was effective in reducing carbon emission, with all of the biochar additions demonstrating an aptitude for carbon dioxide fixation. Notably, the application of BS-1% biochar evinced a statistically significant reduction in the carbon dioxide value. Furthermore, the addition of biochar to the roof substrate was found to be crucial in controlling rainwater runoff and alleviating urban eutrophication, indirectly reducing carbon emissions. This study provides a practical and theoretical framework for the application of biochar to mitigate the urban heat island effect.
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Greenhouse gas emissions of a spring cereal monoculture under conventional tillage and no-till treatments were measured in a peatland in Southwestern Finland for three years in 2018–2021. Nitrous oxide (N 2 O), carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes were measured with an opaque chamber technique approximately biweekly throughout the years. During the growing season, canopy net ecosystem exchange (NEE) was measured with a transparent chamber technique and hourly ecosystem respiration (ER) and gross photosynthesis (GP) were modelled with empiric models. On average, the annual emissions were 6.4 ± 2.4 Mg CO 2 -C ha − 1 yr − 1 , 7.6 ± 3.5 kg N 2 O -N ha − 1 yr − 1 , and − 0.35 ± 0.42 kg CH 4 -C ha − 1 yr − 1 for NEE, N 2 O and CH 4 , respectively. The effect of no-till management on the GHG balance was non-consistent through years and thus generally of minor significance. No-till reduced the annual CO 2 emissions by 24% in 2019 and N 2 O emissions by 33% in 2020 compared to conventional tillage while there were no differences between the treatments in other years. Measured differences in ER occurred mostly during the winter periods, especially after ploughing. The results indicated that no-till may reduce CO 2 and N 2 O emissions from cultivated peat soil, but it does not lead to large consistent reductions during the first years of NT management.
Article
Peatlands are unique ecosystems but when they are drained for agriculture or peat mining, stored carbon is released to the atmosphere as CO2. The aim of the study was to assess the influence of siltation on secondary humification basing on humification indicators (C/N ratio, humification degree, humification index, E4/E6 ratio). It is essential to examine to what extent siltation hampers soil organic matter (SOM) oxidation. The study revealed that after drainage the amount of humus fractions, both acid and alkali soluble, were increasing at the expense of non-soluble carbon pool (residuum). Siltation hampered the transformation of organic matter and the quantities of OC and N in humus fractions were lower in silted soil samples than in not silted ones. The carbon extracted in acid-soluble fraction was not related to the state of siltation and was associated with the depth. The nitrogen content in this fraction did not change after drainage or siltation. The siltation did not affect C/N ratios. In unaltered peats these ratios were typical for fen soils (lowland peats) but in other studied soil samples the values of the C/N ratios suggested secondary transformation. The humification indicators (HI, HD and E4/E6) also revealed that secondary humification was more advanced in strongly silted soils, i.e. the stability of SOM in these soils is lower and the values of these indicators were dependent on the state of siltation. The study revealed that both drainage and siltation of soils changed the relations in SOM fractions. Drainage of peatlands resulted in initiation of the secondary humification of SOM and increase of chemically extractable humus fractions as well as increase of the humification degree. Stable SOM, which can have a mean residence time of centuries, became a potential source of CO2. However, siltation which led to a 50% decrease in SOM, hampered oxidation of SOM and had a stabilizing effect on SOM quality. These findings provide new insights into possibilities of mitigation of C losses from agricultural areas and may serve as a guidance for soil C management.
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The management of agricultural soils affect the composition and scale of their greenhouse gas (GHG) emissions. There is conflicting evidence on the effect of zero-tillage on carbon storage and GHG emissions. Here we assess the effects of zero-tillage over a range of time frames (1–15 years) on carbon storage and GHG release and their controls in the UK Net global warming potential was 30% lower under zero-tillage systems, due to lower carbon dioxide fluxes, with the greatest impacts after longer periods of zero-tillage management. Simultaneously, in zero-tillage systems, soil carbon stocks and the proportion of sequestered recalcitrant carbon increased while the temperature sensitivity of soil respiration decreased with time, compared to conventionally soils. We conclude that zero-tillage could play a crucial role in both reducing GHG emissions and at the same time increase soil carbon sequestration, therefore contributing to mitigate against climate change. Our findings are particularly important in the context of designing new policies (for example the Environmental Land Management Schemes in the UK) that ensure the sustainability of agricultural production in a changing climate.
Article
Greenhouse gas emissions from managed peatlands have not been extensively studied in Western Patagonia. The objective of this study was to assess the annual CO2 emission from microbial carbon (C) mineralization in a peatland site under not saturated conditions at Tierra del Fuego. The annual CO2 emissions were measured from unsaturated soil samples (n=41) under soil incubation at seasonal local temperatures to simulate CO2 emissions for a year, using a non‐dispersive infrared gas analyzer. Spatial models for total soil C and CO2 were calculated using discrete and continuous variables. The annual mean of measured cumulative CO2 was 1358 µg CO2 g soil‐1, lower than Northern peatlands, and 82% of the C mineralization occurred in the warmer season. The modeled CO2 in the warmer season showed levels of CO2 as high as 4 mg CO2 g soil‐1, but 66% of the area showed between 600‐2000 µg CO2 g soil‐1, which is 28‐92% and 9‐32% of CO2 values reported for crop rotations. Consequently, after a potential habilitation of the study area for agricultural use, the soil CO2 emissions from heterotrophic activity would become a C source to the global CO2 emissions. This ecosystem is highly exposed to the effects of the land use change, and global temperature increase.
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Drained organic soils are considered to be hotspots for greenhouse gas (GHG) emissions. Arable lands and intensively used grasslands, in particular, have been regarded as the main producers of carbon dioxide (CO2) and nitrous oxide (N2O). However, GHG balances of former peatlands and associated organic soils not considered to be peatland according to the definition of the Intergovernmental Panel on Climate Change (IPCC) have not been investigated so far. Therefore, our study addressed the question to what extent the soil organic carbon (SOC) content affects the GHG release of drained organic soils under two different land-use types (arable land and intensively used grassland). Both land-use types were established on a Mollic Gleysol (labeled Cmedium) as well as on a Sapric Histosol (labeled Chigh). The two soil types differed significantly in their SOC contents in the topsoil (Cmedium: 9.4–10.9 % SOC; Chigh: 16.1–17.2 % SOC). We determined GHG fluxes over a period of 1 or 2 years in case of N2O or methane (CH4) and CO2, respectively. The daily and annual net ecosystem exchange (NEE) of CO2 was determined by measuring NEE and the ecosystem respiration (RECO) with the closed dynamic chamber technique and by modeling the RECO and the gross primary production (GPP). N2O and CH4 were measured with the static closed chamber technique. Estimated NEE of CO2 differed significantly between the two land-use types, with lower NEE values (−6 to 1707 g CO2-C m−2 yr−1) at the arable sites and higher values (1354 to 1823 g CO2-C m−2 yr−1) at the grassland sites. No effect on NEE was found regarding the SOC content. Significantly higher annual N2O exchange rates were observed at the arable sites (0.23–0.86 g N m−2 yr−1) than at the grassland sites (0.12–0.31 g N m−2 yr−1). Furthermore, N2O fluxes from the Chigh sites significantly exceeded those of the Cmedium sites. CH4 fluxes were found to be close to zero at all plots. Estimated global warming potential, calculated for a time horizon of 100 years (GWP100) revealed a very high release of GHGs from all plots ranging from 1837 to 7095 g CO2 eq. m−2 yr−1. Calculated global warming potential (GWP) values did not differ between soil types and partly exceeded the IPCC default emission factors of the Tier 1 approach by far. However, despite being subject to high uncertainties, the results clearly highlight the importance of adjusting the IPCC guidelines for organic soils not falling under the definition in order to avoid a significant underestimation of GHG emissions in the corresponding sectors of the national climate reporting. Furthermore, the present results revealed that mainly the type of land-use, including the management type, and not the SOC content is responsible for the height of GHG exchange from intensive farming on drained organic soils.
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Temperate grasslands on organic soils are diverse due to edaphic properties but also to regional management practices and this heterogeneity is reflected in the wide range of greenhouse gas (GHG) flux values reported in the literature. In Ireland, most grasslands on organic soils were drained several decades ago and are managed as extensive pastures with little or no fertilisation. This study describes a 2-year study of the net ecosystem carbon balance (NECB) of two such sites. We determined GHG fluxes and waterborne carbon (C) emissions in a nutrient-rich grassland and compared it with values measured from two nutrient-poor organic soils: a deep-drained and a shallow-drained site. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes were determined using the chamber technique, and fluvial C fluxes were estimated by combining drainage water concentrations and flows. The nutrient-rich site was an annual source of CO2 (233 g C m−2 yr−1), CH4 neutral, and a small source of N2O (0.16 g N2O-N m−2 yr−1). Net ecosystem exchange (NEE) at the shallow-drained nutrient-poor site was −89 and −99 g C m−2 yr−1 in Years 1 and 2 respectively, and NEE at the deep-drained nutrient-poor site was 85 and −26 g C m−2 yr−1 respectively. Low CH4 emissions (1.3 g C m−2 yr−1) were recorded at the shallow-drained nutrient-poor site. Fluvial exports from the nutrient-rich site totalled 69.8 g C m−2 yr−1 with 54% as dissolved organic C. Waterborne C losses from the nutrient-poor site reflected differences in annual runoff totalling 44 g C m−2 yr−1 in Year 1 and 30.8 g C m−2 yr−1 in Year 2. The NECB of the nutrient-rich grassland was 663 g C m−2 yr−1 with biomass exports being the major component accounting for 53%. The NECB of the nutrient-poor deep-drained site was less than half of the nutrient-rich site (2-year mean 267 g C m−2 yr−1). Although NEE at the nutrient-poor shallow-drained site was negative in both years, high biomass export meant it was a net C source (2-year mean NECB 103 g C m−2 yr−1). While the impacts of the nutrient and drainage status on NEE, biomass exports and fluvial C losses were confirmed, inter-regional differences in management practice and climate were also significant factors which impacted on the overall NECB of these ecosystems. Contrary to expectation, the NECB of nutrient-poor drained organic soils under grasslands is not necessarily a large C source and this has implications for Ireland's choice of national GHG inventory reporting methodologies. This study can also aid the development of strategies to deliver reduced emissions tailored to local grassland types.
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A large share of peatlands in northwest Germany is drained for agricultural purposes, thereby emitting high amounts of greenhouse gases (GHG). In order to quantify the climatic impact of fen soils in dairy farming systems of northern Germany, GHG exchange and forage yield were determined on four experimental sites which differed in terms of management and drainage intensity: a) rewetted and unutilized grassland (UG), b) intensive and 'wet' grassland (GW), c) intensive and 'moist' grassland (GM) and d) arable forage cropping (AR). Net ecosystem exchange (NEE) of CO2 and fluxes of CH4 and N2O were measured using closed manual chambers. CH4 fluxes were significantly affected by groundwater level (GWL) and soil temperature, whereas N2O fluxes showed a significant relation to the amount of nitrate in top soil. Annual balances of all three gases, as well as the global warming potential (GWP), were significantly correlated to mean annual GWL. Two-year mean GWP, combined from C2-C-equivalents of NEE, CH4 and N2O emissions, as well as C input (slurry) and C output (harvest), was 3.8, 11.7, 17.7 and 17.3 Mg CO2-C-eq ha−1 a−1 for sites UG, GW, GM and AR, respectively (standard error (SE) 2.8, 1.2, 1.8, 2.6). Yield related emissions for the three agricultural sites were 201, 248 and 269 kg CO2-C-eq (GJ net energy lactation (NEL))−1 for sites GW, GM and AR, respectively (SE 17, 9, 19). The carbon footprint of agricultural commodities grown on fen soils depended on long-term drainage intensity rather than type of management, but management and climate strongly influenced interannual on-site variability. However, arable forage production revealed a high uncertainty of yield and therefore was an unsuitable land use option. Lowest yield related GHG emissions were achieved by a three-cut system of productive grassland swards in combination with a high GWL (long-term mean ≤ 20 cm below the surface).
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An extended water regime model was used for calculating the evapotranspiration, groundwater recharge, and peat mineralization (CO2 and N release) for various fen locations with grassland utilization in dependence on the groundwater level. The results show that an increasing groundwater level leads to a strong decline of the actual evapotranspiration Et. For example, increasing the groundwater level from 30 to 120 cm diminishes the Et by up to 230 mm a—1. A positive groundwater recharge only takes place at groundwater levels of 90 cm and more. At smaller distances the capillary rise into the rooting zone during the summer months is greater than the water seepage during the winter months, so that a negative groundwater recharge-balance is reached in the course of a year. The CO2- and the N-release, as well as the annual decline in peat thickness, increase significantly with rising groundwater levels. The results show, that varying the groundwater level can influence the water regime and the peat mineralization significantly. The lower the groundwater level the less is the peat decomposition. The demand for a groundwater level as small as possible is, however, limited by an agricultural utilization of the fens. Choosing the optimum groundwater level should consider the aims (1) peat mineralization, (2) gas emission (CO2, CH4, N2O), and (3) crop production. If a grassland utilization is supposed to be made possible and all three aims above are given equal importance, the groundwater level should be maintained at 30 cm. At this distance, about 90 % of the optimum plant output can be reached. The peat mineralization can be reduced to 30 to 40 % of the maximum peat mineralization. The gas emission amounts to 50—60 % of the maximum value.
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Accounting for greenhouse gas (GHG) emissions and removals in managed ecosystems has generally focused on direct land–atmosphere fluxes, but in peatlands a significant proportion of total carbon loss occurs via fluvial transport. This study considers the composition of this ‘waterborne carbon’ flux, its potential contribution to GHG emissions, and the extent to which it may change in response to land-management. The work describes, and builds on, a methodology to account for major components of these emissions developed for the 2013 Wetland Supplement of the Intergovernmental Panel on Climate Change. We identify two major components of GHG emissions from waterbodies draining organic soil: i) ‘on site’ emissions of methane (and to a lesser extent CO2) from drainage ditches located within the peatland; and ii) ‘off site’ emissions of CO2 resulting from downstream oxidation of dissolved and particulate organic carbon (DOC and POC) within the aquatic system. Methane emissions from ditches were found to be large in many cases (mean 60 g CH4 m−2 year−1 based on all reported values), countering the view that methane emissions cease following wetland drainage. Emissions were greatest from ditches in intensive agricultural peatlands, but data were sparse and showed high variability. For DOC, the magnitude of the natural flux varied strongly with latitude, from 5 g C m−2 year−1 in northern boreal peatlands to 60 g C m−2 year−1 in tropical peatlands. Available data suggest that DOC fluxes increase by around 60 % following drainage, and that this increase may be reversed in the longer-term through re-wetting, although variability between studies was high, especially in relation to re-wetting response. Evidence regarding the fate of DOC is complex and inconclusive, but overall suggests that the majority of DOC exported from peatlands is converted to CO2 through photo- and/or bio-degradation in rivers, standing waters and oceans. The contribution of POC export to GHG emissions is even more uncertain, but we estimate that over half of exported POC may eventually be converted to CO2. Although POC fluxes are normally small, they can become very large when bare peat surfaces are exposed to fluvial erosion. Overall, we estimate that waterborne carbon emissions may contribute about 1–4 t CO2-eq ha−1 year−1 of additional GHG emissions from drained peatlands. For a number of worked examples this represented around 15–50 % of total GHG emissions.
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Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO2 emissions. No significant difference was observed in the CH4 emissions in response to water depth and amelioration. The ameliorations influenced the CO2 and N2O emissions from the peat soil. The application of biochar+compost enhanced the CO2 and N2O emissions but reduced the CH4 emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO2 and N2O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO2, CH4 and N2O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems.
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Globally 15%, and in Europe over 50%, of all peatlands have been drained for agricultural use leading to high carbon (C) losses, severe land subsidence and increased flooding risks. For the restoration of C sequestration and peat formation, abandoned peatlands are being rewetted at a large scale, but this transforms them into strong methane (CH4) sources. Furthermore, due to the high topsoil nutrient contents and/or high buffering capacities of water used for rewetting, this will inevitably result in eutrophication of restored peatlands and downstream areas, which may compromise the regrowth of peat forming vegetation including Sphagnum spp.
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A b s t r a c t. Soil respiration is a very important factor influencing carbon deposition in peat and reflecting the intensity of soil organic matter decomposition, root respiration, and the ease of transporting gases to the surface. Carbon dioxide release from three different peat soil profiles (0-80 cm) of the Polesie Lubelskie Region (Eastern Poland) was analyzed under laboratory condi-tions. Peat samples were incubated at 5, 10, and 20°C in aerobic and anaerobic environments, and their CO 2 -evolution was analy-zed up to 14 days. The respiration activity was found to be in the range of 0.013-0.497 g CO 2 kg -1 DW d -1 . The respiratory quotient was estimated to be in the range of 0.51-1.51, and the difference in respiration rates over 10°C ranged between 4.15 and 8.72 in aerobic and from 1.15 to 6.53 in anaerobic conditions. A strong influence of temperature, depth, the degree of peat decomposition, pH, and nitrate content on respiration activity was found. Lack of oxygen at low temperature caused higher respiration activity than under aerobic conditions. These results should be taken into account when the management of Polish peatlands is considered in the context of climate and carbon storage, and physicochemical properties of soil in relation to soil respiration activity are considered. K e y w o r d s: peat ecosystem, aerobic and anaerobic respi-ration, carbon dioxide INTRODUCTION
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Knowledge on soil microbial respiration (SMR) rates and thus soil-related CO2 losses from Arctic soils is vital because of the crucial importance of this ecosystem within the global carbon (C) cycle and climate system. Here, we measured SMR from various habitats during the growing season in Russian subarctic tundra by applying two different approaches: 14C partitioning approach and root trenching. The variable habitats encompassed peat and mineral soils, bare and vegetated surfaces and included both dry and moist ones. The field experiment was complemented by laboratory studies to measure bioavailability of soil carbon and identify sources of CO2. Differences in bioavailability of soils, measured in the laboratory as basal soil respiration rates, were generally greater than inter-site differences in SMR rates measured in situ, suggesting secondary constraints at field conditions, such as soil C content. There was a tendency towards lower SMR in vegetated peat plateaus compared to upland mineral tundra (on average 137 vs. 185 g CO2 m−2 growing season−1, respectively), but no significant differences were found. Surprisingly, the bare surfaces (peat circles) with 3500-year-old C at the surface exhibited about the largest SMR among all sites as shown by both methods. This was related to the general development of peat plateaus in the region, and uplifting of deeper peat with high C content to the surface during the genesis of peat circles. This observation is particularly relevant for decomposition of deeper peat in vegetated peat plateaus, where soil material similar to the bare surfaces can be found. The data indicate that the large stocks of C stored in permafrost peatlands are principally available for decomposition despite old age.
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Background Peatlands cover 2 to 5 percent of the global land area, while storing 30 and 50 percent of all global soil carbon (C). Peatlands constitute a substantial sink of atmospheric carbon dioxide (CO2) via photosynthesis and organic matter accumulation, but also release methane (CH4),nitrous oxide (N2O), and CO2 through respiration, all of which are powerful greenhouse gases (GHGs). Lowland peats in boreo-temperate regions may store substantial amounts of C and are subject to disproportionately high land-use pressure. Whilst evidence on the impacts of different land management practices on C cycling and GHG fluxes in lowland peats does exist, these data have yet to be synthesised. Here we report on the results of a Collaboration for Environmental Evidence (CEE) systematic review of this evidence. Methods Evidence was collated through searches of literature databases, search engines, and organisational websites using tested search strings. Screening was performed on titles, abstracts and full texts using established inclusion criteria for population, intervention/exposure, comparator, and outcome key elements. Remaining relevant full texts were critically appraised and data extracted according to pre-defined strategies. Meta-analysis was performed where sufficient data were reported. Results Over 26,000 articles were identified from searches, and screening of obtainable full texts resulted in the inclusion of 93 relevant articles (110 independent studies). Critical appraisal excluded 39 studies, leaving 71 to proceed to synthesis. Results indicate that drainage increases the N2O emission and the ecosystem respiration of CO2, but decreases CH4 emission. Secondly, naturally drier peats release more N2O than wetter soils. Finally, restoration increases the CH4 release. Insufficient studies reported C cycling, preventing quantitative synthesis. No significant effect was identified in meta-analyses of the impact of drainage and restoration on DOC concentration. Conclusions Consistent patterns in C concentration and GHG release across the evidence-base may exist for certain land management practices: drainage increases N2O production and CO2 from respiration; drier peats release more N2O than wetter counterparts; and restoration increases CH4 emission. We identify several problems with the evidence-base; experimental design is often inconsistent between intervention and control samples, pseudoreplication is extremely common, and variability measures are often unreported.
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It is generally known that managed, drained peatlands act as carbon sources. In this study we examined how mitigation through the reduction of management and through rewetting may affect the greenhouse gas (GHG) emission and the carbon balance of intensively managed, drained, agricultural peatlands. Carbon and GHG balances were determined for three peatlands in the western part of the Netherlands from 2005 to 2008 by considering spatial and temporal variability of emissions (CO2, CH4 and N2O). One area (Oukoop) is an intensively managed grass-on-peatland, including a dairy farm, with the ground water level at an average annual depth of 0.55 m below the soil surface. The second area (Stein) is an extensively managed grass-on-peatland, formerly intensively managed, with a dynamic ground water level at an average annual depth of 0.45 m below the soil surface. The third area is an (since 1998) rewetted former agricultural peatland (Horstermeer), close to Oukoop and Stein, with the average annual ground water level at a depth of 0.2 m below the soil surface. During the measurement campaigns we found that both agriculturally managed sites acted as carbon and GHG sources but the rewetted agricultural peatland acted as a carbon and GHG sink. The terrestrial GHG source strength was 1.4 kg CO2-eq m-2 yr-1 for the intensively managed area and 1.0 kg CO2-eq m-2 yr-1 for the extensively managed area; the unmanaged area acted as a GHG sink of 0.7 kg CO2-eq m-2 yr-1. Water bodies contributed significantly to the terrestrial GHG balance because of a high release of CH4 and the loss of DOC only played a minor role. Adding the farm-based CO2 and CH4 emissions increased the source strength for the managed sites to 2.7 kg CO2-eq m-2 yr-1 for Oukoop and 2.1 kg CO2-eq m-2 yr-1 for Stein. Shifting from intensively managed to extensively managed grass-on-peat reduced GHG emissions mainly because N2O emission and farm-based CH4 emissions decreased. Overall, this study suggests that managed peatlands are large sources of GHG and carbon, but, if appropriate measures are taken they can be turned back into GHG and carbon sinks within 15 yr of abandonment and rewetting.
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Laboratory columns (80 cm long, 10 cm diameter) of peat were constructed from samples collected from a subarctic fen, a temperate bog and a temperate swamp. Temperature and water table position were manipulated to establish their influence on emissions of CO2 and CH4 from the columns. A factorial design experiment revealed significant (P < 0.05) differences in emission of these gases related to peat type, temperature and water table position, as well as an interaction between temperature and water table. Emissions of CO2 and CH4 at 23°C were an average of 2.4 and 6.6 times larger, respectively, than those at 10°C. Compared to emissions when the columns were saturated, water table at a depth of 40 cm increased CO2 fluxes by an average of 4.3 times and decreased CH4 emissions by an average of 5.0 times. There were significant temporal variations in gas emissions during the 6-week experiment, presumably related to variations in microbial populations and substrate availability. Using columns with static water table depths of 0, 10, 20, 40 and 60 cm, CO2 emissions showed a positive, linear relation with depth, whereas CH4 emissions revealed a negative, logarithmic relation with depth. Lowering and then raising the water table from the peat surface to a depth of 50 cm revealed weak evidence of hysteresis in CO2 emissions between the falling and rising water table limbs. Hysteresis (falling > rising limb) was very pronounced for CH4 emissions, attributed to a release of CH4 stored in porewater and a lag in the development of anaerobic conditions and methanogenesis on the rising limb. Decreases in atmospheric pressure were correlated with abnormally large emissions of CO2 and CH4 on the falling limb. Peat slurries incubated in flasks revealed few differences between the three peat types in the rates of CO2 production under aerobic and anaerobic conditions. There were, however, major differences between peat types in the rates of CH4 consumption under aerobic incubation conditions and CH4 production under anaerobic conditions (bog > fen > swamp), which explain the differences in response of the peat types in the column experiment.
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Drainage, vegetation removal and harvesting, and vegetation restoration have a profound effect on carbon cycling in peatlands. Through laboratory incubations of 114 peat samples collected from the surface layer and just above and just below the water table at 13 sites, we examined the potential for carbon dioxide (CO2) production under aerobic and anaerobic conditions and methane (CH4) production under anaerobic conditions. CO2 production rates ranged from 0.04 to 1.05 mg g−1 d−1 under aerobic conditions and 0.01 to 0.29 mg g−1 d−1 under anaerobic conditions. Rates of CO2 production were generally smallest in the lower parts of the profiles and at the recently restored sites where deep peat was exposed at the surface; they were largest in the freshly-formed surface peat at the undisturbed bog and older restoration sites where a strong cover of vegetation had developed. The CO2 production potentials were negatively correlated with the Von Post Index of decomposition, and aerobic: anaerobic production ratios averaged 4.3: 1. Largest rates of anaerobic CH4 production occurred in samples close to the soil surface with fresh peat accumulation and a high water table, and smallest rates were in samples from the subsurface of sites with a low water table. Anaerobic CH4 production was significantly positively correlated with aerobic and anaerobic CO2 production. These production potentials show that drainage, harvesting, and restoration change the ability of the peat profile to produce and emit CO2 and CH4.
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Using pre-established trial sites on allophanic soils, we investigated the impacts of long to medium-term pastoral management practices, such as fertilisation and grazing intensity, on a range of soil biological and biochemical properties; hot water-extractable C (HWC), water-soluble C (WSC), hot-water extractable total carbohydrates, microbial biomass-C and N and mineralisable N. These properties were examined for their usefulness as soil quality indicators responding to changes in the rhizosphere caused by management practices. Adjacent cropping, market garden and native bush sites located on similar soil types were included to determine the changes in soil biological and biochemical properties resulting from changes in land use. The seasonal variability of HWC and its relationship with other labile fractions of soil organic matter was also examined.
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This study evaluates the hydrological conditions in a harvested bog where various water management schemes have been implemented to ameliorate conditions limiting Sphagnum regeneration. The study sites included a natural bog (natural), a recently drained and harvested bog (drained), which provided the hydrological extremes. Also included are a drained harvested bog with ditches blocked with (1) no other management (blocked), (2) peat bounded by open water at 5-m intervals (5-m), and (3) with straw mulch on the surface (mulch).
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Drainage and cultivation of fen peatlands creates complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater-level (GWL). To date, it remains unclear if such sites are sources or sinks for greenhouse gases like CO2 and CH4, especially if used for cropland. As individual control factors like GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of plant- and microbially mediated C gas fluxes of these soils. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP, ecosystem respiration - Reco, net ecosystem exchange - NEE, CH4) of maize using manual chambers for four years. The study sites were located near Paulinenaue, Germany. Here we selected three soils, which represent the full gradient in pedogenesis, GWL and SOC stocks (0-1 m) of the fen peatland: (a) Haplic Arenosol (AR; 8 kgCm⁻²); (b) Mollic Gleysol (GL; 38 kgCm⁻²); and (c) Hemic Histosol (HS; 87 kgCm⁻²). Daily GWL data was used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47± 30 gCm⁻² a⁻¹ at AR to -305±123 gCm⁻² a⁻¹ at GL and ⁻¹27±212 gCm⁻² a⁻¹ at HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP : Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the effects of GWL-dependent N availability on C formation and transformation processes in the plant-soil system, which promote CO2 input via GPP more than CO2 emission via Reco. The process-oriented approach of dynamic C and N stocks is a promising, potentially generalizable method for system-oriented investigations of the C gas exchange of groundwater-influenced soils and could be expanded to other nutrients and soil characteristics. However, in order to assess the climate impact of arable sites on drained peat- lands, it is always necessary to consider the entire range of groundwater-influenced mineral and organic soils and their respective areal extent within the soil landscape.
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Management of peat soils is regionally important as they cover large land areas and have important but conflicting ecosystems services. A recent management trend for drained peatlands is the control of greenhouse gases (GHG) by changes in agricultural practices, peatland restoration or paludiculture. Due to complex antagonistic controls of moisture, water table management can be difficult to use as a method for controlling GHG emissions. Past studies show that there is no obvious relationship between GHG emission rates and crop type, tillage intensity or fertilization rates. For drained peat soils, the best use options can vary from rewetting with reduced emission to efficient short term use to maximize the profit per amount of greenhouse gas emitted. The GHG accounting should consider the entire life cycle of the peatland and the socio-economic benefits peatlands provide locally. Cultivating energy crops is a viable option especially for wet peat soils with poor drainage, but harvesting remains a challenge due to tractability of wet soils. Paludiculture in lowland floodplains can be a tool to mitigate regional flooding allowing water to be stored on these lands without much harm to crops. This can also increase regional biodiversity providing important habitats for birds and moisture tolerant plant species. However, on many peatlands rewetting is not possible due to their position in the landscape and the associated difficulty to maintain a high stable water table. While the goal of rewetting often is to encourage the return of peat forming plants and the ecosystem services they provide such as carbon sequestration, it is not well known if these plants will grow on peat soils that have been altered by the process of drainage and management. Therefore, it is important to consider peat quality and hydrology when choosing management options. Mapping of sites is recommended as a management tool to guide actions. The environmental status and socio-economic importance of the sites should be assessed both for continued cultivation but also for other ecosystem services such as restoration and hydrological functions (flood control). Farmers need advice, tools and training to find the best after-use option. Biofuels might provide a cost-efficient after use option for some sites. Peat extraction followed by rewetting might provide a sustainable option as rewetting is often easier if the peat is removed, starting the peat accumulation from scratch. Also this provides a way to finance the after-use. As impacts of land use are uncertain, new policies should consider multiple benefits and decisions should be based on scientific evidence and field scale observations. The need to further understand the key processes and long term effects of field scale land use manipulations is evident. The recommended actions for peatlands should be based on local condition and socio-economic needs to outline intermediate and long term plans.
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Pristine peat soils are characterized by large porosity, low density and large water and organic matter contents. Drainage and management practices change peat properties by oxidation, compaction and mineral matter additions. This study examined differences in physical properties (hydraulic conductivity, water retention curve, bulk density, porosity, von Post degree of decomposition) in soil profiles of two peatland forests, a cultivated peatland, a peat extraction area and two pristine mires originally within the same peatland area. Soil hydraulic conductivity of the drained sites (median hydraulic conductivities: 3.3 × 10−5 m/s, 2.9 × 10−8 m/s and 8.5 × 10−8 m/s for the forests, the cultivated site and the peat extraction area, respectively) was predicted better by land use option than by soil physical parameters. Detailed physical measurements were accompanied by monitoring of the water levels between drains. The model ‘DRAINMOD’ was used to assess the hydrology and the rapid fluctuations seen in groundwater depths. Hydraulic conductivity values needed to match the simulation of observed depth to groundwater data were an order of magnitude greater than those determined in field measurements, suggesting that macropore flow was an important pathway at the study sites. The rapid response of depth to groundwater during rainfall events indicated a small effective porosity and this was supported by the small measured values of drainable porosity. This study highlighted the potential role of land use and macropore flow in controlling water table fluctuation and related processes in peat soils.
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Drainage of peatlands affects the fluxes of greenhouse gases (GHGs). Organic soils used for agriculture contribute a large proportion of anthropogenic GHG emissions, and on-farm mitigation options are important. This field study investigated whether choice of a cropping system can be used to mitigate emissions of N2O and influence CH4 fluxes from cultivated organic and carbon-rich soils during the growing season. Ten different sites in southern Sweden representing peat soils, peaty marl and gyttja clay, with a range of different soil properties, were used for on-site measurements of N2O and CH4 fluxes. The fluxes during the growing season from soils under two different crops grown in the same field and same environmental conditions were monitored. Crop intensities varied from grasslands to intensive potato cultivation. The results showed no difference in median seasonal N2O emissions between the two crops compared. Median seasonal emissions ranged from 0 to 919 µg N2O m−2 h−1, with peaks on individual sampling occasions of up to 3317 µg N2O m−2 h−1. Nitrous oxide emissions differed widely between sites, indicating that soil properties are a regulating factor. However, pH was the only soil factor that correlated with N2O emissions (negative exponential correlation). The type of crop grown on the soil did not influence CH4 fluxes. Median seasonal CH4 flux from the different sites ranged from uptake of 36 µg CH4 m−2 h−1 to release of 4.5 µg CH4 m−2 h−1. From our results, it was concluded that farmers cannot mitigate N2O emissions during the growing season or influence CH4 fluxes by changing the cropping system in the field.
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Drained and cultivated organic soils contribute a substantial proportion of estimated anthropogenic greenhouse gas emissions in Sweden. According to rough estimates, different cropping systems give rise to different subsidence rates and, since some of this subsidence originates from oxidation of organic material, soil respiration may also vary with different crops. This field study investigated the possibility of mitigating carbon dioxide (CO2) emissions from cultivated organic soils by using a specific cropping system. The CO2 emission rates from soils under different crops in similar environmental conditions were measured at 11 field sites in southern Sweden representing different types of organic soils. The variation in emissions between the crops tested was low compared with total CO2 emissions from the soil and differences between crops were not consistent. This shows that growing a particular crop cannot be recommended as a mitigation option for limiting CO2 emissions from cultivated organic soils.
Article
Several previous field studies in temperate regions have shown decreased soil respiration after conventional tillage compared with reduced or no-tillage treatments. Whether this decrease is due to differences in plant residue distribution or changes in soil structure following tillage remains an open question. This study investigated (1) the effects of residue management and incorporation depth on soil respiration and (2) biological activity in different post-tillage aggregates representing the actual size and distribution of aggregates observed in the tilled layer. The study was conducted within a long-term tillage experiment on a clay soil (Eutric Cambisol) in Uppsala, Sweden. After 38 y, four replicate plots in two long-term treatments (moldboard plowing (MP) and shallow tillage (ST)) were split into three subplots. These were then used for a short-term trial in which crop residues were either removed, left on the surface or incorporated to about 6 cm depth (ST) or at 20 cm depth (MP). Soil respiration, soil temperature, and water content were monitored during a 10-d period after tillage treatment. Respiration from aggregates of different sizes produced by ST and MP was also measured at constant water potential and temperature in the laboratory. The results showed that MP decreased short-term soil respiration compared with ST or no tillage. Small aggregates (< 16 mm) were biologically most active, irrespective of tillage method, but due to their low proportion of total soil mass they contributed < 1.5% to total respiration from the tilled layer. Differences in respiration between tillage treatments were found to be attributable to indirect effects on soil moisture and temperature profiles and the depth distribution of crop residues, rather than to physical disturbance of the soil.
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It is commonly assumed that agricultural peatlands are net sources of CO2 to the atmosphere because of lowered water tables and intensive land management altering the balance of plant productivity and respiration. Yet actual farm-scale fluxes of CO2 have been infrequently quantified. We measured net ecosystem exchange of CO2 (NEE) using a permanent and a mobile eddy covariance tower installed over dairy farms with year-round rotational grazing on deep peats in New Zealand. The permanent tower was in place for one year and the mobile tower was deployed for periods of 3–4 weeks at three other farms on peat between spring and autumn. At all sites, grazing cycles caused large variations in pasture biomass and consequent daytime NEE and we accounted for these variations using an index of photosynthesising biomass (phytomass index, Lohila et al., 2004) automatically derived from daily CO2 flux measurements. We estimated annual CO2 loss of 190 gC m−2 yr−1 for the permanent site, which is in broad agreement with other agricultural peatland studies. Including other farm-scale exports of C, overall net ecosystem carbon loss estimated for the permanent site was 294 gC m−2 yr−1. Accounting for changes in phytomass index, daytime NEE was similar for permanent-mobile site farm pairings, except when there were very large differences in water table depths between farms in autumn. In contrast, night-time respiration losses were almost identical between farms even when water tables were markedly different, suggesting that spatial differences in NEE in these agricultural peatlands are caused by reduced photosynthesis in dry periods, due to plant water stress, rather than increased respiration. Comparisons between permanent and mobile towers appeared a useful approach for determining spatial variability of CO2 fluxes from peat soils. Taken together, our results suggested that the CO2 losses measured at the permanent site were representative of CO2 losses for farmed peats in the Waikato region when the water table was within ∼0.5 m of the surface. Where water tables were deeper net CO2 losses would be expected to be greater due to reduced pasture photosynthesis and production. Maintaining higher water tables might achieve dual benefits of increasing pasture productivity and reducing CO2 losses.
Article
To date there is still a lack of reliable data on greenhouse gas emissions from drained fens needed to determine the climatic relevance of land use and land use change on peatlands and to supply the National Inventory Report for the German Greenhouse Gas Inventory. In this study we present the results of monthly-based multiyear measurements of CO2, N2O and CH4 flux rates in two drained agriculturally used fen ecosystems in NW Germany (cropland and grassland) over a period of 4.5 y using transparent and opaque closed chambers. CO2 exchange was modelled at high resolution with temperature and photosynthetic active radiation. The measured and modelled values fit very well (R2 ≥ 0.93). Annual GHG and Global Warming Potential (GWP) balances were determined. Net CO2 emissions at the cropland and grassland sites were similarly high, taking into account changes in management; net ecosystem C balance amounted to about 4.0 to 5.0 Mg C ha−1 y−1. Emissions of N2O and CH4 were low at both sites. The mean GWP balance for a time frame of 100 y (GWP100) amounted to about 17.0 to 19.0 Mg CO2-eq. ha−1 y−1. The unexpectedly low greenhouse gas emissions from the cropland site are attributed to the high water table and a change in crop management. The change from corn for silage to corn-cob mix lead transiently to rather small greenhouse gas emissions. The study confirms the need for multiyear measurements taking climatic and management variation into account.
Article
Agricultural drainage of organic soils has resulted in vast soil subsidence and contributed to increased atmospheric carbon dioxide (CO2) concentrations. The Sacramento-San Joaquin Delta in California was drained over a century ago for agriculture and human settlement and has since experienced subsidence rates that are among the highest in the world. It is recognized that drained agriculture in the Delta is unsustainable in the long-term, and to help reverse subsidence and capture carbon (C) there is an interest in restoring drained agricultural land-use types to flooded conditions. However, flooding may increase methane (CH4) emissions. We conducted a full year of simultaneous eddy covariance measurements at two conventional drained agricultural peatlands (a pasture and a corn field) and three flooded land-use types (a rice paddy and two restored wetlands) to assess the impact of drained to flooded land-use change on CO2 and CH4 fluxes in the Delta.We found that the drained sites were net C and greenhouse gas (GHG) sources, releasing up to 341 g C m−2 yr−1 as CO2 and 11.4 g C m−2 yr−1 as CH4. Conversely, the restored wetlands were net sinks of atmospheric CO2, sequestering up to 397 g C m−2 yr−1. However, they were large sources of CH4, with emissions ranging from 39 to 53 g C m−2 yr−1. In terms of the full GHG budget, the restored wetlands could be either GHG sources or sinks. Although the rice paddy was a small atmospheric CO2 sink, when considering harvest and CH4 emissions, it acted as both a C and GHG source. Annual photosynthesis was similar between sites, but flooding at the restored sites inhibited ecosystem respiration, making them net CO2 sinks. This study suggests that converting drained agricultural peat soils to flooded land-use types can help reduce or reverse soil subsidence and reduce GHG emissions.This article is protected by copyright. All rights reserved.
Article
Combination of rewetting and wetland crop cultivation (paludiculture) is pursued as a wider carbon dioxide (CO2) mitigation option in drained peatland. However, information on the overall greenhouse gas (GHG) balance for paludiculture is lacking. We investigated the GHG balance of peatlands grown with reed canary grass (RCG) and rewetted to various extents. Gas fluxes of CO2, methane (CH4) and nitrous oxide (N2O) were measured with a static chamber technique for 10 months from mesocosms sown with RCG and manipulated to ground water levels (GWL) of 0, -10, -20, -30 and -40 cm below the soil surface. Gross primary production (GPP) was estimated from the above ground biomass yield. The mean dry biomass yield across all water table treatments was 6 Mg ha(-1) with no significant differences between the treatments. Raising the GWL to the surface decreased both the net ecosystem exchange (NEE) of CO2 and N2O emissions whereas CH4 emissions increased. Total cumulative GHG emissions (for 10 months) corresponded to 0.08, 0.13, 0.61, 0.68 and 0.98 kg CO2 equivalents m(-2) from the GWL treatments at 0, -10, -20, -30 and -40 cm below the soil surface, respectively. The results showed that a reduction in total GHG emission can be achieved without losing the productivity of newly established RCG when GWL is maintained close to the surface. Further studies should address the practical constrains and long-term productivity of RCG cultivation in rewetted peatlands.
Article
Cultivated organic soils are a remarkable source of greenhouse gases (GHG) in many countries. Keeping the ground water table as high as possible could lower the mineralization rate of the peat and thus the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) from these soils. We studied the effect of raised water table on the emissions of N2O, CO2 and methane (CH4) from undisturbed peat soil profiles of six different Finnish cultivated organic soils during a 5-week outdoor mesocosm experiment. The aim was to determine an optimum water table that would enable grass cultivation but lower the net gas balance of the soil. Raised water table decreased the GHG emissions from each peat type ranging from weakly decomposed Sphagnum peat to highly humified Carex peat. Based on the results, the optimum water table would be 30 cm below the soil surface. The average reduction of the total net emissions with a raise of water table from a typical drainage depth of 70 to 30 cm was 42 % in the outdoors mesocosm experiment and 23 % at a constant temperature (+6 °C). The emissions of both CO2 and N2O declined and the net consumption of CH4 changed to net production as the water table rose. The results were confirmed by long-term measurements at one of the sampled sites. As a conclusion, we see that promoting drainage systems enabling raising of the ground water table and cultivation of crops capable of producing good yields also in wet conditions would be beneficial for the GHG mitigation in agriculture.
Article
Digitised maps of Quaternary deposits, 40K radiation data and Integrated Agricultural Control System databases (IACS) were used in a GIS analysis to estimate the distribution and land use of agricultural peat and gyttja soils in Sweden. The total area of agricultural land (cropland and pastures) in Sweden was estimated at 3,496,665 ha and 8.6% of this area (301,489 ha) was classified as agricultural peat and gyttja soils, with 202,383 ha of deep peat, 50,191 ha of shallow peat and 48,915 ha of gyttja soils. Using detailed information on crop distribution from agricultural databases, it was possible to estimate the cultivation intensity (land use) of the agricultural land. One-quarter of the agricultural area of peat soils was intensively cultivated with annual crops and the remaining area was extensively used, dominated by managed grasslands and pastures. There was great variation in cultivation intensity between areas, from 50% annual crops down to 10%. The gyttja soils were in general more intensively cultivated than the peat soils. The improved estimates of acreage and cultivation intensity of agricultural peat soils were used to calculate annual greenhouse gas emissions from subsidence data. The total carbon dioxide (CO2) emissions from Swedish agricultural peat soils in 2003 were estimated to be between 3100 Gg CO2 and 4600 Gg CO2, which is similar to or lower than previously reported values. Emissions of nitrous oxide (N2O) were estimated at 3.2 Gg N2O in 2003. Estimated combined total emissions of CO2 and N2O from agricultural peat soils in Sweden in 2003 amounted to 4000–5600 Gg CO2-equivalents, which corresponds to approximately 6–8% of the total emissions of all greenhouse gases reported by Sweden (excluding the sink for land use, land use change and forestry — LULUCF). Agricultural peat soils represent a minor fraction of the agricultural land in Sweden but still have a significant effect on total national greenhouse gas emissions.
Article
A lysimeter method using undisturbed soil columns was used to investigate the effect of water table depth and soil properties on soil organic matter decomposition and greenhouse gas (GHG) emissions from cultivated peat soils. The study was carried out using cultivated organic soils from two locations in Sweden: Örke, a typical cultivated fen peat with low pH and high organic matter content and Majnegården, a more uncommon fen peat type with high pH and low organic matter content. Even though carbon and nitrogen contents differ greatly between the sites, carbon and nitrogen density are quite similar. A drilling method with minimal soil disturbance was used to collect 12 undisturbed soil monoliths (50 cm high, Ø29.5 cm) per site. They were sown with ryegrass (Lolium perenne) after the original vegetation was removed. The lysimeter design allowed the introduction of water at depth so as to maintain a constant water table at either 40 cm or 80 cm below the soil surface. CO2, CH4 and N2O emissions from the lysimeters were measured weekly and complemented with incubation experiments with small undisturbed soil cores subjected to different tensions (5, 40, 80 and 600 cm water column). CO2 emissions were greater from the treatment with the high water table level (40 cm) compared with the low level (80 cm). N2O emissions peaked in springtime and CH4 emissions were very low or negative. Estimated GHG emissions during one year were between 2.70 and 3.55 kg CO2 equivalents m−2. The results from the incubation experiment were in agreement with emissions results from the lysimeter experiments. We attribute the observed differences in GHG emissions between the soils to the contrasting dry matter liability and soil physical properties. The properties of the different soil layers will determine the effect of water table regulation. Lowering the water table without exposing new layers with easily decomposable material would have a limited effect on emission rates.
Article
We incubated intact peat cores from depth intervals of 5-15, 15-25, 25-35, and 35-45 cm from ombrotrophic bog, poor fen, and beaver pond margin sections of a cool-temperate peatland. CO2 production was measured over 12-day incubation periods at 4 and 14 °C and under oxic and anoxic conditions. Rates ranged from 0.06 to 0.66 mg CO2 g-1 dry peat d-1 under oxic conditions and from 0.002 to 0.098 mg CO2 g-1 d-1 under anoxic conditions, and rates generally decreased with depth in the profiles. When expressed on a volumetric basis, production rates ranged from 0.3 to 23.4 g CO2 m-3 d-1, and there was much less variation in CO2 production rates within profiles because the bulk density of peat increased with depth. The Q10 quotient, between 4 and 14 °C, ranged from 1.0 to 7.7, depending on sample and incubation conditions, with an average of 2.0 for oxic and 2.7 for anoxic conditions. Oxic:anoxic ratios averaged 7:1, 16:1, and 12:1 for the bog, poor fen, and beaver pond margin samples, respectively. Degree of decomposition (von Post index) was the substrate property most strongly correlated with CO2 production. Based on temperature and incubation data for the peat profiles to a depth of 45 cm, annual decomposition values (k) ranged from 0.016 to 0.060 yr-1 under oxic conditions and from 0.001 to 0.007 yr-1 under anoxic conditions. A model of CO2 emission from the three sites, based on the incubation data and thermal and water table regime, gave good agreement with measured in situ CO2 emission rates (r2 = 0.72, n = 18), although summer emission rates were underpredicted, possibly because of the absence of a root production component in the incubations or because of underestimation of CO2 production rates in field conditions above the water table.
Article
Peatlands play an important role in emissions of the greenhouse gases CO2, CH4 and N2O, which are produced during mineralization of the peat organic matter. To examine the influence of soil type (fen, bog soil) and environmental factors (temperature, groundwater level), emission of CO2, CH4 and N2O and soil temperature and groundwater level were measured weekly or biweekly in loco over a one-year period at four sites located in Ljubljana Marsh, Slovenia using the static chamber technique. The study involved two fen and two bog soils differing in organic carbon and nitrogen content, pH, bulk density, water holding capacity and groundwater level. The lowest CO2 fluxes occurred during the winter, fluxes of N2O were highest during summer and early spring (February, March) and fluxes of CH4 were highest during autumn. The temporal variation in CO2 fluxes could be explained by seasonal temperature variations, whereas CH4 and N2O fluxes could be correlated to groundwater level and soil carbon content. The experimental sites were net sources of measured greenhouse gases except for the drained bog site, which was a net sink of CH4. The mean fluxes of CO2 ranged between 139 mg m−2 h−1 in the undrained bog and 206 mg m−2 h−1 in the drained fen; mean fluxes of CH4 were between −0.04 mg m−2 h−1 in the drained bog and 0.05 mg m−2 h−1 in the drained fen; and mean fluxes of N2O were between 0.43 mg m−2 h−1 in the drained fen and 1.03 mg m−2 h−1 in the drained bog. These results indicate that the examined peatlands emit similar amounts of CO2 and CH4 to peatlands in Central and Northern Europe and significantly higher amounts of N2O.
Article
Samples (140) of peat collected from bogs, fens and swamps in boreal, subarctic and temperate regions of Canada were incubated at 15 or 20°C for 5 d in the laboratory to determine potential rates of CO2 and CH4 exchange under aerobic and anaerobic conditions. Rates of CO2 production ranged between 0.07 and 5.0 mg g−1 d−1, with means of 1.0 and 0.5 mg CO2 g−1 d−1 for aerobic and anaerobic production rates, respectively. Aerobic and anaerobic CO2 production rates were strongly correlated (r = 0.581, P < 0.001, log10 transformation) with the former an average of 2.5 times larger than the latter. CO2 production rates were greatest in the upper part of peat profile and appeared to be related to the botanical origin of the peat. Aerobic CH4 consumption and anaerobic CH4 production rates ranged from 0.01 to 100 μg CH4 g−1 d−1, with means of 13.1 and 3.1 μg CH4 g−1 d−1, respectively. Rates of CH4 exchange were positively correlated (r = 0.368, P < 0.001, log10 transformation). Within profiles, maximum CH4 consumption occurred in samples collected from beneath or at the water table, whereas CH4 production occurred mainly in samples collected from beneath the water table. There was no significant correlation between aerobic CH4 consumption and CO2 production, but anaerobic CH4 production was positively correlated with CO2 production (r = 0.36, P < 0.001).
Article
Northern peatlands contain a considerable share of the terrestrial carbon (C) pool, which climate change will likely affect in the future. The magnitude of this effect, however, remains uncertain, due mainly to difficulties in predicting decomposition rates in the old peat layers. We studied the effects of water level depth (WL) and soil temperature on heterotrophic soil respiration originating from peat decomposition (RPD) in six drained peatlands using a chamber technique. The microbial community structure was determined through PLFA. Within the studied sites, temperature appeared to be the main driver of RPD. However, our results indicate that there exist mechanisms related to lower WL conditions that can tone down the effect of temperature on RPD. These mechanisms were described with a mathematical model that included the optimum WL response of RPD and the effect of average WL conditions on the temperature sensitivity of RPD. The following implications were apparent from the model parameterisation: (1) The instantaneous effect of WL on RPD followed a Gaussian form; the optimum WL for RPD was 61 cm. The tolerance of RPD to the WL, however, was rather broad, indicating that the overall effect of WL was relatively weak. (2) The temperature sensitivity of RPD depended on the average WL of the plot: plots with a high average WL showed higher temperature sensitivity than did those under drier conditions. This variation in temperature sensitivity of RPD correlated with microbial community structure. Thus, moisture stress in the surface peat layer or, alternatively, the lowered temperature sensitivity of RPD in low water level conditions via microbial community structure and biomass may restrict RPD. We conclude that a warmer future climate may raise RPD in drained peatlands only if the subsequent decrease in the moisture of the surface peat layers is minor and, thus, conditions remain favourable for decomposition.
Article
Agricultural peat soils in the Sacramento-San Joaquin Delta, California have been identified as an important source of dissolved organic carbon (DOC) and trihalomethane precursors in waters exported for drinking. The objectives of this study were to examine the primary sources of DOC from soil profiles (surface vs. subsurface), factors (temperature, soil water content and wet–dry cycles) controlling DOC production, and the relationship between C mineralization and DOC concentration in cultivated peat soils. Surface and subsurface peat soils were incubated for 60 d under a range of temperature (10, 20, and 30 °C) and soil water contents (0.3–10.0 g-water g-soil−1). Both CO2–C and DOC were monitored during the incubation period. Results showed that significant amount of DOC was produced only in the surface soil under constantly flooded conditions or flooding/non-flooding cycles. The DOC production was independent of temperature and soil water content under non-flooded condition, although CO2 evolution was highly correlated with these parameters. Aromatic carbon and hydrophobic acid contents in surface DOC were increased with wetter incubation treatments. In addition, positive linear correlations (r2=0.87) between CO2–C mineralization rate and DOC concentration were observed in the surface soil, but negative linear correlations (r2=0.70) were observed in the subsurface soil. Results imply that mineralization of soil organic carbon by microbes prevailed in the subsurface soil. A conceptual model using a kinetic approach is proposed to describe the relationships between CO2–C mineralization rate and DOC concentration in these soils.
Article
Peatlands potentially play a significant role in the global emission of three trace gases: carbon dioxide; methane; and nitrous oxide. We investigated the effect of a relatively small lowering of the water-table (10 cm) on the emission of these gases using repacked, root-free peat columns in the laboratory with peat from a nutrient-rich (eutrophic) site and a more nutrient-poor (mesotrophic) site, respectively. At a static high water-table (at the peat surface) high rates of anaerobic CO2 production were found, which were reflected in high (> 1.18) molar ratios of CO2 and CH4. A static water-table of 10 cm below soil surface led to equal (eutrophic soil) or lower CO2 emission (mesotrophic soil) compared with the high static water-table. However, at a regularly changing water-table (between 0 and 10 cm below the peat surface), CO2 emission at a low water-table was 1.5 (mesotrophic soil) to 3 times (eutrophic soil) higher than at a high-water table. Maximum rates of CO2 emission from the eutrophic soil exceeded those from the mesotrophic soil, except at a static high water-table. Methane emission was about one order of magnitude lower at a low static water-table compared with the static high water-table. There was no clear effect of the nutritional status of the peat on maximum methane emission in the various water-table treatments. The nutritional status of the peat had a profound influence on the effect of water-table lowering on N2O emission: nitrous oxide emission from the eutrophic soil was strongly increased at a low water-table, whereas there was no detectable N2O emission from the mesotrophic soil. Despite a clear effect of the water-table treatments on both trace gas emissions and on redox potentials in the soil, no significant correlation between these variables was found in either soil type.
Article
Five main biogenic sources of CO2 efflux from soils have been distinguished and described according to their turnover rates and the mean residence time of carbon. They are root respiration, rhizomicrobial respiration, decomposition of plant residues, the priming effect induced by root exudation or by addition of plant residues, and basal respiration by microbial decomposition of soil organic matter (SOM). These sources can be grouped in several combinations to summarize CO2 efflux from the soil including: root-derived CO2, plant-derived CO2, SOM-derived CO2, rhizosphere respiration, heterotrophic microbial respiration (respiration by heterotrophs), and respiration by autotrophs. These distinctions are important because without separation of SOM-derived CO2 from plant-derived CO2, measurements of total soil respiration have very limited value for evaluation of the soil as a source or sink of atmospheric CO2 and for interpreting the sources of CO2 and the fate of carbon within soils and ecosystems. Additionally, the processes linked to the five sources of CO2 efflux from soil have various responses to environmental variables and consequently to global warming. This review describes the basic principles and assumptions of the following methods which allow SOM-derived and root-derived CO2 efflux to be separated under laboratory and field conditions: root exclusion techniques, shading and clipping, tree girdling, regression, component integration, excised roots and insitu root respiration; continuous and pulse labeling, 13C natural abundance and FACE, and radiocarbon dating and bomb-14C. A short sections cover the separation of the respiration of autotrophs and that of heterotrophs, i.e. the separation of actual root respiration from microbial respiration, as well as methods allowing the amount of CO2 evolved by decomposition of plant residues and by priming effects to be estimated. All these methods have been evaluated according to their inherent disturbance of the ecosystem and C fluxes, and their versatility under various conditions. The shortfalls of existing approaches and the need for further development and standardization of methods are highlighted.
Article
A lysimeter method was evaluated for its suitability in gas emission studies by studying the effect of temperature on CO2 emissions (dark respiration) from cultivated peat soils. The study was carried out with organic soils from two locations in Sweden, a typical cultivated fen peat with low pH and high organic matter content (Örke) and a more uncommon fen peat with high pH and low organic matter content (Majnegården). A drilling method with minimal soil disturbance was used to collect 12 undisturbed soil lysimeters per site. CO2 emission was measured weekly from the vegetated lysimeters and the results were compared with data from incubation experiments. The CO2 emissions measured in the lysimeter experiment were in the same range as those in other studies and showed a similar increase with temperature as in the incubation experiment. With climatic and drainage conditions being similar in the lysimeter experiment, differences in daytime CO2 emission rates between soils (483 mg ± 6.9 CO2 m-2 h-1 from the Örke soil and 360 ± 7.5 mg CO2 m-2 h-1 from the Majnegården soil) were presumably due to soil quality differences. Q10 values of 2.1 and 3.0 were determined in the lysimeter experiment and of 1.9 to 4.5 in the incubation experiment for Örke and Majnegården respectively. CO2 emission data fitted well to a semi-empirical equation relating CO2 emissions to air temperature. The lysimeter method proved to be well suited for CO2 emission studies.
Institutionen för markvetenskap, avdelningen för lantbrukets hydroteknik
  • K Berglund
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Utsläpp av Växthusgaser från Torvmark (Emissions of Greenhouse Gases from Peat Soils)
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The Global Peatland CO2 Picture: Peatland Status and Drainage Related Emissions in all
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Romano, N., Hopmans, J.W. & Dane, J.H. (2002) Suction Table. In: Dane, J.H. & Topp, C.G. (eds.) Methods of Soil Analysis, Part 4-Physical Methods. Soil Science Society of America, Madison, Wisconsin, USA, 692-698.
Natural Resources Conservation Service, United States Department of Agriculture (USDA)
Soil Survey Staff (2014) Keys to Soil Taxonomy, Twelfth Edition. Natural Resources Conservation Service, United States Department of Agriculture (USDA), Washington DC, 372 pp. Online at: https://www.nrcs.usda.gov/wps/portal/nrcs/detail /soils/survey/class/taxonomy/?cid=nrcs142p2_05 3580, accessed 02 Mar 2018.
Sveriges Geologiska Undersöknings torvinventering och några av dess hittills vunna resultat (Geological Survey of Sweden's peat inventory and some of its achievements so far). Svenska Mosskulturföreningens tidskrift
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Heinichen, J., Hoffmann, M., Höper, H., Jurasinski, G., Leiber-Sauheitl, K., Peichl-Brak, M., Roßkopf, N., Sommer, M. & Zeitz, J. (2016) High emissions of greenhouse gases from grasslands on peat and other organic soils. Global Change Biology, 22, 4134-4149. von Post, L. (1922) Sveriges Geologiska Undersöknings torvinventering och några av dess hittills vunna resultat (Geological Survey of Sweden's peat inventory and some of its achievements so far). Svenska Mosskulturföreningens tidskrift, 36, 1-27 (in Swedish).
Land Use on Organic Soils in Sweden -a Survey on the Land Use of Organic Soils Within Agriculture and Forest Lands During
  • S Pahkakangas
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Pahkakangas, S., Berglund, Ö., Lundblad, M. & Karltun, E. (2016) Land Use on Organic Soils in Sweden -a Survey on the Land Use of Organic Soils Within Agriculture and Forest Lands During 1983-2014. Report 21, Department of Soil and Environment, Uppsala, 37 pp.