Drainage has turned peatlands from a carbon sink into one of the world's largest greenhouse gas (GHG) sources from cultivated soils. We analyzed a unique data set (12 peatlands, 48 sites and 122 ...annual budgets) of mainly unpublished GHG emissions from grasslands on bog and fen peat as well as other soils rich in soil organic carbon (SOC) in Germany. Emissions and environmental variables were measured with identical methods. Site‐averaged GHG budgets were surprisingly variable (29.2 ± 17.4 t CO2‐eq. ha−1 yr−1) and partially higher than all published data and the IPCC default emission factors for GHG inventories. Generally, CO2 (27.7 ± 17.3 t CO2 ha−1 yr−1) dominated the GHG budget. Nitrous oxide (2.3 ± 2.4 kg N2O‐N ha−1 yr−1) and methane emissions (30.8 ± 69.8 kg CH4‐C ha−1 yr−1) were lower than expected except for CH4 emissions from nutrient‐poor acidic sites. At single peatlands, CO2 emissions clearly increased with deeper mean water table depth (WTD), but there was no general dependency of CO2 on WTD for the complete data set. Thus, regionalization of CO2 emissions by WTD only will remain uncertain. WTD dynamics explained some of the differences between peatlands as sites which became very dry during summer showed lower emissions. We introduced the aerated nitrogen stock (Nair) as a variable combining soil nitrogen stocks with WTD. CO2 increased with Nair across peatlands. Soils with comparatively low SOC concentrations showed as high CO2 emissions as true peat soils because Nair was similar. N2O emissions were controlled by the WTD dynamics and the nitrogen content of the topsoil. CH4 emissions can be well described by WTD and ponding duration during summer. Our results can help both to improve GHG emission reporting and to prioritize and plan emission reduction measures for peat and similar soils at different scales.
1. A valid strategy to mitigate the eutrophication of water bodies due to non-point source phosphorus (P) pollution and to reduce the emissions of greenhouse gases is the rewetting of degraded ...peatlands. However, long-term drainage and intensive agricultural use make it unlikely that the original sink functions for nutrients and carbon (C) as well as low-nutrient conditions can be re-established within a human time perspective. 2. We hypothesized that the removal of the upper degraded peat layer can be a suitable measure to avoid the negative implications of excess mobilization of P and C after rewetting. To evaluate the effect of top soil removal (TSR) we performed lab and field experiments in six inundated peatlands in northern Germany without TSR compared to six inundated sites with TSR. In addition, we included data from a rewetted peatland where the degraded peat had been removed from about half of the area and groundwater level was just beneath the soil surface. 3. The results emphasized that following inundation newly formed detritus mud layers overlying the former peat surface are the dominating source for P and methane in particular in sites without TSR but also in sites with TSR, although at significantly lower rates. Although highly decomposed peat released more or less no methane, dissolved organic matter mobilization was highest in this substrate while less decomposed peat was characterized in general by lowest rates of mobilization. 4. Synthesis and applications. Top soil removal prior to rewetting can be a suitable method to avoid the negative consequences of the excess release of phosphorus (P) and carbon post-rewetting. We developed a simple decision support schematic to assist the peatland restoration process and to better understand the implications of top soil removal. Despite the potential benefits, top soil removal should not be declared as a universal method, as it requires detailed consideration prior to application. However, this and other research demonstrate that it is inevitable that without any further management interventions high mobilization of P, dissolved organic matter and methane may persist for centuries following rewetting of peatlands.
Drained peatlands in temperate Europe are a globally important source of greenhouse gas (GHG) emissions. This article outlines a methodology to assess emissions and emission reductions from peatland ...rewetting projects using vegetation as a proxy. Vegetation seems well qualified for indicating GHG fluxes from peat soils as it reflects long-term water level, affects GHG emissions via assimilate supply and aerenchyma and allows fine-scaled mapping. The methodology includes mapping of vegetation types characterised by the presence and absence of species groups indicative for specific water level classes. GHG flux values are assigned to the vegetation types following a standardized protocol and using published emission values from plots with similar vegetation and water level in regions with similar climate and flora. Carbon sequestration in trees is accounted for by estimating the annual sequestration in tree biomass from forest inventory data. The method follows the criteria of the Voluntary Carbon Standard and is illustrated using the example of two Belarusian peatlands.
Manual closed‐chamber measurements are commonly used to quantify annual net CO2 ecosystem exchange (NEE) in a wide range of terrestrial ecosystems. However, differences in both the acquisition and ...gap filling of manual closed‐chamber data are large in the existing literature, complicating inter‐study comparisons and meta analyses. The aim of this study was to compare common approaches for quantifying CO2 exchange at three methodological levels. (1) The first level included two different CO2 flux measurement methods: one via measurements during mid‐day applying net coverages (mid‐day approach) and one via measurements from sunrise to noon (sunrise approach) to capture a span of light conditions for measurements of NEE with transparent chambers. (2) The second level included three different methods of pooling measured ecosystem respiration (RECO) fluxes for empirical modeling of RECO: campaign‐wise (19 single‐measurement‐day RECO models), season‐wise (one RECO model for the entire study period), and cluster‐wise (two RECO models representing a low and a high vegetation status). (3) The third level included two different methods of deriving fluxes of gross primary production (GPP): by subtracting either proximately measured RECO fluxes (direct GPP modeling) or empirically modeled RECO fluxes from measured NEE fluxes (indirect GPP modeling). Measurements were made during 2013–2014 in a lucerne‐clover‐grass field in NE Germany. Across the different combinations of measurement and gap‐filling options, the NEE balances of the agricultural field diverged strongly (–200 to 425 g CO2‐C m−2). NEE balances were most similar to previous studies when derived from sunrise measurements and indirect GPP modeling. Overall, the large variation in NEE balances resulting from different data‐acquisition or gap‐filling strategies indicates that these methodological decisions should be made very carefully and that they likely add to the overall uncertainty of greenhouse gas emission factors. Preferably, a standard approach should be developed to reduce the uncertainty of upscaled estimates.
In 2001 and 2002, fluxes of N
2O, CH
4, CO
2 and N
2 were measured in two constructed wetlands (CW) for domestic wastewater treatment in Estonia. The difference between the median values of N
2O, CH
...4, and N
2 fluxes in the horizontal subsurface flow (HSSF) CWs was non-significant, being 1.3–1.4 and 1.4–4.1 mg m
−
2
d
−
1
for N
2O–N and CH
4–C, and 0.16–0.17 g N m
−
2
d
−
1
for N
2–N respectively. The CO
2–C flux was significantly lower (0.6 g C m
−
2
d
−
1
) in one of the HSSF filters of a hybrid CW, whereas the single HSSF and VSSF filters emitted 1.7 and 2.0 g C m
−
2
d
−
1
. The median value of CH
4–C emission in CWs varied from 1.4 to 42.6 g C m
−
2
d
−
1
, being significantly higher in the VSSF filter beds. We also estimated C and N budgets in one of the HSSF CWs (312.5 m
2) for 2001 and 2002. The total C input into this system was similar in 2001 and 2002, 772 and 719 kg C year
−
1
, but was differently distributed between constituent fluxes. In 2001, the main input flux was soil and microbial accumulation (663 kg C year
−
1
or 85.8% of total C input), followed by plant net primary production (NPP) (10.2%) and wastewater inflow (3.9%). In 2002, 55.7% of annual C input was bound in plant NPP, whereas the increase in soil C formed 28.5% and wastewater inflow 15.7%. The main C output flux was soil respiration, including microbial respiration from soil and litter, and the respiration of roots and rhizomes. It formed 120 (97.5%) and 230 kg C year
−
1
(98.2%) in 2001 and 2002 respectively. The measured CH
4–C flux remained below 0.1% of total C output. The HSSF CW was generally found to be a strong C sink, and its annual C sequestration was 649 and 484 kg C year
−
1
per wetland in 2001 and 2002 respectively. However, negative soil and microbial accumulation values in recent years indicate decreasing C sequestration. The average annual N removal from the system was 38–59 kg N year
−
1
(46–48% of the initial total N loading). The most important flux of the N budget was N
2–N emission (22.7 kg in 2001 and 15.2 kg in 2002), followed by plant belowground assimilation (2.3 and 11.9 kg N year
−
1
in 2001 and 2002), and above-ground assimilation (1.9 and 9.2 kg N year
−
1
, respectively). N
2O emission was low: 0.37–0.60 kg N year
−
1
.
We studied greenhouse gas (GHG) fluxes in two differently loaded riparian
Alnus incana-dominated forests in agricultural landscapes of southern Estonia: a 33-year-old stand in Porijõgi, in which the ...uphill agricultural activities had been abandoned since the middle of the 1990s, and a 50-year-old stand in Viiratsi, which still receives polluted lateral flow from uphill fields fertilized with pig slurry. In Porijõgi, closed-chamber based sampling lasted from October 2001 to October 2009, whereas in Viiratsi the sampling period was from November 2003 to October 2009. Both temporal and spatial variations in all GHG gas fluxes were remarkable. Local differences in GHG fluxes between micro-sites (“Edge”, “Dry” and “Wet” in Porijõgi, and “Wet”, “Slope” and “Dry” in Viiratsi) were sometimes greater than those between sites. Median values of GHG fluxes from both sites over the whole study period and all microsites did not differ significantly, being 45 and 42
mg CO
2–C
m
−2
h
−1, 8 and 0.5
μg CH
4–C
m
−2
h
−1, 1.0 and 2.1
mg
N
2–N
m
−2
h
−1, and 5 and 9
μg
N
2O–N
m
−2
h
−1, in Porijõgi and Viiratsi, respectively. The N
2:N
2O ratio in Viiratsi (40–1200) was lower than in Porijõgi (10–7600). The median values-based estimation of the Global Warming Potential of CH
4 and N
2O was 19 and 185
kg CO
2 equivalents (eq)
ha
−1
yr
−1 in Porijõgi and −14 and 336
kg CO
2 eq
ha
−1
yr
−1 in Viiratsi, respectively. A significant Spearman rank correlation was found between the mean monthly air temperature and CO
2, CH
4 and N
2 fluxes in Porijõgi, and N
2O flux in Viiratsi, and between the monthly precipitation and CH
4 fluxes in both study sites. Higher groundwater level significantly increases CH
4 emission and decreases CO
2 and N
2O emission, whereas higher soil temperature significantly increases N
2O, CH
4 and N
2 emission values. In Porijõgi, GHG emissions did not display any discernable trend, whereas in Viiratsi a significant increase in CO
2, N
2, and N
2O emissions has been found. This may be a result of the age of the grey alder stand, but may also be caused by the long-term nutrient load of this riparian alder stand, which indicates a need for the management of similar heavily loaded riparian alder stands.
Processes driving the production, transformation and transport of methane (CH4) in wetland ecosystems are highly complex. We present a simple calculation algorithm to separate open-water CH4 fluxes ...measured with automatic chambers into diffusion- and ebullition-derived components. This helps to reveal underlying dynamics, to identify potential environmental drivers and, thus, to calculate reliable CH4 emission estimates. The flux separation is based on identification of ebullition-related sudden concentration changes during single measurements. Therefore, a variable ebullition filter is applied, using the lower and upper quartile and the interquartile range (IQR). Automation of data processing is achieved by using an established R script, adjusted for the purpose of CH4 flux calculation. The algorithm was validated by performing a laboratory experiment and tested using flux measurement data (July to September 2013) from a former fen grassland site, which converted into a shallow lake as a result of rewetting. Ebullition and diffusion contributed equally (46 and 55%) to total CH4 emissions, which is comparable to ratios given in the literature. Moreover, the separation algorithm revealed a concealed shift in the diurnal trend of diffusive fluxes throughout the measurement period. The water temperature gradient was identified as one of the major drivers of diffusive CH4 emissions, whereas no significant driver was found in the case of erratic CH4 ebullition events.
Landscapes can be viewed as spatially heterogeneous areas encompassing terrestrial and aquatic domains. To date, most landscape carbon (C) fluxes have been estimated by accounting for terrestrial ...ecosystems, while aquatic ecosystems have been largely neglected. However, a robust assessment of C fluxes on the landscape scale requires the estimation of fluxes within and between both landscape components. Here, we compiled data from the literature on C fluxes across the air–water interface from various landscape components. We simulated C emissions and uptake for five different scenarios which represent a gradient of increasing spatial heterogeneity within a temperate young moraine landscape: (I) a homogeneous landscape with only cropland and large lakes; (II) separation of the terrestrial domain into cropland and forest; (III) further separation into cropland, forest, and grassland; (IV) additional division of the aquatic area into large lakes and peatlands; and (V) further separation of the aquatic area into large lakes, peatlands, running waters, and small water bodies These simulations suggest that C fluxes at the landscape scale might depend on spatial heterogeneity and landscape diversity, among other factors. When we consider spatial heterogeneity and diversity alone, small inland waters appear to play a pivotal and previously underestimated role in landscape greenhouse gas emissions that may be regarded as C hot spots. Approaches focusing on the landscape scale will also enable improved projections of ecosystems’ responses to perturbations, e.g., due to global change and anthropogenic activities, and evaluations of the specific role individual landscape components play in regional C fluxes. WIREs Water 2016, 3:601–617. doi: 10.1002/wat2.1147
This article is categorized under:
Water and Life > Nature of Freshwater Ecosystems
Science of Water > Water and Environmental Change
Science of Water > Water Quality
Aims The influence of changing carbon (C) assimilation and relative C partitioning during plant development on the transfer of absolute C amounts (mg C per plant) into the subsurface should be ...analyzed and estimated. Moreover, an approach to determine the precision of the modeled C transfer values should be developed. Methods Several relative .sup.14C partitioning coefficients were derived from pulse labeling experiments at different developmental stages using spring rye as a model plant. Subsequently, relative .sup.14C allocation was dynamically linked with daily shoot C mass increments to obtain precise information about C partitioning at different plant developmental stages and during the entire growing season. Results The transfer of assimilated C into the subsurface during the plant development is a highly dynamic process, in which the maximum root growth preceded maximum shoot growth by approximately 17 days. The model simulations indicate that 18 ± 2 % of all assimilated C that was not respired by shoots was transferred into the subsurface during the entire growing season. This flow splits into 9 ± 0.8 % C for root growth, 6 ± 0.7 % C for belowground respiration, and 3 ± 0.3 % C for detectable rhizodeposition. Nearly half of the downward-transferred C flowed into the subsurface between elongation growth and the last boot stage. Moreover, highly correlated relationships between root growth, rhizodeposition, and belowground respiration were found. Conclusions Our study clearly shows that the dynamic linking of relative C partitioning with absolute C assimilation can provide detailed and precise information about the downward-transferred C during different developmental stages and the entire growing season.
▶ Based on literature data from 950 study sites/experiments of the temperate and boreal zone, a country-wide assessment of the CH
4 and N
2O emissions from rural landscapes has been undertaken. ▶ The ...estimated Global Warming Potential of all land-use types in Estonia from potential CH
4 and N
2O fluxes is about 6 million t of CO
2 equivalents, whereas N
2O is responsible for 86%. ▶ Avoidance of drainage on peatland soils, development of organic agriculture, and the planting of short-rotation energy forests and energy crops can reduce greenhouse gas emissions.
We estimated CH
4 and N
2O emissions from the main land-use types in rural landscapes using data from the literature (950 study sites/experiments from the temperate and boreal zone published from 1980 to 2009 in 165 scientific papers indexed by the ISI Web of Science) and assessed the emission potential of CH
4 and N
2O from rural landscapes in Estonia. According to this analysis, natural peatlands and marshes appeared to be the most important CH
4 emitters, whereas N
2O is emitted mainly from drained peatlands and marshes, set aside areas, conventional arable lands, fertilized grasslands, and coniferous and mixed forests – all on hydromorphic soils. The estimated median value of annual CH
4-C and N
2O-N fluxes for Estonian rural landscapes are 25,519 and 11,050
t respectively. CH
4 consumption makes up 13.2% of the emission. The largest CH
4 emitters are peatlands (17,746
t
CH
4-C
year
−1; 60%), whereas coniferous and mixed forests on hydromorphic soils with altered hydrologic regime are responsible for the bulk (51%) of N
2O fluxes. The Global Warming Potential (GWP) of Estonian rural land-use types (42,685
km
2) from potential CH
4 and N
2O fluxes is 5.99 million t of CO
2 equivalents, of which N
2O is responsible for 86%. Several measures for the further mitigation of greenhouse gas emission from rural landscapes are proposed.
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