Atmosphere-soil-stream greenhouse gas fluxes from peatlands

The project aims to produce a complete inventory of greenhouse gas fluxes and emissions from a Scottish peatland. Carbon dioxide, methane and nitrous oxide emissions from the land surface (soil and vegetation) to the atmosphere, losses to streamwater and degassing will all be considered. The study is carried out at Auchencorth Moss, Midlothian, with intensive monitoring and measurements being made over a 2-year period, starting March 2006. The site consists of a patchwork of different vegetation communities including areas dominated by Calluna or Juncus, grassy hummocks and hollows and a narrow riparian zone again dominated by Juncus. GHG flux measurements will be made using chambers covering each vegetation type allowing for both a comparison between vegetation types and the subsequent scaling up to catchment level emissions. A flux tower on site provides further data on CO2 net exchange. In addition the concentrations of GHG in the soil are measured using gas permeable tubing. Other land based measurements will include water table depth, soil moisture, soil temperature and soil NO3, NH4 and DOC content. A datalogger is in place adjacent to the stream allowing for almost continuous measurements of stream temperature, conductivity and height; this data along with regular measurements of stream solute and dissolved gas concentrations will be used to estimate both stream gaseous emissions and lateral outputs. Routine measurements of carbon (DOC, DIC, POC, CO2 and CH4) and nitrogen (NO3, NH4, DON, N2O) will also be made along the stream length to measure spatial variability

Review of existing information on the interrelations between soil and climate change. (ClimSoil). Final report

Carbon stock in EU soils – The soil carbon stocks in the EU27 are around 75 billion tonnes of carbon (C); of this stock around 50% is located in Sweden, Finland and the United Kingdom (because of the vast area of peatlands in these countries) and approximately 20% is in peatlands, mainly in countries in the northern part of Europe. The rest is in mineral soils, again the higher amount being in northern Europe. 2. Soils sink or source for CO2 in the EU – Both uptake of carbon dioxide (CO2) through photosynthesis and plant growth and loss of CO2 through decomposition of organic matter from terrestrial ecosystems are significant fluxes in Europe. Yet, the net terrestrial carbon fluxes are typically 5-10 times smaller relative to the emissions from use of fossil fuel of 4000 Mt CO2 per year. 3. Peat and organic soils - The largest emissions of CO2 from soils are resulting from land use change and especially drainage of organic soils and amount to 20-40 tonnes of CO2 per hectare per year. The most effective option to manage soil carbon in order to mitigate climate change is to preserve existing stocks in soils, and especially the large stocks in peat and other soils with a high content of organic matter. 4. Land use and soil carbon – Land use and land use change significantly affects soil carbon stocks. On average, soils in Europe are most likely to be accumulating carbon on a net basis with a sink for carbon in soils under grassland and forest (from 0 - 100 billion tonnes of carbon per year) and a smaller source for carbon from soils under arable land (from 10 - 40 billion tonnes of carbon per year). Soil carbon losses occur when grasslands, managed forest lands or native ecosystems are converted to croplands and vice versa carbon stocks increase, albeit it slower, following conversion of cropland. 5. Soil management and soil carbon – Soil management has a large impact on soil carbon. Measures directed towards effective management of soil carbon are available and identified, and many of these are feasible and relatively inexpensive to implement. Management for lower nitrogen (N) emissions and lower C emissions is a useful approach to prevent trade off and swapping of emissions between the greenhouse gases CO2, methane (CH4) and nitrous oxide (N2O). 6. Carbon sequestration – Even though effective in reducing or slowing the build up of CO2 in the atmosphere, soil carbon sequestration is surely no ‘golden bullet’ alone to fight climate change due to the limited magnitude of its effect and its potential reversibility; it could, nevertheless, play an important role in climate mitigation alongside other measures, especially because of its immediate availability and relative low cost for 'buying' us time. 7. Effects of climate change on soil carbon pools – Climate change is expected to have an impact on soil carbon in the longer term, but far less an impact than does land use change, land use and land management. We have not found strong and clear evidence for either overall and combined positive of negative impact of climate change (atmospheric CO2, temperature, precipitation) on soil carbon stocks. Due to the relatively large gross exchange of CO2 between atmosphere and soils and the significant stocks of carbon in soils, relatively small changes in these large and opposing fluxes of CO2, i.e. as result of land use (change), land management and climate change, may have significant impact on our climate and on soil quality. 8. Monitoring systems for changes in soil carbon – Currently, monitoring and knowledge on land use and land use change in EU27 is inadequate for accurate calculation of changes in soil carbon contents. Systematic and harmonized monitoring across EU27 and across relevant land uses would allow for adequate representation of changes in soil carbon in reporting emissions from soils and sequestration in soils to the UNFCCC. 9. EU policies and soil carbon – Environmental requirements under the Cross Compliance requirement of CAP is an instrument that may be used to maintain SOC. Neither measures under UNFCCC nor those mentioned in the proposed Soil Framework Directive are expected to adversely impact soil C. EU policy on renewable energy is not necessarily a guarantee for appropriate (soil) carbon management

Effects of peatland management on aquatic carbon concentrations and fluxes

Direct land-to-atmosphere carbon exchange has been the primary focus in previous studies of peatland disturbance and subsequent restoration. However, loss of carbon via the fluvial pathway is a significant term in peatland carbon budgets and requires consideration to assess the overall impact of restoration measures. This study aimed to determine the effect of peatland land management regime on aquatic carbon concentrations and fluxes in an area within the UK's largest tract of blanket bog, the Flow Country of northern Scotland. Three sub-catchments were selected to represent peatland land management types: non-drained, drained, and restoration (achieved through drain blocking and tree removal). Water samples were collected on a fortnightly basis from September 2008 to August 2010 at six sampling sites, one located upstream and one downstream within each sub-catchment. Concentrations of dissolved organic carbon (DOC) were significantly lower for the upstream non-drained sub-catchment compared to the drained sub-catchments, and there was considerable variation in the speciation of aquatic carbon (DOC, particulate organic carbon (POC), CO2, and CH4) across the monitoring sites, with dissolved gas concentrations inversely correlated with catchment area and thereby contributing considerably more to total aquatic carbon in the smaller headwater catchments. Significantly higher POC concentrations were observed in the restored sub-catchment most affected by tree removal. Aquatic carbon fluxes were highest from the drained catchments and lowest from the non-drained catchments at 23.5 and 7.9 g C m−2 yr−1, respectively, with variability between the upstream and downstream sites within each catchment being very low. It is clear from both the aquatic carbon concentration and flux data that drainage has had a profound impact on the hydrological and biogeochemical functioning of the peatland. In the restoration catchment, carbon export varied considerably, from 21.1 g C m−2 yr−1 at the upper site to 10.0 g C m−2 yr−1 at the lower site, largely due to differences in runoff generation. As a result of this hydrological variability, it is difficult to make definitive conclusions about the impact of restoration on carbon fluxes, and further monitoring is needed to corroborate the longer-term effects

Carbon concentrations in natural and restoration pools in blanket peatlands

Open-water perennial pools are common natural features of peatlands globally, and peatland restoration often results in new pool creation, yet the concentrations of different forms of aquatic carbon (C) in natural and artificial restoration pools are not well studied. We compared carbon concentrations in both natural pools and restoration pools (4–15 years old) on three blanket peatlands in northern Scotland. At all sites, restoration pools were more acidic and had mean dissolved organic carbon (DOC) concentrations in restoration pools of 23, 22, and 31 mg L−1 compared with natural pool means of 11, 11 and 15 mg L−1 respectively across the three sites. Restoration pools had a greater fulvic acid prevalence than the natural pools and their DOC was more aromatic. Restoration pools were supersaturated with dissolved CO2 at around 10 times atmospheric levels, whereas for natural pools, CO2 concentrations were just above atmospheric levels. Dissolved CH4 concentrations were not different between pool types, but were ~200 times higher than atmospheric levels. Regular sampling at one of the peatland sites over 2.5 years showed that particulate organic carbon (POC) concentrations were generally below 7 mg L−1 except during the warm, dry summer of 2013. At this regularly-sampled site, natural pools were found to process DOC so that mean pool outflow concentrations in overland flow were significantly lower than mean inflow DOC concentrations. Such an effect was not found for the restoration pools. Soil solution and pool water chemistry, and relationships between DOC and CO2 concentrations suggest that different processes are controlling the transformation of C, and therefore the form and amount of C, in natural pools compared to restoration pools

Water-level dynamics in natural and artificial pools in blanket peatlands

Perennial pools are common natural features of peatlands and their hydrological functioning and turnover may be important for carbon fluxes, aquatic ecology and downstream water quality. Peatland restoration methods such as ditch blocking result in many new pools. However, little is known about the hydrological function of either pool type. We monitored six natural and six artificial pools on a Scottish blanket peatland. Pool water levels were more variable in all seasons in artificial pools having greater water level increases and faster recession responses to storms than natural pools. Pools overflowed by a median of 9 and 54 times pool volume per year for natural and artificial pools respectively but this varied widely because some large pools had small upslope catchments and vice versa. Mean peat water-table depths were similar between natural and artificial pool sites but much more variable over time at the artificial pool site, possibly due to a lower bulk specific yield across this site. Pool levels and pool-level fluctuations were not the same as those of local water tables in the adjacent peat. Pool level time-series were much smoother, with more damped rainfall or recession responses than those for peat water tables. There were strong hydraulic gradients between the peat and pools, with absolute water tables often being 20-30 cm higher or lower than water levels in pools only 1-4 m away. However, as peat hydraulic conductivity was very low (median of 1.5×10-5 and 1.4×10-6 cm s-1 at 30 and 50 cm depths at the natural pool site) there was little deep subsurface flow interaction. We conclude that: 1) for peat restoration projects, a larger total pool surface area is likely to result in smaller flood peaks downstream, at least during summer months, because peatland bulk specific yield will be greater; and 2) surface and near-surface connectivity during storm events and topographic context, rather than pool size alone, must be taken into account in future peatland pool and stream chemistry studies

Variability in CO2 concentrations and sources in a peatland stream during storm-flow events

Peatland streams are known to be supersaturated in CO2 with respect to the atmosphere [Billett and Moore, 2007; Dawson et al., 1995; Hope et al., 2001], and as such potentially represent an important conduit for the release of soil derived carbon to the atmosphere. However, relatively little is known about short-term temporal variability in CO2 concentrations in response to the extreme hydrological events which make up a large proportion of the annual flow regime. Here we use submerged, non-dispersive infra-red (NDIR) sensors to make continuous measurements of CO2 concentrations during 18 storm events in a Scottish peatland stream. Individual storms exhibited 3 distinct types of hysteresis loop. We suggest that differences in loop form may be due to differences in the relative contributions of soil water or differences in contributing catchment source area. We found a negative concentration-discharge relationship over the full study period, suggesting that CO2 rich deep peat/ground water was the major source of aquatic CO2 under low flow conditions. By removing the effect of dilution and estimating additions and losses of CO2, we also show the importance of both surface peat CO2 inputs into the stream and evasion loss during stormflow. Downstream CO2 export during the study period was dominated by stormflow events (71%), highlighting the importance of accurately accounting for high flow CO2 sources

Scoping study to determine feasibility of populating the land use component of the LULUCF GHG inventory. Final report

There is a need to protect and enhance the vast stocks of carbon (>10 billion tonnes) stored in UK soils, both to mitigate climate change through increased carbon sequestration in soils and to prevent potential climate change impacts resulting from soil carbon loss. To do this we need to be able to quantify, verify and report the emissions and removals of greenhouse gases (GHG) from soils as a result of land management practices and land use change. The main tool used to (calculate and) report the greenhouse gas emissions and removals associated with changes in soil carbon is the Land Use, Land Use Change and Forestry (LULUCF) component of the UK GHG Inventory. The coverage of soil carbon fluxes in the inventory, particularly with respect to land management rather than land use change, is currently limited. The aim of the project is to determine the feasibility of populating the land use component of the LULUCF GHG inventory. The research needs for this project are divided into four tasks: 1. Scoping the feasibility of populating the land use/management component of the LULUCF inventory in order to capture soil carbon fluxes associated with land management and associated greenhouse gas emissions and removals. This is the main focus of the project. 2. Exploration of the methodology for calculating emissions from the management and use of peatlands. 3. Improving the robustness and transparency of the methodology for calculating emissions from the extraction of peat for horticultural use. 4. Exploration of how to improve the methodology for the Land Use Change component of the inventory to address policy question

Atmosphere-soil-stream greenhouse gas fluxes from peatlands

Peatlands cover approximately 2-3% of the world’s land area yet represent approximately a third of the worlds estimated total soil carbon pool. They therefore play an important role in regulating global atmospheric CO2 and CH4 concentrations, and even minor changes in their ability to store carbon could potentially have significant effects on global climate change. Much previous research has focussed primarily on land-atmosphere fluxes. Where aquatic fluxes have been considered, they are often in isolation from the rest of the catchment and usually focus on downstream losses, ignoring evasion (degassing) from the water surface. However, as peatland streams have been repeatedly shown to be highly supersaturated in both CO2 and CH4 with respect to the atmosphere, they potentially represent an important pathway for catchment GHG losses. This study aimed to a) create a complete GHG and carbon budget for Auchencorth Moss catchment, Scotland, linking both terrestrial and aquatic fluxes, and b) understand what controls and drives individual fluxes within this budget. This understanding was further developed by a short study of C exchange at the peat-aquatic interface at Mer Bleue peatland, Canada. Significant variability in soil-atmosphere fluxes of both CH4 and N2O emissions was evident at Auchencorth Moss; coefficients of variation across 21 field chambers were 300% and 410% for CH4 and N2O, respectively. Both in situ chamber measurements and a separate mesocosm study illustrated the importance of vegetation in controlling CH4 emissions. In contrast to many previous studies, CH4 emissions were lower and uptake greater where aerenchymous vegetation was present. Water table depth was also an important driver of variability in CH4 emissions, although the effect was only evident during either periods of extreme drawdown or when the water table was consistently near or above the peat surface. Significant pulses in both CH4 and N2O emissions were observed in response to fluctuations in water table depth. Despite the variability in CH4 and N2O emissions and the uncertainty in up-scaled estimates, their contribution to the total GHG and carbon budgets was minor. Concentrations of dissolved CO2 in peatland drainage waters ranged from a mean of 2.88 ± 0.09 mg C L-1 in the Black Burn, Scotland, to a mean of 7.64 ± 0.80 mg C L-1 in water draining Mer Bleue, Canada. Using non-dispersive infra-red (NDIR) CO2 sensors with a 10-minute measurement frequency, significant temporal variability was observed in aquatic CO2 concentrations at the 2 contrasting field sites. However, the drivers of this variability differed significantly. At Mer Bleue, Canada, biological activity in the water column led to clear diurnal cycles, whereas in the Black Burn draining Auchencorth Moss, dilution due to discharge was the primary driver. The NDIR sensor data also showed differences in soil-stream connectivity both between the sites (connectivity was weak at Mer Bleue) and across the range of conditions measured at Auchencorth Moss i.e. connectivity increased during periods of stormflow. Compiling the results from both the terrestrial and aquatic systems at Auchencorth Moss indicated that the catchment was functioning as a net sink for GHGs (382 kg CO2-eq ha-1 yr-1) and a net source of carbon (143 kg C ha-1 yr-1). The greatest flux of GHGs was via net ecosystem exchange (NEE). Terrestrial emissions of CH4 and N2O combined returned only ~5% of CO2-equivalents captured by NEE to the atmosphere, whereas evasion of CO2, CH4 and N2O from the stream surface returned ~40%. The budgets clearly show the importance of aquatic fluxes at Auchencorth Moss and highlight the potential for significant error in source/sink strength calculations if they are omitted. Furthermore, the process based understanding of soil-stream connectivity suggests the aquatic flux pathway may play an increasingly important role in the source-sink function of peatlands under future management and climate change scenarios.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A multisite analysis of the role of high flow extremes on aquatic DOC export

The release of soil derived DOC into river systems is a major C transport pathway in many upland catchments, particularly where organic-rich soils dominate. Aquatic C export (of which DOC is the primary component) represents 30-50% of C uptake via NEE in peatland catchments. Both soil-stream transport and downstream export of DOC are highly sensitive to changes in hydrological regime and are therefore greatly influenced by climatic extremes such as storm flow and snow melt. Here we utilise long-term DOC datasets from 8 UK streams provided by the ‘Environmental Change Network’ (ECN), alongside long-term datasets from 6 Swedish streams, to investigate the relative contribution of storm flow events to total annual DOC export. We consider seasonality in the contribution of high flow events to total DOC export, and compare the storm flow responses across catchments considering catchment characteristics such as vegetation community, soil type and hydrological regime. Finally, by combining the information gained in the aforementioned analysis we will consider how DOC export is likely to respond to predicted changes in regional precipitation patterns