Potential of APSIS-InSAR for measuring surface oscillations of tropical peatlands.

Tropical peatland across Southeast Asia is drained extensively for production of pulpwood, palm oil and other food crops. Associated increases in peat decomposition have led to widespread subsidence, deterioration of peat condition and CO2 emissions. However, quantification of subsidence and peat condition from these processes is challenging due to the scale and inaccessibility of dense tropical peat swamp forests. The development of satellite interferometric synthetic aperture radar (InSAR) has the potential to solve this problem. The Advanced Pixel System using Intermittent Baseline Subset (APSIS, formerly ISBAS) modelling technique provides improved coverage across almost all land surfaces irrespective of ground cover, enabling derivation of a time series of tropical peatland surface oscillations across whole catchments. This study aimed to establish the extent to which APSIS-InSAR can monitor seasonal patterns of tropical peat surface oscillations at North Selangor Peat Swamp Forest, Peninsular Malaysia. Results showed that C-band SAR could penetrate the forest canopy over tropical peat swamp forests intermittently and was applicable to a range of land covers. Therefore the APSIS technique has the potential for monitoring peat surface oscillations under tropical forest canopy using regularly acquired C-band Sentinel-1 InSAR data, enabling continuous monitoring of tropical peatland surface motion at a spatial resolution of 20 m.

Net greenhouse gas balance of fibre wood plantation on peat in Indonesia.

Tropical peatlands cycle and store large amounts of carbon in their soil and biomass1-5. Climate and land-use change alters greenhouse gas (GHG) fluxes of tropical peatlands, but the magnitude of these changes remains highly uncertain6-19. Here we measure net ecosystem exchanges of carbon dioxide, methane and soil nitrous oxide fluxes between October 2016 and May 2022 from Acacia crassicarpa plantation, degraded forest and intact forest within the same peat landscape, representing land-cover-change trajectories in Sumatra, Indonesia. This allows us to present a full plantation rotation GHG flux balance in a fibre wood plantation on peatland. We find that the Acacia plantation has lower GHG emissions than the degraded site with a similar average groundwater level (GWL), despite more intensive land use. The GHG emissions from the Acacia plantation over a full plantation rotation (35.2 ± 4.7 tCO2-eq ha-1 year-1, average ± standard deviation) were around two times higher than those from the intact forest (20.3 ± 3.7 tCO2-eq ha-1 year-1), but only half of the current Intergovernmental Panel on Climate Change (IPCC) Tier 1 emission factor (EF)20 for this land use. Our results can help to reduce the uncertainty in GHG emissions estimates, provide an estimate of the impact of land-use change on tropical peat and develop science-based peatland management practices as nature-based climate solutions.

Long-term rise in riverine dissolved organic carbon concentration is predicted by electrolyte solubility theory.

The riverine dissolved organic carbon (DOC) flux is of similar magnitude to the terrestrial sink for atmospheric CO2, but the factors controlling it remain poorly determined and are largely absent from Earth system models (ESMs). Here, we show, for a range of European headwater catchments, that electrolyte solubility theory explains how declining precipitation ionic strength (IS) has increased the dissolution of thermally moderated pools of soluble soil organic matter (OM), while hydrological conditions govern the proportion of this OM entering the aquatic system. Solubility will continue to rise exponentially with declining IS until pollutant ion deposition fully flattens out under clean air policies. Future DOC export will increasingly depend on rates of warming and any directional changes to the intensity and seasonality of precipitation and marine ion deposition. Our findings provide a firm foundation for incorporating the processes dominating change in this component of the global carbon cycle in ESMs.

Rising dissolved organic carbon concentrations in coastal waters of northwestern Borneo related to tropical peatland conversion.

Southeast Asia's peatlands are considered a globally important source of terrigenous dissolved organic carbon (DOC) to the ocean. Human disturbance has probably increased peatland DOC fluxes, but the lack of monitoring has precluded a robust demonstration of such a regional-scale impact. Here, we use a time series of satellite ocean color data from northwestern Borneo to show that DOC concentrations in coastal waters have increased between 2002 and 2021 by 0.31 µmol liter-1 year-1 (95% confidence interval, 0.18 to 0.44 µmol liter-1 year-1). We show that this was caused by a ≥30% increase in the concentration of terrigenous DOC and coincided with the conversion of 69% of regional peatland area to nonforest land cover, suggesting that peatland conversion has substantially increased DOC fluxes to the sea. This rise in DOC concentration has also increased the underwater light absorption by dissolved organic matter, which may affect marine productivity by altering underwater light availability.

Responsible agriculture must adapt to the wetland character of mid-latitude peatlands.

Drained, lowland agricultural peatlands are greenhouse gas (GHG) emission hotspots and a large but vulnerable store of irrecoverable carbon. They exhibit soil loss rates of ~2.0 cm yr-1 and are estimated to account for 32% of global cropland emissions while producing only 1.1% of crop kilocalories. Carbon dioxide emissions account for >80% of their terrestrial GHG emissions and are largely controlled by water table depth. Reducing drainage depths is, therefore, essential for responsible peatland management. Peatland restoration can substantially reduce emissions. However, this may conflict with societal needs to maintain productive use, to protect food security and livelihoods. Wetland agriculture strategies will, therefore, be required to adapt agriculture to the wetland character of peatlands, and balance GHG mitigation against productivity, where halting emissions is not immediately possible. Paludiculture may substantially reduce GHG emissions but will not always be viable in the current economic landscape. Reduced drainage intensity systems may deliver partial reductions in the rate of emissions, with smaller modifications to existing systems. These compromise systems may face fewer hurdles to adoption and minimize environmental harm until societal conditions favour strategies that can halt emissions. Wetland agriculture will face agronomic, socio-economic and water management challenges, and careful implementation will be required. Diversity of values and priorities among stakeholders creates the potential for conflict. Successful implementation will require participatory research approaches and co-creation of workable solutions. Policymakers, private sector funders and researchers have key roles to play but adoption risks would fall predominantly on land managers. Development of a robust wetland agriculture paradigm is essential to deliver resilient production systems and wider environmental benefits. The challenge of responsible use presents an opportunity to rethink peatland management and create thriving, innovative and green wetland landscapes for everyone's future benefit, while making a vital contribution to global climate change mitigation.

Cleaner air reveals growing influence of climate on dissolved organic carbon trends in northern headwaters.

Surface water browning, the result of increasing concentrations of dissolved organic matter (DOM), has been widespread in northern ecosystems in recent decades. Here, we assess a database of 426 undisturbed headwater lakes and streams in Europe and North America for evidence of trends in DOM between 1990 and 2016. We describe contrasting changes in DOM trends in Europe (decelerating) and North America (accelerating), which are consistent with organic matter solubility responses to declines in sulfate deposition. While earlier trends (1990-2004) were almost entirely related to changes in atmospheric chemistry, climatic and chemical drivers were equally important in explaining recent DOM trends (2002-2016). We estimate that riverine DOM export from northern ecosystems increased by 27% during the study period. Increased summer precipitation strengthened upward dissolved organic carbon trends while warming apparently damped browning. Our results suggest strong but changing influences of air quality and climate on the terrestrial carbon cycle, and on the magnitude of carbon export from land to water.

Impact of forest plantation on methane emissions from tropical peatland.

Tropical peatlands are a known source of methane (CH4 ) to the atmosphere, but their contribution to atmospheric CH4 is poorly constrained. Since the 1980s, extensive areas of the peatlands in Southeast Asia have experienced land-cover change to smallholder agriculture and forest plantations. This land-cover change generally involves lowering of groundwater level (GWL), as well as modification of vegetation type, both of which potentially influence CH4 emissions. We measured CH4 exchanges at the landscape scale using eddy covariance towers over two land-cover types in tropical peatland in Sumatra, Indonesia: (a) a natural forest and (b) an Acacia crassicarpa plantation. Annual CH4 exchanges over the natural forest (9.1 ± 0.9 g CH4  m-2  year-1 ) were around twice as high as those of the Acacia plantation (4.7 ± 1.5 g CH4  m-2  year-1 ). Results highlight that tropical peatlands are significant CH4 sources, and probably have a greater impact on global atmospheric CH4 concentrations than previously thought. Observations showed a clear diurnal variation in CH4 exchange over the natural forest where the GWL was higher than 40 cm below the ground surface. The diurnal variation in CH4 exchanges was strongly correlated with associated changes in the canopy conductance to water vapor, photosynthetic photon flux density, vapor pressure deficit, and air temperature. The absence of a comparable diurnal pattern in CH4 exchange over the Acacia plantation may be the result of the GWL being consistently below the root zone. Our results, which are among the first eddy covariance CH4 exchange data reported for any tropical peatland, should help to reduce the uncertainty in the estimation of CH4 emissions from a globally important ecosystem, provide a more complete estimate of the impact of land-cover change on tropical peat, and develop science-based peatland management practices that help to minimize greenhouse gas emissions.

Impact of water table levels and winter cover crops on greenhouse gas emissions from cultivated peat soils.

Drainage and cultivation have turned peatlands from carbon (C) sinks into hotspots for greenhouse gas (GHG) emissions. Raising the water table and planting of winter cover crops are potential strategies to help reduce peat oxidation and re-initiate net C accumulation during the non-cropping period. However, the effects of these practices as well as their interactions on GHG emissions remain unclear. Here, we carried out an outdoor mesocosm experiment to elucidate the effect of water table levels (-30 cm and -50 cm) and winter cover crop cultivation (vetch, rye, no plant) on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes during the winter period (November-April). Soil-atmosphere GHG exchange, GHG concentrations within the peat profile and soil water solute concentrations were monitored. Our results showed that high water table significantly reduced ecosystem respiration, while it had no net effect on N2O and CH4 fluxes. Uptake of available N by the cover crop significantly reduced nitrate in soil solution, thereby lowering the potential for leaching and both direct and indirect N2O emissions. No interactive effects between water table levels and cover crops were detected for any of the measured GHG fluxes. Seasonal variations of GHG fluxes were positively correlated with soil air concentrations at -15 cm and -40 cm depths, which were further regulated by dissolved organic C, nitrate concentration, and anaerobic conditions in the soil. This study suggests that there is great potential to raise water table levels and introduce green cover crops to reduce GHG emissions. Further studies are needed to achieve a complete evaluation of these strategies outside of the growing season, which may provide a significant mitigation benefit in C-rich cultivated peatlands.

Effects of acidity on dissolved organic carbon in organic soil extracts, pore water and surface litters.

Over the past 30-40 years, dissolved organic carbon (DOC) concentrations have increased in soil solutions and surface waters in many acid-sensitive areas of Europe and North America. This has been linked to recovery from acidification in response to decreasing levels of atmospheric pollution. Evidence from radiocarbon dating suggests that DOC in surface waters is typically derived from recently photosynthesised organic matter such as plant litter and exudates, yet there is little information on the pH-sensitivity of organic matter solubility, or its decomposition, in litter layers and in different organic soils. Therefore the purpose of this study was to determine a) the sensitivity of DOC to acidity in different surface layers and soil types, in order to b) improve understanding of the key sources contributing to the increasing DOC trend. Such information is vital for understanding site specific characteristics contributing to inconsistencies in DOC release between catchments, and for improving predictions of carbon fluxes and budgets. Based on data collected at four established field pH-manipulation experiments in upland areas of the United Kingdom, we examined the sources, composition and acid-sensitivity of DOC export from the litter and organic soils. We found that litter generated nearly three times more DOC than the organic soils, consistent with radiocarbon evidence that recent plant inputs are a major source of DOC. Furthermore, litter derived DOC had lower specific ultraviolet light absorbance (SUVA) than organic soil DOC, suggesting greater biodegradability, and was not acid sensitive. In contrast, organic soil DOC concentrations were more strongly related to experimentally manipulated pH, implying that the mobility of this DOC may be subject to physicochemical rather than biotic controls. Our results suggest that physicochemically mediated controls on organic matter solubility may be a key driver behind the widely observed increases in surface water DOC in areas undergoing recovery from acidification.

Misinterpreting carbon accumulation rates in records from near-surface peat.

Peatlands are globally important stores of carbon (C) that contain a record of how their rates of C accumulation have changed over time. Recently, near-surface peat has been used to assess the effect of current land use practices on C accumulation rates in peatlands. However, the notion that accumulation rates in recently formed peat can be compared to those from older, deeper, peat is mistaken - continued decomposition means that the majority of newly added material will not become part of the long-term C store. Palaeoecologists have known for some time that high apparent C accumulation rates in recently formed peat are an artefact and take steps to account for it. Here we show, using a model, how the artefact arises. We also demonstrate that increased C accumulation rates in near-surface peat cannot be used to infer that a peatland as a whole is accumulating more C - in fact the reverse can be true because deep peat can be modified by events hundreds of years after it was formed. Our findings highlight that care is needed when evaluating recent C addition to peatlands especially because these interpretations could be wrongly used to inform land use policy and decisions.

Zones of influence for soil organic matter dynamics: A conceptual framework for data and models.

Soil organic matter (SOM) is an indicator of sustainable land management as stated in the global indicator framework of the United Nations Sustainable Development Goals (SDG Indicator 15.3.1). Improved forecasting of future changes in SOM is needed to support the development of more sustainable land management under a changing climate. Current models fail to reproduce historical trends in SOM both within and during transition between ecosystems. More realistic spatio-temporal SOM dynamics require inclusion of the recent paradigm shift from SOM recalcitrance as an 'intrinsic property' to SOM persistence as an 'ecosystem interaction'. We present a soil profile, or pedon-explicit, ecosystem-scale framework for data and models of SOM distribution and dynamics which can better represent land use transitions. Ecosystem-scale drivers are integrated with pedon-scale processes in two zones of influence. In the upper vegetation zone, SOM is affected primarily by plant inputs (above- and belowground), climate, microbial activity and physical aggregation and is prone to destabilization. In the lower mineral matrix zone, SOM inputs from the vegetation zone are controlled primarily by mineral phase and chemical interactions, resulting in more favourable conditions for SOM persistence. Vegetation zone boundary conditions vary spatially at landscape scales (vegetation cover) and temporally at decadal scales (climate). Mineral matrix zone boundary conditions vary spatially at landscape scales (geology, topography) but change only slowly. The thicknesses of the two zones and their transport connectivity are dynamic and affected by plant cover, land use practices, climate and feedbacks from current SOM stock in each layer. Using this framework, we identify several areas where greater knowledge is needed to advance the emerging paradigm of SOM dynamics-improved representation of plant-derived carbon inputs, contributions of soil biota to SOM storage and effect of dynamic soil structure on SOM storage-and how this can be combined with robust and efficient soil monitoring.

Dynamic Modeling and Target Loads of Sulfur and Nitrogen for Surface Waters in Finland, Norway, Sweden, and the United Kingdom.

The target load concept is an extension of the critical load concept of air pollution inputs to ecosystems. The advantage of target loads over critical loads is that one can define the deposition and the point in time (target year) when the critical (chemical) limit is no longer violated. This information on the timing of recovery requires dynamic modeling. Using a well-documented dynamic model, target loads for acidic deposition were determined for 848 surface waters across Finland, Norway, Sweden, and the United Kingdom for the target year 2050. In the majority of sites ( n = 675), the critical ANC-limit was predicted to be achieved by 2050; however, for 127 sites, target loads were determined. In addition, 46 sites were infeasible, i.e., even a reduction of anthropogenic deposition to zero would not achieve the limit by 2050. The average maximum target load for sulfur was 38% lower than the respective critical load across the study lakes ( n = 127). Target loads on a large regional scale can inform effects-based emission reduction policies; the current assessment suggests that reductions beyond the Gothenburg Protocol are required to ensure surface water recovery from acidification by 2050.

Comparison of the impacts of acid and nitrogen additions on carbon fluxes in European conifer and broadleaf forests.

Increased reactive nitrogen (N) loadings to terrestrial ecosystems are believed to have positive effects on ecosystem carbon (C) sequestration. Global "hot spots" of N deposition are often associated with currently or formerly high deposition of sulphur (S); C fluxes in these regions might therefore not be responding solely to N loading, and could be undergoing transient change as S inputs change. In a four-year, two-forest stand (mature Norway spruce and European beech) replicated field experiment involving acidity manipulation (sulphuric acid addition), N addition (NH4NO3) and combined treatments, we tested the extent to which altered soil solution acidity or/and soil N availability affected the concentration of soil dissolved organic carbon (DOC), soil respiration (Rs), microbial community characteristics (respiration, biomass, fungi and bacteria abundances) and enzyme activity. We demonstrated a large and consistent suppression of soil water DOC concentration driven by chemical changes associated with increased hydrogen ion concentrations under acid treatments, independent of forest type. Soil respiration was suppressed by sulphuric acid addition in the spruce forest, accompanied by reduced microbial biomass, increased fungal:bacterial ratios and increased C to N enzyme ratios. We did not observe equivalent effects of sulphuric acid treatments on Rs in the beech forest, where microbial activity appeared to be more tightly linked to N acquisition. The only changes in C cycling following N addition were increased C to N enzyme ratios, with no impact on C fluxes (either Rs or DOC). We conclude that C accumulation previously attributed solely to N deposition could be partly attributable to their simultaneous acidification.

Terrestrial dissolved organic matter distribution in the North Sea.

The flow of terrestrial carbon to rivers and inland waters is a major term in the global carbon cycle. The organic fraction of this flux may be buried, remineralized or ultimately stored in the deep ocean. The latter can only occur if terrestrial organic carbon can pass through the coastal and estuarine filter, a process of unknown efficiency. Here, data are presented on the spatial distribution of terrestrial fluorescent and chromophoric dissolved organic matter (FDOM and CDOM, respectively) throughout the North Sea, which receives organic matter from multiple distinct sources. We use FDOM and CDOM as proxies for terrestrial dissolved organic matter (tDOM) to test the hypothesis that tDOM is quantitatively transferred through the North Sea to the open North Atlantic Ocean. Excitation emission matrix fluorescence and parallel factor analysis (EEM-PARAFAC) revealed a single terrestrial humic-like class of compounds whose distribution was restricted to the coastal margins and, via an inverse salinity relationship, to major riverine inputs. Two distinct sources of fluorescent humic-like material were observed associated with the combined outflows of the Rhine, Weser and Elbe rivers in the south-eastern North Sea and the Baltic Sea outflow to the eastern central North Sea. The flux of tDOM from the North Sea to the Atlantic Ocean appears insignificant, although tDOM export may occur through Norwegian coastal waters unsampled in our study. Our analysis suggests that the bulk of tDOM exported from the Northwest European and Scandinavian landmasses is buried or remineralized internally, with potential losses to the atmosphere. This interpretation implies that the residence time in estuarine and coastal systems exerts an important control over the fate of tDOM and needs to be considered when evaluating the role of terrestrial carbon losses in the global carbon cycle.

10 Keys for Successful Esthetic-Zone Single Immediate Implants.

The 10 keys for successful esthetic-zone single immediate implants encapsulate in an evidencebased manner the treatment planning and replacement of single hopeless teeth in the maxillary anterior sextant. These include 2 treatment-planning, 5 surgical, and 3 prosthetic keys, which, collectively, aim to minimize soft- and hard-tissue complications for an optimal esthetic implant restoration. The straightforward, advanced, and complex (SAC) classification was designed to aid clinicians in the treatment planning of dental implant cases. Cases are stratified by the degree of surgical and restorative risk and complexity for both the surgical and prosthetic phases of treatment. Based on the 10 keys, the management of an immediate implant in the esthetic zone is considered a complex SAC procedure. As described in this article, a complex SAC procedure requires careful patient selection and treatment planning, along with precise execution by skillful clinicians, to achieve successful results.

Quantifying tropical peatland dissolved organic carbon (DOC) using UV-visible spectroscopy.

UV-visible spectroscopy has been shown to be a useful technique for determining dissolved organic carbon (DOC) concentrations. However, at present we are unaware of any studies in the literature that have investigated the suitability of this approach for tropical DOC water samples from any tropical peatlands, although some work has been performed in other tropical environments. We used water samples from two oil palm estates in Sarawak, Malaysia to: i) investigate the suitability of both single and two-wavelength proxies for tropical DOC determination; ii) develop a calibration dataset and set of parameters to calculate DOC concentrations indirectly; iii) provide tropical researchers with guidance on the best spectrophotometric approaches to use in future analyses of DOC. Both single and two-wavelength model approaches performed well with no one model significantly outperforming the other. The predictive ability of the models suggests that UV-visible spectroscopy is both a viable and low cost method for rapidly analyzing DOC in water samples immediately post-collection, which can be important when working at remote field sites with access to only basic laboratory facilities.

Long-term nitrogen deposition increases heathland carbon sequestration.

The large increases in reactive nitrogen (N) deposition in developed countries since the Industrial Revolution have had a marked impact on ecosystem functioning, including declining species richness, shifts in species composition, and increased N leaching. A potential mitigation of these harmful effects is the action of N as a fertiliser, which, through increasing primary productivity (and subsequently, organic matter production), has the potential to increase ecosystem carbon (C) storage. Here we report the response of an upland heath to 10years of experimental N addition. We find large increases in plant and soil C and N pools, with N-driven C sequestration rates in the range of 13-138kgCkg-1. These rates are higher than those previously found in forest and lowland heath, mainly due to higher C sequestration in the litter layer. C sequestration is highest at lower N treatments (10, 20, and 40kgNha-1yr-1 above ambient), with evidence of saturation at the highest N treatment, reflecting a physiologically aged Calluna vulgaris (Calluna) canopy. To maintain these rates of sequestration, the Calluna canopy should be managed to maximise it's time in the building phase. Scaling our results across UK heathlands, this equates to an additional 0.77Mt CO2e per annum extra C sequestered into plant litter and the top 15cm of heathland soil as a result of N deposition. The bulk of this is found in the litter and organic soil horizons that hold an average of 23% and 54% of soil C, respectively. This additional C represents around 0.44% of UK annual anthropogenic GHG emissions. When considered in the context of falling biodiversity and altered species composition in heathland, policy focus should remain on reducing N emissions.

Historical peat loss explains limited short-term response of drained blanket bogs to rewetting.

This study assessed the short-term impacts of ditch blocking on water table depth and vegetation community structure in a historically drained blanket bog. A chronosequence approach was used to compare vegetation near ditches blocked 5 years, 4 years and 1 year prior to the study with vegetation near unblocked ditches. Plots adjacent to and 3 m away from 70 ditches within an area of blanket bog were assessed for floristic composition, aeration depth using steel bars, and topography using LiDAR data. No changes in aeration depth or vegetation parameters were detected as a function of ditch-blocking, time since blocking, or distance from the ditch, with the exception of non-Sphagnum bryophytes which had lower cover in quadrats adjacent to ditches that had been blocked for 5 years. Analysis of LiDAR data and the observed proximity of the water table to the peat surface led us to conclude that the subdued ecosystem responses to ditch-blocking were the result of historical peat subsidence within a 4-5 m zone either side of each ditch, which had effectively lowered the peat surface to the new, ditch-influenced water table. We estimate that this process led to the loss of around 500,000 m3 peat within the 38 km2 study area following drainage, due to a combination of oxidation and compaction. Assuming that 50% of the volume loss was due to oxidation, this amounts to a carbon loss of 11,000 Mg C over this area, i.e. 3 Mg C ha-1. The apparent 'self-rewetting' of blanket bogs in the decades following drainage has implications for their restoration as it suggests that there may not be large quantities of dry peat left to rewet, and that there is a risk of inundation (potentially leading to high methane emissions) along subsided ditch lines. Many peatland processes are likely to be maintained in drained blanket bog, including support of typical peatland vegetation, but infilling of lost peat and recovery of original C stocks are likely to take longer than is generally anticipated.

Management effects on greenhouse gas dynamics in fen ditches.

Globally, large areas of peatland have been drained through the digging of ditches, generally to increase agricultural production. By lowering the water table it is often assumed that drainage reduces landscape-scale emissions of methane (CH4) into the atmosphere to negligible levels. However, drainage ditches themselves are known to be sources of CH4 and other greenhouse gases (GHGs), but emissions data are scarce, particularly for carbon dioxide (CO2) and nitrous oxide (N2O), and show high spatial and temporal variability. Here, we report dissolved GHGs and diffusive fluxes of CH4 and CO2 from ditches at three UK lowland fens under different management; semi-natural fen, cropland, and cropland restored to low-intensity grassland. Ditches at all three fens emitted GHGs to the atmosphere, but both fluxes and dissolved GHGs showed extensive variation both seasonally and within-site. CH4 fluxes were particularly large, with medians peaking at all three sites in August at 120-230mgm-2d-1. Significant between site differences were detected between the cropland and the other two sites for CO2 flux and all three dissolved GHGs, suggesting that intensive agriculture has major effects on ditch biogeochemistry. Multiple regression models using environmental and water chemistry data were able to explain 29-59% of observed variation in dissolved GHGs. Annual CH4 fluxes from the ditches were 37.8, 18.3 and 27.2gCH4m-2yr-1 for the semi-natural, grassland and cropland, and annual CO2 fluxes were similar (1100 to 1440gCO2m-2yr-1) among sites. We suggest that fen ditches are important contributors to landscape-scale GHG emissions, particularly for CH4. Ditch emissions should be included in GHG budgets of human modified fens, particularly where drainage has removed the original terrestrial CH4 source, e.g. agricultural peatlands.

Investigations of freezing and cold storage for the analysis of peatland dissolved organic carbon (DOC) and absorbance properties.

Although measured rates of biological degradation of DOC are typically low under dark conditions, it is assumed that water samples must be analysed soon after collection to provide an accurate measure of DOC concentration and UV-visible absorbance. To examine the impact of storage on DOC quality and quantity, we took water samples from an ombrotrophic peatland, and stored them in the dark at 4 °C for 138-1082 days. A median of 29% of DOC was lost during storage, but losses of absorbance at 254 nm were less. DOC loss followed a first-order exponential decay function, and was dependent on storage time. DOC half-life was calculated as 1253 days. Specific absorbance at 254 nm suggested that samples containing more aromatic DOC were more resistant to degradation, although time functioned as the primary control. Samples from two fens showed that loss of absorbance was greater at 400 nm rather than 254 nm, after 192 days storage, suggesting that non-aromatic DOC is preferentially degraded. These results suggest that samples can be stored for several months before losses of DOC become detectable, and that it is possible to back-calculate initial DOC concentrations in long-term stored samples based on known decay rates. Freeze/thaw experiments using samples from a range of peatlands suggested that DOC concentration was mostly unaffected by the process, but DOC increased 37% in one sample. Freezing had unpredictable and sometimes strong effects on absorbance, SUVA and E ratios, therefore freezing is not recommended as a method of preservation for these analyses.