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Agricultural management and meteorological conditions have a great impact on grassland dynamics, and regenerative and holistic practices especially have significant potential for enhancing soil quality and fertility, biodiversity and carbon cycling in agricultural ecosystems. We monitored CO 2 fluxes from an agricultural grassland in Southern Finland with the eddy covariance method over a five-year period together with various meteorological variables to study how weather conditions, rotational grazing, cutting height and other selected management practices affect the fluxes. Additionally, we measured CH 4 , N 2 O and CO 2 fluxes with the flux chamber method. Interannual variation in the net ecosystem carbon balance (NECB) was substantial as it alternated between −60 (C sink) and 131 g C m−2 yr−1 (C source). Over the whole five years, the site was near neutral with approximately −10 g C m−2. CH 4 and N 2 O fluxes were small in each measured growing season. Field management greatly affected the annual NECB, and rotational grazing had potential positive impact on assimilation efficiency and taller cutting height also showed occasional higher assimilation during regrowth stage. We utilised the measurement data to calibrate a modified version of the BASGRA grassland model for the site, and ran simulations to isolate the impacts of precipitation and air temperature as key drivers for the ecosystem C exchange. The simulations showed that variations in both precipitation and air temperature had distinct impacts on the primary productivity and heterotrophic respiration, causing the ecosystem to alternate between net carbon source and sink during individual years. Over the five-year period, the calibrated model demonstrated net carbon sink (−70 g C m−2 central estimate) into the ecosystem. • Grassland CO 2 fluxes measured for five years, and the effects of management and weather variation on the NECB assessed. • The annual CO 2 fluxes and NECB of the grassland showed substantial interannual variation. • Over the whole five years, the C budget of the field was near neutral. • Growing season CH 4 and N 2 O fluxes were close to zero. • Modified BASGRA grassland model demonstrated net carbon accumulation into the agroecosystem. [ABSTRACT FROM AUTHOR]

Better monitoring, reporting, and verification (MRV) of the amount, additionality, and persistence of the sequestered soil carbon is needed to understand the best carbon farming practices for different soils and climate conditions, as well as their actual climate benefits or cost efficiency in mitigating greenhouse gas emissions. This paper presents our Field Observatory Network (FiON) of researchers, farmers, companies, and other stakeholders developing carbon farming practices. FiON has established a unified methodology towards monitoring and forecasting agricultural carbon sequestration by combining offline and near-real-time field measurements, weather data, satellite imagery, modeling, and computing networks. FiON's first phase consists of two intensive research sites and 20 voluntary pilot farms testing carbon farming practices in Finland. To disseminate the data, FiON built a web-based dashboard called the Field Observatory (v1.0, https://www.fieldobservatory.org/ , last access: 3 February 2022). The Field Observatory is designed as an online service for near-real-time model–data synthesis, forecasting, and decision support for the farmers who are able to monitor the effects of carbon farming practices. The most advanced features of the Field Observatory are visible on the Qvidja site, which acts as a prototype for the most recent implementations. Overall, FiON aims to create new knowledge on agricultural soil carbon sequestration and effects of carbon farming practices as well as provide an MRV tool for decision support. [ABSTRACT FROM AUTHOR]

Effects of permafrost aggradation on greenhouse gas (GHG) dynamics and climate forcing have not been previously quantified. Here, we reconstruct changes in GHG balances over the late Holocene for a sub-arctic peatland by applying palaeoecological data combined with measured GHG flux data, focusing on the impact of permafrost aggradation in particular. Our data suggest that permafrost initiation around 3000 years ago resulted in GHG emissions, thereby slightly weakening the general long-term peatland cooling impact. As a novel discovery, based on our chronological data of bare peat surfaces, we found that current sporadic bare peat surfaces in subarctic regions are probably remnants of more extensive bare peat areas formed by permafrost initiation. Paradoxically, our data suggest that permafrost initiation triggered by the late Holocene cooling climate generated a positive radiative forcing and a short-term climate warming feedback, mitigating the general insolation-driven late Holocene summer cooling trend. Our work with historical data demonstrates the importance of permafrost peatland dynamics for atmospheric GHG concentrations, both in the past and future. It suggests that, while thawing permafrost is likely to initially trigger a change towards wetter conditions and consequent increase in CH 4 forcing, eventually the accelerated C uptake capacity under warmer climate may overcome the thaw effect when a new hydrological balance becomes established. • Permafrost aggradation triggered by late Holocene cooling led to warming climate forcing. • bare peat surfaces were more extensive and N 2 O forcing stronger in the past, since then the bare area has diminished. • Sub-arctic peatlands have strong impact on atmospheric GHG dynamics but future development pathways remain uncertain. [ABSTRACT FROM AUTHOR]

Better monitoring, reporting and verification (MRV) of the amount, additionality and persistence of the sequestered soil carbon is needed to understand the best carbon farming practices for different soils and climate conditions, as well as their actual climate benefits or cost-efficiency in mitigating greenhouse gas emissions. This paper presents our Field Observatory Network (FiON) of researchers, farmers, companies and other stakeholders developing carbon farming practices. FiON has established a unified methodology towards monitoring and forecasting agricultural carbon sequestration by combining offline and near real-time field measurements, weather data, satellite imagery, modeling and computing networks. FiON's first phase consists of two intensive research sites and 20 voluntary pilot farms testing carbon farming practices in Finland. To disseminate the data, FiON built a web-based dashboard called Field Observatory (v1.0, fieldobservatory.org). Field Observatory is designed as an online service for near real-time model-data synthesis, forecasting and decision support for the farmers who are able to monitor the effects of carbon farming practices. The most advanced features of the Field Observatory are visible on the Qvidja site which acts as a prototype for the most recent implementations. Overall, FiON aims to create new knowledge on agricultural soil carbon sequestration and effects of carbon farming practices, and provide an MRV tool for decision-support. [ABSTRACT FROM AUTHOR]

Drained agricultural boreal peatlands comprise a large source of nitrous oxide (N 2 O) and carbon dioxide (CO 2) but a small sink or source of methane (CH 4). N 2 O fluxes have high spatial and temporal variability and are often measured with the chamber technique. Therefore, continuous measurements of N 2 O fluxes are needed to better understand how N 2 O emissions are triggered and to reduce the uncertainty of annual N 2 O budget estimations. Here we present a two-year-long time series of continuous measurements of CO 2 and N 2 O fluxes of a shallow-peated drained agricultural boreal peatland cultivated for grass silage. The fluxes were measured with the area-averaging eddy covariance technique. Several N 2 O peak events were observed throughout all seasons. The peaks were associated with meteorological or management events, such as soil thawing or freezing, precipitation, fertilization and glyphosate application. The annual N 2 O budget was 4.74 ±0.47 and 6.08 ±0.49 kg N 2 O-N ha−1 y−1 in 2020 and 2021, respectively. The annual CO 2 budget, comprising the sum of net ecosystem exchange and biomass export, was 3.70 ±0.22 and 5.54 ±0.33 t CO 2 -C ha−1 y−1 in 2020 and 2021, respectively. The N 2 O budget during the first, warmer winter was 106% higher than during the second, meteorologically more typical winter, due to the higher frequency of soil freezing–thawing cycles. The average annual N 2 O budget was 36%–50% lower than the IPCC Emission Factor (EF) while the CO 2 budget was in accordance with the IPCC EF. CO 2 emissions dominated the total CO 2 -eq emissions of our site but N 2 O also had a significant contribution of 12%. Our results also suggest that glyphosate application enhanced N 2 O emissions in the last quarter of 2021. However, the full rotation should be measured to confirm whether there is a need to re-evaluate the N 2 O IPCC EF for 'grassland drained boreal' land-use class. [Display omitted] • The shallow peated site is a significant source of N 2 O and CO 2. • Warm winter has higher N 2 O emissions than cold winter by 106%. • N 2 O annual budget needs to be measured over the full grass rotation. • N 2 O emissions contribute more than 10% to the total CO 2 -equivalent emissions. • Glyphosate application seems to enhance N 2 O emissions. [ABSTRACT FROM AUTHOR]

Ecosystems’ potential to provide services, e.g. to sequester carbon, is largely driven by the phenological cycle of vegetation. Timing of phenological events is required for understanding and predicting the influence of climate change on ecosystems and to support analyses of ecosystem functioning. Analyses of conventional camera time series mounted near vegetation has been suggested as a means of monitoring phenological events and supporting wider monitoring of phenological cycle of biomes that is frequently done with satellite earth observation (EO). Especially in the boreal biome, sparsely scattered deciduous trees amongst conifer-dominant forests pose a problem for EO techniques as species phenological signal mix, and render EO data difficult to interpret. Therefore, deriving phenological information from on the ground measurements would provide valuable reference data for earth observed phenology products in a larger scale. Keeping this in mind, we established a network of digital cameras for automated monitoring of phenological activity of vegetation in the boreal ecosystems of Finland. Cameras were mounted at 14 sites, each site having 1–3 cameras. In this study, we used data from 12 sites to investigate how well networked cameras can detect the phenological development of birches ( Betula spp.) along a latitudinal gradient. Birches typically appear in small quantities within the dominant species. We tested whether the small, scattered birch image elements allow a reliable extraction of colour indices and the temporal changes therein. We compared automatically derived phenological dates from these birch image elements both to visually determined dates from the same image time series and to independent observations recorded in the phenological monitoring network covering the same region. Automatically extracted season start dates, which were based on the change of green colour fraction in spring, corresponded well with the visually interpreted start of the season, and also to the budburst dates observed in the field. Red colour fraction turned out to be superior to the green colour-based indices in predicting leaf yellowing and fall. The latitudinal gradients derived using automated phenological date extraction corresponded well with the gradients estimated from the phenological field observations. We conclude that small and scattered birch image elements allow reliable extraction of key phenological dates for the season start and end of deciduous species studied here, thus providing important species-specific data for model validation and for explaining the temporal variation in EO phenology products. [ABSTRACT FROM AUTHOR]

We determine the annual timing of spring recovery from spaceborne microwave radiometer observations across northern hemisphere boreal evergreen forests for 1979-2014. We find a trend of advanced spring recovery of carbon uptake for this period, with a total average shift of 8.1 d (2.3 d/decade). We use this trend to estimate the corresponding changes in gross primary production (GPP) by applying in situ carbon flux observations. Micrometeorological CO2 measurements at four sites in northern Europe and North America indicate that such an advance in spring recovery would have increased the January-June GPP sum by 29 g.C.m-2 [8.4 g.C.m-2 (3.7%)/decade]. We find this sensitivity of the measured springtime GPP to the spring recovery to be in accordance with the corresponding sensitivity derived from simulations with a land ecosystem model coupled to a global circulation model. The model-predicted increase in springtime cumulative GPP was 0.035 Pg/decade [15.5 g.C.m-2 (6.8%)/decade] for Eurasian forests and 0.017 Pg/decade for forests in North America [9.8 g.C.m-2 (4.4%)/decade]. This change in the springtime sum of GPP related to the timing of spring snowmelt is quantified here for boreal evergreen forests. [ABSTRACT FROM AUTHOR]

Phytotoxic Ozone Dose (POD Y ), defined as the accumulated stomatal ozone flux over a threshold of Y , is considered an optimal metric to evaluate O 3 effects on vegetation. POD Y is often computed through the DO 3 SE model, which includes species-specific parameterizations for the environmental response of stomatal conductance. However, the effect of soil water content (SWC) on stomatal aperture is difficult to model on a regional scale and thus often ignored. In this study, we used environmental input data obtained from the WRF-CHIMERE model for 14,546 grid-based forest sites in Southern Europe. SWC was obtained for the upper 10 cm of soil, which resulted in a worst-case risk scenario. POD Y was calculated either with or without water limitation for different Y thresholds. Exclusion of the SWC effect on stomatal fluxes caused a serious overestimation of POD Y . The difference increased with increasing Y (78%, 128%, 237% and 565% with Y = 0, 1, 2 and 3 nmol O 3 m −2 s −1 , respectively). This behaviour was confirmed by applying the same approach to field data measured in a Mediterranean Quercus ilex forest. WRF-CHIMERE overestimated SWC at this field site, so under real-world conditions the SWC effect may be larger than modelled. The differences were lower for temperate species ( Pinus cembra 50–340%, P. sylvestris 57–363% , Abies alba 57–371%) than for Mediterranean species ( P. pinaster 87–356% , P. halepensis 96–429% , P. pinea 107–532%, Q. suber 104–1602%), although a high difference was recorded also for the temperate species Fagus sylvatica with POD3 (524%). We conclude that SWC should be considered in POD Y simulations and a low Y threshold should be used for robustness. [ABSTRACT FROM AUTHOR]

Abstract: The paper is an attempt to assess the uncertainty involved in the modelling process of deriving the flux–effects relationships from the experimental evidences of a network of coordinated experiments on ozone and vegetation (the LRTAP Convention''s ICP Vegetation). Ten modelling steps have been described and analysed. Even if some steps were more critical than others in introducing uncertainty, the whole modelling process seems to be quite robust. The stomatal dose calculation is precise enough when performed on long time periods (e.g. growing season). The main sources of inaccuracy for the stomatal dose calculation can be ascribed to the adoption of different schemes for the calculation of ozone concentration at leaf level (7–10%). The estimation of the ozone effects on vegetation, and particularly the derivation of the plant''s response at the theoretical zero-ozone dose, proves to be the main source of uncertainty of the whole process (up to 17%). In order to improve the precision of this step an increased number of ozone treatments and replicates in the experiments is recommended, while a harmonization/standardization of the calculation algorithm is required to improve the accuracy of the dose calculation. [Copyright &y& Elsevier]

• Water table level and energy fluxes monitored after clear-cut and partial harvest. • A multi-species soil-plant-atmosphere transfer model applied to explore changes. • Harvesting 70% of stand basal area had marginal effects. • Remaining stand's structure and species composition play key role. • Post-harvest vegetation recovery had high importance to energy balance. We quantified the response of peatland water table level (WTL) and energy fluxes to harvesting of a drained peatland forest. Two alternative harvests (clear-cut and partial harvest) were carried out in a mixed-species ditch-drained peatland forest in southern Finland, where water and energy balance components were monitored for six pre-treatment and three post-treatment growing seasons. To explore the responses caused by harvestings, we applied a mechanistic multi-layer soil-plant-atmosphere transfer model. At the clear-cut site, the mean growing season WTL rose by 0.18 ± 0.02 m (error estimate based on measurement uncertainty), while net radiation, and sensible and latent heat fluxes decreased after harvest. On the contrary, we observed only minor changes in energy fluxes and mean WTL (0.05 ± 0.03 m increase) at the partial harvest site, although as much as 70% of the stand basal area was removed and leaf-area index was reduced to half. The small changes were mainly explained by increased water use of spruce undergrowth and field layer vegetation, as well as increased forest floor evaporation. The rapid establishment of field layer vegetation had a significant role in energy balance recovery at the clear-cut site. At partial harvest, chlorophyll fluorescence measurements and model-data comparison suggested the shade-adapted spruce undergrowth was suffering from light stress during the first post-harvest growing season. We conclude that in addition to stand basal area, species composition and stand structure need to be considered when controlling WTL in peatland forests with partial harvesting. Our results have important implications on the operational use of continuous cover forestry on drained peatlands. A continuously maintained tree cover with significant evapotranspiration capacity could enable optimizing WTL from both tree growth and environmental perspectives. Image, graphical abstract [ABSTRACT FROM AUTHOR]

High latitude peatlands act as globally important carbon (C) sinks and are in constant interaction with the atmosphere. Their C storage formed during the Holocene. In the course of time, the aggregate effect of the C fluxes on radiative forcing (RF) typically changes from warming to cooling, but the timing of this shift varies among different peatlands. Here we investigated Holocene peatland development, including vegetation history, vertical peat growth and the lateral expansion of a patterned subarctic fen in northern Finland by means of multiple sampling points. We modelled the Holocene RF by combining knowledge on past vegetation communities based on plant macrofossil stratigraphies and present in situ C flux measurements. The peatland initiated at ca. 9500 calibrated years Before Present (cal yr BP), and its lateral expansion was greatest between ca. 9000 and 7000 cal yr BP. After the early expansion, vertical peat growth proceeded very differently in different parts of the peatland, regulated by internal and external factors. The pronounced surface microtopography, with high strings and wet flarks, started to form only after ca. 1000 cal yr BP. C accumulation within the peatland recorded a high degree of spatial variability throughout its history, including the recent past. We applied two flux scenarios with different interpretation of the initial peatland development phases to estimate the RF induced by C fluxes of the fen. After ca. 4000 cal yr BP, at the latest, the peatland RF has been negative (cooling), mainly driven by C uptake and biomass production, while methane emissions had a lesser role in the total RF. Interestingly, these scenarios suggest that the greatest cooling effect took place around ca. 1000 cal yr BP, after which the surface microtopography established. The study demonstrated that despite the high spatial heterogeneity and idiosyncratic behaviour of the peatland, the RF of the studied fen followed the general development pattern of more southern peatlands. Holocene climate variations and warm phases did not seem to induce any distinctive and consistent peatland-scale patterns in C accumulation, whereas our data suggests that the changes in vegetation related to autogenic succession were reflected in the C accumulation patterns and RF more clearly. • Subarctic peatland carbon dynamics showed idiosyncratic behaviour. • Radiative forcing reconstructions suggested mid-Holocene warming impact, then cooling. • Net cooling effect was driven by C uptake and biomass production. • No consistent response to warm climate was detected. [ABSTRACT FROM AUTHOR]

Simulating the carbon-water fluxes at more widely distributed meteorological stations based on the sparsely and unevenly distributed eddy covariance flux stations is needed to accurately understand the carbon-water cycle of terrestrial ecosystems. We established a new framework consisting of machine learning, determination coefficient (R 2 ), Euclidean distance, and remote sensing (RS), to simulate the daily net ecosystem carbon dioxide exchange (NEE) and water flux (WF) of the Eurasian meteorological stations using a random forest model or/and RS. The daily NEE and WF datasets with RS-based information (NEE-RS and WF-RS) for 3774 and 4427 meteorological stations during 2002-2020 were produced, respectively. And the daily NEE and WF datasets without RS-based information (NEE-WRS and WF-WRS) for 4667 and 6763 meteorological stations during 1983-2018 were generated, respectively. For each meteorological station, the carbon-water fluxes meet accuracy requirements and have quasi-observational properties. These four carbon-water flux datasets have great potential to improve the assessments of the ecosystem carbon-water dynamics., (© 2023. Springer Nature Limited.)

Climate change mitigation requires, besides reductions in greenhouse gas emissions, actions to increase carbon sinks in terrestrial ecosystems. A key measurement method for quantifying such sinks and calibrating models is the eddy covariance technique, but it requires imputation, or gap-filling, of missing data for determination of annual carbon balances of ecosystems. Previous comparisons of gap-filling methods have concluded that commonly used methods, such as marginal distribution sampling (MDS), do not have a significant impact on the carbon balance estimate. By analyzing an extensive, global data set, we show that MDS causes significant carbon balance errors for northern (latitude [Formula: see text]) sites. MDS systematically overestimates the carbon dioxide (CO[Formula: see text]) emissions of carbon sources and underestimates the CO[Formula: see text] sequestration of carbon sinks. We also reveal reasons for these biases and show how a machine learning method called extreme gradient boosting or a modified implementation of MDS can be used to substantially reduce the northern site bias., (© 2023. The Author(s).)

Peatland rewetting has been proposed as a vital climate change mitigation tool to reduce greenhouse gas emissions and to generate suitable conditions for the return of carbon (C) sequestration. In this study, we present annual C balances for a 5-year period at a rewetted peatland in Ireland (rewetted at the start of the study) and compare the results with an adjacent drained area (represents business-as-usual). Hydrological modelling of the 230-hectare site was carried out to determine the likely ecotopes (vegetation communities) that will develop post-rewetting and was used to inform a radiative forcing modelling exercise to determine the climate impacts of rewetting this peatland under five high-priority scenarios (SSP1-1.9, SS1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5). The drained area (marginal ecotope) was a net C source throughout the study and emitted 157 ± 25.5 g C m -2  year -1 . In contrast, the rewetted area (sub-central ecotope) was a net C sink of 78.0 ± 37.6 g C m -2  year -1 , despite relatively large annual methane emissions post-rewetting (average 19.3 ± 5.2 g C m -2  year -1 ). Hydrological modelling predicted the development of three key ecotopes at the site, with the sub-central ecotope predicted to cover 24% of the site, the sub-marginal predicted to cover 59% and the marginal predicted to cover 16%. Using these areal estimates, our radiative forcing modelling projects that under the SSP1-1.9 scenario, the site will have a warming effect on the climate until 2085 but will then have a strong cooling impact. In contrast, our modelling exercise shows that the site will never have a cooling impact under the SSP5-8.5 scenario. Our results confirm the importance of rapid rewetting of drained peatland sites to (a) achieve strong C emissions reductions, (b) establish optimal conditions for C sequestration and (c) set the site on a climate cooling trajectory., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Reconstructions of past climate impact, that is, radiative forcing (RF), of peatland carbon (C) dynamics show that immediately after peatland initiation the climate warming effect of CH 4 emissions exceeds the cooling effect of CO 2 uptake, but thereafter the net effect of most peatlands will move toward cooling, when RF switches from positive to negative. Reconstructing peatland C dynamics necessarily involves uncertainties related to basic assumptions on past CO 2  flux, CH 4 emission and peatland expansion. We investigated the effect of these uncertainties on the RF of three peatlands, using either apparent C accumulation rates, net C balance (NCB) or NCB plus C loss during fires as basis for CO 2 uptake estimate; applying a plausible range for CH 4 emission; and assuming linearly interpolated expansion between basal dates or comparatively early or late expansion. When we factored that some C would only be stored temporarily (NCB and NCB+fire), the estimated past cooling effect of CO 2 uptake increased, but the present-day RF was affected little. Altering the assumptions behind the reconstructed CO 2  flux or expansion patterns caused the RF to peak earlier and advanced the switch from positive to negative RF by several thousand years. Compared with NCB, including fires had only small additional effect on RF lasting less than 1000 year. The largest uncertainty in reconstructing peatland RF was associated with CH 4 emissions. As shown by the consistently positive RF modelled for one site, and in some cases for the other two, peatlands with high CH 4 emissions and low C accumulation rates may have remained climate warming agents since their initiation. Although uncertainties in present-day RF were mainly due to the assumed CH 4 emission rates, the uncertainty in lateral expansion still had a significant effect on the present-day RF, highlighting the importance to consider uncertainties in the past peatland C balance in RF reconstructions., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

Climate warming is anticipated to make high latitude ecosystems stronger C sinks through increasing plant production. This effect might, however, be dampened by insect herbivores whose damage to plants at their background, non-outbreak densities may more than double under climate warming. Here, using an open-air warming experiment among Subarctic birch forest field layer vegetation, supplemented with birch plantlets, we show that a 2.3 °C air and 1.2 °C soil temperature increase can advance the growing season by 1-4 days, enhance soil N availability, leaf chlorophyll concentrations and plant growth up to 400%, 160% and 50% respectively, and lead up to 122% greater ecosystem CO 2 uptake potential. However, comparable positive effects are also found when insect herbivory is reduced, and the effect of warming on C sink potential is intensified under reduced herbivory. Our results confirm the expected warming-induced increase in high latitude plant growth and CO 2 uptake, but also reveal that herbivorous insects may significantly dampen the strengthening of the CO 2 sink under climate warming.

Significant climate risks are associated with a positive carbon-temperature feedback in northern latitude carbon-rich ecosystems, making an accurate analysis of human impacts on the net greenhouse gas balance of wetlands a priority. Here, we provide a coherent assessment of the climate footprint of a network of wetland sites based on simultaneous and quasi-continuous ecosystem observations of CO2 and CH4 fluxes. Experimental areas are located both in natural and in managed wetlands and cover a wide range of climatic regions, ecosystem types, and management practices. Based on direct observations we predict that sustained CH4 emissions in natural ecosystems are in the long term (i.e., several centuries) typically offset by CO2 uptake, although with large spatiotemporal variability. Using a space-for-time analogy across ecological and climatic gradients, we represent the chronosequence from natural to managed conditions to quantify the "cost" of CH4 emissions for the benefit of net carbon sequestration. With a sustained pulse-response radiative forcing model, we found a significant increase in atmospheric forcing due to land management, in particular for wetland converted to cropland. Our results quantify the role of human activities on the climate footprint of northern wetlands and call for development of active mitigation strategies for managed wetlands and new guidelines of the Intergovernmental Panel on Climate Change (IPCC) accounting for both sustained CH4 emissions and cumulative CO2 exchange.

Monitoring and modelling of deposition of air pollutants is essential to develop and evaluate policies to abate the effects related to air pollution and to determine the losses of pollutants from the atmosphere. Techniques for monitoring wet deposition fluxes are widely applied. A recent intercomparison experiment, however, showed that the uncertainty in wet deposition is relatively high, up to 40%, apart from the fact that most samplers are biased because of a dry deposition contribution. Wet deposition amounts to about 80% of the total deposition in Europe with a range of 10-90% and uncertainty should therefore be decreased. During recent years the monitoring of dry deposition has become possible. Three sites have been operational for 5 years. The data are useful for model development, but also for model evaluation and monitoring of progress in policy. Data show a decline in SO(2) dry deposition, whereas nitrogen deposition remained constant. Furthermore, surface affinities for pollutants changed leading to changes in deposition. Deposition models have been further developed and tested with dry deposition measurements and total deposition measurements on forests as derived from throughfall data. The comparison is reasonable given the measurement uncertainties. Progress in ozone surface exchange modelling and monitoring shows that stomatal uptake can be quantified with reasonable accuracy, but external surface uptake yields highest uncertainty.

A statistical model for estimating AOT40 from time-integrated concentration data is presented and validated. AOT40 is a numerical index that describes the ozone exposure of ecosystems in terms of the hourly accumulated exposure over a threshold of 40 ppb. A rather simple model formulation was achieved by approximating the frequency distribution of hourly concentrations by the Gaussian probability distribution. The model represents a relationship between a time-averaged ozone concentration and the corresponding AOT40. Time-averaged concentration data are obtained when employing the passive sampling technique. For testing the method, passive sampling data with a 14-day sampling time were simulated by averaging continuous monitoring data. Data from eight background stations in Europe were used for calibration and testing. In spite of the simplifying assumption, the model performed well for the accumulated exposure when tested against independent data. The results show that it is possible to obtain a reasonable estimate of AOT40 even in the absence of continuous data, if the time-averaged concentration can be measured reliably.