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Reporting the greenhouse gas (GHG) emissions from the LULUCF sector in the GHG inventory requires sound methods for estimating both the inputs and outputs of carbon (C) in managed ecosystems. Soil CO2 balance of forests consists of the CO2 released from decomposing soil organic matter (SOM) and the C entering the soil through aboveground and belowground plant litter input. Peatlands drained for forestry release soil C as CO2 because the drainage deepens the oxic peat layer prone to SOM decomposition. IPCC Guidelines provide default CO2 emission factors for different climatic zones and the defaults or locally adapted static emission factors are commonly in use in GHG inventory reporting for drained peatlands. In this paper, we describe a new dynamic method to estimate the CO2 balance of drained peatland forest soils in Finland. Contrary to static emission factors, the annual CO2 release from soil is in our method estimated using empirical regression models driven by time series of tree basal area (BA), derived from the national forest inventories in Finland, time series of air temperature and the drained peatland forest site type. Aboveground and belowground litter input is also estimated using empirical models with newly acquired turnover rates for tree fine roots and BA as a dynamic driver. All major components of litter input from ground vegetation and live, harvested and naturally died trees are included. Our method produces an increasing trend of emissions from 1.4 to 7.9 Mt CO2 for drained peatland forest soils in Finland for the period 1990–2021, with a statistically significant difference between years 1990 and 2021. Across the period 1990–2021, annual emissions are on average 3.4 Mt and −0.3 Mt in southern and northern parts of Finland, respectively. When combined with data of the CO2 sink created by trees, it appears that in 2021 drained peatland forest ecosystems were a source of 2.3 Mt CO2 in southern Finland and a sink of 2.5 Mt CO2 in northern Finland. We compare the emissions produced by the new method with those produced by the old GHGI method of Finland and discuss the strengths and vulnerabilities of our method in comparison to static emission factors.

Estimates of regional and global freshwater N2O emissions have remained inaccurate due to scarce data and complexity of the multiple processes driving N2O fluxes the focus predominantly being on summer time measurements from emission hot spots, agricultural streams. Here, we present four‐season data of N2O concentrations in the water columns of randomly selected boreal lakes covering a large variation in latitude, lake type, area, depth, water chemistry, and land use cover. Nitrate was the key driver for N2O dynamics, explaining as much as 78% of the variation of the seasonal mean N2O concentrations across all lakes. Nitrate concentrations varied among seasons being highest in winter and lowest in summer. Of the surface water samples, 71% were oversaturated with N2O relative to the atmosphere. Largest oversaturation was measured in winter and lowest in summer stressing the importance to include full year N2O measurements in annual emission estimates. Including winter data resulted in fourfold annual N2O emission estimates compared to summer only measurements. Nutrient‐rich calcareous and large humic lakes had the highest annual N2O emissions. Our emission estimates for Finnish and boreal lakes are 0.6 and 29 Gg N2O‐N/year, respectively. The global warming potential of N2O from lakes cannot be neglected in the boreal landscape, being 35% of that of diffusive CH4 emission in Finnish lakes., Up‐scaling of freshwater N2O emissions at regional to global scales has remained challenging due to sparse data based on summer measurements. We collected seasonal data on N2O concentrations from 112 randomly selected boreal lakes in Finland and determined a representative set of possible drivers. Our data underline the key role of nitrate in regulating seasonal and spatial N2O concentrations. Nitrate explained 78% of the variation in N2O across all lakes. The Global Warming Potential of N2O in our data was 35% of that of diffusive CH4 emission underlining the importance to include N2O in landscape GHG evasion estimates.

Human-made reservoirs are now recognized as potentially significant sources of greenhouse gases, comparable to other anthropogenic sources, yet efforts to estimate these reservoir emissions have been hampered by the complexity of the underlying processes and a lack of coherent budgeting approaches. Here we present a unique modelling framework, the G-res Tool, which was explicitly designed to estimate the net C footprint of reservoirs across the globe. The framework involves the development of statistically robust empirical models describing the four major emission pathways for carbon-based greenhouse gases (GHG) from reservoirs: diffusive CO2 and CH4 emissions, bubbling CH4 emissions from the reservoir surface, and CH4 emissions due to degassing downstream the reservoir, based on an extensive meta-analysis of published data from the past three decades. These empirical models allow the prediction of reservoir-specific emissions, how they may shift over time and account for naturally occurring GHG generating pathways in aquatic networks.

Freshwater reservoirs are a known source of greenhouse gas (GHG) to the atmosphere, but their quantitative significance is still only loosely constrained. Although part of this uncertainty can be attributed to the difficulties in measuring highly variable fluxes, it is also the result of a lack of a clear accounting methodology, particularly about what constitutes new emissions and potential new sinks. In this paper, we review the main processes involved in the generation of GHG in reservoir systems and propose a simple approach to quantify the reservoir GHG footprint in terms of the net changes in GHG fluxes to the atmosphere induced by damming, that is, ´€˜what the atmosphere sees’. The approach takes into account the pre-impoundment GHG balance of the landscape, the temporal evolution of reservoir GHG emission profile as well as the natural emissions that are displaced to or away from the reservoir site resulting from hydrological and other changes. It also clarifies the portion of the reservoir carbon burial that can potentially be considered an offset to GHG emissions.

We studied CO2 release dynamics between a stockpile and the atmosphere and estimated dry matter losses of forest chips made from small-diameter Scots pine, either whole trees or stemwood. A stockpile established in early August in northern Finland was monitored for six months. Based on changes in the basic density of the chip samples, a dry matter loss of 2.6–2.8% occurred during the storage period, but there were no statistically significant differences between the two chip assortments. The dry matter loss derived from the CO2 effluxes was 1.3–1.5%. Even when capturing only about half of the carbon loss deduced from dry mass measurements, the CO2 measurements provided valuable information about decomposition dynamics in stockpiles. The CO2 flux rates were not static, but could differ by an order of magnitude, depending on the spatial location of flux measurement and the evolution of temperature conditions within the pile. Whole-tree chips generated more heat during the first two months after pile construction. The highest emissions and largest mass flows were measured at that time near the top of the pile, where also the humidity had condensed, suggesting that the stockpile structure and temperature gradient probably channeled the gas flows.

This study explores the variability in concentrations of dissolved CH4 and annual flux estimates in the pelagic zone in a statistically defined sample of 207 lakes in Finland. The lakes were situated in the boreal zone, in an area where the mean annual air temperature ranges from −2.8 to 5.9°C. We examined how lake CH4 dynamics related to regional lake types assessed according to the EU water framework directive. Ten lake types were defined on the basis of water chemistry, color, and size. Lakes were sampled for dissolved CH4 concentrations four times per year, at four different depths at the deepest point of each lake. We found that CH4 concentrations and fluxes to the atmosphere tended to be high in nutrient rich calcareous lakes, and that the shallow lakes had the greatest surface water concentrations. Methane concentration in the hypolimnion was related to oxygen and nutrient concentrations, and to lake depth or lake area. The surface water CH4 concentration was related to the depth or area of lake. Methane concentration close to the bottom can be viewed as proxy of lake status in terms of frequency of anoxia and nutrient levels. The mean pelagic CH4 release from randomly selected lakes was 49 mmol m−2 a−1. The sum CH4 flux (storage and diffusion) correlated with lake depth, area and nutrient content, and CH4 release was greatest from the shallow nutrient rich and humic lakes. Our results support earlier lake studies regarding the regulating factors and also the magnitude of global emission estimate. These results propose that in boreal region small lakes have higher CH4 fluxes per unit area than larger lakes, and that the small lakes have a disproportionate significance regarding to the CH4 release.

Question Measurements of ecosystem carbon (C) exchange are usually labour-intensive and expensive. In peatlands, these temporally and spatially limited measurements are often up-scaled over comparable ecosystems, such as ombrotrophic bogs, to provide an estimate for ecosystem level carbon dioxide (CO2) fluxes. Peatlands typically have moisture variations reflected in the presence of microforms (e.g. hummocks and hollows), each with characteristic plant life forms. However, so far the applicability of peatland type (e.g. bog, fen) or microforms for up-scaling has not been assessed. Does the vegetation composition or function of associated species differ so greatly between the same types of peatland that up-scaling is impossible? Location Five ombrotrophic bogs in Northern Europe; in Ireland, Finland and western Russia. Methods We described the variation in vegetation of microforms within and between ombrotrophic bogs using multivariate analyses. Thereafter, we measured CO2 exchange at different microforms and evaluated the relationship between vegetation structure and the light response of photosynthesis. Results Our results show that the community composition of hummocks, lawns and hollows was rather uniform at the plant life-form level. The photosynthetic capacity per leaf area unit was quite similar within microform classes over the different bogs. The observed differences between sites in capacity were mainly related to variation in leaf area. Conclusions A reliable estimate of ecosystem-level photosynthesis requires knowledge of the proportion of different microforms in an area and the leaf area characteristics for each microform in the year(s) in question. Assessments of ecosystem-level photosynthesis are important with regard to current and future changes in climate, as the most dramatic changes in peatlands involve water level drawdown, which in turn is likely to lead to changes in the relative proportions of microforms within peatlands.

Temporal and spatial variation in CH