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Abstract This chapter is a short overview of the art of inferring CO2 sources and sinks from atmospheric mole fraction measurements, with an opening towards other greenhouse gases, such as methane, for which the inference problem is similar. The various components of this Bayesian estimation problem are recalled: the observations (in situ or from satellites), the prior information about the sources and sinks, the physical models that describe atmospheric transport, and the statistical models that describe the errors of all input information pieces. The chapter also discusses the pros and cons of this approach.

Funding: This work was supported by the National Key R&D Program of China (No. 2021YFD2200405). Alterations in plant litter inputs into the soil are expected to significantly affect soil greenhouse gas (GHG) emissions. However, the influence on boreal forest soils is not clear, given the large amount of accumulated soil organic matter that may buffer the impacts from the input of fresh litter. In this study, we conducted a litter manipulation experiment to explore the effects of the litter layer on soil GHG fluxes in a Dahurian larch (Larix gmelinii) forest ecosystem in northeastern China. Three litter treatments were implemented, namely aboveground litter removal (LR), litter double (LD), and unchanged litter input (CK). The associated microclimate, litter characteristics, and soil properties were also measured. The results showed that this larch forest soil acts as a source of CO and NO but acts as a sink for CH for all litter manipulation treatments. LD increased the soil CO and NO fluxes by 15% and 34%, while LR decreased them by 8% and 21%, respectively. However, soil CH uptake decreased by 34% in LD treatment and increased by 22% in LR treatment, respectively. Litter manipulation treatments can not only affect soil GHG fluxes directly but also, via their effects on soil MBC, NH −N, and NO −N content, indirectly affect variations in soil CO, CH and NO fluxes, respectively. Our study highlights the importance of the plant litter layer in regulating soil GHG between the atmosphere and soil in a Dahurian larch forest ecosystem, especially for litter addition. Considering the natural increase in litter quantity over time, this important regulatory function is essential for an accurate estimation of the role of boreal forests in mitigating future climate change.

Niaodao, a lakeside wetland, was used as the focus of this study to investigate the effect of rainfall changes on the greenhouse gas fluxes of wetland ecosystems. Wetland plots with different moisture characteristics (+25%, −25%, +75%, and −75% rainfall treatments and the control treatment (CK)) were constructed to observe in situ field greenhouse gas emissions at 11:00 and 15:00 (when the daily mean values were similar) in the growing season from May to August 2020 by static chamber–gas chromatography and to investigate the responses of wetland greenhouse gases to different rainfall treatments. The results showed the following: (1) The carbon dioxide (CO2) flux ranged from −49.409 to 374.548 mg·m−2·h−1. The mean CO2 emission flux was greater at 11:00 than at 15:00, and the +25% and +75% treatments exhibited substantially higher CO2 emissions. In addition, the CO2 flux showed a small peak at the beginning of the growing season when the temperature first started to rise. All treatments showed the effect of the CO2 source, and their effects were significantly different. (2) The methane (CH4) flux ranged from −213.839 to 330.976 µg·m−2·h−1 and exhibited an absorption state at 11:00 and an emission state at 15:00. The CH4 emission flux in August (the peak growing season) differed greatly between treatments and was significantly negatively correlated with the rainfall amount (p 2O) flux ranged from −10.457 to 16.878 µg·m−2·h−1 and exhibited a weak source effect throughout the growing season, but it was not significantly correlated with soil moisture; it was, however, negatively correlated with soil temperature. (4) The different treatments resulted in significant differences in soil physical and chemical properties (electrical conductivity, pH, total soil carbon, and total soil nitrogen). The rainfall enhancement treatments significantly improved soil physical and chemical properties.

A nationwide peatland survey was conducted across 50 ombrotrophic peatlands (bogs) in Ireland to ascertain a wide range of peat properties. In addition to natural (relatively intact) sites, we surveyed the most prevalent peatland land use categories (LUCs): grassland, forestry and peat extraction (both industrial and domestic), as well as management options (deep drained; shallow drained; rewetting). Furthermore, the entirety of the peat profile (down to the sub-peat mineral soil/bedrock) was sampled. Our results demonstrate that Irish bogs have been drastically altered by human activities and that the sampled peat properties reflect the nature and magnitude of the impact of the land use and management. Environmental Protection Agency 2022-07-25 JG: full report added at author's request

Increasing levels of CO2 in the atmosphere is a contributing cause to climate change. To give a better understanding, natural sources of CO2 is as important as anthropogenic sources, such as burning fossil fuels. The current role of large boreal lakes as emitters of CO2 are poorly understood and there is a clear lack of data from different types of systems. The aim of this thesis was to examine CO2 fluxes from Roxen, Glan and Vättern, three large lakes in Sweden. The purpose of the study was also to compare different approaches to get empirical CO2 flux data, and to investigate if there was difference between the lakes and study periods. Floating chambers were used as method with both direct measured fluxes and calculated fluxes. The direct fluxes were measured with sensors equipped inside the chambers. The calculated fluxes were obtained with gas samples from the chambers, water samples and wind speed in k-wind models. The results showed both temporal and spatial variability between the periods and the lakes. The results also showed a difference between the methods, where CO2 fluxes from sensors (direct measurements) ranged from -36 to 152 mmol m-2 d-1 and the calculated fluxes from the CC-model (Cole & Caraco 1998) ranged from –29 to 58 mmol m-2 d-1. Ökande halter av CO2 i atmosfären är en bidragande faktor till klimatförändringar. För att få en bättre förståelse för de så behövs kunskap om naturliga flöden, inte enbart antropogena källor, som t.ex. förbränning av fossila bränslen som störst fokus kretsar kring. Den nuvarande kunskapsnivån om större nordiska sjöars CO2 utsläpp är begränsad, och det finns en tydlig brist i data från dessa typer av system. Målet med denna uppsats var att utforska CO2 flöden från Roxen, Glan och Vättern, tre stora sjöar i Sverige. Syftet med studien var också att jämföra olika sätt att samla in empiriskt material samt undersöka om det fanns skillnader mellan sjöarna samt de olika studerade perioderna. Flytande kammare användes för att samla in prover som mättes direkt genom en sensor, men de användes också för att ta manuella gasprover som sedan beräknade flödet av CO2 med hjälp av modeller i efterhand. Resultatet visade både på skillnader i tid och rum mellan perioderna och sjöarna. Resultatet visade även att det fanns en skillnad mellan de olika metoderna vi använde oss av, där sensor (direkta mätningar) var mellan -36 to 152 mmol m-2 d-1 och flödesberäkningarna från CC-modellen (Cole & Caraco 1998) var –29 to 58 mmol m-2 d-1. 

Grassland systems are important terrestrial carbon sinks and have great potential for carbon (C) sequestration. Increased atmospheric nitrogen (N) deposition has profoundly affected C balance and greenhouse gas emissions in grassland systems. However, the effects of long-term nitrogen (LN) deposition on net ecosystem carbon budget (NECB) and net global warming potential (NGWP) in grassland systems are still not clearly understood. A field experiment was conducted to test the effect of LN addition (0, 30, 60, 120 and 240 kg N ha(-1) yr(-1)) on NECB and NGWP in a temperate grassland area in Inner Mongolia, China. LN addition significantly increased soil organic carbon density (SOCD) and C sequestration in surface soil (0-30 cm) with the increase of N addition rate from 2005 to 2018. In contrast, a decrease in ecosystem respiration (R-e) was observed, except at low LN concentration (30 kg N ha(-1) yr(-1)). Annual N2O flux was significantly increased, and the CH4 sink was significantly decreased by LN addition. NECB and NGWP were relatively weak in this temperate grassland, ranging from -627.29 +/- 198.81 and -232.87 +/- 23.11 kg CO2 ha(-1) yr(-1), respectively, and significantly decreased with increasing LN application. The offset effect of N2O emission to ecosystem C uptake decreased significantly with increased LN addition, and was stable at high LN addition. This was related to the increase in soil C sequestration due to plant C uptake. These results indicate that LN addition significantly decreased the NECB and NGWP of this grassland. Increased long-term N deposition significantly enhanced soil C sequestration, which has important implications for mitigating climate warming.

Boreal peatlands represent a biogeochemically unique and diverse environment in high-latitude landscape. They represent a long-term globally significant sink for carbon dioxide and a source of methane, hence playing an important role in regulating the global climate. There is an increasing interest in deciphering peatland biogeochemical processes to improve our understanding of how anthropogenic and climate change effects regulate the peatland biogeochemistry and greenhouse gas balances. At present, most studies investigating land-atmosphere exchanges of peatland ecosystems are commonly based on single-tower setups, which require the assumption of homogeneous conditions during upscaling to the landscape. However, the spatial organization of peatland complexes might feature large heterogeneity due to its varying underlying topography and vegetation composition. Little is known about how well single site studies represent the spatial variations of biogeochemical processes across entire peatland complexes. The recently established Kulbäcksliden Research Infrastructure (KRI) includes five peatland study sites located less than 3 km apart, thus providing a unique opportunity to explore the spatial variation in ecosystem-scale processes across a typical boreal peatland complex. All KRI sites are equipped with eddy covariance flux towers combined with installations for detailed monitoring of biotic and abiotic variables, as well as catchment-scale hydrology and hydrochemistry. Here, we review studies that were conducted in the Kulbäcksliden area and provide a description of the site characteristics as well as the instrumentation available at the KRI. We highlight the value of long-term infrastructures with ecosystem-scale and replicated experimental sites to advance our understanding of peatland biogeochemistry, hydrology, ecology, and its feedbacks on the environment and climate system. Frontiers in Earth Science, 11 ISSN:2296-6463

The dataset details greenhouse gas fluxes as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) across six intertidal sites in the winter and summer of 2013. Three of the sites were in Morecambe Bay, North West England and three of the sites were in Essex, South East England, each of these sites consisted of a saltmarsh area and adjacent mudflat area, twenty two sampling quadrats were placed on each area. Light and dark incubations were performed using a benthic chamber on seven of the twenty two quadrats of each site. This data was collected as part of Coastal Biodiversity and Ecosystem Service Sustainability (CBESS): NE/J015644/1. The project was funded with support from the Biodiversity and Ecosystem Service Sustainability (BESS) programme. BESS is a six-year programme (2011-2017) funded by the UK Natural Environment Research Council (NERC) and the Biotechnology and Biological Sciences Research Council (BBSRC) as part of the UK's Living with Environmental Change (LWEC) programme. Each site consisted of a polygon of roughly 400 x 500 m to 1000 x 1000 m in size, dependent upon site length (parallel to shore) and width (perpendicular to shore). Twenty two 1 x 1 m quadrats were randomly placed within each site polygon using R (R Development Core Team, 2014) to specify placement at four different spatial scales (A = 1 quadrat only, B = 3 quadrats at 1 m to 10 m apart, C = 6 quadrats at 10 m to 100 m apart, D = 12 quadrats at 100 m to 1000 m or site maximum). Only the quadrat from scale A, two quadrats from scale B and four quadrats from scale C were sampled for greenhouse gas fluxes. Light and dark incubations were performed using a benthic chamber connected to an infrared gas analyser. This allowed direct measurements of CO2. CH4 and N2O fluxes were measured from gas samples collected at five time points during the dark incubation and stored in glass Exetainer bottles for later processing. The samples were analysed using a gas chromatograph.

© 2022 Jensen, Webb, Simpson, Baulch, Leavitt and Finlay. This is an open- access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Inland waters are important global sources, and occasional sinks, of CO 2 , CH 4, and N 2 O to the atmosphere, but relatively little is known about the contribution of GHGs of constructed waterbodies, particularly small sites in agricultural regions that receive large amounts of nutrients (carbon, nitrogen, phosphorus). Here, we quantify the magnitude and controls of diffusive CO 2 , CH4 , and N 2 O fluxes from 20 agricultural reservoirs on seasonal and diel timescales. All gases exhibited consistent seasonal trends, with CO 2 concentrations highest in spring and fall and lowest in mid-summer, CH 4 highest in mid-summer, and N 2 O elevated in spring following ice-off. No discernible diel trends were observed for GHG content. Analyses of GHG covariance with potential regulatory factors were conducted using generalized additive models (GAMs) that revealed CO 2 concentrations were affected primarily by factors related to benthic respiration, including dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), dissolved organic carbon (DOC), stratification strength, and water source (as δ18 O water ). In contrast, variation in CH 4 content was correlated positively with factors that favoured methanogenesis, and so varied inversely with DO, soluble reactive phosphorus (SRP), and conductivity (a proxy for sulfate content), and positively with DIN, DOC, and temperature. Finally, N 2 O concentrations were driven mainly by variation in reservoir mixing (as buoyancy frequency), and were correlated positively with DO, SRP, and DIN levels and negatively with pH and stratification strength. Estimates of mean CO 2 -eq flux during the open-water period ranged from 5,520 mmol m−2 year 1 (using GAM- predictions) to 10,445 mmol m−2 year−1 (using interpolations of seasonal data) reflecting how extreme values were extrapolated, with true annual flux rates likely falling between these two estimates. Financial support for data collection and analyses were provided in part by Government of Saskatchewan (Award 200160015), Natural Sciences and Engineering Research Council of Canada Discovery grants (to KF, GS, HB, and PL), the Canada Foundation for Innovation (Award RGPIN–2018- 0490), University of Regina. Faculty yes