Greenhouse Gas Flux Measurements Research Articles

Sediment Addition Leads to Variable Responses in Temperate Salt Marsh Greenhouse Gas Fluxes During the Growing Season

AbstractSalt marshes play an important role in coastal carbon cycling. Unfortunately, these systems are threatened by sea level rise. One strategy to increase the resilience of marshes is thin‐layer placement of sediment (TLP). While TLP can boost elevation, little is known about how TLP alters greenhouse gas fluxes. We addressed this knowledge gap by measuring greenhouse gas fluxes in TLP plots that received either 7 cm (TLP‐7 cm) or 14 cm of added sediment (TLP‐14 cm), control plots that received no sediment, and reference plots that served as elevation end goal targets for the TLP plots. We found that mean (± standard error) CO2 uptake was comparable between control and TLP plots (control: −25.84 ± 2.46; TLP‐7 cm: −24.44 ± 3.32; TLP‐14 cm: −23.18 ± 2.08 mmol m−2 hr−1) and significantly less in reference plots (−9.54 ± 2.98 mmol m−2 hr−1). However, TLP plots (TLP‐7 cm: 35.74 ± 12.70, TLP‐14 cm: 19.79 ± 3.47 μmol m−2 hr−1) emitted up to 7 to 22 times more CH4 compared to control (5.77 ± 0.74 μmol m−2 hr−1) and reference (1.63 ± 0.75 μmol m−2 hr−1) plots, respectively. N2O fluxes from the TLP plots exhibited both uptake (TLP‐7 cm) and emission (TLP‐ 14 cm). Overall, the marsh remained a net greenhouse gas sink, at least during the times we measured—during the day and throughout the growing season. This research demonstrates the dynamics of greenhouse gas fluxes in marshes amended with sediment and highlights the need for future diel and annual measurements.

Fossil mosses are emitting methane after maritime Antarctic glacier retreat

In the extraordinary weather conditions of the austral summer of 2023, fossil mosses thawed out from under the Bellingshausen Ice Dome, King George Island, Southern Shetland Archipelago of maritime Antarctica. At the end of the austral summer, we directly measured greenhouse gas fluxes (CH4 and CO2) from the surface of fossil mosses. We showed that fossil mosses were strong emitters of CH4 and weak emitters of CO2. The real-time measured CH4 emissions reached 0.173 μmol m−2 s−1, which is comparable to CH4 efflux in water bodies or wet tundra in the Arctic.

Identifying landscape hot and cold spots of soil greenhouse gas fluxes by combining field measurements and remote sensing data

Abstract. Upscaling chamber measurements of soil greenhouse gas (GHG) fluxes from point scale to landscape scale remain challenging due to the high variability in the fluxes in space and time. This study measured GHG fluxes and soil parameters at selected point locations (n=268), thereby implementing a stratified sampling approach on a mixed-land-use landscape (∼5.8 km2). Based on these field-based measurements and remotely sensed data on landscape and vegetation properties, we used random forest (RF) models to predict GHG fluxes at a landscape scale (1 m resolution) in summer and autumn. The RF models, combining field-measured soil parameters and remotely sensed data, outperformed those with field-measured predictors or remotely sensed data alone. Available satellite data products from Sentinel-2 on vegetation cover and water content played a more significant role than those attributes derived from a digital elevation model, possibly due to their ability to capture both spatial and seasonal changes in the ecosystem parameters within the landscape. Similar seasonal patterns of higher soil/ecosystem respiration (SR/ER–CO2) and nitrous oxide (N2O) fluxes in summer and higher methane (CH4) uptake in autumn were observed in both the measured and predicted landscape fluxes. Based on the upscaled fluxes, we also assessed the contribution of hot spots to the total landscape fluxes. The identified emission hot spots occupied a small landscape area (7 % to 16 %) but accounted for up to 42 % of the landscape GHG fluxes. Our study showed that combining remotely sensed data with chamber measurements and soil properties is a promising approach for identifying spatial patterns and hot spots of GHG fluxes across heterogeneous landscapes. Such information may be used to inform targeted mitigation strategies at the landscape scale.

Global observation gaps of peatland greenhouse gas balances: needs and obstacles

Greenhouse gas (GHGs) emissions from peatlands contribute significantly to ongoing climate change because of human land use. To develop reliable and comprehensive estimates and predictions of GHG emissions from peatlands, it is necessary to have GHG observations, including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), that cover different peatland types globally. We synthesize published peatland studies with field GHG flux measurements to identify gaps in observations and suggest directions for future research. Although GHG flux measurements have been conducted at numerous sites globally, substantial gaps remain in current observations, encompassing various peatland types, regions and GHGs. Generally, there is a pressing need for additional GHG observations in Africa, Latin America and the Caribbean regions. Despite widespread measurements of CO2 and CH4, studies quantifying N2O emissions from peatlands are scarce, particularly in natural ecosystems. To expand the global coverage of peatland data, it is crucial to conduct more eddy covariance observations for long-term monitoring. Automated chambers are preferable for plot-scale observations to produce high temporal resolution data; however, traditional field campaigns with manual chamber measurements remain necessary, particularly in remote areas. To ensure that the data can be further used for modeling purposes, we suggest that chamber campaigns should be conducted at least monthly for a minimum duration of one year with no fewer than three replicates and measure key environmental variables. In addition, further studies are needed in restored peatlands, focusing on identifying the most effective restoration approaches for different ecosystem types, conditions, climates, and land use histories.

The Surface-to-Atmosphere GHG Fluxes in Rewetted and Permanently Flooded Former Peat Extraction Areas Compared to Pristine Peatland in Hemiboreal Latvia

When it comes to greenhouse gas (GHG) reduction, the role of water tables in former peat extraction areas has received considerable interest in recent decades. This study analysed the carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) surface-to-atmosphere fluxes from a rewetted and permanently flooded former peat extraction areas in comparison to pristine peatland in hemiboreal Latvia. Measurements of GHG fluxes combined gas sampling using a closed-chamber (opaque) method with the gas chromatography detection method. Among the studied land-use types, the highest annualised CO2 fluxes (soil heterotrophic and autotrophic respiration) were recorded in rewetted former peat extraction areas with restored vegetation and in undisturbed peatland (4.10 ± 0.21 and 3.45 ± 0.21 t CO2-C ha−1 yr−1, respectively), with the lowest in flooded former peat extraction areas (0.55 ± 0.05 t CO2-C ha−1 yr−1); temperature and groundwater level were found to be significant influencing factors. The highest annualised CH4 fluxes were recorded in undisturbed peatland (562.4 ± 155.8 kg CH4-C ha−1 yr−1), followed by about two-fold and ~20-fold smaller CH4 fluxes in flooded and rewetted areas, respectively. N2O fluxes were negligible in all the studied land-use types, with the highest N2O fluxes in undisturbed peatland (0.66 ± 0.41 kg N2O-N ha−1 yr−1).

Assessing the climate change mitigation potential from food waste composting

Food waste is a dominant organic constituent of landfills, and a large global source of greenhouse gases. Composting food waste presents a potential opportunity for emissions reduction, but data on whole pile, commercial-scale emissions and the associated biogeochemical drivers are lacking. We used a non-invasive micrometeorological mass balance approach optimized for three-dimensional commercial-scale windrow compost piles to measure methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) emissions continuously during food waste composting. Greenhouse gas flux measurements were complemented with continuous oxygen (O2) and temperature sensors and intensive sampling for biogeochemical processes. Emission factors (EF) ranged from 6.6 to 8.8 kg CH4–C/Mg wet food waste and were driven primarily by low redox and watering events. Composting resulted in low N2O emissions (0.01 kg N2O–N/Mg wet food waste). The overall EF value (CH4 + N2O) for food waste composting was 926 kgCO2e/Mg of dry food waste. Composting emissions were 38–84% lower than equivalent landfilling fluxes with a potential net minimum savings of 1.4 MMT CO2e for California by year 2025. Our results suggest that food waste composting can help mitigate emissions. Increased turning during the thermophilic phase and less watering overall could potentially further lower emissions.

Soil profile greenhouse gas concentrations and fluxes from a semiarid grassland and a cropland site in an agro-pastoral ectone of northern China

Despite broad information on greenhouse gas (GHG) emissions from the soil surface, only few studies have examined the depth related GHG concentration and production within the soil. We coupled chamber surface GHG flux measurements with analysis of subsurface GHG concentrations at five depths (0, 10, 30, 50 and 70 cm) using silicon tubes in a grassland and cropland soils in a semi-arid agro-pastoral ecotone over a full year. Grassland and cropland soils behaved as net CO2 and N2O sources, but sinks of CH4. CO2 and N2O concentrations increased but CH4 decreased with soil depth. Subsurface GHG fluxes calculated using Fick’s law decreased with depth. The modeled GHG and measured surface fluxes agreed much better for CO2 than N2O or CH4. Spring-thaw and rainfall events triggered N2O pulses, CH4 uptake peaks and CH4 concentration drops. Annual emissions or uptake based on chamber method were 4820–7580 kg C ha−1 yr−1, 2.4–1.5 kg C ha−1 yr−1, and 0.13–0.14 kg N ha−1 yr−1 for CO2, CH4, and N2O across the grassland and cropland, respectively. Modeled annual accumulation of GHG fluxes dropped with depth, whereas the topsoil (0–20 cm) contributed about 65% for CO2, 68% for N2O and 72% for CH4 of the total profile. The vertical distribution of GHG fluxes reflected those of soil organic carbon and root biomass. The grassland had higher annual CO2 flux but lower CH4 uptake than the cropland. Annual N2O fluxes were similar between the two ecosystems.

Nutrient release and flux dynamics of CO2, CH4, and N2O in a coastal peatland driven by actively induced rewetting with brackish water from the Baltic Sea

Abstract. The rewetting of drained peatlands supports long-term nutrient removal in addition to reducing emissions of carbon dioxide (CO2) and nitrous oxide (N2O). However, rewetting may lead to short-term nutrient leaching into adjacent water and high methane (CH4) emissions. The consequences of rewetting with brackish water on nutrient and greenhouse gas (GHG) fluxes remain unclear, although beneficial effects such as lower CH4 emissions seem likely. Therefore, we studied the actively induced rewetting of a coastal peatland with brackish water, by comparing pre- and post-rewetting data from the peatland and the adjacent bay. Both the potential transport of nutrients into adjacent coastal water and the shift in GHG fluxes (CO2, CH4, and N2O) accompanying the change from drained to inundated conditions were analyzed based on measurements of the surface water concentrations of nutrients (dissolved inorganic nitrogen, DIN, and phosphate, PO43-), oxygen (O2), components of the CO2 system, CH4, and N2O together with manual closed-chamber measurements of GHG fluxes. Our results revealed higher nutrient concentrations in the rewetted peatland than in the adjacent bay, indicating that nutrients leached out of the peat and were exported to the bay. A comparison of DIN concentrations of the bay with those of an unaffected reference station showed a significant increase after rewetting. The maximum estimated nutrient export (mean ± 95 % confidence level) out of the peatland was calculated to be 33.8 ± 9.6 t yr−1 for DIN-N and 0.24 ± 0.29 t yr−1 for PO4-P, depending on the endmember (bay vs. reference station). The peatland was also a source of GHG in the first year after rewetting. However, the spatial and temporal variability decreased, and high CH4 emissions, as reported for freshwater rewetting, did not occur. CO2 fluxes (mean ± SD) decreased slightly from 0.29 ± 0.82 g m−2 h−1 (pre-rewetting) to 0.26 ± 0.29 g m−2 h−1 (post-rewetting). The availability of organic matter (OM) and dissolved nutrients were likely the most important drivers of continued CO2 production. Pre-rewetting CH4 fluxes ranged from 0.13 ± 1.01 mg m−2 h−1 (drained land site) to 11.4 ± 37.5 mg m−2 h−1 (ditch). After rewetting, CH4 fluxes on the formerly dry land increased by 1 order of magnitude (1.74 ± 7.59 mg m−2 h−1), whereas fluxes from the former ditch decreased to 8.5 ± 26.9 mg m−2 h−1. These comparatively low CH4 fluxes can likely be attributed to the suppression of methanogenesis and oxidation of CH4 by the available O2 and sulfate in the rewetted peatland, which serve as alternative electron acceptors. The post-rewetting N2O flux was low, with an annual mean of 0.02 ± 0.07 mg m−2 h−1. Our results suggest that rewetted coastal peatlands could account for high, currently unmonitored, nutrient inputs into adjacent coastal water, at least on a short timescale such as a few years. However, rewetting with brackish water may decrease GHG emissions and might be favored over freshwater rewetting in order to reduce CH4 emissions.

Dynamics of Picea abies mortality and CO2 and CH4 fluxes from spruce trees decomposition in the southwest of the Valdai Upland, Russia

A mass decline of Picea abies (hereinafter – spruce), often associated with outbreaks of Ips typographus, is one of the main reasons for the reduction of spruce forests. In turn, dry and fallen trees can be both stock and source of greenhouse gases at various stages of decomposition. In our study, using an unmanned aerial vehicle, we evaluated the dynamics of spruce decline in two forest types in the southwest of the Valdai Upland (Central Forest State Nature Reserve, Russia), namely Sphagnum-bilberry forests and nemoral spruce forests. It was found that the rate of decline in Sphagnum-bilberry spruce forest was much higher than in nemoral spruce forest. By the fourth year after a windfall on 0.13 km2, 913 spruce individuals had withered in Sphagnum-bilberry forest and 66 ones in the nemoral spruce forest. Based on direct measurements of greenhouse gas fluxes by chamber method on dead trunks and coarse woody debris, it was found that in relative values the highest amount of CO2 is emitted by coarse woody debris of the decay classes 3–4 (800–1800 mg CO2 × m-2 × h-1). Deadwood and coarse woody debris from the first decay classes are assumed to be a source of CH4 (0.0008–0.0070 mg CO2 × m-2 × h-1), and from classes 3–5 they are a stock (from -0.0070 mg CO2 × m-2 × h-1 to -0.0009 mg CO2 × m-2 × h-1). When converted to the total surface areas of deadwood and coarse woody debris of the study sites, it was found that coarse woody debris of the decay classes 3–5 (2.3–13.6 kg CO2 × h-1) made the highest contribution to the integral CO2 emission, and deadwood (67 mg CH4 × h-1) made the highest contribution to the CH4 emission. Significant differences in greenhouse gas fluxes were found both between deadwood and decay classes of coarse woody debris, and between fluxes from deadwood and coarse woody debris of individual decay classes in various forest types. The results have shown the importance of considering deadwood and all available decay classes of coarse woody debris when estimating greenhouse gas fluxes from dead timber and the contribution of debris to the carbon cycle in forest ecosystems.

Comparing airborne algorithms for greenhouse gas flux measurements over the Alberta oil sands

Abstract. To combat global warming, Canada has committed to reducing greenhouse gases to be (GHGs) 40 %–45 % below 2005 emission levels by 2025. Monitoring emissions and deriving accurate inventories are essential to reaching these goals. Airborne methods can provide regional and area source measurements with small error if ideal conditions for sampling are met. In this study, two airborne mass-balance box-flight algorithms were compared to assess the extent of their agreement and their performance under various conditions. The Scientific Aviation's (SciAv) Gaussian algorithm and the Environment and Climate Change Canada's top-down emission rate retrieval algorithm (TERRA) were applied to data from five samples. Estimates were compared using standard procedures, by systematically testing other method fits, and by investigating the effects on the estimates when method assumptions were not met. Results indicate that in standard scenarios the SciAv and TERRA mass-balance box-flight methods produce similar estimates that agree (3 %–25 %) within algorithm uncertainties (4 %–34 %). Implementing a sample-specific surface extrapolation procedure for the SciAv algorithm may improve emission estimation. Algorithms disagreed when non-ideal conditions occurred (i.e., under non-stationary atmospheric conditions). Overall, the results provide confidence in the box-flight methods and indicate that emissions estimates are not overly sensitive to the choice of algorithm but demonstrate that fundamental algorithm assumptions should be assessed for each flight. Using a different method, the Airborne Visible InfraRed Imaging Spectrometer – Next Generation (AVIRIS-NG) independently mapped individual plumes with emissions 5 times larger than the source SciAv sampled three days later. The range in estimates highlights the utility of increased sampling to get a more complete understanding of the temporal variability of emissions and to identify emission sources within facilities. In addition, hourly on-site activity data would provide insight to the observed temporal variability in emissions and make a comparison to reported emissions more straightforward.

Critical method needs in measuring greenhouse gas fluxes

Reaching climate goals depends on appropriate and accurate methods to quantify greenhouse gas (GHG) fluxes and to verify that efforts to mitigate GHG emissions are effective. We here highlight critical advantages, limitations, and needs regarding GHG flux measurement methods, identified from an analysis of >13 500 scientific publications regarding three long-lived GHGs, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). While existing methods are well-suited for assessing atmospheric changes and local fluxes, they are expensive and have limited accessibility. Further, we are typically forced to choose between methods for very local GHG sources and sinks and their regulation (m2-scaled measurements), or methods for aggregated net fluxes at >ha or km2 scales measurements. The results highlight the key need of accessible and affordable GHG flux measurement methods for the many flux types not quantifiable from fossil fuel use, to better verify inventories and mitigation efforts for transparency and accountability under the Paris agreement. The situation also calls for novel methods, capable of quantifying large scale GHG flux patterns while simultaneously distinguishing local source and sink dynamics and reveal flux regulation, representing key knowledge for quantitative GHG flux modeling. Possible strategies to address the identified GHG flux measurement method needs are discussed. The analysis also generated indications of how GHG flux measurements have been distributed geographically and across flux types, which are reported.

Introduction of a guideline for measurements of greenhouse gas fluxes from soils using non‐steady‐state chambers

AbstractSoils represent a major global source and sink of greenhouse gases (GHGs). Many studies of GHG fluxes between soil, plant and atmosphere rely on chamber measurements. Different chamber techniques have been developed over the last decades, each characterised by different requirements and limitations. In this manuscript, we focus on the non‐steady‐state technique which is widely used for manual measurements but also in automatic systems. Although the measurement method appears very simple, experience gained over the years shows that there are many details which have to be taken into account to obtain reliable measurement results.This manuscript aims to share lessons learnt and pass on experiences in order to assist the reader with possible questions or unexpected challenges, ranging from the planning of the design of studies and chambers to the practical handling of the chambers and the quality assurance of the gas and data analysis. This concise introduction refers to a more extensive Best Practice Guideline initiated by the Working Group Soil Gases (AG Bodengase) of the German Soil Science Society (Deutsche Bodenkundliche Gesellschaft). The intention was to collect and aggregate the expertise of different working groups in the research field. As a compendium, this Best Practice Guideline is intended to help both beginners and experts to meet the practical and theoretical challenges of measuring soil gas fluxes with non‐steady‐state chamber systems and to improve the quality of the individual flux measurements and thus entire GHG studies by reducing sources of uncertainty and error.

Greenhouse gas emissions from Mexican inland waters: first estimation and uncertainty using an upscaling approach

ABSTRACT The traditional upscaling approach to greenhouse gas (GHG) emission estimates of inland waters is imprecise, but more precise methods based on environmental drivers are a longstanding challenge. Mexico lacks GHG emission estimates for its inland waters, and only sparse but scientifically validated information is available. This study provides the first GHG emission estimates from Mexican inland waters using 4275 GHG flux measurements from 26 distinctive waterbodies and one local and another global surface area dataset (INEGI and HydroLAKES). GHG emission factors were calculated and subsequently upscaled to estimate total national GHG emissions from the inland waters and compare to other emission measures based on mean global emission factors or size-productivity weighted (SPW) models. Mean (standard error) annual fluxes from all inland waters were 2.2 (5.3) kg CO2 m−2 yr−1, 0.6 (1.14) kg CH4 m−2 yr−1, and 1.0 × 10−3 (6.0 × 10−4) kg N2O m−2 yr−1. Estimates for natural waterbodies are annual average release rates between 74 (87) and 139 (163.23) Tg CO2eq while artificial waterbodies reach between 32 (2) and 21 (21) Tg CO2eq according to INEGI and HydroLAKES datasets, respectively. Considerable uncertainty was determined in the calculated mean emission factor, mostly for anthropogenic emissions. Waterbody area and chlorophyll a concentration were used as proxies to model CO2 and CH4 fluxes through regression analysis. According to SPW and IPCC models, computed mean annual CH4 emission factors were close to our estimates and exhibited a strong influence from eutrophication. In a likely scenario of increased eutrophication in Mexico, an increase in total net emissions from inland waters could be expected.

The climate benefits of topsoil removal and Sphagnum introduction in raised bog restoration

Many raised bogs in Central Europe are in an unfavorable state: drainage causes high emissions of carbon dioxide (CO2) and nitrous oxide (N2O), while rewetting may result in high methane (CH4) emissions. Also, the establishment of typical bog species is often hampered during restoration. Measures like topsoil removal (TSR) or introduction of target vegetation are known to improve restoration success in other systems, but experiences on bogs after long‐term agricultural use are scarce and their climate effects including carbon losses from TSR are unknown. In a field trial in north‐western Germany, consisting of seven plots (intensive grassland, IG, and six restoration approaches), we explored the effects of rewetting, TSR and Sphagnum introduction on greenhouse gas (GHG) emissions. We measured GHG fluxes to obtain two‐year GHG budgets and applied a radiative forcing model to assess the time‐dependent climate effects. Existing uncertainty of decomposition processes in the translocated topsoil has been incorporated by different topsoil accounting scenarios. According to our data, rewetting alone reduced CO2 emissions by approximately 75% compared to IG, but substantially increased CH4 emissions. After TSR and rewetting, on‐site CO2 emissions were close to zero or, with Sphagnum introduction, net negative while CH4 emissions remained very low. The climatic warming effect of TSR including C export becomes less climate warming than rewetting nutrient‐rich peatlands after a few decades. For raised bog restoration, we therefore recommend a TSR sufficient to achieve nutrient‐poor and acidic conditions needed for rapid Sphagnum establishment.

Simultaneous tree stem and soil greenhouse gas (CO2 , CH4 , N2 O) flux measurements: a novel design for continuous monitoring towards improving flux estimates and temporal resolution.

Tree stems and soils can act as sources and sinks for the greenhouse gases (GHG) carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O). Since both uptake and emission capacities can be large, especially in tropical rainforests, accurate assessments of the magnitudes and temporal variations of stem and soil GHG fluxes are required. We designed a new flexible stem chamber system for continuously measuring GHG fluxes in a French Guianese rainforest. Here, we describe this new system, which is connected to an automated soil GHG flux system, and discuss measurement uncertainty and potential error sources. In line with findings for soil GHG flux estimates, we demonstrated that lengthening the stem chamber closure time was required for accurate estimates of tree stem CH4 and N2 O flux but not tree stem CO2 flux. The instrumented stem was a net source of CO2 and CH4 and a weak sink of N2 O. Our experimental setup operated successfully in situ and provided continuous tree and soil GHG measurements at a high temporal resolution over an 11-month period. This automated system is a major step forward in the measurement of GHG fluxes in stems and the atmosphere concurrently with soil GHG fluxes in tropical forest ecosystems.

A Novel Low-Cost, High-Resolution Camera System for Measuring Peat Subsidence and Water Table Dynamics

Peatlands are highly dynamic systems, able to accumulate carbon over millennia under natural conditions, but susceptible to rapid subsidence and carbon loss when drained. Short-term, seasonal and long-term peat surface elevation changes are closely linked to key peatland attributes such as water table depth (WTD) and carbon balance, and may be measured remotely using satellite radar and LiDAR methods. However, field measurements of peat elevation change are spatially and temporally sparse, reliant on low-resolution manual subsidence pole measurements, or expensive sensor systems. Here we describe a novel, simple and low-cost image-based method for measuring peat surface motion and WTD using commercially available time-lapse cameras and image processing methods. Based on almost two years’ deployment of peat cameras across contrasting forested, burned, agricultural and oil palm plantation sites in Central Kalimantan, Indonesia, we show that the method can capture extremely high resolution (sub-mm) and high-frequency (sub-daily) changes in peat surface elevation over extended periods and under challenging environmental conditions. WTD measurements were of similar quality to commercially available pressure transducers. Results reveal dynamic peat elevation response to individual rain events, consistent with variations in WTD. Over the course of the relatively severe 2019 dry season, cameras in deep-drained peatlands recorded maximum peat shrinkage of over 8 cm, followed by partial rebound, leading to net annual subsidence of up to 5 cm. Sites with higher water tables, and where borehole irrigation was used to maintain soil moisture, had lower subsidence, suggesting potential to reduce subsidence through altered land-management. Given the established link between subsidence and CO2 emissions, these results have direct implications for the management of peatlands to reduce high current greenhouse gas (GHG) emissions. Camera-based sensors provide a simple, low-cost alternative to commercial elevation, WTD and GHG flux monitoring systems, suitable for deployment at scale, and in areas where existing approaches are impractical or unaffordable. If ground-based observations of peat motion can be linked to measured GHG fluxes and with satellite-based monitoring tools, this approach offers the potential for a large-scale peatland monitoring tool, suitable for identifying areas of active carbon loss, targeting climate change mitigation interventions, and evaluating intervention outcomes.

Lessons learned from more than a decade of greenhouse gas flux measurements at boreal forests in eastern Siberia and interior Alaska

We summarized our recently-published papers on greenhouse gas exchanges at two important boreal regions underlain by permafrost: eastern Siberia and interior Alaska. Relevant literatures were also referred to, and future research directions on the high-latitude terrestrial processes were suggested. Long-term monitoring of CO2 fluxes at the boreal forests revealed that anomalous weather and disturbances changed the CO2 balance. More than a decade is required to return to a CO2 sink at burned forests in interior Alaska. Anomalous high precipitation altered the forest structure in eastern Siberia, shifting the overstory/understory contributions to the CO2 balance. The CH4 emissions were higher in the two boreal forests than in the other boreal forests. Upscaling the in-situ observations and comparisons with top-down approaches revealed considerable inconsistencies exist among the approaches. We recommend the following directions in future research. First, long-term monitoring is indispensable to detect the effect of climate change on ecosystems. Second, disturbance impacts, including fire, thermokarst, and wet spells, need to be quantified. Third, further observations are necessary for constraining CH4 exchange models. Finally, reconciling top-down and bottom-up approaches is required to reduce uncertainty. Prompt sharing of observed data and model products is crucial to improve our understanding of high-latitude processes.

A Decade of Ecosystem-Scale Research at an Aridland Constructed Treatment Wetland

Cities are increasingly pursuing more resilient and sustainable futures. One way to do so is by the increased use of Urban Ecological Infrastructure (UEI), including constructed treatment wetlands (CTW). This strategy is particularly important for aridland cities with scarce water resources. In this paper I synthesize nearly ten years of systems-level research at the Tres Rios CTW in Phoenix, AZ USA. Since July 2011, a research team that includes dozens of student volunteers has been sampling monthly for herbaceous biomass and productivity, water quality, transpiration rates, and aquatic metabolism. We also quantify belowground biomass and plant tissue nutrient content annually, and measured greenhouse gas fluxes from 2012 - 2014. Our peak summer biomass values are among the highest reported in the literature, and high rates of transpiration are associated with this biomass. Using our whole-system water budgets and tracer studies we have documented a slow movement of surface water into the marsh from adjacent open water areas that is driven by transpirational losses and that we refer to as the “biological tide”. With our nitrogen (N) budgets for the whole system and the vegetated marsh we showed that roughly 50% of the annual N uptake by the vegetated marsh is driven by new water entering via this biological tide. Our aquatic metabolism sampling suggested that the N uptake associated with the autotrophic water column was roughly 27% of the average annual N uptake by the vegetated marsh. The marsh is a source of CH4 and N2O across the air-water interface and the plants are a net source of CH4 but a net sink for N2O. Our combined flux estimates suggest that the Tres Rios marshes are a net sink for greenhouse gas equivalents because of this plant-mediated net uptake of N2O. Finally, over the years our Tres Rios CTW project has provided a platform for dozens of students and young people to experience ecological research, both in the field and in the lab.

An Eddy Covariance Mesonet For Measuring Greenhouse Gas Fluxes in Coastal South Carolina

Coastal ecosystems are vulnerable to climate change and have been identified as sources of uncertainty in the global carbon budget. Here we introduce a recently established mesonet of eddy covariance towers in South Carolina and describe the sensor arrays and data workflow used to produce three site-years of flux observations in coastal ecosystems. The tower sites represent tidal salt marsh (US-HB1), mature longleaf pine forest (US-HB2), and longleaf pine restoration (replanted clearcut; US-HB3). Coastal ecosystems remain less represented in climate studies despite their potential to sequester large amounts of carbon. Our goal in publishing this open access dataset is to contribute observations in understudied coastal ecosystems to facilitate synthesis and modeling analyses that advance carbon cycle science.

Soil greenhouse gas emissions under different land-use types in savanna ecosystems of Kenya

Abstract. Field measurement data on greenhouse gas (GHG) emissions are still scarce for many land-use types in Africa, causing a high level of uncertainty in GHG budgets. To address this gap, we present in situ measurements of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions from the lowlands of southern Kenya. We conducted eight chamber measurement campaigns on gas exchange from four dominant land-use types (LUTs) comprising (1) cropland, (2) bushland, (3) grazing land, and (4) conservation land between 29 November 2017 and 3 November 2018, accounting for regional seasonality (wet and dry seasons and transitions periods). Mean CO2 emissions for the whole observation period were the highest by a significant margin (p value < 0.05) in the conservation land (75±6 mg CO2-C m−2 h−1) compared to the three other sites, which ranged from 45±4 mg CO2-C m−2 h−1 (bushland) to 50±5 mg CO2-C m−2 h−1 (grazing land). Furthermore, CO2 emissions varied between seasons, with significantly higher emissions in the wet season than the dry season. Mean N2O emissions were highest in cropland (2.7±0.6 µg N2O-N m−2 h−1) and lowest in bushland (1.2±0.4 µg N2O-N m−2 h−1) but did not vary with season. In fact, N2O emissions were very low both in the wet and dry seasons, with slightly elevated values during the early days of the wet seasons in all LUTs. On the other hand, CH4 emissions did not show any significant differences across LUTs and seasons. Most CH4 fluxes were below the limit of detection (LOD, ±0.03 mg CH4-C m−2 h−1). We attributed the difference in soil CO2 emissions between the four sites to soil C content, which differed between the sites and was highest in the conservation land. In addition, CO2 and N2O emissions positively correlated with soil moisture, thus an increase in soil moisture led to an increase in emissions. Furthermore, vegetation cover explained the seasonal variation in soil CO2 emissions as depicted by a strong positive correlation between the normalized difference vegetation index (NDVI) and CO2 emissions, most likely because, with more green (active) vegetation cover, higher CO2 emissions occur due to enhanced root respiration compared to drier periods. Soil temperature did not show a clear correlation with either CO2 or N2O emissions, which is likely due to the low variability in soil temperature between seasons and sites. Based on our results, soil C, active vegetation cover, and soil moisture are key drivers of soil GHG emissions in all the tested LUTs in southern Kenya. Our results are within the range of previous GHG flux measurements from soils from various LUTs in other parts of Kenya and contribute to more accurate baseline GHG emission estimates from Africa, which are key to reducing uncertainties in global GHG budgets as well as for informing policymakers when discussing low-emission development strategies.