Season CO2 Emissions Research Articles

More Frequent Spaceborne Sampling of XCO2 Improves Detectability of Carbon Cycle Seasonal Transitions in Arctic‐Boreal Ecosystems

AbstractSurface, aircraft, and satellite measurements indicate pervasive early cold season (Augut–September) CO2 emissions across Arctic regions, consistent with increased ecosystem metabolism in plants and soils. A key remaining question is whether cold season sources will become large enough to permanently shift the Arctic into a net carbon source. Polar orbiting GHG satellites provide robust estimation of regional carbon budgets but lack sufficient spatial coverage and repeat frequency to track sink‐to‐source transitions in the early cold season. Mission concepts such as the Arctic Observing Mission (AOM) advocate for flying imaging spectrometers in highly elliptical orbits (HEO) over the Arctic to address sampling limitations. We perform retrieval and flux inversion simulation experiments using the AURORA mission concept, leveraging a Panchromatic imaging Fourier Transform Spectrometer (PanFTS) in HEO. Our simulations demonstrate the potential benefits of increased CO2 sampling for detecting emissions during the early cold season.

Struvite-phosphorus effects on greenhouse gas emissions and plant and soil response in a furrow-irrigated rice production system in eastern Arkansas

Phosphorus (P) fertilizers with low water solubility, like struvite (MgNH4PO4·6H2O), have been identified to possibly reduce nutrient losses in furrow-irrigated cropping systems. However, there is a lack of research on the impacts of P and nitrogen (N) fertilization on greenhouse gas [GHG; i.e., methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2)] production in furrow-irrigated rice (Oryza sativa). The objective of this study was to evaluate the effects of electrochemically precipitated struvite (ECST), chemically precipitated struvite (CPST), triple superphosphate (TSP), diammonium phosphate (DAP), environmentally smart nitrogen (ESN), and an unamended control (CT) on GHG emissions, global warming potential (GWP), and plant and soil responses at the up-slope position of a furrow-irrigated rice field in east-central Arkansas. Seasonal CH4 and CO2 emissions did not differ (P > 0.05) among fertilizer treatments, while N2O emissions were greater (P = 0.02) from CT (i.e., 5.97 kg ha−1 season−1), which did not differ from ECST, and were lowest from ESN (1.50 kg ha−1 season−1), which did not differ from TSP, CPST, ECST, and DAP. Global warming potential was greatest (P < 0.05) from CT (1612 kg CO2 eq. ha−1 season−1), which did not differ from ECST, and was lowest from ESN (436 kg CO2 eq. ha−1 season−1), which did not differ from TSP, ECST, CPST, and DAP. The combination of numerically greater yield and lower N2O emissions from CPST and ESN suggested that slow-release fertilizers could constitute an effective mitigation tool to reduce GHG emissions, maintain production, and improve sustainability in furrow-irrigated rice systems.

Sheepfolds induce significant increase of seasonal CO2, CH4 and N2O emissions in temperate steppes of Inner Mongolia

IntroductionThe changes in grassland management and grassland types are strongly linked with dynamics in soil physico-chemical properties and vegetation attributes, with important implications for carbon/nitrogen cycling and greenhouse gas (GHG) fluxes. However, the seasonal variations of GHG emissions from sheepfolds, and the underlying biotic and abiotic drivers affecting GHG exchanges across different steppe and management types remain largely unclear.MethodsTaking the Inner Mongolian grassland as a model system, we measured the fluxes of CO2, CH4 and N2O, as well as soil and vegetation variables, in three contrasting grassland management areas (grazing, sheepfold, enclosure) and in three representative (wet typical, dry typical, desert) grassland ecosystems in July, September and November 2016.ResultsOur results showed that: (1) GHG fluxes were mostly higher in the plant growing season (July and September) than in the nongrowing season (November); sheepfold area had significantly higher GHG emissions (in July and mean over the season) than enclosed and grazing areas, with the effects being most pronounced in dry typical steppe. (2) The high GHG emissions in dry typical steppe were closely associated with the interactions among favorable soil temperature and moisture, high total organic carbon (TOC) content, and high aboveground biomass. The important predictors for CO2 emission were soil TOC and pH, whereas that for CH4 and N2O emissions were soil temperature and moisture content, in sheepfold areas. (3) Three GHG emissions were negatively affected by species richness across all steppe and management types, which might be a consequence of indirect effects through the changes in soil TOC and total nitrogen (TN).DiscussionThese results indicate that sheepfold areas are intensive hotspot sources of GHGs in the steppes, and it is of great importance to help to account GHG emissions and develop mitigation strategies for sheepfold areas for sustainable grassland management in the natural steppe based pastoral production ecosystems.

Metabolism and carbonate buffering drive seasonal dynamics of CO2 emissions from two German reservoirs

Biological metabolism drives much of the variation in CO2 in terrestrial ecosystems but does not explain CO2 oversaturation and emission in net autotrophic lakes and reservoirs. The unexplained CO2 could be attributed to the equilibria between CO2 and the carbonate buffering system, which is seldom integrated into CO2 budgets, let alone its interplay with metabolism on CO2 emissions. Here, we perform a process-based mass balance modeling analysis based on an 8-year dataset from two adjacent reservoirs with similar catchment sizes but contrasting trophic states and alkalinity. We find that in addition to the well-acknowledged driver of net metabolic CO2 production, carbonate buffering also determines the total amount and seasonal dynamics of CO2 emissions from the reservoirs. Carbonate buffering can contribute up to nearly 50% of whole-reservoir CO2 emissions, by converting the ionic forms of carbonate to CO2. This results in similar seasonal CO2 emissions from reservoirs with differing trophic state, even in low alkalinity system. We therefore suggest that catchment alkalinity, instead of trophic state, may be more relevant in predicting CO2 emissions from reservoirs. Our model approach highlights the important role of carbonate buffering and metabolism that generate and remove CO2 throughout the reservoirs on a seasonal scale. The inclusion of carbonate buffering could diminish a major uncertainty in the estimation of reservoir CO2 emissions and increase the robustness of aquatic CO2 emission estimates.

Maize/Peanut Intercropping Reduces Carbon Footprint Size and Improves Net Ecosystem Economic Benefits in the Huang-Huai-Hai Region: A Four-Year Study

The dual challenges of global climate change and reductions in the amount of arable land represent growing threats to the stability of global human populations. Efforts to further optimize cropping systems to maximize yields while minimizing greenhouse gas emissions in limited land areas have thus emerged as a focus in modern agriculture. Cereal-intercropping management strategies may represent a promising approach to simultaneously addressing both of these challenges in China. We aimed at comprehensively assessing changes in yield, carbon footprint, and net ecosystem economic benefit when transitioning from maize/peanut monoculture to intercropping in a field-scale study in an effort to aid in the development of low-carbon intercropping systems that do not have an adverse impact on Chinese grain yields. Beginning in June of 2018, a randomized complete block design with three treatments was used to initiate this study: (1) peanut monoculture (P), (2) maize monoculture (M), and (3) maize/peanut intercropping (MP). We compared yield, greenhouse gas emissions, carbon footprint and net ecosystem economic benefit. Results over four years showed that the land equivalent ratio associated with MP was greater than 1. All three of these cropping systems were net CO2 and N2O sources as well as net CH4 sinks, with MP generating significantly (p < 0.05) lower N2O and CO2 flux as well as smaller seasonal N2O and CO2 emissions relative to M. MP additionally reduced the carbon footprint associated with this cropping system by 11.11–31.65% and 30.37–43.62% relative to M and P, respectively. Consistently, MP treatment resulted in respective 70.69% and 26.25% net ecosystem economic benefit (NEEB) increases relative to the M and P conditions while simultaneously enhancing energy use efficiency. In summary, MP systems have potential economic benefit with lower environmental risk alternative to traditional peanut or maize monocropping systems. Converting from peanut or maize monocropping systems to MP systems practices contributed to improved farmland use efficiency, clean production and increased farmers’ income in an agricultural system.

Methane and carbon dioxide emissions from the forest floor of a black spruce forest on permafrost in interior Alaska

High-latitude warming has stimulated CO2 and CH4 emissions from permafrost peatland. This study evaluated growing season CH4 and CO2 emissions from a forest floor of a lowland black spruce forest on permafrost in interior Alaska using automated-closed chambers, anaerobic incubation of peat soils and next-generation sequencing. The CH4 emissions from May to October were 723 ± 432 mg C m−2 and 829 ± 628 mg C m−2 from the two Carex wet plots, 124 ± 76 mg C m−2 from the Sphagnum moss plot, and 11 mg C m−2 from the lichen plot (± denotes standard deviation of different years). The CH4 emissions in the peak season showed diurnal variations with a single peak around noon or double peaks depending on the plots. The CH4 emissions were an order of magnitude lower than those for other northern wetlands, possibly because deep, cold peats regulated CH4 production and oxidation at the dry aerobic surface layer. Low water table positions strongly inhibited CH4 emissions in 2018, suggesting the importance of dissolved CH4 pool at the bottom of the active layer. The future trajectory of CH4 emissions could substantially change with water conditions, deep soil temperatures, and sedge compositions.

Substantial non-growing season carbon dioxide loss across Tibetan alpine permafrost region.

One of the major uncertainties for projecting permafrost carbon (C)-climate feedback is a poor representation of the non-growing season carbon dioxide (CO2 ) emissions under a changing climate. Here, combining in situ field observations, regional synthesis and a random forest model, we assessed contemporary and future soil respired CO2 (i.e., soil respiration, Rs ) across the Tibetan alpine permafrost region, which has received much less attention compared with the Arctic permafrost domain. We estimated the regional mean Rs of 229.8, 72.9 and 302.7g C m-2 year-1 during growing season, non-growing season and the entire year, respectively; corresponding to the contemporary losses of 296.9, 94.3 and 391.2Tg Cyear-1 from this high-altitude permafrost-affected area. The non-growing season Rs accounted for a quarter of the annual soil CO2 efflux. Different from the prevailing view that temperature is the most limiting factor for cold-period CO2 release in Arctic permafrost ecosystems, precipitation determined the spatial pattern of non-growing season Rs on the Tibetan Plateau. Using the key predictors, model extrapolation demonstrated additional losses of 38.8 and 74.5Tg C from the non-growing season for a moderate mitigation scenario and a business-as-usual emissions scenario, respectively. These results provide a baseline for non-growing season CO2 emissions from high-altitude permafrost areas and help for accurate projection of permafrost C-climate feedback.

CO2 emission from soil in silage maize irrigated with wastewater under deficit irrigation in direct sowing practice

It is necessary to understand and measure the impact of tillage and irrigation practices on CO2 emissions from the soil with an environmental sensitivity, while wastewater irrigation increases crop biomass yield. The main objective of the present study was to investigate the changes and reasons in CO2 emissions from soil conventional and conservative tillage under different levels of wastewater irrigation. The CO2 emission from tillage-sowing to harvest over the regular measurements with a EGM-5 infrared gas analyzer device was investigated with three replicates in three deficit irrigation levels (0%, 33%, and 67%) of domestic recycled wastewater in conventional tillage and direct sowing practices. Binary relationships of CO2 emissions with H2O emission, air temperature, and the soil temperature and moisture measured at three different depths (5 cm, 10 cm, 20 cm) were also investigated and strong (p < 0.01) positive linear correlations were determined. Wastewater irrigation and conventional tillage significantly increased CO2 emissions compared to freshwater irrigation and direct sowing practice, while deficit irrigation practice decreased it. The direct sowing reduced seasonal CO2 emissions 25.1% and 26.1% for per unit area (1 ha) of silage maize and per unit of fresh silage yield (1 kg), respectively, compared to conventional tillage. The lowest CO2 emission per unit area and yield was determined in full irrigation treatment with freshwater in direct-sowing, while, in wastewater applications, it was determined in irrigation levels 33% per unit area and 67% per unit yield, under direct sowing. Thirty-three percent and 67% treatments in direct sowing resulted in less seasonal CO2 emissions as 38.7% per unit area and 13.8% per unit fresh silage yield, respectively compared to full irrigation treatment with freshwater in conventional tillage. Mean CO2 emissions in these treatments were found lower 17.9% per unit area and higher 17.8% per unit fresh silage yield compared to the full irrigation treatment with freshwater in direct-sowing. It was concluded that CO2 emissions per unit yield could be decreased with 33% water saving under wastewater irrigation conditions, and could be achieved environmental additional benefits from more decreasing CO2 emission by direct sowing also.

Closing the Winter Gap—Year‐Round Measurements of Soil CO2 Emission Sources in Arctic Tundra

AbstractNon‐growing season CO2 emissions from Arctic tundra remain a major uncertainty in forecasting climate change consequences of permafrost thaw. We present the first time series of soil and microbial CO2 emissions from a graminoid tundra based on year‐round in situ measurements of the radiocarbon content of soil CO2 (Δ14CO2) and of bulk soil C (Δ14C), microbial activity, and temperature. Combining these data with land‐atmosphere CO2 exchange allows estimates of the proportion and mean age of microbial CO2 emissions year‐round. We observe a seasonal shift in emission sources from fresh carbon during the growing season (August Δ14CO2 = 74 ± 4.7‰, 37% ± 3.4% microbial, mean ± se) to increasingly older soil carbon in fall and winter (March Δ14CO2 = 22 ± 1.3‰, 47% ± 8% microbial). Thus, rising soil temperatures and emissions during fall and winter are depleting aged soil carbon pools in the active layer and thawing permafrost and further accelerating climate change.

Nongrowing Season CO2 Emissions Determine the Distinct Carbon Budgets of Two Alpine Wetlands on the Northeastern Qinghai—Tibet Plateau

Alpine wetlands sequester large amounts of soil carbon, so it is vital to gain a full understanding of their land-atmospheric CO2 exchanges and how they contribute to regional carbon neutrality; such an understanding is currently lacking for the Qinghai—Tibet Plateau (QTP), which is undergoing unprecedented climate warming. We analyzed two-year (2018–2019) continuous CO2 flux data, measured by eddy covariance techniques, to quantify the carbon budgets of two alpine wetlands (Luanhaizi peatland (LHZ) and Xiaobohu swamp (XBH)) on the northeastern QTP. At an 8-day scale, boosted regression tree model-based analysis showed that variations in growing season CO2 fluxes were predominantly determined by atmospheric water vapor, having a relative contribution of more than 65%. Variations in nongrowing season CO2 fluxes were mainly controlled by site (categorical variable) and topsoil temperature (Ts), with cumulative relative contributions of 81.8%. At a monthly scale, structural equation models revealed that net ecosystem CO2 exchange (NEE) at both sites was regulated more by gross primary productivity (GPP), than by ecosystem respiration (RES), which were both in turn directly controlled by atmospheric water vapor. The general linear model showed that variations in nongrowing season CO2 fluxes were significantly (p &lt; 0.001) driven by the main effect of site and Ts. Annually, LHZ acted as a net carbon source, and NEE, GPP, and RES were 41.5 ± 17.8, 631.5 ± 19.4, and 673.0 ± 37.2 g C/(m2 year), respectively. XBH behaved as a net carbon sink, and NEE, GPP, and RES were –40.9 ± 7.5, 595.1 ± 15.4, and 554.2 ± 7.9 g C/(m2 year), respectively. These distinctly different carbon budgets were primarily caused by the nongrowing season RES being approximately twice as large at LHZ (p &lt; 0.001), rather than by other equivalent growing season CO2 fluxes (p &gt; 0.10). Overall, variations in growing season CO2 fluxes were mainly controlled by atmospheric water vapor, while those of the nongrowing season were jointly determined by site attributes and soil temperatures. Our results highlight the different carbon functions of alpine peatland and alpine swampland, and show that nongrowing season CO2 emissions should be taken into full consideration when upscaling regional carbon budgets. Current and predicted marked winter warming will directly stimulate increased CO2 emissions from alpine wetlands, which will positively feedback to climate change.

Soil greenhouse gas emissions and grazing management in northern temperate grasslands

Adaptive multi-paddock (AMP) grazing, a grazing system in which individual paddocks are grazed for a short duration at a high stock density and followed by a long rest period, is claimed to be an effective tool to sustainably manage and improve grasslands and enhance their ecosystem services. However, whether AMP grazing is superior to conventional grazing (n-AMP) in reducing soil greenhouse gas (GHG) emissions is unclear. Here, we measured CO2, CH4, and N2O fluxes between August 2017 and August 2019 in 12 pairs of AMP vs. n-AMP ranches distributed across an agro-climatic gradient in Alberta, Canada. We found that field GHG fluxes did not differ between AMP and n-AMP grazing systems, but instead were regulated by specific management attributes, environmental conditions, and soil properties, including cattle stocking rate, cultivation history, soil moisture content, and soil bulk density. Specifically, we found that seasonal mean CO2 emissions increased with increasing cattle stocking rates, while CH4 uptake was lower in grasslands with a history of cultivation. Seasonal mean CO2 emissions increased while CH4 uptake decreased with increasing soil moisture content. In addition, CH4 uptake decreased with increasing soil bulk density. Observed N2O emissions were poorly predicted by the management, environmental conditions, and soil properties investigated in our study. We conclude that AMP grazing does not have an advantage over n-AMP grazing in reducing GHG fluxes from grasslands. Future efforts to develop optimal management strategies (e.g., the use of sustainable stocking rates and avoided cultivation) that reduce GHG emissions should also consider the environmental conditions and soil properties unique to every grassland ecosystem.

Long-term (42 years) effect of thinning on soil CO2 emission in a mixed broadleaved-Korean pine (Pinus koraiensis) forest in Northeast China

Thinning is an important forest management practice that has great potential to influence regional soil carbon storage and dynamics. The present study measured soil respiration (RS, the efflux of CO2 emitted) and its two components (heterotrophic (RH) and autotrophic (RA) respiration) from soil 42 years after thinning in comparison to un-thinning (control). Autotrophic respiration was significantly greater in the thinning plot, approximately 44% higher compared to the control, while both Rs and RH were slightly, but not significantly, higher in the thinning plot. Higher fine root biomass might have contributed to the higher Ra in the thinning plot. Both Rs and RH showed clear soil temperature-dependent seasonal patterns, whereas Ra was less responsive to changes in temperature, especially within one specific season. The annual and season-specific temperature sensitivities of RS and RH were lower in the thinning plot, specifically during the mid-growing season. Furthermore, variations in the season-specific temperature sensitivity of Rs and RH were less intense in the thinning plot. We conclude that forest thinning can reduce the temperature sensitivity of RS and RH during the mid-growing season and increase soil CO2 emission in the long term.

Seasonal energy performance characteristics of novel ejector-expansion air conditioners with low-GWP refrigerants

The objective of this study is to investigate the seasonal performance characteristics of novel ejector-expansion air conditioners (EEACs) with low global warming potential refrigerants. A simplified simulation model for EEACs is developed and validated using measured data. Using a simulation model, the coefficient of performance, cooling seasonal performance factor, and life cycle climate performance of the EEACs employing low global warming potential refrigerants are analyzed at various operating conditions and modes. In addition, the climatic effects on the cooling seasonal performance factors and life cycle climate performances of the EEACs are evaluated at four different weather conditions. The EEAC with R290 exhibits the cooling seasonal performance factor and total CO2 emissions that are 22% higher and 23.3% lower, respectively, than those of the baseline air conditioner with R410A. In general, R290 is the best working fluid for EEACs in terms of the seasonal performance and lifetime environmental factor.

Soil respiration in larch and pine ecosystems of the Krasnoyarsk region (Russian Federation): a latitudinal comparative study

Based on the long-term (12 years) data on soil respiration (SR) measurements in representative conifer forests of the Krasnoyarsk region (Central Siberia), we demonstrated specific characteristics of SR. The study sites located closely to Arctic Circle were related to different latitudes, including 56° N (SAE site, Krasnoyarsk), 60° N (ZOTTO site, Zotino), and 64° N (Tura site, Evenkia). Study sites were selected in forest ecosystems (> 41 years old) and represented a wide range of the climate, stand, permafrost availability, and soil types. However, the mean seasonal values of SR (mean ± SD) varied in a relatively narrow range from 2.11 ± 0.69 in the forest-steppe zone (SAE) to 2.82 ± 1.77 μmol CO2 m−2 s−1 in northern larch taiga (Tura). Nevertheless, a twofold difference in the duration of growing season among northern and southern locations results in a variation of total seasonal CO2 emissions (mean ± SD) from 216 ± 136 g C m−2 in larch stands of northern taiga to 369 ± 115 g C m−2 in larch stands of southern forest-steppe zone. Evaluation of the multiannual dynamics of SR over the past 1.5 decades (1995–2010) showed the escalation of SR in the permafrost larch stands (Tura) in 2005–2010. That has been coupled with the enhanced activity of the soil heterotrophic microbiota in 2007–2010. Our study highlights the importance of further monitoring of SR in permafrost Siberian ecosystems.

CO2, CH4 and N2O fluxes in an alpine meadow on the Tibetan Plateau as affected by N-addition and grazing exclusion

Limited understanding of the effects of enhanced nitrogen (N) addition and grazing exclusion (E) on greenhouse gases fluxes (GHGs: CO2, CH4, and N2O) in grasslands constrains our ability to respond to the challenges of future climate change. In this study, we conducted a field experiment using a static closed opaque chamber to investigate the response of GHG fluxes to N addition (69 kg N ha−1 year−1 applied in 3 splits) and grazing exclusion in an alpine meadow on the Tibetan Plateau during the growing seasons from 2011 to 2013. Our results showed that winter grazing significantly raised soil temperature (ST), while grazing exclusion (E) had no effect on soil moisture (SM), and N fertilizer (F) had no effect on ST or SM. Aboveground biomass (AB) and root biomass (RB) were not significantly affected by E in 2011-2013 (p > 0.05), but F significantly affected AB and RB (p < 0.05). Compared with winter grazing, only E substantially reduced seasonal mean CO2 emissions (by about 20.1%) during the experimental period. E did not significantly directly affect CH4 uptake, whereas N addition reduced seasonal mean CH4 uptake by about 6.5%, and N addition changed seasonal average absorption of N2O into an emission source. CO2 flux is the major contributor to CO2 equivalent emissions in this area. Our results indicate that exclosure from livestock grazing might be a promising measure to reduce CO2 emissions, while enhanced N addition might reduce CH4 uptake and increase N2O emission in the alpine meadow under future climate change.

Land use conversion influences soil respiration across a desert-oasis ecoregion in Northwest China, with consideration of cold season CO2 efflux and its significance

Quantifying annual soil CO2 emissions and the effects of physical and geochemical factors on soil CO2 efflux will improve the carbon budget estimates, as well as enhance predictions of how soil CO2 emission will response to climate change in arid areas. To data, variability in soil respiration rates caused by land use conversion in the desert-oasis ecoregion of Northwest China remains poorly characterized, especially the contribution of cold season (November-February) CO2 emission. Soil respiration was measured in a Haloxylon ammodendron desert shrubland, a Zea mays cropland, a Populus gansuensis forest, and a Tamarix chinensis Lour wetland using a LI-COR 8100 Soil Respiration Observation System from April 2016 to March 2019. Annual soil CO2 emissions totaled 176, 778, 918, and 397 g C m−2 in the desert shrubland, cropland, forest, and wetland, respectively. The ratio of cold season CO2 emissions to the annual varied from 6 to 15% across ecosystems. Therefore, ignoring cold season CO2 emissions would lead to underestimates of carbon losses in the desert-oasis ecoregion. The soil respiration rate at 10 °C was influenced by soil organic carbon content in all four ecosystems. In the cropland and forest, soil respiration rate was affected by the interaction of soil moisture and soil temperature, while in the wetland and desert shrubland, soil respiration was sensitive to a single factor, soil temperature. Land use conversion induced differences in organic matter accumulation, soil temperature, and soil moisture, and as a consequence, produced variability in soil respiration rates across the desert-oasis ecoregion.

Greater Nitrogen Availability, Nitrous Oxide Emissions, and Vegetable Yields with Fall-Applied Chicken Relative to Horse Manure

Optimal manure management can maximize agronomic benefits and minimize environmental impacts. Field experiments were conducted in the Pacific Northwest (Vancouver, Canada) to determine how chicken and horse manures that were fall-applied to meet nitrogen crop demand affect soil ammonium (NH4+) and nitrate (NO3−), apparent net mineralization (ANM) and nitrification (ANN), crop biomass and nutrient concentration, and fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4). Relative to horse manure, chicken manure increased soil NH4+ by 60-fold, ANM by 2-fold, and ANN by 4-fold. Emissions of N2O (+600%) and CO2 (+45%) were greater and growing season CO2 emissions (−40%) were lower after application of chicken than horse manure. Productivity of cover crop (+30%), legume cover crop (−25%), and squash cash crop (+20%) were affected by chicken relative to horse manure. Overall, fall-applied chicken manure increased yields, N availability, and environmental impacts relative to horse manure.

Key indicators of Arctic climate change: 1971–2017

Key observational indicators of climate change in the Arctic, most spanning a 47 year period (1971–2017) demonstrate fundamental changes among nine key elements of the Arctic system. We find that, coherent with increasing air temperature, there is an intensification of the hydrological cycle, evident from increases in humidity, precipitation, river discharge, glacier equilibrium line altitude and land ice wastage. Downward trends continue in sea ice thickness (and extent) and spring snow cover extent and duration, while near-surface permafrost continues to warm. Several of the climate indicators exhibit a significant statistical correlation with air temperature or precipitation, reinforcing the notion that increasing air temperatures and precipitation are drivers of major changes in various components of the Arctic system. To progress beyond a presentation of the Arctic physical climate changes, we find a correspondence between air temperature and biophysical indicators such as tundra biomass and identify numerous biophysical disruptions with cascading effects throughout the trophic levels. These include: increased delivery of organic matter and nutrients to Arctic near‐coastal zones; condensed flowering and pollination plant species periods; timing mismatch between plant flowering and pollinators; increased plant vulnerability to insect disturbance; increased shrub biomass; increased ignition of wildfires; increased growing season CO2 uptake, with counterbalancing increases in shoulder season and winter CO2 emissions; increased carbon cycling, regulated by local hydrology and permafrost thaw; conversion between terrestrial and aquatic ecosystems; and shifting animal distribution and demographics. The Arctic biophysical system is now clearly trending away from its 20th Century state and into an unprecedented state, with implications not only within but beyond the Arctic. The indicator time series of this study are freely downloadable at AMAP.no.

Seasonal evaluation of heat pump system for building heating and ventilation – a case study

This paper presents results obtained from seasonal evaluation of ground source heat pump (GSHP) and exhaust air heat pump (EAHP) systems used for heating and ventilation of a school building. A Matlab simulation program was developed with models of the following elements: the building thermal performance, central heating and ventilation installations, the ground source heat pump with the ground source heat exchanger and exhaust air heat pumps in air handling units. The system based exclusively on the GSHP attaining all heating needs of the central heating and ventilation installations was compared with the combined system of the GSHP and the EAHP. The analysis was based on hourly calculations of all energy capacities and COPs as well as seasonal performance factors. In addition, the energy ratings in terms of seasonal usage of delivered, renewable, auxiliary and primary energy were performed. Those energy ratings enabled the estimation of seasonal CO2 emissions in all analysed systems. The combined application of the GSHP and the EAHP in the building gave the lowest values of primary energy consumption and CO2 emissions among all considered systems.

Factors controlling seasonal CO2 and CH4 emissions in three tropical mangrove-dominated estuaries in Australia

CO2 and CH4 emissions from estuaries of the Southern Hemisphere are greatly under-represented in global estuary emission estimates. This study quantifies seasonal pCO2 and CH4 concentrations and emissions along the salinity gradient of three tropical mangrove-dominated estuaries in Australia. A combination of approaches (i.e. carbon stable isotopes, groundwater inputs, riverine contribution, freshwater flushing times) was used to assess the spatial and seasonal variable factors that controlled the estuary surface water CO2 and CH4 concentrations and hence emissions. Overall, CO2 and CH4 emissions ranged from 21.6 to 110.4 mmol m−2 d−1 and 40.3 to 1047.1 μmol m−2 d−1, respectively, and were within or at the high end compared to estuaries in Australia and globally. In the Johnstone River estuary, high emissions were predominantly driven by groundwater and riverine carbon inputs with exports of CO2 and CH4 to the ocean expected in the wet season. In the Fitzroy River estuary and Constant Creek estuary, in situ production and terrestrial carbon inputs were likely the main factors controlling CO2 and CH4 emissions. The contribution of riverine CO2 may be more important to overall CO2 emissions than the riverine CH4 to overall CH4 emissions in estuaries. The relative contribution of in situ production, the exchange with adjacent coastal habitats (i.e. mangroves, inter-tidal flats), and terrestrial, riverine and groundwater inputs in the wet and in the dry season determined whether CO2 and CH4 were fully ventilated within the estuaries or exported to the open ocean. The revised global estimate for estuary CO2 emission of the latitude 0 to 23.5 °S is 52.1 ± 16.1 mmol m−2 d−1, which is 15% higher than a recent estimate of this latitudinal region.