Increased Carbon Loss Research Articles

Simulated sensitivity of the Amazon rainforest to extreme drought

Abstract The Amazon rainforest is highly biodiverse and the largest intact, tropical forest in the world. Undisturbed tropical forests act as a carbon sink by taking up about 15% of anthropogenic carbon emissions per year. In the past decades, a declining trend in the carbon sink capacity in the Amazon rainforest has been observed due to increased carbon losses and tree mortality. The causes are disputed, but increasing temperatures and more frequent severe droughts are potentially major drivers. We employ a novel modelling framework and hypothesize that previously rare, extreme droughts in the Amazon, such as the ones in 2005 and 2010, constitute the main cause behind the decline of the net carbon sink in aboveground biomass. Our dynamic vegetation model simulates process-based plant hydraulics and drought-induced mortality, and accounts for the diversity of strategies in plant responses to drought based on observed hydraulic vulnerability curves. The simulated impact of the 2005 drought event temporarily turned the annual Amazon net carbon sink to a carbon source of about 0.25 MgC ha-1. In contrast to other dynamic vegetation models our model simulated an increasing trend in carbon losses and a declining trend in the Amazon carbon sink over the past 25 years (net sink rate of -0.018 Mg C ha-1 year-1 or -0.22 Mg C ha-1 per decade) which corresponds well with long-term forest monitoring data (net sink rate of -0.016 Mg C ha-1 year-1). We show that this trend is entirely attributable to drought-induced forest mortality during extreme years. The simulations show a threshold-like behaviour between drought intensity and biomass loss, which is due to xylem vulnerability, indicating the potentially high sensitivity of Amazon forests to extreme drought. Further increases in the severity and frequency of droughts might thus lead to greater carbon release and tree mortality than previously assumed.

Assessment of mangrove structures and biomass on islands along the Java Sea: a case study on Bawean Islands and Karimunjawa Islands

Mangroves on the islands along the Java Sea play a crucial role in supporting biodiversity, protecting coastlines, and sequestering carbon. However, there is a lack of information on mangrove structure and biomass in the area. This study aimed to assess the mangrove structures and biomass on Desa Daun, located on the Bawean Islands, and Kemujan Island, located on the Karimunjawa Islands, respectively. The study utilized a combination of line transect and quadrant plot methods with a size plot of 10x10 m. We established 7 line transects and 28 quadrant plots in the mangrove forest of Desa Daun and similarly set up 7 line transects and 21 quadrant plots on Kemujan Island. Within each quadrant, the mangrove species were identified, and their diameters at breast height (DBH) were recorded. To assess the relative significance of each species, the importance value index (IVI) was calculated, and allometric equations were applied to estimate biomass and carbon storage in the trees. PlanetScope imagery was also used to quantify the carbon stock of mangroves on those islands. In Desa Daun, 13 mangrove species were identified, while 12 species were recorded on Kemujan Island. The species Nypa fruticans and Excoecaria agallocha exhibited the highest IVI in Desa Daun and Kemujan Island, respectively. Notably, Rhizophora apiculata demonstrated the greatest biomass in both locations, with measurements of 43.08 Mg B/ha in Desa Daun and 102.22 Mg B/ha in Kemujan Island. Overall, mangrove stands on Desa Daun stored biomass of 113.60 Mg B/ha and carbon of 50.98 Mg C/ha, whereas mangrove stands on Kemujan Island stored biomass of 295.04 Mg B/ha and carbon of 131.95 Mg C/ha. Mangrove stands of the whole Bawean Islands sequestered 22,941 Mg C, while Karimunjawa Islands hold much higher C stocks, 79,451 Mg C. Despite being smaller in size, the Karimunjawa Islands have more extensive mangrove coverage compared to the Bawean Islands due to their geomorphological characteristics, which in turn influence their mangrove structures and carbon stocks. However, the loss of mangroves in the Karimunjawa Islands due to aquaculture expansions could increase carbon loss in the islands.

Drought and warming interaction cause substantial economic losses in the carbon market potential of China's northern grasslands

Grasslands are being threatened by global drought and warming. Economic assessments of changing grassland carbon sequestration, a prerequisite for nature-based climate-change mitigation policies, are limited when researchers inadequate consider interactions between drought and warming. Here, we quantified the responses of 35 grass biomasses to combined drought and warming, based on manipulation experiments from 34 peer-reviewed papers; subsequently, we matched them with grasslands in northern China—the eastern range of the larger Eurasian Steppe—and further projected the economic implications for carbon market trading and carbon-sequestration costs. The results show that carbon sequestration in all grassland types, except for forbrich steppe, was significantly reduced by the synergistic interactions of drought and warming. Approximately 10 % of the grasslands in central Xinjiang, identified as forbrich steppe, showed resilience to these stressors. In contrast, the rest of northern China's grasslands suffered increased carbon losses due to drought and warming. The combined effects of drought and warming have caused a loss of 1.6 × 104 million Chinese yuan (CNY) in revenue and excess carbon-sequestration costs exceeding 1.1 × 105 million CNY. Overall, our study results indicate that the synergistic effects of drought and warming significantly undermine the economic viability of carbon sequestration in most of northern China's grasslands. As climate change intensifies, understanding and incorporating the complex interactions of drought and warming can aid in the sustainable management of grassland ecosystems and the development of effective climate-change mitigation policies in arenas, including carbon markets.

Seasonal timing of fluorescence and photosynthetic yields at needle and canopy scales in evergreen needleleaf forests.

The seasonal timing and magnitude of photosynthesis in evergreen needleleaf forests (ENFs) has major implications for the carbon cycle and is increasingly sensitive to changing climate. Earlier spring photosynthesis can increase carbon uptake over the growing season or cause early water reserve depletion that leads to premature cessation and increased carbon loss. Determining the start and the end of the growing season in ENFs is challenging due to a lack of field measurements and difficulty in interpreting satellite data, which are impacted by snow and cloud cover, and the pervasive "greenness" of these systems. We combine continuous needle-scale chlorophyll fluorescence measurements with tower-based remote sensing and gross primary productivity (GPP) estimates at three ENF sites across a latitudinal gradient (Colorado, Saskatchewan, Alaska) to link physiological changes with remote sensing signals during transition seasons. We derive a theoretical framework for observations of solar-induced chlorophyll fluorescence (SIF) and solar intensity-normalized SIF (SIFrelative) under snow-covered conditions, and show decreased sensitivity compared with reflectance data (~20% reduction in measured SIF vs. ~60% reduction in near-infrared vegetation index [NIRv] under 50% snow cover). Needle-scale fluorescence and photochemistry strongly correlated (r2 = 0.74 in Colorado, 0.70 in Alaska) and showed good agreement on the timing and magnitude of seasonal transitions. We demonstrate that this can be scaled to the site level with tower-based estimates of LUEP and SIFrelative which were well correlated across all sites (r2 = 0.70 in Colorado, 0.53 in Saskatchewan, 0.49 in Alaska). These independent, temporally continuous datasets confirm an increase in physiological activity prior to snowmelt across all three evergreen forests. This suggests that data-driven and process-based carbon cycle models which assume negligible physiological activity prior to snowmelt are inherently flawed, and underscores the utility of SIF data for tracking phenological events. Our research probes the spectral biology of evergreen forests and highlights spectral methods that can be applied in other ecosystems.

Influence of coal quality on the tendency for slagging formation on a spreader stoker boiler

ABSTRACT During the combustion of solid fuels in power generation systems, one of the biggest problems related to ash is the surface deposition and accumulation of molten or sintered slag, commonly known as slagging. This research evaluated the influence of coal quality on the tendency for slagging based on the evaluation of practical criteria for industry, such as traditional indices, ash load, and coal granulometry. The indices were evaluated from standardized analyses of the composition and fusibility temperatures of the ash of eight bituminous coals. Ash fusibility tests were performed in both oxidizing and reducing atmospheres. Under oxidizing conditions, iron had a dominant influence on the formation characteristics of slagging, resulting in higher melting temperatures. Coals with low frequencies of hard deposit formation, as determined by their ash composition, contributed significantly to deposition problems due to their high ash load and granulometry. Furthermore, large coal particles require more time to burn, which can lead to caking or slag and increased carbon loss in ash. Therefore, when using empirical indices to assess the tendency for slagging, it is essential to consider ash content and ensure an appropriate distribution of coal sizes for combustion.

Livestock trampling regulates the soil carbon exchange by mediating surface roughness and biocrust cover

Despite the considerable attention devoted to the potential importance of biocrusts in global carbon cycling, their photosynthetic and respiratory responses to human activity and the underlying mechanisms are not yet fully understood. To evaluate the effect of livestock trampling disturbance on the carbon balance of biocrust-covered sandy soil, the net photosynthetic rate (NP), gross photosynthetic rate (GP), and soil respiration rate (R) of algae-lichen mixed crust and moss crust before and after addition of 2, 5, 10, and 20 mm water under different trampling intensities (CK, no trampling; LD, trampling five times; MD, trampling 20 times; and HD, trampling 45 times on the undisturbed soil with an area of 415 cm2) were determined. The results showed the surface roughness decreased after an initial increase, whereas the biocrust cover decreased exponentially with increasing trampling intensity. There was negligible variation in surface soil NP, GP, and R (approximately 0.07 μmol CO2·m−2·s−1) during dry soil periods. The carbon exchange rate in each trampling treatment changed significantly even after a small amount of rainfall (2 mm), but the surface soil still served as a carbon source. As simulated rainfall increased to ≥ 5 mm, the biocrust NP and GP declined (more negative values represent greater carbon uptake), and R continued to increase. Most notably, the CK and LD surfaces switched from carbon sources to carbon sinks, while the HD surface soil remained a carbon source. In terms of cumulative carbon exchange, LD trampling did not significantly increase carbon loss and even contributed to carbon gains compared with CK, whereas MD and HD caused severe carbon loss. In summary, impact of livestock trampling disturbance on the biocrust-covered soil carbon exchange is driven by rainfall, and its response to rainfall is mediated by surface roughness and biocrust cover. Specifically, surface soil carbon gains did not decrease or even increased slightly under light trampling, probably due to slight decreases in biocrust cover offset by the photosynthetic contribution of increased surface roughness, whereas heavy trampling resulted in severe carbon losses as the biocrust cover sharply decreased. This study emphasizes the important role of livestock trampling-induced changes in surface soil structure on the carbon exchange of sandy ecosystems.

Wildfire exacerbates high-latitude soil carbon losses from climate warming

Arctic and boreal permafrost soil organic carbon (SOC) decomposition has been slower than carbon inputs from plant growth since the last glaciation. Anthropogenic climate warming has threatened this historical trend by accelerating SOC decomposition and altering wildfire regimes. We accurately modeled observed plant biomass and carbon emissions from wildfires in Alaskan ecosystems under current climate conditions. In projections to 2300 under the RCP8.5 climate scenario, we found that warming and increased atmospheric CO2 will result in plant biomass gains and higher litterfall. However, increased carbon losses from (a) wildfire combustion and (b) rapid SOC decomposition driven by increased deciduous litter production, root exudation, and active layer depth will lead to about 4.4 PgC of soil carbon losses from Alaska by 2300 and most (88%) of these loses will be from the top 1 m of soil. These SOC losses offset plant carbon gains, causing the ecosystem to transition to a net carbon source after 2200. Simulations excluding wildfire increases yielded about a factor of four lower SOC losses by 2300. Our results show that projected wildfire and its direct and indirect effects on plant and soil carbon may accelerate high-latitude soil carbon losses, resulting in a positive feedback to climate change.

Modeling Yield, Biogenic Emissions, and Carbon Sequestration in Southeastern Cropping Systems With Winter Carinata

Sustainable aviation fuel (SAF) production from lipids is a technologically mature approach for replacing conventional fossil fuel use in the aviation sector, and there is increasing demand for such feedstocks. The oilseed Brassica carinata (known as Ethiopian mustard or simply carinata) is a promising SAF feedstock that can be grown as a supplemental cash crop over the winter fallow season of various annual crop rotations in the Southeast US, avoiding land use changes and potentially achieving some of the soil carbon sequestration and ecosystem service benefits of winter cover crops. However, carinata may require more intensive management than traditional cover crops, potentially leading to additional soil greenhouse gas (GHG) emissions through increased carbon losses from soil tillage and nitrous oxide (N2O) emissions from nitrogen fertilizer application. In this work, the 2017 version of the process-based DayCent ecosystem model was used to establish initial expectations for the total regional SAF production potential and associated soil GHG emissions when carinata is integrated as a winter crop into the existing crop rotations across its current suitability range in southern Alabama, southern Georgia, and northern Florida. Using data from academic and industry carinata field trials in the region, DayCent was calibrated to reproduce carinata yield, nitrogen response, harvest index, and biomass carbon-to-nitrogen ratio. The resulting model was then used to simulate the integration of carinata every third winter across all 2.1 Mha of actively cultivated cropland in the study area. The model predicted regional average yields of 2.9–3.0 Mg carinata seed per hectare depending on crop management assumptions. That results in the production of more than two million Mg of carinata seed annually across the study area, enough to supply approximately one billion liters of SAF. Conventional management of carinata led to only modest increases in soil carbon storage that were largely offset by additional N2O emissions. Climate-smart management via adopting no-till carinata establishment or using poultry litter as a nitrogen source resulted in a substantial net soil GHG sink (0.23–0.31 Mg CO2e ha−1 y−1, or 0.24–0.32 Mg CO2e per Mg of seed produced) at the farms where carinata is cultivated.

A data-driven estimate of litterfall and forest carbon turnover and the drivers of their inter-annual variabilities in forest ecosystems across China

Strong influences of climate and land-cover changes on terrestrial ecosystems urgently need to re-estimate forest carbon turnover time (τforest), i.e., the residence time of carbon (C) in the living forest carbon reservoir in China, to reduce uncertainties in ecosystem carbon sinks under ongoing climate change. However, in absence of accurate carbon loss (e.g., forest litterfall), τforest estimate based on the non-steady-state assumption (NSSA) in forest ecosystems across China is still unclear. In this study, thus, we first compiled a litterfall dataset with 1025 field observations, and applied a Random Forest (RF) algorithm with the linkage of gridded environmental variables to predict litterfall from 2000 to 2019 with a fine spatial resolution of 1 km and a temporal resolution of one year. Finally, τforest was also estimated with the data-driven litterfall product. Results showed that RF algorithm could well predict the spatial and temporal patterns of forest litterfall with a model efficiency of 0.58 and root mean square error of 78.7 g C m−2 year−1. Mean litterfall was 205.4 ± 1.1 Tg C year−1 (mean ± standard error) with a significant increasing trend of 0.65 ± 0.14 Tg C year−2 from 2000 to 2019 (p < 0.01), indicating an increasing carbon loss from litterfall. Mean τforest was 26.2 ± 0.1 years with a significant decreasing trend of −0.11 ± 0.02 years (p < 0.01) from 2000 to 2019. Climate change dominated the inter-annual variability of τforest in high latitude areas, and land-cover change dominated the regions with intensive human activities. These findings suggested that carbon loss from vegetation to the atmosphere becomes more quickly in recent decades, with significant implication for vegetation carbon cycling-climate feedbacks. Meanwhile, the developed litterfall and τforest datasets can serve as a benchmark for biogeochemical models to accurately estimate global carbon cycling.

Exploring Dissolved Organic Carbon Variations in a High Elevation Tropical Peatland Ecosystem: Cerro de la Muerte, Costa Rica

Tropical peatlands are distributed mainly in coastal lowlands; however high elevation regions exhibit a large prevalence of small and fragmented peatlands that are mostly understudied. Artificial drainage of peatlands to expand the area of cattle farming, horticulture, and urbanization is increasing carbon losses to the atmosphere and streams worldwide. Here, we present an exploratory characterization of dissolved carbon optical properties in ombrotrophic peat bogs of the Talamanca range of Costa Rica, across an altitudinal gradient (2,400–3,100 m a.s.l.) during the rainy season. Dissolved organic matter (DOM) sources and decomposition processes were evaluated in the light of dissolved organic and inorganic carbon (DOC and DIC), optical properties, and major water chemistry. DOC concentrations ranged from 0.2 up to 47.0 mg/L. DIC concentrations were below 2 mg/L and δ13CDIC values indicated a mixture between soil organic matter, CO2 in soil water, and to a lesser degree DIC derived from bacterial CO2. Absolute fluorescence intensity of humic-like peaks was 6–7 times greater than fresh-like peaks across all sites. Fluorescence peak ratios coupled with the biological and humification indexes point to a greater relative contribution of recalcitrant soil-derived DOM. Excitation/Emission matrices denoted a high prevalence of humic and fulvic acids in the peat bogs, with moderate intensities in soluble microbial by-products-like and aromatic protein regions at three sites. Our data provides a baseline to underpin tropical carbon dynamics across high elevation peatlands.

Model-Based Estimation of Amazonian Forests Recovery Time after Drought and Fire Events

In recent decades, droughts, deforestation and wildfires have become recurring phenomena that have heavily affected both human activities and natural ecosystems in Amazonia. The time needed for an ecosystem to recover from carbon losses is a crucial metric to evaluate disturbance impacts on forests. However, little is known about the impacts of these disturbances, alone and synergistically, on forest recovery time and the resulting spatiotemporal patterns at the regional scale. In this study, we combined the 3-PG forest growth model, remote sensing and field derived equations, to map the Amazonia-wide (3 km of spatial resolution) impact and recovery time of aboveground biomass (AGB) after drought, fire and a combination of logging and fire. Our results indicate that AGB decreases by 4%, 19% and 46% in forests affected by drought, fire and logging + fire, respectively, with an average AGB recovery time of 27 years for drought, 44 years for burned and 63 years for logged + burned areas and with maximum values reaching 184 years in areas of high fire intensity. Our findings provide two major insights in the spatial and temporal patterns of drought and wildfire in the Amazon: (1) the recovery time of the forests takes longer in the southeastern part of the basin, and, (2) as droughts and wildfires become more frequent—since the intervals between the disturbances are getting shorter than the rate of forest regeneration—the long lasting damage they cause potentially results in a permanent and increasing carbon losses from these fragile ecosystems.

Tropical soils could be accelerating global warming

A field study challenges climate simulations by showing increased carbon loss from warmed low-latitude soils.

Seismic Line Disturbance Alters Soil Physical and Chemical Properties Across Boreal Forest and Peatland Soils

Industrial activities for resource extraction have led to a network of seismic lines across Canada’s boreal regions where peatlands often make up over 50% of the landscape. These clearings can have a significant influence on ecosystem functioning through vegetation removal, flattening of microtopography, altering hydrological pathways and impacting biogeochemical processes. Recently, there has been a concerted effort to restore seismic lines to bring back the localized microtopography and encourage ecosystem recovery. A common restoration approach on seismic lines is mounding, which involves using machinery to recreate natural microtopography. Research is scarce on the impact on soil properties following both these disturbances and subsequent restoration on organic soils. The objectives of this study were to 1) identify differences in soil physical and chemical characteristics between areas disturbed by seismic lines and adjacent natural areas, and 2) to determine changes to soil physical and chemical properties following the mounding restoration technique. Research was undertaken at two contrasting boreal ecosites (a poor mesic and a treed fen) near Fort McMurray, Alberta, Canada. In July 2018, we collected soil samples at 34 seismic line locations, both on the line and 20 m into the adjacent undisturbed area. Samples were analyzed for bulk density, volumetric water content (VWC), organic matter content (OM), C:N ratios and δ13C/δ15N isotope analysis. Seismic line disturbances had a significant impact on soil properties, with increased bulk density and VWC on the line at both ecosites. We found an almost 40% reduction in OM on the line compared to natural areas at the poor mesic site, implying changes to carbon cycling, increased mineralization rates and carbon loss from the system. There was also δ13C/δ15N enrichment and narrower C:N ratios on the line, indicating increased decomposition. We found evidence of increased decomposition on the mounds created after restoration at the treed fen. Our results highlight a trade-off between restoration activities that may encourage recovery but also cause increased carbon losses from the system. This research is a first step in gaining a better understanding of these impacts in light of current restoration practices to ensure best management practices for improving ecosystem functioning.

Green manure application accelerates soil organic carbon stock loss under plastic film mulching

This study investigated the offset effect between green manure (GM) application and plastic film mulching (PFM) on soil organic carbon (SOC) stock change during maize cultivation. Within PFM and no-mulching treatments, three different fertilization sub-treatments were applied: (a) chemical fertilizer, (b) barley and (c) hairy vetch. The SOC balance were evaluated by analyzing the net ecosystem carbon budget (NECB). The results showed that the NECB value was negative during maize cultivation regardless of mulching or fertilization condition, indicated SOC loss. The PFM increased maize yield (P < 0.001) by improved soil moisture and temperature. Crop growth was enhanced under PFM relative to no mulching by 23–26%, 16–25% and 1–8% in the sub-treatments, respectively. However, PFM significantly increased carbon losses by 26–29%, 103–107% and 60–62% over no mulching in each fertilization, respectively (P < 0.001). the temperature sensitivity of CO2–C loss was 52–70% higher in PFM than that in no mulching. Accordingly, the NECB was 1.3, 5.6 and 3.0 times lower with PFM relative to the no-mulching value in the three fertilization, respectively. Under no mulching, GM application reduced SOC loss by 33–59% compared with NPK, while under PFM, it accelerated SOC loss by 8–48%. Barley showed the smallest NECB decrease (− 1.0 Mg C ha−1) under no mulching and the largest NECB decrease (− 5.7 Mg C ha−1) under PFM. The findings indicate that GM application is not enough to sustain SOC stock under PFM and suggest that the additional recycling of crop residue, such as maize stover, is necessary to increase the soil C stock.

Short-interval severe fire erodes the resilience of subalpine lodgepole pine forests

Subalpine forests in the northern Rocky Mountains have been resilient to stand-replacing fires that historically burned at 100- to 300-year intervals. Fire intervals are projected to decline drastically as climate warms, and forests that reburn before recovering from previous fire may lose their ability to rebound. We studied recent fires in Greater Yellowstone (Wyoming, United States) and asked whether short-interval (<30 years) stand-replacing fires can erode lodgepole pine (Pinus contorta var. latifolia) forest resilience via increased burn severity, reduced early postfire tree regeneration, reduced carbon stocks, and slower carbon recovery. During 2016, fires reburned young lodgepole pine forests that regenerated after wildfires in 1988 and 2000. During 2017, we sampled 0.25-ha plots in stand-replacing reburns (n = 18) and nearby young forests that did not reburn (n = 9). We also simulated stand development with and without reburns to assess carbon recovery trajectories. Nearly all prefire biomass was combusted ("crown fire plus") in some reburns in which prefire trees were dense and small (≤4-cm basal diameter). Postfire tree seedling density was reduced sixfold relative to the previous (long-interval) fire, and high-density stands (>40,000 stems ha-1) were converted to sparse stands (<1,000 stems ha-1). In reburns, coarse wood biomass and aboveground carbon stocks were reduced by 65 and 62%, respectively, relative to areas that did not reburn. Increased carbon loss plus sparse tree regeneration delayed simulated carbon recovery by >150 years. Forests did not transition to nonforest, but extreme burn severity and reduced tree recovery foreshadow an erosion of forest resilience.

Improving understanding of carbon storage in wood in landfills: Evidence from reactor studies

Approximately 1.5 million tonnes (Mt) of wood waste are disposed of in Australian landfills annually. Recent studies have suggested that anaerobic decay levels of wood in landfills are low, although knowledge of the decay of individual wood species is limited. The objective of this study was to establish the extent of carbon loss for wood species of commercial importance in Australia including radiata pine, blackbutt, spotted gum and mountain ash. Experiments were conducted under laboratory conditions designed to simulate optimal anaerobic biodegradation in a landfill. Bacterial degradation, identified by both light microscopy and electron microscopy, occurred to a varying degree in mountain ash and spotted gum wood. Fungal decay was not observed in any wood samples. Mountain ash, the species with the highest methane yield (20.9 mL CH4/g) also had the highest holocellulose content and the lowest acid-insoluble lignin and extractive content. As the decay levels for untreated radiata pine were very low, it was not possible to determine whether impregnation of radiata pine with chemical preservatives had any impact on decay. Carbon losses estimated from gas generation were below 5% for all species tested. Carbon losses as estimated by gas generation were lower than those derived by mass balance in most reactors, suggesting that mass loss does not necessarily equate to carbon emissions. There was no statistical difference between decay of blackbutt derived from plantation and older, natural forests. Addition of paper as an easily digestible feedstock did not increase carbon loss for the two wood species tested and the presence of radiata pine had an inhibitory effect on copy paper decay. Although differences between some of the wood types were found to be statistically significant, these differences were detected for wood with carbon losses that did not exceed 5%. The suggested factor for carbon loss for wood in landfills in Australia is 1.4%. This study confirms that disposal of wood in landfills in Australia results in long-term storage of carbon, with only minimal conversion of carbon to gaseous end products.

Boreal forest biomass accumulation is not increased by two decades of soil warming

Increased soil organic matter decomposition with increasing temperature has been hypothesized to enhance soil nitrogen availability, consequently stimulating forest biomass production and offsetting decomposition-induced soil carbon losses1–5. This projection, however, is based on evidence gathered from short-term studies (≤10 years)2,3,5. The key question for carbon sequestration is whether such responses are transient or persist over long forest rotation periods. Here we report on biomass production in a typical nitrogen-limited boreal Picea abies forest, exposed to 18 years of soil warming manipulation (+5 °C) at a plot scale (100 m2). We show that two decades of soil warming elicited only short-duration growth responses, thus not significantly increasing aboveground biomass accumulation. Furthermore, in combination with published work from this forest, our results suggest that increased decomposition is slight and ephemeral, and increased fine root production and turnover in deeper soil may be greater than increased decomposition, netting slightly more biomass, perhaps conserving the soil carbon stock. Thus, this long-term study does not support the notion that the projected increase in soil temperatures will cause either an increased carbon loss with decomposition or a compensatory growth increase from nitrogen mineralization. Nearly two decades of data from a boreal forest soil warming experiment (+5 °C) show no significant increase in aboveground biomass accumulation beyond an initial transitory response.

Biosurfactant-facilitated leaching of metals from spent hydrodesulphurization catalyst.

To investigate the capabilities of different types of biosurfactants (rhamnolipids, lipopeptides, sophorolipids) to remove metals and carbon from the hazardous spent hydrodesulphurization (HDS) catalyst generated by petroleum refineries. Biosurfactants were prepared and used to treat spent HDS catalyst. Metal and carbon contents were analysed and compared with those from no-biosurfactant control treatments. All biosurfactant treatments increased carbon loss percentage from the spent HDS catalyst. The lipopeptide treatment LI, containing 17·34mgml-1 of crude biosurfactants, caused the highest carbon loss percentage (44·5%). Rhamnolipids were, in general, better than sophorolipids and lipopeptides as metal-removing agents. The metal content decreased as the concentration of rhamnolipids decreased. The R5 treatment, which contained 0·4mgl-1 of crude rhamnolipids, caused the highest reduction in metal content. Molybdenum, nickle and vanadium contents were reduced by 90, 30 and 70% respectively. Biosurfactants might have potential application for metals and coke removal from spent HDS catalysts. The bioleaching capability depends on the type and concentration of the biosurfactant. This study, after further in-depth investigations, might lead to the development of an eco-friendly and economic technology to treat or even regenerate the environmentally hazardous spent HDS catalysts, which are generated in huge amounts by the petroleum refineries.

Modelling impacts of recent warming on seasonal carbon exchange in higher latitudes of North America

An ecosystem model, ecosys, has been used to examine the effects of recent warming on carbon exchange in higher latitudes of North America. Model results indicated that gradual warming during the past 30 years has increased net ecosystem productivity (NEP) and leaf area index (LAI). Spring increases in LAI advanced by 2.3 days decade−1 and decreases in autumn were delayed by 5.0 days decade−1 from 1982 to 2006. These advances and delays were corroborated by similar trends observed in the normalized difference vegetation index. NEP modelled during this period increased at an average rate of 17.6 Tg C decade−1. Increasing carbon losses modelled with soil warming in autumn, when thaw depth was greatest, offset 34% of increasing carbon gains modelled in spring. If autumn warming continues, carbon losses in this season may further offset enhanced carbon sequestration in spring.

On the causes of trends in the seasonal amplitude of atmospheric CO2.

No consensus has yet been reached on the major factors driving the observed increase in the seasonal amplitude of atmospheric CO2 in the northern latitudes. In this study, we used atmospheric CO2 records from 26 northern hemisphere stations with a temporal coverage longer than 15years, and an atmospheric transport model prescribed with net biome productivity (NBP) from an ensemble of nine terrestrial ecosystem models, to attribute change in the seasonal amplitude of atmospheric CO2 . We found significant (p<.05) increases in seasonal peak-to-trough CO2 amplitude (AMPP-T ) at nine stations, and in trough-to-peak amplitude (AMPT-P ) at eight stations over the last three decades. Most of the stations that recorded increasing amplitudes are in Arctic and boreal regions (>50°N), consistent with previous observations that the amplitude increased faster at Barrow (Arctic) than at Mauna Loa (subtropics). The multi-model ensemble mean (MMEM) shows that the response of ecosystem carbon cycling to rising CO2 concentration (eCO2 ) and climate change are dominant drivers of the increase in AMPP-T and AMPT-P in the high latitudes. At the Barrow station, the observed increase of AMPP-T and AMPT-P over the last 33years is explained by eCO2 (39% and 42%) almost equally than by climate change (32% and 35%). The increased carbon losses during the months with a net carbon release in response to eCO2 are associated with higher ecosystem respiration due to the increase in carbon storage caused by eCO2 during carbon uptake period. Air-sea CO2 fluxes (10% for AMPP-T and 11% for AMPT-P ) and the impacts of land-use change (marginally significant 3% for AMPP-T and 4% for AMPT-P ) also contributed to the CO2 measured at Barrow, highlighting the role of these factors in regulating seasonal changes in the global carbon cycle.