Atmospheric Sink Research Articles

Analysis of Kenya’s Atmospheric Moisture Sources and Sinks

Abstract Achievement of the United Nations Sustainable Development Goals (SDGs) is contingent on understanding the potential interactions among human and natural systems. In Kenya, the goal of conserving and expanding forest cover to achieve SDG 15 “Life on Land” may be related to other SDGs because it plays a role in regulating some aspects of Kenyan precipitation. We present a 40-yr analysis of the sources of precipitation in Kenya and the fate of the evaporation that arises from within Kenya. Using MERRA-2 climate reanalysis and the Water Accounting Model 2 layers, we examine the annual and seasonal changes in moisture sources and sinks. We find that most of Kenya’s precipitation originates as oceanic evaporation but that 10% of its precipitation originates as evaporation within Kenya. This internal recycling is concentrated in the mountainous and forested Kenyan highlands, with some locations recycling more than 15% of evaporation to Kenyan precipitation. We also find that 75% of Kenyan evaporation falls as precipitation elsewhere over land, including 10% in Kenya, 25% in the Democratic Republic of the Congo, and around 5% falling in Tanzania and Uganda. Further, we find a positive relationship between increasing rates of moisture recycling and fractional forest cover within Kenya. By beginning to understand both the seasonal and biophysical interactions taking place, we may begin to understand the types of leverage points that exist for integrated atmospheric water cycle management. These findings have broader implications for disentangling environmental management and conservation and have relevance for large-scale discussions about sustainable development.

Carbonate weathering dominates magnesium isotopes in large rivers: Clues from the Yangtze River

Carbonate weathering regulates the short-term carbon (C) cycle and global climate due to its fast response to hydrological processes. The carbonate weathering flux needs to be well constrained to better understand the climate change at short time scale. Riverine magnesium (Mg) isotopes are sensitive to primary mineral dissolution and so have great potential to trace carbonate weathering. Global large rivers draining continental crust dominate weathering flux to the oceans, but how riverine Mg isotopes respond to carbonate weathering remains unclear. The Yangtze River drainage basin (YRDB) was selected to test the robustness of riverine Mg isotopes (δ26Mg) in tracing continental carbonate weathering because it spans a wide range in lithology, geomorphology and climate. The riverine δ26Mg values within the YRDB show a decreasing trend from the headwater to the mainstream ranging from −1.36‰ to −0.59‰. The dissolved δ26Mg have strong negative correlations with carbonate weathering rate and intensity within the YRDB, indicating a sensitive response of riverine δ26Mg to the carbonate weathering flux. In a compilation of Mg fluxes and δ26Mg in the world's largest rivers, there is similar dominance of carbonate weathering on riverine Mg fluxes and isotopes. Therefore, we propose that riverine δ26Mg in large rivers are a robust tracer of carbonate weathering intensity. Intensifying carbonate weathering under global warming tends to increase riverine Mg and C fluxes to the oceans and thus the atmospheric CO2 sink at the millennial time scale.

Collateral implications of carbon and metal pollution on carbon dioxide emission at land-water interface of the Ganga River.

Atmospheric CO2 source and sink is among the most debated issues that have puzzled climate change geochemist for decades. Here, we tested whether heavy metal pollutants in river sediments favor preservation of organic matter through shielding microbial degradation. We measured CO2 emission and extracellular enzyme activities at land-water interface (LWI) of 7 sites along a 285 km main stem of the Ganga River and 60 locations up- and downstream of two contrasting point sources discharging urban (Assi drain; Asdr) and industrial (Ramnagar drain; Rmdr) wastewaters to the river. We found the lowest CO2 flux at Rmdr mouth characterized by the highest concentrations of Cu, Cr, Zn, Pb, Ni, and Cd. The fluxes were relatively higher at locations up- and downstream Rmdr. Substrate induced respiration (SIR), protease, FDAase, and β-D-glucosidase all showed a similar trend, but phenol oxidase and alkaline phosphatase showed opposite trend at the main river stem and Asdr. Sites rich in terrestrially derived organic matter have high phenol oxidase activity with low CO2 emission. The CO2 emission in the main river stem showed curvilinear relationships with total heavy metals (∑THM; R2 = 0.68; p < 0.001) and TOC (R2 = 0.65; p < 0.001). The dynamic fit model of main stem data showed that the ∑THM above 337.4 µg g-1 were able to significantly decrease the activities of protease, FDAase, and β-D-glucosidase. The study has implications for understanding C-cycling in human-impacted river sediments where metal pollution shields microbial degradation consequently carbon and nutrient release and merits attention towards river management decisions.

Responses of the marine carbonate system to a green tide: A case study of an Ulva prolifera bloom in Qingdao coastal waters

As an environmental nuisance, Ulva prolifera green tides have occurred annually in the southern Yellow Sea since 2007. While it is expected that high levels of biological activity during these blooms can alter seawater carbonate chemistry, there has been little research on the responses of marine carbonate system to green tides. Here, the effects of the bloom on the carbonate system were examined on three cruises in June, July, and September, corresponding to the early-, late-, and after-bloom periods of the U. prolifera bloom in Qingdao coastal waters in 2018. Among these three stages, the pH (National Bureau of Standards scale), dissolved inorganic carbon (DIC), total alkalinity (TA), and partial pressure of CO2 (pCO2) were all affected by bloom, with the highest pH and lowest DIC and TA concentrations of the surface seawater occurring at the late-bloom stage. While pCO2 continuously increased from the beginning to the end of the bloom. TA increased by ∼40 μmol kg−1 between the early- and after-bloom periods likely due to the shifts in the carbonate system equilibrium caused by increased CO32− concentrations and the organic matter released by U. prolifera during decomposition. Compared to nearby areas with no U. prolifera bloom, the green tide, along with increasing temperature, reduced the pH and DIC but increased the TA and pCO2. This large-scale bloom also turned the coastal waters from being an atmospheric CO2 sink to a strong source, with the estimation of air-sea CO2 fluxes about 1.69 ± 1.70, 2.28 ± 1.16, and 7.44 ± 5.84 mmol m−2 d−1 during the early-, late-, and after-bloom periods, respectively. This bloom event also promoted the formation of CaCO3 and was an important source of low molecular weight organic acids. These new findings provide nuances for the current conversations on the role of biological processes in modulating marine carbonate system and the contribution of organic matter to alkalinity.

Anthropogenic emission is the main contributor to the rise of atmospheric methane during 1993-2017.

Atmospheric methane (CH4) concentrations have shown a puzzling resumption in growth since 2007 following a period of stabilization from 2000 to 2006. Multiple hypotheses have been proposed to explain the temporal variations in CH4 growth, and attribute the rise of atmospheric CH4 either to increases in emissions from fossil fuel activities, agriculture and natural wetlands, or to a decrease in the atmospheric chemical sink. Here, we use a comprehensive ensemble of CH4 source estimates and isotopic δ13C-CH4 source signature data to show that the resumption of CH4 growth is most likely due to increased anthropogenic emissions. Our emission scenarios that have the fewest biases with respect to isotopic composition suggest that the agriculture, landfill and waste sectors were responsible for 53 ± 13% of the renewed growth over the period 2007–2017 compared to 2000–2006; industrial fossil fuel sources explained an additional 34 ± 24%, and wetland sources contributed the least at 13 ± 9%. The hypothesis that a large increase in emissions from natural wetlands drove the decrease in atmospheric δ13C-CH4 values cannot be reconciled with current process-based wetland CH4 models. This finding suggests the need for increased wetland measurements to better understand the contemporary and future role of wetlands in the rise of atmospheric methane and climate feedback. Our findings highlight the predominant role of anthropogenic activities in driving the growth of atmospheric CH4 concentrations.

Potential of Clumped Isotopes in Constraining the Global Atmospheric Methane Budget

AbstractAtmospheric methane (CH4) and its isotopic composition trends over the last decades are explained by various flux scenarios, from tropical wetland emission increases through to reductions in global hydroxyl (OH). In this study, we develop a modeling framework to assess the potential usefulness of clumped isotope measurements to distinguish between the main drivers of change in the CH4 burden. We model interhemispheric differences of 0.12‰ and 0.38‰ and seasonal cycles of 0.02‰–0.04‰ and 0.21‰–0.32‰ for Δ13CH3D and Δ12CH2D2, respectively, which is insignificant relative to the uncertainty of measurements that could eventually be made. We show, however, that measurements of Δ12CH2D2 specifically could provide constraints for understanding trends in the global total source and sink magnitudes, which has not been possible with the current sets of observables. Changes in OH concentration of 10% developed across three decades result in a difference of up to 2‰ in Δ12CH2D2, which would be observable given current measurement uncertainty limits. For this type of global‐scale analysis, we show that measurements of Δ13CH3D would be unlikely to provide additional useful information. We suggest an emphasis should now be on developing the methods to make measurements from ambient air samples, followed by measurements of Δ13CH3D and Δ12CH2D2 from sampling at clean Northern and Southern Hemisphere sites, combined with more accurate and precise laboratory measurements of the clumped kinetic isotope effects relevant for the atmospheric sinks.

USCγ Dominated Community Composition and Cooccurrence Network of Methanotrophs and Bacteria in Subterranean Karst Caves.

ABSTRACTKarst caves have recently been demonstrated to act as a sink for atmospheric methane, due in part to consumption by microbes residing in caves that can oxidize methane at atmospheric levels. However, our knowledge about the responsible atmospheric methane-oxidizing bacteria (atmMOB) in this vast habitat remains limited to date. To address this issue, weathered rock samples from three karst caves were collected in Guilin City and subjected to high-throughput sequencing of pmoA and 16S rRNA genes. The results showed that members of the high-affinity upland soil cluster (USC), especially upland soil cluster gamma (USCγ), with absolute abundances of 104 to 109 copies · g−1 dry sample, dominated the atmMOB communities, while Proteobacteria and Actinobacteria dominated the overall bacterial communities. Moreover, USCγ was a keystone taxon in cooccurrence networks of both the atmMOB and the total bacterial community, whereas keystone taxa in the bacterial network also included Gaiella and Aciditerrimonas. Positive links overwhelmingly dominated the cooccurrence networks of both atmMOB and the total bacterial community, indicating a consistent response to environmental disturbances. Our study shed new insights on the diversity and abundances underlining atmMOB and total bacterial communities and on microbial interactions in subterranean karst caves, which increased our understanding about USC and supported karst caves as a methane sink.IMPORTANCE Karst caves have recently been demonstrated to be a potential atmospheric methane sink, presumably due to consumption by methane-oxidizing bacteria. However, the sparse knowledge about the diversity, distribution, and community interactions of methanotrophs requires us to seek further understanding of the ecological significance of methane oxidation in these ecosystems. Our pmoA high-throughput results from weathered rock samples from three karst caves in Guilin City confirm the wide occurrence of atmospheric methane-oxidizing bacteria in this habitat, especially those affiliated with the upland soil cluster, with a gene copy number of 104 to 109 copies per gram dry sample. Methanotrophs and the total bacterial communities had more positive than negative interactions with each other as indicated by the cooccurrence network, suggesting their consistent response to environmental disturbance. Our results solidly support caves as an atmospheric methane sink, and they contribute to a comprehensive understanding of the diversity, distribution, and interactions of microbial communities in subsurface karst caves.

Mercury accumulation response of rice plant (Oryza sativa L.) to elevated atmospheric mercury and carbon dioxide

New observations and updated models now suggest terrestrial ecosystems are net sink of atmospheric mercury (Hg), and the critical constrained process to identify the strengths of terrestrial sink is whether the large amount of Hg stored in vegetation originates from the soil as well as from the atmosphere. In this study, field open top chambers (OTCs) experiments reveal that rice plant can assimilate gaseous elemental mercury (GEM, Hg0) from the atmosphere through stomata, and Hg concentrations in rice leaves, upper and bottom stalks and grains increased with Hg0 levels in air, showing significantly quadratic linear relationships. Coupling field stable isotope soil amendment experiments, atmospheric source of Hg in rice plant is quantified with more than 90% of Hg accumulation in rice aboveground biomass from air and approximately 80% of rice root Hg from soil. Furthermore, elevated atmospheric carbon dioxide (CO2) exposure led to lower Hg concentration in rice tissues through reduction stomatal conductance of rice leaf, and subsequently impact the capacity of Hg storage in rice aboveground parts from the atmosphere. The findings from experiments provide a foundation for future quantification of atmospheric sink of crops in local and larger scales and comprehensive evaluation atmosphere - terrestrial processes and exposure risks in the global Hg cycling.

Soil carbon dioxide effluxes from riparian areas of two hydrogeomorphic settings in the Ozark National Forest, USA

Riparian buffers serve as conduits through which carbon (C) cycles from terrestrial landscapes to aquatic systems and, ultimately, to oceanic or atmospheric sinks. Riparian areas have also been identified as zones of concentrated biogeochemical activity that often produce greater amounts of greenhouse gases than neighboring upland terrestrial and adjacent aquatic systems. Little work has explored how hydrologic classification of a stream may influence the magnitude of riparian soil processes. A three-way factorial field study examined soil carbon dioxide (CO2) effluxes across flow regime (Groundwater and Runoff streams), season (autumn, winter, spring, and summer), and distance from stream edge (0, 10, and 20 m). Soil CO2 efflux differed between flow regimes across seasons (P = 0.01), where Runoff sites had greater spring soil surface CO2 efflux (i.e., soil respiration mean ± 1 SE = 2.98 ± 0.29 μmol CO2 m−2 s−1) than Groundwater sites (1.40 ± 0.30 μmol CO2 m−2 s−1). Soil CO2 effluxes from Runoff sites were related to soil temperature (rs value range = 0.58 to 0.82, all P < 0.0001) and soil moisture (rs value range = −0.35 to 0.27, P = 0.02 to 0.03). However, effluxes were unrelated to soil moisture at Groundwater sites. Results of this study suggest that consideration of the riparian zone and demonstrated differences in flow regime are needed to understand forested stream C budgets. Anthropogenic landscape alteration and climate change can modify the natural flow regime which, in turn, may have consequences for aquatic C dynamics in streams draining altered riparian zones, particularly in forested settings.

Drivers of Atmosphere-Ocean CO2 Flux in Northern Norwegian Fjords

High-latitude fjords and continental shelves are shown to be sinks for atmospheric CO2, yet large spatial-temporal variability and poor regional coverage of sea-air CO2 flux data, especially from fjord systems, makes it difficult to scale our knowledge on how they contribute to atmospheric carbon regulation. The magnitude and seasonal variability of atmosphere-sea CO2 flux was investigated in high-latitude northern Norwegian coastal areas over 2018 and 2019, including four fjords and one coastal bay. The aim was to assess the physical and biogeochemical factors controlling CO2 flux and partial pressure of CO2 in surface water via correlation to physical oceanographic and biological measurements. The results show that the study region acts as an overall atmospheric CO2 sink throughout the year, largely due to the strong undersaturation of CO2 relative to atmospheric concentrations. Wind speed exerted the strongest influence on the instantaneous rate of sea-air CO2 exchange, while exhibiting high variability. We concluded that the northernmost fjords (Altafjord and Porsangerfjord) showed stronger potential for instantaneous CO2 uptake due to higher wind speeds. We also found that fixation of CO2 was likely a significant factor controlling ΔpCO2 from April to June, which followed phenology of spring phytoplankton blooms at each location. Decreased ΔpCO2 and the resulting sea-air CO2 flux was observed in autumn due to a combined reduction of the mixed layer with entrain of high CO2 subsurface water, damped biological activity and higher surface water temperatures. This study provides the first measurements of atmospheric CO2 flux in these fjord systems and therefore an important new baseline for gaining a better understanding on how the northern Norwegian coast and characteristic fjord systems participate in atmosphere carbon regulation.

Geographic variability in freshwater methane hydrogen isotope ratios and its implications for global isotopic source signatures

Abstract. There is growing interest in developing spatially resolved methane (CH4) isotopic source signatures to aid in geographic source attribution of CH4 emissions. CH4 hydrogen isotope measurements (δ2H–CH4) have the potential to be a powerful tool for geographic differentiation of CH4 emissions from freshwater environments, as well as other microbial sources. This is because microbial δ2H–CH4 values are partially dependent on the δ2H of environmental water (δ2H–H2O), which exhibits large and well-characterized spatial variability globally. We have refined the existing global relationship between δ2H–CH4 and δ2H–H2O by compiling a more extensive global dataset of δ2H–CH4 from freshwater environments, including wetlands, inland waters, and rice paddies, comprising a total of 129 different sites, and compared these with measurements and estimates of δ2H–H2O, as well as δ13C-CH4 and δ13C–CO2 measurements. We found that estimates of δ2H–H2O explain approximately 42 % of the observed variation in δ2H–CH4, with a flatter slope than observed in previous studies. The inferred global δ2H–CH4 vs. δ2H–H2O regression relationship is not sensitive to using either modelled precipitation δ2H or measured δ2H–H2O as the predictor variable. The slope of the global freshwater relationship between δ2H–CH4 and δ2H–H2O is similar to observations from incubation experiments but is different from pure culture experiments. This result is consistent with previous suggestions that variation in the δ2H of acetate, controlled by environmental δ2H–H2O, is important in determining variation in δ2H–CH4. The relationship between δ2H–CH4 and δ2H–H2O leads to significant differences in the distribution of freshwater δ2H–CH4 between the northern high latitudes (60–90∘ N), relative to other global regions. We estimate a flux-weighted global freshwater δ2H–CH4 of −310 ± 15 ‰, which is higher than most previous estimates. Comparison with δ13C measurements of both CH4 and CO2 implies that residual δ2H–CH4 variation is the result of complex interactions between CH4 oxidation, variation in the dominant pathway of methanogenesis, and potentially other biogeochemical variables. We observe a significantly greater distribution of δ2H–CH4 values, corrected for δ2H–H2O, in inland waters relative to wetlands, and suggest this difference is caused by more prevalent CH4 oxidation in inland waters. We used the expanded freshwater CH4 isotopic dataset to calculate a bottom-up estimate of global source δ2H–CH4 and δ13C-CH4 that includes spatially resolved isotopic signatures for freshwater CH4 sources. Our bottom-up global source δ2H–CH4 estimate (−278 ± 15 ‰) is higher than a previous estimate using a similar approach, as a result of the more enriched global freshwater δ2H–CH4 signature derived from our dataset. However, it is in agreement with top-down estimates of global source δ2H–CH4 based on atmospheric measurements and estimated atmospheric sink fractionations. In contrast our bottom-up global source δ13C-CH4 estimate is lower than top-down estimates, partly as a result of a lack of δ13C-CH4 data from C4-plant-dominated ecosystems. In general, we find there is a particular need for more data to constrain isotopic signatures for low-latitude microbial CH4 sources.

Contribution of Biological Effects to Carbonate‐System Variations and the Air–Water CO2 Flux in Urbanized Bays in Japan

AbstractWe evaluated the contribution of net biological effects (photosynthesis + respiration + decomposition) to the carbonate parameters and air–water CO2 fluxes in Tokyo Bay, Ise Bay, and Osaka Bay in Japan. The carbonate parameters (fugacity of CO2, total alkalinity, and dissolved inorganic carbon) were measured mainly by cargo ships traveling between Japan and other countries. We used the measurement data from three inner bays and surrounding outer bays in Japan along with reference data from previous studies for complementary analysis. We found that (a) the inner and outer bays in this study were strong annual atmospheric CO2 sinks, (b) the annual biological effect on the air–water CO2 fluxes was about 6%–27% of the measured CO2 fluxes, and it affected the seasonal variation of the CO2 flux, and (c) the biological effect was largest in Tokyo Bay, and almost the same in Ise and Osaka Bays. The intensity of the biological effect corresponded mainly with nutrient concentrations, which seemed to be controlled by the wastewater treatment in urbanized areas around the bays. Our results suggest that labile carbon/nutrient ratio of wastewater should be a major consideration for evaluating the biological effect on the carbon cycle in urbanized bays, which will continue to expand globally.

Anaerobic Digestion and Hot Water Pretreatment of Tropically Grown C4 Energy Grasses: Mass, Carbon, and Energy Conversions from Field Biomass to Fuels

The efficacy of C4 grasses as feedstocks for liquid fuel production and their climate mitigation potential remain unresolved in the tropics. To identify highly convertible C4 grasses, we measured final fuels and postprocess biomass produced in two laboratory-scale conversion pathways across 12 species and varieties within the Poaceae (grass) family. Total mass, carbon, and energy in final fuels and postprocess biomass were assessed based on field mass and area-based production. Two lignocellulosic processes were investigated: (1) anaerobic digestion (AD) to methane and (2) hot water pretreatment and enzymatic hydrolysis (HWP-EH) to ethanol. We found AD converted lignocellulose to methane more efficiently in terms of carbon and energy compared to ethanol production using HWP-EH, although improvements to and the optimization of each process could change these contrasts. The resulting data provide design limitations for agricultural production and biorefinery systems that regulate these systems as net carbon sources or sinks to the atmosphere. Median carbon recovery in final fuels and postprocess biomass from the studied C4 grasses were ~5 Mg C ha−1 year−1 for both methane and ethanol, while median energy recovery was ~200 MJ ha−1 year−1 for ethanol and ~275 MJ ha−1 year−1 for methane. The highest carbon and energy recovery from lignocellulose was achieved during methane production from a sugarcane hybrid called energycane, with ~10 Mg C ha−1 year−1 and ~450 MJ ha−1 year−1 of carbon and energy recovered, respectively, from fuels and post-process biomass combined. Carbon and energy recovery during ethanol production was also highest for energycane, with ~9 Mg C ha−1 year−1 and ~350 MJ ha−1 year−1 of carbon and energy recovered in fuels and postprocess biomass combined. Although several process streams remain unresolved, agricultural production and conversion of C4 grasses must operate within these carbon and energy limitations for biofuel and bioenergy production to be an atmospheric carbon sink.

Assessment of Annual Physico-Chemical Variability via High-Temporal Resolution Monitoring in an Antarctic Shallow Coastal Site (Terra Nova Bay, Ross Sea)

The Southern Ocean is an important atmospheric carbon sink, and potential changes in the carbon flux in this region will affect the ocean as a whole. Thus, to monitor the variability of its physico-chemical parameters is becoming a priority. This study provides the first high-resolution all-year-round record of observed and computed physico-chemical data from a shallow coastal site in Terra Nova Bay (Ross Sea). From November 2018 to November 2019, an underwater observatory deployed at a 25 m depth under an ice pack recorded pressure (p), temperature (t), electrical conductivity (C), dissolved oxygen (DO), pH in total scale (pHT), and illuminance (Ev). Practical salinity (SP), density (ρ), tidal constituents, carbonate system parameters (total alkalinity (TA), carbon dioxide partial pressure (pCO2), calcite, and aragonite (ΩCa, ΩAr)), together with sea ice concentration (SIC) and chlorophyll-a (Chl-a), were derived from measured and satellite data. t, DO, and pHT displayed the lowest values between July and November (–1.95 °C, 6.61 mL L−1, 7.97) whereas the highest in January (+1.08 °C, 10.61 mL L−1, 8.35). SP had the lowest values (33.72 PSU) in February and the highest (34.87 PSU) in September. Ev peaked in March (201 lux), with the highest values (&gt;50 lux) in correspondence to the lowest values of SIC and a delayed trend, between December and March, with respect to Chl-a values (0.2–1.1 mg m−3). ΩCa and ΩAr showed their highest average monthly values (±s.d.) in January (ΩCa: 3.41 ± 0.27; ΩAr: 2.14 ± 0.17), when DO had maximum values. The lowest Ω occurred in September (ΩCa: 2.11 ± 0.02; ΩAr: 1.32 ± 0.02), at the end of phytoplankton activity. No undersaturation for both calcite and aragonite was recorded during the study period. This study highlights that biological activities and physico-chemical variables of the investigated shallow coastal site are coupled and, in many cases, influence each other.

Improved understanding of dynamic water and mass budgets of high‐alpine karst systems obtained from studying a well‐defined catchment area

AbstractLarge areas of Europe, especially in the Alps, are covered by carbonate rocks and in many alpine regions, karst springs are important sources for drinking water supply. Because of their high variability and heterogeneity, the understanding of the hydrogeological functioning of karst aquifers is of particular importance for their protection and utilisation. Climate change and heavy rainfall events are major challenges in managing alpine karst aquifers which possess an enormous potential for future drinking water supply. In this study, we present research from a high‐alpine karst system in the UNESCO Biosphere Reserve Großes Walsertal in Austria, which has a clearly defined catchment and is drained by only one spring system. Results show that (a) the investigated system is a highly dynamic karst aquifer with distinct reactions to rainfall events in discharge and electrical conductivity; (b) the estimated transient atmospheric CO2 sink is about 270 t/a; (c) the calculated carbonate rock denudation rate is between 23 and 47 mm/1000a and (d) the rainfall‐discharge behaviour and the internal flow dynamics can be successfully simulated using the modelling package KarstMod. The modelling results indicate the relevance of matrix storage in determining the discharge behaviour of the spring, particularly during low‐flow periods. This research and the consequent results can contribute and initiate a better understanding and management of alpine karst aquifers considering climate change with more heavy rainfall events and also longer dry periods.

Photodegradation of Molecular Iodine on SiO2 Particles: Influence of Temperature and Relative Humidity

AbstractA molecular derivatization method followed by gas chromatographic separation coupled with mass spectrometric detection was used to study photodegradation of molecular I2 adsorbed on solid SiO2 particles. The heterogeneous photodegradation of I2 was studied as a function of temperature and relative humidity in synthetic air to better understand its environmental fate. Two sets of experiments were carried out. In the first set of experiments, the temperature was T = (298 ± 1) K and relative humidity was varied from ≤ 2% to 75%RH under given experimental conditions. In the second set of experiments, the relative humidity within the Pyrex bulb was 40%RH and the temperature was varied from 283 ± 1 ≤ T (K) ≤ 323 ± 1. The obtained results show a considerably enhanced atmospheric lifetime of molecular iodine adsorbed on solid media that does not depend on relative humidity of the environment. The obtained results show that the rate constant for the photolysis of molecular iodine adsorbed on model SiO2 particles depends on temperature and is reported to be J (T)=(1.24 ± 1.4)×10−2×exp[(1482±345)/T]/s over the measured temperature range. The heterogeneous atmospheric residence time () of I2 adsorbed on solid media is calculated to range from 2 to 4.1 h. The experimentally obtained heterogeneous lifetime of I2 is shown to be considerably longer than its destruction by its principal atmospheric sink, photolysis. The observed enhanced atmospheric lifetime of I2 on heterogeneous media will likely have direct consequences on the atmospheric transport of I2 that influences the toxicity or the oxidative capacity of the atmosphere.

An eco-Marxist reinterpretation of formal abstraction in Ecological Economics

An eco-Marxist reinterpretation of formal abstraction in Ecological Economics

Ideas and perspectives: patterns of soil CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;, and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O fluxes along an altitudinal gradient – a pilot study from an Ecuadorian neotropical montane forest

Abstract. Tropical forest soils are an important source and sink of greenhouse gases (GHGs), with tropical montane forests, in particular, having been poorly studied. The understanding of this ecosystem function is of vital importance for future climate change research. In this study, we explored soil fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in four tropical forest sites located on the western flanks of the Andes in northern Ecuador. The measurements were carried out during the dry season from August to September 2018 and along an altitudinal gradient from 400 to 3010 m a.s.l. (above sea level). During this short-term campaign, our measurements showed (1) an unusual but marked increase in CO2 emissions at high altitude, possibly linked to changes in soil pH and/or root biomass, (2) a consistent atmospheric CH4 sink over all altitudes with high temporal and spatial variability, and (3) a transition from a net N2O source to sink along the altitudinal gradient. Our results provide arguments and insights for future and more detailed studies on tropical montane forests. Furthermore, they stress the relevance of using altitudinal transects as a biogeochemical open-air laboratory with a steep in situ environmental gradient over a limited spatial distance. Although short-term studies of temporal variations can improve our understanding of the mechanisms behind the production and consumption of soil GHGs, the inclusion of more rigorous sampling for forest management events, forest rotation cycles, soil type, hydrological conditions and drainage status, ground vegetation composition and cover, soil microclimate, and temporal (seasonality) and spatial (topographic positions) variability is needed in order to obtain more reliable estimates of the CO2, CH4, and N2O source/sink strength of tropical montane forests.

Estimating the gaseous carbon budget of a degraded tidal wetland

Wetlands play an important role in the global carbon cycle but are intensively disturbed by humans. Estimating the gaseous carbon budget of degraded wetlands has great significance for wetland conservation. The Shanyutan wetland is a degraded tidal wetland in Southeast China. We compared the landscape patterns of Shanyutan in 2009 and 2019 based on remote sensing images and determined the sediment CO2 flux (excluding root respiration) in various land types. We combined the sediment CO2 flux with the wetland CH4 flux, and the CH4 and CO2 fluxes of aquaculture ponds, as well as net plant carbon sequestration (NPCS) from previous studies, and calculated the gaseous carbon budget of Shanyutan for the 10-year period. Our results show that the areas of aquaculture ponds and mudflats increased over the 10-year period, whereas those of vegetated marsh and sand decreased. Determination of the sediment CO2 flux indicates that sediment CO2 flux is higher in vegetated marsh and lower in bare land, with the highest annual flux in Spartina alterniflora marsh and the lowest in sand. The gaseous carbon budget shows that aquaculture ponds and bare land are sources of atmospheric carbon, whereas vegetated marsh serves as a sink. The entire wetland was an atmospheric carbon sink in 2009, with a carbon sequestration rate of 1364.4 tC·a−1; however, it became a source in 2019 due to destruction, with a carbon efflux of 1072.6 tC·a−1. Moreover, the gaseous carbon balance in Shanyutan had a climate-warming potential, with an equivalent CO2 production of 5971.8 t·a−1 in 2009, and this potential increased ~9 times over the 10-year period. Finally, we conclude that restoring the carbon cycle of Shanyutan has considerable future economic value.

Monsoon‐Enhanced Silicate Weathering as a New Atmospheric CO2 Consumption Mechanism Contributing to Fast Late Miocene Global Cooling

AbstractFast late Miocene global cooling since ∼7 Ma accompanied by less changeable atmospheric CO2 levels revealed by existing proxy reconstructions has suggested an intriguing tectonic‐climate link that remains controversial. Here, we present late Cenozoic clay mineral records of the silicate weathering intensity from the Chinese Loess Plateau and northeastern Tibetan Plateau to demonstrate a remarkable increase in silicate weathering intensity at ∼9–7 Ma induced by enhanced monsoon. This change caused CO2 consumption ranging from 0.18 to 1.8 × 1011 mol C yr−1 over the East Asian monsoon region, accounting for 0.2%–2% of the modern continental silicate weathering flux, thus providing an additional atmospheric CO2 sink. Moreover, we propose that this additional sink may have contributed to the large atmospheric CO2 consumption and fast global cooling in the late Miocene, which ultimately caused the onset of the Northern Hemisphere glaciation at ∼7 Ma.