Contrasting intra-annual inorganic carbon dynamics and air–water CO2 exchange in Dhamra and Mahanadi Estuaries of northern Bay of Bengal,India

Limnology - Surface water partial pressure of carbon dioxide [pCO2 (water)], total alkalinity (TA), dissolved inorganic carbon (DIC), and air–water CO2 flux were measured in two estuaries of...     

CO2 dynamics along Danish lowland streams: water–air gradients, piston velocities and evasion rates

We measured CO₂ concentration and determined evasion rate and piston velocity across the water–air interface in flow-through chambers at eight stations along two 20 km long streams in agricultural landscapes in Zealand, Denmark. Both streams were 9–18-fold supersaturated in CO₂ with daily means of 240 and 340 μM in January–March and 130 and 180 μM in June–August. Annual CO₂ medians were 212 μM in six other streams and 460 μM in four groundwater wells, while seven lakes were weakly supersaturated (29 μM). Air concentrations immediately above stream surfaces were close to mean atmospheric conditions except during calm summer nights. Piston velocity from 0.4 to 21.6 cm h^?1 was closely related to current velocity permitting calculation of evasion rates for entire streams. CO₂ evasion rates were highest in midstream reaches (170–1,200 mmol m^?2 day^?1) where CO₂-rich soil water entered fast stream flow, while rates were tenfold lower (25–100 mmol m^?2 day^?1) in slow-flowing lower reaches. CO₂ evasion mainly derived from the input of CO₂ in soil water. The variability of CO₂ evasion along the two lowland streams covered much of the range in sub-Arctic and temperate streams reported previously. In budgets for the two stream catchments, loss of carbon from soils via the hydrological cycle was substantial (3.2–5.7 mmol m^?2 day^?1) and dominated by CO₂ consumed to form HCO₃ ^? by mineral dissolution (69–76%) and export of organic carbon (15–23%) relative to dissolved CO₂ export (7–9%).     

Estimating oxygen exchange across the air–water interface of a hypereutrophic lake

Patterns of estimates of oxygen flux (J) across the air–water interface of hypereutrophic Onondaga Lake, NY, U.S.A., are characterized for time scales ranging from diel to seasonal for an 8-month period. The analysis is supported by a high frequency (most often hourly) monitoring program, conducted with a robotic buoy, that included measurements of dissolved oxygen (DO), temperature, and fluorometric chlorophyll a in the lake's surface waters, vertical profiles of DO through the epilimnion, and wind speed and solar radiance. The magnitude and direction of J is demonstrated to vary dramatically at diel, day-to-day, and seasonal time scales. Thus, large errors in estimates of J may result from extrapolating flux calculations made from short-term data to longer time periods. The variations in J were driven by variations in metabolic activity and meteorology, and were mediated by departures from equilibrium DO concentrations and wind-driven turbulence. Extended periods of high J values are shown to coincide with intervals of large departures from equilibrium DO concentrations, but day-to-day differences are driven mostly by variations in wind. A distinct diel pattern of J estimates is manifested for average conditions, with substantially higher J values during daylight hours. This pattern reflects the common diel patterns of the drivers of both higher DO oversaturation and wind speed over those hours. It is demonstrated that the magnitude of J is substantial relative to net changes in the epilimnetic DO pool, and thus must be accommodated accurately in estimates of primary production and community respiration that are to be based on diel monitoring of DO in the water columns of productive lakes.     

Influence of sulfate enrichment on the carbon dioxide and phosphate fluxes across the sediment–water interface

Fluxes of CO2 and o-P across the sediment-water interfacewere measured adding different amounts of sulfatein order to quantify the influence in these processes againsta control, and using chloramphenicol as an inhibitor ofbacterial activity. These experiments were performed underoxic and anoxic conditions. Results show that the additionof sulfate stimulated the fluxes of CO2 and o-P, whilethe use of chloramphenicol decreased these fluxes. Theratio of o-P release to Org-C release ranged from 1 to 5 underoxic conditions and from 18 to 42 under anoxicconditions.     

Students’ conceptions of the carbon cycle: identifying and interrelating components of the carbon cycle and tracing carbon atoms across the levels of biological organisation

This study investigates students’ conceptions of the carbon cycle with regard to the components they believe to be relevant to the carbon cycle, how they interrelate these components, the ways in which they trace carbon atoms, and the different levels of biological organisation they consider when doing so. A total of 142 students aged 13–16 years (grades 8–10) participated in the study. A total of 130 students completed the diagnostic task, and an additional 12 students completed both the diagnostic task and were interviewed. The primary results show that the students identified few components of the carbon cycle, tended to trace carbon atoms exclusively at the level of the organism, and had difficulties identifying organic carbon compounds, especially during processes in which carbon compounds are transformed. Considering the main educational implications, we recommend using an instructional strategy that traces carbon atoms across the different levels of biological organisation whilst connecting fragmented knowledge by integrating knowledge from physiology, biochemistry and ecology when teaching the carbon cycle.     

Malate relations of plants and crassulacean acid metabolism: protons,carbon dioxide and water.—A review

Abstract

This review discusses the central role of malate in plant metabolism and in a large array of physiological processes in general. This is related to the function of crassulacean acid metabolism (CAM) as an ecophysiological adaptation to limited water supply.     

Effects of temperature and carbon dioxide on green sturgeon blood–oxygen equilibria

There are three Northeast Pacific Rivers still supporting spawning populations of green sturgeon, Acipenser medirostris, but all have been modified hydrologically and thermally by dam construction. Age 1- to 3-year-old green sturgeon, progeny of artificially spawned, wild-caught Klamath River adults, were used to assess the effects of temperature and carbon dioxide on critical hematological parameters related to evolutionary adaptations of this species to its physical environment. In vitro measurement of the effect of temperature and carbon dioxide on blood–oxygen affinity and equilibrium curve shape yielded the following data for the respective temperature treatments (11, 15, 19, and 24°C): half-saturation values (P₅₀’s, kPa, a measure of affinity) 1.26, 1.44, 1.63, 1.69 for low-PCO₂ treatments and 2.08, 2.41, 2.74, 2.94 for high-PCO₂ treatments; Bohr factors ?0.322, ?0.327, ?0.366, ?0.536; and non-bicarbonate buffer values (slykes) ?6, ?3, ?5, ?8. Temperature sensitivities (ΔH, kJ mol O ₂ ^?1 ) between these respective temperatures were ?34.20, ?15.24, ?6.74 for low-PCO₂ treatments and ?20.05, ?27.00, and ?11.55 for the high-PCO₂ treatments. These data suggest that juvenile green sturgeon may tolerate moderate environmental hypoxia, moderate aerobic activity, low to moderate hypercapnia, and moderate temperature changes in their environments.     

Effects of temperature and carbon dioxide on green sturgeon blood–oxygen equilibria

There are three Northeast Pacific Rivers still supporting spawning populations of green sturgeon, Acipenser medirostris, but all have been modified hydrologically and thermally by dam construction. Age 1- to 3-year-old green sturgeon, progeny of artificially spawned, wild-caught Klamath River adults, were used to assess the effects of temperature and carbon dioxide on critical hematological parameters related to evolutionary adaptations of this species to its physical environment. In vitro measurement of the effect of temperature and carbon dioxide on blood–oxygen affinity and equilibrium curve shape yielded the following data for the respective temperature treatments (11, 15, 19, and 24°C): half-saturation values (P₅₀’s, kPa, a measure of affinity) 1.26, 1.44, 1.63, 1.69 for low-PCO₂ treatments and 2.08, 2.41, 2.74, 2.94 for high-PCO₂ treatments; Bohr factors −0.322, −0.327, −0.366, −0.536; and non-bicarbonate buffer values (slykes) −6, −3, −5, −8. Temperature sensitivities (ΔH, kJ mol O₂⁻¹) between these respective temperatures were −34.20, −15.24, −6.74 for low-PCO₂ treatments and −20.05, −27.00, and −11.55 for the high-PCO₂ treatments. These data suggest that juvenile green sturgeon may tolerate moderate environmental hypoxia, moderate aerobic activity, low to moderate hypercapnia, and moderate temperature changes in their environments.     

Fluxes of nitrous oxide, methane and carbon dioxide during freezing–thawing cycles in an Inner Mongolian steppe

Combined measurements of nitrification activity and N₂O emissions were performed in a lowland and a montane tropical rainforest ecosystem in NE-Australia over a 18 months period from October 2001 until May 2003. At both sites gross nitrification rates, measured by the BaPS technique, showed a strong seasonal pattern with significantly higher rates of gross nitrification during wet season conditions. Nitrification rates at the montane site (1.48?±?0.24–18.75?±?2.38 mg N kg^?1 day^?1) were found to be significantly higher than at the lowland site (1.65?±?0.21–4.54?±?0.27 mg N kg^?1 day^?1). The relationship between soil moisture and gross nitrification rates could be described best by O’Neill functions having a soil moisture optimum of nitrification at app. 65% WFPS. At the lowland site, for which continuous measurements of N₂O emissions were available, nitrification was positively correlated with N₂O emission. Nitrification contributed significantly to N₂O formation during dry season (app.85%) but less (app. 30%) during wet season conditions. In average 0.19‰ of the N metabolized by nitrification was released as N₂O. The N₂O fraction loss for nitrification was positively correlated with changes in soil moisture and varied slightly between 0.15 and 0.22‰. Our results demonstrate that combined N₂O emission and microbial N turnover studies covering prolonged observation periods are needed to clarify and quantify the role of the microbial processes nitrification and denitrification for annual N₂O emissions from soils of terrestrial ecosystems.     

Climatic impact of land use in LCA—carbon transfers between vegetation/soil and air

Background, aim, and scope  

Human use of land areas leads to impacts on nature in several ways. Within the framework of the UNEP/SETAC Life Cycle Initiative, it was stated that life cycle assessment (LCA) of land use should assess at least the impact on biodiversity, the impact on biotic production, and the impact on the regulating functions of the natural environment. This study focuses on the climatic impact of land use as determined by the CO₂ transfers between vegetation/soil and the atmosphere in the course of terrestrial release and re-storage of carbon.     

The surface organization of diacylglycerol pyrophosphate and its interaction with phosphatidic acid at the air–water interface

Diacylglycerol pyrophosphate (DGPP), a phosphorylated form of phosphatidic acid (PA), gained attention recently due to its role as signaling lipid. However, little is known about its surface organization and potential impact on membrane-mediated function. In this work we investigated the interfacial behavior of Langmuir monolayers formed with pure DGPP and of its mixtures with PA. We found that changes of the subphase pH affect the surface behavior of DGPP. At pH 8, DGPP forms liquid expanded monolayers with a compressibility modulus of about 60 mN m^?1 at collapse. On acidic solutions, the compressibility modulus increases to 90 mN m^?1 and the average molecular area is smaller. At pH 8, DGPP and its precursor PA form thermodynamically favored topographically homogeneous non-ideal mixtures. The interaction among these lipids leads to a non-ideal diminution of the mean molecular area and consequently, to an increase of the compressibility modulus, with variations of the surface electrostatics. The favorable interaction of PA and DGPP, leading to changes of the film packing suggest that DGPP may act as a structural signal transducer in membrane-mediated cellular processes.     

Distribution of soil phytolith-occluded carbon in the Chinese Loess Plateau and its implications for silica–carbon cycles

Background and aims

Plants absorb and carry soluble silica from soils and then deposit SiO₂?·?nH₂O within themselves producing amorphous silica particles known as phytoliths. Trace amount of organic carbon is occluded during phytolith formation referred to as phytolith-occluded carbon (PhytOC). This carbon fraction has been recognized as an important way of carbon biosequestration. Previous studies have investigated the PhytOC contents of many crop plants and their contribution to global carbon sink. However, the PhytOC in soil is less focused. In this study, we investigated the distribution of soil PhytOC in the Chinese Loess Plateau (CLP).

Methods

Twenty-six soil profiles were collected in the Chinese Loess Plateau. A wet oxidation method was used for phytolith extraction. Occluded carbon was determined by element analyzer.

Results

Our results showed that the soil PhytOC density (SPCD) ranged from 0.757 to 23.110 g/m² among different soil profiles. The SPCD of profiles in the Southern CLP was generally higher than that in the Northern CLP. It was estimated that 5.35 Mt of PhytOC was stored in the upper soil of the CLP. We also estimated the annual phytolith flux into the Yellow River from the CLP by soil erosion and about 2.5 Mt of phytoliths eroded and transported into rivers per year.

Conclusions

Our study indicated that PhytOC was one of the potential biosequestration way and phytoliths had an important influence on biogeochemical cycle of silica. Our results suggested that the soil PhytOC was mainly influenced by different plant communities.     

Dynamics of dissolved oxygen isotopic ratios: a transient model to quantify primary production,community respiration,and air–water exchange in aquatic ecosystems

Dissolved O(2) is an important aquatic ecosystem health indicator. Metabolic and gas exchange (G) rates, which control O(2) concentration, are affected by nutrient loading and other environmental factors. Traditionally, aquatic metabolism has been reported as primary production:community respiration (P:R) ratios using diel measurements and interpretations of dissolved O(2) and/or CO(2) concentrations, and recently using stable isotopes (delta(18)O, Delta(17)O) and steady state assumptions. Aquatic ecosystems, such as rivers and ponds, are not at steady state and exhibit diel changes, so steady state approaches are often inappropriate. A dynamic O(2) stable isotope model (photosynthesis-respiration-gas exchange; PoRGy) is presented here, requiring a minimum of parameters to quantify daily averaged P, R, and G rates under transient field conditions. Unlike steady state approaches, PoRGy can address scenarios with 100% O(2) saturation but with delta(18)O-O(2) values that are not at air equilibrium. PoRGy successfully accounts for isotopic G when applied to an oxygen isotope equilibration laboratory experiment. PoRGy model results closely matched the diel O(2) and delta(18)O-O(2) data from three field sites with different P:R:G ratios and various P, R and G rates. PoRGy provides a new research tool to assess ecosystem health and to pose environmental impact-driven questions. Using daily averaged rates was successful and thus they can be used to compare ecosystems across seasons and landscapes.     

Computational study of glucosepane–water and hydrogen bond formation: an electron topology and orbital analysis

The collagen protein provides tensile strength to the extracellular matrix in addition to localising cells, proteins and protein cofactors. Collagen is susceptible to a build up of glycation modifications as a result of an exceptionally long half-life. Glucosepane is a collagen cross-linking advanced glycation end product; the structural and mechanical effects of glucosepane are still the subjects of much debate. With the prospect of an ageing population, the management and treatment of age-related diseases is becoming a pressing concern. One area of interest is the isolation of hydrated glucosepane, which has yet to be reported at an atomistic level. This study presents a series of glucosepane–water complexes within an implicit aqueous environment. Electronic structure calculations were performed using density functional theory and a high level basis set. Hydrogen bonds between glucosepane and explicit water were identified by monitoring changes to covalent bonds, calculating levels of electron donation from Natural Bonding Orbital analysis and the detection of bond critical points. Hydrogen bond strength was calculated using second-order perturbation calculations. The combined results suggest that glucosepane is very hydrophilic, with the imidazole feature being energetically more attractive to water than either hydroxyl group, although all hydrogen bonds, regardless of bond strength, were electrostatic in nature. Our results are in growing support of an earlier hypothesis that cross-links may result in an increase in interstitial water retention, which would permit the collagen fibril to swell, thereby potentially affecting the tensile and compression properties and biological function of connective tissues.     

Biogeochemical changes at the sediment–water interface during redox transitions in an acidic reservoir: exchange of protons,acidity and electron donors and acceptors

Redox transitions induced by seasonal changes in water column O₂ concentration can have important effects on solutes exchange across the sediment–water interface in systems polluted with acid mine drainage (AMD), thus influencing natural attenuation and bioremediation processes. The effect of such transitions was studied in a mesocosm experiment with water and sediment cores from an acidic reservoir (El Sancho, SW Spain). Rates of aerobic organic matter mineralization and oxidation of reduced inorganic compounds increased under oxic conditions (OX). Anaerobic process, like Fe(III) and sulfate reduction, also increased due to higher O₂ availability and penetration depth in the sediment, resulting in higher regeneration rates of their corresponding anaerobic e^? acceptors. The contribution of the different processes to oxygen uptake changed considerably over time. pH decreased due to the precipitation of schwertmannite and the release of H⁺ from the sediment, favouring the dissolution of Al-hydroxides and hydroxysulfates at the sediment surface. The increase in dissolved Al was the main contributor to water column acidity during OX. Changes in organic matter degradation rates and co-precipitation and dissolution of dissolved organic carbon and nitrogen with redox-sensitive Fe(III) compounds affected considerably C and N cycling at the sediment–water interface during redox transitions. The release of NO₂^? and NO₃^? during the hypoxic period could be attributed to ammonium oxidation coupled to ferric iron reduction (Feammox). Considering the multiple effects of redox transitions at the sediment–water interface is critical for the successful outcome of natural attenuation and bioremediation of AMD impacted aquatic environments.     

Effect of tillage and straw return on carbon footprints,soil organic carbon fractions and soil microbial community in different textured soils under rice–wheat rotation: a review

Reviews in Environmental Science and Bio/Technology - Measuring the influence of long-term agricultural tillage practices on soil organic carbon (SOC) is of great importance to farmers and...     

The effect of Chinese tallow tree (Sapium sebiferum) ecotype on soil–plant system carbon and nitrogen processes

The EICA hypothesis predicts that shifts in allocation of invasive plants give rise to higher growth rates and lower herbivore defense levels in their introduced range than conspecifics in their native range. These changes in traits of invasive plants may also affect ecosystem processes. We conducted an outdoor pot experiment with Chinese tallow tree (Sapium sebiferum, Euphorbiaceae) seedlings from its native (Jiangsu, China, native ecotype) and introduced ranges (Texas, USA, invasive ecotype) to compare their relative performances in its native range and to examine ecotype effects on soil processes with and without fertilization. Consistent with predictions, plant (shoot and root) mass was significantly greater and leaf defoliation tended to be higher, while the root:shoot ratio was lower for the invasive ecotype relative to the native ecotype. Seasonal amounts of soil–plant system CO₂ and N₂O emissions were higher for the invasive ecotype than for the native ecotype. Soil respiration rates and N₂O emission increases from fertilization were also greater for the invasive ecotype than for the native ecotype, while shoot-specific respiration rates (g CO₂–C g⁻¹ C day⁻¹) did not differ between ecotypes. Further, soil inorganic N (ammonium and nitrate) was higher, but soil total N was lower for soils with the invasive ecotype than soils with the native ecotype. Compared with native ecotypes, therefore, invasive ecotypes may have developed a competition advantage in accelerating soil processes and promoting more nitrogen uptake through soil–plant direct interaction. The results of this study suggest that soil and ecosystem processes accelerated by variation in traits of invasive plants may have implications for their invasiveness.     

Identification of barley genetic regions influencing plant–microbe interactions and carbon cycling in soil

Plant and Soil - Forest management towards increased carbon (C) sequestration has repeatedly been suggested as a “natural climate solution”. We evaluated the potential of altered...