Differences In CO2 Fluxes Research Articles

Variation of CO2 fluxes, net ecosystem production, and calcification in tropical waters of seagrass and coral reef

Carbonate system alteration in Indonesia's seagrass and coral reef ecosystems must be better understood. Changes in CO2 fluxes, ecosystem production, and calcification can impact the availability of resources and habitats for seagrass and coral reef species, which can have cascading effects on the overall health and diversity of marine ecosystems. The study aims to identify diurnal and seasonal CO2 flux, net ecosystem production (NEP), and net ecosystem calcification (NEC) in the tropical waters (Sire Bay, Lombok) around seagrass and coral reef ecosystems. Field sampling was conducted in two seasons and measured the seawater carbonate system and physicochemical characteristics. We found a significant difference in CO2 flux between seagrass and coral reefs in April but not for NEP and NEC in April or October. Both ecosystems act as CO2 sources in April, and CO2 sinks in October. The NEP of coastal water tends to be autotrophic in April and heterotrophic in October. The calcification rate was inversely proportional to the NEP, where the NEC was higher in October than in April. There was a low relationship between CO2 flux and NEP and NEC, indicating that changes in CO2 flux do not directly affect NEP and NEC in Sire Bay waters.

Effect of Moisture on CO<sub>2</sub> Flux of the Palsa Mire Soils (North of Western Siberia)

The effect of the moisture content on peat soils has been studied in discontinuous permafrost area in the north of the Western Siberia (Nadym region). СО2 flux was measured in palsa mire soils (Cryic Histosol) and surrounding bogs (Fibric Histosol) using the closed chamber method for 4 years at the peak of the growing season (August). Despite a significant difference in soil moisture (34.8 ± 13.2 and 56.2 ± 2.1% on average), no significant difference in CO2 emission between these ecosystems was found in any of the observation years (on average 199.1 ± 90.1 and 182.1 ± 85.1 mg CO2 m–2 h–1, respectively). Experimental wetting or drying (with two times difference in moisture content) of peat soil plots by transplantation method showed no significant effect on CO2 emission even 3 years after the experiment start. The absence of significant differences in CO2 flux between ecosystems and experiments was explained by the presence of permafrost and the influence of many multidirectional factors mitigating changes in CO2 production by soils. CO2 flux enhancing from the soils of the bog is possible due to the additional contribution of the methanotrophic filter, as well as the lateral runoff of dissolved CO2 over the permafrost table from palsa mire surrounding the bogs. The absence of a response of CO2 emission to a significant change in moisture may indicate a wide optimum of this parameter for microbiological activity in peat soils of the studied region. The results indicate that, in the study of cryogenic soils of hydromorphic landscapes, it is necessary, in addition to biogenic sources, to take into account additional factors, often of a physical nature, that change the balance of CO2 fluxes and CO2 emission by soils, respectively.

Carbon Dioxide, Methane and Nitrous Oxide Fluxes from Tree Stems in Silver Birch and Black Alder Stands with Drained and Naturally Wet Peat Soils

The aim of this study was to evaluate the impact of groundwater level, soil temperature and general soil chemistry on greenhouse gas (GHG)—carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)—fluxes from tree stems in deciduous stands with nutrient-rich naturally wet and drained peat soils. In total, nine sample plots were established in the central and north-eastern part of Latvia. The studied tree species were silver birch (Betula pendula Roth.) and black alder (Alnus glutinosa (L.) Gaertb.). Tree stands of different ages and tree dimensions were selected for the study. GHG fluxes were measured with a circular-type non-transparent chamber of fixed area and volume, which was connected to the “Gasmet DX4040” mobile spectrometer. Ambient and soil temperature at a depth of 10 cm were measured, soil parameters (pH and content of carbon (C), nitrogen (N), potassium (K), phosphorus (P)) down to 30 cm depth were analyzed, and groundwater levels and weather conditions (wind, cloudiness, precipitation) were determined. The study found that CO2 fluxes from tree stems show a distinct seasonal pattern and a strong positive correlation with soil temperature. Significant differences in CO2 fluxes were found between temperature ranges below and above 5 °C, indicating that this temperature represents a threshold value. CH4 emissions from the tree stems increased with increasing groundwater levels. The impact of groundwater level becomes insignificant if the depth of the groundwater exceeds 30 cm. No significant N2O fluxes from tree stems were detected for most of the study period, except for March, April and June in black alder stands. As with CH4, N2O emissions exhibit an increase as groundwater levels rise. The C and N contents in soil have a significant impact on N2O fluxes from tree stems. There is a tendency for the N2O flux to increase along with increasing C and N contents in soil.

Deep soil CO2 flux with strong temperature dependence contributes considerably to soil-atmosphere carbon flux

The diffusion of CO2 produced by carbon mineralization in vertical profiles is an important CO2 emission process. However, because of the relatively slow rate of change in the subsoil environment compared with the surface soil, carbon mineralization and diffusion are often ignored, and the mechanisms that transfer deep carbon to the soil-atmosphere interface are still unclear. We studied vertical differences in CO2 flux and its driving mechanism in layers situated from 0 to 200 cm in Robinia pseudoacacia plantations with different stand ages on the Loess Plateau under a typical temperate continental semi-arid monsoon climate. The results showed that (1) in the 0–200 cm layer, CO2 flux showed a bimodal seasonal trend, and total CO2 flux of Robinia pseudoacacia forests with a 10 years stand age fluctuated more actively among the months (Standard Deviation: 3.28%–9.57%). (2) Dynamic evaluation of contribution rate showed a stable (21.81–24.42%) contribution of deep CO2 flux to soil atmosphere interface. (3) Temperature sensitivity of CO2 flux (expressed as Q10) significantly increased with soil depth, moisture and soil CO2 flux presented stronger quadratic function relation in deep layers than shallow layers. There was a significant positive correlation between deep CO2 flux and soil organic carbon (SOC), but there was a weak negative correlation in the shallow layers. The CO2 flux in the shallow layers was mainly regulated by soil organic carbon, whereas that in the deep layers was more regulated by soil temperature.(4) Compared with the traditional hydrothermal two-factor model, the new T&M&C (temperature & moisture & organic carbon) model can improve the model precision by 20–25%, especially in the prediction of CO2 flux in deep layers. Overall, this study is significant for understanding the stability and dynamic changes in the soil carbon pool, and the mechanism of deep organic carbon diffusion to the soil-atmosphere interface in the Loess Plateau.

Dynamics of Soil Organic Carbon and CO2 Flux under Cover Crop and No-Till Management in Soybean Cropping Systems of the Mid-South (USA)

The transition of natural landscapes to agricultural uses has resulted in severe loss of soil organic carbon, significantly contributing to CO2 emissions and rising global temperatures. However, soil has the largest store of terrestrial carbon (C), a considerable sink and effective strategy for climate change mitigation if managed properly. Cover crops (CC) and no-till (NT) management are two management strategies that are known to increase percent organic carbon (%OC); however, adoption of these practices has been low in the mid-South due to lack of region-specific research and resistance to unproven practices. Therefore, the purpose of this study was to evaluate the impacts of CC-NT treatments in soybean cropping systems on soil percent organic carbon (%OC) and CO2 flux following long-term implementation. Results showed significantly greater %OC in NT (1.27% ± 0.03) than reduced till (RT; 1.10% ± 0.03; p < 0.001) and greater in both CC (rye: 1.23% ± 0.03, rye + clover: 1.22% ± 0.03) than no cover (1.11% ± 0.03; p < 0.001). Bacterial abundance (p = 0.005) and pH (p = 0.006) were significant predictors of %OC. There was no overall significant difference in CO2 flux between tillage or CC treatments; however, there were significant differences between NT and RT in July of 2020 when %RH increased (p < 0.001). Bacterial abundance negatively impacted CO2 flux (p < 0.05), which contradicts most studies. The rate of proportional change and pattern of variability in C pools suggested loss of %OC in RT treatments that were not apparent when considering %OC alone. The results of this study provide valuable insight into C turnover and the effectiveness of CC use in the Mid-South to increase soil C stocks.

Comparison Between Tributary and Main Stream and Preliminary Influence Mechanism of CO2 Flux Across Water-air Interface in Wanzhou in the Three Gorges Reservoir Area

The main stream of the Three Gorges Reservoir area in Wanzhou and its tributary (the Pengxi River) were selected as a survey area to monitor the CO2 concentration. Twelve related indicators were selected during the blooming period from April to September 2019, which were divided into Climate factors, Water environment factors, Carbon source factors, Nutrient factors, and Sediment factors. These factors were considered for further discussion of the impact pathways and contribution to CO2 flux. The average CO2 fluxes of Gaoyang (the Pengxi River), Huangshi (the Pengxi River), and Wanzhou (the main stream) were (1.445±1.739), (3.118±2.963), and (2.899±1.144) mmol·(m2·h)-1, respectively, showing that Gaoyang < Wanzhou < Huangshi. The CO2 flux of tributary showed a large variation, while the main stream had a relatively small variation, which is a stable "source" of CO2. The main stream of the Yangtze River, as a hub for the transportation of biomass from land to sea, has higher carbon concentration and higher flow rate than its tributaries, which makes the CO2 flux of the main stream usually larger than that of the tributary. However, the difference in hydrological conditions result in spatial differences in CO2 flux at different points of the same tributary. Gaoyang is located in the reservoir bay, which is conducive to the growth of phytoplankton and the CO2 flux is lower; Huangshi is located in a river with a faster flow rate. The backwater support and backflow of the main stream make the CO2 flux significantly greater than that at Wanzhou. The effects of various indicators on the CO2 flux are also markedly different in the tributary and main stream. Temperature (T), DO, dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) have significant effects on CO2 fluxes in the tributary, while NH4+-N has a significant impact on CO2 fluxes in the main stream. Nutrient factors and carbon source factors contribute 32.37% and 27.25%, respectively, to CO2 flux, accounting for more than half of the total, followed by climate factors, water environment factors, and sediment factors, which contribute 18.81%, 13.49%, and 8.08%, respectively. Reservoir CO2 emission control can focus on controlling the eutrophication and carbon sources; phenomena such as global warming and sedimentation will also have a certain impact on the CO2 emission of reservoirs.

Spatial and temporal variability of &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emissions from the Dong River in south China

Abstract. CO2 efflux at the water–air interface is an essential component of the riverine carbon cycle. However, the lack of spatially resolved CO2 emission measurements prohibits reliable estimation of the global riverine CO2 emissions. By deploying floating chambers, seasonal changes in river water CO2 partial pressure (pCO2) and CO2 emissions from the Dong River in south China were investigated. Spatial and temporal patterns of pCO2 were mainly affected by terrestrial carbon inputs (i.e., organic and inorganic carbon) and in-stream metabolism, both of which varied due to different land cover, catchment topography, and seasonality of precipitation and temperature. Temperature-normalized gas transfer velocity (k600) in small rivers was 8.29 ± 11.29 and 4.90 ± 3.82 m d−1 for the wet season and dry season, respectively, which was nearly 70 % higher than that of large rivers (3.90 ± 5.55 m d−1 during the wet season and 2.25 ± 1.61 m d−1 during the dry season). A significant correlation was observed between k600 and flow velocity but not wind speed regardless of river size. Most of the surveyed rivers were a net CO2 source while exhibiting substantial seasonal variations. The mean CO2 flux was 300.1 and 264.2 mmol m−2 d−1 during the wet season for large and small rivers, respectively, 2-fold larger than that during the dry season. However, no significant difference in CO2 flux was observed between small and large rivers. The absence of commonly observed higher CO2 fluxes in small rivers could be associated with the depletion effect caused by abundant and consistent precipitation in this subtropical monsoon catchment.

Short-term effect of adding nitrogen in forest soil of an urban rainforest

The deposition of atmospheric nitrogen has been increased in urban forest ecosystems, yet it is not clear how this increase affects soil respiration in the short term. The soil respiration could contribute to CO2 flux to the atmosphere; therefore, it is essential to understand how nitrogen addition affects soil respiration and its autotrophic and heterotrophic compartments. We established a randomized block experiment to investigate the effects of adding 2.5 kg ha-1 (which corresponds to ~ 40% of the total annual deposition) in soil respiration during five days in an urban tropical forest. The CO2 flux of the autotrophic and heterotrophic compartments was individualized and measured using an infrared gas analyzer (IRGA). Two measurements per day (9-11 and 21-23 hours) were assessed for five consecutive days. Days and nights show no difference in CO2 flux among all compartments. The heterotrophic respiration was strong negatively affected by nitrogen addition, about 34%. Autotrophic respiration was positively impacted by nitrogen addition, but no significant differences were found. Heterotrophic respiration is the primary source of CO2 from the forest soil.

Native shrubland and managed buffelgrass savanna in drylands: Implications for ecosystem carbon and water fluxes

Land cover and land-use change (LCLUC) between woody- and grass-dominated ecosystems in drylands comprise one of the largest uncertainties in the land CO2 sink. This is especially true for the widespread transition from shrublands to grasslands/savannas caused by the establishment of exotic C4 grass species for grazing or through biological invasion of these species, where information about its impacts on ecosystem CO2 fluxes is limited. For studying this, we used three years of eddy covariance measurements of net ecosystem production (NEP), gross primary production (GPP), ecosystem respiration (Reco) and evapotranspiration (ET) over a Sonoran Desert shrubland and an adjacent grazing savanna of buffelgrass (Cenchrus ciliaris L.), established 35 years ago. At monthly, seasonal and annual time scales, we assessed whether between-site differences in CO2 fluxes were related to differences in ecosystem water use, measured as the fraction ET to precipitation, water use efficiency (WUE, i.e. the ratio between GPP and ET) and/or to the relation between Reco and GPP. Although the savanna had higher WUE than the shrubland, its summer NEP was limited by water use, due to limitations in leaf area index and likely rooting patterns. Conversely, the savanna had higher NEP than the shrubland during fall to spring due to increased WUE; possibly due to activity of buffelgrass and remaining woody species using (summer) water from deeper soil layers. However, differences across these seasons compensated each other at the inter-annual scale, and both sites had comparable net carbon sinks over the three-year study period. Further studies are needed to understand and reduce the uncertainty associated with carbon and water fluxes associated with LCLUC in dryland ecosystems.

Plot-scale spatiotemporal variations of CO2 concentration and flux across water-air interfaces at aquaculture shrimp ponds in a subtropical estuary.

Human activities have increased anthropogenic CO2 emissions, which are believed to play important roles in global warming. The spatiotemporal variations of CO2 concentration and flux at fine spatial scales in aquaculture ponds remain unclear, particularly in China, the country with the largest aquaculture. In this study, the plot-scale spatiotemporal variations of water CO2 concentration and flux, both within and among ponds, were researched in shrimp ponds in Shanyutan Wetland, Min River Estuary, Southeast China. The average water CO2 concentration and flux across the water-air interface in the shrimp ponds over the shrimp farming period varied from 22.79 ± 0.54 to 186.66 ± 8.71μmolL-1 and from - 0.50 ± 0.04 to 2.87 ± 0.78molm-2day-1, respectively. There was no remarkable difference in CO2 concentration and flux within the ponds, but significantly spatiotemporal differences in CO2 flux were observed between shrimp ponds. Chlorophyll a, pH, salinity, air temperature, and morphometry were the important factors driving the spatiotemporal patterns of CO2 flux in the shrimp ponds. Our findings highlighted the importance and spatiotemporal variations of CO2 flux in the important coastal ecosystems.

Effects of tillage on CO2 fluxes in a typical karst calcareous soil

It is widely believed that soil disturbance by tillage was the primary cause of historical soil organic carbon (SOC) loss and high carbon dioxide (CO2) emission levels in the calcareous karst region. Nevertheless, the mechanisms underlying CO2 fluxes resulting from the soil property changes caused by tillage are poorly understood. A one-year simulation experiment using different tillage frequencies was conducted to quantify the impacts of tillage and soil property changes on CO2 flux. Treatments included conservation tillage (T0), semiannual tillage (T1), tillage every four months (T2), bimonthly tillage (T3), and monthly tillage (T4). The effects of tillage on soil CO2 flux had a strong seasonal pattern. CO2 fluxes in higher tillage frequencies of T3 and T4 were significantly higher than those of other treatments in spring, summer, and autumn. For viable tillage management, CO2 fluxes in T1 and T2 were significantly higher than those in T0 in spring and autumn. No significant differences in CO2 flux were found among treatments in winter. Tillage also had a significant influence on soil biogeochemical properties. Aggregate stability, dissolved organic carbon (DOC), and microbial biomass carbon (MBC) significantly decreased in T2, T3, and T4, whereas SOC significantly decreased just in T3 and T4 after 1 year. A structural equation model analysis showed that the annual cumulative soil CO2 flux was directly affected by annual changes in SOC (∆SOC), DOC (∆DOC), and MBC (∆MBC). Tillage frequency directly influenced annual changes in large macroaggregates (∆AG) and ∆MBC. These results indicated that tillage practice indirectly lowered SOC by reducing large macroaggregates and microbial biomass, which in turn, enhanced CO2 flux. Our results suggested that tillage disturbance in the karst soil significantly increased SOC loss through enhanced CO2 flux compared with that in the non-karst soil in a similar climate. In contrast, reducing or eliminating tillage in the wet-hot season could lower CO2 flux rate by minimizing large macroaggregate disturbance and, by extension, microbial access to mobile carbon sources.

Effects of forest regeneration practices on the flux of soil CO2 after clear-cutting in subtropical China

Reforestation after clear-cutting is used to facilitate rapid establishment of new stands. However, reforestation may cause additional soil disturbance by affecting soil temperature and moisture, thus potentially influencing soil respiration. Our aim was to compare the effects of different reforestation methods on soil CO2 flux after clear-cutting in a Chinese fir plantation in subtropical China: uncut (UC), clear-cut followed by coppicing regeneration without soil preparation (CC), clear-cut followed by coppicing regeneration and reforestation with soil preparation, tending in pits and replanting (CCRP), and clear-cut followed by coppicing regeneration and reforestation with overall soil preparation, tending and replanting (CCRO). Clear-cutting significantly increased the mean soil temperature and decreased the mean soil moisture. Compared to UC, CO2 fluxes were 19.19, 37.49 and 55.93 mg m−2 h−1 higher in CC, CCRP and CCRO, respectively (P < 0.05). Differences in CO2 fluxes were mainly attributed to changes in soil temperature, litter mass and the mixing of organic matter with mineral soil. The results suggest that, when compared to coppicing regeneration, reforestation practices result in additional CO2 released, and that regarding the CO2 emissions, soil preparation and tending in pits is a better choice than overall soil preparation and tending.

Response of ecosystem CO2 fluxes to grazing intensities \u2013 a five-year experiment in the Hulunber meadow steppe of China

Grazing is the primary land use in the Hulunber meadow steppe. However, the quantitative effects of grazing on ecosystem carbon dioxide (CO2) fluxes in this zone remain unclear. A controlled experiment was conducted from 2010 to 2014 to study the effects of six stocking rates on CO2 flux, and the results showed that there were significant differences in CO2 fluxes by year, treatment, and month. The effects of light and intermediate grazing remained relatively constant with grazing year, whereas the effects of heavy grazing increased substantially with grazing duration. CO2 flux significantly decreased with increasing grazing intensity and duration, and it was significantly positively correlated with rainfall, soil moisture (SM), the carbon to nitrogen ratio (C/N ratio), soil available phosphorus (SAP), soil NH4+-N, soil NO3−N, aboveground biomass (AGB), coverage, height, and litter and negatively correlated with air temperature, total soil N (TN) and microbial biomass N (MBN). A correspondence analysis showed that the main factors influencing changes in CO2 emissions under grazing were AGB, height, coverage, SM, NH4+-N and NO3−N. Increased rainfall and reduced grazing resulted in greater CO2 emissions. Our study provides important information to improve our understanding of the role of livestock grazing in GHG emissions.

CO2 fluxes at south taiga bog in the European part of Russia in summer

This paper estimates CO2 emission and net ecosystem exchange (NEE) between the atmosphere and the surface of bog in the south taiga of the European part of Russia for the summer periods of 2013–2015. Flux measurements are carried out by the static chamber method every 7–10 days in three experimental sites with homogenous conditions of soil moisture and vegetation type. Statistically significant differences in CO2 fluxes and NEE are found between different experimental sites. It is shown that an assessment of the significance of bogs in CO2 balance with the atmosphere must be made with consideration for the spatial heterogeneity of bogs.

Temporal variability of CO2 fluxes at the sediment-air interface in mangroves (New Caledonia)

Carbon budgets in mangrove forests are uncertain mainly due to the lack of data concerning carbon export in dissolved and gaseous forms. Temporal variability of in situ CO2 fluxes was investigated at the sediment–air interface in different seasons in different mangrove stands in a semi-arid climate. Fluxes were measured using dynamic closed incubation chambers (transparent and opaque) connected to an infra-red gas analyzer. Microclimatic conditions and chl-a contents of surface sediments were determined. Over all mangrove stands, CO2 fluxes on intact sediments were relatively low, ranging from −3.93 to 8.85 mmolCO2·m−2·h−1 in the light and in the dark, respectively. Changes in the fluxes over time appeared to depend to a great extent on the development of the biofilm at the sediment surface. We suggest that in intact sediments and in the dark, CO2 fluxes measured at the sediment–air interface rather reflect the metabolism of benthic organisms than sediment respiration (heterotrophic and autotrophic). However, without the biofilm, sediment water content and air temperature were main drivers of seasonal differences in CO2 fluxes, and their influence differed depending on the intertidal location of the stand. After removal of the biofilm, Q10 values in the Avicennia and the Rhizophora stands were 1.84 and 2.1, respectively, revealing the sensitivity of mangrove sediments to an increase in temperature. This study provides evidence that, if the influence of the biofilm is not taken into account, the in situ CO2 emission data currently used to calculate the budget will lead to underestimation of CO2 production linked to heterotrophic respiration fueled by organic matter detritus from the mangrove.

Characteristics of direct CO2 emissions in four full-scale wastewater treatment plants

Direct CO2 emissions from wastewater treatment plants (WWTPs), which are commonly excluded from the greenhouse gas emission inventory as proposed by the International Panel on Climate Change, should be partly taken into consideration, because some of the fossil organic carbons (i.e. detergents, cosmetics, and pharmaceuticals) are also biodegradable, leading to the emission of CO2 during wastewater treatment. For the purpose of understanding the characteristics of direct CO2 emissions during biological nutrient removal from urban WWTPs, we investigated four different processes. Full-scale tests were carried out continuously during a two-year period, consisting of the anoxic/anaerobic/oxic (A2O) process, the anoxic/oxic (AO) process, the oxidation ditch, and the sequencing batch reactor (SBR) processes. Our experimental results show large differences in CO2 fluxes in the various treatment tanks (or periods), e.g. the aerated units/periods in four different WWTPs all contributed more than 96.0% of the entire direct CO2 emission caused by aerobic respiration and aeration stripping. On the other hand, CO2 emissions from non-aerated areas were quite low giving rise to small amounts of CO2 emissions during anaerobic metabolism. The direct emission of CO2 when treating per m3 wastewater (g CO2/m3 wastewater) corresponded with the following descending order among the four processes: SBR (347.34) > oxidation ditch (343.78) > A2O (175.68) > AO (173.37). However, this order changed into SBR (0.97) > oxidation ditch (0.76) > AO (0.68) > A2O (0.58) when treating per kilogram COD (kg CO2/kg COD).

Factors controlling soil organic carbon persistence along an eroding hillslope on the loess belt

The integration of hydrologic, geomorphic and biogeochemical approaches is required to determine organic carbon (OC) persistence and dynamics within landscapes. Here, we studied the persistence of OC along an eroding hillslope using soil in situ surface heterotrophic respiration measurement as an indicator. Along this topographical gradient, we quantified the space-time distribution of soil water and temperature as well as the amount of labile OC (i.e. NaOCl-non-resistant) in relation to CO2 fluxes. We used a Generalized Least Square (GLS) regression model (i) to identify the role of each abiotic factor as well as their interactions, and (ii) to quantify spatial differences in CO2 fluxes along the hillslope.We observed significant differences in respiration along the topographical gradient, i.e. 30% more at the downslope and 50% more at the backslope, relative to the uneroded summit position. Soil OC persistence along the hillslope was mainly controlled by the labile OC stock and moisture content. Our in-situ measurements also indicated that the temperature sensitivity of soil OC (as expressed by Q10 values) was strongly related to soil water content. The large stock of OC stored in colluvial soils has a higher temperature sensitivity (Q10 = 3.72 ± 0.17) than in non-depositional slope positions (Q10 = 1.77 ± 0.18 to 2.59 ± 0.13). Given the large stock of labile OC, its high temperature sensitivity and the high water contents that are needed to stabilize OC, we conclude that the OC stored in colluvial soils is particularly vulnerable to OC mineralization under drier/warmer conditions. When considering the large amount of OC that has been buried globally as a result of agricultural erosion during the last decades, the long-term stability of this pool under future land use and/or climate disturbance is an area of concern.

Alterations in the photomineralization of allochthonous DOM related to elevated atmospheric CO2

Climate-related shifts in forest composition and chemistry will likely affect the quantity and quality of dissolved organic matter (DOM) entering inland waters, and consequently, carbon dioxide (CO2) evasion. We examined the photodegradation of DOM derived from 2 common riparian plant species (Populus tremuloides and Salix alba) grown at ambient (360 ppm) and elevated (720 ppm) atmospheric CO2 concentrations. Rates and total photolytic CO2 production were determined for sterilized leachates ranging from 5 to 100 mg L−1 dissolved organic carbon (DOC). Based on multiple regression analysis, DOC concentration, followed by plant species, best predicted the rate and total flux of CO2. Photolytic CO2 production increased linearly with DOC concentration; however, the 5 mg L−1 treatment had the greatest rate per unit carbon, suggesting a self-shading effect of increasing DOC. The atmospheric CO2 conditions under which the plants were grown had no statistically significant effect, despite observed differences in CO2 fluxes between ambient and elevated Populus leachates. Fluorescence data suggest differences in photolytic CO2 production among treatments are related to differences in plant chemistry within the humic fraction. Thus, the magnitude of the photolytic CO2 flux from fresh waters in the future will depend primarily on climate-related changes in the quantity of terrestrial DOM inputs and secondarily by DOM source.

Modeling the impacts of climate variability and hurricane on carbon sequestration in a coastal forested wetland in South Carolina

The impacts of hurricane disturbance and climate variability on carbon dynamics in a coastal forested wetland in South Carolina of USA were simulated using the Forest-DNDC model with a spatially explicit approach. The model was validated using the measured biomass before and after Hurricane Hugo and the biomass inventories in 2006 and 2007, showed that the ForestDNDC model was applicable for estimating carbon dynamics with hurricane disturbance. The simulated results indicated that Hurricane Hugo in 1989 substantially influenced carbon storage immediately after the disturbance event. The simulated net ecosystem exchange (NEE) for the 58-year period (1950-2007) indicated that the hurricane reduced CO2 sequestration due primarily to the increased decomposition of a large amount of litter and woody debris, including fallen trees (over 80% of pre-hurricane trees), debris and branches, and dead roots. The inter-annual fluctuation of soil CO2 flux showed that the climate variability interfered substantially soil carbon dynamics in the forest. The results showed that there were substantial spatial and temporal differences in CO2 flux (3.2 - 4.8 Mg·C·ha −1 ) and wood biomass due to the differences in physical and biogeochemical characteristics in the forest.

オープンパス型とクローズドパス型の渦相関法によるＣＯ２フラックスの系統的差異と密度変動補正の影響

Since both open- and closed-path eddy covariance techniques have been used in ecosystem observation networks such as AsiaFlux, estimating the random and systematic differences in CO2 fluxes observed by the two techniques is important. In the present study, CO2 fluxes measured by open- and closed-path eddy covariance systems were compared using year-round data obtained in a single-cropping rice paddy and in a larch forest. The two sites were similar in eddy covariance instrumentation and data processing, but dissimilar in canopy height and structure, phenology, and climate. For both sites, differences in half-hourly CO2 fluxes measured by the open- and closed-path systems followed a Laplace distribution, but were significantly biased, resulting in the open-path system measuring lower values than the closed-path system and in a larger carbon sequestration by vegetation being estimated with the open-path system. The systematic difference between the two systems mainly arose from an inconsistency between the open-path CO2 flux and the WPL correction for the effect of air density fluctuations, and increased with the magnitude of the WPL correction. During the growing season, the systematic difference at the paddy site was consistently smaller than that at the larch site because of the much low Bowen ratio and the resulting small WPL correction term caused by standing water in the paddy field. The WPL correction term was large and thus, the systematic difference became apparent in late winter because of the high Bowen ratios at the paddy and larch site, each covered with dried soil and snowpack, respectively. The year-round, half-hourly data accumulated after quality control tests showed that, between the two systems, relative differences existed of 9.9% (N=6074) for the paddy site and 15.8% (N=4591) for the larch site.