Storage Flux Research Articles

Impact of CO2 storage flux sampling uncertainty on net ecosystem exchange measured by eddy covariance

Complying with several assumption and simplifications, most of the carbon budget studies based on eddy covariance (EC) measurements quantify the net ecosystem exchange (NEE) by summing the flux obtained by EC (FC) and the storage flux (SC). SC is the rate of change of a scalar, CO2 molar fraction in this case, within the control volume underneath the EC measurement level. It is given by the difference in the quasi-instantaneous profiles of concentration at the beginning and end of the EC averaging period, divided by the averaging period. The approaches used to estimate SC largely vary, from measurements based on a single sampling point usually located at the EC measurement height, to measurements based on profile sampling. Generally a single profile is used, although multiple profiles can be positioned within the control volume. Measurement accuracy reasonably increases with the spatial sampling intensity, however limited resources often prevent more elaborated measurement systems. In this study we use the experimental dataset collected during the ADVEX campaign in which turbulent and non-turbulent fluxes were measured in three forest sites by the simultaneous use of five towers/profiles. Our main objectives are to evaluate both the uncertainty of SC that derives from an insufficient sampling of CO2 variability, and its impact on concurrent NEE estimates.Results show that different measurement methods may produce substantially different SC flux estimates which in some cases involve a significant underestimation of the actual SC at a half-hourly time scales. A proper measuring system, that uses a single vertical profile of which the CO2 sampled at 3 points (the two closest to the ground and the one at the lower fringe of the canopy layer) is averaged with CO2 sampled at a certain distance and at the same height, improves the horizontal representativeness and reduces this (proportional) bias to 2–10% in such ecosystems. While the effect of this error is minor on long term NEE estimates, it can produce significant uncertainty on half-hourly NEE fluxes.

Experimental warming alters soil hydro-thermal properties and heat flux in a winter wheat field

ABSTRACTGlobal warming has profound effects on the distribution of water and heat in soil. This study aimed to examine the effects of warming on water storage, thermal properties, and heat flux changes at different depth (5–10, 10–20, and 20–40 cm) in a winter wheat (Triticum aestivum L.) field. The experiment with simulated warming, manipulated with infrared heaters, and its control combined with a nitrogen fertilization treatment was conducted in the North China Plain. The results showed that warming of around 2°C at 5 cm soil depth reduced soil water storage by 3.2%-11.1% before the jointing stage. However, the difference in soil water storage between warming and non-warming conditions behaved inversely before and after mid-April. Experimental warming significantly reduced soil volumetric heat capacity and thermal conductivity. In the winter, the warming depressed the upward heat flux by 42.4%-50.1% at the 5–10 cm layer, whereas the warming increased the downward heat flux by 5.5%-12.3% in the spring. Our observation indicates that the effects of warming on the exchange process of mass and energy between soil and the atmosphere should be further studied in agro-ecosystem regions.

Thermal mitigation of hydroponic green roof based on heat balance

The creation of green rooftops is an important method for mitigating heat build-up in urban rooftop environments because they lower the sensible heat flux over the rooftop and conductive heat flux into the building. We propose a model for assessing thermal mitigation effects through a hydroponic urban greening system based on heat balance. We conducted an experiment with two different rooftops at two study sites, which were monitored for two months in two different years. Each rooftop was divided into two areas: one bare, the other covered by the hydroponic urban greening system. Parameters measured in both areas were air temperature, surface temperature, and conductive heat flux. The data were analyzed using three thermal mitigation indices. However, it was difficult to show a uniform relationship between the latent heat flux and mitigation indices during the period of analysis. This suggests it would be necessary to include factors such as latent heat flux, conductive heat flux, and water heat storage flux to assess the thermal mitigation effect. Our research indicated that the composition of heat balance terms could estimate thermal mitigation effects in the green roof area independent of the year. The results suggest a principle for assessing the mitigation effects of urban greening on the thermal environment.

Micrometeorology of an ephemeral desert city, the Burning Man experiment

Observations are presented from a 12-day micrometeorological experiment investigating impacts of an ephemeral city (Black Rock City, Nevada, population 70,000), which emerges each year on a flat, arid, vegetation-free playa in late summer for the week-long ‘Burning Man’ event. Analysis focuses on observations from a 28m tower deployed in the center of the city prior to, and throughout the event. Wind profiles show a reduction in wind speed, particularly below 5m and indicate an increase in roughness length. Surface radiation and energy fluxes were remarkably unchanged after the development of the city. Both cases resembled other arid surfaces and somewhat other urban surfaces, though with little anthropogenic and much less heat storage flux than traditional cities. CO2 fluxes increased rapidly from 5.2gCm−2d−1 on the first full day of measurement to 24.8 during the event and peaked during the exodus (33.3gCm−2d−1). Inventory modeling revealed sources were mostly stationary, especially on-site electricity generation for air conditioning units. The car-free nature of the main event reduced the mobile sources to less than metabolic sources from the population itself and the CO2 flux per capita was three times smaller than on arrival and exodus days.

Optimal use of buffer volumes for the measurement of atmospheric gas concentration in multi-point systems

Abstract. Accurate multi-point monitoring systems are required to derive atmospheric measurements of greenhouse gas concentrations both for the calculation of surface fluxes with inversion transport models and for the estimation of non-turbulent components of the mass balance equation (i.e. advection and storage fluxes) at eddy covariance sites. When a single analyser is used to monitor multiple sampling points, the deployment of buffer volumes (BVs) along sampling lines can reduce the uncertainty due to the discrete temporal sampling of the signal. In order to optimize the use of buffer volumes we explored various set-ups by simulating their effect on time series of high-frequency CO2 concentration collected at three Fluxnet sites. Besides, we proposed a novel scheme to calculate half-hourly weighted arithmetic means from discrete point samples, accounting for the probabilistic fraction of the signal generated in the averaging period. Results show that the use of BVs with the new averaging scheme reduces the mean absolute error (MAE) up to 80 % compared to a set-up without BVs and up to 60 % compared to the case with BVs and a standard, non-weighted averaging scheme. The MAE of CO2 concentration measurements was observed to depend on the variability of the concentration field and on the size of BVs, which therefore have to be carefully dimensioned. The optimal volume size depends on two main features of the instrumental set-up: the number of measurement points and the time needed to sample at one point (i.e. line purging plus sampling time). A linear and consistent relationship was observed at all sites between the sampling frequency, which summarizes the two features mentioned above, and the renewal frequency associated with the volume. Ultimately, this empirical relationship can be applied to estimate the optimal volume size according to the technical specifications of the sampling system.

Higher late summer methane emission from central than northern European lakes

<p>Quantifying methane (CH<sub>4</sub>) emissions from lakes is important for regional and global greenhouse gas emission inventories. However, regional and global estimates suffer from methodologically inconsistent data sets and from the situation that systematic flux measurements are presently available only for some regions in the world. In particular, many temperate regions dominated by agricultural land use, like central Europe, lack regional multi-lake studies of lacustrine CH<sub>4</sub> emissions. We compare estimates of diffusive and ebullitive flux from 30 small central European and 17 small boreal lakes based on standardized measurements during a single visit per lake in late summer. Furthermore, we assess the amount of CH<sub>4</sub> accumulated in the hypoxic deep-water layers in late summer. This provides an estimate of the potential release of CH<sub>4</sub> from these lakes during autumn mixing (storage flux). The results show that emissions per unit area of lake surface from central European lakes are significantly higher than those from boreal lakes, with average estimates of diffusive and ebullitive flux being as much as six and 27 times higher, respectively. CH<sub>4</sub> concentration in the surface water was significantly related with lake area and maximum depth in the boreal lakes. However, no significant relationships between diffusive and ebullitive fluxes and lake basin morphometry were found in central European or boreal lakes, as proposed in earlier studies, although the short measurement period (6 h) may not have been adequate for reliably quantifying ebullition in our study. As expected, storage flux was related to relative depth and relative volume of the hypoxic water layer in both regions. We discuss the relevance of the higher observed diffusive and ebullitive fluxes for regional estimates in central Europe based on an example of previous emission estimates from small lakes in Switzerland. Our results suggest that diffusive and ebullitive CH<sub>4</sub> emissions from these lakes might be considerably higher than estimated based on widely applied relationships for predicting lacustrine CH<sub>4</sub> emissions developed in northern European and North American regions. The results also confirm that modifications are necessary when applying these relationships to central European lakes. Our study highlights the inter-regional variability in lacustrine CH<sub>4</sub> emissions and the need for regionally developed calibration data for validating and developing predictive models for estimating CH<sub>4</sub> emissions from lakes at the landscape scale.</p>

Arctic sea surface height variability and change from satellite radar altimetry and GRACE, 2003–2014

AbstractArctic sea surface height (SSH) is poorly observed by radar altimeters due to the poor coverage of the polar oceans provided by conventional altimeter missions and because large areas are perpetually covered by sea ice, requiring specialized data processing. We utilize SSH estimates from both the ice‐covered and ice‐free ocean to present monthly estimates of Arctic Dynamic Ocean Topography (DOT) from radar altimetry south of 81.5°N and combine this with GRACE ocean mass to estimate steric height. Our SSH and steric height estimates show good agreement with tide gauge records and geopotential height derived from Ice‐Tethered Profilers. The large seasonal cycle of Arctic SSH (amplitude ∼5 cm) is dominated by seasonal steric height variation associated with seasonal freshwater fluxes, and peaks in October–November. Overall, the annual mean steric height increased by 2.2 ± 1.4 cm between 2003 and 2012 before falling to circa 2003 levels between 2012 and 2014 due to large reductions on the Siberian shelf seas. The total secular change in SSH between 2003 and 2014 is then dominated by a 2.1 ± 0.7 cm increase in ocean mass. We estimate that by 2010, the Beaufort Gyre had accumulated 4600 km3 of freshwater relative to the 2003–2006 mean. Doming of Arctic DOT in the Beaufort Sea is revealed by Empirical Orthogonal Function analysis to be concurrent with regional reductions in the Siberian Arctic. We estimate that the Siberian shelf seas lost ∼180 km3 of freshwater between 2003 and 2014, associated with an increase in annual mean salinity of 0.15 psu yr−1. Finally, ocean storage flux estimates from altimetry agree well with high‐resolution model results, demonstrating the potential for altimetry to elucidate the Arctic hydrological cycle.

Continuous CO<sub>2</sub>/CH<sub>4</sub>/CO measurements (2012–2014) at Beromünster tall tower station in Switzerland

Abstract. The understanding of the continental carbon budget is essential to predict future climate change. In order to quantify CO2 and CH4 fluxes at the regional scale, a measurement system was installed at the former radio tower in Beromünster as part of the Swiss greenhouse gas monitoring network (CarboCount CH). We have been measuring the mixing ratios of CO2, CH4 and CO on this tower with sample inlets at 12.5, 44.6, 71.5, 131.6 and 212.5 m above ground level using a cavity ring down spectroscopy (CRDS) analyzer. The first 2-year (December 2012–December 2014) continuous atmospheric record was analyzed for seasonal and diurnal variations and inter-species correlations. In addition, storage fluxes were calculated from the hourly profiles along the tower. The atmospheric growth rates from 2013 to 2014 determined from this 2-year data set were 1.78 ppm yr−1, 9.66 ppb yr−1 and −1.27 ppb yr−1 for CO2, CH4 and CO, respectively. After detrending, clear seasonal cycles were detected for CO2 and CO, whereas CH4 showed a stable baseline suggesting a net balance between sources and sinks over the course of the year. CO and CO2 were strongly correlated (r2 > 0.75) in winter (DJF), but almost uncorrelated in summer. In winter, anthropogenic emissions dominate the biospheric CO2 fluxes and the variations in mixing ratios are large due to reduced vertical mixing. The diurnal variations of all species showed distinct cycles in spring and summer, with the lowest sampling level showing the most pronounced diurnal amplitudes. The storage flux estimates exhibited reasonable diurnal shapes for CO2, but underestimated the strength of the surface sinks during daytime. This seems plausible, keeping in mind that we were only able to calculate the storage fluxes along the profile of the tower but not the flux into or out of this profile, since no Eddy covariance flux measurements were taken at the top of the tower.

The fate of cumulative applications of 15N-labelled fertiliser in perennial and annual bioenergy crops

The fate of nitrogen (N) fertiliser applied to bioenergy crops is a key issue to allow high biomass production while minimising environmental impacts due to N losses. The aim of this study was to follow the fate in the soil-plant system of N fertiliser applied to perennial (Miscanthus×giganteus and switchgrass), “semi-perennial” (fescue and alfalfa) and annual (sorghum and triticale) bioenergy crops. Crops received 15N-labelled fertiliser (urea ammonium nitrate solution) during 4 or 5 successive years on the same subplots, at a rate varying from 24 to 120kgNha−1yr−1. Biomass production, N and 15N removal at harvest were measured each year. The 15N recovery in crop residues, non-harvested crop parts and soil was measured at the end of the 15N-labelling period. Perennial crops had higher biomass production but generally lower 15N recovery in harvested biomass than other crops, particularly when harvested late (end of winter). At the end of the 4 or 5-year period, the proportion of 15N recovered in harvested biomass was 13–34% for perennials, 23–38% for semi-perennials and 34–39% for annual crops. Perennial crops stored large amounts of N in their belowground organs; the mean 15N recovery in these organs was 12%, corresponding to a N storage flux of 14kgNha−1 yr−1. The 15N recovery in soil (including crop residues) was higher for perennials (average 36%) than semi-perennials (28%) and annual crops (19%), corresponding to a N immobilisation rate of 43, 15 and 12kgNha−1yr−1 respectively. The mean overall 15N recovery in the soil-plant system was 69% in perennials, 61% in semi-perennials to 56% in annual crops, suggesting that important fertiliser losses occurred through volatilisation and denitrification. Perennial bioenergy crops had the better efficiency by storing fertiliser-N in soil organic matter and living belowground biomass used as N reserves for succeeding years.

단일 높이에서 관측된 저장 플럭스를 사용할 때 발생하는 논의 이산화탄소, 수증기, 현열의 순생태계교환량 오차

Using eddy covariance method, net ecosystem exchange (NEE) of CO2 (FCO2 ), H2O (LE), and sensible heat (H) can be approximated as the sum of eddy flux (FC) and storage flux term (FS). Depending on strength and distribution of sink/source of scalars and magnitude of vertical turbulence mixing, the rates of changes in scalars are different with height. In order to calculate FS accurately, the differences should be considered using scalar profile measurement. However, most of flux sites for agricultural lands in Asia do not operate profile system and estimate FS using single-level scalars from eddy covariance system under the assumption that the rates of changes in scalars are constant regardless of the height. In this study, we measured FC and FS of CO2, H2O, and air temperature (Ta) using eddy covariance and profile system (i.e., the multi-level measurement system in scalars from eddy covariance measurement height to the land surface) at the Chengmicheon farmland site in Korea (CFK) in order to quantify the differences between FS calculated by single-level measurements (FS_single i.e., FS from scalars measured by profile system only at eddy covariance system measurement height) and FS calculated by profile measurements and verify the errors of NEE caused by FS_single. The rate of change in CO2, H2O, and Ta were varied with height depending on the magnitudes and distribution of sink and source and the stability in the atmospheric boundary layer. Thus, FS_single underestimated or overestimated FS (especially 21% underestimation in FS of CO2 around sunrise and sunset (0430-0800 h and 1630-2000 h)). For FCO2 , the errors in FS_single generated 3% and 2% underestimation of FCO2 during nighttime (2030-0400 h) and around sunrise and sunset, respectively. In the process of nighttime correction and partitioning of FCO2 , these differences would cause an underestimation in carbon balance at the rice paddy. In contrast, there were little differences at the errors in LE and H caused by the error in FS_single, irrespective of time.

Powering up the “biogeochemical engine”: the impact of exceptional ventilation of a deep meromictic lake on the lacustrine redox, nutrient, and methane balances

The Lake Lugano North Basin has been meromictic for several decades, with anoxic waters below 100m depth. Two consecutive cold winters in 2005 and 2006 induced exceptional deep mixing, leading to a transient oxygenation of the whole water column. With the ventilation of deep waters and the oxidation of large quantities of reduced solutes, the lake's total redox-balance turned positive, and the overall hypolimnetic oxygen demand of the lake strongly decreased. The disappearance of 150 t dissolved phosphorous (P) during the first ventilation in March 2005 is attributed to the scavenging of water-column-borne P by newly formed metal oxyhydroxides and the temporary transfer to the sediments. The fixed nitrogen (N) inventory was reduced by ~30% (~1000 t). The water-column turnover induced the nitratation of the previously NO3--free deep hypolimnion by oxidation of large amounts of legacy NH4+ and by mixing with NO3--rich subsurface water masses. Sediments with a strong denitrifying potential, but NO3--starved for decades, were brought in contact with NO3--replete waters, invigorating benthic denitrification and rapid fixed N loss from the lake in spite of the overall more oxygenated conditions. Similarly, a large microbial aerobic CH4 oxidation (MOx) potential in the hypolimnion was capitalized with the ventilation of the deep basin. Almost all CH4, which had been built up over more than 40 years (~2800 t), was removed from the water column within 30 days. However, boosted MOx could only partly explain the disappearance of the CH4. The dominant fraction (75%) of the CH4 evaded to the atmosphere, through storage flux upon exposure of anoxic CH4-rich water to the atmosphere. As of today, the North Basin seems far from homeostasis regarding its fixed N and CH4 budgets, and the deep basin's CH4 pool is recharging at a net production rate of ~66 t y-1. The size of impending CH4 outbursts will depend on the frequency and intensity of exceptional mixing events in the future.

Genome-scale metabolic model of Rhodococcus jostii RHA1 (iMT1174) to study the accumulation of storage compounds during nitrogen-limited condition.

BackgroundRhodococcus jostii RHA1 growing on different substrates is capable of accumulating simultaneously three types of carbon storage compounds: glycogen, polyhydroxyalkanoates (PHA), and triacylglycerols (TAG). Under nitrogen-limited (N-limited) condition, the level of storage increases as is commonly observed for other bacteria. The proportion of each storage compound changes with substrate, but it remains unclear what modelling approach should be adopted to predict the relative composition of the mixture of the storage compounds. We analyzed the growth of R. jostii RHA1 under N-limited conditions using a genome-scale metabolic modelling approach to determine which global metabolic objective function could be used for the prediction.ResultsThe R. jostii RHA1 model (iMT1174) produced during this study contains 1,243 balanced metabolites, 1,935 unique reactions, and 1,174 open reading frames (ORFs).Seven objective functions used with flux balance analysis (FBA) were compared for their capacity to predict the mixture of storage compounds accumulated after the sudden onset of N-limitation. Predictive abilities were determined using a Bayesian approach. Experimental data on storage accumulation mixture (glycogen, polyhydroxyalkanoates, and triacylglycerols) were obtained for batch cultures grown on glucose or acetate. The best FBA simulation results were obtained using a novel objective function for the N-limited condition which combined the maximization of the storage fluxes and the minimization of metabolic adjustments (MOMA) with the preceding non-limited conditions (max storage + environmental MOMA). The FBA solutions for the non-limited growth conditions were simply constrained by the objective function of growth rate maximization. Measurement of central metabolic fluxes by 13C-labelling experiments of amino acids further supported the application of the environmental MOMA principle in the context of changing environment. Finally, it was found that the quantitative predictions of the storage mixture during N-limited storage accumulation were fairly sensitive to the biomass composition, as expected.ConclusionsThe genome-scale metabolic model analysis of R. jostii RHA1 cultures suggested that the intracellular reaction flux profile immediately after the onset of N-limited condition are impacted by the values of the same fluxes during the period of non-limited growth. PHA turned out to be the main storage pool of the mixture in R. jostii RHA1.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-015-0190-y) contains supplementary material, which is available to authorized users.

Methane and carbon dioxide emissions from 40 lakes along a north–south latitudinal transect in Alaska

Abstract. Uncertainties in the magnitude and seasonality of various gas emission modes, particularly among different lake types, limit our ability to estimate methane (CH4) and carbon dioxide (CO2) emissions from northern lakes. Here we assessed the relationship between CH4 and CO2 emission modes in 40 lakes along a latitudinal transect in Alaska to lakes' physicochemical properties and geographic characteristics, including permafrost soil type surrounding lakes. Emission modes included direct ebullition, diffusion, storage flux, and a newly identified ice-bubble storage (IBS) flux. We found that all lakes were net sources of atmospheric CH4 and CO2, but the climate warming impact of lake CH4 emissions was 2 times higher than that of CO2. Ebullition and diffusion were the dominant modes of CH4 and CO2 emissions, respectively. IBS, ~10% of total annual CH4 emissions, is the release to the atmosphere of seasonally ice-trapped bubbles when lake ice confining bubbles begins to melt in spring. IBS, which has not been explicitly accounted for in regional studies, increased the estimate of springtime emissions from our study lakes by 320%. Geographically, CH4 emissions from stratified, mixotrophic interior Alaska thermokarst (thaw) lakes formed in icy, organic-rich yedoma permafrost soils were 6-fold higher than from non-yedoma lakes throughout the rest of Alaska. The relationship between CO2 emissions and geographic parameters was weak, suggesting high variability among sources and sinks that regulate CO2 emissions (e.g., catchment waters, pH equilibrium). Total CH4 emission was correlated with concentrations of soluble reactive phosphorus and total nitrogen in lake water, Secchi depth, and lake area, with yedoma lakes having higher nutrient concentrations, shallower Secchi depth, and smaller lake areas. Our findings suggest that permafrost type plays important roles in determining CH4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing permafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.

黄河小浪底人工混交林冠层CO2储存通量变化特征

PDF HTML阅读 XML下载 导出引用 引用提醒 黄河小浪底人工混交林冠层CO2储存通量变化特征 DOI: 10.5846/stxb201404260833 作者: 作者单位: 北京林业大学林学院,中国林业科学研究院林业研究所 国家林业局林木培育重点实验室,中国林业科学研究院林业研究所 国家林业局林木培育重点实验室,中国科学院地理科学与资源研究所陆地水循环及地表过程重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金 (31100322); 国家林业局公益性行业项目(GYHY20110400904) Variation characteristics of carbon storage flux over a mixed plantation of the Xiaolangdi area Author: Affiliation: College of Forestry,Beijing Forestry University,Research Institute of Forestry,CAF,Research Institute of Forestry,CAF,Key Laboratory of Water Cycle and Related Land Surface Processes,Institute of Geographic Sciences and Natural Resources Research,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于黄河小浪底人工混交林2008年的CO2浓度和碳通量数据,分析了不同天气条件下CO2浓度在时间和空间上的变化特征,对比了CO2浓度廓线法和涡度相关法估算的CO2储存通量,研究了CO2储存通量的日、季变化特征。结果表明:人工混交林冠层上方月平均CO2浓度具有明显的季节变化规律。月平均CO2浓度最大值出现在3月(370 μmol/mol),最低值出现在8月(347 μmol/mol)。涡度相关法估算的CO2储存通量比廓线法所得结果偏低9%。生长季,冠层CO2储存通量和净生态系统碳交换量(NEE)日平均值分别为-0.0004和-0.091 mg CO2 m-2 s-1,冠层CO2储存通量在NEE中仅占0.4%。2008年CO2储存通量和NEE分别为-46.1、-1133 g CO2 m-2 a-1。在年尺度上,CO2储存通量占NEE的4.1%。因此,在日和年尺度上计算黄河小浪底人工混交林NEE时,CO2储存通量可以忽略。 Abstract:Forest plays an important role in carbon cycle and global climate change. To estimate accurately net ecosystem carbon exchange (NEE) between forest ecosystem and the atmosphere and understand the ecophysical factors influencing NEE, it is necessary to study the variation characteristics of CO2 storage flux. In this study, the eddy covariance method and the profile method were used to measure CO2 flux and CO2 concentration over a warm-temperate mixed plantation in the Xiaolangdi area in 2008, respectively. The temporal and spatial variations of CO2 concentration under sunny and cloudy sky conditions above the forest canopy were analyzed. CO2 storage flux obtained by the eddy covariance was compared with those derived from the profile method and the diurnal and seasonal variations of CO2 storage flux were investigated. The results showed that the diurnal and seasonal variations in CO2 concentration were obvious. In the sunny days of the growing season, CO2 concentrations above the plantation canopy decreased continuously and the minimal CO2 concentration appeared at 12:00. After 12:30, CO2 concentration increased slowly. However, in the cloudy days, the maximal and minimal CO2 concentrations occurred in the early morning and at about 14:30, respectively. At the annual scale, CO2 concentration peaked in March, with a value of 370 μmol/mol. The minimal CO2 concentration occurred in August, with a value of 347 μmol/mol. CO2 storage flux estimated by the eddy covariance method was 9% lower than that obtained by the profile method. During the growing season of 2008, monthly mean CO2 storage flux was -0.0004 mg CO2 m-2 s-1 and NEE was -0.091 mg CO2 m-2 s-1. At the daily scale, the proportion of CO2 storage flux to NEE was only 0.4%. In 2008, CO2 storage flux and NEE were -46.1 and -1133 g CO2 m-2 a-1, respectively. On an annual scale, CO2 storage flux only accounted for 4.1% of NEE. Therefore, at the longer time (daily or annual) scale, CO2 storage flux could be neglected when NEE is estimated in the mixed plantation of the Xiaolangdi area. 参考文献 相似文献 引证文献

An integral-balance nonlinear model to simulate changes in soil moisture, groundwater and surface runoff dynamics at the hillslope scale

We present a system of ordinary differential equations (ODEs) capable of reproducing simultaneously the aggregated behavior of changes in water storage in the hillslope surface, the unsaturated and the saturated soil layers and the channel that drains the hillslope. The system of equations can be viewed as a two-state integral-balance model for soil moisture and groundwater dynamics. Development of the model was motivated by the need for landscape representation through hillslopes and channels organized following stream drainage network topology. Such a representation, with the basic discretization unit of a hillslope, allows ODEs-based simulation of the water transport in a basin. This, in turn, admits the use of highly efficient numerical solvers that enable space–time scaling studies. The goal of this paper is to investigate whether a nonlinear ODE system can effectively replicate observations of water storage in the unsaturated and saturated layers of the soil. Our first finding is that a previously proposed ODE hillslope model, based on readily available data, is capable of reproducing streamflow fluctuations but fails to reproduce the interactions between the surface and subsurface components at the hillslope scale. However, the more complex ODE model that we present in this paper achieves this goal. In our model, fluxes in the soil are described using a Taylor expansion of the underlying storage flux relationship. We tested the model using data collected in the Shale Hills watershed, a 7.9-ha forested site in central Pennsylvania, during an artificial drainage experiment in August 1974 where soil moisture in the unsaturated zone, groundwater dynamics and surface runoff were monitored. The ODE model can be used as an alternative to spatially explicit hillslope models, based on systems of partial differential equations, which require more computational power to resolve fluxes at the hillslope scale. Therefore, it is appropriate to be coupled to runoff routing models to investigate the effect of runoff and its uncertainty propagation across scales. However, this improved performance comes at the expense of introducing two additional parameters that have no obvious physical interpretation. We discuss the implications of this for hydrologic studies across scales.

Inferences from CO<sub>2</sub> and CH<sub>4</sub> concentration profiles at the Zotino Tall Tower Observatory (ZOTTO) on regional summertime ecosystem fluxes

Abstract. The Siberian region is still sparsely covered by ecosystem observatories, which motivates the exploitation of existing data sets to gain spatially and temporally better-resolved carbon budgets. The Zotino Tall Tower Observatory (ZOTTO; 60°48' N, 89°21' E) observations of CO2 and CH4 mole fractions as well as meteorological parameters from six different heights up to 301 m allow for an additional estimate of surface–atmosphere fluxes of CO2 and CH4 for the middle Siberian region beginning 2009. The total carbon flux is calculated from the storage and the turbulent flux component. The gradients between the different tower levels determine the storage flux component, which dominates the regional fluxes, especially during nighttime. As a correction term, the turbulent flux component was estimated by the modified Bowen ratio method based on the sensible heat flux measurements at the top of the tower. The obtained average nighttime fluxes (23:00 to 04:00 local time) are 2.7 ± 1.1 μmol (m2 s)−1 for CO2 and 5.6 ± 4.5 nmol (m2 s)−1 for CH4 during the summer months June–September in 2009 and 2011. During the day, the method is limited due to numeric instabilities because of vanishing vertical gradients; however, the derived CO2 fluxes exhibit reasonable diurnal shapes and magnitudes compared to the eddy covariance technique, which became available at the site in 2012. Therefore, the tall tower data facilitate the extension of the new eddy covariance flux data set backward in time. The diurnal signal of the CH4 flux is predominantly characterized by a strong morning transition, which is explained by local topographic effects.

Energy flux partitioning and evapotranspiration in a sub‐alpine spruce forest ecosystem

AbstractIn this study, we examined the year 2011 characteristics of energy flux partitioning and evapotranspiration of a sub‐alpine spruce forest underlain by permafrost on the Qinghai–Tibet Plateau (QPT). Energy balance closure on a half‐hourly basis was H + λE = 0.81 × (Rn − G − S) + 3.48 (W m−2) (r2 = 0.83, n = 14938), where H, λE, Rn, G and S are the sensible heat, latent heat, net radiation, soil heat and air‐column heat storage fluxes, respectively. Maximum H was higher than maximum λE, and H dominated the energy budget at midday during the whole year, even in summer time. However, the rainfall events significantly affected energy flux partitioning and evapotranspiration. The mean value of evaporative fraction (Λ = λE/(λE + H)) during the growth period on zero precipitation days and non‐zero precipitation days was 0.40 and 0.61, respectively. The mean daily evapotranspiration of this sub‐alpine forest during summer time was 2.56 mm day−1. The annual evapotranspiration and sublimation was 417 ± 8 mm year−1, which was very similar to the annual precipitation of 428 mm. Sublimation accounted for 7.1% (30 ± 2 mm year−1) of annual evapotranspiration and sublimation, indicating that the sublimation is not negligible in the annual water balance in sub‐alpine forests on the QPT. The low values of the Priestley–Taylor coefficient (α) and the very low value of the decoupling coefficient (Ω) during most of the growing season suggested low soil water content and conservative water loss in this sub‐alpine forest. Copyright © 2013 John Wiley & Sons, Ltd.

Dynamic metabolic modelling of volatile fatty acids conversion to polyhydroxyalkanoates by a mixed microbial culture

In this work, we present a dynamic metabolic model that describes the uptake of complex mixtures of volatile fatty acids (VFA) and respective conversion into PHA by mixed microbial cultures (MMC). This model builds upon a previously published flux balance analysis model [1] that identified the minimization of TCA cycle activity as the key metabolic objective to predict PHA storage fluxes and respective composition. The model was calibrated either with experimental data of PHA production from fermented sugar cane molasses or from synthetic mixtures of VFA. All PHA production experiments were performed using a MMC selected with fermented sugar cane molasses under feast and famine regimen. The model was able to capture the process dynamics denoted by an excellent fit between experimental and computed time profiles of concentrations with the regression coefficients always above 0.92. The introduced VFA uptake regulatory factor reflects the decrease of acetyl-CoA and propionyl-CoA available to TCA cycle in conformity with the hypothesis that the minimization of TCA cycle is a key metabolic objective for MMC subjected to feast and famine regimen for the maximization of PHA production.

Segregated flux balance analysis constrained by population structure/function data: The case of PHA production by mixed microbial cultures

In this study we developed a segregated flux balance analysis (FBA) method to calculate metabolic flux distributions of the individual populations present in a mixed microbial culture (MMC). Population specific flux data constraints were derived from the raw data typically obtained by the fluorescence in situ hybridization (FISH) and microautoradiography (MAR)-FISH techniques. This method was applied to study the metabolic heterogeneity of a MMC that produces polyhydroxyalkanoates (PHA) from fermented sugar cane molasses. Three populations were identified by FISH, namely Paracoccus sp., Thauera sp., and Azoarcus sp. The segregated FBA method predicts a flux distribution for each of the identified populations. The method is shown to predict with high accuracy the average PHA storage flux and the respective monomeric composition for 16 independent experiments. Moreover, flux predictions by segregated FBA were slightly better than those obtained by nonsegregated FBA, and also highly concordant with metabolic flux analysis (MFA) estimated fluxes. The segregated FBA method can be of high value to assess metabolic heterogeneity in MMC systems and to derive more efficient eco-engineering strategies. For the case of PHA-producing MMC considered in this work, it becomes apparent that the PHA average monomeric composition might be controlled not only by the volatile fatty acids (VFA) feeding profile but also by the population composition present in the MMC.

Impact of human activities on organic carbon transport in the Yellow River

Abstract. Using data from four field investigations between 2003 and 2009 along the Yellow River mainstream, we examined the transport features and seasonal variations of organic carbon, with a focus on contrasting the impacts of human activities with those of natural processes. Particulate organic carbon (POC) in the Yellow River originated mainly from the Loess Plateau, and thus the POC content in suspended sediments was much lower than in the world's other large rivers. Owing to both natural and human influences, dissolved organic carbon (DOC) has only a weak correlation with discharge. DOC varied as a result of human activities such as agricultural irrigation and pollution in the whole basin except for the upstream Qinghai–Tibetan Plateau. Our study also suggested that while reservoirs are a POC sink over short periods, a long-term POC storage flux cannot be easily estimated as discharge and sediment regulations have completely changed the relationship between the fluxes of water, sediments, and rainfall. However, this carbon sink can be obtained reliably through high-frequency sampling over long time periods. In addition, the annual water and sediment regulation (WSR) scheme has imposed an extremely severe human disturbance on the transport pattern of river organic carbon. Our study demonstrated for the first time that in a WSR event of less than 20 days, large proportions of the annual DOC (35%) and POC (56%) fluxes of the Yellow River were transported to the estuarine and coastal zone, potentially influencing estuarine and coastal geochemistry and ecosystems profoundly.