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1.
This study was conducted in six plots along an elevation gradient in the Qinghai spruce (Picea crassifolia Kom.) forest ecosystem of the Qilian Mountains, northwest China. Soil CO2 efflux over bare soil (R s) and moss covered soil (R s+m) were investigated from June to September in 2010 and 2011 by means of an automated soil CO2 flux system (LI-8100). The results showed that R s ranged from 1.51 to 3.96 (mean 2.64 ± 0.72) μmol m?2 s?1 for 2010, and from 1.41 to 4.09 (mean 2.55 ± 0.70) μmol m?2 s?1 for 2011. The daily change trend of R s resembled that of air temperature (T a), and there was a hysteresis between R s and soil temperature (T s). The seasonal variations of R s at lowlands (i.e., Plot 1, Plot 2 and Plot 3) were driven by soil moisture and temperature (T a and T s), while that at highlands (i.e., Plot 4, Plot 5 and Plot 6) were obviously affected by temperature. There were higher values at Plot 2 and Plot 6, which were caused by the interaction between soil moisture and temperature. In addition, soil CO2 efflux over moss covered soil (R s+m) was 8.83 % less than that over bare soil (R s), indicating that moss was another factor affecting R s. It was concluded that R s had temporal and spatial variations and was mainly controlled by temperature and soil moisture; the main determinants differed at different elevations; moss could reduce R s.  相似文献   

2.
Effective soil thermal conductivity (λ eff) describes the ability of a multiphase soil to transmit heat by conduction under unit temperature gradient. It is a critical parameter for environmental science, earth and planetary science, and engineering applications. Numerous models are available in the literature, but their applicability is generally restricted to certain soil types or water contents (θ). The objective of this study was to develop a new model in the similar form of the Johansen 1975 model to simulate the λ eff(θ) relationship of soils of various soil textures and water contents. An exponential type model with two parameters is developed and a new function for calculating dry soil thermal conductivity is presented. Performance of the new model and six other normalized models were evaluated with published datasets. The results show that the new model is able to well mimic λ eff(θ) relationship of soils from sand to silt loam and from oven dry to full saturation. In addition, it has the best performance among the seven models under test (with root-mean-square error of 0.059 W m?1 °C?1, average deviations of 0.0009 W m?1 °C?1, and Nash–Sutcliffe efficiency of 0.994). The new model has potential to improve the reliability of soil thermal conductivity estimation and be incorporated into numerical modeling for environmental, earth and engineering studies.  相似文献   

3.
As a powerful tool, the wavelet transform method has been widely used in feature extraction for hyperspectral data, while few studies are focused on soil moisture retrieving. The objective of this study was to evaluate the effectiveness of discrete wavelet transform (DWT) for soil moisture retrieving. In this study, a total of 78 measurements of soil moisture and hyperspectral data were collected through soil sampling as well as laboratory quantitative control. There were 13 different mother wavelets capable of decomposing hyperspectral data that were recommended, along with six decomposition levels from 5 to 10. The performances of two feature extraction methods namely band selection and DWT were compared, using three indexes, i.e., R 2, R adj and root mean square error (RMSE) introduced to validate soil moisture retrieving results. The experimental results indicated that the wavelet transform method could significantly reduce the dimensionality of hyperspectral data, resulting in a much more effective performance. Among the 78 estimation models using the wavelet transform, there were 42 models superior to band selection, with 24 models yielding good correlations between the predicted soil moisture and the measured ones (R 2 ≥ 0.7, RMSE ≤ 0.050, p ≤ 0.05). Furthermore, when the wavelet decomposition level was 9 and the mother wavelets were Daubechies 2, Daubechies 4, Reserve Biorthogonal 3.3 and Biorthogonal 6.8, the retrieving results were optimum. Additionally, the experimental results proved that the wavelet analysis technique was capable of preserving high- and low-frequency spectral information at different decomposition scales, and could correctly reflect the variation of soil moisture. Thus, it would be helpful in further environmental monitoring.  相似文献   

4.
Cylinders of synthetic periclase single crystals were annealed at 0.15–0.5 GPa and 900–1200 °C under water-saturated conditions for 45 min to 72 h. Infrared spectra measured on the quenched products show bands at 3,297 and 3,312 cm?1 indicating V OH ? centers (OH-defect stretching vibrations in a half-compensated cation vacancy) in the MgO structure as a result of proton diffusion into the crystal. For completely equilibrated specimens, the OH-defect concentration, expressed as H2O equivalent, was calculated to 3.5 wt ppm H2O at 1,200 °C and 0.5 GPa based on the calibration method of Libowitzky and Rossmann (Am Min 82:1111–1115, 1997). This value was confirmed via Raman spectroscopy, which shows OH-defect-related bands at identical wavenumbers and yields an H2O equivalent concentration of about 9 wt ppm using the quantification scheme of Thomas et al. (Am Min 93:1550–1557, 2008), revised by Mrosko et al. (Am Mineral 96:1748–1759, 2011). Results of both independent methods give an overall OH-defect concentration range of 3.5–9 (+4.5/?2.6) ppm H2O. Proton diffusion follows an Arrhenius law with an activation energy E a = 280 ± 64 kJ mol?1 and the logarithm of the pre-exponential factor logDo (m2 s?1) = ?2.4 ± 1.9. IR spectra taken close to the rims of MgO crystals that were exposed to water-saturated conditions at 1,200 °C and 0.5 GPa for 24 h show an additional band at 3,697 cm?1, which is related to brucite precipitates. This may be explained by diffusion of molecular water into the periclase, and its reaction with the host crystal during quenching. Diffusion of molecular water may be described by logDH2O (m2 s?1) = ?14.1 ± 0.4 (2σ) at 1,200 °C and 0.5 GPa, which is ~ 2 orders of magnitude slower than proton diffusion at identical P-T conditions.  相似文献   

5.
Landfills are one of the major sources of methane (CH4) emission which is a very potent greenhouse gas. The use of a natural process for microbial CH4 oxidation through biocovers provides a source reduction of CH4 emission. Previous studies have mostly focused on biochemical properties, and limited research has been conducted with regards to the geotechnical characterization of compost based biocovers. This paper presents the results of a comprehensive laboratory investigation on pure compost and compost–sand mixtures (with mix ratio of 3:1, 1:1, and 1:3 w/w) to determine the compaction, shear strength, compressibility, and hydraulic and thermal conductivity properties of compost based biocovers. Direct shear and ring shear tests have shown that the cohesion (c) and friction angle (?) are in the range of 2.1–19.7 kPa and 44.1°–54.7°, respectively. Based on the results of one dimensional consolidation tests, the coefficient of consolidation (Cv) values are in the range of 1.71–0.63 m2/year, which is a function of the moisture and organic contents of the samples. The lowest hydraulic conductivity ranges from 6.09 × 10?8 to 1.78 × 10?7 cm/s which occur at optimum moisture contents. Thermal conductivity is measured under various porosities and moisture contents. By increasing the dry density and sand content of the mixtures, thermal conductivity increases. The results presented in this paper will contribute to a better understanding of the geotechnical behaviour of compost based biocover, and thus to a more cost-effective design of biocovers.  相似文献   

6.
Increased nitrogen (N) input to ecosystems could alter soil organic carbon (C) dynamics, but the effect still remains uncertain. To better understand the effect of N addition on soil organic C in wetland ecosystems, a field experiment was conducted in a seasonally inundated freshwater marsh, the Sanjiang Plain, Northeast China. In this study, litter production, soil total organic C (TOC) concentration, microbial biomass C (MBC), organic C mineralization, metabolic quotient (qCO2) and mineralization quotient (qmC) in 0–15 cm depth were investigated after four consecutive years of N addition at four rates (CK, 0 g N m?2 year?1; low, 6 g N m?2 year?1; moderate, 12 g N m?2 year?1; high, 24 g N m?2 year?1). Four-year N addition increased litter production, and decreased soil organic C mineralization. In addition, soil TOC concentration and MBC generally increased at low and moderate N addition levels, but declined at high N addition level, whereas soil qCO2 and qmC showed a reverse trend. These results suggest that short-term N addition alters soil organic C dynamics in seasonally inundated freshwater marshes of Northeast China, and the effects vary with N fertilization rates.  相似文献   

7.
Artificial neural networks (ANNs) are used by hydrologists and engineers to forecast flows at the outlet of a watershed. They are employed in particular where hydrological data are limited. Despite these developments, practitioners still prefer conventional hydrological models. This study applied the standard conceptual HEC-HMS’s soil moisture accounting (SMA) algorithm and the multi layer perceptron (MLP) for forecasting daily outflows at the outlet of Khosrow Shirin watershed in Iran. The MLP [optimized with the scaled conjugate gradient] used the logistic and tangent sigmoid activation functions resulting into 12 ANNs. The R 2 and RMSE values for the best trained MPLs using the tangent and logistic sigmoid transfer function were 0.87, 1.875 m3 s?1 and 0.81, 2.297 m3 s?1, respectively. The results showed that MLPs optimized with the tangent sigmoid predicted peak flows and annual flood volumes more accurately than the HEC-HMS model with the SMA algorithm, with R 2 and RMSE values equal to 0.87, 0.84 and 1.875 and 2.1 m3 s?1, respectively. Also, an MLP is easier to develop due to using a simple trial and error procedure. Practitioners of hydrologic modeling and flood flow forecasting may consider this study as an example of the capability of the ANN for real world flow forecasting.  相似文献   

8.
In this work, we estimated soil moisture (SM) by using dielectric constant properties of soil with radar backscattering coefficient (bc) from simulated annealing techniques of RISAT-1 (radar imaging satellite, based on synthetic aperture radar (SAR) technique) data. We examined the performance of simulated annealing in retrieving SM where the vegetation cover is not very high (NDVI ≈ 0.35 for wheat-dominated area on January 19, 2013).To overcome the land surface model limits on SM estimation accuracy, point measurement spatial coverage limits, and microwave remote sensing spatial-temporal sampling limits, we reduced uncertainties through a combination of these approaches. Near-surface SM measurements from the 5.35-GHz (C-band) channels of RISAT-1 were collocated against ground-truth data (collected during the flight time of RISAT-1 over the study area), to establish SAR-SM relationships for FRS-1(circular horizontal (RH) and circular vertical (RV)) data set of RISAT-1. Comparison with the limited ground-based point (total 24 points) measurements of SM content exhibited a net improvement when near-surface SM observations were assimilated. Comparison of the SM derived from the sigma naught (σ 0) (of RISAT-1 data set FRS-1) using the inversion algorithm with the observed measurements (using time domain reflectometry) of SM showed root mean square error of 0.24, nRMSE = 0.03, R-RMSE = 0.38, MAE = 0.63, NRMSE = 1.02, NSE = 1, d = 0.87, r 2 = 0.65, and RMSE% = 12.79 for RH polarized image while RV polarized image failed each statistical test for predicting good SM with respect to the observed SM. The ability to extract additional information comes at the expense of including more measurements, especially at frequencies lower than the L-band. This approach is therefore intended for future space-borne systems.  相似文献   

9.
Collapsible soils are problematic by nature. They undergo collapse or sudden settlement or subsidence under a given stress when their water content is increased. Collapse is characterised by collapse potential expressed as ΔH/H x 100, where ΔH is collapse compression. The amount of stress applied and the water content at the time of collapse govern the amount of collapse. In other words, collapse potential depends upon the amount of stress and the water content. Loess and other wind-blown silts are examples of collapsible soils. This paper presents a parametric study on the collapse behaviour of a lateritic soil. Remoulded specimens of a lateritic soil passing through a 425 µm sieve were compacted in 1-D consolidometer or oedometer at a density of 13 kN/m3 for studying collapse under varied initial moisture contents and initial surcharge pressures. Collapse compression of the samples was induced by saturating the specimens with water contents corresponding to 100% degree of saturation. After collapse occurred, the 1-D consolidation tests were continued up to an applied stress of 160 kPa. Collapse behaviour was studied for the applied initial pressures (σi) of 10, 20 and 40 kPa and for the initial water contents (wi) of 5%, 10%, 15% and 20%. Collapse compression and collapse potential decreased with increasing wi for all σi.  相似文献   

10.
Radon gas is a human health hazard; long-term exposure to high radon concentrations through inhalation is the second leading cause of lung cancer. Nova Scotia has been previously identified as a potential high risk region because of the geology. As such, the gas transport through Halifax’s fine grained leucomonzogranite (FGL) unit of the South Mountain Batholith needed to be quantified to further remediation efforts. Using controlled laboratory experiments, four different soil columns were created using the Halifax Regional Municipality’s (HRM) highest producing field tills and bedrock. Permeability, diffusivity, radon-222 gas concentrations, and gas transit time/speed were measured in both dry tills (field moisture) and wet tills (simulated rain event moisture). Columns with HRM till displayed the highest radon concentrations, and were less permeable with additional moisture. Radon diffusivity calculated from CO2 was 7.52 × 10?8 m2 (dry), and 3.37 × 10?8 m2 (wet); diffusivity calculated from 222Rn was 7.30 × 10?7 m2 (dry), and 6.47 × 10?7 m2 (wet). The average FGL transit time in a 60 cm column was 3.57 days (dry), and 3.82 days (wet). Locally this study presents two different methods for diffusivity calculations, for a unit lacking previous diffusivity information. The radon gas concentrations and transport speeds quantified the transport mechanisms within the till. Globally, the correlation between soil moisture, and radon/permeability values was established using these results. The link between diffusivity and permeability was also confirmed using field tills. Implications were made for building foundations, as well as the depth and type of material necessary to reduce radon gas from reaching the surface.  相似文献   

11.
New empirical relations are derived for source parameters of the Koyna–Warna reservoir-triggered seismic zone in Western India using spectral analysis of 38 local earthquakes in the magnitude range M L 3.5–5.2. The data come from a seismic network operated by the CSIR-National Geophysical Research Institute, India, during March 2005 to April 2012 in this region. The source parameters viz. seismic moment, source radius, corner frequency and stress drop for the various events lie in the range of 1013–1016 Nm, 0.1–0.4 km, 2.9–9.4 Hz and 3–26 MPa, respectively. Linear relationships are obtained among the seismic moment (M 0), local magnitude (M L), moment magnitude (M w), corner frequency (fc) and stress drop (?σ). The stress drops in the Koyna–Warna region are found to increase with magnitude as well as focal depths of earthquakes. Interestingly, accurate depths derived from moment tensor inversion of earthquake waveforms show a strong correlation with the stress drops, seemingly characteristic of the Koyna–Warna region.  相似文献   

12.
The main scope of this work is applying an aerobic composting model for remediation of petroleum hydrocarbon-contaminated soil. For this purpose, the reaction kinetics was integrated with the mass and energy balances over the composting system. Literature pilot scale data for bioremediation of diesel oil-contaminated soil was used for model validation. Comparisons of simulation results with experimental data for diesel concentration and oxygen concentration showed good agreement during the remediation process. With validated model for bioremediation of diesel oil-contaminated soil, the influence of amendment type, bulking agent, amendment/soil ratio, bulking agent/soil ratio, moisture content and airflow rate were investigated on diesel biodegradation. The simulation results showed that maximum degradation of diesel occurred in the presence of yard waste as amendment. Furthermore, addition of bulking agent (wood chips) increased the diesel degradation about 6 %. In presence of yard waste as amendment and wood chips as bulking agent, the optimal values for maximum remediation were amendment/soil ratio (2.5 kg kg?1), bulking agent/soil ratio (2.25 kg kg?1), initial moisture content (62.5 %) and airflow (0.520 m3 day?1 kgBVS?1).  相似文献   

13.
Spectral analysis method was applied to aeromagnetic data obtained for Ikogosi warm spring (IWS) area of southwestern Nigeria. This was done with the objective of determining the bottom of the magnetized crust called Curie point depth (CDP) and understand the nature and extent of the local geothermal system at depth beneath IWS. The depth to the centroid, Z o, of the deepest distribution of the magnetic dipoles was obtained by computing least-squares fit to the lowest-frequency segment of the azimuthally averaged log power spectrum. The average depth to the top of the deepest crustal block was computed as the depth to the top, Z t, of the second lowest-frequency segment of the spectrum. The depth to the bottom of the deepest magnetic dipoles, the inferred Curie point depth, was then calculated from Z b?=?2Z o???Z t. The Curie depth estimates for IWS range between 4.68 and 11.38 km (below sea level). We also estimate the heat flow and Curie temperature using a one-dimensional conductive heat transport model. The average heat flow, 42 mW m?2, and geothermal gradient, 32°C/km, obtained suggest a low enthalpy thermal regime. The Curie temperature for the region varies between 153°C and 350°C. Also, an inverse linear relationship between heat flow and Curie depths was determined. Good agreement between the Curie point depths derived from heat flow data and magnetic data suggests that the Curie point depth analysis is useful to estimate the regional thermal structure and the tectonic settings.  相似文献   

14.
This study aimed to evaluate boron (B) adsorption and the capacity of a surface complexation model for simulating this process in calcareous soils. Ten surface soils were collected from different land use areas in Hamedan, Western Iran, to characterize B sorption by soils. The mean B adsorbed by the sample soils varied from 8.9 to 32.8 %. Two empirical models including linear and Freundlich equations fitted well to the experimental data. The linear distribution (K d) values varied from 1.32 to 6.86 L kg?1, while the parameters of Freundlich equation including n and K Fr ranged from 1.16 to 1.33 and 3.31–16.81, respectively. The comparison of two empirical models indicated that B adsorption followed a nonlinear pattern. The soil organic matter had positive correlations with Freundlich and linear distribution coefficients. However, empirical models were not suitable for explaining the mechanism of B adsorption, so a surface complexation model was used to simulate and predict the B adsorption process. B adsorption modeling was conducted using Visual MINTEQ and PHREEQC, based on the assemblage of major surface components (hydrous ferric oxides, aluminum hydroxides, calcium carbonate, and humic acids). B adsorption was successfully modeled by surface complexation. The significant contribution of organic matter to B complexes was resulted from both experimental data and mechanistic modeling.  相似文献   

15.
∑25PCB congeners including dioxin-like compounds were analyzed at three sites of Manipur India to assess the level of polychlorinated biphenyls (PCBs) in air and soil. The ∑25PCBs were higher in urban air (average 2,454 pg/m3), followed by the mountain air (average 2,109 pg/m3) and rural air (average 1,756 pg/m3). PCB levels observed in urban air were higher compared to PCB levels reported in major Indian metropolitan cities especially along the coastal region and were comparable with the pristine sites of India and also with some pockets of China and Europe. The heavier congeners (tetra, penta, tri and hexa) were dominant in both air and soil samples and show significant correlation with the ambient temperature. Emission of PCB congeners was investigated from soil surface. The total organic carbon present in soil shows the significant correlation (r 2 = 0.8; p < 0.05) with the PCBs could indicate that the PCBs originated from the similar sources. Principal component analysis revealed that the sources of higher chlorinated PCB congeners are local emissions while long-range atmospheric transport process is responsible behind elevated levels of lower chlorinated PCBs. Total calculated toxic equivalent (TEQ) levels in soil (37.17–160.5 pg/g) were superior to reported TEQ level of agricultural soil in Delhi, India (0.01–105.40 pg/g). Back trajectory analysis showed that the observed high levels of PCB at Manipur may due to movement of air masses, mostly from the Northern and Southern India and to some extent from Myanmar.  相似文献   

16.
This study was focused on the correlations between the physical and mechanical properties and geostatistical analysis of the clay of high plasticity (CH) soil based on the experimental data and the data collected from various research studies. Four types of CH soil with liquid limit (LL) of 50, 62, 76 and 88% were collected from the field, tested, compared with the data from literature and qualified using hyperbolic model. X-ray diffraction analyses showed the major constituents of the CH soil with LL of 50% were calcium silicate (Ca2SiO4), aluminum silicate (Al2SiO5) and quartz (SiO2) and the major constituents of the CH soil with LL of 88% were montmorillonite (Na, Ca) 0.33(Al, Mg) 2(Si4O10) (OH)2·nH2O, kaolinite (Al2Si2O5(OH)4) and quartz (SiO2). The index properties, compacted properties, free swelling and compressive strength of the CH soils were investigated and quantified with over 1000 data collected from the literature. Using the mean (μ), standard deviation (σ), variation (σ2) and coefficient of variation parameters of CH soils properties such as density (γ), index properties (LL and PL), compaction properties (OMC and γdmax), swelling index (FS), initial void ratio (eo), compression index (Cc) and undrained shear strength (Su) properties were also studied. Liquid limit of CH soils varied between 50 and 110% and plasticity index varied between 26 and 72%. The wet unit weight (γwet) for the CH soils varied from 1.30 to 2.19 g/cm3. Undrained shear strength (Su) of CH soils were varied from 10 to 184 kPa and quantified very well as a function of liquid limit, plasticity index, moisture content and dry density using the experimental data and data collected from the literature.  相似文献   

17.
Pore water solutes increase to depths of up to six meters in unsaturated 10 kyr-old glacial outwash sediments in the Trout Lake Basin of northern Wisconsin, USA. After correction for evapotranspiration, these increases reflect weathering gradients produced from plagioclase, calc-magnesium pyroxenes, and amphiboles. In spite of relatively abundant K-feldspar, solute K and Rb reflect negative gradients produced by nutrient plant uptake and cycling. Weathering rates are calculated from solute gradients (b solute), hydraulic fluxes (q h ), volumetric BET surface areas (S v ), and mineral-specific stoichiometric coefficients (β) such that $ R_{\text{solute}} = \frac{{q_{h} }}{{b_{\text{solute}} \beta {\kern 1pt} {\kern 1pt} S_{v} }} $ Average plagioclase weathering rates (R plag = 1.6–3.1 × 10?15 mol m?2 s?1) bracket rates calculated for other Quaternary glaciated landscapes. Deeper soil pore waters are as chemically concentrated as underlying groundwaters which, based on hydrologic analyses, have traveled distances up to several kilometers over transient times of hundreds of years. Pore water recharge essentially sets solute compositions close to thermodynamic saturation, thus limiting additional weathering potential along these ground water flow paths. Solid-state elemental and mineral gradients, unlike solute gradients, are essentially invariant with soil depth, reflecting low weathering intensities produced over the relatively short geologic time since sediment deposition. A spreadsheet calculator reproduces modest mass loses from such profiles and indicates that present-day weathering is kinetically and not saturation/transport controlled.  相似文献   

18.
Tibetan Plateau (TP) is the highest and most extensive plateau in the world and has been known as the roof of the world, and it is sensitive to climate change. The researches of CO2 fluxes (F C) in the TP region play a significant role in understanding regional and global carbon balance and climate change. Eddy covariance flux measurements were conducted at three sites of south-eastern TP comprising Dali (DL, cropland ecosystem), LinZhi (LZ, alpine meadow ecosystem) and Wenjiang (WJ, cropland ecosystem); amongst those DL and LZ are located in plateau region, while WJ is in plain region. Dynamics of F C and influences of vegetation, meteorological (air temperature, photosynthetically active radiation, soil temperature and soil water content) and terrain factors (altitude) were analysed on the basis of data taken during 2008. The results showed that, in the cool sub-season (March, April, October and December), carbon sink appeared even in December with fluxes of (?0.021 to ?0.05) mg CO2 m?2 s?1 and carbon source only in October (0.03 ± 0.0048) mg CO2 m?2 s?1 in DL and WJ site. In LZ site, carbon sink was observed in April: (?0.036 ± 0.0023) mg CO2 m?2 s?1 and carbon sources in December and March (0.008–0.010 mg CO2 m?2 s?1). In the hot sub-season (May–August), carbon source was observed only in May with (0.011 ± 0.0022), (0.104 ± 0.0029) and (0.036 ± 0.0017) fluxes in LZ, DL and WJ site, respectively, while carbon sinks with (?0.021 ± 0.0041), (?0.213 ± 0.0007) and (?0.110 ± 0.0015) mg CO2 m?2 s?1 fluxes in LZ, DL, and WJ, respectively. Comparing with plain region (WJ), carbon sinks in plateau region (DL and LZ) lasted for a longer time, and the absorption sum was large and up to (–357.718 ± 0.0054) and (?371.111 ± 0.0039) g C m?2 year?1, respectively. The LZ site had the weakest carbon sink with (?178.547 ± 0.0070) g C m?2 year?1. Multivariate analysis of covariance showed that altitude (AL) as an independent factor explained 39.5 % of F C (P < 0.026). F C had a quadratic relationship with Normalized difference vegetation index (NDVI) (R 2 ranges from 0.485 to 0.640 for three sites), an exponential relationship with soil temperature at 5-cm depth (ST 5) at night time and a quadratic relationship with air temperature (T a) at day time. Path analysis indicated that photosynthetically active radiation (PAR), sensible heat fluxes (H) and other factors all had direct or indirect effects on F C in all of the three tested sites around the south-eastern TP.  相似文献   

19.
Using the Eddy Covariance (EC) technique, we analyzed temporal variation in net ecosystem CO2 exchange (NEE) and determined the effects of environmental factors on the balance between ecosystem photosynthesis and respiration in a reed (Phragmites australis) wetland in the Yellow River Delta, China. Our results indicated that diurnal and seasonal patterns of NEE and its components (ecosystem respiration (R eco), gross primary production (GPP)) varied markedly among months for the growing season (May to October). The cumulative CO2 emission was 1,657 g CO2 m?2, while 2,612 g CO2 m?2 was approximately accumulated as GPP, which resulted in the reed wetland being a net sink of 956 g CO2 m?2. The ratio of R eco to GPP in reed wetland was 0.68, which was close to other temperate wetlands. Soil temperature and soil moisture exerted the primary controls on R eco during the growing season. Daytime NEE values during the growing season were strongly correlated with photosynthetically active radiation. Aboveground biomass showed significant linear relationships with 24-h average NEE, daytime GPP, and R eco, respectively. Thus, we conclude that the coastal wetland acted as a carbon sink during the growing season despite the variations in environmental conditions, and long-term flux measurements over these ecosystems are undoubtedly necessary.  相似文献   

20.
Watershed degradation due to soil erosion and sedimentation is considered to be one of the major environmental problems in Iran. In order to address the critical conditions of watershed degradation in arid and semiarid regions, a study based on the Modified Pacific Southwest Inter-Agency Committee (MPSIAC) model was carried out at Golestan watershed, northeast of Iran. The model information layers comprising nine effective factors in erosion and sedimentation at the watershed site were obtained by digitalization and spatial interpolation of the basic information data in a GIS program. These factors are geology, soil, climate, runoff, topography, land cover, land use, channel, and upland erosion. The source data for the model were obtained from available records on rainfall and river discharge and sediment, topography, land use, geology, and soil maps as well as field surveys and laboratory analysis. The results of the MPSIAC model indicated that 60.75 % (194.4 km2) and 54.97 % (175.9 km2) of the total watershed area were classified in the heavy sedimentation and erosion classes, and the total basin sediment yield and erosion were calculated as 4,171.1 and 17,813.4 m3 km?2 year?1, respectively. In the sensitivity analysis, it was found that the most sensitive parameters of the model in order of importance were topography (slope), land cover and use, runoff, and channel erosion (R 2?=?0.92–0.94), while geology, climate (rainfall), soil, and upland erosion factors were found to have moderate effect to the model output (R 2?=?0.74–0.59).  相似文献   

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