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1.
A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA) and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO x decreased by 25 ± 4 μmol kg−1 and DIC by 106 ± 16 μmol kg−1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of TA increased by 33 ± 8 μmol kg−1 (2009) and 33 ± 15 μmol kg−1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al. (2009) suggested that denitrification may enhance the CO2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake of CO2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show that patterns of seasonal change in concentrations of TA in river inputs differ between river systems.  相似文献   

2.
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3.
During 2007–2008, three CO2 flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO2 flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m−2 day−1 (April 2008) with total emission rates of 164 ± 9.5 (March 2007), 59 ± 2.5 (December 2007) and 109 ± 6.6 t day−1 (April 2008). The mean CO2 flux estimated from the entire crater floor area was 1,102 g m−2 day−1 for April 2008 with a total emission rate of 144 ± 5.9 t day−1. Significant change in CO2 flux was not detected during the period of survey, and the mapping of the CO2 flux highlighted lineaments reflecting the main local and regional tectonic patterns. The 3He/4He ratio (as high as 8.1 R A) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO2/3He ratios for the high 3He/4He gases tend to have the MORB-like values (1.41 × 109), and the CO2/3He ratios for the lower 3He/4He gases fall within the range for the arc-type gases. The high 3He/4He ratios, the MORB-like CO2/3He ratios for the high 3He/4He gases and high proportion of MORB-CO2 (M = 25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.  相似文献   

4.
Organic matter mineralisation in the hypolimnion of an eutrophic Maar lake   总被引：2，自引：0，他引：2  
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5.
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6.
The belowground part of terrestrial ecosystem is a huge carbon pool. It is believed that of the total 2500Gt carbon stored in global terrestrial ecosystem, soil carbon storage within the 1 m surface layer ac- counts for 2000Gt, which is 4-fold of vegetation car- bon storage[1,2]. Compared with the carbon in the vegetation, carbon in the deep soil layers is much more stable, and it will stay in soil profile permanentlyunless geological vicissitude occurs. Essentially, forest restoration is the…  相似文献   

7.
To quantify the contribution of hyporheic community respiration to whole running-water ecosystem respiration in a cultural landscape setting, we studied the vertical hydraulic exchange in riffle–pool sequences of the River Lahn (Germany). We used flow through curves from four tracer experiments to estimate flow velocities in the surface and subsurface water. Generally, vertical exchange velocities were higher in riffle sections and a high temporal variability was observed (range of values 0.11–1.08 m day−1). We then used (1) the exchange velocities and (2) time series of dissolved oxygen concentration in surface and subsurface water to calculate hyporheic respiration. Hyporheic respiration was estimated in a range of 10–50 mg O2 m−3 day−1 for the upper sediment layer (first 20 cm). It was much lower in the deeper sediment layer (20–40 cm), ranging from 0 to 10 mg O2 m−3 day−1 (volumes are volumes of interstitial water; the average porosity was 20%). We determined primary production and respiration of the biofilm growing on the sediment by modelling dissolved oxygen concentration time series for a 2,450 m long stream reach (dissolved oxygen concentrations with diurnal variations from 8 to 16 mg L−1). Modelled respiration rates ranged from 2 to 21 g O2 m2 day−1. All information was integrated in a system analysis with numerical simulations of respiration with and without sediments. Results indicated that hyporheic respiration accounted for 6 to 14% of whole ecosystem respiration. These values are much lower than in other whole system respiration studies on more oligotrophic river systems.  相似文献   

8.
It is sometimes assumed that steric sea-level variations do not produce a gravity signal as no net mass change, thus no change of ocean bottom pressure is associated with it. Analyzing the output of two CO2 emission scenarios over a period of 2000 years in terms of steric sea-level changes, we try to quantify the gravitational effect of steric sea-level variations. The first scenario, computed with version 2.6 of the Earth System Climate Model developed at the University of Victoria, Canada (UVic ESCM), is implemented with a linear CO2 increase of 1% of the initial concentration of 365 ppm and shows a globally averaged steric effect of 5.2 m after 2000 years. In the second scenario, computed with UVic ESCM version 2.7, the CO2 concentration increases quasi-exponentially to a level of 3011 ppm and is hold fixed afterwards. The corresponding globally averaged steric effect in the first 2000 years is 2.3 m. We show, due to the (vertical) redistribution of ocean water masses (expansion or contraction), the steric effect results also in a small change in the Earth’s gravity field compared to usually larger changes associated with net mass changes. Maximum effects for computation points located on the initial ocean surface can be found in scenario 1, with the effect on gravitational attraction and potential ranging from 0.0 to −0.7·10−5 m s−2 and −3·10−3 to 6·10−3 m2 s−2, respectively. As expected, the effect is not zero but negligible for practical applications.  相似文献   

9.
We present an uncertainty analysis of ecological process parameters and CO2 flux components (R eco, NEE and gross ecosystem exchange (GEE)) derived from 3 years’ continuous eddy covariance measurements of CO2 fluxes at subtropical evergreen coniferous plantation, Qianyanzhou of ChinaFlux. Daily-differencing approach was used to analyze the random error of CO2 fluxes measurements and bootstrapping method was used to quantify the uncertainties of three CO2 flux components. In addition, we evaluated different models and optimization methods in influencing estimation of key parameters and CO2 flux components. The results show that: (1) Random flux error more closely follows a double-exponential (Laplace), rather than a normal (Gaussian) distribution. (2) Different optimization methods result in different estimates of model parameters. Uncertainties of parameters estimated by the maximum likelihood estimation (MLE) are lower than those derived from ordinary least square method (OLS). (3) The differences between simulated Reco, NEE and GEE derived from MLE and those derived from OLS are 12.18% (176 g C·m−2·a−1), 34.33% (79 g C·m−2·a−1) and 5.4% (92 g C·m−2·a−1). However, for a given parameter optimization method, a temperature-dependent model (T_model) and the models derived from a temperature and water-dependent model (TW_model) are 1.31% (17.8 g C·m−2·a−1), 2.1% (5.7 g C·m−2·a−1), and 0.26% (4.3 g C·m−2·a−1), respectively, which suggested that the optimization methods are more important than the ecological models in influencing uncertainty in estimated carbon fluxes. (4) The relative uncertainty of CO2 flux derived from OLS is higher than that from MLE, and the uncertainty is related to timescale, that is, the larger the timescale, the smaller the uncertainty. The relative uncertainties of Reco, NEE and GEE are 4%−8%, 7%−22% and 2%−4% respectively at annual timescale. Supported by the National Natural Science Foundation of China (Grant No. 30570347), Innovative Research International Partnership Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-1) and National Basic Research Program of China (Grant No. 2002CB412502)  相似文献   

10.
The ocean takes up approximately 2 GT carbon per year due to the enhanced CO2 concentrations in the atmosphere. Several options have been suggested in order to reduce the emissions of CO2 into the atmosphere, and among these are CO2 storage in the deep ocean. Topographic effects of dissolution and transport from a CO2 lake located at 3,000-m depth have been studied using the z-coordinate model Massachusetts Institute of Technology general circulation model (MITgcm) and the σ-coordinate model Bergen ocean model (BOM). Both models have been coupled with the general ocean turbulence model (GOTM) in order to account for vertical subgrid processes. The chosen vertical turbulence mixing scheme includes the damping effect from stable stratification on the turbulence intensity. Three different topographic scenarios are presented: a flat bottom and the CO2 lake placed within a trench with depths of 10 and 20 m. The flat case scenario gives good correlation with previous numerical studies of dissolution from a CO2 lake. When topography is introduced, it is shown that the z-coordinate model and the σ-coordinate model give different circulation patterns in the trench. This leads to different dissolution rates, 0.1 μmol cm − 2 s − 1 for the scenario of a 20-m-deep trench using BOM and 0.005–0.02 μmol cm − 2 s − 1 for the same scenario using the MITgcm. The study is also relevant for leakages of CO2 stored in geological formations and to the ocean.  相似文献   

11.
Sediment cores from central Lake Constance were dated with210Pb and137Cs. A sedimentation rate of (0.11±0.02) g·cm−2·y−1 was determined with the210Pb method.137Cs measurements revealed sedimentation rates of (0.11±0.01) g·cm−2·y−1 and (0.08±0.01) g·cm−2·y−1 respectively for two different cores sampled at the same location. The lower Cs-dated value indicates incomplete core recovery and demonstrates the sensitivity of this simple dating method to small losses of material at the water/sediment interface. An unambiguous application of the137Cs method is, therefore, only possible if complete core recovery is ensured. Sedimentation rates based on particulate matter, collected in sediment traps at various water depths, agree with the results of the radioisotope methods. Estimates of 30–125 days residence times for suspended particulate matter were calculated from7Be measurements.  相似文献   

12.
《Continental Shelf Research》2007,27(10-11):1584-1599
Historic data from the Russian-American Hydrochemical Atlas of Arctic Ocean together with data from the TRANSDRIFT II 1994 and TUNDRA 1994 cruises have been used to assess the spatial and inter-annual variability of carbon and nutrient fluxes, as well as air–sea CO2 exchange in the Laptev and western East Siberian Seas during the summer season. Budget computations using summer data of dissolved inorganic phosphate (DIP), dissolved inorganic nitrogen (DIN) and dissolved inorganic carbon (DIC) gives that the Laptev Sea shelf is a net sink of DIP and DIN of 2.5×106, 23.2×106 mol d−1, respectively, while it is a net source of DIC (excluding air–sea exchange) of 1249×106 mol d−1. In the East Siberian Seas the budget computations give 0.5×106, −11.4×106 and −173×106 mol d−1 (minus being a sink) for DIP, DIN, and DIC, respectively. In summers, the Laptev Sea Shelf is net autotrophic while the East-Siberian Sea Shelf is net heterotrophic, and both systems are weak net denitrifying. The Laptev Sea Shelf takes up 2.1 mmol CO2 m−2 d−1 from atmosphere, whereas the western part of the East-Siberian Sea Shelf loose 0.3 mmol CO2 m−2 d−1 to the atmosphere. The variability of DIP, DIN and DIC fluxes during summer in the different regions of the Laptev and East Siberian Seas depends on bottom topography, river runoff, exchange with surrounding seas and wind field.  相似文献   

13.
Main channel habitats of the Ohio, Missouri, and Upper Mississippi Rivers were surveyed during the summers of 2004, 2005 and 2006 using a probability-based sampling design to characterize inter-annual and inter-river variation in suspended chlorophyll a (CHLa) and related variables. Large (fivefold) differences in CHLa were observed with highest concentrations in the Upper Mississippi (32.3 ± 1.8 μg L−1), intermediate values in the Missouri (19.7 ± 1.1 μg L−1) and lowest concentrations in the Ohio (6.8 ± 0.5 μg L−1). Inter-annual variation was small in comparison to inter-river differences suggesting that basin-specific factors exert greater control over river-wide CHLa than regional-scale processes influencing climate and discharge. The rivers were characterized by variable but generally low light conditions as indicated by depth-averaged underwater irradiance <4 E m−2 day−1 and high ratios of channel depth to euphotic depth (>3). Despite poor light conditions, regression analyses revealed that TP was the best single predictor of CHLa (R 2 = 0.40), though models incorporating both light and TP performed better (R 2 = 0.60). Light and nutrient conditions varied widely within rivers and were inversely related, suggesting that riverine phytoplankton may experience shifts in resource limitation during transport. Inferred grazing and sedimentation losses were large yet CHLa concentrations did not decline downriver indicating that growth and loss processes were closely coupled. The contribution by algae to suspended particulate organic matter in these rivers (mean = 41%) was similar to that of lakes (39%) but lower relative to reservoirs (61%).  相似文献   

14.
The data of short-period seismograms had been collected widely in the mainland area of China not including Xinjiang and Tibet. The physical quantities of Lg wave are determined respectively in the five subregions. The group velocities of priminary arrival and maximum amplitude of Lg wave are equal to 3.54±0.02 km/s and 3.30±0.05 km/s, respectively. The periods of Lg waves are between 0.2s to 1.2s, averaging 0.7s. The γ-values of Lg waves in the five subregions are equal to 0.0034±0.0001 km−1 for East, 0.0031±0.0004 km−1 for Southwest, 0.0027±0.0004 km−1 for Northeast, 0.0022±0.0001 km−1 for South, and 0.0021±0.0002 km−1 for Northwest subreqion, respectively. The average γ-value for the five subregions, γ=0.0027±0.0006 km−1. The relations among the amplitude ratioH/Z, the station correctionD z andD h of amplitudes, and among them and station site condition are discussed. The subregional magnitude calibration functions ofm Lg had been established according to each regional γ-value. From these, the unified magnitude calibration function of Chinese mainland not including Xinjiang and Tibet was given by
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15.
The purposes of this study were to assess if Lake Apopka (FL, USA) was autotrophic or heterotrophic based on the partial pressure of dissolved carbon dioxide (pCO2) in the surface water and to evaluate factors that influence the long-term changes in pCO2. Monthly average pH, alkalinity and other limnological variables collected between 1987 and 2006 were used to estimate dissolved inorganic carbon (DIC), pCO2 and CO2 flux between surface water and atmosphere. Results indicated that average pCO2 in the surface water was 196 μatm, well below the atmospheric pCO2. Direct measurements of DIC concentration on three sampling dates in 2009 also supported pCO2 undersaturation in Lake Apopka. Supersaturation in CO2 occurred in this lake in only 13% of the samples from the 20-year record. The surface-water pCO2 was inversely related to Chl a concentrations. Average annual CO2 flux was 28.2 g C m−2 year−1 from the atmosphere to the lake water and correlated significantly with Chl a concentration, indicating that biological carbon sequestration led to the low dissolved CO2 concentration. Low pCO2 and high invasion rates of atmospheric CO2 in Lake Apopka indicated persistent autotrophy. High rates of nutrient loading and primary production, a high buffering capacity, a lack of allochthonous loading of organic matter, and the dominance of a planktivorous–benthivorous fish food web have supported long-term net autotrophy in this shallow subtropical eutrophic lake. Our results also showed that lake restoration by the means of nutrient reduction resulted in significantly lower total phosphorus (TP) and Chl a concentrations, and higher pCO2.  相似文献   

16.
Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H2O were carried out at a pressure range from 250 MPa to 30–75 MPa in order to characterize effects of magma ascent rate and temperature on bubble nucleation kinetics, especially on the bubble number density (BND, the number of bubbles produced per unit volume of liquid). A first series of experiments at 800°C and fast decompression rates (10–90 MPa/s) produced huge BNDs (≈ 2 × 1014 m−3 at 10 MPa/s ; ≈ 2 × 1015 m−3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (1015–1016 m−3). A second series of experiments at 700°C and 1 MPa/s produced BNDs (≈ 9×1012 m−3) close to those observed at 800°C and 1 MPa/s (≈ 6 × 1012 m−3), showing that temperature has an insignificant effect on BNDs at a given decompression rate. Our study strengthens the theory that the BNDs are good markers of the decompression rate of magmas in volcanic conduits, irrespective of temperature. Huge number densities of small bubbles in natural silicic pumices from Plinian eruptions imply that a major nucleation event occurs just below the fragmentation level, at which the decompression rate of ascending magmas is a maximum (≥ 1 MPa/s).  相似文献   

17.
The Raman spectrograms of hydrocarbon standard samples show that: (1) the Raman spectrogram of normal paraffin has very strong peaks of methyl and methylene (from 2700 cm-1 to 2970 cm-1); (2) branch methyl has the particular peak of 748 cm-1±; (3) six cyclic has the particular peak of 804 cm-1±; (4) phenyl has two particular peaks of 988 cm-1± and 3058 cm-1± and the 988 cm-1± peak is stronger than the 3058 cm-1± peak; and (5) hexene has three alkenyl spectrum peaks of 1294 cm-1±, 1635 cm-1± and 2996 cm-1±, with the 1635 cm-1± peak being the strongest, showing that the number of carbon in hy-drocarbon does not affect its Raman spectrogram, and the hydrocarbon molecular structure and base groups affect its Raman spectrogram, the same hydrocarbons (such as normal paraffin) have the same Raman spectrogram; the types (such as CH4, C2H6, C3H8) and the content of hydrocarbon in oil inclu-sions are not estimated by their characteristic Raman peaks. According to the Raman spectrograms of hydrocarbon compositions, the Raman spectrogram of hydrocarbon inclusion can be divided into five types: saturated hydrocarbon Raman spectrogram, fluoresce Raman spectrogram, saturated hydro-carbon bitumen Raman spectrogram, bitumen Raman spectrogram, and ethane Raman spectrogram. And according to the characteristics of Raman spectrogram, hydrocarbon inclusions can be divided into five types: saturated hydrocarbon inclusion, less saturated hydrocarbon (oil or gas) inclusion, saturated hydrocarbon bitumen inclusion, bitumen inclusion, and methane water inclusion.  相似文献   

18.
High-resolution sampling, measurements of organic carbon contents and 14C signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application of 14C tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12×104 kg C hm−2 to 30.75×104 kg C hm−2 in the alpine meadow ecosystems, with an average of 26.86×104 kg C hm−2. Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO2 flux ranges from 103.24 g C m−2 a−1 to 254.93 gC m−2 a−1, with an average of 191.23 g C m−2 a−1. The CO2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m−2 a−1 to 181 g C m−2 a−1. More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%281.23% of total CO2 emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow ecosystem of the Tibetan Plateau will be changed, which needs further research. Supported by the National Natural Science Foundation of China (Grant Nos. 40231015, 40471120 and 40473002) and the Guangdong Provincial Natural Science Foundation of China (Grant No. 06300102)  相似文献   

19.
The sorption of AuCl4 −,AuCl2 − and Au(S2O3)3- on δ-MnO2 was investigated at pH2–11.6, 0.01 mol/L and 0.1 mol/L NaNO3 solutions. At pH 4 in two electrolyte strength solutions, Au sorption densities on δ-MnO2 are 0.18–0.21 and 0.28μmoL/m2 for AuCl4 − and Au(S2O3)2 3-, respectively, and the Au surface coverage is approximate to or lower than 1%. This adsorption of the two Au complexes decreases as the solution pH increases, which conforms to the sorption regularity of the anion on δ-MnO2. The Au sorption decreases in the sequence of Au(S2O3)2 3- >AuCl4 − >AuC12 −. The intrinsic equilibrium constants (logK int) of the three Au complexes are 1.17–2.7, much higher than those of Cu and Cd. The hydrolysis products of AuCl4 - are preferentially adsorbed by δ-MnO2 and the inner-sphere Au-surface complexes are formed on the surface. Project supported by the National Studying-abroad Foundation, the National Natural Science Foundation of China (Grant No. 49573200) and the Australian Mining Industry.  相似文献   

20.
Based on the stem analysis of 59 individuals of Pinus elliottii in combination with tree biomass models, we calculated annual biomass increment of forest plots at Qianyanzhou Ecological Station, Chinese Academy of Sciences in subtropical China. In addition, canopy layer and community NPP were calculated based on 12 years’ litter fall data. NPP of the 21-year-old forest was estimated by using the BIOME BGC model; and both measured NPP and estimated NPP were compared with flux data. Community biomass was 10574 g · m−2; its distribution patterns in tree layer, shrub layer, herbaceous layer, tree root, herbaceous and shrub roots and fine roots were 7542, 480, 239, 1810, 230, 274 and 239 g · m−2, respectively. From 1999 to 2004, the average annual growth rate and litter fall were 741 g · m−2 · a−1 (381.31 gC · m−2 · a−1) and 849 g · m−2 · a−1 (463 gC · m−2 · a−1), respectively. There was a significant correlation between annual litter fall and annual biomass increment; and the litter fall was 1.19 times the biomass increment of living trees. From 1985 to 2005, average NPP and GPP values based on BGC modeling were 630.88 (343.31–906.42 gC · m−2 · a−1) and 1 800 gC · m−2 · a−1 (1351.62–2318.26 gC · m−2 · a−1). Regression analysis showed a linear relationship (R 2=0.48) between the measured and simulated tree layer NPP values. NPP accounted for 30.2% (25.6%–32.9%) of GPP, while NEP accounted for 57.5% (48.1%–66.5%) of tree-layer NPP and 41.74% (37%–52%) of stand NPP. Soil respiration accounted for 77.0% of measured tree NPP and 55.9% of the measured stand NPP. NEE based on eddy covariance method was 12.97% higher than the observed NEP. Supported by the National Key Basic Research Special Foundation of China (Grant No. 2002CB4125), International Joint Research Project under Ministry of Science and Technology of China (Grant No. 2006DFB91920)  相似文献   

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