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1.
The aim of this research was to measure the rate of carbon dioxide (CO2) exchange between the soil and atmosphere in the inter-tidal forest floor of the Indian Sundarbans mangrove ecosystem and to study its response with soil temperature and soil water content. Soil CO2 effluxes were monitored every month at two stations (between April, 2011 and March, 2012); one situated at the land–ocean boundary of the Bay of Bengal (outer part of the mangrove forest) and the other lying 55 km inshore from the coast line (inner part of the mangrove forest). The static closed chamber technique was implemented at three inter-tidal positions (landward, seaward and bare mudflats) in each station. Fluxes were measured in the daytime every half an hour by circulating chamber headspace air through a sampling manifold assembly and a closed-path non-dispersive infrared gas analyser. The fluxes ranged between 0.15 and 2.34 μmol m?2 s?1 during the annual course of sampling. Effluxes of higher magnitude were measured during summer; however, it abruptly decreased during the monsoon. CO2 flux from the forest floor was strongly related to soil temperature, with the highest correlation found with temperature at 2 cm depth. No such significant relationship between soil water content and CO2 efflux could be properly ascertained; however, excessively high soil water content was found to be the only reason which hampered the rate of effluxes during the monsoon. On the whole, landward (LW) sites of the mangrove forest emitted more than the seaward (SW) sites. Q 10 values (obtained from simple exponential model) which denote the multiplicative factor by which the efflux rate increases for a 10 °C rise in temperature ranged between 2.07 and 4.05.  相似文献   

2.
Large areas of natural coastal wetlands have suffered severely from human-driven damages or conversions (e.g., land reclamations), but coastal carbon flux responses in reclaimed wetlands are largely unknown. The lack of knowledge of the environmental control mechanisms of carbon fluxes also limits the carbon budget management of reclaimed wetlands. The net ecosystem exchange (NEE) in a coastal wetland at Dongtan of Chongming Island in the Yangtze estuary was monitored throughout 2012 using the eddy covariance technique more than 14 years after this wetland was reclaimed using dykes to stop tidal flooding. The driving biophysical variables of NEE were also examined. The results showed that NEE displayed marked diurnal and seasonal variations. The monthly mean NEE showed that this ecosystem functioned as a CO2 sink during 9 months of the year, with a maximum value in September (?101.2 g C m?2) and a minimum value in November (?8.2 g C m?2). The annual CO2 balance of the reclaimed coastal wetland was ?558.4 g C m?2 year?1. The ratio of ecosystem respiration (ER) to gross primary production (GPP) was 0.57, which suggests that 57 % of the organic carbon assimilated by wetland plants was consumed by plant respiration and soil heterotrophic respiration. Stepwise multiple linear regressions suggested that temperature and photosynthetically active radiation (PAR) were the two dominant micrometeorological variables driving seasonal variations in NEE, while soil moisture (M s) and soil salinity (PSs) played minor roles. For the entire year, PAR and daytime NEE were significantly correlated, as well as temperature and nighttime NEE. These nonlinear relationships varied seasonally: the maximum ecosystem photosynthetic rate (A max), apparent quantum yield (?), and Q 10 reached their peak values during summer (17.09 μmol CO2?m?2 s?1), autumn (0.13 μmol CO2?μmol?1 photon), and spring (2.16), respectively. Exceptionally high M s or PSs values indirectly restricted ecosystem CO2 fixation capacity by reducing the PAR sensitivity of the NEE. The leaf area index (LAI) and live aboveground biomass (AGBL) were significantly correlated with NEE during the growing season. Although the annual net CO2 fixation rate of the coastal reclaimed wetland was distinctly lower than the unreclaimed coastal wetland in the same region, it was quite high relative to many inland freshwater wetlands and estuarine/coastal wetlands located at latitudes higher than this site. Thus, it is concluded that although the net CO2 fixation capacity of the coastal wetland was reduced by land reclamation, it can still perform as an important CO2 sink.  相似文献   

3.
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   

4.
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   

5.
Surface coal mining inevitably deforests the land, reduces carbon (C) pool and generates different land covers. To re-establish the ecosystem C pool, post-mining lands are often afforested with fast-growing trees. A field study was conducted in the 5-year-old unreclaimed dump and reclaimed coal mine dump to assess the changes in soil CO2 flux and compared with the reference forest site. Changes in soil organic carbon (SOC) and total nitrogen stocks were estimated in post-mining land. Soil CO2 flux was measured using close dynamic chamber method, and the influence of environmental variables on soil CO2 flux was determined. Woody biomass C and SOC stocks of the reference forest site were threefold higher than that of 5-year-old reclaimed site. The mean soil CO2 flux was highest in 5-year-old reclaimed dump (2.37 μmol CO2 m?2 s?1) and lowest in unreclaimed dump (0.21 μmol CO2 m?2 s?1). Soil CO2 flux was highly influenced by environmental variables, where soil temperature positively influenced the soil CO2 flux, while soil moisture, relative humidity and surface CO2 concentration negatively influenced the soil CO2 flux. Change in soil CO2 flux under different land cover depends on plant and soil characteristics and environmental variables. The study concluded that assessment of soil CO2 flux in post-mining land is important to estimate the potential of afforestation to combat increased emission of soil CO2 at regional and global scale.  相似文献   

6.
The speciation of CO2 in dacite, phonolite, basaltic andesite, and alkali silicate melt was studied by synchrotron infrared spectroscopy in diamond anvil cells to 1,000 °C and more than 200 kbar. Upon compression to 110 kbar at room temperature, a conversion of molecular CO2 into a metastable carbonate species was observed for dacite and phonolite glass. Upon heating under high pressure, molecular CO2 re-appeared. Infrared extinction coefficients of both carbonate and molecular CO2 decrease with temperature. This effect can be quantitatively modeled as the result of a reduced occupancy of the vibrational ground state. In alkali silicate (NBO/t = 0.98) and basaltic andesite (NBO/t = 0.42) melt, only carbonate was detected up to the highest temperatures studied. For dacite (NBO/t = 0.09) and phonolite melts (NBO/t = 0.14), the equilibrium CO2 + O2? = CO3 2? in the melt shifts toward CO2 with increasing temperature, with ln K = ?4.57 (±1.68) + 5.05 (±1.44) 103 T ?1 for dacite melt (ΔH = ?42 kJ mol?1) and ln K = ?6.13 (±2.41) + 7.82 (±2.41) 103 T ?1 for phonolite melt (ΔH = ?65 kJ mol?1), where K is the molar ratio of carbonate over molecular CO2 and T is temperature in Kelvin. Together with published data from annealing experiments, these results suggest that ΔS and ΔH are linear functions of NBO/t. Based on this relationship, a general model for CO2 speciation in silicate melts is developed, with ln K = a + b/T, where T is temperature in Kelvin and a = ?2.69 ? 21.38 (NBO/t), b = 1,480 + 38,810 (NBO/t). The model shows that at temperatures around 1,500 °C, even depolymerized melts such as basalt contain appreciable amounts of molecular CO2, and therefore, the diffusion coefficient of CO2 is only slightly dependent on composition at such high temperatures. However, at temperatures close to 1,000 °C, the model predicts a much stronger dependence of CO2 solubility and speciation on melt composition, in accordance with available solubility data.  相似文献   

7.
The spatial and temporal variations of the flux of CO2 were determined during 2007 in the Recife estuarine system (RES), a tropical estuary that receives anthropogenic loads from one of the most populated and industrialized areas of the Brazilian coast. The RES acts as a source of nutrients (N and P) for coastal waters. The calculated CO2 fluxes indicate that the upstream inputs of CO2 from the rivers are largely responsible for the net annual CO2 emission to the atmosphere of +30 to +48 mmol m?2 day?1, depending on the CO2 exchange calculation used, which mainly occurs during the late austral winter and early summer. The observed inverse relationship between the CO2 flux and the net ecosystem production (NEP) indicates the high heterotrophy of the system (except for the months of November and December). The NEP varies between ?33 mmol m?2 day?1 in summer and ?246 mmol m?2 day?1 in winter. The pCO2 values were permanently high during the study period (average ~4,700 μatm) showing a gradient between the inner (12,900 μatm) and lower (389 μatm) sections on a path of approximately 30 km. This reflects a state of permanent pollution in the basin due to the upstream loading of untreated domestic effluents (N/P?=?1,367:6 μmol kg?1 and pH?=?6.9 in the inner section), resulting in the continuous mineralization of organic material by heterotrophic organisms and thereby increasing the dissolved CO2 in estuarine waters.  相似文献   

8.
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   

9.
Field experiments on the CO2 flux of alpine meadow soil in the Qilian Mountain were conducted along the elevation gradient during the growing season of 2004 and 2005. The soil CO2 flux was measured using the Li-6400-09 soil respiration chamber attached to the Li-6400 portable photosynthesis system. The effects of water and heat and roots on the soil CO2 flux were statistically analyzed. The results show that soil CO2 flux along the elevation gradient gradually decreases. The soil CO2 flux was low at night, with lowest value occurring between 0200 and 0600 hours, started to rise rapidly during 0700–0830 hours, and then descend during 1600–1830 hours. The peak CO2 efflux appears during 1100–1600 hours. The diurnal average of soil CO2 efflux was between 0.56 ± 0.32 and 2.53 ± 0.76 μmol m−2 s−1. Seasonally, soil CO2 fluxes are relatively high in summer and autumn and low in spring and winter. The soil CO2 efflux, from the highest to the lowest in the ranking order, occurred in July and August (4.736 μmol m−2 s−1), June and September, and May and October, respectively. The soil CO2 efflux during the growing season is positively correlated with soil temperature, root biomass and soil water content.  相似文献   

10.
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   

11.
Rates of CO2 emission from bare salt-marsh sediments in areas of short and tall formSpartina alterniflora were measured monthly for 1 yr. Maximum emission rates, as high as 325 ml CO2m?2h?1, were observed during summer months, while minimum rates, 10.2 ml CO2 m?2h?1, were observed during the winter. An exponential function of inverse soil temperature explained most of the seasonal variability, but other factors are involved in regulating CO2 emissions as demonstrated by rates that were higher in spring than in late summer at equivalent temperatures. Annual CO2 emissions from bare sediments were 27.3 and 18.6 mol C m?2 yr?1 in communities of short and tallS. alterniflora, respectively. It was estimated that losses of dissolved inorganic carbon from the turnover of pore water, up to 14.6 mol C m?2 yr?1 at the creek bank (tall,S. alterniflora) site, and diffusion of CO2 from the root system ofS. alterniflora through the culms, 12.3 to 16.2 mol C m?2 yr?1, could also be important pathways of carbon loss from marsh sediments. If the internal flux of CO2 from the root system through the culm is refixed within the leaves, then the observed rate of 9.8 μI CO2 min?1 cm?2 of culm cross sectional area appears to make a small but significant contribution to total photosynthesis.  相似文献   

12.
Biological soil crusts (BSCs) are an important cover in arid desert landscapes, and have a profound effect on the CO2 exchange in the desert system. Although a large number of studies have focused on the CO2 flux at the soil–air interface, relatively few studies have examined the soil CO2 concentration in individual layers of the soil profile. In this study, the spatiotemporal dynamics of CO2 concentration throughout the soil profile under two typical BSCs (algae crusts and moss crusts) and its driving factors were examined in a revegetated sandy area of the Tengger Desert from Mar 2010 to Oct 2012. Our results showed that the mean values of the vertical soil CO2 concentrations under algal crusts and moss crusts were 600–1,200 μmol/mol at the 0–40 cm soil profiles and increased linearly with soil depth. Daily CO2 concentrations showed a single-peak curve and often had a 1–2 h time delay after the maximum soil temperature. During the rainy season, the mean soil CO2 concentration profile was 1,200–2,000 μmol/mol, which was 2–5 times higher as compared to the dry season (400–800 μmol/mol). Annually, soil moisture content was the key limiting factor of the soil CO2 concentration, but at the daily time scale, soil temperature was the main limiting factor. Combined with infiltration depth of crusted soils, we predicted that precipitation of 10–15 mm was the most effective driving factor in arid desert regions.  相似文献   

13.
The present analysis adjusts previous estimates of global ocean CaCO3 production rates substantially upward, to 133 × 1012 mol yr?1 plankton production and 42 × 1012 mol yr?1 shelf benthos production. The plankton adjustment is consistent with recent satellite-based estimates; the benthos adjustment includes primarily an upward adjustment of CaCO3 production on so-called carbonate-poor sedimentary shelves and secondarily pays greater attention to high CaCO3 mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO3 sediment accumulation rates remain about the same as they have been for some years: ~20 × 1012 mol yr?1 on shelves and 11 × 1012 mol yr?1 in the deep ocean. The differences between production and accumulation of calcareous materials call for dissolution of ~22 × 1012 mol yr?1 (~50 %) of shelf benthonic carbonate production and 122 × 1012 mol yr?1 (>90 %) of planktonic production. Most CaCO3 production, whether planktonic or benthonic, is assumed to take place in water depths of <100 m, while most dissolution is assumed to occur below this depth. The molar ratio of CO2 release to CaCO3 precipitation (CO2↑/CaCO3↓) is <1.0 and varies with depth. This ratio, Ψ, is presently about 0.66 in surface seawater and 0.85 in ocean waters deeper than about 1000 m. The net flux of CO2 associated with CaCO3 reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 × 1012 mol C yr?1, at a time scale of 102–103 years. The CaCO3-mediated influx of CO2 is approximately offset by CO2 release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO3 and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified.  相似文献   

14.
This study investigates the performance of empirical and semiempirical models to predict soil moisture from the data of RADARSAT II synthetic aperture radar (SAR) for the Yarmouk basin in Jordan. Data of SAR were obtained for May and June 2010 and were processed to obtain backscatter (σ o ) data for the study area. Results showed significant correlations between soil moisture content (m v ) and horizontally polarized σ o , with coefficient of determination (R 2) of 0.64. The root mean square error for the SAR volumetric soil moisture content was 0.09 and 0.06 m3/m3 for the empirical and semiempirical regression models, respectively. Both models had different clustering patterns in the soil moisture maps in the study area. The spatial agreement between maps of soil moisture was in the range of 55 to 65 % when the maps were reclassified based on intervals of 5 % m v for both models. In terms of soil moisture interval, both models showed that most of soil moisture changes between the two images (dates) were in the range of ±5 %. Some high differences in ?m v were observed between the two models. These were mainly attributed to the non-inverted pixels in the soil moisture maps produced by the semiempirical model. Therefore, this model may be applied for a limited range of soil moisture prediction. The use of regression model could predict a wider range for soil moisture when compared with the semiempirical model. However, more work might be needed to improve the empirical model before scaling it up to the whole study area.  相似文献   

15.
Mid-shelf sediments off the Oregon coast are characterized as fine sands that trap and remineralize phytodetritus leading to the consumption of significant quantities of dissolved oxygen. Sediment oxygen consumption (SOC) can be delayed from seasonal organic matter inputs because of a transient buildup of reduced constituents during periods of quiescent physical processes. Between 2009 and 2013, benthic oxygen exchange rates were measured using the noninvasive eddy covariance (EC) method five separate times at a single 80-m station. Ancillary measurements included in situ microprofiles of oxygen at the sediment–water interface, and concentration profiles of pore water nutrients and trace metals, and solid-phase organic C and sulfide minerals from cores. Sediment cores were also incubated to derive anaerobic respiration rates. The EC measurements were made during spring, summer, and fall conditions, and they produced average benthic oxygen flux estimates that varied between ?2 and ?15 mmol m?2 d?1. The EC oxygen fluxes were most highly correlated with bottom-sensed, significant wave heights (H s). The relationship with H s was used with an annual record of deepwater swell heights to predict an integrated oxygen consumption rate for the mid-shelf of 1.5 mol m?2 for the upwelling season (May–September) and 6.8 mol m?2 y?1. The annual prediction requires that SOC rates are enhanced in the winter because of sand filtering and pore water advection under large waves, and it counters budgets that assume a dominance of organic matter export from the shelf. Refined budgets will require winter flux measurements and observations from cross-shelf transects over multiple years.  相似文献   

16.
We have investigated the effect of undercooling and deformation on the evolution of the texture and the crystallization kinetics of remelted basaltic material from Stromboli (pumice from the March 15, 2007 paroxysmal eruption) and Etna (1992 lava flow). Isothermal crystallization experiments were conducted at different degrees of undercooling and different applied strain rate (T = 1,157–1,187 °C and $ \dot{\gamma }_{i} $ γ · i  = 4.26 s?1 for Stromboli; T = 1,131–1,182 °C and $ \dot{\gamma }_{i} $ γ · i  = 0.53 s?1 for Etna). Melt viscosity increased due to the decrease in temperature and the increase in crystal content. The mineralogical assemblage comprises Sp + Plg (dominant) ± Cpx with an overall crystal fraction (?) between 0.06 and 0.27, increasing with undercooling and flow conditions. Both degree of undercooling and deformation rate deeply affect the kinetics of the crystallization process. Plagioclase nucleation incubation time strongly decreases with increasing ΔT and flow, while slow diffusion-limited growth characterizes low ΔT—low deformation rate experiments. Both Stromboli (high strain rate) and Etna (low strain rate) plagioclase growth rates (G) display relative small variations with Stromboli showing higher values (4.8 ± 1.9 × 10?9 m s?1) compared to Etna (2.1 ± 1.6 × 10?9 m s?1). Plagioclase average nucleation rates J continuously increase with undercooling from 1.4 × 106 to 6.7 × 106 m?3 s?1 for Stromboli and from 3.6 × 104 to 4.0 × 106 m?3 s?1 for Etna. The extremely low value of 3.6 × 104 m?3 s?1 recorded at the lowest undercooling experiment for Etna (ΔT = 20 °C) indicates that the crystallization process is growth-dominated and that possible effects of textural coarsening occur. G values obtained in this paper are generally one or two orders of magnitude higher compared to those obtained in the literature for equivalent undercooling conditions. Stirring of the melt, simulating magma flow or convective conditions, facilitates nucleation and growth of crystals via mechanical transportation of matter, resulting in the higher J and G observed. Any modeling pertaining to magma dynamics in the conduit (e.g., ascent rate) and lava flow emplacement (e.g., flow rate, pāhoehoe–‘a‘ā transition) should therefore take the effects of dynamic crystallization into account.  相似文献   

17.
Weathering of rocks that regulate the water chemistry of the river has been used to evaluate the CO2 consumption rate which exerts a strong influence on the global climate. The foremost objective of the present research is to estimate the chemical weathering rate (CWR) of the continental water in the entire stretch of Brahmaputra River from upstream to downstream and their associated CO2 consumption rate. To establish the link between the rapid chemical weathering and thereby enhance CO2 drawdown from the atmosphere, the major ion composition of the Brahmaputra River that drains the Himalaya has been obtained. Major ion chemistry of the Brahmaputra River was resolved on samples collected from nine locations in pre-monsoon, monsoon and post-monsoon seasons for two cycles: cycle I (2011–2012) and cycle II (2013–2014). The physico-chemical parameters of water samples were analysed by employing standard methods. The Brahmaputra River was characterized by alkalinity, high concentration of Ca2+ and HCO3 ? along with significant temporal variation in major ion composition. In general, it was found that water chemistry of the river was mainly controlled by rock weathering with minor contributions from atmospheric and anthropogenic sources. The effective CO2 pressure (log\({{\text{P}}_{{\text{C}}{{\text{O}}_{\text{2}}}}}\)) for pre-monsoon, monsoon and post-monsoon has been estimated. The question of rates of chemical weathering (carbonate and silicate) was addressed by using TDS and run-off (mm year?1). It has been found that the extent of CWR is directly dependent on the CO2 consumption rate which may be further evaluated from the perspective of climate change mitigation The average annual CO2 consumption rate of the Brahmaputra River due to silicate and carbonate weathering was found to be 0.52 (×106 mol Km?2 year?1) and 0.55 (×106 mol Km?2 year?1) for cycle I and 0.49 (×106 mol Km?2 year?1) and 0.52 (×106 mol Km?2 year?1) for cycle II, respectively, which were significantly higher than that of other Himalayan rivers. Estimation of CWR of the Brahmaputra River indicates that carbonate weathering largely dominates the water chemistry of the Brahmaputra River.  相似文献   

18.
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   

19.
The carbon cycle of global inland waters is quantitatively comparable to other components in the global carbon budget. Among inland waters, a significant part is man-made lakes formed by damming rivers. Man-made lakes are undergoing a rapid increase in number and size. Human impacts and frequent algae blooms lead to it necessary to make a better constraint on their carbon cycles. Here, we make a primary estimation on the air–water CO2 transfer flux through an algae bloom year for a subtropical man-made lake—Hongfeng Lake, Southwest China. To do this a new type of glass bottles was designed for content and isotopic analysis of DIC and other environmental parameters. At the early stage of algae bloom, CO2 was transferred from the atmosphere to the lake with a net flux of 1.770 g·C·m?2. Later, the partial pressure (pCO2) of the aqueous CO2 increased rapidly and the lake outgassed to the atmosphere with a net flux of 95.727 g·C·m?2. In the remaining days, the lake again took up CO2 from the atmosphere with a net flux of 14.804 g·C·m?2. As a whole, Lake Hongfeng released 4527 t C to the atmosphere, accounting for one-third of the atmosphere/soil CO2 sequestered by chemical weathering in the whole drainage. With an empirical mode decomposition method, we found air temperature plays a major role in controlling water temperature, aqueous pCO2 and hence CO2 flux. This work indicates a necessity to make detailed and comprehensive carbon budgets in man-made lakes.  相似文献   

20.
The delivery of dissolved carbon from rivers to coastal oceans is an important component of the global carbon budget. From November 2013 to December 2014, we investigated freshwater-saltwater mixing effects on dissolved carbon concentrations and CO2 outgassing at six locations along an 88-km-long estuarine river entering the Northern Gulf of Mexico with salinity increasing from 0.02 at site 1 to 29.50 at site 6 near the river’s mouth. We found that throughout the sampling period, all six sites exhibited CO2 supersaturation with respect to the atmospheric CO2 pressure during most of the sampling trips. The average CO2 outgassing fluxes at site 1 through site 6 were 162, 177, 165, 218, 126, and 15 mol m?2 year?1, respectively, with a mean of 140 mol m?2 year?1 for the entire river reach. In the short freshwater river reach before a saltwater barrier, 0.079 × 108 kg carbon was emitted to the atmosphere during the study year. In the freshwater-saltwater mixing zone with wide channels and river lakes, however, a much larger amount of carbon (3.04 × 108 kg) was emitted to the atmosphere during the same period. For the entire study period, the river’s freshwater discharged 0.25 × 109 mol dissolved inorganic carbon (DIC) and 1.77 × 109 mol dissolved organic carbon (DOC) into the mixing zone. DIC concentration increased six times from freshwater (0.24 mM) to saltwater (1.64 mM), while DOC showed an opposing trend, but to a lesser degree (from 1.13 to 0.56 mM). These findings suggest strong effects of freshwater-saltwater mixing on dissolved carbon dynamics, which should be taken into account in carbon processing and budgeting in the world’s estuarine systems.  相似文献   

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