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1.
《Applied Geochemistry》2005,20(3):627-638
Concentrations of total Hg and methylmercury (MMHg) in riparian soil, mine-waste calcine, sediment, and moss samples collected from abandoned Hg mines in Wanshan district, Guizhou province, China, were measured to show regional dispersion of Hg-contamination. High total Hg and MMHg concentrations obtained in riparian soils from mined areas, ranged from 5.1 to 790 mg kg−1 and 0.13 to 15 ng g−1, respectively. However, total Hg and MMHg concentrations in the soils collected from control sites were significantly lower varying from 0.1 to 1.2 mg kg−1 and 0.10 to 1.6 ng g−1, respectively. Total Hg and MMHg concentrations in sediments varied from 90 to 930 mg kg−1 and 3.0 to 20 ng g−1, respectively. Total Hg concentrations in mine-waste calcines were highly elevated ranging from 5.7 to 4400 mg kg−1, but MMHg concentrations were generally low ranging from 0.17 to 1.1 ng g−1. Similar to the high Hg concentrations in soil and sediments, moss samples collected from rocks ranged from 1.0 to 95 mg kg−1 in total Hg and from 0.21 to 20 ng g−1 in MMHg. Elevated Hg concentrations in mosses suggest that atmospheric deposition might be an important pathway of Hg to the local terrestrial system. Moreover, the spatial distribution patterns of Hg contamination in the local environment suggest derivation from historic Hg mining sites in the Wanshan area.  相似文献   

2.
《Applied Geochemistry》2006,21(11):1955-1968
Elemental Hg–Au amalgamation mining practices are used widely in many developing countries resulting in significant Hg contamination of surrounding ecosystems. The authors examined for the first time Hg contamination in air, water, sediment, soil and crops in the Tongguan Au mining area, China, where elemental Hg has been used to extract Au for many years. Total gaseous Hg (TGM) concentrations in ambient air in the Tongguan area were significantly elevated compared to regional background concentrations. The average TGM concentrations in ambient air in a Au mill reached 18,000 ng m−3, which exceeds the maximum allowable occupational standard for TGM of 10,000 ng m−3 in China. Both total and methyl-Hg concentrations in stream water, stream sediment, and soil samples collected in the Tongguan area were elevated compared to methyl-Hg reported in artisanal Au mining areas in Suriname and the Amazon River basin. Total Hg concentrations in vegetable and wheat samples ranged from 42 to 640 μg kg−1, all of which significantly exceed the Chinese guidance limit for vegetables (10 μg kg−1) and foodstuffs other than fish (20 μg kg−1). Fortunately, methyl-Hg was not significantly accumulated in the crops sampled in this study, where concentrations varied from 0.2 to 7.7 μg kg−1.  相似文献   

3.
《Applied Geochemistry》2006,21(11):1855-1867
Methylmercury (MeHg) and total Hg (THg) concentrations in soil profiles were monitored in the Thur River basin (Alsace, France), where a chlor-alkali plant has been located in the city of Vieux-Thann since the 1930s. Three soil types were studied according to their characteristics and location in the catchment: industrial soil, grassland soil and alluvial soil. Contamination of MeHg and THg in soil was important in the vicinity of the plant, especially in industrial and alluvial soil. Concentrations of MeHg reached 27 ng g−1 and 29,000 ng g−1 for THg, exceeding the predictable no effect concentration. Significant ecotoxicological risk exists in this area and remedial actions on several soil types are suggested. In each type of soil, MeHg concentrations were highest in topsoil, which decreased with depth. Concentrations of MeHg were negatively correlated with soil organic matter and total S, particularly when MeHg concentrations exceeded 8 ng g−1. Under these conditions, MeHg concentrations in soil seemed to be influenced by THg, soil organic matter and total S concentrations. It was found that high MeHg/THg ratios (near 2%) in soil were mainly related to the combined soil environmental conditions such as low THg concentrations, low organic C/N ratios (<11) and relatively low pH (5–5.5). Nevertheless, even when the MeHg/THg ratio was low (∼0.04%), MeHg and THg concentrations were elevated, up to 13 ng g−1 and to 29,000 ng g−1, respectively. Thus, both THg and MeHg concentrations should be taken into account to assess potential environmental risks of Hg.  相似文献   

4.
Emission of phosphine, a gaseous form of P, is presently considered a potential pathway of the P biogeochemical cycle in aquatic sediments. This study investigated the emission fluxes of phosphine and its potential production mechanisms in the intertidal marshes of the Yangtze Estuary. It is shown that the relatively high emission fluxes of phosphine were measured in warm seasons, with the values of 3.85–24.9 ng m?2 h?1 and 4.21–36.5 ng m?2 h?1 in August and September, respectively. In contrast, lower fluxes of phosphine appeared in May (1.23–6.32 ng m?2 h?1) and January (0.21–0.91 ng m?2 h?1). Also, the fluxes of phosphine were generally higher in the freshwater marsh, compared with the brackish marsh. The spatio-temporal pattern of phosphine emissions was observed to be mainly associated with sediment structure, temperature and salinity. Meanwhile, the significant correlations of phosphine emissions with sedimentary P and alkaline phosphatase activities reflect that phosphine probably derives from the microbial transformations of PO4 and organic P. In addition, it is estimated that approximately 1.08 × 106 g of phosphine is released annually from sediments into the pelagic water of the Yangtze Estuary. Therefore, it is concluded that phosphine emissions may be an important internal source of P, making a significant contribution to the occurrence of algal blooms especially during warm seasons.  相似文献   

5.
A field experiment is being carried out at the Diavik diamond mine in northern Canada to investigate the influence of unsaturated flow behavior on the quality of drainage from mine waste rock piles in a region of continuous permafrost. This paper is part of a series describing processes affecting the weathering of waste rock and transport of reaction products at this site; here the focus is on unsaturated water flow and its role in mass loading. Two 15 m-high instrumented test piles have been built on 60 m by 50 m collection systems, each consisting of lysimeters and a large impermeable high-density polyethylene (HDPE) liner. Collection lysimeters are installed nearby to investigate infiltration in the upper 2 m of the waste rock. Porosity, water retention curves, and hydraulic conductivity functions are estimated from field measurements and for samples ranging in size from 200 cm3 to 16 m3. Net infiltration in 2007 is estimated to have been 37% of the rainfall for mean annual rainfall conditions. Early-season infiltration freezes and is remobilized as the waste rock thaws. Wetting fronts migrate at rates of 0.2–0.4 m d−1 in response to common rainfall events and up to 5 m d−1 in response to intense rainfall. Pore water and non-reactive solutes travel at rates of <10−2 to 3 × 10−2 m d−1 in response to common rainfall events and up to 0.7 m d−1 in response to intense rainfall. Time-varying SO4 mass loading from the base of the test piles is dictated primarily by the flow behavior, rather than by changes in solute concentrations.  相似文献   

6.
A sediment-trap monitoring program measured the fluxes of settling particles and organic carbon in Yuanyang Lake, northern Taiwan, from July 2004 to July 2006 and assessed their relations to the amounts of normal monthly and typhoon-event precipitation. The flux of settling particles varied from 0.7 mg cm?2 month?1 to 14.7 mg cm?2 month?1, and the monthly precipitation ranged from 56 mm to 1218 mm during the survey period. The contributions from typhoon-event precipitation to monthly rainfall amounts were generally larger than 70%. Higher inputs of both particulate and organic carbon into the lake were found during typhoon seasons. Of the annual settling particle loading of 14.9 tons year?1 to the lake floor, 69% occurred during the typhoon months, and 62% of the annual organic carbon loading of 2.3 tons year?1 happened during the typhoon months. These results show the importance of typhoon events on the fluxes of settling particles and organic carbon and their delivery to lakes.  相似文献   

7.
《Applied Geochemistry》2006,21(11):1868-1879
Ultra-clean sampling methods and approaches typically used in pristine environments were applied to quantify concentrations of Hg species in water and microbial biomass from hot springs of Yellowstone National Park, features that are geologically enriched with Hg. Microbial populations of chemically-diverse hot springs were also characterized using modern methods in molecular biology as the initial step toward ongoing work linking Hg speciation with microbial processes. Molecular methods (amplification of environmental DNA using 16S rDNA primers, cloning, denatured gradient gel electrophoresis (DGGE) screening of clone libraries, and sequencing of representative clones) were used to examine the dominant members of microbial communities in hot springs. Total Hg (THg), monomethylated Hg (MeHg), pH, temperature, and other parameters influential to Hg speciation and microbial ecology are reported for hot springs water and associated microbial mats.Several hot springs indicate the presence of MeHg in microbial mats with concentrations ranging from 1 to 10 ng g−1 (dry weight). Concentrations of THg in mats ranged from 4.9 to 120,000 ng g−1 (dry weight). Combined data from surveys of geothermal water, lakes, and streams show that aqueous THg concentrations range from l to 600 ng L−1. Species and concentrations of THg in mats and water vary significantly between hot springs, as do the microorganisms found at each site.  相似文献   

8.
The radioactive isotope 36Cl, with a half-life of 301 ka, is a valuable chronometer for estimation of groundwater residence time up to 2 millions of years. Aerial thermonuclear fission bomb tests, performed during the late 1950s, injected a massive amount of this isotope into the atmosphere, which exceeded the natural fallout signal. Since this bomb pulse, atmospheric 36Cl deposition tends to return to natural fallout rate. The monitoring of this attenuation can provide a good opportunity to extend the use of this chronometer to shorter time spans. Venice’s lagoon alimentation zone shows groundwaters with residence times distributed over last fifty years. This permits the estimation of a continuous 36Cl deposition curve, free from latitudinal and seasonal variations of the signal. Three old groundwater samples, with residence times comprised in the range −900 to −8000 BP, allow the estimation of a mean natural deposition of 49 at m−2 s−1 and are in good agreement with 36Cl fallout observed for the last 40,000 years by (Plummer et al., 1997). For the bomb pulse period, a fallout of 5300 at m−2 s−1 was calculated. This was followed by a strong attenuation period, taking place until the 1980s, during which the fallout reached values ranging between 167 and 354 at m−2 s−1. The attenuation reached then a plateau: it experienced a slower lowering until the actual deposition, with fallout values calculated between 124 and 252 at m−2 s−1. This persistence of high deposition rate was classically attributed to biological and atmospherical recycling processes or underestimation of the natural atmospheric production of the 36Cl. Additional source of 36Cl production has been envisaged through the activation of chlorine radicals from stratospherical CFCs, leading to a 36Cl production rate comparable with that of Ar spallation from the first approximation. Lastly, the latitudinal factor of the attenuation of the fallout rate is discussed and the impact of the jet streams is proposed as an explanation for the discrepancies in the attenuation rate.  相似文献   

9.
Mercury concentrations were determined in stream sediments from the Camaquã River Basin, located in the shield region of the state of Rio Grande do Sul, southern Brazil. The resulting geochemical data show that overbank floodplain deposits exhibit higher concentrations than sediments collected from the active channel bed. In addition, higher Hg concentrations were measured in the fine(<63 μm) sediment fraction of the samples. Total Hg concentrations in the fine fraction of active stream sediments from Lavras do Sul County, which have been influenced by past gold mining activities, have decreased during the last five years to values ≤142 ng g−1. However, in a settling pond containing abandoned mine wastes, the Hg concentration of a bulk sample remained exceptionally high (5220 ng g−1). Preliminary speciation results show that Hg0 is the predominant species in most of the samples. This was the form of Hg released by the gold amalgamation activities in the area, and appears to be relatively stable under the existing Eh and pH conditions.  相似文献   

10.
Sediment samples (213 sites) collected from the tectonic-active continental margin, offshore southwestern Taiwan were analyzed for grain sizes, organic carbon, nitrogen and carbon isotopic composition to obtain mass accumulation rate of terrestrial organic carbon and carbon budget to evaluate fate of terrestrial organic carbon from small mountainous rivers on the continental margin offshore southwestern Taiwan. Terrestrial organic carbon accumulation rates range from 0.29 to 45.6 g C m−2 yr−1 with a total accumulation budget of 0.063 Mt yr−1, which accounts for less than 13% of total river particulate organic carbon loads exported from the adjacent rivers, the Gaoping (a.k.a., Kaoping), Erhjen and Tsengwen rivers. This low burial efficiency of terrestrial organic carbon demonstrated that a majority of river-borne particles together with organic materials was moved away from the study area.For the river-borne particles from the Gaoping river, a pair of depocenters in the upper slope flanking the Gaoping submarine canyon are the locations where the maximum TCorg accumulation rate were observed which hold up to 45% (0.016 Mt yr−1) of the calculated accumulation found in the study region. On the other hand, the occurrence of higher-fraction terrestrial organic carbon in the upper and middle Gaoping submarine canyon suggests that a majority of particulate organic carbon of the Gaoping river was transported directly into the deep-sea basin through the Gaoping submarine canyon. Our results demonstrated that active margin with narrow shelf and slope is not an efficient sink for the large amount of terrigenous organic carbon supplied by the small rivers, but, a transient environment for these river derived particles.  相似文献   

11.
Streams and rivers are major exporters of C and other dissolved materials from watersheds to coastal waters. In streams and rivers, substantial amounts of terrigenous organic C is metabolized and degassed as CO2 to the atmosphere. A long-term evaluation of CO2 dynamics in streams is essential for understanding factors controlling CO2 dynamics in streams in response to changes in climate and land-use. Long-term changes in the partial pressure of CO2 (pCO2) were computed in the Anacostia River and the lower Potomac River in the Chesapeake Bay watershed. Long-term estimates were made using routine monitoring data of pH, total alkalinity, and dissolved nutrients from 1985 to 2006 at 14 stations. Longitudinal variability in pCO2 dynamics was also investigated along these rivers downstream of the urban Washington D.C. metropolitan area. Both rivers were supersaturated with CO2 with respect to atmospheric CO2 levels (392 μatm) and the highly urbanized Anacostia waters (202–9694 μatm) were more supersaturated than the Potomac waters (557–3800 μatm). Long-term variability in pCO2 values may be due to changes in river metabolism and organic matter and nutrient loadings. Both rivers exchange significant amounts of CO2 with the atmosphere (i.e., Anacostia at 0.2–72 mmol m−2 d−1 and Potomac at 0.12–24 mmol m−2 d−1), implying that waterways receiving organic matter and nutrient subsidies from urbanized landscapes have the potential to increase river metabolism and atmospheric CO2 fluxes along the freshwater–estuarine continuum.  相似文献   

12.
Boom Clay is studied as a potential host formation for the disposal of high-and intermediate level long-lived radioactive waste in Belgium. In such a geological repository, generation of gases (mainly H2 from anaerobic corrosion) will be unavoidable. In order to make a good evaluation of the balance between gas generation vs. gas dissipation for a particular waste form and/or disposal concept, good estimates for gas diffusion coefficients of dissolved gases are essential. In order to obtain an accurate diffusion coefficient for dissolved hydrogen in saturated Boom Clay, diffusion experiments were performed with a recently developed through-diffusion set-up for dissolved gases. Due to microbial activity in the test set-up, conversion of hydrogen into methane was observed within several experiments. A complex sterilisation procedure was therefore developed in order to eliminate microbiological disturbances. Only by a combination of heat sterilisation, gamma irradiation and the use of a microbial inhibitor, reliable, reproducible and accurate H2(g) diffusion coefficients (measured at 21 °C) for samples oriented parallel (Deff = 7.25 × 10−10 m2/s and Deff = 5.51 × 10−10 m2/s) and perpendicular (Deff = 2.64 × 10−10 m2/s) to the bedding plane were obtained.  相似文献   

13.
Chemical proxies are useful analogs for reconstructing physical properties of sea water, such as sea surface temperature (SST) and sea surface salinity (SSS). Time series of these inferred properties would allow for reconstructions of past El Niño–Southern Oscillation (ENSO) events, where no instrumental records exist. In this study, a monthly oxygen isotope record from a Porites coral is used to explain how past ENSO events are recorded in the coral skeletons. The sample covers a 12 year period and was collected from Nanwan Bay, Taiwan. During El Niño events the coral skeleton is shown to produce a δ18O–SST correlation with a slope of −0.12 ± 0.04‰ °C−1. During other times, this value is significantly different, with a slope of −0.21 ± 0.04‰ °C−1. Coral that grew during El Niño summers have δ18O values which are enriched by ∼0.2‰, relative to other times. A possible mechanism to explain this difference may be enhanced penetration of Kuroshio Current waters into the South China Sea during summer. The observed contrast in the correlation of δ18O–SST variability in this sample supports the influence of El Niño in eastern Asia.  相似文献   

14.
《Quaternary Research》2014,81(3):538-544
Measurements of 137Cs concentration in soils were made in a representative catchment to quantify erosion rates and identify the main factors involved in the erosion in the source region of the Yellow River in the Tibetan Plateau. In order to estimate erosion rates in terms of the main factors affecting soil loss, samples were collected taking into account the slope and vegetation cover along six selected transects within the Dari County catchment. The reference inventory for the area was established at a stable, well-preserved, site of small thickness (value of 2324 Bq·m− 2). All the sampling sites had been eroded and 137Cs inventories varied widely in the topsoil (14.87–25.56 Bq·kg− 1). The effective soil loss values were also highly variable (11.03–28.35 t·km− 1·yr− 1) in line with the vegetation cover change. The radiometric approach was useful in quantifying soil erosion rates and examining patterns of soil movement.  相似文献   

15.
We report the structure of a novel sunscreen based on the scytoneman skeleton. This pigment, scytonemin-3a-imine, was isolated from cultures of the cyanobacterium, Scytonema hoffmani, only when grown under high to intense (300–1500+ μmol quanta m−2 s−1) light conditions, with or without added UVR (ultraviolet radiation). It was also isolated from samples of natural cyanobacterial mats growing in shallow/short hydroperiod fresh water (Florida Everglades), soils (Loxahatchee, Florida) and saline cyanobacterial mats (Eleuthera, The Bahamas). These natural samples were all growing under intense (e.g. > 1500 μmol quanta m−2 s−1) light conditions. Scytonemin-3a-imine may eventually become a biomarker for such biota.Characterization included UV/Vis spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, matrix assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometry (MS and MSn), and both 1- and 2-D 1H nuclear magnetic resonance (NMR) spectrometry. Derivatization (NaBH4 reduction, acetylation, deuterium exchange) were utilized to confirm structural features. The UV/Vis spectrum had maxima at 237, 366, 437 and 564 nm. The absorption of UVR is in line with other scytoneman-based pigments. The strong visible absorption bands (437 and 564 nm) indicate an alternate or additional physiological role for the pigment. We propose that it may protect both the chlorophyll reaction centers and the cytochromes from excess radiation. We speculate that excitation of the cytochromes, potentially leading to excess electron transport, or photo-oxidative destruction of the cytochromes, may enhance reactive oxygen species (ROS) generation.  相似文献   

16.
《Quaternary Research》2014,81(3):531-537
We investigate the changes at nine glaciers in the Ningchan and Shuiguan river source, eastern Qilian Mountains, between 1972 and 2010. According to analysis of topographic maps and multispectral satellite data, all nine glaciers in the study area have retreated, by a maximum of 250 ± 57.4 m and a minimum of 91 ± 57.4 m. The total glacier area decreased by 1.20 km2, corresponding to 9.9% of the glacierized area in 1972. Comparing the two DEMs generated from the topographic maps and Real-Time Kinematic GPS data, the mean glacier thinning rate was 0.64 m yr− 1 between 1972 and 2010. The most significant thinning generally occurred on the termini. The ice-volume loss was about 106.8 ± 46.7 × 10− 3 km3 (equal to 90.8 ± 39.7 × 10− 3 km3 w.e.), which suggested a mean water discharge of 0.1 ± 0.05 m3/s during 1972–2010. Based on analysis of meteorological data, the summer temperature (June–August) tends to increase over a similar time period. The consistency of temperature increase and glacier shrinkage allows us to suggest that air temperature plays an important role in glacier changes in this region.  相似文献   

17.
The Quaternary Tasse basalts are exposed near the north shore of Quesnel Lake in southeastern British Columbia. They host a variety of mantle xenoliths consisting predominantly of spinel lherzolite with minor dunite and pyroxenite. Mineralogically, the xenoliths are composed of olivine, orthopyroxene, clinopyroxene and spinel characterized by forsterite (Fo87–93), enstatite (En90–92), diopside (En45–50–Wo40–45–Fs5), and Cr-spinel (6 − 11 wt.% Cr), respectively. All of the mantle xenoliths are coarse-grained and show granoblastic textures. Clinopyroxene and spinel display textural evidence for chemical reactions with percolating melts.The mantle xenoliths are characterized by restricted Mg-numbers (89 − 92) and low abundances of incompatible elements (Ba = 2 − 11 ppm; Sr = 3 − 31 ppm) and Yttrium (1 − 3 ppm). On the basis of REE patterns, the xenoliths are divided into three groups reflecting the various degrees of mantle metasomatism: (1) Group 1 consists of concave-up LREE patterns (La/Smcn = 0.48 − 1.16; Gd/Ybcn = 0.71 − 0.92); (2) Group 2 possesses flat to moderately LREE-enriched patterns (La/Smcn = 1.14 − 1.92; Gd/Ybcn = 0.87 − 1.09); and (3) Group 3 is characterized by strongly LREE-enriched patterns (La/Smcn = 1.53 − 2.45; Gd/Ybcn = 1.00 − 1.32). On MORB-normalized trace element diagrams, the majority of the xenolith samples share the enrichment of LILE (Rb, Ba, K), U, Th, Pb, Sr and the depletion of HFSE (Nb, Ta, Ti, Y) relative to REE. These geochemical characteristics are consistent with a compositionally heterogeneous subcontinental lithospheric mantle source that originated as subarc mantle wedge peridotite at a convergent plate margin.The Tasse basalts have alkaline compositions characterized by low SiO2 (44 − 46 wt.%) and high alkali (Na2O + K2O = 5.1 − 6.6 wt.%) contents. They are strongly enriched in incompatible elements (TiO2 = 2.4 − 3.1 wt.%; Ba = 580 − 797 ppm; Sr = 872 − 993 ppm) and, display OIB-like trace element patterns (La/Smn = 3.15 − 3.85; Gd/Ybn = 3.42 − 4.61). They have positive εNd (+ 3.8 to + 5.5) values, with 338 − 426 Ma depleted mantle model ages, and display uniform OIB-like Sr (87Sr/86Sr = 0.703346 − 0.703591) and Pb (206Pb/204Pb = 19.40 − 19.58; 207Pb/204Pb = 15.57 − 15.60; 208Pb/204Pb = 38.99 − 39.14) isotopic compositions. The basalts erupted discontinuously along a > 1000 km long SE-NW-trending linear belt with minimal compositional variation indicative of a homogenous mantle source. The Sr − Nd − Pb isotope and trace element systematics of the alkaline basalts suggests that they originated from partial melting of an upwelling asthenospheric mantle source. Melting of the asthenospheric mantle might have stemmed from extension of the overlying lithosphere in response to the early stages of back-arc basin opening in the Omineca and Intermontane belts. Ridge subduction beneath the Canadian Cordillera might have played an important role in the weakening of the lithospheric mantle prior to its extension. Alternatively, melting of the upwelling asthenosphere in response to the delamination of the lithospheric mantle beneath the Rocky Mountain Trench might have generated the alkaline lavas.  相似文献   

18.
《Quaternary Science Reviews》2005,24(10-11):1217-1222
Tide gauge data at seven sites of the Permanent Service for Mean Sea Level (PSMSL), with information for relative sea-level during the past 140–200 yr, were analyzed to examine the rates and causes of the global sea-level rise (GSLR) during the twentieth century. By subtracting linear trends for relative sea-level rise during the past 100 yr from the observed data, we get the apparent GSLRs of ∼1 mm yr−1 for five sites around the Baltic Sea and Brest. The rate for San Francisco is significantly larger than this, with an optimum value ∼2 mm yr−1. The spatial difference of ∼1 mm yr−1 between these sites is reasonably explained by the recent melting of the Greenland ice sheet with an equivalent sea-level rise of ∼1 mm yr−1. The predicted relative sea-level change for this melting scenario is 0.5 mm yr−1 at sites around the Baltic Sea and Brest, and 1.5 mm yr−1 for San Francisco. The residuals between observations and predictions, ∼0.5 mm yr−1 at all sites, may be contributed by thermal expansion of seawater and/or other melting sources. These results suggest the rate of twentieth-century GSLR to be 1.5 mm yr−1.  相似文献   

19.
Organic matter is an important factor that cannot be neglected when considering global carbon cycle. New data including organic matter geochemistry at the small watershed scale are needed to elaborate more constrained carbon cycle and climatic models. The objectives are to estimate the DOC and DIC yields exported from small tropical watersheds and to give strong constraints on the carbon hydrodynamic of these systems. To answer these questions, we have studied the geochemistry of eleven small watersheds around Basse-Terre volcanic Island in the French West Indies during different hydrological regimes from 2006 to 2008 (i.e. low water level versus floods). We propose a complete set of carbon measurements, including DOC and DIC concentrations, δ13C data, and less commonly, some spectroscopic indicators of the nature of organic matter. The DOC/DIC ratio varies between 0.07 and 0.30 in low water level and between 0.25 and 1.97 during floods, indicating that organic matter is mainly exported during flood events. On the light of the isotopic composition of DOC, ranging from ? 32.8 to ? 26.2‰ during low water level and from ? 30.1 to ? 27.2‰ during floods, we demonstrate that export of organic carbon is mainly controlled by perennial saprolite groundwaters, except for flood events during which rivers are also strongly influenced by soil erosion. The mean annual yields ranged from 2.5 to 5.7 t km? 2 year? 1 for the DOC and from 4.8 to 19.6 t km? 2 year? 1 for the DIC and exhibit a non-linear relationship with slopes of watersheds. The flash floods explain around 60% of the annual DOC flux and between 25 and 45% of the DIC flux, highlighting the important role of these extreme meteorological events on global carbon export in small tropical volcanic islands. From a carbon mass balance point of view the exports of dissolved carbon from small volcanic islands are important and should be included in global organic carbon budgets.  相似文献   

20.
The concentration and the role of colloids in the transport of elements in the vicinity of a fossil reactor at Bangombé, Gabon, were assessed. Colloid sampling was conducted in seven boreholes around and in the extinguished natural reactor. The ground waters are of Na–Mg–Ca–HCO3 type, with variable salinities, pH 4.6–6.8 and anaerobic Eh values. Filtered ground water and colloid samples were taken from the reactor and the surroundings. Filtered fluids and colloid samples collected on membranes and resuspended in solution were analysed by ICP-MS and ICP-AES in order to examine the element association in the colloid phase within the size range 3000 to 400 to 50 nm. The colloid concentrations for the size 400 to 50 nm range from 80 to 300 ng ml−1. They consist of silica particles associated with ferrihydrite coated with organics. Trace element results show that metals including Pb, Sc, Y, La, Ce, Pr, Nd, Bi, Th and U are associated to various degrees with the colloid phase. The distribution ratios of these trace elements between the water and the colloid phase (Kp) were experimentally determined. The high Pb distribution ratios of 10+7 ml g−1 are specifically discussed. Values range from 10+6 to 10+5 ml g−1for the trivalent elements (Sc, Y, La, Ce, … , Bi). For uranium, a Kp of the order of 10+5 ml g−1 may be calculated and compared with data gained using the surface complexation model. These Kp values suggest that the uranium is partially sorbed or associated with ground water colloids. Measurements from the reactor zone show that about 2–4% of the uranium is associated with the colloid phase, which contributes partially to the uranium transport. The rather low colloid concentrations are due to the relatively high concentrations of Ca, Mg and Na in these quasi-neutral waters. These soluble elements contribute to the attachment of the colloids, restricting their transport. This indicates that the colloid phase may not be an important transport medium for the radionuclides in the Bangombé system if their association is reversible. The Bangombé colloid results are compared with those studied for other systems.  相似文献   

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