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1.
 The rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium sorption were measured as part of an investigation to determine strontium chemical transport properties of a surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. Batch experimental techniques were used to determine the rate of strontium sorption and strontium distribution coefficients (Kds) between aqueous and solid phases. Rate experiments indicate that strontium in solution reached an apparent equilibrium with the sediment in 26 h. Kds were derived using the linear isotherm model at initial sodium concentrations from 100 to 5,000 mg/l and initial potassium concentrations from 2 to 150 mg/l. Kds ranged from 56±2 to 62±3 ml/g at initial aqueous concentrations of sodium and potassium equal to or less than 300 and 150 mg/l, respectively. Kds ranged from 4.7±0.2 to 19±1 ml/g with initial aqueous concentrations of sodium between 1,000 and 5,000 mg/l. These data indicate that sodium concentrations greater than 300 mg/l in wastewater increase the availability of strontium for transport beneath waste disposal ponds at the INEL by decreasing strontium sorption on the surficial sediment. Wastewater concentrations of sodium and potassium less than 300 and 150 mg/l, respectively, have little effect on the availability of strontium for transport. Received: 6 February 1997 · Accepted: 31 March 1997  相似文献   

2.
 The effects of calcium and magnesium on the distribution of strontium between a surficial sediment and simulated wastewater solutions were measured as part of an investigation to determine strontium transport properties of surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. The investigation was conducted by the U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy. Batch experimental techniques were used to determine strontium linear sorption isotherms and distribution coefficients (K d's) using simulated wastewater solutions prepared at pH 8.0±0.1 with variable concentrations of calcium and magnesium. Strontium linear sorption isotherm K d's ranged from 12±1 to 85±3 ml/g, increasing as the concentration of calcium and magnesium decreased. The concentration of sorbed strontium and the percentage of strontium retained by the sediment were correlated to aqueous concentrations of strontium, calcium, and magnesium. The effect of these cation concentrations on strontium sorption was quantified using multivariate least-squares regression techniques. Analysis of data from these experiments indicates that increased concentrations of calcium and magnesium in wastewater discharged to waste disposal ponds at the INEL increases the availability of strontium for transport beneath the ponds by decreasing strontium sorption to the surficial sediment. Received: 8 November 1996 · Accepted: 6 January 1997  相似文献   

3.
Idaho State University and the US Geological Survey, in cooperation with the US Department of Energy, conducted a study to determine and evaluate strontium distribution coefficients (Kds) of subsurface materials at the Idaho National Engineering and Environmental Laboratory (INEEL). The Kds were determined to aid in assessing the variability of strontium Kds and their effects on chemical transport of strontium-90 in the Snake River Plain aquifer system. Data from batch experiments done to determine strontium Kds of five sediment-infill samples and six standard reference material samples were analyzed by using multiple linear regression analysis and the stepwise variable-selection method in the statistical program, Statistical Product and Service Solutions, to derive an equation of variables that can be used to predict strontium Kds of sediment-infill samples. The sediment-infill samples were from basalt vesicles and fractures from a selected core at the INEEL; strontium Kds ranged from ~201 to 356 ml g-1. The standard material samples consisted of clay minerals and calcite. The statistical analyses of the batch-experiment results showed that the amount of strontium in the initial solution, the amount of manganese oxide in the sample material, and the amount of potassium in the initial solution are the most important variables in predicting strontium Kds of sediment-infill samples.  相似文献   

4.
The sorption behavior and solid-phase associations of phosphorus (P) in fine-grained sediments (<63 μm) from two upstream tributaries and one downstream main stem site of the Spoon River in west-central Illinois were characterized to better understand phosphorus bioavailability in this agriculturally dominated watershed. The P sorption affinities, as indicated by linear distribution coefficients (K d), of all sediments were 330–5,150 L/kg, and negatively correlated with equilibrium phosphorus concentration (EPCo) values, which ranged between 0.2 and 2.2 μM. pH values measured at the conclusion of the sorption experiments varied only slightly (7.45–8.10) but were nonetheless strongly positively correlated to EPCo values, and negatively correlated to K d values, suggesting the importance of pH to the observed sorption behavior. K d values were generally lower and EPCo values higher at the main stem site than at the upstream tributary sites, suggesting dissolved reactive P (DRP) bioavailability (specifically orthophosphate) increased downstream. The solid phase associations of P were operationally assessed with the streamlined SEDEX (sedimentary extraction) procedure, and most sediment P (≥50%) was released during the step designed to determine iron oxide–associated P. On average, 70–90% of the total sediment P pool was potentially bioavailable, as estimated by the sum of the iron oxide-, authigenic carbonate-, and organic-associated P fractions. Considerable calcium was also extracted from some sediments during the step designed to specifically remove iron oxide–associated P. It is hypothesized that the severe drought conditions that persisted between April and October, 2005 allowed authigenic carbonates (perhaps partly amorphous) to accumulate, and that these carbonates dissolved during the iron oxide extraction step. The extensive benthic algal populations also present may have aided carbonate precipitation, which under more normal hydrologic conditions would be periodically flushed downstream and replaced by fresh sediment. This suggests antecedent hydrologic conditions played a dominant role in the P sorption and solid phase associations identified.  相似文献   

5.
The partitioning of radioactive trace elements between seawater and particulate matter from surface sediments and sediment traps was investigated in laboratory experiments. For the elements Na, Zn, Se, Sr, Cd, Sn, Sb, Cs, Ba, Hg, Th and Pa (group I) constant distribution coefficients (Kd) were found after a few days of equilibration, whereas the elements Be, Mn, Co and Fe (group II) showed an increasing Kd over the whole time of observation of 108 days. The time dependence of Kd is described by an adsorption-desorption equilibrium (group I elements), followed by a lattice transport reaction step (group II elements). The reaction rate constants are compared to Mn oxidation rates and to adsorption rate constants derived from in situ measurements of the UTh disequilibrium as available from literature.  相似文献   

6.
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM), and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K d(PAR)), upwelling PAR (K u(PAR)), particle beam attenuation coefficient (c p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K d(PAR), particle beam attenuation coefficients (c p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic suspended matter (SPMI) and diffuse attenuation coefficient K d(PAR) (r 2 = 0.92) and also for particle beam attenuation coefficient (c p; r 2 = 0.93). The obtained SPMI specific attenuation—K d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r 2 = 0.80) correlation with K u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results are discussed and compared to similar studies from both temperate and tropical estuaries.  相似文献   

7.
The shallow aquifer beneath the Western Snake River Plain (Idaho, USA) exhibits widespread elevated arsenic concentrations (up to 120 μg L−1). While semi-arid, crop irrigation has increased annual recharge to the aquifer from approximately 1 cm prior to a current rate of >50 cm year−1. The highest aqueous arsenic concentrations are found in proximity to the water table (all values >50 μg L−1 within 50 m) and concentrations decline with depth. Despite strong vertical redox stratification within the aquifer, spatial distribution of aqueous species indicates that redox processes are not primary drivers of arsenic mobilization. Arsenic release and transport occur under oxidizing conditions; groundwater wells containing dissolved arsenic at >50 μg L−1 exhibit elevated concentrations of O2 (average 4 mg L−1) and NO3 (average 8 mg L−1) and low concentrations of dissolved Fe (<20 μg L−1). Sequential extractions and spectroscopic analysis of surficial soils and sediments indicate solid phase arsenic is primarily arsenate and is present at elevated concentrations (4–45 mg kg−1, average: 17 mg kg−1) relative to global sedimentary abundances. The highest concentrations of easily mobilized arsenic (up to 7 mg kg−1) are associated with surficial soils and sediments visibly stained with iron oxides. Batch leaching experiments on these materials using irrigation waters produce pore water arsenic concentrations approximating those observed in the shallow aquifer (up to 152 μg L−1). While As:Cl aqueous phase relationships suggest minor evaporative enrichment, this appears to be a relic of the pre-irrigation environment. Collectively, these data indicate that infiltrating irrigation waters leach arsenic from surficial sediments to the underlying aquifer.  相似文献   

8.
Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO3–HClO4) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.  相似文献   

9.
Snow was sampled and analyzed for total mercury (THg) on the Idaho National Engineering and Environmental Laboratory (INEEL) and surrounding region prior to the start-up of a large (9-11 g/h) gaseous mercury emission source. The objective was to determine the effects of the source on local and regional atmospheric deposition of mercury. Snow samples collected from 48 points on a polar grid near the source had THg concentrations that ranged from 4.71 to 27.26 ng/L; snow collected from regional background sites had THg concentrations that ranged from 0.89 to 16.61 ng/L. Grid samples had higher concentrations than the regional background sites, which was unexpected because the source was not operating yet. Emission of Hg from soils is a possible source of Hg in snow on the INEEL. Evidence from Hg profiles in snow and from unfiltered/filtered split samples supports this hypothesis. Ongoing work on the INEEL is investigating Hg fluxes from soils and snow.  相似文献   

10.
Regional variations in initial 87Sr/86Sr ratios (r i) of Mesozoic plutons in central Idaho locate the edge of Precambrian continental crust at the boundary between the late Paleozoic-Mesozoic accreted terranes and Precambrian sialic crust in western Idaho. The r i values increase abruptly but continuously from less than 0.704 in the accreted terranes to greater than 0.708 across a narrow, 5 to 15 km zone, characterized by elongate, lens-shaped, highly deformed plutons and schistose metasedimentary and metavolcanic units. The chemical and petrologic character of the plutons changes concomitantly from ocean-arc-type, diorite-tonalite-trondhjemite units to a weakly peraluminous, calcic to calcalkalic tonalite-granodiorite-granite suite (the Idaho batholith). Plutons in both suites yield Late Cretaceous ages, but Permian through Early Cretaceous bodies are confined to the accreted terranes and early Tertiary intrusions are restricted to areas underlain by Precambrian crust. The two major terranes were juxtaposed between 75 and 130 m.y. ago, probably between 80 and 95 m.y. Oxygen and strontium isotopic ratios and Rb and Sr concentrations of the plutonic rocks document a significant upper-crustal contribution to the magmas that intrude Precambrian crust. Magmas intruding the arc terranes were derived from the upper mantle/subducted oceanic lithosphere and may have been modified by anatexis of earlier island-arc volcanic and sedimentary units. Plutons near the edge of Precambrian sialic crust represent simple mixtures of the Precambrian wall-rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0.7035. Rb/Sr varies linearly with r i, producing “pseudoisochrons” with apparent “ages” close to the age of the wall rocks. Measured δ 18O values of the wall rocks are less than those required for the assimilated end-member by Sr-O covariation in the plutons, however, indicating that wall-rock δ 18O was reduced significantly by exchange with circulating fluids. Metasedimentary rocks of the Belt Supergroup are similarly affected near the batholith, documenting a systematic depletion in 18O as much as 50 km from the margin of the batholith. Plutons of the Bitterroot lobe of the Idaho batholith are remote from the accreted terranes and represent mixtures of Precambrian wall-rocks with melts dominated by continental lower crust (r i>0.708) rather than mantle. “Pseudoisochrons” resulting from these data are actually mixing lines that yield apparent “ages” less than the true age of the wall rocks and meaningless “ri”. Assimilation/ fractional-crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region.  相似文献   

11.
A hypothesis was tested to determine if a relationship exists between rates of submarine groundwater discharge and the distribution of seagrass beds in the coastal, nearshore northeastern Gulf of Mexico. As determined by nonparametric statistics, four of seven seagrass beds in the northeastern Gulf of Mexico had significantly greater submarine groundwater discharge compared with adjacent sandy areas, but the remainder exhibited the opposite relationship. We were thus unable to verify if a relationship exists between submarine groundwater discharge and the distribution of seagrass beds in the nearshore sites selected. A second objective of this study was to determine the amount of nitrogen and phosphorus delivered to nearshore areas by submarine groundwater discharge. We considered new nutrient inputs to be delivered to surface waters by the upward flux of fresh water. This upward flux of water encounters saline porewaters in the surficial sediments and these porewaters contain recycled nutrients; actual nutrient flux from the sediment to overlying waters includes both new and recycled nutrients. New inputs of nitrogen to overlying surface waters for one 10-km section of coastline, calculated by multiplying groundwater nutrient concentrations from freshwater wells by measured seepage rates, were on the order of 1,100±190 mol N d−1. New and recycled nitrogen fluxes, calculated by multiplying surficial porewater concentrations by measured seepage rates, yielded fluxes of 3,600 ±1,000 mol N d−1. Soluble reactive phosphate values were 150±40 mol P d−1 using freshwater well concentrations and 130±3.0 mol P d−1 using porewater concentrations. These values are comparable to the average nutrient delivery of a small, local river.  相似文献   

12.
Biogeochemical processes induced by the deposition of gravity layer in marine sediment were studied in a 295-day experiment. Combining voltammetric microelectrode measurements and conventional analytical techniques, the concentrations of C, O2, N-species, Mn and Fe have been determined in porewaters and sediments of experimental units. Dynamics of the major diagenetic species following the sudden sediment deposition of few cm-thick layer was explained by alternative diagenetic pathways whose relative importance in marine sediments is still a matter of debate. Time-series results indicated that the diffusion of O2 from overlying waters to sediments was efficient after the deposition event: anoxic conditions prevailed during the sedimentation. After a few days, a permanent oxic horizon was formed in the top few millimetres. At the same time, the oxidation of Mn2+ and then Fe2+, which diffused from anoxic sediments, contributed to the surficial enrichment of fresh Mn(III/IV)- and Fe(III)-oxides. Vertical diffusive fluxes and mass balance calculations indicated that a steady-state model described the dynamic of Mn despite the transitory nature of the system. This model was not adequate to describe Fe dynamics because of the multiple sources and phases of Fe2+. No significant transfer of Mn and Fe was observed between the underlying sediment and the new deposit: Mn- and Fe-oxides buried at the original interface acted as an oxidative barrier to reduced species that diffused from below. Nitrification processes led to the formation of a NO3−/NO2− rich horizon at the new oxic horizon. Over the experiment period, NO3− concentrations were also measured in the anoxic sediment suggesting anaerobic nitrate production.  相似文献   

13.
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14.
《Applied Geochemistry》1998,13(2):269-280
A slow flow, plug-through reactor was developed for measuring equilibrium and kinetic parameters of biogeochemical reactions on intact sections of sediment cores. The experimental approach was designed to preserve the structural, geochemical and microbiological integrity of the sediment sections and, hence, retrieve reaction parameters that apply to in-situ conditions.Inert tracer breakthrough experiments were performed on a variety of unconsolidated surface sediments from lacustrine, estuarine and marine depositional environments. The sediments studied cover wide ranges of composition, porosity (46–83%) and mean grain size (10−4−10−2 cm). Longitudinal dispersion coefficients were determined from the breakthrough curves of Br−. The curves were also used to check for early breakthrough or trailing, that is, features indicative of non-ideal flow conditions. Sediment plugs that exhibited these features were eliminated from further experiments.Dimensionless equilibrium adsorption coefficients (K) of NH4+, were calculated from measured retardation times between the breakthrough of NH4+ and Br−. The values of K at 5°C vary between 0.3 and 2.3, with the highest value obtained in a fine-grained marine sediment, the lowest in a coarse-grained lake sediment. The values for the marine and estuarine sediments agree with values reported in the literature. The dependencies of K on ionic strength (range 0.2-0.7m) and temperature (range 5–25°C) in an estuarine sediment confirm that the main sorption mechanism for NH4+ is ion exchange.The reactor was used in recirculation mode to measure steady-state rates of dissimilatory SO42− reduction in a salt-marsh sediment. Recirculation homogenizes solute concentrations within the reactor, hence facilitating the derivation of reaction rate expressions that depend on solution composition. The rate of microbial S04− reduction was found to be nearly independent of the dissolved SO42− concentration in the range of 2.2−1 mM. Fitting of the experimental rates to a Monod relationship resulted in a maximum estimate of the half-saturation concentration, Ks, of 240 μM. This value is comparable to those reported for a pure culture of SO42−-reducing bacteria, but is significantly smaller than the only other Ks value reported in the literature for SO42− utilization in a natural marine sediment.  相似文献   

15.
The competitive adsorption and the release of selected heavy metals and their speciation distribution before and after adsorption in the Yellow River sediments are discussed. The adsorption of metals onto sediments increases with increasing pH value and decreases with increasing ionic strength. The competitive coefficient K c and the distribution coefficient K d are obtained to analyze the competitive abilities of selected heavy metals, which are ranked as Pb > Cu >> Zn > Cd. The competition among selected heavy metals becomes more impetuous with increasing ion concentration in water. Speciation analysis was done by an improved analytical procedure involving five steps of sequential extraction. Cu, Pb and Zn were mainly transformed into the carbonate-bound form (50.8–87.7%) in adsorption. Most of (60.7–77.3%) Cd was transformed into the exchangeable form, and the percentage of carbonate-bound Cd was 19.7–30.4%. The release reaction was so quick that the release capacity of selected heavy metals from sediments to aqueous solution reached half of the maximum value only in 30 s. As opposed to adsorption, the release capacities of selected heavy metals were ranked as Cd > Zn >> Cu > Pb. In this study, Cd produces the most severe environmental hazards, because its concentration in the release solution is 85.8 times more than the human health criteria of US EPA.  相似文献   

16.
Sorption isotherms, time-dependent adsorption and surface complexation modeling studies were used to investigate the post-depositional mobility of three of the platinum group-elements (Pd, Rh, and Pt) in semi-arid soil and sediment samples with varying surface properties. The acidity constants (Log Ka1 and Log Ka2), optimized from batch titration data, ranged from 4.69 to 5.34 for Log Ka1 and from −6.51 to −7.61 for Log Ka2, suggesting the occurrence of both protonation and deprotonation reactions on the solid surfaces. Partition coefficients and removal rates of the metals had a general trend of Pd > Pt > Rh. The sediment sample, with the highest clay content and exchangeable cation concentrations, also had the highest affinity for the metals. The times required for sediment to adsorb 63% of the metals were 2.63 h, 4.08 h and 10.64 h for Pd, Pt and Rh, respectively. The FITEQL program successfully optimized the conditional binding constants of the metals on the solids from batch adsorption data. The constants decreased in the order of Pd > Rh > Pt, which was consistent with the observed high affinity of the solids for Pd. The modeling results also showed that aqueous Pd was the least sensitive to pH followed by Rh and Pt. However, metal adsorption below the points of zero net proton charges (ca. pH 6.7) is attributable to the involvement of permanent negatively charged binding sites in the adsorption process. Notably, partition coefficients, removal rates and conditional binding constants all showed a high affinity of Pd for the solids. A similarity between the model outputs and the batch adsorption data indicates the suitability of the model for describing the mobility and retention of the three metals in semi-arid soils and sediments.  相似文献   

17.
The mobility of strontium in subsurface is largely influenced by sorption on to clay minerals. In the present study, kaolinite clay samples collected from the Kalpakkam nuclear plant site were employed to understand the sorption characteristics of strontium by batch method. The effect of several parameters such as time, strontium ion concentration, pH, temperature and ionic strength was investigated. The kinetic studies suggested pseudo-second-order mechanism. The experimental sorption data was fitted to Langmuir adsorption model for obtaining the sorption capacity of the sorbent. The maximum sorption capacity was 5.77 mg/g at 298 K and was found to increase with an increase in temperature. It was observed that the distribution coefficient (K d) of strontium on clay increased as the pH of the solution increased. The distribution coefficient was found to decrease with an increase in concentration of Na+ and Ca2+ ions. This variation of K d suggests that cation exchange is the predominant sorption process. It was also observed that sorption process is endothermic. The thermodynamic parameters such as ∆G 0, ∆H 0 and ∆S 0 were calculated. The negative values obtained for ∆G 0 indicated that the sorption of strontium on clay was spontaneous at all studied concentrations. ∆G 0 becomes more negative with an increase in temperature, suggests that the sorption process is more favorable at higher temperatures.  相似文献   

18.
The present work attempts to describe the spatial distribution of heavy metals in the surficial sediments of the Xiamen Bay influencing by the characters of the sediments. In this paper, the distribution of trace metals, as well as the main properties (i.e. grain size, TOC, AVS) based on surface sediments collected at 40 stations across the Xiamen Bay was done. The relation of the sediment properties to heavy metal concentrations was evaluated with Pearson’s correlation analysis. According to the grain size distribution, cluster analysis is used to classify the sampling stations into groups regarding the depositional environment. Basing on the data, the hydrodynamic feature and the contamination of surface sediment by selected metals were discussed. The results show that the distribution of various types of sediments and the variations of their concentrations of heavy metals are controlled largely by the hydrodynamic conditions. As for the surface sediments, Xiamen West Harbour shows a serious situation with Arsenic, Pb and Zn.  相似文献   

19.
Previous measurements from cool microtidal temperate areas suggest that microphytobenthic incorporation of nitrogen (N) exceeds N removal by denitrification in illuminated shallow-water sediments. The present study investigates if this is true also for fully nontidal sediments in the Baltic Sea., Sediment-water fluxes of inorganic (DIN) and, organic nitrogen (DON) and oxygen, as well as denitrification, were measured in early autumn and spring, in light and dark, at four sites representing different sediment types. All sediments were autotrophic during the daytime both in the autumn and spring. On a 24-h time scale, they were autotrophic in the spring and heterotrophic in early autumn. Sediments funcitoned as sources of DIN and DON during the autumn and sinks during the spring, with DON fluxes dominating or being as important as DIN fluxes. Microphytobenthos (MPB) activity controlled fluxes of both DIN and DON. Significant differences between sites were found, although sediment type (sand or silt) had no consistent effect on the magnitude of MPB production or nutrient fluxes. The clearest effect related to sediment type was found for denitrification, although only in the autumn, with higher rates in silty sediments. Estimated N assimilation by MPB, based on both net primary production (0.7–6.5 mmol N m−2 d−1) and on 80% of gross primary production (1.9–9.4 mmol N m−2 d−1) far exceeded measured rates of denitrification (0.01–0.16 mmol N m−2 d−1). A theoretical calculation showed that MPB may incorporate between 40% and 100% of the remineralized N, while denitrification removes, <5%. MPB assimilation of N appears to be a far more important N consuming process than denitrification in these nontidal, shallow-water sediments.  相似文献   

20.
Heavy metal contamination and their distribution in different size fractions of the surficial sediment in Haihe River, China have been investigated. These results reveal that the heavy metal contamination of Haihe River is closely related to the contaminating sources along the river and has the order: Cd > Cu > Pb > Cr. The contents of these heavy metals in the sediment of Haihe River are at least two times higher than their background values and the highest contaminating metal, Cd, is 15.5 times higher than its background value and determined in the urban area of Tianjin city. The surficial sediments of Haihe River, with 70% particles smaller than 20 μm, belong to sandy clay containing about 28% clay and 42% silt. Electron micrographs and x-ray analysis show that the concentrations of heavy metals depend on the particle size of sediments. The highest concentrations for most metals exist in fine-grained sediments, which are mainly composed of silicates, oxides, and hydroxides of Si, Fe, and Al. In contrast, lower levels of heavy metals are usually found in the coarse sandy sediments, which are composed of quartz, feldspar, and other rocky substances. Based on the results in the present study of the surficial sediments of Haihe River, the contents of Cr, Cu, Pd, and Cd in finer sediments are 2.4, 3.9, 2.8, and 3.6 times higher than those in coarse sandy sediments, respectively. Obviously, because of rapid industrial development in this area during the last few decades, the surficial sediments of Haihe River, especially those finer fractions, have been seriously contaminated by heavy metals.  相似文献   

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