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1.
C. Christiansen F. Gertz M. J. C. Laima L. C. Lund-Hansen T. Vang C. Jürgensen 《Environmental Geology》1997,29(1-2):66-77
The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of
P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000
tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m–2 yr–1) and 477 ton of P (on average 0.9 g m–2 yr–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension
frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than
net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic
matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of
organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive
sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate
from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity
(56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic
N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively.
Received: 10 July 1995 · Accepted: 19 January 1996 相似文献
2.
Air-flow geometry in air sparging of fine-grained sands 总被引：1，自引：0，他引：1
Laboratory visualization experiments in fine- to very fine-grained sands (grain diameter <0.21 mm) reveal a previously unrecognized
air-flow geometry. This air-flow geometry is termed "chamber flow" and is characterized by: (1) a significant horizontal component,
(2) pervasive air-flow coverage within a region demarcated by a distinct, irregular boundary, and (3) the presence of predominantly
vertical inlet and outlet channels. The attributes of chamber flow differ significantly from channelized flow and pervasive/bubbly
flow, which occur at larger grain sizes and have been described in the literature by several researchers. Previous research,
which indicates a dramatic increase in contaminant removal time in sediments <0.2 mm, indirectly corroborates the phenomena
observed in this study. The extent of sediment column affected by chamber flow of sparge air ranges from 4–54% on an area
basis, and is approximately 28% on a volume basis. These values indicate that chamber air flow has the potential to affect
a much larger percentage of the sediment column than either channelized or pervasive/bubbly flow. Because of the irregularity
of air-flow chambers, in terms of both form and frequency, a detailed knowledge of stratigraphy is important to maximize air-sparging
efficiency at sites where chamber flow is likely to occur.
Electronic Publication 相似文献
3.
Toward a geochemical mass balance of major elements in Lake Qinghai,NE Tibetan Plateau: A significant role of atmospheric deposition 总被引：1，自引：0，他引：1
Sediments in Lake Qinghai archive important information about past environmental changes. In order to faithfully interpret the sediment records and constrain the elemental cycles, it is critical to trace various sources of sediments in the lake. The results show that the elemental input–output budgets are imbalanced for most major elements between riverine fluxes and mass accumulation rate (MAR) of Lake Qinghai sediments. A realistic model must include contributions of dry/wet atmospheric deposition that allow the major element mass balance for the lake to be defined. The budget estimation is based on mass balances of Si and Al, which are relatively immobile and carried to the lake via particulate forms. Estimated annual budget of dry atmospheric deposition is ∼1.3 ± 0.3 × 103 kt/a (accounting for ∼65% of the total inputs) to the lake sediments, assuming local loess within the catchment as a candidate for dry atmospheric deposition to the lake. The resultant flux of 300 ± 45 g/m2/a falls within the flux average of the desert area (400 g/m2/a) and the loess plateau (250 g/m2/a), consistent with the geographical setting of Lake Qinghai. The role of atmospheric deposition would be more significant if wet deposition via rainfall and snow were taken into account. This highlights the potential importance of dust as a significant source for sediment preservation flux for other catchments worldwide. The results also indicate that nearly all Ca input was preserved in the lake sediments under modern conditions, consistent with Ca2+ supersaturation of the lake water. 相似文献
4.
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
5.
Charles S. Hopkinson Anne E. Giblin Jane Tucker Robert H. Garritt 《Estuaries and Coasts》1999,22(4):863-881
Benthic metabolism and nutrient exchange across the sediment-water interface were examined over an annual cycle at four sites along a freshwater to marine transect in the Parker River-Plum Island Sound estuary in northeastern Massachusetts, U.S. Sediment organic carbon content was highest at the freshwater site (10.3%) and decreased along the salinity gradient to 0.2% in the sandy sediments at the marine end of the estuary. C:N ratios were highest in the mid estuary (23:1) and lowest near the sea (11:1). Chlorophyll a in the surface sediments was high along the entire length of the estuary (39–57 mg chlorophyll a m−2) but especially so in the sandy marine sediments (172 mg chlorophyll a m−2). Chlorophyll a to phaeophytin ratios suggested most chlorophyll is detrital, except at the sandy marine site. Porewater sulfide values varied seasonally and between sites, reflecting both changes in sulfate availability as overlying water salinity changed and sediment metabolism. Patterns of sediment redox potential followed those of sulfide. Porewater profiles of inorganic N and P reflected strong seasonal patterns in remineralization, accumulation, and release. Highest porewater NH4 + values were found in upper and mid estuarine sediments, occasionally exceeding 1 mM N. Porewater nitrate was frequently absent, except in the sandy marine sediments where concentrations of 8 μM were often observed. Annual average respiration was lowest at the marine site (13 mmol O2 m−2 d−1 and 21 mmol TCO2 m−2 d−1) and highest in the mid estuary (130 mmol O2 m−2 d−1 and 170 mmol TCO2 m−2 d−1) where clam densities were also high. N2O and CH4 fluxes were low at all stations throughout the year: Over the course, of a year, sediments varied from being sources to sinks of dissolved organic C and N, with the overall spatial pattern related closely to sediment organic content. There was little correlation between PO4 3− flux and metabolism, which we attribute to geochemical processes. At the two sites having the lowest salinities, PO4 3− flux was directed into the sediments. On average, between 22% and 32% of total system metabolism was attributable to the benthos. The mid estuary site was an exception, as benthic metabolism accounted for 95% of the total, which is attributable to high densities of filter-feeding clams. Benthic remineralization supplied from less than 1% to over 190% of the N requirements and 0% to 21% of the P requirements of primary producers in this system. Estimates of denitrification calculated from stoichiometry of C and N fluxes ranged from 0% for the upper and mid estuary site to 35% for the freshwater site to 100% of sediment organic N remineralization at the marine site. We hypothesize that low values in the upper and mid estuary are attributable to enhanced NH4 + fluxes during summer due to desorption of exchangeable ammonium from rising porewater salinity. NH4 + desorption during summer may be a mechanism that maintains high rates of pelagic primary production at a time of low inorganic N inputs from the watershed. 相似文献
6.
Erwin Suess 《Geochimica et cosmochimica acta》1973,37(11):2435-2447
Surface area measurements as well as organic carbon, nitrogen and phosphorus analyses on various grain size fractions of carbonate mud samples confirm that in natural environments of carbonate deposition, surface sorption processes take place which are similar to those described earlier for dissolved organics and artificially suspended calcite particles in both seawater and synthetic solutions.The specific surface area of the sediment increases from 1.8m2/g for the coarse-grained fraction to 12.5 m2/g for the fine material; likewise organic carbon, nitrogen and phosphorus increase with increasing surface area so that there are 1.20 mg C, 0.175 mg N and 0.06–0.20 mg P associated with every square meter of carbonate surface irrespective of the mineralogy of the sediment particles.It appears that the organic matter in these sediments is similar in composition, structure and quantity to the organic layers produced in sorption experiments. With their apparently defined structure and ubiquitous nature, these layers could determine the mineralogy and orientation of submarine carbonate cement or could even be a prerequisite to calcification in general. 相似文献
7.
Variability of dissolved reactive phosphate flux rates in nearshore estuarine sediments: Effects of groundwater flow 总被引：1，自引：0，他引：1
Theoretical diffusive flux rates for dissolved reactive phosphate (DRP) were determined for sediments in a small area of the Indian River, Florida for the period March–May 1982. Flux rates from the sediment varied from 29 to 70 × 10?6g per m2 per day in seagrass associated sediments to 3–25 × 10?6g per m2 per day for an area devoid of seagrass. Simultaneous measurements of groundwater seepage velocities indicated greater velocities in seagrass associated sediments (1.03 × 10?6m per sec) than an area devoid of grass (0.77 × 10?6m per sec). Measured seepage flux accounted for more than 99% of the combined estimated diffusive and seepage flux of DRP for nearshore seagrass sediments. Also noted was an apparent direct relationship between tidal height, DRP and seepage velocity in nearshore sediments (25 m from shore) which further demonstrates the importance of hydrogeologic variables to these areas. 相似文献
8.
新疆艾比湖地区盐尘的沉积通量及其物质组成 总被引：1，自引：0，他引：1
以新疆准噶尔盆地西部的艾比湖地区为研究区,通过野外降尘监测、采样分析等方法,研究了艾比湖地区含盐粉尘的沉积通量和物质组成特征.结果表明:艾比湖干涸湖底是盐尘的输出源,盐尘的化学组成主要是无水芒硝、白钠镁矾、氯化钠等盐碱粉尘及Cr、Pb、Mn、Cu、Ni等潜在毒性元素.艾比湖地区盐尘的沉积通量约为79~381 g·m-2·a-1,盐的沉积通量约为4~61 g·m-2·a-1.盐尘的粒径分布以2~63μm的粉砂粒级为主,大于63μm的砂粒级所占比例很小.特殊的地形条件、大风天气、稀疏的植被覆盖、疏松的大面积尘源是艾比湖湖底风蚀和盐尘输送的有利条件. 相似文献
9.
Grain‐size distributions on high‐energy sandy beaches and their relation to wave dissipation 
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下载免费PDF全文 Grain size and sorting represent two key parameters when characterizing sediments or modelling beach morphology and sediment transport. Traditionally, an average value for grain size or sorting is often assumed for the entire area, determined from only a few sediment samples, ignoring any spatial (or temporal) variability in sediment characteristics. This contribution uses a data set of physical surface sediment samples from 53 beach locations around the south‐west peninsula of the United Kingdom, in addition to bi‐monthly, high spatial resolution (mean 240 samples) digital grain‐size surveys from a high‐energy, oceanic, sandy beach (Perranporth, North Cornwall). Systematic spatial variations in grain size and sorting were consistently observed in the seaward direction across the intertidal zone of sandy beaches, with grain‐sizes coarsening and sorting improving by up to 51·7% and 64·3%, respectively. This variability was deterministically related to the time‐averaged, antecedent‐adjusted energy dissipated by breaking waves, with the observed maximum grain‐size and sorting values correlating with the location of peak wave energy dissipation (r2 = 0·998, P < 0·01). 相似文献
10.
Terezinha Cássia de Brito Galvão Aloisio Rodrigues Pereira Arnaldo Teixeira Coelho Paula Rodrigues Pereira Joaquim Fernandes Teixeira Coelho 《Geotechnical and Geological Engineering》2011,29(1):49-55
Soil erosion, transport and deposition of sediments represent invisible threats that along time can affect negatively the
existing infrastructure of roads and dams, and the quality of air and water resources. In the last decades, a great number
of researches were devoted to study erosion and sediments transportation processes. However, they addressed mostly areas of
agriculture, water impoundments for dams, and land conservation. A lack of studies for erosion processes in urban areas is
evident, in special those aiming to diminish the deposition of sediments originated from urban areas into the rivers and air,
in special as airborne particulate. Traditionally, the costs associated in controlling erosion and sediments in urban areas
are high and in some case, out of the range for most developing countries. Factors responsible for those high prices are the
use of heavy equipments for soil grading and transportation, the use of costly building materials, and the need for employing
more specialized personnel. In the case of gullies in urban areas, another concern is to ensure proper equipment access to
the area for remediation operations. Hereby, it is presented a cost-effective method to recover an extensive gully erosion
area of about 11,000 m2 located in urban area. Estimated sediments released from this area to the water resources and air were estimated on about
66,000,000 tons. In this study area, bioengineering works were performed in 60 days, with hardly any sediment generated outside
the work area resulting from bioengineering operations. A combination of bioengineering techniques were chosen for this study
area, which was a mixture of rigid and biological products including biologs, silt fence, biodegradable straw blankets sewn
with plastic threads derived from recycled PET bottles, among others. An efficient drainage system was implemented for preventing
upland flow, sub-seepage and seepage. Biologs were used aiming to fulfill a double role, the first as barrier to soil sediments
flow, and the second as filler for empty spaces, avoiding expensive grading operations. All engineering works were concluded
in about 60 days at a cost of US0.89/m < sup > 2 < /sup > . This price is cost-effective if compared with the traditional engineering cost of approximately US 0.89/m2. This price is cost-effective if compared with the traditional engineering cost of approximately US 2.92/m2 because it includes extensive use of grading and soil transportation. An environmental advantage of the bioengineering method
is the immediate reduction of airborne particulates. Furthermore, the overall visual aesthetics improved shortly after the
implementation of the works because the bare ground was substituted by native vegetation. After 6 months the vegetation in
the gully erosion area was totally established. Monitoring was performed after 12 months and no erosion and sediment transport
was visually noticed. The ease implementation of this technique without the need for specialized workers in combination with
low prices makes this method a model for developing countries. 相似文献
11.
Concentration and mass loadings of heavy metals adsorbed on sediment from an urban road surface in Beijing were investigated.
The buildup and washoff processes are discussed. Results showed that masses of sediments smaller than 500 μm in diameter varied
from 11.2 to 25.5 g/m2. On average, sediments smaller than 125 μm accounted for 42.9% of sediments smaller than 500 μm in mass. Cd, Cr, Cu, and
Ni were more likely to attach to smaller sediments than bigger ones, compared to Pb and Zn. Mass loading of the sediments
generally increased with antecedent dry periods, but the linear relationship was better for smaller sediments than for bigger
ones. Heavy metal concentrations adsorbed on sediments with diameter less than 40 μm generally decreased more obviously than
those adsorbed on bigger ones after rainfall events. 相似文献
12.
Sediment trapping and transport in the ACE Basin,South Carolina 总被引：1，自引：0，他引：1
A study took place during May 1998 and May 1999 to examine the processes controlling localized accumulation of fine-grained sediments in the lower Ashepoo River. This region, referred to as the Mud Reach, is an area of muddy bottom sediments bounded by fine sands. The Mud Reach is located downstream of the landward extent of the salt intrusion where an estuarine turbidity maximum commonly occurs. Tidal time-series measurements made in the Mud Reach during May 1998, when river discharge was at a 10-yr high, showed high concentrations of suspended sediment (0.05–1 g I−1) during maximum tidal current velocity with concentrations in the bottom 30 cm exceeding 70 g I−1 (fluid mud). A correlation between salinity stratification and increased suspended sediment concentration suggests that inhibited vertical mixing enhances the settling of flocculated sediments to the bed. Measurements made during May 1999 show a two-order-of-magnitude decrease in the concentration of near-bed sediments. A decrease in river discharge during the 1999 observation period of more than 100 m3 s−1 suggests that changes in the hydrography and in the supply of sediments to the system both may be important factors in the trapping of fine-grained sediments in the region. The source of sediments is likely from muddy deposits in the Fenwick Cut, a man-made section of the Atlantic Intracoastal Waterway about 2 km north of the Mud Reach that connects the Ashepoo and Edisto Rivers. The Fenwick Cut appears to be an effective area for trapping sediments where shoaling has increased by 130% in the last decade. Current measurements show that flow velocities decrease through the Cut, likely allowing for the settling of suspended particles that form the thick deposits of unconsolidated mud observed during both years. 相似文献
13.
14.
长江口水下三角洲沉积物粒度组成及其在减沙背景下的响应 总被引：1，自引：0，他引：1
近年来长江口水下三角洲对入海泥沙减少的响应问题越来越受到关注。通过分析长江水下三角洲百年沉积速率的分布特征及位于水下三角洲泥质沉积区不同位置4个浅孔的粒度、~(210)Pb和~(137)Cs数据,探讨其对流域入海水沙变化及水动力变化的响应。研究结果显示,1954年后长江口北支萎缩是导致CDZS10孔所在区域沉积物粒度较其他3孔明显粗的主要原因。而CDZS10孔沉积物上粗下细则是由20世纪80年代三峡蓄水后长江入海泥沙显著下降、海洋动力明显增强引起的。另外,北支萎缩及三峡水库调蓄作用导致泥质区南移,并向杭州湾和嵊泗列岛延伸发展。 相似文献
15.
JON TUNNICLIFFE MICHAEL CHURCH RANDOLPH J. ENKIN 《Boreas: An International Journal of Quaternary Research》2012,41(1):84-101
Tunnicliffe, J., Church, M. & Enkin, R. J. 2012 (January): Postglacial sediment yield to Chilliwack Lake, British Columbia, Canada. Boreas, Vol. 41, pp. 84–101. 10.1111/j.1502‐3885.2011.00219.x. ISSN 0300‐9483. Seismic records and evidence from sediment cores at Chilliwack Lake provide the basis for a long‐term (postglacial) sediment budget for a 324‐km2 Cordilleran catchment. Chilliwack Lake (11.8 km2 surface area), situated in the North Cascade Mountains, near Chilliwack, British Columbia, was formed behind a valley‐wide recessional moraine in the final phase of post‐Fraser alpine glaciation. Seismic surveys highlight the postglacial lacustrine record, which is underlain by a thick layer of sediments related to deglacial sedimentation. Sediment cores provide details of grain‐size fining from the delta to the distal lake basin. The cores also show a record of intermittent fire and debris flows. Magnetic measurements of lake sediments provide information on grain size, as well as a dating framework. The total postglacial lake‐floor deposit volume is estimated to be 397 ± 27 × 106 m3. Including estimates of fan and delta deposition, the specific postglacial yield to the lake is calculated to be ～86 ± 13 Mg km2 a?1. The sediment volume in the uppermost (Holocene) lacustrine layer is 128 ± 9 × 106 m3, representing ～41 ± 4 Mg km2 a?1 in the Holocene. Compared with other Cordilleran lakes of similar size, particularly those with glacial cover in the watershed, Chilliwack Lake has experienced relatively modest rates of sediment accumulation. This study provides an important contribution to a growing database of long‐term (postglacial) sediment yield data for major Cordilleran lakes, essential for advancing our understanding of the pace of landscape evolution in formerly glaciated mountainous regions. 相似文献
16.
The Corsica River, located on Maryland’s eastern shore, has been the site of restoration efforts targeting sediment and nutrient
load reductions. Previous work has indicated that agricultural activities supply most of these materials; however, their dynamics
and fate are largely unknown. To address these needs, bottom sediments have been collected and analyzed for their chemical
and textural properties. Long-term (decadal) accumulation rates are determined with 210Pb (half-life 22.3 years), verified with 137Cs, and range from 0.18 to 0.84 g/cm2/year in the subtidal region and 0.3–1.89 g/cm2/year in the marshes. These estimates are compared with likely sediment sources to determine the direction of exchange with
the adjacent estuary (Chester River), which is a subtributary of Chesapeake Bay, with the Chester River likely supplying 0.94 × 103 t/year of sediment to the Corsica, ∼16% of the total sediment input. The radiochemical data are used to interpret profiles
of grain size and nitrogen and to provide improved estimates of nitrogen burial. Comparison of the Corsica River to similar
systems highlights the importance of marshes in trapping sediment and nutrient inputs from the watershed. 相似文献
17.
The variation during 15 years in the shoreline along the North Sinai coast has been determined by analysing TM and ETM true
colour Landsat images from 1986 to 2001. The analyses identified erosion and accretion patterns along the coast. The shoreline
has advanced west of El Bardawil inlet1, El Bardawil inlet2, and El Arish Harbour, where the wave-induced littoral transport
has been halted by jetty construction and beach growth rates are 20,681, 69,855 and 20,160 m2/year, respectively. On the downdrift side of the constructed jetties to the east, the shoreline is retreating and beaches
erode at rates of −71,710, −69,968, and −11,760 m2/year, respectively. Sedimentological analyses of beach sediment samples have indicated selective transport of heavy minerals
according to their densities and grain sizes. A general correspondence has been found between variation in grain size, sorting
and heavy-mineral content of beach sand and the patterns of shoreline changes. 相似文献
18.
Van T.H.Phan Fabrizio Bardelli Pierre Le Pape Raoul-Marie Couture Alejandro Fernandez-Martinez Delphine Tisserand Rizlan Bernier-Latmani Laurent Charlet 《地学前缘(英文版)》2019,10(5):1715-1729
The cumulative effects of periodic redox cycling on the mobility of As,Fe,and S from alluvial sediment to groundwater were investigated in bioreactor experiments.Two particular sediments from the alluvial floodplain of the Mekong Delta River were investigated:Matrix A(14 m deep)had a higher pyrite concentration than matrix B(7 m deep)sediments.Gypsum was present in matrix B but absent in matrix A.In the reactors,the sediment suspensions were supplemented with As(Ⅲ)and SO_4~(2-),and were subjected to three full-redox cycles entailing phases of nitrogen/CO_2,compressed air sparging,and cellobiose addition.Major differences in As concentration and speciation were observed upon redox cycling.Evidences support the fact that initial sediment composition is the main factor controlling arsenic release and its speciation during the redox cycles.Indeed,a high pyrite content associated with a low SO_4~(2-)content resulted in an increase in dissolved As concentrations,mainly in the form of As(Ⅲ),after anoxic half-cycles;whereas a decrease in As concentrations mainly in the form of As(Ⅴ),was instead observed after oxic half-cycles.In addition,oxic conditions were found to be responsible for pyrite and arsenian pyrite oxidation,increasing the As pool available for mobilization.The same processes seem to occur in sediment with the presence of gypsum,but,in this case,dissolved As were sequestered by biotic or abiotic redox reactions occurring in the Fe—S system,and by specific physico-chemical condition(e.g.pH).The contrasting results obtained for two sediments sampled from the same core show that many complexes and entangled factors are at work,and further refinement is needed to explain the spatial and temporal variability of As release to groundwater of the Mekong River Delta(Vietnam). 相似文献
19.
Geochemistry and mineralogy of shallow alluvial aquifers in Daudkandi upazila in the Meghna flood plain, Bangladesh 总被引：1，自引：0，他引：1
M. Aziz Hasan Mattias von Br?mssen Prosun Bhattacharya Kazi Matin Ahmed Arif Mohiuddin Sikder Gunnar Jacks Ondra Sracek 《Environmental Geology》2009,57(3):499-511
The shallow alluvial aquifers of the delta plains and flood plains of Bangladesh, comprises about 70% of total land area are
mostly affected by elevated concentrations of arsenic (As) in groundwater exposing a population of more than 35 million to
As toxicity. Geochemical studies of shallow alluvial aquifer in the Meghna flood plain show that the uppermost yellowish grey
sediment is low in As (1.03 mg/kg) compared to the lower dark grey to black sediment (5.24 mg/kg) rich in mica and organic
matter. Sequential extraction data show that solid phase As bound to poorly crystalline and amorphous metal (Fe, Mn, Al)-oxyhydroxides
is dominant in the grey to dark grey sediment and reaches its maximum level (3.05 mg/kg) in the mica rich layers. Amount of
As bound to sulphides and organic matter also peaks in the dark grey to black sediment. Vertical distributions of major elements
determined by X-ray fluorescence (XRF) show that iron (Fe2O3), aluminum (Al2O3) and manganese (MnO) follow the general trend of distribution of As in the sediments. Concentrations of As, Mn, Fe, HCO3
−, SO4
2− and NO3
− in groundwater reflect the redox status of the aquifer and are consistent with solid phase geochemistry. Mineralogical analysis
by X-ray diffraction (XRD) and scanning electron microscopy (SEM) fitted with energy dispersive X-ray spectrometer (EDS) revealed
dominance of crystalline iron oxides and hydroxides like magnetite, hematite and goethite in the oxidised yellowish grey sediment.
Amorphous Fe-oxyhydroxides identified as grain coating in the mica and organic matter rich sediment suggests weathering of
biotite is playing a critical role as the source of Fe(III)-oxyhydroxides which in turn act as sink for As. Presence of authigenic
pyrite in the dark grey sediment indicates active reduction in the aquifer. 相似文献
20.
Michael G. LaMontagne Valeria Astorga Anne E. Giblin Ivan Valiela 《Estuaries and Coasts》2002,25(2):272-281
To determine the removal of regenerated nitrogen by estuarine sediments, we compared sediment N2 fluxes to the stoichiometry of nutrient and O2 fluxes in cores collected in the Childs River, Cape Cod, Massachusetts. The difference between the annual PO4 3− (0.2 mol P m−2 yr−1) and NH4 + (1.6 mol N m−2 yr−1) flux and the Redfield N∶P ratio of 16 suggested an annual deficit of 1.5 mol N m−2 yr−1. Denitrification predicted from O2∶NH4 + flux ratios and measured as N2 flux suggested a nitrogen sink of roughly the same magnitude (1.4 mol N m−2 yr−1). Denitrification accounted for low N∶P ratios of benthic flux and removed 32–37% of nitrogen inputs entering the relatively highly nutrient loaded Childs River, despite a relatively brief residence time for freshwater in this system. Uptake of bottom water nitrate could only supply a fraction of the observed N2 flux. Removal of regenerated nitrogen by denitrification in this system appears to vary seasonally. Denitrification efficiency was inversely correlated with oxygen and ammonium flux and was lowest in summer. We investigated the effect of organic matter on denitrification by simulating phytoplankton deposition to cores incubated in the lab and by deploying chambers on bare and macroaglae covered sediments in the field. Organic matter addition to sediments increased N2 flux and did not alter denitrification efficiency. Increased N2 flux co-varied with O2 and NH4 + fluxes. N2 flux (261±60 μmol m−2 h−1) was lower in chambers deployed on macroalgal beds than deployed on bare sediments (458±70 μmol m−2 h−1), and O2 uptake rate was higher in chambers deployed on macroalgal beds (14.6±2.2 mmol m−2 h−1) than on bare sediments (9.6±1.5 mmol m−2 h−1). Macroalgal cover, which can retain nitrogen in the system, is a link between nutrient loading and denitrification. Decreased denitrification due to increasing macroalgal cover could create a positive feedback because decreasing denitrification would increase nitrogen availability and could increase macroalgae cover. 相似文献