Chemical Composition Of Sediments Research Articles

Chemical and mechanical erosion rates in Iceland as deduced from river dissolved and solid material

This study investigates dissolved, suspended loads and sands of major Icelandic rivers and determines chemical and mechanical erosion rates as well as rates of CO₂ consumption by the chemical weathering. A steady state model of erosion is used to locally calculate the river suspended load fluxes needed to balance chemical weathering. The total dissolved solid concentrations range from 20 to 179 mg/kg. The highest concentrations are for spring fed rivers draining young rocks in the vicinity of active volcanoes, and the lowest for direct runoff rivers draining old Tertiary rocks. Total dissolved loads, “corrected” for atmospheric, geothermal, and magmatic inputs are used together with mean annual discharges to estimate low-temperature chemical erosion rates of 16 to 111 t/km²/yr. These rates increase with runoff but decrease with the age of the rocks. Icelandic chemical erosion rates are higher than the world average for silicate rocks, reflecting both high reactivity of the basalt and high runoff, but lower than those for other basalt-draining rivers (in Réunion, Java, Azores or Deccan). CO₂ consumption rates associated to chemical denudation range between 0.18 and 2.12 10⁶ mol/km²/yr with an average value of 0.74 10⁶ mol/km²/yr, higher than the world average for rivers draining silicate rocks. Chemical compositions of suspended sediments and sands are similar, showing a very low weathering stage. The elements most soluble during the weathering show slightly lower concentrations in the suspended sediments. River sediment chemical compositions are assumed to reflect a mixture between 3 initially pristine rock end-members: high Mg-basalt, tholeiite and rhyolite. The most insoluble elements (REE and Th) are used to re-define the mean chemical composition of the initially unaltered rocks of each drainage basin. A mass budget between the unaltered rock of the catchments and the river dissolved and suspended loads (steady state model of erosion) is used to calculate the average annual solid load of the rivers, which range from 650 to 4300 mg/l. For some rivers there is a good agreement between calculated and measured suspended loads but for others the calculated load is much higher than the measured one. The difference stems from groundwater inputs, man-made dams and other sedimentary traps. If the relevancy of the steady state model of erosion can be questioned, the accuracy of sediment load measurements is also questionable. Pros and cons of both methods are argued. The calculated solid loads lead to very high mechanical erosion rates, ranging from 940 to 10200 t/km²/yr. Those increase with the glacier cover but decrease with the age of the catchment rocks. Icelandic mechanical erosion rates rank among the maximum reported rates, underscoring the importance of glaciers, tectonics, glassy basaltic rocks and high runoff. In association with low chemical weathering rates, these place Icelandic rivers as an end-member in the observed anti-correlation between mechanical to chemical erosion ratios and temperature for volcanic islands.

Characterising physicochemical sediment conditions at selected bacterial decayed wooden pile foundation sites in the Netherlands, Germany, and Italy

We investigated the relationship between wood degradation caused by erosion bacteria and the physicochemical properties of foundations with wooden piles from sites in the Netherlands, Germany, and Italy. Wooden foundation piles have been widely used to stabilise urban settlements along coastal areas and river sites for several millennia. Recently a number of these buildings have suffered from structural instability because their foundations have suddenly lost supporting strength. This loss of strength has been associated with the activity of erosion bacteria that can colonise and destroy wood under low-oxygen conditions, such as those that exist below the groundwater level. Knowledge of bacterial species involved in this process and their growth requirements is sparse, but it has been documented that the damage to wooden foundation piles caused by these bacteria can occur relatively rapidly. Redox potential (platinum electrodes) measurements, sediment, and sedimental water samples were obtained from nine European sites. Sediments were characterised and analysed for total contents of carbon, nitrogen, sulphur, phosphate, and major cations, whereas sedimental water was analysed for pH, conductivity, total and dissolved carbon and nitrogen, NH 4 + , NO 3 - , SO 4 2 - , PO 4 3 - , Cl - , and major cations. The chemical sediment composition was governed mainly by sediment type (sand, clay), whereas sediment water composition reflected the exposure to sea or freshwater and the redox status of the sampling location. Bacterial wood decay was detected at all sites but with different magnitude orders reflecting the different environments. When the physicochemical properties of sedimental water from foundations in sandy sediments were compared with wood degradation levels, it was observed that decreasing total nitrogen concentration, but not that of phosphate, accompanied increasing bacterial wood decay.

Geochemistry of surface sediments in the southwestern East/Japan Sea

We analyzed 77 surface sediment samples collected in the southwestern East/Japan Sea from the Korea Strait through the Ulleung Basin and the Korea Plateau for grain size, calcium carbonate, organic carbon, and major (Na, Mg, Al, Fe, K, Ca, and Ti) and trace elements (P, Mn, Sr, Li, Sc, V, Cr, Co, Ni, Zn, Cu, and Pb). The chemical composition of the surface sediments was found to be highly variable spatially. Cluster analysis of surface sediment chemical compositions indicated five major geochemical sedimentary environments: basin, lower slope, coast and upper slope, inner shelf, and outer shelf. Continental-shelf sediments were rich in shell fragments and had relict and coarse-grained characteristics. Recent fine-grained sediments were only distributed in coastal, slope, and basin areas. Concentrations of Al, K, Ca, Ti, Cr, and Sc were highest in the coastal and upper slope areas and decreased with water depth. Elemental ratios using major and trace elements indicated that coastal and upper slope detrital sediments were mixtures of sediments derived from the Changjiang (Yangtze) and Nakdong Rivers. Although the concentrations of organic carbon, P, Mn, V, Co, Ni, Cu, and Pb increased with water depth, their distribution patterns indicated authigenic (V, Cu, and Pb) and diagenetic (Fe, P, Mn, Co, and Ni) origins. The distribution pattern with water depth suggested that the chemical composition of surface sediment was determined by sedimentologic and geochemical processes, such as the supply of detrital and biogenic materials, and authigenic and post-depositional diagenetic processes in sediments.

An advanced multivariate statistical approach to study coastal sediment data

AbstractThe present paper deals with the application of classical and fuzzy principal components analysis to a large data set from coastal sediment analysis. Altogether 126 sampling sites from the Atlantic Coast of the USA are considered and at each site 16 chemical parameters are measured. It is found that four latent factors are responsible for the data structure (“natural”, “anthropogenic”, “bioorganic”, and “organic anthropogenic”). Additionally, estimating the scatter plots for factor scores revealed the similarity between the sampling sites. Geographical and urban factors are found to contribute to the sediment chemical composition. It is shown that the use of fuzzy PCA helps for better data interpretation especially in case of outliers.

Monitoring the variations of the Socotra upwelling system during the last 250 kyr: A biogenic and geochemical approach

A combination of changes in the species composition of the radiolarian populations, and in the sediment chemical composition (content and mass accumulation rates of carbonate, organic carbon, and selected major and trace elements, with special attention paid to Ba) is used to reconstruct the variations in upwelling activity over the last 250 kyr in the Socotra gyre area (Somali–Socotra upwelling system, NW Indian Ocean). In the Socotra gyre (Core MD 962073 at 10°N), the variations in upwelling intensity are reconstructed by the upwelling radiolarian index (URI) while the thermocline/surface radiolarian index (TSRI) testifies to productivity variations during non-upwelling intervals. Despite an origin related both to marine and terrigenous inputs, the geochemical records of organic carbon, silica, and trace elements (Ba, P, Cu, and Zn) normalized to Al are controlled by the variations in surface paleoproductivity. The data indicate a continuous increase in upwelling intensity during the last 250 kyr with a maximum activity within the MIS 3, while high productivity periods in between the upwelling seasons occurred both during glacial and interglacial intervals. A comparison of our data with published observations from another gyre of the Somalian upwelling area located at 5°N in the Somali gyre area shows differences regarding periods of upwelling activity and their geochemical imprint. Three hypotheses are proposed to explain these differences: (1) changes in the planktonic community, resulting in more silica-rich deposits in the Socotra gyre, and more carbonate-rich deposits in the Somali gyre, that are controlled by differences in the source water of the upwelling; (2) a more important terrigenous input in the southern gyre; and (3) a different location of the sites relative to the geographic distribution of the upwelling gyres and hydrologic fronts.

Geochemical signature as paleoenvironmental markers in Holocene sediments of the Tinto River estuary (Southwestern Spain)

High absolute concentrations of metals associated to sulfide deposits located at the river source (Fe, Cu, Zn, Pb, Cd, and As) have been determined from the study of major and trace element concentrations in sediment samples obtained in two vibracores in the Tinto River estuary. In most cases, the enrichment factor (EF) for these metals is over 2. Cu, Zn and As have much higher EF, over 10 in surficial samples. Fe oxy-hydroxide precipitation in high-chlorinity zones and its scavenging effect on metals is the main control process on the chemical composition of sediment. Vertical evolution of the sedimentary and geochemical characteristics of the cores show that the estuary has undergone a process of progressive shallowness and a relative increase in acidic river water volume with respect to seawater. This effect has originated a downstream displacement of acid mixing processes affecting the estuary, which is reflected in higher metal concentrations in sediments of the outer zones of the system.

Influence of the sea rush Juncus maritimus on metal concentration and speciation in estuarine sediment colonized by the plant.

Metal accumulation by Juncus maritimus and the role of this plant on the physical and chemical composition of sediments, from the Douro river estuary (NW Portugal), were investigated. The contents of Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were determined (by atomic absorption spectrophotometry) in sediments, rhizosediments (those among plant roots and rhizomes), and different plant tissues (roots, rhizomes, leaves, and stems). Metal fractionation in sediments through sequential extraction was carried out and used for interpretation of sediment/J. maritimus interactions. Two estuarine sites with different characteristics were studied: site I displayed sandy sediment with lower organic matter and metals more weakly bound to it than site II sediment, which was muddy. At both sites, higher metal contents were observed in rhizosediments than in the surrounding sediment, but metals were more weakly bound to rhizosediment. Therefore, J. maritimus markedly influenced the sediments among its roots and rhizomes, changing metal distribution and speciation. Different patterns of both metal uptake and metal distribution among J. maritimus tissues were observed at the two sites. Plant bioaccumulation was only observed for Cd, Cu, and Zn, being similar for Cd atthe two sites and significantly higher for Cu and Zn (9 and 4 times higher, respectively) at site I. In conclusion, J. maritimus was shown to have potential for phytoextraction (or phytostabilization) of Cd, Cu, and Zn in estuarine environment. However, an eventual application of J. maritimus for this purpose will require a periodic removal of the plants together with their own rhizosediment.

Geochemical response of a closed-lake basin to 20th century recurring droughts/wet intervals in the subtropical Pampean Plains of South America

Laguna Mar Chiquita is a highly variable closed saline lake located in the Pampean Plains of central Argentina. Presently is the largest saline lake in South America (∼ 6,000 km2) and also one of the largest in the world. During the 20th century the hydrological balance of the region was characterized by contrasting scenarios. Well-defined wet or dry climatic phases had ruled the lake level fluctuations and the rivers discharge, mainly controlling the geochemical composition of sediments. Sediments accumulated during positive hydrological balances (i.e., high lake level) are mainly composed of allogenic mineral due to higher riverine inputs into the lake. This fluvial-dominated lake phases are recorded as sediments enriched in Al2O3, SiO2, K2O, Fe2O3 and TiO2 and in trace elements such as Co, Cr, Cs, Rb, Sc, Hf, Ta, Th as well as rare earth elements (REE). Sediments accumulated during dry phases (i.e., low lake levels and high salinity) are evaporite mineral-rich with elevated concentrations of CaO, MnO, MgO, and P2O5. High contents of As and U are probably due to a co-precitation during high evaporative phases. The calibration of the sediment chemical composition of Laguna Mar Chiquita to well-defined water-level fluctuations of the 20th century shows that elemental geochemistry can be a useful proxy to study former lake-water fluctuations. It may further provide a comparative model to evaluate past environmental conditions in other saline lacustrine basins.

Elemental composition of marine sponges from the Berlengas natural park, western Portuguese coast

AbstractAnalytical studies of sponges have recently become a matter of interest, since these organisms have been reported to accumulate high levels of some elements, including heavy metals, which may have an anthropogenic origin, allowing their application as environmental pollution indicators. In the present work, 35 sponges collected in August 1998 at the Berlengas Natural Park were classified and analysed by secondary target energy‐dispersive x‐ray fluorescence spectrometry (EDXRF). Some major, minor and trace elements could be determined: Al, Si, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Zr, I and Pb. To assess some local influences on the sponge composition, two sediment samples were also taken from the area and analysed. Besides these elements, sponges are constituted by fairly high percentages of elements that do not emit characteristic x‐ray lines. Therefore, absorption corrections for quantitative calculations were carried out taking into account the ratio between the inelastic and elastic scattered incident radiation from a silver secondary target to calculate the mean atomic number of the light matrix. Calibration was performed using chemical compounds and standard reference materials. Precision, accuracy and detection limits for the range of elements determined by the method are particularly suitable for the chemical analysis of these organisms. Results for the sediment chemical composition indicated the existence of high Ca and low Si levels and confirmed the absence of any trace metal contamination in the region. The sponge composition showed low Si contents, even in siliceous specimens. Certain high elemental contents determined in some species indicated a clear selective bioaccumulation of particular trace elements, such as Ni, Zn and As, which is not dependent on local influences. Copyright © 2003 John Wiley & Sons, Ltd.

Some statistical relationships between stream sediment and soil geochemistry in northwestern Wisconsin—can stream sediment compositions be used to predict compositions of soils in glaciated terranes?

Mean stream sediment chemical compositions from northwestern Wisconsin in the north central United States, based on more than 800 samples, differ significantly from mean A-horizon and C-horizon soil compositions, based on about 380 samples of each horizon. Differences by a factor greater than 1.5 exist for some elements (Ca, Mn, Mg, P, Ti, Ni, Pb, Se, Zn). A very large database of stream sediment geochemistry exists for the region (more than 2200 samples) and for the U.S. (roughly 400,000 samples), whereas data on the chemistry of soils is much sparser both regionally and nationally. Therefore, we have attempted to quantify trends in compositional differences between stream sediments and nearby soils to test whether the abundant stream sediment data can be used to predict soil compositions. A simple computational technique of adjusting the stream sediment compositions according to the ratio of means of soils and stream sediments was conducted. A variety of techniques of correction and interpolation of data were tested and indicate that repetitive testing of results allows an optimum correction to be achieved. Predicted soil compositions compared to analytically determined soil compositions show a range of results from relatively good correspondence for some elements to rather poor correspondence for others. In general, predictions are best at midranges of compositions. The technique does not predict well more extreme or anomalous values. Thus, this technique appears to be useful for estimating background soil compositions and delineating regional compositional trends in soils in situations where large amounts of stream sediment analyses and smaller amounts of soil analyses are available. The technique also provides probabilistic qualifications on the expected error between predicted and actual soil compositions so that individual users can judge if the technique provides data of sufficient accuracy for specific needs.

Effects of lining and drying on the chemical composition of sediments and influence of organic carbon on carp growth in aquaculture ponds

Chemical characteristics and P-fractionation of sediments from the Deroua fish culture farm (Beni Mellal, Morocco) were analysed in 1998 and 1999. The high concentrations of organic N and organic C in the sediments reflect the high productivity of phytoplankton in the lined ponds. Despite the fact that these ponds were not frequently fertilized, inorganic P was more important in the sediments. The P released from CaCO3≈P was the principal source of P for phytoplankton. The mineralization rate of organic C during the drying period was about 87 µg g−1 day−1 in the sediments. The mineralization rate of organic N seems to be less, compared with organic C. The experimental results indicate that the C:N ratio and texture of sediments could explain the immobilization of organic N. All forms of P remained almost unchanged after the drying period except for Fe(OOH)≈P. The ferric (oxy) hydroxides protect NaOHext-P from the bacterial lyses and stabilize therefore their concentration. The inorganic P represented about 88% of Total P in the sediments and may influence the mineralization rate of organic P. The growth of silver carp were reduced in presence of high concentrations of organic C in sediments (> 30 mg/g). Compounds toxic to fish such as Fe2+, Mn2+, H2S and CH4 were then released in the water column.

Diatom—chemistry relationships in Yellowstone Lake (Wyoming) sediments: Implications for climatic and aquatic processes research

We analyzed sediment elemental composition (C, N, P, and Si) and planktonic diatom fossils from the top 32 cm of a short core (55 cm) from Yellowstone Lake (Wyoming), tracking deposition from about 1650 to 1998. Associations between fossil communities and sediment chemistry were measured by rank‐order correlation to gauge decadal scale relationships between lake chemistry and phytoplankton community composition. Strong associations were found between the abundance of individual diatom species and the chemical composition of sediments, suggesting that sediment chemistry can directly track the elemental composition of seston. Among three fossil measures (relative frustule abundance, relative biovolume, and absolute biovolume), associations between sediment chemistry and relative biovolume were strongest. We then compared measures and trends in sediment elemental composition to in‐lake seston chemistry to assess transport processes that alter sediment composition relative to source material. On the basis of elemental stoichiometry, sediments were enriched in P and depleted in C and N compared with seston. Trends of increasing C and N accumulation along with decreasing Si accumulation were consistent with patterns of increasing productivity, increasing lake N levels, and decreasing dominance of diatoms, respectively. A sharp increase in sediment C:N ratio, with a decrease in diatom absolute biovolume and absolute C and N levels, was associated with a prolonged drought in the 1930s. These trends suggest alteration of ecosystem properties by a combination of climatic variation and increasing N availability, adding complexity to larger goals of climatic reconstruction by diatom—nutrient chemistry—climate transfer functions in large lakes of the region.

Geochemistry of Diagenesis of Sediments in the Barents Sea: Forms of Iron and Sulfur

The chemical composition of sediments of cores taken from different areas of the Barents Sea was studied. The study involves reactive iron (Fe react ) and reduced sulfur. The surficial oxidized layer with a thick- ness of 0.5-25 cm is characterized by increased content of Fe(III) in the form of oxyhydroxides and possibly hydroxophosphates. This layer is locally enriched in Mn. Reactive iron in sediments of horizons, which underlie the oxidized layer, is probably present mainly in the composition of silicates. The role of sulfides (acid-soluble phases and pyrite) among Fe react forms is predominantly subordinate. The core of pre-Holocene sediments is characterized by a strong correlation between the total content of reduced sulfur and its isotopic composition. This testifies to authigenic origin of pyrite in the pre-Holocene mud.

Variability of dust inputs to the CANIGO zone

Abstract The variability of dust inputs in the Canary Islands Azores Gibraltar Observations (CANIGO) area is discussed for the period 1997–1998. The samples were collected daily at “Pico de la Gorra”, at the top of Gran Canaria Island (1980 m). A seasonal pattern of Saharan dust events was observed during this period with maximum fluxes in winter and summer. The intensity of events was higher in 1998 than in 1997. Seasonal patterns, composition, and relationship of dust inputs with meteorological data can help define the effects of episodic dust inputs on the surface oceanic reservoir and their correlation with the sinking particulate flux, trace metal distributions in the water column and sediment chemical composition in the CANIGO region.

Assessment of Injury to Fish and Wildlife Resources in the Grand Calumet River and Indiana Harbor Area of Concern, USA

This article is the second in a series of three that describes the results of a Natural Resource Damage Assessment (NRDA) conducted in the Grand Calumet River and Indiana Harbor Area of Concern (IHAOC). The assessment area is located in northwest Indiana and was divided into nine reaches to facilitate the assessment. This component of the NRDA was undertaken to determine if fish and wildlife resources have been injured due to exposure to contaminants that are associated with discharges of oil or releases of other hazardous substances. To support this assessment, information was compiled on the chemical composition of sediment and tissues; on the toxicity of whole sediments, pore water, and elutriates to fish; on the status of fish communities; and on fish health. The data on each of these indicators were compared to regionally relevant benchmarks to assess the presence and extent of injury to fish and wildlife resources. The results of this assessment indicate that injury to fish and wildlife resources has occurred throughout the assessment area, with up to five distinct lines of evidence demonstrating injury within the various reaches. Based on the frequency of exceedance of the benchmarks for assessing sediment and tissue chemistry data, total polychlorinated biphenyls is the primary bioaccumulative contaminant of concern in the assessment area. It is important to note, however, that this assessment was restricted by the availability of published bioaccumulation-based sediment quality guidelines, tissue residue guidelines, and other benchmarks of sediment quality conditions. The availability of chemistry data for tissues also restricted this assessment in certain reaches of the assessment area. Furthermore, insufficient information was located to facilitate identification of the substances that are causing or substantially contributing to effects on fish (i.e., sediment toxicity, impaired fish health, or impaired fish community structure). Therefore, substances not included on the list of COCs cannot necessarily be considered to be of low priority with respect to sediment injury (e.g., metals, polycyclic aromatic hydrocarbons, alkanes, alkenes, organochlorine pesticides, phthalates, dioxins, and furans, etc.).

An assessment of injury to sediments and sediment-dwelling organisms in the Grand Calumet River and Indiana Harbor Area of Concern, USA.

This article is the first in a series of three that describe the results of a Natural Resource Damage Assessment (NRDA) conducted in the Grand Calumet River and Indiana Harbor Area of Concern (IHAOC). The assessment area is located in northwest Indiana and was divided into nine reaches to facilitate the assessment. This component of the NRDA was undertaken to determine if sediments and sediment-dwelling organisms have been injured due to exposure to contaminants that have accumulated in sediments as a result of discharges of oil or releases of other hazardous substances from industrial, municipal, and nonpoint sources. To support this assessment, information was compiled on the chemical composition of sediment and pore water; on the toxicity of whole sediments, pore water, and elutriates; and on the status of benthic invertebrate communities. The data on each of these indicators were compared to regionally relevant benchmarks to assess the presence and extent of injury to surface water resources ( i.e., sediments) or biological resources ( i.e., sediment-dwelling organisms). The results of this assessment indicate that sediment injury has occurred throughout the assessment area, with up to four distinct lines of evidence demonstrating injury within the various reaches. The primary contaminants of concern ( i.e., those substances that are present at concentrations that are sufficient to cause or substantially contribute to sediment injury) include metals, polycyclic aromatic hydrocarbons, and total polychlorinated biphenyls.

Spatial trends in the chemical composition of sediments on the continental shelf and slope off the Mediterranean coast of Israel

In order to determine whether observed trends in total trace metal content were natural or due to anthropogenic inputs, major and trace elements were measured on three size fractions (fine sand (250–63 μm), silt and clay (<63 μm) and clay (<2 μm)) of sediment collected off the Mediterranean coast of Israel. Partitioning of trace metals into carbonate/exchangeable, iron oxide and residual phases for each grain size was also determined. The dominant source of particles was Nile derived material. There was a decrease in Fe/Al, Ti/Al and non-carbonate Mg/Al in the fine sand fraction, interpreted as a decrease in heavy minerals towards the north and an increase in K/Al due to increased feldspars and micas. There was a simultaneous increase in CaCO 3 both towards the north and onshore in all grain size fractions due to a northward increase in local biogenic fragments and river detritus. This is consistent with circulation and sediment transport models for the southeast Levantine basin. The background trend in trace metals corresponds to changes in mineralogy. While the fine sand fraction appeared free of contamination, in the finer fractions there is a significant enrichment of Zn, and Cd towards the north, which is not accounted for by changes in mineralogy. The sediments were also enriched in Cu, Zn and Cd near Tel Aviv and Hadera. The peaks near Tel Aviv may correspond to waste discharged through the Yarqon and an old sewage pipe, whilst near Hadera, the Alexander and Hadera Rivers and the terminal for a coal-fired power station may be the source of contamination. There was also clear evidence for contamination by Pb in the finest sediments. However, there was no enrichment in Pb around the point sources of the other trace metals, therefore it was concluded that the majority of Pb contamination was from the atmosphere. All trace metal contamination may be subject to ‘smearing’ by sediment transport, particularly in the clay fraction.

Microbial respiration and chemical composition of different sediment fractions in waterbodies of the upper Paraná River floodplain, Brazil.

Four size fractions of the sediment of six environments of the upper Paraná River floodplain were analyzed for carbon, nitrogen, and phosphorus contents and microbial respiration (oxygen consumption). Particle size did not affect nitrogen and phosphorus content or microbial activity, but did affect carbon content (F = 4.274, df = 3; 20, p = 0.020). The carbon concentration of ultra-fine particles was significantly lower than that of other sizes of sediment particles. Microbial respiration values were well predicted by sediment chemical composition, as shown by multiple regression (microbial respiration = -0.39 - 0.210C + 0.108N + 0.796P; F = 7.0495, p = 0.0022). However, phosphorus was the element which best explained the microbial respiration (partial coefficient = 0.796, p = 0.0039, n = 23). Considering that i) phosphorus was the best predictor of microbial respiration; ii) phosphorus is trapped in the series of reservoirs located upstream from the section of the floodplain studied; and iii) microbial respiration is a measure of decomposition rates and nutrient cycling, we hypothesize that the long-term accumulation of litter detritus and reduction of nutrient cycling in environments of the upper Paraná River floodplain are probable impacts of this decrease in phosphorus caused by the upstream reservoirs.

Enrichment of high field strength elements in stream sediments of a granulite terrain in Sri Lanka — evidence for a mineralized belt

Size fractions (<63, 63–125, 125–177 and 177–250 μm) of stream sediments draining high-grade metamorphic sources from the Walawe Ganga Basin located in a high-grade metamorphic terrain of Sri Lanka have been analysed for their major and trace element composition. The chemical compositions of sediments were compared with those of the probable metamorphic source rocks in the tributary basins. Rocks in the area are characterized by higher contents of some of the large ion lithophile (LIL) elements such as K, Rb, Ba, Sr, Pb and high field strength elements (HFSE) compared to similar granulitic terrains. Geochemically, the terrain is comparable to the post-Archean upper crust. The size fractions of stream sediments indicate that most of the HFSE and related trace elements are more enriched in the 63–125 and 125–177 μm size fractions compared to the <63 and the 177–250 μm fractions. Studies of elemental ratios in sediments show that the geochemistry of most elements such as Ti, Nb, Zr, Hf, Th, La and Ce in sediments is mainly controlled by the heavy mineral phases. However, geochemical data of these rocks do not correlate with elemental content in stream sediments. Only alkali, alkaline earth and some trace elements such as Cr, Mn, Co, Ni, and Y roughly correlate with the chemical composition of the probable source rocks. Nevertheless, most of the HFSE and related trace elements (e.g. Ti, V, Nb, Zr, Hf, Th, La, Ce) are highly enriched (factor of 10 or more) in sediments compared to the probable source rocks. Compared to the <63 μm fraction, other selected fractions indicate higher enrichment relative to their probable source rocks. This presumably indicates the presence of HFSE-rich mineral sources such as granitic pegmatites in the drainage area.

Chemical composition of the sediment from Lake 20 (Antarctica)

Lake 20 (19,000 m2) is located on the coast of the Ross Sea, in the North-Central part of Victoria Land, and its surface is ice-free between the end of December and early February. Within the framework of the Italian National Research Programme in Antarctica, a study was made of the chemical composition of sediments from the lake, with the intention of using this information to contribute to a better understanding of the processes involved in the long range transport of pollutants and their role in global changes. A sediment core from Lake 20 (Antarctica), 18 cm long, was collected in 1994, sliced into 2 cm sections and analysed using X Ray fluorescence spectrometry for 17 elements (Si, Al, Ca, K, Fe, Mg, Ti, S, P, Pb, Zn, Cu, Ni, Mn, Cr, Na, Cl), by CHN Elemental Analyser for C and N, by Flameless Atomic Absorption Spectrometry for As, and by Cold Vapour Atomic Absorption Spectrometry for Hg. The chemical composition of the sediments is consistent with the known geochemical characteristics of the drainage basin. While the chemical analyses reveal that sedimentation in Lake 20 has changed through time, the variations along the core are most probably related to the climatic evolution of the area, to the consequent changes in weathering processes, and possibly to an increase in the primary productivity of the lake, rather than to anthropogenic influences on the biogeochemical cycles of the elements.