Surface Sediment Distribution Research Articles

Temperature and water depth effects on brGDGT distributions in sub-alpine lakes of mid-latitude North America

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) in lake sediments are increasingly being used to reconstruct past temperatures. However, recent studies suggest that brGDGT distributions and concentrations vary with lake size and environmental conditions, such as seasonality and its effects on water column temperature and chemistry. To test their use as a paleothermometer in high-altitude environments of mid-latitude North America, we analyzed brGDGT distributions in lake surface sediments across a range of lake depths and elevations in the Rocky Mountains of Wyoming and Colorado. Our results suggest that brGDGT distributions and the MBT′5Me index correlate with water column temperatures, which are sensitive to both lake water depth and air temperatures. Based on these relationships, we developed a calibration to mean summer air temperatures using a Bayesian regression model that incorporates the MBT′5Me index and lake water depth. We applied our calibration to lake sediments from Lower Paintrock Lake in northern Wyoming to test its use as a paleothermometer. Reconstructed temperature trends are consistent with pollen-inferred temperatures at the same site and with known regional climate history, demonstrating that our calibration can be successfully applied to infer temperatures in high-altitude environments of mid-latitude North America.

Pollen distribution and transportation patterns in surface sediments of Liaodong Bay, China

Understanding pollen transport pathways and dispersal mechanism from the land to sea is a prerequisite for marine palynological study. Palynological analysis of 164 surface sediment samples in Liaodong Bay, and 39 analogous surface alluvium samples from its five inflowing rivers, identifies the distribution patterns, pathways and possible sources of pollen and spores. The results show that pollen and spore assemblages in surface sediments are well correlated to regional vegetation distribution, and the variations of pollen assemblage in different parts of Liaodong Bay reflected local vegetation changes along the coast. High pollen concentrations are mainly distributed in the estuaries of inflowing rivers, coastal waters and sea muddy areas. The pollen assemblage characteristics of alluvial samples are similar to those from coastal waters with water depths <8.5 m. Samples from the alluvium and surface sediments of coastal waters were dominated by herbaceous pollen taxa including Artemisia, Amaranthaceae, Poaceae, Cyperaceae and Typha. Herbaceous pollen percentages and concentrations decreased as the water depth increased, indicating that pollen and spores in the coastal waters of Liaodong Bay are mainly carried by the inflowing rivers. However, pollen assemblages for samples with water depth >8.5 m are significantly different from those of the alluvium. In samples taken below a depth of 8.5 m, the arboreal pollen is dominated by airborne Pinus, and there is a high number of the waterborne Selaginella fern spores, both of which are sourced from a wider region. In the Liaodong Bay, both wind and ocean current transportation determines the pollen distribution patterns in deeper waters, while fluvial and longshore current transportation determines the pollen assemblages found in shallow waters. The dispersal characteristics of pollen assemblages between the land and the sea in Liaodong Bay provide a theoretical basis for the interpretation of fossil pollen assemblages and past sea level changes.

Lateral sediment transport and late Quaternary changes of eolian sedimentation in the East Sea (Japan Sea)

• GSDs reveal offshore limit of lateral sediment transport in the East Sea. • Lateral sediment transport from the Korean Peninsula is within ~70 km offshore. • Eolian sediments in the SKP were transported by upper westerlies and winter monsoons. • East Asian winter monsoon intensity controlled eolian sedimentation in the East Sea. We investigated grain size records of a sediment core (05-P21) from the South Korea Plateau in the East Sea, located ca. 270 km east of the east coast of the Korean Peninsula. To verify an exclusive eolian origin for the detrital components of the sediments, we first examined how far offshore lateral-sediment-transport contributions from the eastern margin of the Korean Peninsula could reach, based on spatial changes in the grain size distribution (GSD) of surface sediments. To distinguish grain populations representing different transport processes, we performed end-member analyses (EMAs) of the GSDs of detrital fractions using the AnalySize software. EMA of the surface sediment GSDs showed that they consist of three end-member (EM) grain populations representing contributions from lateral (EM1 and EM2) and eolian transport (EM3). EM contributions by lateral transport reached only ca. 70 km seaward, confirming the exclusive eolian origin of detrital components of the 05-P21 core sediments. EMA of GSDs of the 05-P21 sediments distinguished two EM grain populations with fine (3.6 µm) and coarse (9.5 µm) median sizes, suggesting transport by upper westerlies and winter monsoon northwesterly surface winds, respectively. Variation in the proportions of fine and coarse EMs since ca. 186 ka indicated controls by both orbital and sub-orbital scale changes in intensity of the East Asian winter monsoon in association with global ice volume changes and Dansgaard–Oeschger cycles.

Benthic diatoms in relation to environmental factors in an allochthonous river from Patagonia, Argentina

Natural and human pressures increasingly threatening the biodiversity and water resources of dryland rivers. Fluvial environments of Patagonia harbour high diatom diversity, but their management value is overlooked. The aim of this study is to explore the diatom distribution in surface sediments of the Chubut River and evaluate their relationship with environmental variables. In total, 243 diatom taxa were identified in 16 littoral zone sites. The physical and chemical variables independently explained the variance in diatom data, whereas sediment texture had a low influence. Conductivity, major ions (HCO3–, Cl–, SO42–, Na+, K+, Ca2+ and Mg2+) and pH were the main environmental drivers explaining the diatom composition. As the highlighted variables increased near the mouth, so did the relative abundances of marine–brackish taxa such as Amphora copulatoides, Sarcophagodes alfred-wegeneri, Nitzschia fonticola and Tryblionella apiculata. Meanwhile, the presence of high pollution-tolerant diatoms can be put forward to explain the river health deterioration towards downstream areas. The marine–brackish taxa found at freshwater sites reflect a weak tidal influence in the estuary compared with other coastal systems of Patagonia. This study provides valuable information to test the hypothesis on the ecological status of aquatic resources and the potential effects of climatic and hydrological changes in the area.

Advances in Understanding Mobilization Processes of Trace Metals in Marine Sediments.

Different mobilization mechanisms control the metal distribution in surface sediments of the Belgium coastal zone (BCZ) and the anoxic Gotland basin (GB). This mobilization was studied using DGT (diffusive gradients in thin films): vertical one-dimensional (1D) profiles of Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn were measured at 5 mm intervals, while two-dimensional (2D) high-resolution (100 μm) images of smaller zones of the sediment profile were obtained on separate DGT probes. Removal of dissolved Cd, Cu, and Pb in BCZ sediments caused steep vertical gradients at the sediment-water interface that were well replicated in 1D profiles and 2D images. While 1D profiles showed apparent coincident maxima of Co, Mn, and Fe, 2D images revealed mutually exclusive Co and Fe mobilization. Correlation analysis supported this observation and showed a consistent linkage between Co and Mn. Sharp maxima of some metals in the vertical 1D profiles of GB sediment were attributed to localized mobilization in microniches. Examination of an ∼1 mm diameter Cu and Ni maximum in 2D, defined by ∼300 data points, showed that the metals were supplied from localized decomposition of reactive organic material, rather than from reductively dissolving Fe or Mn oxides, and that they were removed as their sulfides.

Polycyclic aromatic hydrocarbon (PAH) distribution in surface sediments from Yazhou Bay of Sanya, South China, and their source and risk assessment

The distribution, source, and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in surface sediments were analyzed and discussed at 15 sampling sites in Yazhou Bay, Sanya. Results showed that the total PAH content in the surface sediments of Yazhou Bay ranged from 13.20 ng/g to 40.37 ng/g, and the average content was 31.53 ng/g. Component analysis showed that the distribution of various PAHs in the surface sediments of Yazhou Bay was relatively average, and 3- and 4-ring PAHs were the dominant species. PAHs were traced by characteristic ratio method and principal component analysis. PAHs in the surface sediments mainly came from combustion sources, including incomplete combustion of petroleum, coal, and biomass, which also indicated the existence of petroleum sources. The ecological risk assessment results of surface sediments showed that, compared with effect range low and effect range median (ERM) of the ecological risk of 14 kinds of PAHs detected, no ecological risk existed for PAHs of all sampling sites in Yazhou Bay. The mean ERM quotient analysis also showed that PAHs in the sediments in Yazhou Bay were at a low risk level.

Physicochemical characteristics and spatial distribution pattern of the Yercaud Lake surface sediments, South India

Freshwater lakes and sediments need to be monitored continuously for environmental assessment and geochemical explorations. Lake sediments are major sinks for organic matter and for all geochemical elements. In the present study, total organic matter (TOC), nitrogen (TN), and geochemical analysis of major oxides was carried out on Yercaud Lake surface sediments, located at a higher elevation in South India to infer sediment distribution pattern and source for organic matter. Particle size distribution of lake surface sediments suggests that the sediments are predominantly silty sand and sandy silt, poorly to very poorly sorted and symmetrically skewed. TOC/TN ratio (6.54–12.65) reveal that the organic matter (OM) is derived from the in situ lake sources particularly from the vascular plants and lake biota accumulation. Weathering indices that fall from [chemical index of alteration (CIA)] 88.59–93.08 values and A‐CN‐K plot reflects intense chemical weathering of the bedrock exposures in the source area, which was accelerated under warmer and humid climate conditions in the sub‐tropical regions. Al2O3/TiO2 ratio (6.94–26.62) indicates weathering particularly of the exposed charnockite rocks around the lake basin.

Grain size distribution and chemistry of the brackish Lake sediment in Korea

To determine the grain size distribution and chemical characteristics of bottom surface sediments in shallow brackish lagoons, we studied sediment samples collected from the entire horizontal lake area and in vertical profiles from three stations in Lakes Youngrang and Hwajinpo, on the eastern coast of Korea. Vertical and horizontal grain size distributions of the bottom sediments indicated predominantly sand- and silt in both lakes. The vertical distribution of C/N ratios ranged from 6.14 to 11.92 in Lake Youngrang, and 6.74 to 12.34 in Lake Hwajinpo. The horizontal distribution of C/N ratios in Lake Youngrang ranged from 6.1 to 17.6, whereas they ranged from 4.4 to 12.1 in Lake Hwajinpo. C/N ratios showed locally different responses to the origin of allochthonous (partial region) and autochthonous (entire region) organic materials. Horizontally, bottom sediment with low δ&lt;sup&gt;13&lt;/sup&gt;C and high δ&lt;sup&gt;15&lt;/sup&gt;N in Lake Youngrang were likely to be influenced by autochthonous organic material derived from primary production, and would be affected by N inputs from sources. In contrast, high δ&lt;sup&gt;13&lt;/sup&gt;C and low δ&lt;sup&gt;15&lt;/sup&gt;N sediments in Lake Hwajinpo were likely to be influenced by cyanobacteria.

Interaction between seabed morphology and water mass in the South Eastern Arabian Sea: deductions of water mass flow

Geomorphic analysis utilizing multibeam bathymetry and sediment profiler data along with conductivity, temperature and depth (CTD) measurements was undertaken to investigate morphological aspects of bottom current features that prevail in the area. The aim of the study was to deduce the prevailing water mass in the area and to infer interactions between water mass and seabed of South Eastern Arabian Sea. Morphological and bottom current features were identified and analysed. Based on morphological components and their structural orientation, deduction of flow pattern and direction of current flow in the area were attempted. Deconstructing structural aspects of typical bottom current features such as contourite drifts and scours reveal origin under influence of consistent exogenic bottom current having definitive flow pattern. Sub-surface seismic profiles were analysed to infer the presence of a consistently aggrading seafloor. The aspect distribution computed exhibits a prominent trend ranging between 200° and 275° indicating NNW-SSE orientation of erosive features which is usually synonymous with flow direction in the area. Backscatter intensity analysis undertaken for the area revealed seafloor with patches of loose to compact surface sediment distribution. Variation in reflection intensity level from surface sediments was utilized to demarcate zones that are susceptible in future to consistent turbulence-induced erosion. Temperature salinity (TS) diagram for values from CTD measurements was plotted overlaying isopycnals and the resulting plots tagged for various water masses that prevail in the Arabian Sea. Owing to the depth of the study area (~ 1800 m) and structural orientation of bottom current features, dominant oceanographic agent from TS plot was deduced to be the North Indian Deep Water (NIDW). Surface and sub-surface morphology of existing features were interpreted for influence of bottom current action. Geomorphic analysis of seabed is an efficient method to understand the flow pattern and of prevailing water masses and can be applied as passive indicators of bottom current flow. This approach of deducing flow pattern and intensity of water mass movement by analysing morphology of the undersea features can be effectively used globally especially in areas where adequate data and observations for deep water masses are scarce.

Geological controls on dispersal and deposition of river flood sediments on the Hidaka shelf, Northern Japan

Abstract The distribution and characteristics of marine surface sediments are a basic marine geological information. Large river floods are a frequent natural hazard that transport substantial terrigenous sediments into the marine environment. In August 2003, TY ETAU (0310) caused heavy rainfall in the southern coast of Hokkaido, north Japan, where some mountainous rivers in the Hidaka region flooded. Two deposition modes for the 2003 flood sediments can be identified by comparing the pre- and post-flood surface sediment distribution. Shore-normal shallow depressions off the mouth of the Saru and Atsubetsu rivers served as channels for the discharged floodwater preventing dispersion and maintaining the necessary water density to transport the materials as density bottom currents. This action also promoted long-distance transport of flood materials across the continental shelf. Absence of depression on the inner shelf off the mouth of the Niikappu and Shizunai rivers may have dispersed floodwaters near the river mouth and deposited the flood materials close to the shore. Marine geological mapping suggests that the differences in submarine topography (the presence or absence of shallow depressions) are closely related to the regional geological structure. Thus, submarine geology is a controlling factor of the seafloor environments influenced by the river flood.

Pollen dispersal patterns in marine surface sediments from the San Jorge Gulf, SE Patagonia (Argentina)

This paper analyzes the distribution patterns of pollen and spore assemblages in modern surface sediments recovered from the bottom of the San Jorge Gulf (SJG) and from offshore sites, in relation to the location of different phytogeographic provinces surrounding the SJG, including the distant forest from southwestern Patagonia. Results reveal that pollen spectra are dominated by Chenopodiaceae-Amaranthaceae, Poaceae, Asteraceae subf. Asteroideae, Colliguaja integerrima and Ephedra sp.; which represents the vegetation adjacent to the SJG. Overall, the pollen distribution in surface sediments reflects the location of the different phytogeographic provinces and will be used as modern-analogues to document vegetation history around the SJG. Pollen assemblages also reveal the latitudinal variation of vegetation taxa in the Patagonian steppe, which is characterized by a slight increase in herbaceous pollen and a decrease in high shrubs (e.g. Colliguaja integerrima) towards the southern-central part of the SJG. Furthermore, we identified two pollen taxa from the southwestern Patagonian forest, Nothofagus and Podocarpus that could be used as indicators of past dynamics and variations of the Southern Westerly Wind Belt (SWWB) in the SJG during the Late Pleistocene and Holocene. High pollen concentrations are recorded at the central part of the SJG (480–8080 grains/g), while low concentrations are measured in the northern and southern parts of the Gulf, as well as at offshore sites (26–1806 grains/g). The pollen distribution in the study area is most likely governed by the SWWB in combination with the marine sediment composition and surface currents flowing through the SJG.

Seasonal and spatial variations in elemental distributions in surface sediments of Chilika Lake in response to change in salinity and grain size distribution

Chilika lake, the largest brackish water lagoon in Asia, has a unique setting, where the north-eastern part receives freshwater from the terrestrial runoff, and the south-eastern part receives seawater from the Bay of Bengal. The seasonal variability in the quantity of inflowing water and their mixing in the lake controls the mobilization and precipitation of various elements. Seasonal sediment samples were collected from both the river and seawater influenced regions of the lake to understand the spatio-seasonal distributions of various elements along the salinity gradient. The major elements present in the sediments are mostly derived from the parent rock weathering in the source region and subsequently transported into the lake by the rivers. Seasonal variations in trace element concentrations are more prominent in the north-eastern part of the lake (i.e., low salinity region), and their higher concentrations have been observed during the post-rainy period. The affinity of the elements (Al, Fe, Mn, Li, V, Co, Cr, Cu, Th, and Zn) towards fine-grain sediments suggests that the size distribution pattern controls their accumulation, retention, and remobilization. The concentrations of Cr, Cu, and Pb exceeded the effects range low, and effects range median benchmarks indicating the potential biological risk in the low salinity region as compared to the high salinity region. The statistical analysis indicated that the concentrations of elements in the region proximal to the sea mouth are controlled by grain size and physicochemical condition of the lake water. In contrast, the element concentrations in the interior region are associated with anthropogenic activities and weathering processes. Continuous monitoring and assessment of element concentrations of the lake sediments can help to protect the lake ecology from the harmful element contaminations.

Distribution and Characteristics of Sandy Sediments along the Northeastern Continental Shelf of Korea in the East Sea

Kim, S.-R.; Chun, J.-H.; Um, I.-K., and Cukur, D., 2020. Distribution and characteristics of sandy sediments along the northeastern continental shelf of Korea in the East Sea. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 532–536. Coconut Creek (Florida), ISSN 0749-0208.In this study, the distribution and provenance of sandy surface sediments were investigated along the northeastern continental shelf of Korea. A total of 154 surface sediment samples from river, beach, continental shelf and shelf edge substrates were collected and analyzed for their grain size and mineral composition. Coarse-grained sandy sediments (mean grain size, –1.3 to 1.0 φ) showed that the inner shelf and shelf break were clearly separated by outer shelf silt sediment (mean grain size, ∼5 φ). The mineral composition of continental shelf sandy sediments differed between Gangneung and Donghae sites. Sandy sediments from Gangneung site consist mainly of quartz, feldspar, and mica, whereas those from Donghae site are composed chiefly of opaque minerals, including quartz and feldspar. Differences in mineral composition between the Gangneung and Donghae sites reflect the influence of geology on land. Sandy sediments were supplied directly to shelf edges during the low stand by small rivers, and not mixed by coastal currents.

Grain-Size Distribution of Surface Sediments in the Bohai Sea and the Northern Yellow Sea: Sediment Supply and Hydrodynamics

The grain-size distribution of surface sediments in the Bohai Sea (BS) and the northern Yellow Sea (NYS), and its relationship with sediment supply and hydrodynamic environment were investigated based on grain-size compositions of surface sediments and modern sedimentation rates. The results showed that the surface sediments in the BS and the NYS were primarily composed of silty sand and clayey silt with a dominant size of silt. In addition, the Yellow River delivered high amount of water and sediments to the BS, and they are dominated in surface sediments (mainly silt) in the Bohai Bay, the Yellow River mouth, the center of the BS, and the north coast of Shandong Peninsula. The coarse-grained sediments were mainly deposited at the river mouth due to the estuarine filtration and physical sorting. Meanwhile, there was a significant relationship among the modern sedimentation rate, the surface sediment grain size distribution and sediment transport pattern. The areas with coarser surface sediments generally corresponded low sedimentation rates because of strong erosion; whereas the sedimentation rate was relatively high at the place that the surface sediments were fine-grained. Furthermore, the grain-size trend analysis showed that the areas with fine-grained surface sediments such as the mud area in the central BS and the upper Liaodong Bay were the convergent centers of surface sediments, except for the Bohai Bay and the subaqueous Yellow River Delta where offshore sediment transport was evident.

A review on the study of transports of runoff-sediment-pollutant systems on urban surfaces

As a complex three-phase particle flow and the main carrier of non-point pollution, the coordinated transport processes and environmental effects of the runoff-sediment- pollutant systems on urban surfaces are very complicated. In this paper, the existing research on the transports of runoff-sediment-pollutant systems is summarized and analyzed from the perspectives of, the spatial-temporal distribution of urban surface sediment with absorbed pollutants, the hydrodynamic characteristics and simulation methods of urban surface rainfall-runoff, as well as the coordinated transport and reduction effects of runoff-sediment-pollutant systems. It is considered that the sediment dynamics theory can be used to study the urban surface sediment movement law during the rainfall-runoff process, and that the sediment deposition plays an important role in the reduction of particle pollutants due to the absorption effect. Finally, the following research actions should be carried out in the future: enlarging urban sample size; studying on dynamic characteristics of overland flow on different underlying surface; studying on incipient motion law for non-uniform sediment on urban surfaces, as well as sediment transport capacity for overland flow based on flow power theory.

Particle size characteristics of surface sediments and their environmental significance: a comparative study of deserts in arid western Inner Mongolia, China

Based on the analysis of particle size mechanical composition and parameter distribution of surface sediments in the Hobq Desert (HD), the Ulan Buh Desert (UBD) and the northern part of the Mu Us Desert (MUD) in western Inner Mongolia, and combining the sedimentary environment discrimination method and the particle size lognormal fitting method, this research compares and explores the particle size characteristics and the significance of sensitive components in the sedimentary environment to the provenance in the three deserts. The results are shown as follows: (1) Sediment samples in the HD are dominated by fine sand (48.9%), in the UBD by fine sand and medium sand (41.10% and 42.90%, respectively) and in the MUD by medium sand (41.62%). (2) $$\sigma_{1}$$ and $$S_{K1}$$ in the HD and the UBD are well sorted and symmetric, but are averagely sorted and show highly positive skewness in the MUD. (3) The sediment samples in the HD and the UBD are mainly aeolian sediments, with lacustrine sediments being secondary. By contrast, the sediment samples in MUD is largely made up of lacustrine deposits. (4) By fitting the particle size frequency curves of all samples, five components, namely C1, C2, C3, C4 and C5 ranging from fineness to coarseness, are obtained. It is also indicated that the sediments in the study area do not undergo a wide range of mixing, but mainly experience in situ sedimentation. The most of these sediments may belong to lakeshore deposits that have been modified by wind for a long time, and are accompanied by long-distance westerly dust, weathered debris from bedrock, and active paleosand dunes of riverbed sediments.

Grain-Size Distribution of Surface Sediments in the Chanthaburi Coast, Thailand and Implications for the Sedimentary Dynamic Environment

This paper analyzes the grain-size distribution of surface sediments of the Chanthaburi coast of Thailand to investigate the sedimentary environment and its evolution to better use and protect the coast. The Flemming triangle method, the grade-standard deviation method, and the Gao–Collins grain-size trend analysis method (GSTA model) were used to study the dynamic sedimentary environment of the area and provide preliminary identification of source materials. There are seven types of surface sediments on this coast, with grain sizes (φ) generally consisting of sand and silt. Sorting is generally poor, and becomes gradually poorer with distance offshore. Skewness is generally positive. The study area is mainly composed of sand and silt, indicating that the hydrodynamics are strong. The results of grade-standard deviation analysis indicate that sediment grain size b (3.25–4.5φ) is a sensitive indicator of environmental change. This sediment type exhibits a relatively complex transport trend, mainly characterized by northwestward and northeastward transport from sea to land. Sediments at the mouth of the Chanthaburi Estuary and the Welu River fluctuate under the influence of tidal currents. Based on the results of grade-standard deviation analysis and grain-size trend analysis, the study area was divided into three provinces, representing different sedimentary environments and material sources. Compared with tidal-controlled estuaries in the temperate regions of eastern China, the two tropical estuaries examined in this study exhibited smaller suspended sediment loads, runoff amounts, and tidal ranges. However, hydrodynamic conditions were generally stronger. The main reasons for the similarities and differences in the transport trends of sediments in these estuaries were differences in hydrodynamic conditions and the specifics of regional topography.

Clay minerals and organic matter in shelf sediments off Coromandel Coast of India: Implications for provenance, transportation and depositional processes

Surface sediments collected from 25 stations in the Bay of Bengal were analyzed for grain size, organic matter and clay minerals to understand the spatial distribution, transport pathways, depositional process and provenance of the marine sediments. Granulometric analysis reveals the decreasing trend of grain size with increasing depth from coast to offshore region. The predominance of sandy sediments at shallower region represents their terrigenous origin and prevalence of high energy condition. The sediments from 50-100 m water depth are found to contain higher concentration of organic matter (TOC, TN and Sulfur) suggesting the high productivity zone. The C/N value ranges from 4 to 8 in 52% of sediments which indicates the source of both marine and terrestrial inputs. And 36% of sediment having C/N ratio <4 denotes that they are mainly derived from a marine source of phytoplankton and zooplankton remain and faeces while 12% of sediments C/N ratio ranges from 8 to 14 which suggests terrestrial organic matter input through local riverine systems. The C/S ratio of samples varies from 0.57 to 4.69 with mean value of 2.47 indicates the prevalence of semi-anoxic to anoxic marine conditions. The positive correlation of mud with TOC and sulfur denotes that their distribution is mainly controlled by finer fractions of sediments. Illite, Kaolinite and Smectite are the dominant clay minerals in the order of abundance occurring in the study area, which indicates the terrestrial sources. High amount of illite and kaolinte in the study area is influenced by Pennar River which drains through Archean granites, charnockites, khondalites suites of rock formations and Nellore pegmatites. The abundance of smectite in the study area is mainly from Deccan basalts by Krishna River and also from Cuddapah basin by Pennar River. In the study area, the clay minerals, organic carbon, nitrogen and sulfur distribution in surface sediments are chiefly controlled by the provenance and currents.

Speciation of heavy metals and their distribution in surface sediments of the northwestern part of the ROPME Sea Area

Speciation of heavy metals and their distribution in surface sediments of the northwestern part of the ROPME Sea Area

Links between surface sediment composition, morphometry and hydrodynamics in a large shallow coastal lagoon

This study addresses the surface sediment composition and distribution in Mirim Lagoon, a large coastal shallow transboundary system located on the border of South Brazil and Uruguay, which is 3749 km2 and maximum depth is around 6 m, in relation to the hydrodynamic conditions evolved from predominant winds. Surface water currents in the marginal area displayed maximum speed values of 0.25 to 0.3 m s−1 flowing parallel to the coastline either under NE of SW wind predominance. The marginal zone, above the 6 m bathymetric contour comprise sandy sediments, indicating that under such a combination of bathymetric and hydrodynamic conditions, the resuspension of fine sediments is dominant. Lower surface current velocity observed in the central zone of the lagoon located below the 6 m isobath (i.e., 0.05 m s−1), together with an increase in the maximum width of the lagoon, promoted conditions for deposition of the clay sediment fraction. Therefore, the combined use of sedimentological and hydrodynamic data represents a useful tool to infer patterns of deposition and resuspension in coastal systems. Given the large size of the Mirim Lagoon and associated difficulties in sampling and monitoring the system, the information presented here is important for environmental management, and particularly for planning future paleolimnological research and set the coring stations on appropriate coordinates within the central region, where relatively calm conditions and dominance of clay sediments are observed.