Composition Of Surface Sediments Research Articles

Clay mineral composition and transport pattern of surface sediments in the Ganges Submarine Delta

The Ganges Submarine Delta is a key land-sea transitional area in the northeastern Indian Ocean. An understanding of sediment distribution, provenance, and transportation in this area is of great importance for understanding its sedimentary environment and the sediment “source-sink” system of the northeastern Indian Ocean. This study aimed to identify the provenances and transport patterns of fine-grained sediments in the Ganges Submarine Delta through analysis of the grain size and clay mineral content of 84 surface sediment samples. Sediment illite, chlorite, kaolinite, and smectite contents were ∼66%, 18%, 11%, and 5%, respectively. Sediment illite content decreased from north to south; smectite and chlorite decreased and increased from northwest to southeast, respectively; kaolinite content was highest in the south. Spatial cluster analysis of the four clay minerals grouped the study area into two provinces: province I in the north is characterized by a clay mineral assemblage similar to that of the Ganges-Brahmaputra rivers; province II in the south is characterized by deep water and changes to clay mineral characteristics due to the mixing of material originating from the Indian Peninsula. This study used the illite/(smectite+chlorite+kaolinite) and kaolinite/illite ratios to discuss sediment transport paths in the two provinces. Himalayan material is widely distributed throughout the study area, and mainly transported from the estuary to the southwestern area by the tides, plume, and monsoons; sediments of the Mahanadi river are transported from southwest to northeast by the southwest monsoon, thereby affecting the sediment composition of province II.

Source apportionment of organic carbon and nitrogen in sediments from river and lake in the highly urbanized Changjiang Delta

While the impact of human activities on organic matter pollution is recognized, how these impacts vary seasonally in the Changjiang Delta needs further investigation. This study addresses this gap by investigating seasonal variations in organic matter sources and ecological responses to human activities in Changjiang Delta sediments. Total organic carbon (TOC), total nitrogen (TN), and carbon (δ13C) and nitrogen (δ15N) isotopic compositions of surface sediments collected from the Taipu River and Dalian Lake wetland were analyzed. Both water bodies exhibited similar seasonal trends for TOC and TN, with the Taipu River containing an average of 0.46% and 0.03% higher concentrations of TOC and TN, respectively, compared to Dalian Lake. Additionally, the organic index (OI) and organic nitrogen (ON) index were elevated in both water bodies during the wet season. Sediments from Dalian Lake remained uncontaminated to moderately contaminated, while those from the Taipu River were generally classified as moderately to heavily contaminated. Stable isotope analysis identified terrestrial C3 plants (averaging 25.5%), C4 plants (averaging 16.0%), and municipal wastewater (averaging 16.0%) as the main contributors to organic matter in the sediments. These findings suggest that terrestrial plant material and municipal wastewater are key targets for managing organic matter contamination in the Changjiang Delta. Implementing strategic land-use planning and targeted interventions to minimize these inputs can significantly improve water quality and ecosystem health.

Elemental composition of smectite minerals in continental rise sediments from the Amundsen Sea, West Antarctica, as a tool to identify detrital input from various sources throughout late Quaternary glacial-interglacial cycles

Detrital smectite is a ubiquitous clay mineral in marine sediments and has a variable total Fe, Al, and Mg composition depending on the source, i.e., bedrock or unconsolidated sedimentary strata, the smectite is derived from. Analyses of elemental composition of smectite minerals in marine sediments can help to differentiate the smectite sources and, thus, sediment provenance, with potentially far-reaching paleo-environmental implications. In this study, we investigated the smectite compositions of modern-latest Holocene seafloor surface sediments deposited offshore from the Amundsen Sea drainage sector, where the West Antarctic Ice Sheet is currently unstable and losing mass due to ocean-forced melting, to detect and understand the variabilities of their elemental composition and geographical distribution. The smectite composition in continental rise sediments was compared to that of potential source areas on the Amundsen Sea continental shelf and in the sub-Antarctic South Pacific basin. Furthermore, we analyzed the smectite composition of sediments in continental rise cores deposited during the last glacial and last interglacial periods to reconstruct source variations over glacial-interglacial cycles. In particular, high contents of Al–Fe-rich smectite indicate that the glacial sediments had been supplied from the coastal region around Pine Island Bay by the cross-shelf advance of the West Antarctic Ice Sheet during the last glacial period. This clearly contrasts with the smectite minerals in rise sediments deposited during the present and the last interglacial periods that are composed of two distinct smectite types (Mg-rich and Al-rich, respectively), indicating their supply from multiple sources. During interglacials, Mg-rich smectite is probably transported by Circumpolar Deep Water from the sub-Antarctic South Pacific basin to the continental rise, while Al-rich smectite is supplied as part of ice rafted debris and by marine currents from the coasts around the Amundsen Sea embayment. Our research demonstrates that analysis of the elemental composition of smectite minerals on the Amundsen Sea continental margin provides a valuable tool to trace variations in sources for detrital sediment components and their pathways throughout glacial-interglacial cycles.

Microplastics abundance, distribution and composition in surface waters, sediments and fish species from Amir-Kalayeh Wetland, Northern Iran.

Microplastics (MPs) pollution is considered as a globally pervasive threat to aquatic ecosystems and many studies reported this pollution in different aquatic ecosystems. However, studies on MPs pollution in wetlands are still scarce. Therefore, the aim of present study was to investigate the presence of MPs in the surface water, sediment and different fish species of Amir-Kalayeh wetland, Northern Ian. Surface water and sediment samples were collected from six stations during June to July 2022. Moreover, the gills and gastrointestinal tract (GIT) of 54 fish specimens belonging to four species including Cyprinus carpio, Tinca tinca, Esox lucius and Silurus glanis were analysed. MPs were detected in all samples with an average of 2.15 ± 1.98 items/m3 for surface water, 51.66 ± 32.20 items/kg dry weight for sediments, 0.17 ± 0.17 items/individual for fish GIT and 0.12 ± 0.12 items/individual for fish gills. There was no significant relationship between MPs abundance in surface waters and sediments as well as between MPs abundance in environmental matrices and fish (P > 0.0.5). In terms of feeding habit, no significant differences were observed between the number of MPs found in omnivorous and carnivorous fish species (P > 0.05). Moreover, no significant relationship was detected between the MPs abundance in fish tissues and body size (P > 0.05). MPs were mainly fibers, mostly transparent, and in a range size of 70-5000 µm. The dominant MPs type was nylon in all samples. This study will help increase our knowledge about MPs pollution in inland freshwater systems and suggests that management policies take essential steps to reduce this insidious problem in freshwater ecosystems.

First Pediastrum–temperature transfer function and its application to mid-to-late Holocene reconstruction in Central Asia

The green alga Pediastrum is an ecologically significant component of freshwater ecosystems, but its potential as an independent proxy for quantitative paleoenvironmental reconstruction is relatively unexplored. Here we use multivariate statistical analysis to explore the relationship between the Pediastrum composition of lake surface sediments and environmental variables. The findings highlight the mean growing season air temperature between March and October (TMar-Oct) as the most important factor determining the Pediastrum composition. We then establish the first transfer function between the Pediastrum taxa and TMar-Oct, which enables us to provide a quantitative temperature reconstruction for the past ∼8.2 kyr based on sedimentary subfossil Pediastrum records from Bosten Lake in Xinjiang, China. Our findings reveal an exceptionally warm climate during ∼4.8–3.6 kyr, with temperatures ∼4 °C higher compared to those during ∼8.2–4.8 kyr. This unusually warm climate is verified by the carbonate clumped isotopes record of the same core and other paleoclimate records. These findings contribute to our understanding of past temperature changes in Central Asia and provide a basis for future research on long-term lake ecosystem dynamics under past climatic warming.

Grain-size, coarse fraction lithology and clay mineral compositions of surface sediments from Ross Sea, Antarctica: implications for their provenance and delivery mode

Knowledge on spatial distribution, provenance and delivery mode of surface sediment aids in interpretation of nearby sediment records for paleoenvironmental reconstruction. Such knowledge, however, remains largely unknown for the modern Ross Sea, Antarctica: a key region for understanding the dynamical behavior of Antarctic Ice Sheet over geological past. In this study, we address this gap by analyzing the grain-size distribution, coarse fraction (>250 μm) lithology, and clay mineralogy of a set of surface sediment samples covering the whole Ross Sea continental shelf. Our data reveals that the sediments were mostly delivered by icebergs and bottom currents. Iceberg delivery was significantly controlled by factors such as water depth, proximity to the iceberg sources, and invasion of the Modified Circumpolar Deep Water. Bottom current activity was stronger in the Western Ross Sea (WRS) than in the Eastern Ross Sea (ERS), controlled by the formation and transport of Dense Shelf Water. Three major sorts of coarse fraction were identified, including the quartz-rich Iceberg Rafted Detritus (IRD) originating from West Antarctic glaciers and primarily distributed in the ERS, the mafic rocks-rich IRD from the Ferrar Group as well as the McMurdo Volcanic Group and mainly found in the WRS, and deformed silt traced back to the grounding zone of the David Glacier-Dragalski Ice Tongue system. The distribution of clay minerals is dominated by a distinct binary mixing pattern. Smectite and kaolinite are mainly present in the ERS, derived from beneath the West Antarctic Ice Sheet. Higher illite and chlorite contents were found offshore of the Southern Victoria Land, derived from the East Antarctic craton. Overall, these results demonstrate that the glaciers draining into Ross Sea from both the East and West Antarctic Ice Sheets are highly dynamical in the context of modern climate conditions, with implications for potential contribution to future sea level rise.

Chemical composition of marine surface sediments around Tokara Islands (GB21-2 and 21-3 Cruise), Japan

Chemical composition of marine surface sediments around Tokara Islands (GB21-2 and 21-3 Cruise), Japan

Chemodiversity of riverine dissolved organic matter: Effects of local environments and watershed characteristics

Riverine dissolved organic matter (DOM) is crucial to global carbon cycling and aquatic ecosystems. However, the geographical patterns and environmental drivers of DOM chemodiversity remain elusive especially in the waters and sediments of continental rivers. Here, we systematically analyzed DOM molecular diversity and composition in surface waters and sediments across 97 broadly distributed rivers using data from the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) consortium. We further examined the associations of molecular richness and composition with geographical, climatic, physicochemical variables, as well as the watershed characteristics. We found that molecular richness significantly decreased toward higher latitudes, but only in sediments (r = -0.24, p < 0.001). The environmental variables like precipitation and non-purgeable organic carbon showed strong associations with DOM molecular richness and composition. Interestingly, we identified that less-documented factors like watershed characteristics were also related to DOM molecular richness and composition. For instance, DOM molecular richness was positively correlated with the soil sand fraction for waters, while with the percentage of forest for sediments. Importantly, the effects of watershed characteristics on DOM molecular richness and composition were generally stronger in waters than sediments. This phenomenon was further supported by the fact that 11 out of 13 watershed characteristics (e.g., the percentages of impervious area and cropland) showed more positive than negative correlations with molecular abundance especially in waters. As the percentage of forest increased, there was a continuous accumulation of the compounds with higher molecular weight, aromaticity, and degree of unsaturation. In contrast, human activities accumulated the compounds with lower molecular weight and oxygenation, and higher bioavailability. Our findings imply that it may be possible to use a small set of broadly available data types to predict DOM molecular richness and composition across diverse river systems. Elucidation of mechanisms underlying these relationships will provide further enhancements to such predictions, especially when extrapolating to unsampled systems.

Clay mineral assemblages of late Holocene turbidites in the Gaoping Submarine Canyon of the northeastern South China Sea and their responses to typhoon activities

Submarine canyons are the principal conduits for turbidity currents transporting sediments to the deep sea. Thus, turbidites, as sedimentary products of turbidity currents, can be used to trace sediment sources and transport processes and to reconstruct mechanisms of turbidity currents in submarine canyons during the geological past. Herein, clay mineral assemblage of late Holocene turbidites at Core MD18–3565 in the Gaoping Submarine Canyon is investigated to reveal the triggering mechanisms of turbidity currents. High-resolution grain-size analysis of typical coarse-grained layers characterized by basal erosion surface and fining-upward sequence in the core verifies their turbidity current origin. A total number of 318 such turbidite layers, covering ∼30% of the total thickness (19.68 m) of the core, are recognized in the late Holocene sediments (33–3954 cal yr BP). Clay mineral assemblage of the turbidites is composed mainly of illite (52–60%) and chlorite (35–45%), with small quantities of smectite (0–5%) and kaolinite (0–4%), while clay mineral assemblage of the non-turbidite sediments (hemipelagites) is composed of approximately the same contents of illite (51–62%) and chlorite (34–43%), but with slightly higher smectite (0–10%) and kaolinite (1–6%). Despite the small differences in smectite and kaolinite contents, the provenance analysis identifies the Gaoping river as the predominant source of sediments in the turbidite layers, while the hemipelagite layers receive small amounts of sediments from the neighboring Erhjen, Tsengwen, and Pachang rivers besides the Gaoping river in southwest Taiwan. In combination with clay mineral compositions of surface sediments in the adjacent continental shelf and slope, as well as in-situ observational results by subaqueous moorings, we believe that the turbidity currents, in which the Gaoping river directly supplied clay minerals to the submarine canyon to form the turbidites, have been triggered mainly by typhoons passing through Taiwan. The frequency of turbidites generally keeps pace with long-term variations of El Niño-Southern Oscillation (ENSO) events, implying the potential modulation of ENSO on occurrences of late Holocene typhoon activities in the Western Pacific.

Comparison Study on Sedimentomorphological Characteristics Using Integrated Geo-Techniques: A Case Study of Two Representative Areas in Kuwait

Intensive aeolian processes occur due to the scarcity of rainfall and lack of vegetation cover in arid regions. The study of recent surface sediments in arid areas is important for environmental assessments, evaluation of natural resources, and land use planning. In this study, two areas were chosen as they show changes in lithology, environment and landforms. The two study areas are Al-Rawdatain in the northern part, and Al-Managish in the southern part of Kuwait. The current study aims to define the sedimentomorphic zones in these areas, with an emphasis on Quaternary geomorphological evolution by providing an integrated approach based on satellite images, topographic maps, field measurements, and laboratory analysis. Remote sensing data were spatially analyzed to classify and detect the temporal changes in the surface sediments and geomorphology based on the field measurements (n = 42) as ground truthing points for supervising the classification. Samples from both areas were collected and subjected to grain size (dry mechanical sieving) and X-Ray Diffraction (XRD) analysis. The resulting data were statistically analyzed for grain size distributions and mineralogy based on the US standard set of sieves. The study found that the Aeolian sand sheet deposits are the most frequent recent surface deposits in Kuwait and cover most of the other sediments. The direction of movement of the sand sheets is from NW towards SE. The mineralogical composition of the aeolian recent surface sediments revealed that they are mostly derived from the Dibdibba Formation and Tigris-Euphrates fluvial terrace deposits. Quartz is the most frequent component of the studied surface sediments in the study areas (66%). The calcite mineral is also found in subordinate amounts in the study areas (10%).

Chemical composition of marine surface sediments around Tokara Islands (GB21-1 Cruise), Japan

Chemical composition of marine surface sediments around Tokara Islands (GB21-1 Cruise), Japan

Changes of organic matter composition in surface sediments from the Pearl River estuary to the coastal South China Sea revealed by rapid molecular screening using FTICR-MS

The Pearl River drains the second largest watershed in China, funnelling large amounts of freshwater and organic matter into the northern part of the South China Sea through an estuary characterized by pronounced biogeochemical gradients. In this study we used a newly developed single injection Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) method to analyze organic extracts of surface sediments transitioning from freshwater to marine settings in the Pearl River estuary and coastal South China Sea. Results show a complex mixture of molecular markers, with distinct fingerprints characterizing the freshwater and saline sites. Notable examples include steroidal and thiophenic species at the freshwater site, indicative of possible anthropogenic organic matter inputs from the continent; on the other hand, samples from the coastal site are uniquely characterized by putative tetrapyrrole species, indicative of phaeopigments sourced from marine phytoplankton. This study demonstrates the potential application of single injection FTICR-MS in rapidly probing the dynamic changes of organic matter sources and fates occurring in estuaries influenced by anthropogenic activities.

Bacterial diversity in surface sediments of collapsed lakes in Huaibei, China

The collapse lake area due to coal mining in Huaibei shows high biodiversity, but the bacterial community composition and diversity in the lake sediments are still rarely studied. Therefore, based on 16S rRNA high-throughput sequencing and combined with analysis of environmental factors, we comparatively analyzed the bacterial community composition and diversity of surface sediments from East Lake (DH) and South Lake (NH) and Middle Lake (ZH) in the collapse lake area of Huaibei. The bacterial community compositions are significantly different in the sediments among Huaibei collapsed lakes, with DH having the largest number of species, and NH having a higher species diversity. Pseudomonadota is the most abundant phylum in the sediments of DH and NH, while the most abundant phyla in ZH are Bacteroidales, Chloroflexales, Acidobacteriales, and Firmicutes. Anaerolineae (24.05% ± 0.20%) is the most abundant class in the DH sediments, and Gammaproteobacteria (25.94% ± 0.40%) dominates the NH sediments, Bacteroidia (32.12% ± 1.32%) and Clostridia (21.98% ± 0.90%) contribute more than 50% to the bacteria in the sediments of ZH. Redundancy analysis (RDA) shows that pH, TN, and TP are the main environmental factors affecting the bacterial community composition in the sediments of the collapsed lake area. The results reveal the bacterial community composition and biodiversity in the sediments of the Huaibei coal mining collapsed lakes, and provide new insights for the subsequent ecological conservation and restoration of the coal mining collapsed lakes.

Toxic metal pollution of aquatic ecosystems of European Union nature protection areas in a region of intensive agriculture (Lake Gopło, Poland)

The paper presents the results of research into toxic metal concentrations in the surface layer of bottom sediments in Lake Gopło. The research objectives were to identify the levels and spatial variability of Cu, Pb, Cd, Zn, Ni, Cr, As and Hg concentrations, their potential sources and the determinants of pollution levels. Metal contamination of the sediments was assessed using the geoaccumulation index (Igeo), pollution load index (PLI) and ecological risk index (RI). Chemometric methods (Pearson correlation, principal component analysis (PCA) and cluster analysis (CA) were used to determine the relationship between sampling sites and concentrations of toxic metals, thereby identifying the sources of contamination. The research found that grain-size composition, carbonate content and organic matter content in the bottom surface sediments of Lake Gopło are all characterised by low diversity. Therefore, the lithological features of the sediments are not a major factor in the concentrations and spatial variability of the metals. It was found that the metal concentrations in the great majority of samples were above regional geochemical background levels. The geochemical indices (Igeo, PLI, RI) indicate that the degree of toxic metal pollution in the sediments is slight in the central and southern parts of the lake and high in the northern part. The chemical analysis results showed that the samples in the central and southern parts of the lake differ little in their shares and concentrations of individual metals. This provides evidence that, as well as geogenic sources, their presence in sediments can be associated with non-point sources related to agricultural activities and with atmospheric sources (mainly the products of fossil fuel combustion). The higher concentrations of metals (especially Ni, Cd, Cr and Hg) in the northern part of the lake are influenced by the supply of industrial and communal pollutants from the lakeside town of Kruszwica. A factor limiting the migration of pollutants from the northern part of the lake towards the south is the lake’s morphology of the lake, which hinders water exchange between the northern part and the rest of the lake.

Surface sediment composition and depositional environments in tropical Lake Sentani, Papua Province, Indonesia

Tropical Lake Sentani in the Indonesian Province Papua consists of four separate basins and is surrounded by a catchment with a very diverse geology. We characterized the surface sediment (upper 5 cm) of the lake’s four sub-basins based on multivariate statistical analyses (principal component analysis, hierarchical clustering) of major element compositions obtained by X-ray fluorescence scanning. Three types of sediment are identified based on distinct compositional differences between rivers, shallow/proximal and deep/distal lake sediments. The different sediment types are mainly characterized by the correlation of elements associated with redox processes (S, Mn, Fe), carbonates (Ca), and detrital input (Ti, Al, Si, K) derived by river discharge. The relatively coarse-grained river sediments mainly derive form the mafic catchment geology and contribution of the limestone catchment geology is only limited. Correlation of redox sensitive and detrital elements are used to reveal oxidation conditions, and indicate oxic conditions in river samples and reducing conditions for lake sediments. Organic carbon (TOC) generally correlates with redox sensitive elements, although a correlation between TOC and individual elements change strongly between the three sediment types. Pyrite is the quantitatively dominant reduced sulfur mineral, monosulfides only reach appreciable concentrations in samples from rivers draining mafic and ultramafic catchments. Our study shows large spatial heterogeneity within the lake’s sub-basins that is mainly caused by catchment geology and topography, river runoff as well as the bathymetry and the depth of the oxycline. We show that knowledge about lateral heterogeneity is crucial for understanding the geochemical and sedimentological variations recorded by these sediments. The highly variable conditions make Lake Sentani a natural laboratory, with its different sub-basins representing different depositional environments under identical tropical climate conditions.

Geochemical Composition of Surface Sediments in the Bashang Area, North China and its Environmental Significance

The geochemical characteristics of sediments are important for reconstructing paleoclimatic and paleoenvironmental conditions in the Asian summer monsoon marginal area. However, robust reconstructions require an understanding of the key factors and mechanisms governing the spatial variations in the composition and ratio of chemical elements in the modern sediments of the Asian summer monsoon marginal area. In this study, 128 surface sediment samples were collected from the Bashang area, which is situated in the Asian summer monsoon marginal area, and examined for their major and trace element compositions and grain size. Principal component analysis (PCA) and redundancy analysis (RDA) were used to analyse the relationship between geochemical data and modern temperature and precipitation data. The results showed that the CIA values of sediments in the Bashang area are mainly affected by temperature rather than precipitation and the Rb/Sr value in the study area reflects the level of precipitation in the corresponding period and the temperature controlling the leaching and weathering. In addition, SiO2/Al2O3 and Zr/Ti ratios have good positive relationships with the coarse-grained fraction of sediments and thus can be used as grain size proxies. We propose that the exact environmental significance indicated by these proxies should be stated explicitly before using them as proxies for paleoenvironmental reconstructions of the Asian summer monsoon marginal area.

Micromorphological and mineralogical features of saline playa surface sediments from two large Trans-Uralian lakes

The proposed paper is devoted to the features of mineralogical composition and microstructure of saline playa surface sediments from two large drainless lakes in the south west of Western Siberia. The material composing the surface sediments of both playas is an unlithified mixture of clay and sand, with a significant admixture of organic matter. Coarse material is represented mainly by quartz, with an insignificant admixture of feldspar grains and micaceous fragments. In general, terrigenous component is characterized by a comparatively low degree of sorting. Clay material is scarce and composed, presumably of chlorite-hydromica material with a significant admixture of undecomposed organic matter, and traces of ferruginization. Carbonates and evaporates are the most common authigenic minerals. In both cases carbonates occur as microconcretions that correspond to the zone enriched with cysts, plant detritus and other degrading organic matter. Evaporates occur both as the efflorescence on the surfaces of the crusts. The study results have shown that surface crusts contain zones enriched with Artemia salina cysts, which are a significant component of sediments. Degrading crusts promote secondary mineral formation, especially formation of carbonates. Surface crusts of two studied playa environments differ in proportion of terrigenous material, clay minerals, as well as the composition of evaporates and carbonates.

Effects of river inputs on particulate organic matter composition and distributions in surface waters and sediments of the Mersin Bay, Northeastern Mediterranean Sea

Terrestrial inputs-induced eutrophication in the P-depleted Northeastern (NE) Mediterranean shelf waters has led to changes in particulate organic matter (POM) composition and distributions in the water column and surface sediments. The present study aimed to understand the impacts of terrestrial nutrient and POM inputs on coastal eutrophication, bulk POM composition and concentrations in surface waters and sediments of the Mersin Bay, located at the Cilician Basin of NE Mediterranean Sea. The present results showed that the regional rivers and wastewater discharges markedly increased nutrient concentrations, leading to enhanced eutrophication and POM concentrations surface waters of the Mersin inner bay. The C/N and C/P molar ratios derived from the regressions of POM data in surface waters were 6.92 and 129, respectively. The higher C/N and C/P molar ratios in the surface sediments of productive Mersin Bay indicated selective decay of N, P-containing organic matter buried in muddy sediments. Close positive correlations were found in sediment organic matter and mud contents, indicating the crucial role of fine particles in transport and enrichment of organic matter in the muddy shelf sediments of NE Mediterranean Sea.

Spatial distributions and risk assessment of heavy metals and PAH in the southwestern Nigeria coastal water and estuaries, Gulf of Guinea

Spatial distributions and risk assessment of heavy metals (HM) and polycyclic aromatic hydrocarbon (PAH) in water and sediments of two southwestern Nigeria estuaries (Awoye A1-A6 and Abereke: AB1-AB7 and the adjoining coastal waters: I1–I12, C1–C7) were investigated. The physicochemical characteristics were measured in situ, while the HM and PAH were determined using atomic absorption spectrophotometer and gas chromatography coupled with flame ionization detection. The physicochemical characteristics of the water body were within the World Health Organization and United State Environmental Protection Agency stipulated limits for coastal water, except for pH (<6) and dissolved oxygen (<5 mg/l) attributed to a high level of human activities at the impacted stations (I1–I12). The HM in the water samples were within the permissible limits for coastal water bodies except for high Pb values (>1 mg/l) at the Awoye estuary linked to point source effluents of petroleum spills from downstream petroleum transportation. The calculated sediment contamination factor (CF) for HM indicated a considerable (3 < CF < 6) contamination of Cu (CF–Cu) at the sampling stations. Whereas the CF-Cr were within the moderate contamination range (1< CF < 3). The pollution load index (PLI) and ecological risk index (RI) suggest low-risk pollution of heavy metals to the aquatic ecosystems. The assessment of PAH revealed a dominant high molecular weight PAH composition in both surface water and sediments, mainly dominated by 4–6 rings PAH. The PAH diagnostic ratio BaA/(Ba + Chry) and IP/(IP + BghiP) points to the mixed (pyrogenic and petrogenic) origin of PAH across the two tropical estuaries and the coastal waters.

A high-altitude calibration set of modern biotic proxies from the Western Himalaya, India: Pollen–vegetation relation, anthropogenic and palaeoclimatic implications

We analysed the pollen composition, non-pollen palynomorphs (NPPs) and stable carbon isotope data (δ13C values) of surface sediments (soil), from the proglacial deposits (outwash plain and the two levels of kame-terraces) of the Chorabari Glacier, Kedarnath, India. The main objective was to develop the modern-proxy analogues, for the calibration of fossil records, for use in palaeoclimatic reconstructions. The pollen–vegetation relation is incompatible (non-linear) with the present vegetation, as the pollen assemblages are marked by the prolific over-representation of extra-local pollen, especially Pinus, over the local herbaceous taxa. Multivariate principal component analysis (PCA) was applied on the palynological data to ascertain the major groups of pollen in relation to the vegetation types and reveal variations in the pollen records between the kame-terraces and the outwash plain. δ13C values of the soil organic matter (SOM) show an average of − 27.0‰, indicating a C3 dominant vegetation. The pollen records have also revealed the anthropogenic activities in the form of degradation of tree-line and over-grazing by the domesticated animals. The NPPs reflect the prevalence of grazers in the present times, and would be useful in tracing the advent and intensification of grazing in the region. The modern pollen analogues show a good correlation with the fossil pollen data. The present study provides the much needed modern biotic analogues for vegetation-based past climatic reconstructions from the alpine regions of the Western Himalaya.