| 1. |
- Das, Supriyo Kumar, et al.
(författare)
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Phosphorus dynamics in shallow eutrophic lakes : an example from Zeekoevlei, South Africa
- 2009
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 619, s. 55-66
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Tidskriftsartikel (refereegranskat)abstract
- Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO4 (3-)), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO3 and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column.
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| 2. |
- Misra, Satabdi, et al.
(författare)
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Multi-proxy approach on the hydrocarbon generation perspective of Barjora Basin, India
- 2020
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 112
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Tidskriftsartikel (refereegranskat)abstract
- Barjora Basin in India is a small basin characterized by a high organic richness of early mature nature. The present study aims to find the source of organic matter (OM) and hydrocarbon generation potential of Barjora Basin. Systematically collected coal and shale samples from R-II seam of the basin were used for proximate and ultimate analyses, Rock Eval pyrolysis along with total organic carbon (TOC) content, organo-micropetrographic framework, thermal maturity, carbon isotopic signature, biomarker composition, functional group studies and estimation of relative aliphaticity and aromaticity through Fourier Transform infrared spectroscopy (FTIR). The novelty of the present work lies in the application of multiple proxies such as stable isotope ratio of organic carbon (delta C-13), biomarker signatures, thermal maturity parameters, organo-micropetrography and estimation and quantification of functional groups for palaeoenvironmental reconstruction and to assess the hydrocarbon productivity of the basin. A dominant terrestrial OM input in Barjora Basin is indicated by the TOC to total nitrogen ratio (C/N), delta C-13 and biomarker compositions. High gelification index (GI), tissue preservation index (TPI), and carbon preference index (CPI) values indicate that coals are deposited in wet swamp forest regime under high rainwater conditions and shales are formed in upper delta plain regime under high groundwater activity. In addition, large liptinite content, TPI and GI designate short transportation of the OM before burial leading to organic richness of the Barjora Basin. Moreover, high liptinite content, type II-III admixed kerogen input, S-2/S-3 ratio, TPI and index for hydrocarbon generation (I-HG) signify higher potential of the basin for hydrocarbon generation.
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| 3. |
- Ray, Sumit Kumar, et al.
(författare)
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Modern analogue to past coseismic ground uplift in North Andaman, India
- 2021
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Ingår i: Catena (Cremlingen. Print). - : Elsevier. - 0341-8162 .- 1872-6887. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- Dynamics of surface geological processes, triggered by coseismic ground uplift following the 2004 Sumatra-Andaman earthquake (M-w > 9.2), provide a modern analogue for assessing the paleoseismic significance of an enigmatic subsurface peat occurrence within beach sands in the western coast of North Andaman Island. The megathrust earthquake uplifted vast stretches of coastal intertidal zones to supratidal levels. As a result, intertidal flora, including mangroves, desiccated and perished. Mass mortality of the flora continued even three years after the earthquake and generated a large volume of forest debris. Coastal waves pushed the debris to the high tide line where the accumulated debris would be gradually buried, and would subsequently transform into linear peat bodies keeping a record of the seismic event in 2004. Accordingly, we have interpreted a linear strand-parallel peat occurrence in beach sand as a record of earlier mass mortality of plants likely associated with a coseismic ground uplift. Stable isotope studies indicate that local intertidal flora is the source of the peat organic matter. Moreover, the 1817 CE calibrated mean AMS radiocarbon age of the peat suggests recurrence of a megathrust earthquake in the Andaman subduction zone about 200 years ago.
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| 4. |
- Das, Supriyo Kumar, et al.
(författare)
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Biomarker evidence of macrophyte and plankton community changes in Zeekoevlei, a shallow lake in South Africa
- 2009
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 41:3, s. 507-521
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Tidskriftsartikel (refereegranskat)abstract
- Zeekoevlei is the largest freshwater lake in South Africa and has a century-long history of anthropogenic impact that caused hyper-eutrophic conditions. We used biomarkers (alkanes and pigments), stable isotopes (delta C-13 and delta N-15), rates of primary palaeoproduction and total inorganic carbon (TIC) accumulation rates in the lake sediments to investigate changes in plankton and macrophyte communities in response to anthropogenic activities in this shallow lake. Specific alkanes (I C-15 pound,C-17,C-19, pristane, phytane and n-C-29/n-C-17 ratio) and pigment (chlorophyll a, beta,beta-carotene, echinenone, fucoxanthin and zeaxanthin) concentrations in lake waters indicated the present-day hyper-eutrophic condition and seasonal fluctuations of cyanobacteria, zooplankton and diatom populations. Eutrophic conditions were initiated in the lake with the start of recreational activities and construction of a sewage treatment plant in the early 1920s. The lake transformed from a eutrophic to a hyper-eutrophic waterbody following damming, pondweed eradication and accelerated catchment-derived nutrient input. The change in lake trophic state was recorded by a sharp decline in the terrestrial to aquatic ratio (TAR) of specific n-alkanes, low carbon preference index (CPI) and increased delta C-13 values in the sediment core. In addition, the aquatic macrophyte n-alkane proxy (P-aq) values (similar to 1) indicated a slow takeover by floating macrophytes after the eradication of submerged pondweeds in 1951. Elevated n-alkane (I C-15 pound,C-17,C-19), total alkane and pigment (chlorophyll a, beta,beta-carotene, zeaxanthin and zeaxanthin to beta,beta-carotene ratio) concentrations, low delta N-15 values and low TIC accumulation rates in the upper middle section of the core indicated the beginning of intense cyanobacterial blooms after the dredging in 1983. Although the cyanobacterial population has decreased in recent years, hyper-eutrophic conditions are reflected by low CPI < 0.04 and TAR < 1 values at the top of the sediment core.
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| 5. |
- Das, Supriyo Kumar, et al.
(författare)
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Elemental (C, N, H and P) and stable isotope (delta N-15 and delta C-13) signatures in sediments from Zeekoevlei, South Africa : a record of human intervention in the lake
- 2008
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 39:3, s. 349-360
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Tidskriftsartikel (refereegranskat)abstract
- We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and total phosphorus (TP) as well as stable carbon and nitrogen isotopes (delta C-13 and delta N-15) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater lake in South Africa. Typical C/N (10-12), H/C ratios (>= 1.7) and delta C-13(organic) values (-22 to -19 parts per thousand) together with the increase in TOC concentration indicate elevated primary productivity in lower middle (18-22 cm) and top (0-8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant, rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent with this, measured delta(15) N-organic values (similar to 11) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are evident from the low delta N-15 values (similar to 3 parts per thousand) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (similar to 0) and high TP (100-2,200 mg l(-1)) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation in the upper mid-section (12-14 cm) of the core.
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| 6. |
- Das, Supriyo Kumar, et al.
(författare)
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Evaluating branched tetraether lipid-based palaeotemperature proxies in an urban, hyper-eutrophic polluted lake in South Africa
- 2012
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Ingår i: Organic Geochemistry. - : Elsevier. - 0146-6380 .- 1873-5290. ; 53, s. 45-51
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate the application of the branched glycerol dialkyl glycerol tetraether (br GDGT) based palaeotemperature and palaeoenvironmental proxy to a hyper-eutrophic, polluted and shallow oxic lake. Lake Zeekoevlei is the largest freshwater lake in South Africa, located close to Cape Town. We use published lake-based and soil-based calibration equations, and compare the reconstructed mean annual air temperature (MAT) with regional (South African) and local (Cape Town) instrumental temperature records. The distribution of br GDGTs in the lake sediments is influenced by air temperature. The lake-based calibration equation, which uses the methylation index of branched tetraethers/cyclisation ratio of branched tetraethers (MBT/CBT), formulated for African lakes (Tierney et al., 2010), fits well with the instrumental temperature records. Moreover, the CBT-derived pH likely reflects historic socioeconomic changes in catchment. Our results suggest that a polluted/hyper-eutrophic status and shallow water urban setting do not preclude application of the MBT/CBT-MAT proxy. However, further research is necessary to understand the behaviour of br GDGT–producing bacteria in polluted and highly productive lakes.
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| 7. |
- Das, Supriyo Kumar, et al.
(författare)
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Major and trace element geochemistry in Zeekoevlei, South Africa : A lacustrine record of present and past processes
- 2008
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Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 23:8, s. 2496-2511
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Tidskriftsartikel (refereegranskat)abstract
- This study reports a multi-parameter geochemcial investigation in water and sediments of a shallow hyper-eutrophic urban freshwater coastal lake, Zeekoevlei, in South Africa. Zeekoevlei receives it greater fraction of dissolved major and trace elements from natural Sources (e.g., chemical weathering and sea salt). Fertilizers, agricultural wastes, raw sewage effluents and road runoff in contrast, constitute the predominant anthropogenic sources, which supply As, Cd, Cu, Pb and Zn in this lake. The overall low dissolved metal load results from negligible industrial Pollution, high pH and elevated metal Uptake by phytoplankton. However, the surface sediments are highly polluted with Pb, Cd and Zn. Wind-induced sediment resuspension results in increased particulate and dissolved element concentrations in bottom waters. Low C/N ratio (10) indicates primarily an algal Source for the sedimentary organic matter. Variation in sedimentary organic C content with depth indicates a change in primary productivity in response to historical events (e.g., seepage from wastewater treatment plant, dredging and urbanization). Primary productivity controls the enrichment of most of the metals ill sediments, and elevated productivity with higher accumulation of planktonic debris (and siltation) results in increased element concentration in surface and deeper sediments. Aluminium, Fe and/or Mn oxy-hydroxides, clay minerals and calcareous sediments also play an important role in adsorbing metals in Zeekoevlei Sediments.
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| 8. |
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| 9. |
- Das, Supriyo Kumar, et al.
(författare)
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Sources and historic changes in polycyclic aromatic hydrocarbon input in a shallow lake, Zeekoevlei, South Africa
- 2008
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Ingår i: Organic Geochemistry. - : Elsevier. - 0146-6380 .- 1873-5290. ; 39:8, s. 1109-1112
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the source, seasonality and historical changes in polycyclic aromatic hydrocarbons (PAHs) in Zeekoevlei, a shallow freshwater lake in South Africa. PAH input follows historical changes in land use pattern and recreational activities in Zeekoevlei since the early 1990s. Because anthropogenic activity in the catchment is low, this has resulted in an overall low PAH concentration in the water column and sediments. PAHs of mainly petrogenic origin dominate.
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| 10. |
- Hoshino, Yosuke, et al.
(författare)
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Cryogenian evolution of stigmasteroid biosynthesis
- 2017
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 3:9
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentary hydrocarbon remnants of eukaryotic C-26-C-30 sterols can be used to reconstruct early algal evolution. Enhanced C-29 sterol abundances provide algal cellmembranes a density advantage in large temperature fluctuations. Here, we combined a literature review with new analyses to generate a comprehensive inventory of unambiguously syngenetic steranes in Neoproterozoic rocks. Our results show that the capacity for C-29 24ethyl- sterol biosynthesis emerged in the Cryogenian, that is, between 720 and 635 million years ago during the Neoproterozoic Snowball Earth glaciations, which were an evolutionary stimulant, not a bottleneck. This biochemical innovation heralded the rise of green algae to global dominance of marine ecosystems and highlights the environmental drivers for the evolution of sterol biosynthesis. The Cryogenian emergence of C-29 sterol biosynthesis places benchmark for verifying older sterane signatures and sets a new framework for our understanding of early algal evolution.
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