| 1. |
- Kumar Ranjan, Rajesh, et al.
(författare)
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Elemental and stable isotope records of organic matter input and its fate in the Pichavaram mangrove–estuarine sediments (Tamil Nadu, India)
- 2011
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Ingår i: Marine Chemistry. - : Elsevier. - 0304-4203 .- 1872-7581. ; 126:1-4, s. 163-172
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Tidskriftsartikel (refereegranskat)abstract
- In order to evaluate the sources and fate of organic matter (OM) in the Pichavaram mangrove–estuarine ecosystem, Corg, Ntot, C/Natm, and stable isotopes (δ13Corg and δ15Norg) of five 210Pb dated sediment cores were investigated. Core A was collected from the Vellar Estuary, cores B, C, and D from mangrove forests, and core E was from the Coleroon Estuary. In mangrove sediments, Corg, Ntot, and C/Natm concentration varied from 1.2 ± 0.52%, 0.08 ± 0.03%, and 16.6 ± 4.1%, respectively. In the estuaries, Corg, Ntot, and C/Natm varied from 0.37 ± 0.19%, 0.03 ± 0.01%, and 12.3 ± 2.9%, respectively. In mangrove forests the δ13Corg and δ15Norg values varied from − 24.3 ± 1.8‰ and 4.2 ± 0.86‰, whereas in estuaries these values were − 23.2 ± 1.6‰ and 5.1 ± 1.3‰, respectively. The variation represents variable inputs of marine and terrestrial OM in these area, OM degradation, replacement of native vegetation due to increasing salinity, and early diagenetic changes. Some of these changes could be attributed to anthropogenic activities that have been happening in the Pichavaram complex over the last few decades. OM once deposited in the sediments is rapidly decomposed or remineralized in both mangrove and estuarine sites. The rate of Corg burial is more in mangrove forests than estuaries. Early diagenetic changes are modeled in the cores based on C/N stoichiometry. This was most applicable in mangrove sediments (core C) where ~ 56% C was remineralized representing a first order diagenetic model.
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| 2. |
- Das, Supriyo K., et al.
(författare)
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Elemental (C, N, H and P) and stable isotope (del15 N and del13C) signatures in sediments from Zeekoevlei, South Africa : a record of human intervention in the lake
- 2007
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Ingår i: Journal of Paleolimnology. - : Springer. - 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 (δ13C and δ15N) 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 δ13Corganic values (−22 to −19‰) 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 δ15Norganic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are evident from the low δ15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- Kumar Ranjan, Rajesh, et al.
(författare)
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Sediment biomarker profiles trace organic matter input in the Pichavaram mangrove complex, southeastern India
- 2015
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Ingår i: Marine Chemistry. - : Elsevier. - 0304-4203 .- 1872-7581. ; 171, s. 44-57
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Tidskriftsartikel (refereegranskat)abstract
- The nature and distribution of lipid biomarkers (n-alkanes, n-alkanols, sterols and triterpenols) were investigated in five dated sediment cores from the Pichavaram mangrove-estuarine complex in order to: 1) identify the organic matter (OM) sources and its preservation and 2) trace recent changes associated with coastal processes and anthropogenic activities. The mangrove sediment extracts have higher biomarker concentration (22.6 +/- 13.3 mu g/g dry weight) than the estuarine extracts (6.42 +/- 4.92 mu g/g dry weight). Triterpenols are dominant biomarkers in both estuarine and mangrove sediments, and constitute greater than50% of the total lipid extracts. The presence of n-alkanols (n-C-26,C-28,C-30) and abundance of phytosterols (stigmasterol and beta-sitosterol) and triterpenols (taraxerol, beta-amyrin, germanicol, and lupeol) indicate that mangrove vegetation is the primary source of sedimentary OM. The high abundance and unimodal distribution of the long-chain n-alkanes (mainly n-C-25,C-27,C-29), and high values of Terrestrial Aquatic Ratio (TAR 2.4 to 41) and Carbon Preference Index (CPI greater than 8) indicate dominance (and better preservation) of higher plant derived immature OM in mangrove sediments. In contrast the weak dominance of high molecular weight n-alkanes, low CPI (0.75 to 0.90) and TAR (1.9 to 5.7) values, and the presence of high C-27 and C-28 sterols indicate that phytoplankton/algal derived OM is more pronounced in estuarine sediments. Diagenetic changes in sedimentary OM indicate that some of the lipid fractions are reactive, and as a result, they degrade more rapidly than bulk OM. These compounds follow first order decay kinetics, and concur with the downcore diagenetic changes in coastal areas. Resistance to degradation among the different lipid classes show the trend: n-alkane greater than sterol greater than triterpenol greater than n-alkanol. Finally, the study indicates that less freshwater discharge from the Coleroon River is causing a gradual change in mangrove vegetation. There is less input of OM derived from mangrove vegetation into recent sediments. Biomarker trends also indicate that less salt tolerant Rhizophora spp. are gradually replaced by more salt tolerant vegetation consisting of Sueda spp. and Aviccenia spp.
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| 7. |
- Minu, Andrew, et al.
(författare)
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Temporal and spatial distribution of trace metals in the Rufiji delta mangrove, Tanzania
- 2018
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Ingår i: Environmental Monitoring & Assessment. - : SPRINGER. - 0167-6369 .- 1573-2959. ; 190:6
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Tidskriftsartikel (refereegranskat)abstract
- Spatial and temporal distribution of trace metals and their cycling is a key issue for understanding the ongoing biogeochemical processes in coastal environments. Sediment cores were collected from six different sampling locations from the Rufiji delta mangrove forests in southeastern coastal Tanzania that are perceived to be impacted by urban development and agricultural activities in the catchment, and pollution in upstream sections of the Rufiji River. The chronology and sediment accumulation rates at these sampling sites were derived based on the distribution of Pb-210(excess) method. The trace metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were sequentially extracted as per the BCR method and analyzed. The results indicate that the mass accumulation rates range from 0.40 g cm(-2) year(-1) (cores NR3 and NR4) to 1.75 g cm(-2) year(-1) (core SR1). Trace metals in the cores are mainly associated with the residual phase and their abundances in sediments are ranked as Cr amp;gt; Zn amp;gt; Ni amp;gt; Cu amp;gt; Pb amp;gt; Cd. The results imply that trace metals in the Rufiji delta mangroves are mainly of crustal origin, and they are less sensitive to weathering. Further, these metals are least available for uptake by plants and they pose limited threat to the biota.
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| 8. |
- Ranjan, Rajesh Kumar, et al.
(författare)
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Polycyclic aromatic hydrocarbons fingerprints in the Pichavaram mangrove-estuarine sediments, southeastern India
- 2012
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Ingår i: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 53, s. 88-94
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Tidskriftsartikel (refereegranskat)abstract
- The sources and historical deposition of 16 polycyclic aromatic hydrocarbons (PAHs) were investigated in dated sediment cores from the Pichavaram mangrove–estuarine complex. The ΣPAH flux in mangrove and estuarine sediments was 0.064 ± 0.031 μg/cm2/yr and 0.043 ± 0.020 μg/cm2/yr, respectively. The PAH flux in sediments increased up-core, coinciding with rapid urbanization since the 1970s. The flux showed a decrease in recent years (since 1990), coinciding with less riverine discharge, and perhaps more effective implementation of environmental regulations. The sediments were dominated by low molecular weight PAHs, suggesting anthropogenic input. Ratios of specific PAH isomer pairs suggested a greater input of petrogenic vs. pyrogenic derived PAHs. Notably, the deposition of high molecular weight PAHs increase in mangrove surface sediments was due to lignite and firewood combustion. Because of their overall low concentration in sediments it is unlikely these PAHs pose an immediate ecological hazard.
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