| 1. |
- 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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| 2. |
- 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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