| 1. |
- Baskar, Sushmitha, et al.
(författare)
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Biogenic evidences of moonmilk deposition in the Mawmluh cave, Meghalaya, India
- 2011
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Ingår i: Geomicrobiology Journal. - : Taylor & Francis. - 0149-0451 .- 1521-0529. ; 28:3, s. 252-265
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Tidskriftsartikel (refereegranskat)abstract
- Moonmilk, a microcrystalline secondary cave deposit, actively forms on the floor of Krem Mawmluh - a limestone cave in Meghalaya, Northeastern India. Due to the abundance of micrite and calcified microbial filaments, we hypothesize that these deposits form as a result of ongoing microbial interactions. Consistent with this idea, we report electron microscopic and microbiological evidences for the biological origin of moonmilk in Krem Mawmluh. Scanning electron microscopy indicated abundant calcified microbial filaments, needle calcite, fibre calcites (micro-fibre and nano-fibre calcite crystals), biofilm and microbial filaments in the moonmilk. The total viable culturable microbes showed high population densities for microbes in the moonmilk and moonmilk pool waters. In vitro culture experiments, confirmed the capability of many of the isolated strains to precipitate calcite and some of the identified isolates belonged to the Bacillus sp. and Actinomycetes. These results clearly support the biogenic nature of the deposits.
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| 2. |
- Bhandari, Rajendra, 1986-
(författare)
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Provenance, transport, and the fate of organic matter and sediments drained through Himalayan Rivers in Nepal
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite its small area (ca. 595,000 km2), the Himalayan region transfers disproportionally high amounts of sediments and organic matter (OM) through a network of rivers into the oceanic sink. Such a high contribution is due to the synergistic effects of active tectonics, variable precipitation, and steep slopes aided by human perturbations on exhumed and young mountain terrains. Seasonality in the mobilization and transport of fresh biogenic OM and petrogenic carbon, including paleosols, is dominant in this unique landscape with implications for climate change and the global carbon budget. However, a comprehensive assessment of sources and the fate of organic carbon (OC) in Himalayan rivers remains elusive, driving considerable uncertainty in estimates of the fluvial transport of carbon, its budget, and its impacts on the global carbon cycle. Four rivers from diverse physiographic zones with specific rock types were selected from the Nepal Himalayas to characterize the OM sources and their fate using C:N ratios, lipid biomarkers, and lignin phenols. The seasonal OC fluxes were estimated, and strontium (Sr) and neodymium (Nd) isotope data were utilized to elucidate the provenance. Finally, monitoring of runoff plots and RUSLE modeling was conducted to estimate soil erosion from different land-use practices. The suspended sediment load in these rivers was proportional to the erosional intensity. Unlike suspended sediments, OM in bedload samples was derived from multiple sources with weak terrigenous dominance. The influence of seasonality on OM and elemental concentrations was evident in the new data. The abundance of sedimentary lipids in these small rivers represents high OM sequestration and corroborates the inference derived from diagnostic lignin ratios. These rivers transport > 90% POC and ca. 75% DOC during the short monsoon season, highlighting rapid transport/mobilization of OC from the Nepal Himalayas. The high strontium isotope (87Sr/86Sr) ratio in silicates drives the high radiogenic Sr input, which exceeds the global average. The clusters in Sr and Nd isotope data represent specific physiographic zones and rock types that can help infer OM provenance and trace the fate of carbon from source to sink. Data from the runoff plots suggest that irrigated croplands drive topsoil erosion. The soil erosion rate in the watersheds is high (> 24 tons ha-1 yr-1). This is attributed to anthropogenic disturbance associated with cropping patterns, soil disturbance, and waterlogging. The contrasting features in the Himalayan region and new data on the role of mountain rivers invite global attention to infer ongoing and future changes in OM flux.
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| 3. |
- Bhattacharya, Aparajita, et al.
(författare)
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Environmental assessment of abandoned mine tailings in Adak, Vasterbotten district (northern Sweden)
- 2006
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Ingår i: Applied Geochemistry. - : Elsevier. - 0883-2927 .- 1872-9134. ; 21:10, s. 1760-1780
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Tidskriftsartikel (refereegranskat)abstract
- Sulfide-rich mine tailings in Adak that are exposed to weathering cause acid mine drainage characterized by low PH (2-4) and high SO4 (UP to 800 mg L-1). Surface water, sediment and soil samples collected in this study contain higher concentrations of As, Cu, Fe and Zn, compared to the target and/or intervention limits set by international regulatory agencies. In particular, high As concentrations in water (up to 2900 mu g L- 1) and sediment (up to 900 mg kg(-1)) are of concern. There is large variability in trace element concentrations, implying that both physical (grain size) and chemical factors (pH, secondary phases as sulfides, Al-oxides or clay minerals) play an important role in their distribution. The low PH keeps the trace elements dissolved, and they are transported farther downstream. Trace element partition coefficients are low (log K-d = 0.3-4.3), and saturation indices calculated with PHREEQC are < 0 for common oxide and sulfidic minerals. The sediment and soil samples indicate an enhanced pollution index (up to 17), and high enrichment factors for trace elements (As up to 38,300; Zn up to 800). Finally, leaves collected from different plant types indicate bioaccumulation of several elements (As, Al, Cu, Fe and Zn). However, some of the plants growing in this area (e.g., Salix, Equisetum) are generally resistant to metal toxicity, and hence, liming and phytoremediation could be considered as potential on-site remediation methods.
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| 4. |
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| 5. |
- Choudhary, Preetam, et al.
(författare)
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An environmental record of changes in sedimentary organic matter from Lake Sattal in Kumaun Himalayas, India
- 2009
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 407:8, s. 2783-2795
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Tidskriftsartikel (refereegranskat)abstract
- Sattal a small mountainous lake in the Kumaun Himalayas has been impacted by various cultural activities in recent years. We explored the effects of human-induced changes in this lake by using various geochemical proxies. Shifts in TOC and N flux, C/N ratio, stable isotopes (delta C-13 and delta N-15), n-alkane, and pigment concentrations in sediments indicate a steady increase in primary productivity over the last few decades. The trophic status of the lake has changed from mesotrophic to eutrophic condition. The C/N, CPI, and TAR based ratios in sediments indicate accumulation of algal matter derived primarily from in situ production, with limited input of terrestrial organic matter from the watershed. The low (between 0.1 and 1 parts per thousand) delta N-15 values imply N-2-fixation by cyanobacteria, and the decrease in delta C-13 values up-core represent the effect of sewage input and land based runoff, or possible contribution from microbial biomass. The pigments change from non-N-2 fixing cyanobacterial species to the N-2-fixing community, and are consistent with the proxy-based productivity shifts inferred in the lake. The deeper sediments are affected by post-diagenetic changes causing an increase in delta C-13 (and possibly delta N-15) due to mineralization of organic C and N.
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| 6. |
- Choudhary, Preetam, et al.
(författare)
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Biogeochemical records of paleoenvironmental changes in Nainital Lake, Kumaun Himalayas, India
- 2009
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 42:4, s. 571-586
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Tidskriftsartikel (refereegranskat)abstract
- Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns about sediment and water pollution. Lead-210 dated sediment cores from the lake represent similar to 95 years of accumulation and yield a mean sedimentation rate of similar to 4.7 mm year(-1). Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (delta C-13, delta N-15, and delta S-34), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC flux varies from 1.0 to 3.5 g m(-2) year(-1). Sediments are anoxic (Eh -328 to -187 mV) and have low (0.10-0.30 g m(-2) year(-1)) N, but high (0.37-1.0 g m(-2) year(-1)) S flux. Shifts in delta C-13, delta N-15, and delta S-34 suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the lake has remained largely unchanged, and the perceived human-induced impacts are limited.
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| 7. |
- Choudhary, Preetam, et al.
(författare)
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Distribution of polycyclic aromatic hydrocarbons in Kumaun Himalayan Lakes, northwest India
- 2010
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Ingår i: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 41:9, s. 891-894
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Tidskriftsartikel (refereegranskat)abstract
- Sources and historical deposition of polycyclic aromatic hydrocarbons (PAHs) were investigated in dated sediment cores from Lakes Nainital and Bhimtal in the Kumaun Himalaya The data show that PAH deposition has increased in recent years and is associated with an increase in anthropogenic activity. The lake sediments dominantly contain low molecular weight (LMW) PAHs. derived mainly from petrogenic sources Concentrations of individual and total PAHs were categorized on the basis of sediment quality criteria. According to this, the pollutants pose a potential threat to aquatic life.
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| 8. |
- Choudhary, Preetam, et al.
(författare)
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Organic geochemical record of increased productivity in Lake Naukuchiyatal, Kumaun Himalayas, India
- 2010
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Ingår i: ENVIRONMENTAL EARTH SCIENCES. - : Springer. - 1866-6299 .- 1866-6280. ; 60:4, s. 837-843
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Tidskriftsartikel (refereegranskat)abstract
- Organic geochemical proxies have been studied in a 45-cm-long core retrieved from Lake Naukuchiyatal in Kumaun Himalayas, India. Increase in TOC, N, hydrocarbons and pigments concentration from bottom to surface sediments of the core indicates increase in the lake productivity. Stable isotopes (δ13C and δ 15 N), biomarkers (TAR, CPI and n-ΣC15,17,19) and C/N atomic (between 9 and 12) suggest dominance of algal derived organic matter in these sediments. Decrease in organic δ13C values (between −27 and −31‰) in surface sediments indicate influence of sewage and land runoff in shifting organic δ13C values, whereas low (between −0.23 and 2.2‰) δ15N values together with high pigment concentrations (zeaxanthin and echinenone) represent dominance of cyanobacteria in the lake.
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| 9. |
- Collins, Matthew D., et al.
(författare)
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Arsenicicoccus bolidensis gen. nov., sp nov., a novel actinomycete isolated from contaminated lake sediment
- 2004
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Ingår i: INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY. - : Microbiology Society. - 1466-5026 .- 1466-5034. ; 54, s. 605-608
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Tidskriftsartikel (refereegranskat)abstract
- An unknown Gram-positive, catalase-positive, facultatively anaerobic, non-spore-forming, coccus-shaped bacterium originating from sediment was characterized using phenotypic, molecular chemical and molecular phylogenetic methods. Chemical studies revealed the presence of a cell-wall murein based on ll-diaminopimelic acid (type ll-Dpm-glycine1), a complex mixture of saturated, monounsaturated and iso- and anteiso-methyl-branched, non-hydroxylated, long-chain cellular fatty acids and tetrahydrogenated menaquinones with eight isoprene units [MK-8(H4)] as the major respiratory lipoquinone. This combination of characteristics somewhat resembled members of the suborder Micrococcineae, but did not correspond to any currently described species. Comparative 16S rRNA gene sequencing confirmed that the unidentified coccus-shaped organism is a member of the Actinobacteria and represents a hitherto-unknown subline related to, albeit different from, a number of taxa including Intrasporangium, Janibacter, Terrabacter, Terracoccus and Ornithinicoccus. Based on phenotypic and phylogenetic considerations, it is proposed that the unknown bacterium originating from lake sediment be classified as a new genus and species, Arsenicicoccus bolidensis gen. nov., sp. nov. (type strain CCUG 47306T=DSM 15745T).
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| 10. |
- 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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