Добірка наукової літератури з теми "Diatoms Victoria"

Phytoplankton was sampled on a monthly basis for 1 year at five stations on the La Trobe River in Gippsland, Victoria. In the upper, mostly forested, reaches of the river, chlorophyll a concentrations and cell densities were uniformly very low, and the dominant algae were detached benthic diatoms and flagellated species. In the plains section of the river, downstream of an impoundment (Lake Narracan), spring and autumn blooms occurred, with a marked reduction in abundance in midsummer and midwinter. The lowland planktonic flora was dominated by centric diatoms, particularly Melosira distans in autumn and Skeletonema potamos in spring.

The lipid compositions of fine particulate matter (<35 �m diameter) have been analysed from two temperate sites (Western Port Bay, WPB, and Corner Inlet, CI, Victoria) and two tropical sites (Bowling Green Bay, BGB, and Lizard Island Lagoon, LIL, North Queensland) in the Australian coastal zone. Identification of lipid biomarker molecules (especially fatty acids, fatty alcohols and sterols) has, in conjunction with microscopy, enabled identification and, in some instances, quantification of a range of biological inputs. Estimated contributions of biomass to total particulate mass in the temperate samples were: seagrass detritus (~10-15%) > bacteria (~34%) > live diatoms (≤ 1%). Similar estimations for the tropical samples were: BGB, bacteria (- 1%) > live diatoms (< 1%); and LIL, bacteria (~20-30%) > copepod detritus (≥ 1%) > live diatoms (< 1 %). Biomarkers also indicated the presence of coral mucus and a distinctive bacterial chemotype, possessing branched chain alcohols, in the LIL sample.

The dietary habits of six species of Dinotoperla were determined by field and laboratory observations, nymphal gut analysis, and examination of mouthparts. All the species (D. bassae, D. brevipennis, D. christinae, D. eucumbene, D. fontana and D. thwaitesi) could be classified as herbivore-detritivores, and in each there was a shift from a diet primarily of fine particulate matter to a more polyphagous habit with increasing nymphal size. The diets of the six species were similar, consisting of diatoms, filamentous green algae (except in D. eucumbene), fupgal hyphae, fine particulate matter and vascular plant tissue. However, differences were observed in the nutritional quality of their diets in terms of protein and calorific content. The two smallest species studied, D. brevipennis and D. eucumbene, consumed mostly fine particulate matter-the least nutritionally valuable of available food items (apart from wood, which was not eaten by Dinotoperla nymphs). D. eucumbene was also the slowest growing of the six species. The fastest-growing species, D. bassae, was also the largest, and the nymphs of this species consumed the highest-quality diet, eating large amounts of filamentous green algae and diatoms.

Labeo fisheri is an endemic and endangered freshwater fish of Sri Lanka. Mainly restricted to the upper reaches of the Mahaweli River basin, it has been previously reported living in deep rapids and among large rocks and boulders. An accidental record of a Labeo fisheri specimen from Victoria Reservoir led us to further study this habitat during the period from January to August 2017. This study was carried out to confirm the presence of a population of Labeo fisheri within the Victoria Reservoir and report its new habitat type in deep stagnant waters. We further investigated the food habits by analyzing the gut contents of L. fisheri in the Victoria Reservoir. Seven individuals were recorded from fishermen’s gill net catch in three fish landing sites along Victoria Reservoir, with an average total length of 24.80 ± 4.30 cm, average standard length of 19.70 ± 3.86 cm and average body weight of 197.69 ± 107.12 g. Based on gut content analysis, only phytoplankton, especially diatoms and cyanobacteria, were found in the gut of L. fisheri. This new population is facing the direct threat of fishing. Effective conservation measures are doubtful, since a fishery is well established in the Victoria Reservoir and the fishing gear used is not species-specific. More research is necessary to understand the population dynamics of L. fisheri in the Victoria Reservoir. In order to conserve it at this locality, community-based conservation measures are recommended.

Lake sediments consist of the input of suspended solids by river discharges, the autochthonous produced particulate matter in the water column and the settled material on the lake bottom. The loading, transport, formation and decay of the sediments entering the Lake Victoria from Tanzanian side was monitored for the period 2000 to 2005. The sedimentation study focused on; quantification of settling fluxes of particulate nutrients and organic carbon at the off-shore(Pelagic) and near-shore(Littoral) monitoring stations. Monitored data on sedimentation rate and settling velocities has been sampled and analysed in the period November 2000 to March 2005. The mean sedimentation rate at littoral stations for total particulate phosphorous (TPP) was about twice as compared to pelagic stations. The same situation was observed for total particulate carbon (TPC), however, total particulate silica did not show a clear pattern of variability between littoral and pelagic stations though there was a general tendency of decreasing towards the pelagic stations. Mean value for TPC /TPP sedimentation rate ratio was 117.61 for littoral and 90.74 for pelagic stations respectively compared to TBSi/TPP which was 3.15 for littoral and 2.10 for pelagic stations. The results show that sedimentation rates are highest at the littoral stations compared to pelagic stations. The differences in settling velocities indicate that the settling material consists dead and living material with a contribution of diatoms. The stoichiometriccomposition of the settling material indicates nitrogen limitation and a non-dominance of diatoms.

AbstractMeltwater habitats in the Darwin Glacier region, Victoria Land (80°S), were sampled in December 2007 and January 2009 to characterize their microbial and metazoan ecology, nutrient status and geochemistry. Targeted areas included terrestrial ponds of the Grant Valley, Lake Wellman, Tentacle Ridge and Diamond Hill, and supraglacial ponds and cryoconite holes of the lower Darwin Glacier. Geochemistry ranged from Na-Cl dominated terrestrial ponds to Na-HCO3dominated, dilute supraglacial ponds and cryoconites. All showed the nitrate enrichment typical of inland ponds of Victoria Land (up to 13 g.l-1NO3-N), with some precipitating nitratine (NaNO3) salt. Elevated pH indicated ongoing photosynthetic processes. Benthic microbial mats were thin and poorly developed, dominated by oscillatoriacean cyanobacteria. Nitrogen-fixing genera were generally absent and diatoms were rare. A large (20 μm long)Cyanothecespecies was the most abundant cyanobacterium in the water and in sediments of the cryoconites. DNA finger-printing identified distinct differences in cyanobacterial and bacterial community structure between the cryoconites, terrestrial ponds and ponds on glacial margins. Eleven metazoan species were identified, with rotifers being the most abundant. Pond substrate (terrestrial rock, ice-cored moraine or supraglacial ice) proved to be a more significant influence on biogeochemistry than other aspects of geography or climatic conditions.

Abstract. We describe and test a new model of biological marine silicate cycling, implemented in the Kiel Marine Biogeochemical Model version 3 (KMBM3), embedded in the University of Victoria Earth System Climate Model (UVic ESCM) version 2.9. This new model adds diatoms, which are a key component of the biological carbon pump, to an existing ecosystem model. This new model combines previously published parameterizations of a diatom functional type, opal production and export with a novel, temperature-dependent dissolution scheme. Modelled steady-state biogeochemical rates, carbon and nutrient distributions are similar to those found in previous model versions. The new model performs well against independent ocean biogeochemical indicators and captures the large-scale features of the marine silica cycle to a degree comparable to similar Earth system models. Furthermore, it is computationally efficient, allowing both fully coupled, long-timescale transient simulations and “offline” transport matrix spinups. We assess the fully coupled model against modern ocean observations, the historical record starting from 1960 and a business-as-usual atmospheric CO2 forcing to the year 2300. The model simulates a global decline in net primary production (NPP) of 1.4 % having occurred since the 1960s, with the strongest declines in the tropics, northern midlatitudes and Southern Ocean. The simulated global decline in NPP reverses after the year 2100 (forced by the extended RCP8.5 CO2 concentration scenario), and NPP returns to 98 % of the pre-industrial rate by 2300. This recovery is dominated by increasing primary production in the Southern Ocean, mostly by calcifying phytoplankton. Large increases in calcifying phytoplankton in the Southern Ocean offset a decline in the low latitudes, producing a global net calcite export in 2300 that varies only slightly from pre-industrial rates. Diatom distribution moves southward in our simulations, following the receding Antarctic ice front, but diatoms are outcompeted by calcifiers across most of their pre-industrial Southern Ocean habitat. Global opal export production thus drops to 75 % of its pre-industrial value by 2300. Model nutrients such as phosphate, silicate and nitrate build up along the Southern Ocean particle export pathway, but dissolved iron (for which ocean sources are held constant) increases in the upper ocean. This different behaviour of iron is attributed to a reduction of low-latitude NPP (and consequently, a reduction in both uptake and export and particle, including calcite scavenging), an increase in seawater temperatures (raising the solubility of particulate iron) and stratification that “traps” the iron near the surface. These results are meant to serve as a baseline for sensitivity assessments to be undertaken with this model in the future.

AbstractWright Valley, Victoria Land contains numerous aquatic habitats suitable for the growth of algae in summer. Excepting diatoms and lichen phycobionts, algal diversity and distribution in the valley was documented. Using cultures and environmental cloning eight cyanobacterial and 14 eukaryotic species were revealed. The cyanobacterium Microcoleus vaginatus and the chlorophycean Chlorococcum sp. 1 were the most common, both occurring in more than one habitat (ponds, soils or streams). Ponds harboured the most diverse communities. Habitat specialization was rare. Chlamydomonads were not found outside ponds, but species capable of zoospore production were able to colonize ponds and soils. Nostocalean cyanobacteria were not detected. Results suggest dispersal within and between valleys, with little evidence of Antarctic endemism. All but one cyanobacterium with similar internally transcribed spacer (ITS) length to clones from Miers Valley proved to be different species when 16S rRNA gene sequences were also considered; thus, ITS length is unreliable for assessing identity and biogeography of these cyanobacteria. Comparison with a 454 16S rRNA gene soil dataset from Wright Valley indicated the occurrence of only one of the cyanobacterial species, the distribution of which may be limited by salinity.

A lake sediment core spanning 9900 years, collected from a small lake on western Victoria Island, provides a high-resolution record of diatom community dynamics over the Holocene. Ten radiocarbon dates and 210Pb dating provided the core chronology. Loss-on-ignition (LOI) gradually increased over the Holocene whereas carbonate content and magnetic susceptibility showed an inverse trend. Biogenic silica content had apparent cyclicity over ~1500 year periods. Major shifts in diatom assemblages at 8100-8000 calendar years before present (cal yrs BP), 5800-5700 cal yrs BP, and 3800-3500 cal yrs BP occurred simultaneously with millennial-scale climate changes reported from the region. There is evidence of diatom community response to centennial scale variations such as the 'Medieval Warm Period' (~1000-700 calendar years before present, cal yrs BP), 'Little Ice Age' (~800-150 cal yrs BP) and recent warming. Variations of the taxa within the genera Staurosira, Pseudostaurosira, Fragilaria, and Staurosirella, usually combined into one genus in Arctic lake sediment studies, suggest these taxa may be more useful in paleolimnological studies than previously believed. Although recent changes in diatom community composition, production and species richness were apparent they were surpassed at other periods throughout the Holocene. The rate of community compositional change in the last few centuries was rapid, however it was not exceptional in the lake history.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009.
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Our understanding of the long-term climate variability in Australia is limited by the number of high-resolution climate reconstructions. High-resolution palaeoenvironmental studies in Australia spanning more than a millennium are required to identify regional coherency among records and to recognise the relationships between climate and environmental conditions. This research project aims to investigate the nature of decadal-centennial scale climate and hydroclimate variability in south-eastern Australia. A record of hydrological change is established for the past millennium at West Basin Lake, a maar lake located in western Victoria. Palaeoclimate variability is inferred from sedimentary diatom analysis and is used to reconstruct lake water salinity. These data are interpreted in conjunction with element concentration data. The record indicates that West Basin Lake underwent hydrological variability on a decadal-centennial timescale. The diatom record shows evidence of a more variable climate during 932-550 cal BP and less saline conditions from 500-100 cal BP. The record also identifies a multi-decadal period of increased salinity from 625-575 cal BP. This suggests a more variable climate during the past millennium than observed since European settlement. The record established from this study provides a regionally coherent palaeoclimate reconstruction of the last millennium for western Victoria, Australia.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2015

The purpose of this study was to reconstruct climatic change of the last two millennia in western Victoria using fossil diatoms as the primary proxy. Due to their short life span and sensitivity to changing water chemistry, diatoms are ideal for reconstructing short term changes in suitable environments. The primary aim of the project was to redress a paucity of highly-resolved climate studies from the Australian mainland and represents one of the first sub-decadally resolved studies of its kind in this regard. Sediments from two crater lakes were examined from the volcanic province of western Victoria. The study region is influenced by El Niño-Southern Oscillatio (ENSO), the Indian Ocean Dipole and the Southern Annular Mode and is currently experiencing the most severe and prolonged drought since instrumental records began (Murphy and Timbal, 2008; Ummenhofer et al., 2009). The two study lakes – Lake Elingamite and Lake Surprise – have differing morphology and catchment history and lie approximately 100 km apart. Lake Elingamite is a broad, currently shallow (maximum depth = 3.4 m), oligosaline (3470 μS/cm) maar lake which shows evidence of significant catchment and lake disturbance since European settlement in the region. A 178 cm core was retrieved from this lake, representing a ca. 1500 year record. Lake Surprise is one of only two “true crater lakes” in the western Victorian volcanic province (Timms, 1975). It is fresh (220 μS/cm) with a maximum depth of 12 m and has a more complex morphometry than Lake Elingamite. It is located within a National Park and does not have the same degree of catchment disturbance as Lake Elingamite. Two cores were retrieved from Lake Surprise, a frozen spade core of the most recent sediments and a hammer-driven piston core of the older sediments. The combination of both cores provide a 344 cm record of the last ca. 1425 years. Cores from both lakes were sampled contiguously for fossil diatom analysis. In order to quantitatively reconstruct palaeo-conductivity fluctuations from the study sites, a diatom-conductivity transfer function was developed with an intentionally short conductivity gradient, using only sites with a conductivity < 22,000 μS/cm in the modern calibration set (min: 81 μS/cm; max: 21,540 μS/cm; SD: 5592.7 μS/cm). The resulting model is robust, with a jack-knifed r² of 0.89 and an RMSEP of 0.238 log μS/cm (equating to 9.8% of gradient length), which compares favourably to other diatomconductivity or salinity transfer functions. At a sample-specific level, reconstruction confidence was tested by squared-chord distance using the modern analogue technique tool. The Lake Surprise diatom-inferred (DI) conductivity record shows a good coherence with the Palmer Drought Severity Index developed for south-eastern Australia for the 20th Century (Ummenhofer et al., 2009), confirming the lake’s climatic sensitivity. Comparisons between DI conductivity and instrumental climate data were not possible for Lake Elingamite due to the degree of recent lake and catchment disturbance. Importantly, the climate signal evident in the full Lake Surprise record is replicated in the Lake Elingamite record, indicating that the lakes are reflecting a common, regionalscale, climate forcing. Lake Surprise proved to be the more sensitive of the lakes and, in places where the DI reconstruction has poor modern analogues, the interpretation is supported by the Lake Elingamite record. Results show a strong centennial-scale agreement with a reconstruction of El Niño events from Ecuador (Moy et al., 2002), confirming the influence of ENSO on the climate of the study region. At decadal-scale, the DI conductivity record provides a history of drought frequency, intensity and duration enabling the current drought to be viewed in an historical perspective for the first time. Results demonstrate that, while the current drought is unusual in terms of its severity and duration, it is not unprecedented. At centennial-scale, evidence is presented of extended periods of dry and wet climates, including a prolonged humid period prior to European settlement in the study region.
Thesis (Ph.D.) -- University of Adelaide, School of Social Sciences, 2010

Hatch cover jenis hidraulik (hydraulic type hatch cover) terdiri dari beberapa panel yang terbuat dari bahan pelat baja yang terpasang melintang diatas lubang palka. Hatch cover jenis ini memiliki paking diantara panel ataupun terhadap ambang palka kapal. Jenis ini untuk membuka dan menutupnya dilakukan secara mekanis dan hidraulik, pada panel ujung palka memiliki lengan yang terhubung dengan sistem hidraulik. Panel ujung akan terbuka dan menarik panel didepannya. Setiap palka memiliki empat panel yang terbagi dua, bagian depan dan belakang. Sehingga pada saat terbuka panel akan tegak terlipat diujung palka. Disini penulis mencoba untuk mengangkat permasalahan yang dihadapi dalam pelaksanaan pengangkutan muatan di MV. Wooyang Victory pada saat melakukan proses bongkar ataupun muat di pelabuhan. Kendala-kendala atau permasalahan yang dihadapi dalam pelaksanaan bongkar muat yang menyangkut dengan hatch cover tipe hidraulik yaitu sering pecahnya pipa hidraulik pada saat awak kapal membuka hatch cover yang mengakibatkan tidak berputarnya roda hatch cover, tidak terlaksananya perawatan sesuai dengan planned maintenance system dan juga tidak terangkatnya piston hydraulic jack pada roda hatch cover sehingga terjadi keterlambatan dalam proses bongkar muat. Dikarenakan tidak terlaksananya perawatan Jika pipa hidraulik pecah dan piston hydraulic jack tidak terangkat pada saat proses bongkar muat, maka hatch cover tidak berfungsi. Palka tidak bisa ditutup ataupun dibuka.