No description available.

No description available.

The boreal forest of Canada extends across 58% of Canada’s land area providing a large range of ecosystem services including flood control, water filtration, and carbon storage. Despite conservation efforts to protect this ecosystem, the boreal region is still under stress from global stressors including climate change. Anthropogenic climate-change is expected to raise temperatures and decrease precipitation over much of the boreal region increasing the duration and magnitude of droughts. This potential change to a more arid climate could have drastic affects on water levels and stream flows across much of the boreal region. Changes in hydrology, as a consequence of anthropogenic climate change, may result in large changes to aquatic ecosystems. To assess the susceptibility of lakes to climate in northwestern Ontario over the past two millennia, sediment cores from a headwater lake were obtained from near-shore cores to reconstruct changes in drought. The cores were located at a depth where changes in pelagic and benthic diatom assemblages (P: B boundary) were apparent in modern-day sediments because the location has been shown to be susceptible to change. The lake chosen for reconstruction was Gall Lake, a small (surface area = 19 ha, max depth = 18 m, mean depth = 8.5 m), mesotrophic lake (total phosphorus (TP) level of 12.3 μg/L, July 2008), with a gentlysloping eastern basin. This headwater lake in the Winnipeg River Drainage Basin (WRDB) is part of a hydrologically-rich region that is expected to experience increased aridity. Multivariate analysis of diatom assemblages over the past two millennia suggested that the instrumental record does not encompassed the natural variability of this system. The largest decreases in diatom-inferred (DI) depth were synonymous with iii the Medieval Climate Anomaly (MCA), a phenomenon not yet observed this far northeast in North America. The MCA has been proposed as a surrogate for climate change over the next century, therefore the prolonged aridity observed in Gall Lake could aid in the calibration of general circulation models currently used to forecast changes in climate, as well as a scenario that can be used to develop adaptation strategies to future environmental change. / Thesis (Master, Biology) -- Queen's University, 2011-05-27 17:41:02.022

South Africa is a semi arid country and the provision of water clean water to a steadily growing population is currently one of the major challenges facing governmental organisations. Water resources in South Africa are subject to many forms of pollution. resulting in eutrophication and salinisation. Hence, there is a need to monitor chemical and organic pollution in South African rivers. Chemical monitoring is expensive and not all the elements of water quality can be monitored and measured in a particular sample. The synergistic effects of water quality determinants cannot be demonstrated if only the chemical composition of a water resource is monitored. Biological monitoring can provide a rapid indication of water quality and at a lower cost than traditional monitoring. Organisms within a river are exposed to all water quality variables present in a system and can provide an integrated reflection of the health of their environment. Diatoms are found in all aquatic ecosystems and have demonstrable responses to many of the elements of water quality that have been identified as causing aquatic pollution. These elements include total dissolved solids, pH and plant nutrients such as nitrates and phosphates. The relationship between the structure of a given diatom community and the water quality to which the community is exposed, has lead to the development of several indices of water quality. Diatom indices of aquatic pollution have been developed in France, Belgium, Germany, Britain and Japan. Existing diatom indices have been tested for use in Finland, Poland, Britain, the Himalayas and South America. Several diatom indices were tested in this study for application in the Vaal and Wilge Rivers. The tested diatom indices correlated well with measured water quality variables such as pH and the chemical variables responsible for eutrophication and salinisation. The demonstrated correlations were comparable to those demonstrated by European authors. Several indices proved successful in indicating general water quality, namely the Biological Diatom lndex (BDI), the Specific Pollution sensitivity lndex (SPI) and the Generic Diatom lndex (GDI). The Eutrophication and Pollution lndex (EPI) successfully indicated levels of plant nutrients together with the ionic composition measured at various sites in the Vaal and Wilge Rivers. It is recommended that these indices be further tested in different regions within South Africa. / Thesis (M. Omgewingswetenskappe)--North-West University, Potchefstroom Campus, 2004.

South Africa is a semi arid country and the provision of water clean water to a steadily growing population is currently one of the major challenges facing governmental organisations. Water resources in South Africa are subject to many forms of pollution. resulting in eutrophication and salinisation. Hence, there is a need to monitor chemical and organic pollution in South African rivers. Chemical monitoring is expensive and not all the elements of water quality can be monitored and measured in a particular sample. The synergistic effects of water quality determinants cannot be demonstrated if only the chemical composition of a water resource is monitored. Biological monitoring can provide a rapid indication of water quality and at a lower cost than traditional monitoring. Organisms within a river are exposed to all water quality variables present in a system and can provide an integrated reflection of the health of their environment. Diatoms are found in all aquatic ecosystems and have demonstrable responses to many of the elements of water quality that have been identified as causing aquatic pollution. These elements include total dissolved solids, pH and plant nutrients such as nitrates and phosphates. The relationship between the structure of a given diatom community and the water quality to which the community is exposed, has lead to the development of several indices of water quality. Diatom indices of aquatic pollution have been developed in France, Belgium, Germany, Britain and Japan. Existing diatom indices have been tested for use in Finland, Poland, Britain, the Himalayas and South America. Several diatom indices were tested in this study for application in the Vaal and Wilge Rivers. The tested diatom indices correlated well with measured water quality variables such as pH and the chemical variables responsible for eutrophication and salinisation. The demonstrated correlations were comparable to those demonstrated by European authors. Several indices proved successful in indicating general water quality, namely the Biological Diatom lndex (BDI), the Specific Pollution sensitivity lndex (SPI) and the Generic Diatom lndex (GDI). The Eutrophication and Pollution lndex (EPI) successfully indicated levels of plant nutrients together with the ionic composition measured at various sites in the Vaal and Wilge Rivers. It is recommended that these indices be further tested in different regions within South Africa. / Thesis (M. Omgewingswetenskappe)--North-West University, Potchefstroom Campus, 2004.

No description available.

Iron plays an important role in the regulation of biological productivity and the carbon cycle of the Southern Ocean. Recently, synchrotron X-ray spectromicroscopy revealed that molar iron to silicon (Fe:Si) ratios in living diatom samples collected from surface waters and ice in the coastal Antarctic are significantly higher than reported dissolved Fe:Si ratios of Circumpolar Deep Water. Upwelling of Circumpolar Deep Water is a dominant source of iron and silicon to coastal Southern Ocean surface waters. Thus with higher Fe:Si ratios, diatom production preferentially depletes dissolved iron relative to silicon, potentially contributing to perennial iron limitation in this region. Combining diatom and water column dissolved iron and silicon datasets with a simple inverse box model we estimate the regional coupled iron and silicon budget. Upwelling of subsurface waters cannot supply enough iron to balance the loss due to diatom production, which indicates that the closed budget requires additional iron sources or additional methods of silicon removal. To evaluate the ecological and biogeochemical impacts of the high Fe:Si ratio, a three-dimensional ocean biogeochemistry and ecosystem model is used to simulate the sensitivity of ocean productivity and nutrient cycling to a wide range of Fe:Si ratios in modeled diatoms. The Fe:Si ratio of diatoms regulates the surface iron and macronutrient distribution in vast regions beyond the Southern Ocean. A globally higher Fe:Si ratio strongly decreases subpolar productivity and is partially compensated by the moderate increase in subtropical productivity. Our results indicate that the Fe:Si ratio of diatoms has a global impact controlling the distribution of both micro- and macro-nutrients and associated biological production.

No description available.

The late Quaternary palaeoclimatic history of the lowland Southern Hemisphere Tropics of South America (SHTSA) has been little studied and analysis of key climatic events, such as the Last Glacial Maximum (centred ~ 21,000 years ago (21 cal. ka BP)) and the glacial-Holocene transition is limited. Studies from the SH tropical Andes and the Atlantic seaboard demonstrate a strengthening of the South American summer monsoon during the LGM, in tune with the ~ 20 kyr precession orbital cycle. However, palynological studies from SHTSA suggest a drier LGM. There are difficulties in interpreting different palaeoenvironmental proxy records and the extent to which they reflect changes in temperature, precipitation, and/or atmospheric CO2 concentrations. In particular, the palaeoenvironmental significance of palynological data is often unclear. Also, high frequency, millennial-scale events have not been captured in records from the lowland SHTSA due to a lack of high resolution temporal records. Diatoms have been used widely in other parts of the world to reconstruct lake level change and therefore provide an independent proxy for precipitation, and an understanding of the modern diatom ecology is essential for accurate palaeoreconstruction. The main rationale of this thesis is to address the uncertainty of the glacial-Holocene climate in South America. To this end, this thesis aims to: (a) investigate the distribution, ecology, and flora of diatom taxa at Laguna La Gaiba (17°45’S, 57°40’W) (LLG) in the heart of lowland tropical South America, where very few modern diatom studies exist; (b) determine whether modern diatom assemblages at LLG will provide a useful analogue for palaeoenvironmental reconstructions, in particular, lake depth reconstruction; (c) provide a detailed late Quaternary lake level reconstruction for the lowland interior of SHTSA, based upon fossil diatom analysis of a sedimentary core in LLG. Descriptive, quantitative and multivariate analyses were applied to modern diatom assemblages and environmental variables to ascertain the modern diatom environment of LLG. Diatom, pollen, and geochemical analyses, chronologically constrained by 18 AMS 14C dates, were performed on a sediment core extracted from LLG. Key findings indicate: (1) Aulacoseira ambigua, A. ambigua var. robusta. A. distans and A. granulata var. angustissima were the most abundant species. Shallowwater species, such as Staurosira and Eunotia spp., dominated the shallows and littoral zone, whilst deep-water species, such as Aulacoseira sp., dominated in open water; (2) The highest percent variance in the diatom data was explained by depth and pH; (3) Analysis of fossil diatom assemblages from the LLG core demonstrated that the Last Glacial Maximum (LGM) and late glacial period (prior to 12.5 kyr BP) was drier than present. This corroborates and significantly strengthens pollen-based palaeo-hydrological reconstructions from the same core; (4) An abrupt shift from 12.5 kyr BP from shallow water to deep water diatoms signals major flooding of LLG associated with the transition from relatively drier glacial conditions to wetter Holocene conditions and also highlights an anomalously wet period centred over 12.2 kyr BP that falls within the Younger Dryas chronozone; (5) Deep-water diatoms remain high throughout the Holocene, which means that the mid-Holocene aridity inferred from the pollen data (expansion of seasonally-dry tropical forest) is not captured by the diatom data. These results not only present the modern diatom ecology of a little studied area in lowland Bolivia, but also highlight the potential of diatoms as a proxy for past lake level fluctuations, improving the understanding of late Quaternary palaeoclimate of tropical South America. Used as part of a multiproxy reconstruction, this record has provided a more complete picture of the variation between regions of late Quaternary climate change in South America, as evidence of a dry LGM climate contrasts with the robust, well-dated climate archives of the central Andes and E Brazil. This suggests the climate in the continental interior of SHTSA was not driven by the precesionally-forced monsoon cycle but is in step with changes in glacialinterglacial cycle boundary conditions.

Approximately 6.6 million years ago in the Eastern Equatorial Pacific a large increase in biogenic mass accumulation rates (MAR’s) occurred. This increased level of biogenic mass accumulation persisted until about 4.4 Ma at which time levels returned to those similar to before the transition at 6.6 Ma. The exact nature of the change that facilitated this transition in biogenic MAR’s, however, was not understood. Here we present the results of a study which characterizes the diatom assemblage spanning the depositional transition at 6.6 Ma from sediments taken from ODP Hole 850B. A close inspection of lithology reveals a clear change in lithology from a diatom nannofossil ooze to a nannofossil diatom ooze at 6.6 Ma. This transition is immediately followed by the occurrence of laminated diatom ooze (LDO). Diatom absolute abundance data reveals three levels of productivity associated with pre-transitional, post-transitional, and LDO formational sediments. An increase in the absolute abundance of Thalassionema nitzschioides was the major contributor to the formation of post-transitional, and LDO sediments. The known ecological preferences of this species indicate an overall increase in nutrient availability followed by sporadic changes in nutrient availability. These changes in nutrient availability could be associated with the establishment, or increase in strength, of an upwelling cell and/or the increase in nutrients made available via upwelling due to a shoaling of the thermocline.