No description available.

A sediment core from Himmerfjärden estuary, south of Stockholm, was examined to detect records of eutrophication on the site since the opening of the sewage treatment plant Himmerfjärdsverket in 1974. The core was analysed with respect to the diatom record and lithology. Four macrofossil that were found in the sediment were dated using 14C-dating.    This study aims to detect changes in the environment of Himmerfjärden by using the diatom stratigraphy record. The results have been interpreted and discussed regarding natural environmental and climate change and/or anthropogenic impact, and detected changes will be associated with the history of the sampling site. The results show that the lowermost zone started to deposit around 1300-1490 cal yr BP and the homogeneous sediment indicates that the area was not suffering from hypoxia at that time. There is a successive transition towards more distinct lamination further up in the core which show that the environment in Himmerfjärden have changed and become hypoxic. This may have to do with factors such as the opening of heavily trafficked Södertälje Canal, and also the increased nutrient input from Himmerfjärdsverket.    This study could be a part of the process of working towards a “good environmental status” in the Baltic Sea. However, continued and improved work is needed for further and more accurate interpretations.

In the North Pacific Subtropical Gyre, a nearly-annual phytoplankton bloom forms near the subtropical front at ~30° N. Mixed communities of nitrogen-fixing diatom symbioses (diatom-diazotroph associations) increase 10²-10³ fold in these blooms. In July 2008 (31.46˚N 140.49˚W) and August 2009 (25.18 °N 154 °W), two blooms were sampled to determine diatom-diazotroph association species composition, physical, and chemical characteristics of the water column. In both 2008 and 2009, the dominant diatom-diazotroph association was the Hemiaulus hauckii-Richelia intracellularis symbiosis. The 2009 subtropical front bloom was missed; however, another bloom closer to Hawaii was sampled where diatom-diazotroph association abundance was 10-fold lower (10² cells Lˉ¹) than 2008 despite surface chlorophyll a values that were 3 times greater. Both blooms showed substantial changes in phytoplankton size structure with the >10 μm size chlorophyll a fraction increasing from 10 to 40 % in 2008. In the 2009 bloom, the non-symbiotic pennate diatom Mastogloia woodiana numerically dominated (>150,000 cells Lˉ¹) and formed aggregates that resulted in substantially higher % of netplankton chlorophyll a fractions. Summer open ocean blooms from the two years share a common trend of Hemiaulus dominance of the diatom-diazotroph association population and size structure changes. However, non-symbiotic species can dominate the overall bloom, and diatom-diazotroph association species may not be responsible for the chlorophyll a increase. These two years may represent different types of blooms or temporal changes within summer diatom blooms. The increased biomass in the larger-size fraction suggests these blooms are potential sites for carbon export from the surface layer. / text

To test the applicability of anuran tadpole functional ecology with regards to diet as a tool to determine ecosystem function of aquatic habitats, all the presently known as southern Africa anuran species’ tadpoles were assigned to ecomorphological guilds. The data set included 106 anuran tadpole species and 84 variables, which include: 23 habitat; 49 morphological; 9 behavioral; and 3 development (time metamorphosis) related variables. Although the data set for the guild delineation did not include genetic data, a phylogeny (evolutionary approach) was used to obtain a tree where species are grouped together based on shared characteristics, similar to that of a cluster analysis where each cluster or group is a guild. Maximum parsimony was employed with PAUP 4.0b10 to construct consensus trees using heuristic search settings. The phylogenetic/taxonomic affiliation of the species in each ecomorphological guilds’ was also observed by constructing a phylogenetic tree. The 12S and 16S mitochondrial gene sequences were retrieved from Genbank, to represent the major lineages documented in the anurans of southern Africa thus far. The ecomorphological guild delineation was further supported by quantify tadpole gut contents to determine their trophic status. Information on the feeding behavior of four guilds was obtained by analyzing a representative anuran tadpole species from each. The IUCN red list of threatened species was consulted to obtain the conservation status of the 106 anuran species used for this study, which made it possible to determine whether there is a link between species found in the same ecomorphological guilds and those species’ conservation status. Considering the high diversity of anuran species in the Phongolo region (offering access to a variety of tadpole guilds), and the ability to analyse the diatom communities found in the gut contents of tadpoles. A portion of this study supplemented the assessment of ecosystem functioning and management of aquatic resources of the lower Phongolo River and floodplain, by providing information regarding the health. Diatom bioassessment was applied as a tool for inferring water quality. The polygenetic approach proved to be very effective for the guild delineation, permitting the recognition of 10 fully characterized ecomorphological guilds, a number of which corresponded with previously characterized guilds. Terminology had to be produced for three new guilds, based on the guild defining criteria. The polygeny of the anuran species within the guild, although belonging to different genera and families belonged to the same phylogenetic clade. The trophic analysis supports the guild delineation, since a clear distinction could be made between the percentage and combination of materials from each trophic category ingested by tadpoles from different ecomorphological guilds. Even though some similarity can be seen between species, based on the criteria for the endangered status, there was still no true correlation between IUCN status and ecomorphological guild. The fact that the critically endangered, endangered and vulnerable species are distributed over so many guilds further emphasizes the extent of amphibian decline. The majority of the diatom species found in the Phongolo River and floodplain favor brackish water, with a moderate to high electrolyte content. Indicating that the Phongolo River and the section of the floodplain considered for this study had a high salinity. This might be due to the water bodies’ close proximity to the coast. The diatom index scores indicated the presence of organic pollutants and labelled these water bodies as mesotrophic to eutrophic. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

To test the applicability of anuran tadpole functional ecology with regards to diet as a tool to determine ecosystem function of aquatic habitats, all the presently known as southern Africa anuran species’ tadpoles were assigned to ecomorphological guilds. The data set included 106 anuran tadpole species and 84 variables, which include: 23 habitat; 49 morphological; 9 behavioral; and 3 development (time metamorphosis) related variables. Although the data set for the guild delineation did not include genetic data, a phylogeny (evolutionary approach) was used to obtain a tree where species are grouped together based on shared characteristics, similar to that of a cluster analysis where each cluster or group is a guild. Maximum parsimony was employed with PAUP 4.0b10 to construct consensus trees using heuristic search settings. The phylogenetic/taxonomic affiliation of the species in each ecomorphological guilds’ was also observed by constructing a phylogenetic tree. The 12S and 16S mitochondrial gene sequences were retrieved from Genbank, to represent the major lineages documented in the anurans of southern Africa thus far. The ecomorphological guild delineation was further supported by quantify tadpole gut contents to determine their trophic status. Information on the feeding behavior of four guilds was obtained by analyzing a representative anuran tadpole species from each. The IUCN red list of threatened species was consulted to obtain the conservation status of the 106 anuran species used for this study, which made it possible to determine whether there is a link between species found in the same ecomorphological guilds and those species’ conservation status. Considering the high diversity of anuran species in the Phongolo region (offering access to a variety of tadpole guilds), and the ability to analyse the diatom communities found in the gut contents of tadpoles. A portion of this study supplemented the assessment of ecosystem functioning and management of aquatic resources of the lower Phongolo River and floodplain, by providing information regarding the health. Diatom bioassessment was applied as a tool for inferring water quality. The polygenetic approach proved to be very effective for the guild delineation, permitting the recognition of 10 fully characterized ecomorphological guilds, a number of which corresponded with previously characterized guilds. Terminology had to be produced for three new guilds, based on the guild defining criteria. The polygeny of the anuran species within the guild, although belonging to different genera and families belonged to the same phylogenetic clade. The trophic analysis supports the guild delineation, since a clear distinction could be made between the percentage and combination of materials from each trophic category ingested by tadpoles from different ecomorphological guilds. Even though some similarity can be seen between species, based on the criteria for the endangered status, there was still no true correlation between IUCN status and ecomorphological guild. The fact that the critically endangered, endangered and vulnerable species are distributed over so many guilds further emphasizes the extent of amphibian decline. The majority of the diatom species found in the Phongolo River and floodplain favor brackish water, with a moderate to high electrolyte content. Indicating that the Phongolo River and the section of the floodplain considered for this study had a high salinity. This might be due to the water bodies’ close proximity to the coast. The diatom index scores indicated the presence of organic pollutants and labelled these water bodies as mesotrophic to eutrophic. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

This thesis presents improvements to a method for measuring the production of biogenic silica (bSiO2) by diatoms, a group of microscopic algae with siliceous cell walls (frustules) that dominate the marine cycling of silicon (Si) and account for a significant proportion of global marine primary productivity. Using the fluorescent dye PDMPO, diatom bSiO2 can be labeled as it is produced and then quantified using fluorometry to determine community-wide bSiO2 production. A distinct advantage of PDMPO over more traditional tracers of bSiO2 production is that the combination of measurements of PDMPO by fluorometry and by fluorescence microscopy allows for the quantification of cell (and thus taxa) specific bSiO2 production within a mixed community. However, the robustness of PDMPO as a quantitative tracer of diatom bSiO2 production has not been sufficiently investigated. To address this, experiments were conducted both in the lab, and at two field locations where diatoms are known to be abundant, namely the continental shelf off the west coast of Vancouver Island, and Saanich Inlet, a highly productive fjord located on southern Vancouver Island. Laboratory culture experiments demonstrated that concentrations of PDMPO >500 nmol L-1 reduced growth rate in the diatom Thalassiosira pseudonana, and affected the Si:PDMPO ratio of incorporation. The relationship between SiO2 and PDMPO incorporation was significantly affected by diatom species, though this effect was small (8%) when cells were lysed. From these experiments, a Si:PDMPO incorporation ratio of 4200 ± 380:1 was determined, which predicted 30% more bSiO2 production for PDMPO incorporation than previous studies, and better agreed with bSiO2 production rates determined using established methods in Saanich Inlet. However, bSiO2 production rates were over-estimated by the PDMPO method when rates were less than 1 µmol L-1 d-1. In a few cases, this occurred when dinoflagellates were numerically dominant, but for the majority of samples, dinoflagellates were low in abundance, and over-estimation by PDMPO may be related to low dissolved Si(OH)4 concentration. Protocols for quantifying PDMPO fluorescence by microscopy were optimized by using a low numerical aperture microscope objective. Additionally, measurements of fluorescence intensity were calibrated using a fluorescent microscope slide as a standard, which served to correct for unevenness of illumination across the field of view. With these protocol modifications, quantification of PDMPO by microscopy agreed with PDMPO measured by fluorometry. When PDMPO was measured by microscopy in the field, the contribution of diatom taxa to PDMPO fluorescence differed from their contribution to cell numbers. In many cases this was due to large diatom taxa producing more bSiO2 per cell than smaller taxa. However, much of the difference between cell numbers and PDMPO fluorescence was not explained by differences in cell size. This suggests that the diatom taxa had different specific bSiO2 production rates, which could be estimated using PDMPO. This thesis highlights the strength of the PDMPO tracer for understanding diatom community dynamics. The use of PDMPO should allow the relationship between diatom community composition, growth and productivity to be better illuminated in the oceans. / Graduate / 0416 / jelong@uvic.ca

The marine silicon and carbon cycles are intrinsically linked by a unique group of primary producers; the diatoms. These siliceous-walled phytoplankton play a significant role in carbon export, making them a critical component of the global biological carbon pump with the power to affect climatic change. In this thesis, the silicon isotope composition (δ30Si) preserved in diatom opal is used together with the δ30Si of sponge opal, a powerful new proxy for deepwater silicic acid concentration, to document the Cenozoic Silicon cycle, shedding light on its role in carbon cycling and global climatic change. This study has developed a novel size-separation methodology to produce the first core top calibration of diatom δ30Si. The calibration demonstrates that diatom δ30Si exhibits a strong negative correlation with surface water silicic acid concentration, supportive of its application as a proxy for silicic acid utilisation. The refined method is used to produce a diatom δ30Si record, for the first time combined with sponge δ30Si, to gain insight into the Southern Ocean silicon cycle over one of the largest Cenozoic climatic shifts; the onset of Antarctic glaciation (~33.7 Ma). The two δ30Si records yield the first geochemical footprint to demonstrate that diatom proliferation, coincident with the onset of Antarctic circumpolar current flow, was a precursor event to the Eocene-Oligocene Transition. Diatoms are shown to have played a role in climate cooling through enhanced export and burial of organic carbon on the seafloor. The first long term reconstruction of silicic acid concentration in subsurface waters of the Southern Ocean, which spans the Late Eocene to the earliest Pliocene, provides new evidence that oceanic vertical mixing rates, coupled with the efficient removal of silicon from the surface by the diatoms, have been the most important factor in controlling the silicon chemistry of the ocean over the Cenozoic.

The freshwater ecosystems in the western Canadian Arctic are threatened by multiple and interacting stressors, as high-latitude regions are undergoing rapid change resulting from climate warming and other human-related activities. However, due to the paucity or absence of monitoring data, little is known about long-term changes in lake ecosystems. This thesis addresses this knowledge gap by using paleolimnological techniques to assess the responses of freshwater ecosystems in the Mackenzie Delta region to three major stressors predicted to become increasingly important, namely impacts from accelerated permafrost thaw, marine storm surges, and hydrocarbon exploration. Using a paired-lake design, six reference lakes were compared to six lakes impacted by retrogressive thaw slumps, an important form of thermokarst in this region. While all of the study lakes have undergone ecologically significant biological changes over the last ~200 years as a result of warming, lakes impacted by thaw slumps have changed more due to the cumulative effects of warming and heightened permafrost thaw. In addition to warming, the outer Mackenzie Delta is a low-lying landscape that is susceptible to inundation by marine storm surges from the Beaufort Sea. A large storm event in 1999 flooded >10,000 hectares of the outer delta. My paleolimnological data show that this marine intrusion resulted in diatom assemblage changes in flooded lakes on a landscape-scale that were unprecedented in the recent past, suggesting recent warming, and associated sea-ice decreases, are making this region more susceptible to storm-surge damage. Finally, lakes impacted by sumps used to dispose of the drilling by-products of hydrocarbon exploration exhibit distinct water chemistry, and are particularly elevated in potassium and chloride, which form a major component of some drilling fluids. Related to this, a discernible change in cladoceran assemblages coeval with the time of sump construction suggest that sump failure has resulted in biological changes in affected lakes. Collectively, this research shows that the ecosystems of the western Canadian Arctic are under threat from multiple stressors that have resulted in changes to the chemistry and biology of the freshwater resources of this region. / Thesis (Ph.D, Biology) -- Queen's University, 2013-04-17 09:30:14.671

Lakes Magadi (Kenya) and Manyara (Tanzania) occupy closed basins in the southern Gregory Rift valley. Water in these lakes is presently shallow and saline, testifying to the dominance of evaporation (E) over precipitation (P). Past changes in the P: E ratio, and hence in palaeoclimate, can be reconstructed from evidence of the former extent of these lakes. Lake-level fluctuations engender marked variation in water chemistry, and consequently on the composition of the limnological biota. One approach is to examine the sedimentary record of diatoms (unicellular algae), which are excellent indicators of water chemistry and relative water depth, and whose modem distribution is sufficiently well known to allow the quantitative reconstruction of chemical parameters. Diatom analysis of 116 samples from a series of radiometrically dated (14C and U/Ib) sediment cores has revealed significant changes amongst the diatom assemblages during the Late Quaternary. Conductivity and pH have been estimated from the fossil samples by transfer functions (Gasse unpublished, Gasse 1986b). However, the interpretation of fossil diatom assemblages is often problematical in hypersaline environments. Difficulties arise as a result of the operation of taphonomic and diagenetic processes which can severely alter the composition of the diatom assemblagesfr om the ambient population at the time of deposition. Probably the most important factor responsible for assemblage diagenesis in saline lakes is silica dissolution, and this is explored further by a series of laboratory experiments. Results indicate that silica dissolution acts differentially between species, by removing the smaller, more delicate taxa first, and causing the relative enrichment of large robust forms in the fossil samples. A similar dissolution gradient may be reflected in modem samples studied near hot springs at Magadi. Differential dissolution is potentially an important source of error in palaeoenvironmental reconstructions, but, with the outcome of these experiments, it has been possible to assess the extent to which the dissolution process may have shaped the diatom records from Magadi and Manyara. The bulk of the palaeolimnological evidence is focussed upon two periods, 30,000-20,000 BP and 12,700-9,500 BP. The earlier period is most clearly dated in the core from Manyara, where the diatom record suggests the development of an intermediate level lake between c. 27,500 BP and c. 26,000 BP. This is a more complete representation of the same lake phase found in earlier studies from Manyara by Holdship (1976) based on diatoms, and by Casanova (1986a) on stromatolites 20M above the present lake. This time interval may also be represented by the central portion of the Magadi cores NF1 and NF2 but here dating is more problematical. The period 12,700-9,500 BP was one of major lacustrine transgression across Africa although the fine-structure of this event is less well known. Cores NF1 and NF2 from Magadi provide a detailed register of this phase indicating a major highstand from c. 12,700-11,000 BP when the lake became deep enough to stratify and deposit laminated couplets. At c. 11,000 BP the diatoms show that salinity increased greatly from fresh-oligosaline to meso-hypersaline which was probably a consequence of lake level falling.

The class Bacillariophyceae, encompasses all diatoms that possess a raphe. Members of the orders Bacillariales, Rhopalodiales and Surirellales have a canal raphe system. Historically, the possession of this character was considered support for a close evolutionary relationship. To investigate phylogenetic relationships, a three gene dataset was constructed for 49 strains representing 9 of the 11 orders within the Bacillariophyceae. We provide the first formal tests of homology of the canal raphe system and the first demonstration that the Rhopalodiales are nested within the Surirellales. Results strongly reject the monophyly of Bacillariales, Rhopalodiales, and Surirellales thereby discounting the canal raphe as a homologous character. The Surirellales include three families: Surirellaceae, Entomoneideaceae, and Auriculaceae, while Rhopalodiales has only three genera in one family, the Rhopalodiaceae. In order to test familial and generic concepts, I expanded taxon representation and collected DNA sequence data for 125 strains. Taken together, only 5 of the 12 genera (Entomoneis, Stenopterobia, Cymatopleura, Petrodictyon and Epithemia) were found to be monophyletic. Our current concepts of the two most species-rich genera, Surirella and Campylodiscus, are too broad as the analyses resolved taxa from these two genera into multiple independent lineages. The “Robustoid” lineage, comprised of Surirella Robustae, Campylodiscus Robusti, and Stenopterobia, exhibits a high degree of endemism within ancient Lake Ohrid, with 17 species considered endemic or relict taxa. A dataset of three molecular markers and 71 Robustoid taxa from Lake Ohrid, Europe, and North America was used to construct a preliminary phylogeny. The aim was to investigate phylogenetic relationships and test hypotheses of speciation and morphological evolution. The recovered paraphyly of Lake Ohrid taxa eliminates the possibility that the Ohrid Robustoids as a whole are a product of intralacustrine speciation. However, sister relationships between putative Ohrid endemics and unexplored morphological diversity within some species complexes (e.g. Campylodiscus marginatus, Scoliodiscus spp.) leave open the possibility that these lineages may be the result of intralacustrine speciation. / text