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Norint įvertinti vandens telkinio būklę, pakanka patyrinėti kurią nors gyvųjų organizmų grupę. Viena iš tokių indikatorinių sistematinių grupių yra titnagdumbliai (Bacillariophyceae). Dauguma tyrėjų teigia, kad titnagdumbliai yra idealūs indikatoriai biologiniam monitoringui, nes didelis skaičius ekologiškai jautrių rūšių tiek vandenyje, tiek nuosėdose, tiksliai nusako esamą ekologinę situaciją (Dixit et al. 1992). Aulacoseira granulata, Fragilaria crotonensis, Asterionella formosa, Cyclotella sp. Synedra sp. Rhizosolenia sp., Diatoma, Achnanthes, Cyclotella, Stephanodiscus dažnos mezotrofiniuose vandens telkiniuose. Stephanodiscus hantzschii intensyvus vystymasis vandens telkinyje yra aukšto trofiškumo rodiklis bei užterštumo organinėmis medžiagomis indikatorius. Apskritai, išskyrus Stephanodiscus sp., titnagdumbliai stipriai eutrofinių ir hipertrofinių sąlygų ežere nepakenčia. / As is well known as a better state of body water, the more species of living organisms can live in it, and the deterioration of water quality, with a consequent reduction in plant and soil or water surface the number of living species. It remains only for not demanding, resistant to water pollution types. So in order to assess the water situation, it is sufficient to explore any group of living organisms. One such indicator is the systematic group of diatoms (Bacillariophyceae). Aulacoseira granulata, Fragilaria crotonensis, Asterionella formosa, Cyclotella sp. Synedra sp. Rhizosolenia sp., Diatoma, Achnanthes, Cyclotella, Stephanodiscus common in mesotrophic waters. Intensive development of Stephanodiscus hantzschii in water body is a high trophic rate and contamination of organic matter indicator. In general, except for Stephanodiscus sp. diatoms can not stand strongly eutrophic and hypertrophic conditions in the lake.

Until recently it has been widely believed that significant anthropogenic influences on the environment began in Canada following the onset of European colonization. However, our paleolimnological data indicate that centuries prior to European settlement, ponds on Ellesmere and Bathurst Island were impacted by Thule Inuit whalers, whose activities altered nutrient levels in nearby ponds. Two Thule Inuit whaling sites were selected based on input from several archaeologists, to ensure good coverage of the Thule geographic range and proximity to freshwater ponds. Multiple independent paleolimnological proxies have been used to analyze a pond from Ellesmere Island, showing taxonomic shifts in diatoms assemblages coinciding with 1.5 - 2‰ shifts in d15N, during the period of Thule occupation (ca. 1000 – 1670 AD). Increases in the relative abundance of Amphora ovalis, indicate nutrient concentrations above average for the High Arctic. Elevated levels of nitrogen and phosphorus were observed in the pond indicating the continuing influence of nutrient inputs centuries after the abandonment of the camp. Meanwhile, on Bathurst Island, the orientation of the Deblicquy site, such that the large majority of the Thule nutrient inputs are focused towards one of our two study ponds, provided us with the opportunity to compare two ponds that are essentially identical with the exception of the degree of Thule influence. In our “impacted” site, a marked increase in Stephanodiscus minutulus, coincides with a 2‰ shift in d15N. While our a priori determined control site shows no major changes in geochemistry or algal composition. Previous research on Bathurst Island used water chemistry and surface sediment diatoms to construct a diatom-inferred total nitrogen model for Bathurst Island. However, this study was limited by excluding unbuffered, low pH sites which characterize the western half of Bathurst Island. By expanding the previous Bathurst Island dataset to include western sites, we have been able to construct a diatom-inferred pH model which will prove invaluable in future climate research in this region. Together, these three studies serve to highlight the sensitivity of freshwater ecosystems to relatively minor anthropogenic disturbances and represent some of the earliest known anthropogenic impacts on North American aquatic ecosystems. / Thesis (Master, Biology) -- Queen's University, 2007-12-20 15:20:46.342

The acidification and metal contamination of freshwater resources are major environmental concerns in many areas, with Sudbury (Ontario, Canada) having been amongst the most severely impacted. Many scientific investigations have examined the effects of these environmental stressors on aquatic systems, but relatively little is known about the biological recovery process following smelter emission reductions. Therefore, paleolimnological techniques were utilized to determine if diatom and scaled chrysophyte assemblages have recovered toward their pre-disturbance conditions as a result of reduced anthropogenic inputs. Pre-industrial algal assemblages were primarily dominated by circumneutral to alkaline and pH-indifferent taxa. However, there was a shift toward acid-tolerant species in all study lakes with the onset of open pit roasting and smelting operations. Coinciding with emission reductions, scaled chrysophyte assemblages in two of the three study sites have shown evidence of biological recovery. Given the population growth of the city of Sudbury over the last century, and the lack of scientific information regarding cultural eutrophication trends in the region, paleolimnological techniques were also used to track long-term biological changes within diatom assemblages related to cultural disturbances. Historically, oligotrophic diatom taxa primarily dominated the algal assemblages in each of the four study lakes. With the onset of urban environmental stressors there was a shift toward taxa which thrive in more productive systems. In addition, diatom assemblages appear to track increased lakewater pH through time. Finally, geochemical analysis tracked the increase in copper and nickel concentrations in lake sediment with the onset of open pit roasting and smelting activities and the subsequent decline in concentration with emission controls. Metal concentrations in recently deposited lake sediments remain elevated compared to pre-industrial concentrations. Paleolimnological studies comparing pre- and post-disturbance algal assemblages are of interest to lake managers as these data will aid in setting realistic mitigation targets for freshwater systems impacted by acidification, cultural eutrophication, and metal contamination, and will help gauge biological recovery mechanisms. Furthermore, this study provides insight in to the role other environmental stressors (e.g., climate change) may play in the biological recovery process. / Thesis (Master, Biology) -- Queen's University, 2008-07-10 12:04:59.828

Paleoclimatic research in the Canadian Arctic has increased in recent decades; however, there is still much to learn about the nature and extent of past climate change in this vast, environmentally sensitive region. This thesis uses diatom assemblages in dated lake sediment cores as proxy indicators to infer how climate has changed over the Holocene in two very different lakes in the central Canadian Arctic: one located in a poorly-studied geographical region, and another possessing limnological characteristics that are unusual in an Arctic context. Lake TK-2 is located in the low Arctic tundra. Paleolimnological studies from this region are lacking, as most have centered on sites in the High Arctic Archipelago or around Subarctic treeline. Marked changes in the diatom assemblages in TK-2 throughout the Holocene included potential evidence for the 8.2k cooling event, which has not been previously reported from other Canadian Arctic paleolimnological studies. In addition, diatom shifts occurring ~7000 and ~3500 cal yr BP are indicative of mid-Holocene warming and subsequent Neoglacial cooling, respectively, the timings of which agree with those from other studies farther south. Finally, shifts in the diatom assemblages in the upper sediment layers, beginning in the early-to-mid 19th century, are consistent with reduced ice cover, related to recent warming. Stygge Nunatak Pond, a small, closed-basin pond located on a nunatak in the High Arctic on Ellesmere Island, is characterized by unusually high ionic concentrations for an inland Arctic pond. As in TK-2, Stygge’s diatom assemblages changed substantially throughout the Holocene, but especially in the most recent sediments. Diatom shifts near ~10,500 cal yr BP suggest an early onset for the Holocene Thermal Maximum (and for the successive Neoglacial cooling trend) in this region, consistent with previous studies from the High Arctic. Marked diatom assemblage changes occurred in the most recent sediments, and are indicative of climate warming and reduced ice cover, as well as increased ionic concentration due to enhanced evaporative concentration. The dynamic nature of the diatom assemblage changes at the Stygge site suggests that sediments from these rare athalassic ponds represent an especially sensitive archive of Arctic climatic and environmental change. / Thesis (Master, Biology) -- Queen's University, 2008-11-12 16:46:47.174

In response to sulphur dioxide emission reductions in North America and Europe, there has been a recent shift in research focus towards understanding ecosystem recovery. Evidence for reversibility in the effects of acidification on lake ecosystems within North America has been, for the most part, constrained to a single locality (Sudbury, Ontario). Lakes in a fume-kill area near Wawa, Ontario, present a new and rare opportunity for studying potentially rapid chemical and biological recovery patterns from extreme acidification. Several lakes acidified (pH ~3) during a period of local iron sintering from 1939 to 1998, and although minimal historical data are available, striking biological recovery has recently been observed. This study used paleolimnological techniques to track diatom (class Bacillariophyceae) responses to historical water quality changes in five fume-kill lakes near Wawa. Prior to the onset of iron sintering, the sediment-recorded diatom assemblages were dominated by species that are typically found in circumneutral or slightly alkaline lakes. Following the known occurrence of lake acidification, there was a striking shift in the sediment record towards dominance by acid- and metal-tolerant species. Water quality of the fume-kill lakes has since improved (i.e. pH has increased from ~3 to ~7 and metal concentrations have decreased). In four of the five lake cores, this was reflected by a decrease in the relative abundance of acid-tolerant species. Surprisingly, diatom communities were not progressing towards pre-disturbance species assemblages. Factors impeding the return of native species might include metal enrichment in surface sediment and potentially altered lake thermal regimes. Documenting and understanding recovery trajectories is necessary to help lake managers evaluate policy decisions regarding the efficacy of emission reduction programs and mitigation measures. This thesis provides evidence from one location in addition to Sudbury that the ecological effects of severe lake acidification can be reversed if SO2 emissions are sufficiently reduced. It also further demonstrates the complexity of recovery patterns in acidified and metal-contaminated lakes. / Thesis (Master, Biology) -- Queen's University, 2009-04-26 18:38:20.58

A two-part paleolimnological study was conducted to examine changes in historical and modern water-quality in Lake of the Woods (LoW) in response to multiple stressors, such as climate change and shoreline residential development. Changes in diatom assemblages were analyzed in the modern and pre-industrial sediment intervals of 17 study sites, and in high-resolution 210Pb-dated sedimentary records from three northwestern bays (Clearwater, Poplar, and White Partridge bays). Patterns in diatom assemblage changes revealed pronounced and synchronous shifts over the last ca. 150 years. The most notable shift in the diatom community structure (~1970 AD) was characterized by an overall shift towards a higher relative abundance of small, centric Cyclotella taxa and planktonic, pennate diatoms (e.g., Asterionella formosa, Fragilaria crotonensis), and a corresponding lower relative abundance of heavily silicified Aulacoseira taxa and small benthic Fragilaria taxa and Achnanthes taxa. Lakewater total phosphorus (TP) concentrations were inferred from sedimentary diatom assemblages. DI-TP reconstructions revealed either no change or a decline in DI-TP since pre-industrial (pre-1850) times at majority (88%) of the top-bottom study sites, and no distinct directional change over the past ca. 150 years at the northwestern bays. Therefore, we concluded that TP was not an important driver of the floristic changes we observed. Chl-a trends indicate that primary production increased during the last ca. 100 years, likely tracking increases in microbial blooms. Changes in diatom assemblage composition and primary productivity have occurred during a period of substantial warming for this region of northwestern Ontario. Strong correlations (r >0.50, p<0.005) between diatom compositional changes, chl-a trends, and local air temperature records and lake-ice phenology suggest that climate-induced changes in lakewater properties may have been key factors driving the observed changes. From these data, we conclude that climate warming, rather than changing shoreline development and TP changes, has had the most pronounced effect on algal communities in the LoW. Estimates of pre-impact lake trophic status can aid in setting realistic mitigation targets for lakes impacted by multiple stressors. Therefore, paleolimnological studies comparing pre- and post-disturbance algal assemblages, such as the investigations we have conducted, are of interest from a lake management perspective. / Thesis (Master, Biology) -- Queen's University, 2010-05-28 13:38:59.472

Freshwater ecological issues are increasingly being recognized within the context of multiple stressors, even though relatively little is known about the limnological and biological consequences of the interactions between various environmental impacts. Moreover, long-term monitoring data are often lacking. To help address these issues, the overall goal of this thesis was to use paleolimnological approaches to document how multiple environmental stressors have altered limnological communities in south-central Ontario lakes. During the last two centuries, Ontario lakes have been subjected to varying intensities of different environmental impacts, including increases in shoreline residential development, forest clearance and regrowth, the deposition of strong acids via the atmosphere, invasion by non-indigenous species, and climate change. I used multiple paleolimnological approaches to: 1) demonstrate how multiple natural and anthropogenic stressors have affected biological assemblages across lakes in the Muskoka-Haliburton region of south-central Ontario, and 2) reconstruct the limnological histories of four lakes from Algonquin Park that have recorded the near complete extirpation of native crayfish species. In the Muskoka-Haliburton lakes, I assessed the extent of limnological changes that have occurred during the past ~15 years by resampling lakes from an earlier survey, using identical paleolimnological methods. Limnological monitoring data document that, since 1992, the lakes have experienced declines in lakewater calcium and SO4 concentrations, while pH declined marginally; in contrast dissolved organic carbon, silica and Total Kjeldahl Nitrogen increased. Marked regional increases in planktonic diatom taxa, including Cyclotella stelligera, Asterionella formosa and Fragilaria crotonensis, occurred in many lake systems, while colonial scaled chrysophyte algae have undergone a widespread decline in favour of unicellular forms (i.e., Mallomonas spp.), driven by interactions between resource limitation and climate change. In the Algonquin Park study lakes, crustacean zooplankton remains revealed a marked decline in daphniid species with high Ca requirements, in favour of smaller Bosmina spp., while diatom and chrysophyte analysis suggest varying degrees of industrial acidification in the four study lakes. The paleolimnological data suggest that the crayfish decline may have began prior to the long-term monitoring record, likely as a result of declines in pH and lakewater Ca related to atmospheric acid deposition. / Thesis (Ph.D, Biology) -- Queen's University, 2012-09-27 12:53:20.518

Productivity in large areas of the world's oceans is limited by low concentrations of dissolved iron in surface waters. Phytoplankton have adapted to persist in these environments by reducing their requirements for iron (Fe) in key metabolic pathways, in some cases by replacing Fe-containing catalysts with their iron-free functional equivalents. This thesis examines the requirements and biochemical roles for copper (Cu) and manganese (Mn) in Fe-limited centric marine diatoms. A major finding of my research is that diatoms have elevated requirements for Mn and Cu when grown in Fe-deficient seawater. Iron deficiency induces oxidative stress and increases the cellular concentrations of toxic oxygen radicals and damage products in Thalassiosira pseudonana. The increased Mn-requirement is used, in part, to activate Mn-containing isoforms of the antioxidant enzyme superoxide dismutase. Cultures co-limited by Fe and Mn exhibit high levels of oxidative stress and an inefficient detoxification pathway that further reduces cell growth. Diatoms isolated from the metal poor open ocean require more Cu to divide than related species from metal-rich coastal waters. This pattern is in stark contrast to all other known nutritive trace metals. One part of the diatom Cu requirement that is independent of provenance is for efficient Fe transport. The additional Cu requirement of oceanic species appears to be due to the constitutive expression of a Cu-containing electron transport protein, possibly plastocyanin. Coastal species, which have higher Fe-requirements for growth, retain the Fe-containing functional homologue cytochrome c6. By employing metals other than Fe within photosynthesis and antioxidant pathways, marine diatoms are able to increase their fitness in Fe-deficient environments. However, Mn and Cu also occur in low concentrations in the open ocean and thus may co-limit growth of natural populations of phytoplankton. Metal enrichment experiments i

This study examined samples part of a larger project exploring environmental changes at Lake Hawdon, mid Canterbury, involving Queen’s University Belfast and the University of Canterbury. The author was responsible for the analysis of 85 fossil diatom samples from Lake Hawdon to create a high resolution study to assess their use as a biological proxy of past environmental changes through the Late Glacial Inter-Glacial Transition. Qualitative interpretations suggest three main phases of environmental change in Lake Hawdon during ~17,000 to 10,000 cal. BP. The first is a cool stage where taxa such as Cocconeis placentula and fragilarioid complex taxa Staurosirella pinnata and Pseudostaurosira brevistriata suggest a cool shallow lake with increasing macrophyte growth. The second phase suggests cold deepening water from at 13,928 +/- 142 to 12,686 +/- 166 cal. BP, dominated by Pseudostaurosira brevistriata, which coincides with the Antarctic Cold Reversal. The third phase represents a warm deep water phase after 12,686 +/- 166 cal. BP, dominated by planktonic taxon Cyclotella stelligera and epiphytic taxon Epithemia sorex, suggesting that Lake Hawdon does not exhibit the Younger Dryas event. Pollen and chironomid data from Lake Hawdon, generated by other project members, are included in the quantitative analyses to further inform palaeoenvironmental inferences generated from diatom data. Chironomid temperature reconstructions complement diatom interpretations for all three phases of change in the lake however diatom resolution allows changes to be detected earlier than other proxies suggest. Stabilisation of the landscape ~12, 686 +/- 166 cal. BP is suggested by tree pollen appearing near the end of the diatom cold phase, confirming with the diatoms and chironomid data that there was a warming out of the cold phase. Interpretations from Lake Hawdon add to other proxy studies in New Zealand that suggest an Antarctic Cold Reversal type event, but fail to highlight the Younger Dryas event. The generation of a transfer function was attempted with the diatom data based on Northern Hemisphere datasets, but a Principal Component Analysis plot highlighted major dissimilarities between the New Zealand fossil data and modern European data. This raised the issue of having morphologically similar but genetically separate taxa, potentially displaying convergent environmental adaptation, a crucial area for further research globally, and particularly in isolated areas like New Zealand.