Thesis (doctoral)--Universität Lausanne, 1917. / Includes bibliographical references (p. 47-49).

Thesis (Ph.D.)--Baylor University, 2006. / Includes bibliographical references (p. 127-145).

No description available.

No description available.

The role of crustacean zooplankton in changing the size structure of phytoplankton communities was examined in Lake Memphremagog, Quebec. The hypothesis that zooplankton have a selective effect on various algal size classes, within the net- and nannoplankton, was tested during different periods of the growing season in controlled field experiments. Depending on the pattern of loss rates imposed by zooplankton on different algal size fractions, it is shown that zooplankton can both accelerate and decelerate successional events in the phytoplankton. Manipulation of zooplankton biomass produced significant changes in algal phosphorus demand, estimated from observations on the short-term dynamics of orthophosphorus. It is shown that the presence of zooplankton reduces the phosphorus deficiency of the phytoplankton in early periods of the season. Empirical relationships are also presented, based on literature observations, to predict variation in feeding selectivity of cladocerans and variation in the biomass of zooplankton among lake ecosystems.

Thesis (M.S.)--Oregon State University, 1988. / Typescript (photocopy). Includes bibliographical references (leaves 140-142). Also available on the World Wide Web.

Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, 2003. / Bibliography: leaves 309-329.

Thesis (M.S.) in Oceanography--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 42-48).

In field experiments designed to induce dense phytoplankton crops by phosphate and nitrate additions to enclosures in a bed of Potamogeton filiformis in Loch Fitty, the anticipated phytoplankton were not produced. Bioassays showed that phytoplankton were limited by phosphorus and nitrogen. No evidence for an allelopathic effect was found. Macrophyte uptake was responsible for removing 36% of the nitrate added, and the sediment responsible for a part of the phosphate uptake. Some phytoplankton uptake was inferred from the increased zooplankton numbers in enclosures receiving phosphate and nitrate. Nutrient additions had no effect on macrophyte standing crop, as predicted, because the sediment provided an adequate nutrient supply. With decay of macrophytes and nutrient release, phytoplahkton increased in certain enclosures, but not others, probably as a result of large increases in zooplankton numbers and hence grazing pressure. The filamentous alga Rhizoclonium became abundant at the end of the season in enclosures receiving phosphate and nitrate, but did not appear to harm the macrophytes. Epiphytes were only visibly obvious in one enclosure. Failure to produce dense phytoplankton crops in the field led to a laboratory study of the effects of phytoplankton-induced carbon competition on macrophytes. Phytoplankton species were shown to have a smaller total resistance to CO2 fixation than macrophytes and hence greater photosynthetic rates under most CO2 concentrations. The boundary layer was the largest component of the total resistance in macrophytes, suggesting that the thin leaves of many macrophytes were a response to this rather than an aid to diffusion. The linear leaves of other species could be adaptations to reduce the boundary layer thickness. A pH-drift technique confirmed that the best phytoplankton species were more efficient at carbon removal than any macrophyte shoots. The macrophytes were even less efficient when the whole plant was considered. The carbon compensation point was shown to rise under the low light conditions that would be found under a dense phytoplankton crop. Macrophytes showed seasonal changes in carbon extractive ability, but the range was less than published data for phytoplankton from a lake, probably because the latter consists of a series of populations, which are closely adapted to the prevailing conditions. Different leaf types of heterophyllous macrophytes had different CO2 compensation points and one leaf type could use HCO3. A growth experiment confirmed that carbon competition with phytoplankton could have a detrimental effect on macrophytes.

Laboratory and field experiments examined several aspects of the interaction of freshwater phytoplankton species and plankton communities with nitrogen and phosphorus nutrient resources. The laboratory studies focused on the following three main areas: 1) effects of nutrient 'patchiness' on phytoplankton community structure; 2) kinetics of phosphate (PO₄⁻³ ) and ammonium (NH₄⁺) uptake of phytoplankton grown under non-steady-state but limiting rates of nutrient supply; 3) the effect of different N:P supply ratios on phytoplankton NH₄⁺ and PO₄⁻³ uptake kinetics and community structure. Nutrient 'patchiness' was simulated by altering the frequency of nutrient addition to cultures. Under conditions of infrequent addition (once per 18 days) dominance shifted to a larger species, and the average cell size of another species increased. Observations of PO₄⁻³ uptake kinetics were not consistent with most other studies where kinetics were determined under steady-state conditions. With respect to PO₄⁻³, the duration over which maximum uptake rates were sustained was species specific. There was a short lag before maximum uptake rates were realized, and whether maximum uptake rates occurred at the lowest or at intermediate dilution rates depended on the time scale over which the uptake measurements were made. NH₄⁺ uptake rates were found to be greatly enhanced during the first few minutes of uptake. When natural plankton assemblages were grown under N:P supply ratios of 5:1, 15:1 and 45:1 (by atoms), the treatments selected for different competitive dominants. An N:P ratio of 45:1 resulted in total dominance by Synechococcus sp.; cultures grown under 5:1 and 15:1 supply ratios were dominated by Synedra radians, Nitzschia holsatica and Scenedesmus sp. NH₄⁺ and PO₄⁻³ uptake kinetics were not the same in cultures grown under different supply ratios, and ratios of saturated PO₄⁻³ to NH₄⁺ uptake rates were a good indicator of the N:P supply ratio under which the cultures were grown. This relationship was used to derive an index termed the Relative Field investigations were conducted on an oligotrophic coastal lake. NH₄⁺ and PO₄⁻³ uptake rates of size fractionated plankton (< and > 3 um), at a range of substrate concentrations, revealed that a large portion of the total uptake (50-90 % and 65-85 % for NH₄⁺ and PO₄⁻³, respectively) was attributable to cells in the < 3 um fraction. In addition, saturating PO₄⁻³, uptake rates of the > 3 um cells were less sensitive to incubation time than smaller cells. The ratio of saturated PO₄⁻³ to NH₄⁺ uptake rates were consistent with nutrient bioassay experiments, and indicated that N:P supply ratios in the lake were in the range where both N and P could be limiting to phytoplankton growth. / Science, Faculty of / Botany, Department of / Graduate