The availability of phosphorus from the anoxic hypolimnia of lakes to epilimnetic plankton was investigated by experimental studies on eight lakes in Ontario and Quebec. Availability was determined with a short-term bioassay based on the standardized retardation of planktonic uptake of phosphorus tracer in the presence of orthophosphate; availability was also estimated by SRP (soluble reactive phosphorus) analysis, since approximately 90% of SRP was available in anoxic waters. / Iron concentrations were high in some hypolimnia, but should become diluted after mixing with surface water. When iron concentrations after mixing exceeded 0.20 mg/L, aeration lowered availability and SRP. Therefore, samples from anoxic hypolimnia were kept anoxic. The fate of hypolimnetic phosphorus at turnover was studied by construction of a budget for SRP, total phosphorus, particulate iron containing phosphorus and particulate biological phosphorus at fall turnover in Lake Magog. Despite high concentrations of hypolimnetic iron, only 30% of the upwelling hypolimnetic phosphorus combined with iron after complete mixing, 30% was incorporated into biomass and 38% stayed potentially available as SRP. / In two lakes, hypolimnetic iron was undetectable hydrogen sulfide concentrations were high. H(,2)S interfered with the SRP analysis and poisoned plankton. After degassing, routine SRP analysis was possible, and availability was close to 100%. Iron and H(,2)S interference in the SRP analysis were circumvented by degassing or by maintaining anoxia. A simpler method, the analysis of TRP (total reactive phosphorus) after aeration, was developed which analyses SRP quantitatively in anoxic waters.

The overall aim of this thesis was to determine the relative importance of heterotrophy and autotrophy in lake plankton. Empirical analyses using extensive surveys of literature data revealed three specific patterns in metabolism and biomass structure in freshwater plankton. First, the ratio of phytoplankton production to plankton respiration (P/R ratio) tends to be low in unproductive lakes ($<$1), and increases along gradients of enrichment. Second, the contribution of planktonic heterotrophs (bacteria and zooplankton) to community respiration is highest in oligotrophic lakes. Third, planktonic heterotrophs dominate community biomass in oligotrophic lakes, whereas phytoplankton increasingly dominate plankton biomass along gradients of enrichment. These three distinct patterns were then tested simultaneously in a set of lakes that span a wide trophic gradient. Results indicated that the plankton of oligotrophic and mesotrophic lakes were characterized by P/R ratios well below unity, and a high contribution of heterotrophs to both community respiration and biomass. These trends are completely the opposite in the most productive lakes. The plankton communities of oligotrophic temperate lakes are predominantly heterotrophic and extensively utilize external inputs of carbon, and therefore only the plankton of eutrophic lakes conformed to the classical phytoplankton-based food web. In most lakes, excess heterotrophic activity could be supported by inputs of organic matter from the drainage basin. Excess plankton respiration, fueled by allochthonous organic carbon, could represent an important source of CO$ sb2$ to lakes.

Zooplankton play a vital role in the world's oceans in terms of transport of carbon out of the surface layer and providing food for fish. Zooplankton are patchily distributed on all scales, and this has important consequences for both sampling and understanding their role in the ocean. The distribution of zooplankton on different scales forms the focus of this study. Three Atlantic Meridional Transect (AMT) cruises were carried out and data made available from three previous cruises. Zoo plankton data were collected using a combination of vertical nets and using an optical plankton counter (OPC) sampling from the pumped seawater supply. Validation of methods showed that the OPC data could reliably be converted to carbon and numerical abundance estimates for open ocean conditions. Spectral analysis suggested that surface zooplankton heterogeneity followed a power law relationship over several scales. Over the 30 to 1000 km range this was approximately -1, and for smaller and larger scales the slope was reduced. Chlorophyll was less patchy, following temperature and salinity over the same range with a slope of -1.8. Analysis of large scale heterogeneity showed clear latitudinal trends in diversity, particularly evident in the copepod genera, with low diversity at high latitudes. The size structure appeared to be more closely related to the productivity of the area, with high zooplankton biomass associated with larger zooplankton. Regions with similar copepod communities were identified. These were found to be similar to other pelagic regions, but less closely related to watermasses or production regimes. Multiple linear regression of surface zooplankton biomass showed a strong relationship with the physics (temperature and salinity), chlorophyll and the time of day, accounting for 55% of the variability. Use of the regression equations to predict new transects gave R²=0.34. Improvement could be made by dividing the transect into smaller regions. Neural networks gave enhanced predictability (R² = 0.77 for the training set, and R²= 0.47 for the novel set) with a simpler model, although similar variables were important. This study has shown that copepods show latitudinal gradient in diversity, associated with seasonality, and form regions of similarity that do not conform to biogeochemical provinces or the watermasses. Neural networks may be used to predict zooplankton abundance from a few readily available parameters.

The aim of this thesis is to incorporate the smallest organisms, in particular the heterotrophic bacteria and their predators, more fully into current descriptions of aquatic community structure and dynamics. A strong, positive empirical relationship was found between bacterial abundance and chlorophyll concentration in freshwater and marine systems. Common members of the photosynthetic phytoplankton (all chrysophyceans) were shown to be major, even dominant, grazers of these bacteria. This phagotrophic capability is quantitatively important to the bacterioplankton, to the mixotrophs themselves, and in some cases, to the structure of the limnological community as a whole. Grazing by mixo- and heterotrophic protozoans is concentrated on the largest bacterial cells that also have the greatest growth rates. Relatively lower removal rates of the tiniest cells, with low growth rates, is proposed to explain their numerical dominance in lakes.

Thesis (Ph. D. - Biological Sciences)--University of Arizona. / Includes bibliographical references.

Diss. Umeå : Univ., 2005.

Thesis (Ph. D.)--University of Michigan, 1939. / Thesis note on label mounted on t.p. "Reprinted from Ecological monographs, 11 ... January, 1941." "Literature cited": p. 18-19.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xxii, 277 p.; also includes graphics. Includes bibliographical references (p. 252-277). Available online via OhioLINK's ETD Center.

Zugl.: Aachen, Techn. Hochsch., Diss., 2009

Thesis (M.A.)--California State University, Fullerton, 1982. / Photocopy of typescript. Includes bibliographical references (leaves 55-57).