Several hypotheses concerning the role of fishes in influencing nutrient dynamics in freshwater ecosystems were examined in Lake Memphremagog (Quebec-Vermont). Phosphorus excretion by fishes provides a negligible amount (< 0.33%) in comparison to the quantity taken up by the seston. The phosphorus pools present in the seston and fish community were approximately equal and both were twice the phosphorus content in the zooplankton. Part of this nutrient reservoir is released during the decomposition of fish carcasses. The potential is dependent upon post-spawning mortality rate, the fate of phosphorus in decomposing fish tissue, and the concentrations of allochthonous phosphorus entering the lake. Daily losses of epilimnetic phosphorus from the seston due to fish (up to 40%) and enhancement of nutrient excretion by zooplankton due to size-selective predation are important when open water fish populations are mainly planktivores. When benthic, detrital, or faculative consumers predominate, as in Lake Memphremagog, the effect of fishes on nutrient dynamics through foraging pressure is probably small.

No description available.

Call number: LD2668 .T4 1937 H61

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 18, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Laura McCann. Includes bibliographical references.

Thesis (M.Sc.(Agric)(Animal Science)) -- University of Pretoria, 2001. / Includes bibliographical references.

Digitized by Kansas Correctional Industries

No description available.

Interspecific competition for phosphorus was studied in continuous lake water cultures of phytoplankton communities from Lake Memphremagog, and its outcome shown to depend primarily on the size of the competitors. Comparison of the activity of the inducible enzyme alkaline phosphatase between the lake and cultures operated at various dilution rates (0.06-0.93 day('-1)) established that in situ phosphorus limitation rarely depressed average community growth rates much below 0.6 day('-1). Growth rates under comparable, or even more severe (0.2-0.3 day('-1)) limitation in culture decreased significantly with increasing cell size. Phosphorus uptake kinetics and cell quotas measured by track autoradiography on the competing species showed that biomass and quota-specific uptake rates varied inversely with cell size in highly significant allometric regressions, correctly predicting that competitive outcome should depend on size. Substituted in a variable internal stores model of phosphorus limited growth, the allometric functions for uptake, cell quota, and maximum growth rate correctly predicted observed growth rates except in competition much stronger than natural (D = 0.06-0.2 day('-1)). Failure of the model to encompass cell senescence and death due to severe nutrient stress appeared to account for the discrepancy. Neither the absolute difference in growth rates due to cell size nor the direction of selection among the naturally co-occurring species varied systematically with the intensity of competition, indicating that spatio-temporal variation of limiting phosphorus supply in nature is unlikely to directly select the size or taxonomic composition of phytoplankton communities.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographic references (p. [175]-197).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1958. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 122-130).