Large-volume (20-liter) bioassays were carried out in order to assess the effects of major nutrients and micro-nutrients on natural phytoplankton populations in water collected from a site close to the mouth of Yaquina Bay, Oregon. Seven long-term experiments were conducted during the years 1975-1976. A stripping technique employing activated carbon was used to reduce the trace metal and dissolved organic load of a portion of the water. Various combinations of major nutrients (nitrate, phosphate, and silicate) and micro-nutrients (trace metals and vitamins) were added to both the carbon-stripped and the non-carbon-stripped water in order to assess the effects of various nutrient substances on the growth rate, biomass yield, and species composition of the phytoplankton populations which developed from small natural inocula. The major nutrients and the micro-nutrients appear to have fundamentally different effects on the species composition and population growth characteristics of the phytoplankton. The micro-nutrients had marked systematic effects on the species composition of the phytoplankton populations which developed in the experimental vessels, while the major nutrients had minimal effects on species composition. The micro-nutrients appeared essential for the achievement of maximal population growth rates and minimal lags, while the major nutrients had no effect on growth rates or lags. Both the major nutrients and micro-nutrients had significant effects on the final biomass yields. There were seasonal variations in the control of final biomass yields by major nutrients and micro-nutrients. / Graduation date: 1977

A simplified autoradiographic method for estimating species-specific phytoplankton production rates in mixed natural communities was evaluated in the laboratory and employed in the field. Laboratory experiments were designed to test the reliability and variability of the simplified method. Assays of ¹⁴C uptake by liquid scintillation spectrometry were used to evaluate assays by autoradiographic silver grain counts. Linear relationships between the two assays were found for varying activities within a species. With corrections for radiation geometry and self-absorption, a linear relationship was obtained for species from 400 to 50,000 μm³ in cell volume. The coefficient of variation for microscopic grain counting at densities from 10 to 70 grains per 100 μm² was 4% of the mean. Counts of replicate autoradiographs from individual incubations yielded coefficients of variation of 7 and 14% for grain densities of 11 and 30 per 100 μm², respectively. The frequency distribution of grains deposited over different cells of a species with varying photosynthetic activities is indicative of the physiological state of the alga. Samples from five depths at one station in Yaquina Bay, Oregon were incubated in situ with ¹⁴C, daily from 2 April to 7 May 1974. Phytoplankton biomass during the spring bloom reached 7106 μm³ cell volume l⁻¹ and integral production reached 172 mgC m⁻² hr⁻¹. Total community carbon uptake increased with biomass during the study but species-specific uptake decreased as ambient nitrate + nitrite levels decreased. Species-specific production rates were estimated for 22 consecutive days: 16 April to 7 May 1974. Three taxa, Chaetoceros debilis Cleve, Thalassiosira decipiens (Grun.) Jorg., and unidentified flagellates were responsible for over 65% of the community biomass and over 85% of the primary production after 20 April 1974, Carbon-specific uptake rates were calculated for 20 species. Maximum carbon-specific uptake rates (expressed as the percent of the estimated cell carbon content assimilated per hour) for six abundant diatom species ranged from 111 to 158%, but average activity over the study period for 20 species was much lower. Carbon-specific uptake rates (% cell C hr⁻¹) averaged over all samples for the three dominant taxa were: Chaetoceros debilis, 22%; Thalassiosira decipiens, 21%; and flagellates, 54%. Flagellates were always two to three times more productive than the dominant diatoms on a carbon specific basis. Photosynthesis:biomass ratios (P/B) of the three dominant taxa decreased proportionately during the study The percent of total biomass and percent of total carbon uptake contributed by the three dominant taxa were proportional over the period studied. Average daily carbon-specific uptake rates demonstrate that Thalassiosira decipiens succeeded Chaetoceros debilis due to a change in their relative production rates. / Graduation date: 1977

A phytoplankton bloom dominated by the pennate diatom Nitzschia curta (Van Heurck) Hasle was observed during January-February 1983 at a receding ice-edge in the Western Ross Sea, Antarctica. The core of the bloom was found between 100-150 Km from the ice-edge. Nitzschia curta cell densities up to 22 x 10⁶ cells/1 were observed. The nanoplankton contributed to 18% (average) of the total biomass. The contribution of another pennate diatom, Nitzschia closterium (Ehrenberg) W. Smith, was significant in two offshore stations (22% and 90%). Other diatom species, dinoflagellates and other phytoplankton groups were very few in number. A wind-driven upwelling event occurred along the ice-edge. The presence of off-shore species (e.g. Nitzschia kerguelensis) close to the ice suggests the existence of an eddy circulation. Results of elemental composition experiments with 10 Antarctic diatoms showed that the C:Si:N ratio for Antarctic diatoms, when compared to the Redfield-Richards ratio for diatoms of other environments, have less carbon and more silicon per unit nitrogen. Comparison of laboratory results with the field data confirms the anomalous elemental composition of the major bloom species observed in the Ross Sea. Blooms like the one observed in this study seem to be restricted to the Western part of the Ross Sea and appear to be produced in inshore waters late in the austral summer. / Graduation date: 1985

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1982. / Supervised by Robert B. Gagosian (W.H.O.I.). Vita. Includes bibliographies.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1982. / Includes bibliographical references.

Prairie wetlands provide valuable habitat for waterfowl and wildlife and buffer the impacts of upland land uses. Their contribution to Canadas greenhouse gas inventory is poorly understood. The purpose of this study was to compare the spatial and temporal variation in nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from Pond 1 at the St. Denis Wildlife Management Area, Saskatchewan and the Deep Crop Wetland (DCW) at the Manitoba Zero Tillage Research Association farm, Manitoba. Nitrous oxide flux was low on all measurements days: at Pond 1 flux ranged from -1.47 to 6.01 ng N2O-N m-2 s-1 in 2004 and -6.98 to 5.74 ng N2O-N m-2 s-1 in 2005 and flux from the DCW never exceeded 2.50 ng N2O-N m-2 s-1 in 2005. Methane flux from Pond 1 was substantially higher in 2005 (-469.10 to 3776.08 µmol CH4 m-2 d-1) than in 2004 (-251.55 to 191.55 µmol CH4 m-2 d-1). This increase in methane from Pond 1 followed a major increase in water volume in 2005 after snowmelt. Methane flux in 2005 from the open water and riparian sampling points at the DCW ranged from -13.64 to 110.47 µmol CH4 m-2 d-1 and -4.51 to 40.23 µmol CH4 m-2 d-1, respectively. Carbon dioxide flux from Pond 1 and the DCW in 2005 were very similar: open water flux ranged from -96.42 to 95.42 mmol CO2 m-2 d-1 at Pond 1 and 3.21 to 38.94 mmol CO2 m-2 d-1 at the DCW. Despite the similarity in CO2 flux, the DCW had 10- to 15-fold higher levels of macrophytes, phytoplankton and metaphyton biomass and similar levels of periphyton to Pond 1 in 2005. These biomass differences were not, however, reflected in the CO2 or CH4 flux. Pond 1 and the DCW were net sources for greenhouse gases but contributed less greenhouse gas than reports from other aquatic systems.

The methodology of phytoplankton production measurements in the Laurentian Great Lakes and other freshwater lakes has remained largely unchanged in the past 40 years. In most studies photosynthesis from a single water sample is measured across an in vitro light gradient usually using an artificial light source then extrapolating to the in situ environment. These traditional methods are laborious, thus limiting the amount of observations in space and time, and may not accurately represent in situ photosynthesis. Active chl a fluorescence, intrinsically linked to photosynthesis, can be measured in situ and instantaneously. Various bio-optical models that scale these fluorescence measurements to phytoplankton production are gaining widespread attention in the marine environment but have not been extensively tested in freshwater ecosystems. The methodology and efficacy of the various bio-optical models are tested in this thesis using a large dataset of active fluorescence profiles and ancillary water chemistry parameters against synchronously derived in vitro phytoplankton production collected across mixing, trophic and taxonomic gradients in Lake Erie. From this analysis, the most common bio-optical model parameterization yields photosynthetic rates that are largely incongruent with in vitro measurements. Bio-optical models are largely a function of two parameters, the absorption spectrum of photosystem II (aPSII) and the photochemical efficiency of PSII (fPSII). In Lake Erie fPSII is relatively constrained suggesting that even nutrient limited phytoplankton achieve balanced growth by adjusting the supply of energy through changes in light harvesting (aPSII) to match the demand for photosynthetic energy. This thesis goes on to demonstrate the success of bio-optical models depends largely on the formulation of aPSII. Alternative methods to derive aPSII, largely ignored in published bio-optical models, are reviewed, formulated, and when incorporated into a bio-optical model and compared to synchronous in vitro production measurements, this novel bio-optical model outperforms all other comparative studies performed across a taxonomic gradient.

Electron flow through Photosystem II (PSII) is essential to all life on Earth. The efficiency of this process in freshwater phytoplankton can be depressed by nutrient limitation, ultraviolet radiation (UVR), and excessive photosynthetically active radiation (PAR). The effects of nutrients and radiation on PSII function of natural communities were assessed using changes in the variable fluorescence of PSII (PSII VF), as determined by a pulse amplitude modulation (PAM) fluorometer. The net susceptibility to photoinhibition of PSII depends upon the sensitivity of the assemblage to photodamage and the efficiency of recovery. Damage and recovery rates were quantified by fitting changes in FV:FM during experimental spectral exposures to the model of Kok (1956). Phytoplankton from deep chlorophyll maxima were found to exhibit much higher photosynthetic impairment under UVR exposure than epilimnetic communities in two lakes, due to differences in both damage and recovery rates. In six temperate lakes of the Dorset-Haliburton region, the susceptibility to UVR-induced photoinhibition of PSII was found to be a function of the water transparency (dissolved organic carbon content) of the systems from which the plankton were isolated, with no obvious taxonomic pattern to the responses. Nutrient (nitrogen & phosphorus) supplementation of communities from the Dorset Lakes and from Lake Ontario did not have strong effects on PSII VF, and did not alter the response of Lake Ontario phytoplankton to spectral irradiance. Diurnal changes in FV:FM of Lake Ontario phytoplankton were modeled and average values for the upper half of the water column showed reasonable agreement with observed data; however it is suggested that the addition of a model to simulate vertical mixing could improve the depth-specific accuracy of the predictions. It is concluded that the light history (photoacclimation status) of phytoplankton is the major determinant of the sensitivity of PSII to UVR, and that the nutrient status and taxonomic composition of phytoplankton communities have a comparatively minor influence.

Prairie wetlands provide valuable habitat for waterfowl and wildlife and buffer the impacts of upland land uses. Their contribution to Canadas greenhouse gas inventory is poorly understood. The purpose of this study was to compare the spatial and temporal variation in nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from Pond 1 at the St. Denis Wildlife Management Area, Saskatchewan and the Deep Crop Wetland (DCW) at the Manitoba Zero Tillage Research Association farm, Manitoba. Nitrous oxide flux was low on all measurements days: at Pond 1 flux ranged from -1.47 to 6.01 ng N2O-N m-2 s-1 in 2004 and -6.98 to 5.74 ng N2O-N m-2 s-1 in 2005 and flux from the DCW never exceeded 2.50 ng N2O-N m-2 s-1 in 2005. Methane flux from Pond 1 was substantially higher in 2005 (-469.10 to 3776.08 µmol CH4 m-2 d-1) than in 2004 (-251.55 to 191.55 µmol CH4 m-2 d-1). This increase in methane from Pond 1 followed a major increase in water volume in 2005 after snowmelt. Methane flux in 2005 from the open water and riparian sampling points at the DCW ranged from -13.64 to 110.47 µmol CH4 m-2 d-1 and -4.51 to 40.23 µmol CH4 m-2 d-1, respectively. Carbon dioxide flux from Pond 1 and the DCW in 2005 were very similar: open water flux ranged from -96.42 to 95.42 mmol CO2 m-2 d-1 at Pond 1 and 3.21 to 38.94 mmol CO2 m-2 d-1 at the DCW. Despite the similarity in CO2 flux, the DCW had 10- to 15-fold higher levels of macrophytes, phytoplankton and metaphyton biomass and similar levels of periphyton to Pond 1 in 2005. These biomass differences were not, however, reflected in the CO2 or CH4 flux. Pond 1 and the DCW were net sources for greenhouse gases but contributed less greenhouse gas than reports from other aquatic systems.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2009. / Härtill 6 uppsatser.