The voluminous limnological literature contains few studies of mountain streams. Though there are a few papers on the benthic algae (see Budde 1928, Raabe 1951) only Pennak (1943) reports year-round quantitative data on the phytoplankton. Brinley (1950) gives some phytoplankton information in a summer study of streams in Rocky Mountain National Park.

This thesis examines the phytoplankton ecology of Wilson Inlet, Western Australia with relation to the changing physical, chemical and biological environment.

Bibliography: leaves 309-329. This thesis attempts to contribute to the understanding of how turbulence affects phytoplankton in freshwater systems, focussing on the temporal and spatial scales in phytoplankton dynamics ranging from photochemistry in the surface mixed layer to a small-scale shear and growth to intra-seasonal changes in community composition in a lake subject to high disturbances.

This research investigated the factors influencing the structure of the phytoplanktori community in Chaffey Dam, which is located in sub-tropical Australia. In particular, the research aimed to determine the influence of light at time scales ranging from seconds to seasons, on the growth and photophysiology of the cyanobacterium Anabaena circinalis. On a large scale, field monitoring programs between 1987 and 1997 indicated that the phytoplankton community of Chaffey Dam was dominated by colonial or relatively large phytoplankton that move either with the aid of flagella or can be positively buoyant. Diatoms contributed only a minor component, which may be the result of the reservoir being stratified for much of the year. Several of the dominant taxa bloomed in each of the seasons during the eleven year period, with some blooms lasting >9 months, indicating that environmental variability between seasons can be low. In contrast to other studies, A. circinalis was more likely to grow and bloom during the cooler months (March-October). A two-year intensive monitoring program (1995-1997) identified a seasonal progression that was similar in both years. Chlorophytes occurred in spring, Ceratium in mid summer, a relatively clear period in February, A. circinalis in March and cryptomonads in winter. On a smaller scale, short-term (2-3 day) in-situ and laboratory enclosure experiments found that the light and nutrient requirements of the dominant taxa varied. In comparison to most other phytoplankton, A. circinalis cells disappeared at very rapid rates when supplied irradiances <10 (umol photons m-2 s-1. Over several days of darkness, the filaments broke apart and the cell numbers declined. The experiments also showed that at certain times, field populations of A. circinalis were subject to high losses at all irradiances. Laboratory studies investigating the influence of inter- and intra-daily changes in light availability showed that the growth rate of A. circinalis was not affected by the frequency of daytime light:dark cycles, indicating that the rate of water mixing will not have major influence on its growth if the total daily light dose is maintained. It was also found that A. circinalis cultures did not accumulate large reserves of energy in the form of carbohydrate, other than that required for one night. This strategy may enable the colonies to have a high level of buoyancy each morning so that they float quickly to the surface waters and obtain sufficient light each day to minimise losses. However, this strategy limits the ability of A. circinalis to grow and maintain vital cell processes during extended periods of low irradiances and may be a factor causing them to be susceptible to cell breakdown. Weekly measurements of algal growth rates in Chaffey Dam identified two factors that may have acted singly or simultaneously to influence the development of A. circinalis blooms during 1996 and 1997. The blooms developed during a 4-6 week period when the mean irradiance in the surface mixed layer (SML) was sufficient to prevent high losses. Secondly, the blooms developed when soluble phosphorus in the epilimnion was relatively high but soluble nitrogen was low. This may have favoured A. circinalis, which has the potential to fix atmospheric nitrogen. The decline of A. circinalis blooms was correlated with a deepening of the SML and a reduction of the mean daytime irradiance within the SML. Their decline did not appear to be related to nutrient limitation or to changes in zooplankton concentrations. This research also developed a physiological technique for tracking daily changes in the mean daytime irradiance of A. circinalis and for estimating cell growth rate. This method is based on chlorophyll-a fluorescence quenching analysis of the state transition mechanism, which regulates light availability between the photosystems. The mean daytime irradiance of A. circinalis showed a strong relationship with the degree of non-photochemical quenching (qn), whereas the relative change to the maximum fluorescence showed a strong relationship with cell growth. It is anticipated that this method will provide a useful research tool for determining the relative importance of light and other factors on the net growth of A. circinalis and other cyanobacteria.

Bibliography: leaves 309-329. / xvii, 329 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis attempts to contribute to the understanding of how turbulence affects phytoplankton in freshwater systems, focussing on the temporal and spatial scales in phytoplankton dynamics ranging from photochemistry in the surface mixed layer to a small-scale shear and growth to intra-seasonal changes in community composition in a lake subject to high disturbances. / Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, 2003

Typescript (photocopy) / vi, 271 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Botany, 1982

Graduation date: 1969

The impacts of oil sands processed materials (OSPM) on phytoplankton and periphyton community growth and stable carbon and nitrogen isotopes were examined. Estimates of plankton and periphyton community growth, measured as chl a and dry weight, were low and similar in reference and OSPM reclamation wetlands. The use of stable isotope analyses revealed higher δ15N of plankton and periphyton in OSPM wetlands than reference wetlands, possibly due to increased TN concentrations in some OSPM wetlands. In the laboratory, water-soluble fractions (WSF) of two types of OSPM (mature fine tailings, MFT and consolidated tailings, CT) and an amendment material (peat-mineral mixture), potential fill materials in wetland or end pit lake reclamation, were examined for phytoplankton community growth and stable carbon and nitrogen isotopes. All WSF treatments had higher chl a compared to reference water and maximum growth was observed at a 50:50 ratio of peat:CT or peat:MFT. In general, WSFs of peat had the highest concentration of total nitrogen (TN) whereas WSFs of MFT had the highest total phosphorus (TP; 3x higher). The results suggested that the addition of peat as an amendment to OSPM (particularly for MFT), contributing additional TN, could improve phytoplankton community growth in oil sands reclamation. At higher percentages of MFT WSF, there was increased turbidity due to fine clay particles that likely contributed to reduced phytoplankton growth. Turbidity could be an important factor limiting phytoplankton growth and thus reducing dietary resources and biological detritus (via sedimentation) in the initial development of an end pit lake. The WSFs also promoted the unfavourable growth of filamentous algae, highest at intermediate concentrations of peat and CT WSFs and inhibited in MFT WSFs due to light limitation. Stable N isotopes of plankton and filamentous algae suggests that 15N enrichment of algae could be a useful indicator of nutrient inputs, including OSPM seepage into natural aquatic systems, for oil sands regional monitoring programs.

Plankton metabolic balance (PMBm) of the surface mixed layer was calculated as the ratio of areal rates of gross photosynthesis (AGP) to community respiration (AR), and estimated for four Laurentian Great Lakes coastal sites of contrasting physical, optical and nutrient regime: western Lake Ontario, Hamilton Harbour, Georgian Bay and Woods Bay. The applied methods were the oxygen light-and-dark bottle and 14C bottle methods as well as the oxygen stable isotope method (18O method). PMBm was net autotrophic in most of the cases (73% of the observations). Within- and inter-system variations in PMBm were heavily dependent on both a ratio of light-saturated photosynthesis to community respiration (Pmax/R) and a ratio of euphotic to mixing depths (Zeu/Zm). While short-term within-system variations in PMBm were driven by the interplay of chlorophyll a (Chl a), total phosphorus (TP) and Zeu/Zm ratio, its inter-lake long-term variability had a different behaviour. Average ratios of AGP/AR were dependent only on DOC or single physical parameters such as Zeu or Zm, while PMBm determined as the ratio between average AGP and AR was controlled by the joint effect of DOC, TP and Chl a. DOC affected average AGP/AR ratios primarily via its control over fluctuations of the physical environment and had a depressing effect on AGP rates but did not control rates of AR. Independent measurements of volumetric rates of photosynthesis (P) and community respiration (R) were made by 18O method adjusted for wind-driven gas exchange and compared against estimates from bottle estimates. The 18O method in Lake Ontario gave internally inconsistent results (e.g. negative absolute rates of P and R) and poor agreement with independent estimates of P, R and P/R despite superficially plausible estimates for P/R. The low productivity of Lake Ontario and frequent disturbances of water column masked the biological signal in both DO abundance and its isotopic signature, and thus invalidated the assumptions of steady state conditions. However, in Hamilton Harbour and some other relatively sheltered sites that were sampled occasionally, 18O method predicted absolute rates of P that were well correlated well with bottle estimates. Isotope model estimates for R and P/R in the harbour were not well correlated with bottle estimates but were of comparable magnitude on average, and differences were explicable in terms of physical forces and the different time scales of response for the two methods. The Hamilton Harbour hypolimnion presented an anomalous behavior in oxygen stable isotopes (18O depletion) where seasonal development of DO depletion was not accompanied by the progressive isotope enrichment expected from respiratory fractionation. The Lake Ontario and harbour hypolimnion results both appear to show that simple steady state models that assume literature values for fractionation processes and ignore physical dynamics are of limited applicability to lakes.

This thesis develops, validates and applies an empirical model that provides the first spatially explicit estimates of gross and net phytoplankton production in Lake Victoria. Gross and net phytoplankton production are in turn used to estimate the maximum sustainable yield (MSY) of Lake Victoria's fishery following an empirical formula and the carbon efficiency transfer method. Chapter 2 presents results from three inshore areas where diurnal and sub-seasonal gross and net phytoplankton production was derived using an adapted version of the phytoplankton production model developed by Fee (1990). Spatial and temporal trends of chlorophyll (chl), PI parameters, the vertical attenuation of PAR (kPAR), Secchi depths (SD) and respiration rates are identified. kPAR and SD are highly correlated to chl within the euphotic zone, as well as to each other. Furthermore, the two PI parameters, PBM and aB, exhibit a strong linear relationship and both decline along an increasing chl gradient, presumably due to increased light-limitation, a taxonomic shift from diatoms to cyanobacteria with increasing chl as well as an increased need for biologically fixed nitrogen. These hypotheses are supported by observed synchronous changes in the PSII:PSI ratio of phytoplankton and changes in the chl-specific attenuation of PAR (kchl). Relationships are also derived between biomass-specific respiration rates (RB) with chl and PBM; similar to PI parameters RB decreases with increasing chl. Owing to these correlative trends, only one parameter is required to estimate gross phytoplankton production through the empirical model developed in this thesis. The empirical model predicts that gross phytoplankton production increases in a near linear fashion between chl of 0 to 10 mg. m-3, begins to flatten out as chl approaches 20 mg. m-3 and then slightly decreases when chl exceeds 40 mg. m-3 where the maximum PPG of 13. 1 g O&#8322;. m-2. day-1 is reached and is in close agreement with a theoretical argument proposed by Talling (1965). Areal respiration and consequently net phytoplankton production are sensitive to chl within the mixed layer as well as mixed layer depths. Overall, the lakewide averages of gross and net phytoplankton production are 9. 68 and 2. 2 g O&#8322;. m-2. day-1 respectively. Significant temporal variability was observed on sub-seasonal scales within the inshore of Lake Victoria, and changes in limnological parameters coincided with changes in water column temperatures in each of the three bays. In Fielding Bay, the availability of meteorological data revealed that strong nocturnal wind events decreased both the water column temperature and chl, while both parameters generally increased in the absence of any such wind event. Lateral exchange of water with deeper areas through strong wind events essentially flushes Fielding Bay causing the observed decreases in both the water column temperature and chl; this hydrodynamic event also influences other limnological parameters according to their respective correlative regression equations with chl. Spatial trends were also observed between inshore areas. The deepest area, Napoleon Gulf, has the lowest values of chl while the shallowest area, Inner Murchison Bay, has the highest chl as the mean depth of a bay sets an approximate upper limit on chl. With respect to diurnal variability, PI parameters decline through the day, kPAR increases over the day and no statistically valid trends were ascertained for chl and RB. Chapter three examined spatial and seasonal patterns of chlorophyll fluorescence, temperature, dissolved oxygen and water transparency from four lakewide cruises. Significant spatial variability of each parameter confirmed that lakewide data is required to generate spatially explicit estimates of phytoplankton production. Complex patterns in the thermal structure during each cruise illustrated that physical processes in Lake Victoria are at times more complex that a previously stated unidirectional hypothesis of warm water in the north and cool water in the south (Spigel and Coulter 1996), and these patterns influence spatial patterns in dissolved oxygen and Secchi depths. Similar to Chapter 2, estimates of chl within the mixed layer were highly correlated to mixed depths, while lakewide averages of chl are lower than previously reported offshore values (Mugidde 1993, 2001).