Brian Sanderson

Investigations of the temporal variation of cyanobacterial and other phytoplanktonic cells at the offtake of a large reservoir, and their survival following passage through it

The survival and subsequent growth potential of Anabaena spp. and other filamentous cyanobacteria and the cells of Aulacoseira spp. (diatom) and Ceratiumhirundinella (dinoflagellate) following passage through the Multi Level Inlet Tower (MLIT) and offtake works at Chaffey Reservoir in New South Wales, Australia was investigated in late summer. The study aimed to test whether the phytoplankton cells were destroyed or otherwise rendered less viable during passage through the outlet works. The reservoir was strongly thermally stratified with a shallow surface mixed layer, which contributed to considerable temporal variability in the numbers of phytoplankton cells present immediately opposite the intake portal of the outlet works. To compensate, considerable replicate sampling was undertaken both upstream and downstream of the MLIT. Results indicate limited destruction of cyanobacteria, with fewer cells present immediately downstream compared to upstream. Greater destruction of cells was indicated at lower mean daily discharge rates compared to higher discharge rates. Filament lengths of both cyanobacteria and Aulacoseira were also reduced during passage. There was no apparent reduction in Ceratium cell number. Laboratory incubation studies on surviving cells collected downstream indicated no impairment on the viability of any taxa. Calculations of rates-of-strain likely to be experienced by the phytoplankton as they transited through the offtake revealed very high stress being applied to the filaments and cells at the valve, and within the spillway sections of the works. These were several orders of magnitude greater than published values shown to disrupt cells and filaments, and to impair viability for subsequent growth in laboratory studies. However, exposure times to the high rates-of-strain at Chaffey Reservoir were brief, which may reduce the impacts of the high turbulence. The conclusions were that unless cyanobacterial cell destruction during passage through an outlet works can be shown to be more effective at larger reservoirs, the withdrawal of warm, cyanobacterial infested waters from close to the surface is unlikely to provide an acceptable management action for the prevention of cold water pollution downstream.

Grazing Constants are Not Constant: Microzooplankton Grazing is a Function of Phytoplankton Production in an Australian Lagoon

Twenty-one dilution method experiments were used to measure phytoplankton growth rate, grazing rate by microzooplankton, and phytoplankton concentrations that saturate grazing in Tuggerah Lake—a large lagoon in New South Wales, Australia. Individual experiments conformed to the saturating grazing model with no evidence of a threshold phytoplankton concentration to initiate grazing. Phytoplankton concentrations that saturated grazing were highly variable between experiments and were positively correlated with chlorophyll a concentration in the lagoon. Plankton models often use a saturating grazing function that includes several constants, but constants are found to be variable from one dilution experiment to the next. Another formulation is proposed in which grazing is a quadratic function of phytoplankton growth. This enables the 21 measurements of zooplankton grazing to be fitted using only two invariant parameters. No evidence is found for saturation of microzooplankton grazing when it is calculated as a function of phytoplankton growth. When phytoplankton growth is high, about 80% of it is grazed. When phytoplankton growth is low, about 45% is grazed. Calculations illustrate that this type of grazing stabilizes the planktonic producers and grazers, as expected.

Nutrient sources for charophytes and Najas marina in Myall Lake, Australia, indicated by carbon and nitrogen stable isotope ratios

Submerged macrophytes can assimilate mineral nutrients through both shoots and roots (MARSHNER 1995). Several studies have addressed the relative importance of roots and shoots in nutrient uptake by submerged plants (BARKO et al. 1991). The availability and form of nutrients in the surrounding water and in the interstitial water affect the plant nutrient uptake rates (CARIGNAN 1982). CEDERGREEN & MADSEN (2003) reported higher nitrate reductase activity in roots than in shoots. Stable isotope techniques have recently been used effectively to investigate the interactions of plants with their biotic and abiotic environment (DAwsoN et al. 2002). The preferential uptake of the lighter isotope by a plant and the availability of sources lead to isotope discrimination (DAwsoN et al. 2002, FRY 2006). Thus, stable isotope ratios are efficient indicators ofthe abundance of carbon and nitrogen sources for plants (FRy 2006). W e analyzed the carbon and nitrogen stable isotope ratios of benthic macrophytes from various sites in an oligohaline shallow lake to identify: (l) the nutrient sources for the plants under different conditions, (2) the preferential uptake of the lighter isotopes, and (3) the effect ofthe morphological characteristics of different plant species on nutrient uptake.