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SEMINAR: CWR PhD thesis presentations.

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Today's date is Wednesday, May 12, 2021
CWR PhD thesis presentations. : Influence of physical processes and wastewater effluent on phytoplankton dynamics in the Perth coastal margin, Western Australia Other events...
The availability of nutrients, light, and physical properties of the water, including small-scale fluid motion, influence phytoplankton dynamics. The Western Australia (WA) coast is characterized by low nutrient concentrations, nitrogen limitation, low primary production (oligotrophic) and lack of large-scale upwelling. The Perth coastal margin (WA) is semi-enclosed from the open ocean by chains of submerged reefs and islands. Alongshore coastal currents, driven by southerly winds, prevail and contribute to a highly dispersive environment. This research investigated how physical processes, occurring at a range of spatial and temporal scales, influence phytoplankton dynamics in the temperate coastal margin of Perth. The thesis is organised in three main components.

First, the relative importance of the main sources of nutrients, including treated wastewater effluent, was assessed. Analysis of a 14-year field monitoring record revealed seasonal variations in nutrients and chlorophyll-a (Chl-a) concentrations. Dissolved inorganic nitrogen (DIN) and Chl-a concentrations were higher in the winter period than in summer. Remote-sensing information was used to place the seasonal variations of Chl-a into an oceanographic context. Three-dimensional hydrodynamic-ecological simulations were used to determine the drivers of seasonal variations and reconcile the major inputs of DIN: superficial runoff, groundwater, wastewater effluent, atmospheric deposition and exchange with surrounding coastal waters. The results showed that the increase of DIN concentration during winter was driven by enhanced exchange with offshore waters, caused by changes in the wind field. This suggested that additional wastewater nutrient removal is not likely to affect these dynamics.

Second, the hydrodynamic-ecological model was used to assess the effect of an alternative scenario that considered the wastewater effluent as a resource instead as a waste. This involved running scenario simulations corresponding to a less-stringent wastewater nutrient removal during summer, the season of lowest nutrient and Chl-a levels. The simulation results indicated a moderate Chl-a increase, within the level of historical variability observed in the monitoring data, suggesting that such scenario could enhance the ecological services provided by the coastal ecosystem preserving its oligotrophic state.

Finally, the influence of turbulence on the phytoplankton community was investigated in situ. The results suggested that chain-forming diatoms, the dominant phytoplankton life-form observed when nitrogen availability increases in winter, have a competitive advantage in accessing peak nutrient concentrations in the turbulent heterogeneous microenvironment. By forming cell chains of length longer than the Batchelor scale these diatoms can experience the microscale nutrient gradients that are associated with high turbulence in coastal ecosystems. This implies that coupling the influence of small-scale turbulence into process-based hydrodynamic-ecological models could improve our ability to predict phytoplankton dynamics.

Overall, this thesis quantified how different processes affect the phytoplankton dynamics in the Perth coastal margin and demonstrated that physical processes, operating at different spatial and temporal scales, strongly influence the variations in the abundance and the composition of the phytoplankton community.

PS* This seminar is free and open to the public & no RSVP required.

****All Welcome****
Speaker(s) Daniel A. Machado , PhD thesis presentations -Centre for Water Research
Location CWR Conference Room , Mathematics Link Building, The University of Western Australia
Contact Askale Abebe <[email protected]> : 6488 7565
URL http://www.cwr.uwa.edu.au/~machado/
Start Tue, 23 Apr 2013 16:00
End Tue, 23 Apr 2013 17:00
Submitted by Askale Abebe <[email protected]>
Last Updated Mon, 22 Apr 2013 11:26
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