Twomey, L. Curtin University of Technology, rtwomeyl@alpha2.curtin.edu.au
Thompson, P. University of Tasmania, pthompso@postoffice.newnham.utas.edu.au

 
NUTRIENT LIMITATION AND NITROGEN UPTAKE BY PHYTOPLANKTON IN WILSON INLET, WESTERN AUSTRALIA
 
Wilson Inlet is a relatively shallow, 14 km long by 4 km wide estuary located on the south coast of Western Australia. Exchange with the ocean is seasonal as during most of the fall and winter a sand bar closes off the estuary. Single nutrient deletion bioassays were conducted on the phytoplankton community from October 1997 to September 1998. The roles of nitrogen, phosphorus, silicate, iron, trace metals and vitamins in potentially limiting phytoplankton biomass were studied. Nitrogen and phosphorus were the nutrients most likely to limit phytoplankton biomass. Nitrogen uptake experiments were conducted on the endemic phytoplankton community to determine which forms of soluble nitrogen were preferred. Nitrogen-15 in the form of ammonium, nitrate and urea was added to unfiltered estuary water and incubated for 4 hours in situ to determine the uptake rate for each treatment. On every day sampled the most preferred nitrogen source was ammonium. The preference for ammonium in the bottom water of the estuary was particularly strong and there was little evidence of either nitrate or urea uptake. There is strong evidence to suggest that nitrogen for the spring phytoplankton bloom is ammonium derived from the sediments during relatively prolonged periods of salinity stratification and anoxia.
 
Day: Friday, Feb. 5
Time: 10:30 - 10:45am
Location: Sweeney Center
 
Code: CS55FR1030S