Bradshaw, E. G. Geological Survey of Denmark and Greenland (GEUS), egb@geus.dk
Olrik, K. G. Laboratory for Environmental Biology, m-b-l@vip.cybercity.dk
Anderson, N. Geological Survey of Denmark and Greenland (GEUS), nja@geus.dk

 
FACTORS CONTROLLING THE SEASONAL ABUNDANCE OF CYCLOSTEPHANOS DUBIUS (FRICKE) ROUND IN EUTROPHIC, DANISH LAKES
 
Cyclostephanos dubius is a common planktonic diatom in many eutrophic Danish lakes. It has a weighted averaged (WA) optimum for TP of 176 g/L in the NW European diatom dataset. As a result, where it occurs in abundance in sediment cores, it considerably influences TP reconstructions from diatom-inferred WA models. At some sites it appears to have been present for hundreds of years, the implication being that the lakes have been eu- to hypertrophic for some time. Alternatively, its abundance may reflect other factors (alkalinity, temperature, grazing etc): in these circumstances the reconstructed values are erroneous, or at least should be treated with some caution. The role of TP and other factors can be assessed using experimental cultures but here we take an alternative approach, that of using constrained ordination. Phytoplankton samples from the Danish Water-Environment Monitoring Programme have been re-analysed to obtain species-specific diatom abundances. Up to 19 samples are taken annually from these lakes whilst water chemistry data are also recorded. Constrained ordination was then used to examine which limnological factors explain, in a predictive sense, the seasonal abundance of Cyclostephanos dubius.
 
Day: Thursday, Feb. 4
Time: 10:30 - 10:45am
Location: Sweeney Center
 
Code: CS62TH1030S