Sawatzky, C. L. Utah State University, cornelia@cc.usu.edu
Wurtsbaugh, W. L. Utah State University, wurts@cc.usu.edu
Luecke, C. Utah State University, luecke@cc.usu.edu

 
ALKALINE PHOSPHATASE ACTIVITY AS A MEASURE OF SPATIAL-TEMPORAL PHOSPHORUS LIMITATION IN A HIGH MOUNTIAN LAKE WITH A DEEP CHLOROPHYLL LAYER
 
Although most studies addressing nutrient limitation have focused on the epilimnion, algal growth in deep-chlorophyll layers may also be nutrient limited. To study this we used alkaline phosphatase activity to measure phosphorus limitation, and ammonium-enhancement assays to assess nitrogen limitation of phytoplankton in an oligotrophic lake in Idaho(USA) over the course of summer stratification and mixing. Immediately following stratification, phosphatase levels were low [0.3-1.2 mg/m^3/min/(mg chl m^3)], with the greatest limitation in the epilimnion. Within 10 days epilimnetic phosphatase activity tripled. As the summer progressed phosphorus limitation remained constant in surface waters, in the metalimnion and eventually in the hypolimnion. By fall, peak phosphatase activity occurred in the metalimnion. The descent of peak activity and the increase of activity in the meta- and hypolimnion corresponded with the descent of the deep chlorophyll maximum from 9-21 m. This suggests that the deep chlorophyll maximum may have descended due to nutrient depletion in the upper layers, and the consequential sedimentation of nutrients, coupled the increased grazing pressure by Dapnia in mid-late summer.
 
Day: Thursday, Feb. 4
Time: 12:15 - 12:30pm
Location: Sweeney Center
 
Code: CS62TH1215S