Vadeboncoeur, Y. National Environmental Research Institute,
Lodge, D. University of Notre Dame,
Carpenter, S. C. University of Wisconsin,

Phytoplankton increases with whole-lake fertilization, but less is known about the response of periphyton. Using whole-lake fertilization experiments we determined 1) if the response of periphyton is substratum-specific, and 2) if the contribution of periphyton to whole-lake primary production changes with fertilization. Five lakes in northern Wisconsin (USA) were monitored from 1991 - 1995. During the summers of 1993 - 1995, four lakes were fertilized with nitrogen and phosphorus (0.4 - 2.0 mg P m-3 d-1). Wood constituted up to 16% of benthic surface area in the lakes, with the remainder being organic sediments. Periphyton production on wood (epixylon) increased with fertilization, but production of algae on sediments (epipelon) decreased due to light reducing phytoplankton blooms. Areal production of epipelon was about 10x that of epixylon. Thus, despite the fertilization effect, epixylon constituted a maximum of 1.8% of total benthic primary production. Before fertilization, 50 - 70% of whole-lake (benthic + pelagic) primary production was epipelic. At the highest fertilization rates, the epipelic contribution was only 10 - 20%. Whole-lake primary production increased with fertilization. However, due to the compensatory decline in epipelic production, the overall increase in whole-lake primary production was about 1/2 of the increase for phytoplankton alone.
Day: Monday, Feb. 1
Time: 02:45 - 03:00pm
Location: Sweeney Center
Code: SS45MO0245S