Aquatic Sciences Meeting, Albuquerque 2001

CS41 Phytoplankton: Nutrient Dynamics and Physiology

Date: Friday, February 16, 2001, Time: 11:15:00 AM

Location: Galisteo

Nydick, K, R, Colorado State University, Fort Collins, USA, koren@nrel.colostate.edu

Moraska, B, M, Colorado State University, Fort Collins, USA, bmoraska@lamar.colostate.edu

Baron, J, S, U. S. Geological Survey, Fort Collins, USA, jill@nrel.colostate.edu

Johnson, B, M, Colorado State University, Fort Collins, USA, brett@cnr.colostate.edu

MESOCOSM EXPERIMENTS TO DETERMINE IF SUBTLE NITROGEN ADDITIONS CAN ALTER PRIMARY PRODUCTION IN SMALL MOUNTAIN LAKES, SNOWY RANGE, WYOMING

Phosphorus is most often considered the limiting nutrient in freshwater systems, but nitrogen may also play an important role, especially in harsh environments where N-fixation may not be energetically favorable. We conducted enclosure experiments in two mountain lakes (Snowy Range, WY) to test whether or not subtle increases in nitrogen could alter pelagic and benthic primary production. Three nutrient treatments were added in triplicate to 500 L plastic mesocosms secured to the lake bottom. Nitrogen and phosphorus treatments received approximately 1 mg NO3-N and 0.2 mg/L PO4-P, respectively. Combined N and P treatments received both additions; control enclosures received none. We measured pH, dissolved oxygen, primary production, and algal biomass before and at 1 to 2 week intervals after adding treatments. Preliminary results show indirect evidence for increased primary production for the N-alone and combined N and P treatments only. Water clarity decreased while pH increased in both experiments. Dissolved oxygen concentration increased for these treatments in the second experiment only. Pelagic and benthic primary production and algal biomass measurements will be discussed in relation to these water quality changes.

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Aquatic Sciences Meeting, Albuquerque 2001

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