HETEROCYTE DENSITIES AS PROXIES FOR QUANTIFYING NITROGEN FIXATION IN OZARK LAKES (S)
Heterocyte densities have sometimes been used to estimate N fixation rates by phytoplankton, but this approach has never been used for man-made lakes in the south-central U.S. We performed a simple experiment to quantify the potential relationship between N fixation rates and heterocyte densities for Lake Fayetteville, AR. Microcosms were used to grow the natural phytoplankton assemblage under varying N:P ratios by holding P constant and varying N among treatments. The N enrichments were conducted using isotopically enriched nitrate (600 ‰) in order to estimate N fixation with a two source mixing model and by mass balance. The two-source mixing model allowed us to estimate the fraction of N in phytoplankton that was derived by N fixation (fN-fix). Heterocyte densities were positively correlated with fN-fix and allowed us to develop a prediction model (r2 = 0.95; F1,12 = 235.8; p < 0.0001) and apply it to estimate N fixation in Lake Fayetteville, Arkansas. Preliminary results indicate that the average number of heterocytes per trichome measured over a growing season could reasonably predict the average N fixation rate for that season.
Hallett, S. J., University of Arkansas, USA, email@example.com
Baker, B. C., University of Arkansas, USA, firstname.lastname@example.org
Scott, J. T., University of Arkansas, USA, email@example.com
Time: 17:30 - 19:00
Location: Poster/Exhibit Hall
Presentation is given by student: Yes