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Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007

ASSESSMENT OF THE IMPORTANCE OF NITROGEN FIXATION ON THE WHOLE LAKE NITROGEN BUDGET FOR LAKE JESUP

D.A. Tomasko PBS&J Tampa, FL J.P. Montoya School of Biology, Georgia Institute of Technology Atlanta, GA T.K. Frazer Department of Fisheries and Aquatic Sciences, University of Florida Gainesville, FL

In the TMDL report for Lake Jesup (FDEP 2005), measured concentrations of TN were

higher

than

could

be

modeled

from

typical

loading

sources.

To

address

this

discrepancy,

estimated rates of nitrogen These rates, however, were

fixation were used to balance the in-lake TN values for Lake Jesup. extrapolated from measures made on Lake George, which has much

better water assistance in budgets and Jesup were

quality than Lake Jesup. As a consequence, Seminole County asked PBS&J for determining the potential importance of nitrogen fixation on Lake Jesup’s nutrient water quality. In August 2006, preliminary measurements of N2-fixation in Lake made using a high-sensitivity stable isotope tracer method from 10 stations

throughout the characterization

lake. At each station, of suspended particles and

water and sediments were sampled for isotopic surface sediments, respectively. Measurements were

also made mean rate

o f N 2 - f i x a t i o n r a t e s i n w a t e r o f N 2 - f i x a t i o n f o r a l l s t a t i o n s

from each of these stations. On a volumetric basis, the was 45 ± 21 nmol N L-1 h-1 (mean ± SD, N=26). Based

on these results, the “excess” TN that could not could be produced within a period of time (122

be accounted for from traditional loading sources days) less than the estimated turnover time of the

lake. Results from this source of nitrogen input budget.

study support the premise that to Lake Jesup and provides a

N2-fixation mechanism

is a potentially significant for balancing the nitrogen

________________________________________________________________________

NOTES

Session 5A – Page 7

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