Thursday, May 29, 2008 - 10:00 AM
510

Nitrogen dynamics in florida spring runs

James B. Heffernan, Biological Sciences, Florida International University, OE 167, University Park, Miami, FL 33199, Matthew J. Cohen, School of Forest Resources and Conservation, University of Florida, PO Box 110410, Gainesville, FL 32611-0410, and Thomas K. Frazer, Department of Fisheries and Aquatic Sciences, University of Florida, 7922 NW 71st Street, Gainesville, FL 32653.

Nitrate concentrations have risen dramatically over the past 50 years in many artesian springs of North and Central Florida, prompting concern about enrichment effects in downstream river and coastal ecosystems.  In this study, we constructed nitrogen mass balance from available data for 10 spring-fed rivers to evaluate (1) the magnitude of nitrate and total nitrogen retention by these systems, and (2) the relative importance of assimilatory and dissimilatory pathways of nitrate removal. While nitrate concentration declined with downstream position in all systems, longitudinal changes in total N concentration varied considerably, suggesting additional sources of organic nitrogen in some systems.  In comparison to other lotic systems, the magnitude of  nitrate declines was particularly large when considered as a function of hydrologic residence time.  Despite the high productivity of rooted macrophytes and macroalgae in spring-fed streams and rivers, observed nitrate retention greatly exceeded estimates of autotrophic demand.  While hydrologic and biogeochemical characteristics of spring run hyporheic zones are largely undescribed, the combination of abundant macrophytes and coarse sediments may provide an ideal environment for high rates of denitrification. 


Web Page: mass balance, denitrification, uptake

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