Wurtsbaugh, W. A.. Utah State University, wurts@cc.usu.edu
Miracle, M. A.. Universidad de Valencia, rosa.miracle@uv.es
Camacho, A. Universidad de Valencia, antonio.camacho@uv.es
Armengol, J. Universidad de Valencia, javier.armengol@uv.es

 
NITROGEN FLUX BETWEEN STRATA AND THROUGH THE FOOD WEB MEASURED WITH A WHOLE-LAKE N-15 EXPERIMENT
 
Nutrient flux through pelagic food webs is complicated by limited transport of inorganic nutrients and some organisms through different strata. Deep-chlorophyll layers in oligotrophic systems often contribute significantly to primary productivity, but the importance of this production for the rest of the food web and for other strata is unknown. To address this, we injected N-15 ammonia and rhodamine into the metalimnion of a 1-ha, Spanish, karst lake. The N-15, taken up by phytoplankton, traced the importance of biologically-mediated fluxes, whereas the rhodamine traced physical transport. Eddy diffusivity (K= 0.0068) was extremely low in this small, sheltered lake, limiting nitrogen transport between strata. In contrast, the "biodiffusivity" of N15 was 11 times greater, indicating that biological processes dominate transport. After 28 days, del-N15 values of zooplankton approached those of the seston, indicating that production of the dominant picoplankton in the deep chlorophyll layer was used effectively by higher trophic levels. After mixing, N-15 in seston declined exponentially in the lake, with a half-life of 168 days. N-15 tracer experiments provide a powerful tool for assessing nutrient transport in lakes.
 
Day: Thursday, Feb. 4
Time: 12:00 - 12:15pm
Location: Sweeney Center
 
Code: SS39TH1200S