5th UF Water Institute Symposium Abstract

Submitter's Name	Mitra Khadka
Session Name	Springs III - Chemical Processes and Nutrient Fluxes
Author(s)	Mitra Khadka,  Department of Geological Sciences, University of Florida (Presenting Author)
	Jonathan Martin,  Department of Geological Sciences, University of Florida
	Junbing Pu, Institute of Karst Geology, Chinese Academy of Geological Sciences, Guilin, China
	Robin Treilles, National School of Public Works, Lyon, France
	Benthic fluxes of nutrients and trace metals in a spring-fed Silver River
	River benthic sediments act as a biogeochemical reactor and could provide important sources or sinks of solutes to or from river water, depending on the magnitude of fluxes of porewater and solutes. Solute fluxes across the sediment-water interface are driven by advective and diffusive processes. We assess relative importance of these two processes on solute budget in the Silver River, particularly for redox-sensitive nutrients and trace metals, by measurements of river water and porewater chemistry, hydraulic gradients and sediment hydraulic conductivity. Gradients of increasing Fe, Mn, soluble reactive phosphorous (SRP), NH4, and H2S concentrations in sediment porewater relative to the river water indicate diffusive fluxes of the solutes from sediments to the overlying river water. On the other hand, decreasing NO3 concentration gradients in porewater with sediment depth suggest that river bottom sediments act as a natural filter for NO3 removal from the river water column. Highly permeable river bottom sediments with hydraulic conductivities ranging from 1 × 10-3 to 5.06 × 10-4 m/s and orientation of hydraulic gradients towards the river suggest advection also provides an additional mechanism to transport solutes to the river. Interbedded layers of course-grained sediments and fine-grained sediments suggests that most of the advective flow could be horizontal rather than vertical. Our results show that nutrient and metal inputs from sediments to the water column could boost algal blooms in the Silver River and subsequently affects benthic and lotic ecosystems.