Tuesday, June 5, 2007
496

Discriminating between reaction rate and transport rate limitations of hyporheic denitrification across a land use gradient in 9 Western Wyoming streams

Andrew K. Myers, Department Watershed Science, Utah State University, Logan, UT 84321, Michelle A. Baker, Biology Department, Utah State University, and Chris D. Arp, USGS, Alaska Science Center.

Land use practices have the potential to affect hydrological and biogeochemical process in streams.    We studied 9 streams near Grand Teton National Park that cover a land use gradient from urban (Ur), agricultural (Ag), to forested (Fst) to assess land use influence on hyporheic denitrification.  We hypothesized that the role of the hyporheic zone as a nitrogen sink is governed by hydrologic transport and/or substrate availability. We tested this hypothesis by modeling tracer data with a 2-storage zone solute transport model to quantify hyporheic exchange and by measuring potential denitrification enzyme activity (DEA) in hyporheic sediments. Physical characteristics of sites varied with highest W/D, velocity, and discharge going from Fst, Ag, Ur streams.  Our results suggest that in-channel storage is greatest from Ag, Ur, and Fst streams and that the inverse is true for hyporheic cross sectional area and mean residence times.  While Fst streams had greatest capacity for hyporheic exchange, DEA rates were lowest.in these streams with one exception.  Land use appears to influence the capacity for hyporheic denitrification in two ways 1) Ur and Ag practices supply substrates that build the microbial potential for denitrification but 2) channelization, sediment deposition and other hydrologic alterations decrease hyporheic exchange.

See more of Poster Session - Hyporheic Processes
See more of Contributed Sessions

See more of The NABS 55th Annual Meeting