HR: 1340h
AN: H13D-1544    [Abstracts]
TI: The Influence of Sediment Size on Dissolved Inorganic Nitrogen in Hyporheic Mesocosms
AU: * Harvey, B N
EM: bnharvey@ucdavis.edu
AF: University of California, Davis, Aquatic Ecosystems Analysis Laboratory, Center for Watershed Sciences, One Shields Avenue, Davis, CA 95616, United States
AU: Johnson, M L
EM: mbjohnson@ucdavis.edu
AF: University of California, Davis, Aquatic Ecosystems Analysis Laboratory, Center for Watershed Sciences, One Shields Avenue, Davis, CA 95616, United States
AU: Kiernan, J D
EM: jdkiernan@ucdavis.edu
AF: University of California, Davis, Aquatic Ecosystems Analysis Laboratory, Center for Watershed Sciences, One Shields Avenue, Davis, CA 95616, United States
AU: Green, P G
EM: pggreen@ucdavis.edu
AF: University of California, Davis, Civil and Environmental Engineering, One Shields Avenue, Davis, CA 95616, United States
AB: Dissolved inorganic nitrogen (DIN) is composed of nitrate, nitrite and ammonia. The availability of DIN in streams is important to water quality and to stream ecosystems in general because at low concentrations DIN can limit primary productivity, while at high concentrations DIN contributes to eutrophication. An important location of nitrogen transformations in streams is the interstitial spaces between streambed sediments. As surface water passes transiently along shallow subsurface flow paths, the activities of interstitial biofilms and invertebrates alter the form and availability of nitrogen. Heterotrophic consumers release nitrogen as ammonia. Nitrifying bacteria further transform ammonia to nitrate under aerobic conditions. While under anaerobic conditions denitrifying bacteria can transform nitrate to nitrogen gas. Studies in natural streambeds have suggested the size of streambed sediments can influence whether the streambed serves as a net source or sink for DIN in transient sub-surface water. We tested whether the size distribution of streambed sediments in isolation from the effects of streambed topography and groundwater upwelling could alter DIN production or uptake as stream water passed transiently along interstitial flow paths. We filled pipes with contrasting sediment mixes, and placed them in a stream so that surface water flowed through the sediments. After an incubation period allowing biofilm development, we measured nitrate + nitrite and ammonia in interstitial water drawn at several distances along the pipes. These measurements revealed that both sediment types were net sources of DIN, with the majority of DIN production occurring near the beginning of subsurface flow paths. Concentrations of DIN were greater in the finer sediments at any given distance along the pipes. However, higher surface water exchange rates through the coarser sediments caused net DIN production in the coarse sediments, and therefore DIN release to surface water, to equal DIN production in the fine sediments.
DE: 0469 Nitrogen cycling
DE: 1830 Groundwater/surface water interaction
SC: Hydrology [H]
MN: 2007 Fall Meeting