Denitrifïcations in Sediments from the Hyporheic Zone Adjacent to a Small Forested Stream

Abstract

Denitrification was assayed by the acetylene blockage technique in hyporheic sediments. Samples were obtained along transects perpendicular to the stream at two sites: (1) the base of a slope dominated by old-growth redwood and (2) the base of a slope dominated by alder regenerating from a clearcut in 1965. Denitrification was evident at in situ nitrate concentrations at all locations tested. Activity was stimulated by nitrate but nitrate plus glucose had no additional effect. Denitrifying potentials increased with increasing distance from the stream channel. Dissolved oxygen was 100% of the concentration expected in equilibrium with the atmosphere in water obtained from monitoring wells immediately adjacent to the stream but was as low as 7% of the expected value in water 11.4 m inland. Both nitrate and dissolved organic carbon decreased over summer in wells at the base of the alder-forested slope. A 48-h injection of nitrate-amended stream water into hyporheic water 8.4 m inland stimulated nitrous oxide production in the presence of acetylene. Nitrous oxide was generated as nitrate and acetylene were co-transported to a well 13 m down-gradient. The acetylene-block experiments coupled with the chemistry data suggest that denitrification can modify the chemistry of water during passage through the hyporheic zone.

Investigating patterns and controls of groundwater up-welling in a lowland river by combining Fibre-optic Distributed Temperature Sensing with observations of vertical hydraulic gradients

“…(e.g. Malcolm et al, 2002Malcolm et al, , 2004; , 1999;Storey et al, 2004;Duff and Triska, 1990;Hinkle et al, 2001;Jones et al, 1995;Findlay et al, 1993Findlay et al, , 2003Fisher et al, 1998;Hill and Cardaci, 2004;Zarnetzke et al, 2011a) as well as (ii) hyporheic flow paths and residence times (Zarnetzke et al, 2011b;Fisher et al, 1998;Bencala et al, 1993;Duff and Triska, 2000;Jones et al, 1995). Hence, a detailed understanding of groundwater-surface water exchange flow patterns is essential for the quantitative assessment of biogeochemical cycling at aquifer-river interfaces (White, 1993;Krause et al, 2011a).…”

A physical explanation for the development of redox microzones in hyporheic flow

“…When stream water enters a hyporheic flow path, it is typically rich in dissolved oxygen (O 2 ), nitrate (NO 3 À ), and organic carbon. These reactants are delivered to the microbially colonized sediment matrix [Baker et al, 2000], creating a bioreactor that is more efficient per time than the stream water column, especially for anaerobic processes [Duff and Triska, 1990]. As O 2 is consumed through aerobic respiration, other terminal electron acceptors are utilized, leading to the zonation of redox processes in sediments [Vroblesky and Chapelle, 1994;Hedin et al, 1998].…”

Balancing watershed nitrogen budgets: accounting for biogenic gases in streams

“…However, both in-stream processes as well as watershed connectivity through groundwater flow paths must be considered. It has been demonstrated that streams can be hotspots for denitrification and N removal (Duff and Triska 1990;McClain et al 2003). Among aquatic ecosystems, streams have denitrification rates that are high per unit area, but variable over time and space (Piña-Ochoa and Á lvarez-Cobelas 2006).…”