The role of water exchange between a stream channel and its hyporheic zone in nitrogen cycling at the terrestrial-aquatic interface

Abstract

The subsurface riparian zone was examined as an ecotone with two interfaces. Inland is a terrestrial boundary, where transport of water and dissolved solutes is toward the channel and controlled by watershed hydrology. Streamside is an aquatic boundary, where exchange of surface water and dissolved solutes is bi-directional and flux is strongly influenced by channel hydraulics. Streamside, bi-directional exchange of water was qualitatively defined using biologically conservative tracers in a third order stream.In several experiments, penetration of surface water extended 18 m inland. Travel time of water from the channel to bankside sediments was highly variable. Subsurface chemical gradients were indirectly related to the travel time. Sites with long travel times tended to be low in nitrate and DO (dissolved oxygen) but high in ammonium and DOC (dissolved organic carbon). Sites with short travel times tended to be high in nitrate and DO but low in ammonium and DOC. Ammonium concentration of interstitial water also was influenced by sorption-desorption processes that involved clay minerals in hyporheic sediments. Denitrification potential in subsurface sediments increased with distance from the channel, and was limited by nitrate at inland sites and by DO in the channel sediments. Conversely, nitrification potential decreased with distance from the channel, and was limited by DO at inland sites and by ammonium at channel locations. Advection of water and dissolved oxygen away from the channel resulted in an oxidized subsurface habitat equivalent to that previously defined as the hyporheic zone. The hyporheic zone is viewed as stream habitat because of its high proportion of surface water and the occurrence of channel organisms. Beyond the channel's hydrologic exchange zone, interstitial water is often chemically reduced. Interstitial water that has not previously entered the channel, groundwater, is viewed as a terrestrial component of the riparian ecotone. Thus, surface water habitats may extend under riparian vegetation, and terrestrial groundwater habitats may be found beneath the stream channel.

Influence of stream‐groundwater interactions in the streambed sediments on NO3− flux to a low‐relief coastal stream

“…The change in biologically reactive solute transport to the stream during floods will be controlled by hydrological residence time and rates and types of biochemical processes near the groundwater-surface water interface [Burt and Pinay, 2005;Triska et al, 1993]. For the two floods studied in 2006, concentrations of nitrate in stream water had a significant dip that is consistent with the ''dilution effect'' found in agricultural catchments under some conditions [Poor and McDonnell, 2007].…”

Characterization of the key pathways of dissimilatory nitrate reduction and their response to complex organic substrates in hyporheic sediments

“…Lefebvre et al (2006) contend that riffles promote hydrologic connectivity between the surface and subsurface environment, and as a consequence, denitrification potential within riffles is suppressed by the ingress of dissolved oxygen contained within infiltrating surface water. The relationship between oxygen delivery and denitrification within the hyporheic zone is likely true of many aquatic systems; however, the facultative nature of denitrifiers enables denitrification to proceed in anoxic microsites within oxygenated environments (Triska et al 1993;Baker et al 2000). As a result, the supply of electron donors to sustain the denitrification reaction, whether organic carbon or reduced inorganic species, may actually be more important than the nonlocalized presence or absence of oxygen in governing the prevalence of denitrification within the river bed (Holmes et al 1996;Fischer et al 2005;Mermillod-Blondin et al 2005).…”

“…Denitrification is most commonly coupled to the oxidation of organic carbon and is dependent upon the absence of oxygen, although denitrification can occur within anoxic microsites in seemingly well-oxygenated sediments (Triska et al 1993;Baker et al 2000). In excess, nitrogen can contribute to eutrophication of aquatic ecosystems; therefore, its removal in the hyporheic zone has clear ecological significance (Mulholland et al 2009).…”

Chironomid larvae stimulate biogeochemical and microbial processes in a riverbed covered with fine sediment

“…Our results also indicated the occurrence of anaerobic processes such as denitrification and anaerobic mineralization of OM, whereas O 2 contents could be above 0.5 mg l -1 . This occurrence is probably due the physical heterogeneity of sediments resulting in anaerobic micro-environments (Triska et al, 1993).…”