Denitrification Potential in Relation to Lithology in Five Headwater Riparian Zones

Abstract

The influence of riparian zone lithology on nitrate dynamics is poorly understood. We investigated vertical variations in potential denitrification activity in relation to the lithology and stratigraphy of five headwater riparian zones on glacial till and outwash landscapes in southern Ontario, Canada. Conductive coarse sand and gravel layers occurred in four of the five riparian areas. These layers were thin and did not extend to the field-riparian perimeter in some riparian zones, which limited their role as conduits for ground water flow. We found widespread organic-rich layers at depths ranging from 40 to 300 cm that resulted from natural floodplain processes and the burial of surface soils by rapid valley-bottom sedimentation after European settlement. The organic matter content of these layers varied considerably from 2 to 5% (relic channel deposit) to 5 to 21% (buried soils) and 30 to 62% (buried peat). Denitrification potential (DNP) was measured by the acetylene block method in sediment slurries amended with nitrate. The highest DNP rates were usually found in the top 0- to 15-cm surface soil layer in all riparian zones. However, a steep decline in DNP with depth was often absent and high DNP activity occurred in the deep organic-rich layers. Water table variations in 2000-2002 indicated that ground water only interacted frequently with riparian surface soils between late March and May, whereas subsurface organic layers that sustain considerable DNP were below the water table for most of the year. These results suggest that riparian zones with organic deposits at depth may effectively remove nitrate from ground water even when the water table does not interact with organic-rich surface soil horizons.

Changes in discharge and solute dynamics between hillslope and valley-bottom intermittent streams

“…In this sense, the alluvial aquifer acts as a wellmixed groundwater reservoir and can exhibit a chemical signature distinct from hillslope groundwater (Hooper et al, 1998). Moreover, the alluvial zone can strongly affect nearstream subsurface hydrology, and thus the ability of riparian zones to regulate solute fluxes (Pinay et al, 1995;Hill et al, 2004). When the stream and riparian zone are surrounded by an alluvium with a large fraction of coarse material (hereafter, the alluvial riparian zone), high hydraulic conductivity can favour the mixing of surface-subsurface water bodies and modify stream flow as well as stream chemistry in many different ways (e.g.…”

Groundwater nutrient concentrations near an incised midwestern stream: effects of floodplain lithology and land management

“…Recent attention has focused on the important role that subsurface lithology and stratigraphy play in controlling nutrient cycling and transport in riparian zones Hill et al 2004). Subsurface variations in soil texture, organic matter content, denitriWcation potential, and other physical and chemical properties aVect dynamics of dissolved organic carbon cycling (Jacinthe et al 2003), nitrate removal (Hill et al 2004;DeVito et al 2000;Vidon and Hill 2004;Haycock and Burt 1993;Gold et al 1998) and phosphate concentrations (Carlyle and Hill 2001).…”

Longitudinal changes in biota along four New Zealand streams: Declines and improvements in stream health related to land use

“…These include fencing to keep stock from streams, and planting of vegetation in riparian zones between pastures and streams. Riparian vegetation can limit the erosion of fine sediments and particulate nutrients into streams, and it can also take up nutrients directly or enhance microbial uptake, including denitrification (Hill et al 2004). riparian trees can also minimise solar heating of stream water while providing large amounts of organic matter to fuel stream food webs (wallace et al 1997).…”