TY - JOUR

T1 - Interpreting spatial patterns in redox and coupled water–nitrogen fluxes in the streambed of a gaining river reach

AU - Heppell, Catherine M.

AU - Heathwaite, A. Louise

AU - Binley, Andrew

AU - Byrne, Patrick

AU - Ullah, Sami

AU - Lansdown, Katrina

AU - Keenan, Patrick

AU - Trimmer, Mark

AU - Zhang, Hao

PY - 2014/3

Y1 - 2014/3

N2 - Water pathways through permeable riverbeds are multi-dimensional, including lateral hyporheic exchange flows as well as vertical (upwelling and downwelling) fluxes. The influence of different pathways of water on solute patterns and the supply of nitrate and other redox-sensitive chemical species inthe riverbed is poorly understood but could be environmentally significant. For example, nitrate-rich upwelling water in the gaining reaches of groundwater-fed rivers has the potential to supply significant quantities of nitrate through the riverbed to surface waters, constraining opportunities to deliver the goalsof the EU Water Framework Directive to achieve ‘good ecological status’. We show that patterns in porewater chemistry in the armoured river bed of a gaining reach (River Leith, Cumbria) reflect the spatial variability in different sources of water; oxic conditions being associated with preferential discharge from groundwater and reducing conditions with longitudinal and lateral fluxes of water due to water movement from riparian zones and/or hyporheic exchange flows. Our findings demonstrate the important control of both vertical and lateral water fluxes on patterns of redox-sensitive chemical species in the river bed. Furthermore, under stable, baseflow conditions (<Q90) a zone of preferential discharge, comprising 20 % of the reach by area contributes 4–9 % of the total nitrate being transported through the reach in surface water, highlighting the need to understand the spatial distribution of such preferential discharge locations at the catchment scale to establish their importance for nitrate delivery to the stream channel.

AB - Water pathways through permeable riverbeds are multi-dimensional, including lateral hyporheic exchange flows as well as vertical (upwelling and downwelling) fluxes. The influence of different pathways of water on solute patterns and the supply of nitrate and other redox-sensitive chemical species inthe riverbed is poorly understood but could be environmentally significant. For example, nitrate-rich upwelling water in the gaining reaches of groundwater-fed rivers has the potential to supply significant quantities of nitrate through the riverbed to surface waters, constraining opportunities to deliver the goalsof the EU Water Framework Directive to achieve ‘good ecological status’. We show that patterns in porewater chemistry in the armoured river bed of a gaining reach (River Leith, Cumbria) reflect the spatial variability in different sources of water; oxic conditions being associated with preferential discharge from groundwater and reducing conditions with longitudinal and lateral fluxes of water due to water movement from riparian zones and/or hyporheic exchange flows. Our findings demonstrate the important control of both vertical and lateral water fluxes on patterns of redox-sensitive chemical species in the river bed. Furthermore, under stable, baseflow conditions (<Q90) a zone of preferential discharge, comprising 20 % of the reach by area contributes 4–9 % of the total nitrate being transported through the reach in surface water, highlighting the need to understand the spatial distribution of such preferential discharge locations at the catchment scale to establish their importance for nitrate delivery to the stream channel.

KW - Hyporheic

KW - Nitrate

KW - Hydrological pathways

KW - Groundwater-fed

KW - Rivers

KW - water quality

KW - Pollution

U2 - 10.1007/s10533-013-9895-4

DO - 10.1007/s10533-013-9895-4

M3 - Journal article

VL - 117

SP - 491

EP - 509

JO - Biogeochemistry

JF - Biogeochemistry

SN - 0168-2563

IS - 2-3

ER -