Implications of groundwater-surface water connectivity for nitrogen transformations in the hyporheic zone
Lead Research Organisation:
Lancaster University
Department Name: Lancaster Environment Centre
Abstract
Rivers have (rather controversially) been described as 'simply outcrops of groundwater'. Many of the rivers in the UK are supplied mainly from groundwater sources, especially during the summer months when rainfall is characteristically low. The hyporheic zone is a critical interface between surface and subsurface waters in groundwater catchments. Here, the mixing of groundwater and surface water and the resulting biological and chemical reactions, may exert a lot of control on the water quality of the river and also its ecology: so much so that the hyporheic zone has been ascribed pollutant attenuating properties by some. Groundwater abstraction, effluent disposal and diffuse nutrient pressures - especially nitrogen - may all compromise the capacity of the hyporheic zone to influence the water quality of a river. Although quite a few researchers have recognised that the hyporheic zone has some special control on the river habitat, most have looked at it only from the perspective of the relationship between river water and the upper few centimetres of the sediments of the riverbed. They have ignored the fact that as well as downward flux from the river into the sediments of the riverbed there will also be upward flows from groundwater through the hyporheic zone and into the river. We are especially interested in what happens to the chemistry of groundwater as it moves through the hyporheic zone. We will look in detail at the relationship between different nitrogen species, such as nitrate and ammonium and chemical reactions known collectively as 'redox' or reduction-oxidation reactions. Redox reactions use electron acceptors other than oxygen for organic carbon oxidation as the amount of oxygen in the riverbed sediments is exhausted. These reactions and their relationship with nitrogen are important because the hyporheic zone has been proposed as a zone in which nitrogen attenuation occurs. This has led to the proposition that the movement of groundwater through this zone will reduce the concentration of nitrogen reaching the river water. In this project, we will investigate further the claim that the hyporheic zone can attenuate groundwater contaminants such as nitrate. We want to look much more carefully at the pattern of flow from groundwater through the hyporheic zone. We propose that groundwater flux is influenced by the permeability of the river bed and this is in turn influenced by the physical structure and topography of the riverbed. We believe that where the permeability of the riverbed is high and flux from groundwater towards the river is high, we will find different patterns of biogeochemical activity in the hyporheic zone compared to where the permeability is low. We like to think of the riverbed rather like a cheese grater with fast and slow flow pathways corresponding to 'holes' in the riverbed. We expect these holes to be quite dynamic as winter storms change the superficial topography of the riverbed sediments and rearrange the patterns of pool-riffle and fast-slow flow features in the underlying sediments of a river. The reason why these flow pathways are important is they may allow 'hotspots' of biogeochemical activity within the hyporheic zone that could be important controls on the ecology of groundwater-fed rivers because they either release or transform nitrogen through processes such as nitrification or denitrification. The latter converts nitrate, which can damage the ecology of a river where it is present at high concentrations, into nitrogen gas, which is harmless. If we are able to show clearly how important the hyporheic zone is in influencing the water quality in rivers that are groundwater-fed, we will be able to provide evidence that can be used to protect this zone, and can also be used in helping the UK meet the requirements of critical European legislation such as the Water Framework Directive.
Organisations
Publications
Lansdown K
(2012)
Characterization of the key pathways of dissimilatory nitrate reduction and their response to complex organic substrates in hyporheic sediments
in Limnology and Oceanography
Byrne P
(2013)
Control of river stage on the reactive chemistry of the hyporheic zone
in Hydrological Processes
Byrne P
(2014)
Diffusive equilibrium in thin films provides evidence of suppression of hyporheic exchange and large-scale nitrate transformation in a groundwater-fed river
in Hydrological Processes
Lansdown K
(2014)
Fine-scale in situ measurement of riverbed nitrate production and consumption in an armored permeable riverbed.
in Environmental science & technology
Clifford J
(2010)
Geophysical characterization of riverbed hydrostratigraphy using electrical resistance tomography
in Near Surface Geophysics
Hu H
(2014)
Impact of microforms on nitrate transport at the groundwater-surface water interface in gaining streams
in Advances in Water Resources
Ullah S
(2012)
In situ measurement of redox sensitive solutes at high spatial resolution in a riverbed using Diffusive Equilibrium in Thin Films (DET)
in Ecological Engineering
Ullah S
(2013)
Influence of emergent vegetation on nitrate cycling in sediments of a groundwater-fed river
in Biogeochemistry
Heppell C
(2013)
Interpreting spatial patterns in redox and coupled water-nitrogen fluxes in the streambed of a gaining river reach
in Biogeochemistry
Krause S
(2009)
Nitrate concentration changes at the groundwater-surface water interface of a small Cumbrian river
in Hydrological Processes
Käser D
(2012)
ON THE IMPORTANCE OF CONSIDERING CHANNEL MICROFORMS IN GROUNDWATER MODELS OF HYPORHEIC EXCHANGE
in River Research and Applications
Käser D
(2013)
Prospective modelling of 3D hyporheic exchange based on high-resolution topography and stream elevation
in Hydrological Processes
Binley A
(2013)
Revealing the spatial variability of water fluxes at the groundwater-surface water interface
in Water Resources Research
Käser D
(2009)
Spatio-temporal variations of hyporheic flow in a riffle-step-pool sequence
in Hydrological Processes
Dudley-Southern M
(2015)
Temporal responses of groundwater-surface water exchange to successive storm events
in Water Resources Research
Lansdown K
(2015)
The interplay between transport and reaction rates as controls on nitrate attenuation in permeable, streambed sediments
in Journal of Geophysical Research: Biogeosciences
Description | Control of river stage on the reactive chemistry of the hyporheic zone, P Byrne, A Binley, AL Heathwaite, CM Heppell, K Lansdown, H Zhang, M Trimmer and P Keenan. |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Other academic audiences (collaborators, peers etc.) |
Results and Impact | A |
Year(s) Of Engagement Activity | 2012 |
URL | http://presentations.copernicus.org/EGU2012-10070_presentation.pdf |