Large woody debris -A river restoration panacea for streambed nitrate attenuation?

Lead Research Organisation: University of Birmingham
Department Name: Sch of Geography, Earth & Env Sciences


For centuries, large woody debris has been removed from UK and European rivers to reduce potential flood risks caused by these obstacles and blockage. However, the removal of large woody debris has been shown to severely impact on ecosystem services provided by rivers, including habitat functioning and the potential to reduce nutrient and sediment loading by acting as both a physical and biochemical barriers. This caused detrimental impacts on in-stream and floodplain biota as well as society in the provision of clean drinking water.

Recent EU and UK environmental policies (notably the European Water Framework Directive) are promoting a significant shift in management practices, strongly emphasizing the reintroduction of in-stream wood to improve the resilience of lowland river ecosystems to environmental change by increasing their capacity to attenuate excess nitrate pollution. As obstacle in the river, woody debris is expected to increase the down-welling of surface water into the streambed and enhance its contact time in the very reactive streambed zone, resulting in increased chemical turnover and nitrate attenuation. However, the impacts of large woody debris on the main drivers of biogeochemical processes in the streambed, the exchange fluxes between groundwater and surface water as well as the residence time of water in the streambed are poorly understood. To improve design of large woody debris structures to efficiently remove nitrate from the streambed, river basin management and restoration programmes require scientific evidence for the effectiveness of different large woody debris designs for water quality improvement.

This project will therefore provide the scientific evidence required for assessing the efficiency of different permanent and mobile designs of large woody debris for enhancing the uptake of nitrogen in lowland rivers. Our research focuses specifically on lowland streams as these represent the majority of UK rivers under threat of critically high nitrate concentrations. The findings of this project will directly inform river restoration practice and decide whether, to what degree and with what design, large woody debris will be deployed in UK lowland streams to reduce critically high nitrate loads.

We will combine novel monitoring techniques and environmental tracer technologies with innovative numerical modelling approaches to identify the occurrence of streambed hotspots of increased biogeochemical turnover that are facilitated by large woody debris. We will quantify to what degree excess nitrate concentrations can be reduced in this reactive hotspots and what different designs of large woody debris structures best facilitate this ecosystem service. We will improve sophisticated numerical models to quantify how effective permanent and mobile large woody debris may attenuate excess nitrate from lowland rivers. By developing and simulating a set of scenarios, assuming wider ranges of environmental conditions then observed experimentally, we will predict how efficiently different large woody debris structures in lowland rivers can reduce nitrate pollution under changing environmental conditions.

Knowledge of how in-stream wood facilitates the occurrence of biogeochemical hotspots will assist river managers in adopting techniques which deliver benefits to both in-stream biota and water quality for human uses. This project, twinned with the proposed policy advice documents we will develop, will provide an ideal opportunity for the formation of science-based restoration activities which are able to deliver quantitative water quality improvements for little to no additional cost.

Planned Impact

This project will create direct academic and societal impact by providing scientific evidence for the potential of LWD in enhancing streambed nitrate attenuation in lowland rivers. Our research results on LWD design-specific nutrient turnover will directly inform decisions of UK regulators and restoration agencies including EA/DEFRA, River Restoration Council (RRC), River and Wildlife Trusts on if, where and how to implement LWD as adaptation and mitigation strategies in national river restoration programmes. Direct links for policy implementation have been established by Co-I researcher M. Klaar as part of her Environment Agency secondment.

We will deploy an efficient knowledge exchange strategy for facilitation of the excellent research undertaken by an interdisciplinary team of expert scientists. The end-users and beneficiaries from the scientific community, industries, regulatory bodies and policy backgrounds are directly involved in the project planning and management and will be engaged via a project Advisory Board. The Advisory Board includes partners from the Environment Agency, RRC, Association of River Trusts, TrUck (Trees in the River Uck, a collaboration of EA/ Woodland Trust/ Wildlife Trust and SEW), South East Water (SEW) and Forestry Research (FR) and will meet for three main project management meetings and a tailored practitioners workshop. To optimise the scientific exchange with other UK funded research and to support the interactions between cross-theme scientific working groups, partners from collaborating CWC and other relevant projects e.g. NERC's Macronutrient Cycles Programme and Defra's DTC's will also be invited to the three main project meetings.

The international dissemination of project results will be achieved by publication in high impact scientific journals and presentation in international and national scientific conferences. These means of facilitation will be supported by the strong links to the UNESCO- IHP and FRIEND programmes (see letter of support) as well as the investigators' involvements in EGU, AGU, BHS, IAH and IAHS programme committees. The project's close links with the Birmingham Institute for Advanced Studies will support the dissemination of research to a wider scientific community as well as the interested public. The dissemination of the results will directly benefit from the UoB PI's and Co-I's expertise as working group leaders in the NERC funded Knowledge Transfer Network on "Groundwater-Surface Water Interactions and Hyporheic Zones", providing well-established links to regulatory bodies, water industries, environmental consultancies and public media.

A practitioner workshop for the design, installation and maintenance of LWD will be organised in association with the River Restoration Council to facilitate the technological developments and experiences of this project to scientists, regulators and river restoration managers.

A project website will support the efficient dissemination of the project's research results, featuring conference presentations of the project partners and providing access to freely available open source code and software produced by the project with add-ins of simplified examples. The website will support multi-directional knowledge exchange by including interactive features such as a project WIKI as well as pod- and vodcasts and a metadata catalogue. Data will additionally be made available via NERC data archives as well as through the communication gateways of project partners including the Wildlife Trust's Biological Records Centre and Environment Agency Central Data Bureau. Design outputs on LWD structures will be furthermore made available on the River Restoration Centre (RRC) web-forum.


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Romeijn P (2021) Macrophyte Controls on Urban Stream Microbial Metabolic Activity. in Environmental science & technology

Description Spatial patterns in riverbed material have the potential to create hotspots of nitrogen attenuation. These hotspots can be identified by a new disctibuted sensor network.
Exploitation Route the findings will inform river managers and restoration practitioners in the way they manage streambed sediments.
Sectors Agriculture, Food and Drink,Environment

Description Regulators and decission makers have been informed about the hydrological impacts of riparian forests in a stakeholder meeting in 2015.
First Year Of Impact 2015
Sector Environment
Impact Types Policy & public services

Description Collaboration with JABBS Foundation 
Organisation JABBS Foundation
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution FO-DTS investigation of soil water fluxes in irrigated forest plantation
Collaborator Contribution Funding of PhD studentship
Impact No outputs yet
Start Year 2019
Description Collaboration with Leeds University 
Organisation University of Leeds
Department School of Law
Country United Kingdom 
Sector Academic/University 
PI Contribution joint data analysis and publications
Collaborator Contribution joint data analysis and publications
Impact scientific paper in preparation
Start Year 2016
Description Collaboration with Severn Rivers Trust 
Organisation Severn Rivers Trust
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution Based on the outcomes of our NERC funded research we have established relationships with the Severn River Trust to further develop woody debris solutions to remediate excess nutrient concentrations in agricultural freshwater bodies.
Collaborator Contribution The Severn Rivers Trust provides direct and in-kind support for the installation of engineering infrastructure in a recent research pilot.
Impact Workshop and joint research project development
Start Year 2020
Description Academic conference (Australia) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation at the International Symposium for Ecohydraulics, in Melbourne, Australia. The talk introduced the new concepts our research seeks to address, which generated a great deal of interest from other academics, policy makers (UK, US and Australia), river restoration practictioners and industry (water companies)
Year(s) Of Engagement Activity 2016
Description Conference presentations at EGU General Assembly 2016 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Attempting to link hydro-morphology, transient storage and metabolism in streams: Insights from reactive tracer experiments
Marie J. Kurz, Christian Schmidt, Phillip Blaen, Julia L. A. Knapp, Jennifer D. Drummond, Eugenia Martí, Jay P. Zarnetske, Adam S. Ward, Stefan Krause

Geomorphic and substrate controls on spatial variability in river solute transport and biogeochemical cycling
Phillip Blaen, Marie Kurz, Julia Knapp, Clara Mendoza-Lera, Joe Lee-Cullin, Megan Klaar, Jen Drummond, Anna Jaeger, Jay Zarnetske, Joerg Lewandowski, Eugenia Marti, Adam Ward, Jan Fleckenstein, Thibault Datry, Scott Larned, and Stefan Krause
Year(s) Of Engagement Activity 2016
Description Expert Panel- Sussex Flow Initiative 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Outlined the potential of the research project to deliver environmental benefits within Natural Flood Management projects. Engaged with an audience comprised of land owners, habitat restoration professionals, policy makers and industry, which sparked an increased interest in the possibility of environmental improvements using instream wood
Year(s) Of Engagement Activity 2015
Description Multi-pollutant interactions in hyporheic zones 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact AGU Fall Meeting
Year(s) Of Engagement Activity 2017
Description Presentation at the British Hydrological Society 'Forest Hydrology' meeting. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Invited talk at the British Hydrological Society's National Meeting, which drew together a wide range of audiences, including government, professional practitioners, academics, industry and members of the public. The talk highlighted the project, and outlined the study approach and probable outcomes, which generated a great deal of interest in the research topic.
Year(s) Of Engagement Activity 2015