The impacts of a suite of Nature-based Solutions on hydrology and water quality in an agricultural landscape

Murphy, Darragh

The impacts of a suite of Nature-based Solutions on hydrology and water quality in an agricultural landscape

dc.contributor.advisor	Harrison, Simon
dc.contributor.advisor	Weatherill, John
dc.contributor.advisorexternal	Bourke, Mary
dc.contributor.author	Murphy, Darragh	en
dc.contributor.funder	Environmental Protection Agency	en
dc.date.accessioned	2025-02-04T16:40:40Z
dc.date.available	2025-02-04T16:40:40Z
dc.date.issued	2024
dc.date.submitted	2024
dc.description.abstract	Across much of the world, rural catchments have been substantially modified by human activity to meet the demand for greater production of a limited number of crops for human and livestock consumption. Much of the expansion of tillage and pasture areas has been at the expense of transitional zones such as wetlands, floodplains and riparian zones, and of hydraulically and geomorphologically complex stream environments which can mediate the flux of water and nutrients through catchments. Modifications to rural catchments to limit over-bank flooding may bring about more severe flooding downstream as flood peaks are conveyed more quickly through straightened channels. In Ireland, as agricultural activity has increased over the past 70 years, the impacts of agriculture on water quality have increased in kind, with a current estimate of 50% of rivers in Ireland being in satisfactory ecological condition. Field surfaces, farm drains and hard-standing areas can harbor high loadings of organic and mineral nutrients and sediment which are mobilized by rainfall to adjacent water ways. In the relative absence natural sites of retention and processing of these water quality pressures, large fluxes may be conveyed downstream during high-flow events, harming aquatic communities and affecting drinking water supplies. Nature-based Solutions (NbS) are applied in landscapes which have been modified by human activities, with the goals of reinstating and supporting natural processes which mediate and mitigate the flux of pressures such as high stream discharges and agricultural pollution. NbS features may operate passively within landscapes, requiring low initial and ongoing costs and are therefore advocated to complement or replace traditional engineering solutions to anthropogenic pressures. In Ireland, however, empirical data on the potential to of NbS features to mitigate target pressures is lacking. This is especially true in agricultural catchments where flood peak mitigation and water quality management are affected by complex biological and geo-chemical cycling of nutrients, as well as the cultural and social constraints imposed by modern farming practices. This thesis investigates the performance of four NbS features reduction of flood peaks discharges and the flux of agricultural water quality pressures on a farm in Ireland. In addition to examination of key biological (sediment retention, nutrient uptake, sward health) and hydrological (peak discharge reduction) effects of NbS features, the success of these features was contingent on bringing no harm to the farming enterprise or channel morphology within the study area. We found that the four studied NbS features - a flood detention basin, a runoff-treatment woodland swale, in-stream boulder weirs and leaky wooden dams – brought about notable improvements to water quality and/or reduced stream discharges during high-flow events. Specifically, this research has demonstrated that the storage of stream water on farm pastures during peak discharge periods may bring about reductions in downstream discharge, and nutrients and sediment concentrations; and that such short-term (12-24hours) inundation of pasture during winter does not impair summer growth of the sward. In-stream features were also shown to reduce stream discharges during high-flow periods but their scouring effects on stream and channel sediments were cause for concern. The study also found that modest, yet scientifically led, modifications to open farm drains may improve water quality and reduce the risk of contamination of downstream water courses. Importantly, however, the effects of all NbS features were strongly influenced by antecedent hydrological conditions, upstream nutrient loading and the stoichiometry of nutrient-enriched water flowing through the features. In summary, NbS features may be utilized for targeted mitigation of anthropogenic and natural issues, but they require careful, context-specific management to ensure they do not cause more harm than good.	en
dc.description.status	Not peer reviewed	en
dc.description.version	Accepted Version	en
dc.format.mimetype	application/pdf	en
dc.identifier.citation	Murphy, D. 2024. The impacts of a suite of Nature-based Solutions on hydrology and water quality in an agricultural landscape. PhD Thesis, University College Cork.
dc.identifier.endpage	286
dc.identifier.uri	https://hdl.handle.net/10468/16963
dc.language.iso	en
dc.publisher	University College Cork	en
dc.relation.project	Environmental Protection Agency (Project Code 2018-W-LS-20)
dc.rights	© 2024, Darragh Murphy.
dc.rights.uri	https://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject	Nature-based Solutions	en
dc.subject	Flooding	en
dc.subject	Water quality	en
dc.subject	Agriculture	en
dc.title	The impacts of a suite of Nature-based Solutions on hydrology and water quality in an agricultural landscape	en
dc.type	Doctoral thesis	en
dc.type.qualificationlevel	Doctoral
dc.type.qualificationname	PhD - Doctor of Philosophy