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Title: Identifying critical source areas of phosphorus transfers in agricultural catchments
Author: Thomas, Ian Alistair
ISNI:       0000 0004 6057 5068
Awarding Body: Ulster University
Current Institution: Ulster University
Date of Award: 2016
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Environmentally sustainable intensification of agriculture is needed to achieve both global food security and water quality objectives under international agri-environmental legislation. Amongst a suite of possible measures, effective mitigation of critical source areas (CSAs) of diffuse phosphorus (P) transfers is necessary to reduce eutrophication and water quality impairment. To improve CSA identification and mitigation, CSAs were modelled using ‘big data’ from advanced remote sensing and water quality monitoring in four intensively monitored Irish agricultural catchments (—7.5-12 km2). In these complex landscapes, delineation was constrained by digital elevation model (DEM) resolution and the influence of microtopographic features. To address this, optimal DEM resolutions of 1-2 m and bare-earth point densities of 2-5 points m'2 were identified (derived from high resolution Light Detection and Ranging (LiDAR) data) for spatially modelling hydrologically sensitive areas (HSAs) and surface runoff pathways. An HSA Index was then developed, based on optimal 2 m LiDAR DEMs and a soil topographic index (STI), which also considers the hydrological disconnection of overland flow via topographic impediment from flow sinks (e.g. depressions or hedgerows). A ‘next generation’ GIS-based CSA index of dissolved P losses from legacy soil P sources was also developed, by integrating the HSA Index with mobile soil P data (water extractable P; WEP). CSA maps were validated using high frequency water quality data collected in 2009-2014 by catchment outlet bankside P analysers (r2 = 0.86). HSA and CSA maps identified ‘breakthrough points’ and ‘delivery points’ along surface runoff pathways where diffuse pollutants could be transported between fields or delivered to the open drainage network, respectively. The CSA approach identified 1.1-5.6% of catchment areas at highest risk of legacy P delivery, compared with 4.0-26.5% of catchment areas based on an existing approach that uses above optimum agronomic soil P status. The tools could be used to cost-effectively target mitigation measures and best management practices at the sub­field scale within a ‘treatment-train’ strategy, to reduce diffuse pollution and support sustainable agricultural production.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available