About the Project
The ability of wetlands to retain agricultural pollutants such as nitrogen (N), phosphorus (P) and faecal indicator organisms (FIOs) makes them attractive nature-based solutions for managing diffuse pollution and important local-scale features for improving water quality. Wetland characteristics influence hydrological and biogeochemical processes and in turn pollutant-trapping efficiency, which has led to increased use of wetlands as so called ‘kidneys of the landscape’. Field wetlands in agricultural landscapes are typically small, constructed wetlands located in areas of less productive land with the intention of reducing diffuse pollution via their capacity for removing nutrients, sediments and FIOs from runoff, thus disconnecting hydrological delivery of those pollutants to receiving waters. The resulting nutrient cycling in field wetlands following the retention of P, N and also carbon (as either DOC or DIC) can, however, lead to ‘pollution swapping’. This is recognised as an unintended consequence of a mitigation option, whereby the specific management for one pollutant could inadvertently increase the release of another pollutant. For example, while denitrifying bacteria in wetland soils reduce nitrate, the processes of denitrification and methanogenesis in wetland soils can also provide a source of greenhouse gas (GHG) emissions to the atmosphere. Conversion of agricultural land to field wetlands at what can be quite localised scales, with the best intention to manage water quality via nature-based solutions, may therefore inadvertently increase agricultural GHG emissions.
Why does this matter? Agriculture is already one of the key contributors to global GHG emissions and there is increasing pressure for the sector to reduce its GHG emissions. This requires understanding of gas fluxes and air quality effects associated with different land management options. Pollution swapping through use of agricultural field wetlands may potentially have counterproductive consequences if farmers and landowners are encouraged to install wetlands as a means of improving habitat and water quality but then inadvertently increase emissions of GHGs such as CO2, CH4 (methane) and N2O, leading to a loss of trust across the farming community with respect to the advice and guidance that they receive. To ensure sound practitioner advice for environmentally beneficial outcomes, we need underpinning evidence to holistically evaluate the potential for trade-offs in pollutant management arising from the installation of agricultural field wetlands. This is critically important for informing wider agricultural policy and future stewardship schemes designed to deliver multiple benefits for Scotland’s environment.
The overarching aim of this studentship is to quantify the impacts of field wetlands on agricultural GHG emissions and carbon sequestration potential. The specific objectives are to:
O1: Develop a conceptual framework and typology of agricultural field wetlands for Scotland;
O2: Quantify inflow / outflow concentrations of water quality parameters and spatial and temporal CO2, CH4 and N2O flux from the different field wetland typologies under investigation;
O3: Evaluate GHG flux impacts from wetlands relative to (i) size of wetland contributing catchment area; and (ii) magnitude of multi-aquatic pollutant net retention;
O4: Use scenario modelling to estimate the cumulative effects of multiple wetlands distributed across the landscape and guide future decision-making and policy design.
This interdisciplinary studentship will therefore use a combined field and modelling-based approach. The project will integrate water quality, GHG and GIS data in order to analyse and evaluate GHG flux impacts from wetlands relative to the size of wetland, contributing catchment area, catchment land use, and the efficiency of water pollutant retention. Using a GIS data-based approach, you will develop a range of future scenarios that link climate, land use and distribution of wetland creation to estimate the interactive and cumulative effects of water quality mitigation versus GHG emission at larger catchment scales. A key research and knowledge exchange outcome will be the development of a simple matrix of conditions, (e.g. physical, edaphic, or agronomic) under which agricultural field wetlands will deliver positive net environmental benefits.
Applicants are strongly advised to make an informal enquiry about the PhD to the primary supervisor well before the final submission deadline. Applicants must send a completed application form (available here https://www.hydronationscholars.scot/apply), their Curriculum Vitae and a covering letter to the primary supervisor by the final submission deadline of 8th January.
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