Organic matter (OM) is an essential component of freshwater ecosystems, fuelling the microbial food-web and primary production, influencing rates of greenhouse gas exchange with the atmosphere and changing water quality and ecosystem health through light attenuation. In contrast to upland rivers, lowland catchments are relatively understudied with regards to OM cycling, despite having highly modified inputs from intensive agricultural activity and growing urban populations, particularly via sewage effluent. For example, previous research has identified that there has been a long-term rise in the concentration of dissolved organic carbon (DOC) in the River Thames over the last 100 years, largely attributable to the population driven increase in the volume of sewage effluent entering the catchment (Noacco et al. 2017). However, there are significant knowledge gaps with regards to the composition of effluent OM and how it interacts with the microbial community and existing OM pool in freshwaters. This is important, as rivers, as well as supporting high levels of biodiversity and providing numerous ecosystem services, are responsible for processing approximately 2.8 Pg of terrestrial organic carbon annually, roughly equivalent to terrestrial net production, and therefore play an important role in the global carbon cycle. Modification of the natural processes controlling OM cycling in freshwater may therefore have widespread consequences.
This project aims to investigate the role of urbanisation (particularly via sewage effluent) on the dynamics and biological processes that are responsible for the biological turnover and fate of dissolved organic matter (OM) in lowland rivers and streams. This project will address three key questions:
1. What is the molecular composition of sewage effluent OM and how does it differ from riverine OM influenced by natural and agricultural sources?
2. How does effluent OM interact with the microbiologically driven processes that determine the fate of OM in the freshwater environment?
3. What are the wider impacts of effluent OM on the health of freshwater ecosystems in urban rivers?
You will work closely with the project partner, Thames 21, a charitable organisation set up with the aim of enhancing waterway environments in the Thames catchment, supervised by John Bryden and Dr Nathalie Gilbert. Using their data and knowledge from their existing monitoring programmes, exemplar rivers will be selected within the Thames catchment, covering a range of impacted rivers, from highly urban headwaters characterised by sewage misconnections, to sites where a clear impact of sewage effluent can be seen by comparing upstream sites with receiving waters.
You will receive training in the use of state-of-the-art techniques available at the Centre for Ecology & Hydrology (CEH) and the University of Bristol to address these questions. These include high-resolution mass spectrometry (at Bristol) to characterise the chemodiversity of OM using novel techniques developed in recent NERC funded research, and high throughput DNA sequencing, flow cytometry and enzyme assays to explore the microbiological controls determining the turnover and fate of OM from sewage effluent in receiving rivers. Field surveys in the Thames catchment will be conducted to understand the patterns in OM diversity in three urban river sites representing contrasting conditions. Laboratory bioassays and stable isotope labelling experiments will be used to perform controlled experiments to determine the fate and microbiological turnover of specific OM compounds identified from the field sampling and analysis programme at the three urban river sites, allowing the student to link specific compounds to specific biotic responses for the first time.
Applicants for a studentship must have obtained, or be about to obtain, a 2.1 degree or higher. Substantial relevant post-graduate experience may also be sufficient, please contact the supervisors for more information.
To apply please go to https://www.gw4fresh.co.uk/how-to-apply/doctoral-students/