A spatial evaluation of urea concentrations in UK rivers
Lead supervisors: Dr David Clark
Location: School of Life Sciences, University of Essex
Duration: 6 weeks
Suitable undergraduate degrees: Biological Sciences, Ecology, Environmental Science, Geography, Biogeochemistry, Microbiology
Microorganisms fulfill one of the most important ecosystem functions globally, by cycling nitrogen (N) between different forms, thus influencing the health of the world’s aquatic ecosystems. However, our knowledge of these processes is hampered by our lack of understanding of a fundamental suite of pathways within the nitrogen cycle, namely the degradation of urea. Urea, an organic form of nitrogen formed from metabolism and decay, accounts for >50% of global N fertiliser usage , and run-off of urea into aquatic ecosystems provides a C- and N-source for harmful algae , with environmental, economic, and health costs.
Genomic evidence shows that some microorganisms that conduct important steps of the nitrogen cycle can use urea as a substrate to fuel processes such as nitrification , complete ammonia oxidation , and anaerobic ammonia oxidation . The ability to use urea allows these microbes to ‘cheat’ the competition for substrates such as ammonia by making their own. The existence of a ‘cryptic N pool’ – accessible to some microorganisms but not others – means that we have likely underestimated the amount of substrate in a river to fuel nitrification. Thorough investigation of the microorganisms using urea, and their ecological dynamics, is therefore warranted to understand when, where, and how urea may contribute to aquatic nitrogen cycling.
Further study of urea as an input to the aquatic N cycle is hindered by a lack of available baseline data on riverine urea concentrations with monitoring bodies such as the Environment Agency not routinely measuring this nitrogen source. Therefore, the aim of this project is to establish ambient urea concentrations in a range of local rivers (NE Essex, S Suffolk), focussing on the Colne and Stour catchments. Multiple urea-assays will be compared, with a view to optimising sample preservation and compatibility with high-throughput approaches. Urea concentration data will also be compared to other UK rivers via meta-analytical/data mining approaches.
Together, these data will help to form a network of river sites that represent a gradient of urea exposure. Concurrently, this newly established study system will allow us to explore the ecological dynamics of urea-utilising microbial communities via a suite of molecular and experimental approaches, with ambient urea concentrations informing both a targetted sampling design and experimental conditions.
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