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2020_62: The role of hydrodynamics in mediating effects of climate change on ecosystem stability and functioning

About This PhD Project

Project Description

Supervisors: Dr Samraat Pawar (); Professor Matthew Piggott, Department of Earth Science & Engineering; Professor Graham Hughes, Department of Civil and Environmental Engineering; Dr Erik van Sebille, external

Department: Life Sciences

The world's freshwater and marine ecosystems are responsible for >50% of the global primary productivity and therefore play a key role in the global carbon balance and biogeochemical cycles. Hydrodynamics-driven turnover in species and interactions combined with climatic forcing means that freshwater and marine ecosystems are not expected to be at a steady state over timescales longer than ~weeks to years. Yet, practically all global climate-carbon cycle models calculate CO2 flux from aquatic ecosystems assuming that they are at steady state. This issue is all the more important now that hydrodynamic regimes are rapidly changing due to global warming.
Therefore, to develop the next generation of carbon cycle models under global climate change, we need an empirically grounded theoretical framework that incorporates non-steady-state aquatic ecosystem dynamics. This project will tackle the challenge by merging individual-based models (IBMs) of hydrodynamics-mediated nutrient and population movement, ecological metabolic theory (EMT), and ecosystem network dynamics theory. This will be combined with data from controlled freshwater micro- and mesocosms. The modelling will focus on Nutrient-Phytoplankton-Bacterial (N-P-B) communities in lentic (non-flowing) freshwaters because, (a) N-P-B communities form the (microbial) core of the freshwater and marine biological carbon pump, and (b) evidence has rapidly accumulated recently that lentic freshwater ecosystems are a major carbon source that significantly offsets and/or affect the oceanic and terrestrial sinks.

The project will address three key questions at increasing spatio-temporal and complexity scales:
1. How do environmental temperature and hydrodynamics affect species interactions (e.g., competition vs mutualism) in N-P-B communities?
2. How does ecosystem volume affect the stability and resilience of N-P-B communities?
3. How does physical mixing combined with microbial locomotion affect carbon flow within, and efflux-influx from/to the ecosystem?

The overall approach will be to use a novel combination of simulation and analytical approaches to model dynamic N-P-B ecosystems/communities under different hydrodynamic and temperature regimes, potentially coupled with lab experiments to
parameterize or validate the theory. Specifically, (1) EMT and a global database on metabolic traits maintained in Pawar’s Lab will be used to parameterize the locomotion and life history strategies of individual cells of N-P-B populations in dynamically mixing
ecosystems of different sizes (across scales), (2) Hybrid Lagrangian-Eulerian methods currently being developed in Piggott and Van Sebille's Labs will be used to model emergent dynamics of interactions between individuals and populations, and (3) Ecosystem network theory will be used to predict the ecosystem level consequences of mixing-mediated interactions. The parameterization of realistic ecological behavior and variation of model microbes in the IBMs will be achieved through the BioTraits database, which covers hundreds of species and thousands of experimental measurements of microbial physiology and other traits relevant to microbe-microbe life history and interactions. This will generate empirically-grounded predictions that may be tested using burgeoning empirical data from experimentally warmed aquatic micro- and mesocosms (e.g., in Hughes’ Lab). One promising additional avenue would be to model interactions of microbial species with species at higher trophic levels (e.g., zooplankton, fish) to predict effects of mixing and spatial variability /patchiness on food web dynamics.

Application Information

The project will start in October 2020, and the studentship will be funded by the Science and Solutions for a Changing Planet Doctoral Training Partnership:

The project will be partly based between Silwood Park and South Kensington campuses, and is an exciting and novel foray into research at the interface of physics and ecology.

Candidates should apply directly (or direct questions) to Samraat () with a CV and cover letter.

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