Photo of Dr Joshua Dean

Dr Joshua Dean BSc (Hons) - Massey University; PhD - La Trobe University

Lecturer in Biogeochemical Cycles Geography and Planning

    Research

    Disentangling the role of rivers as greenhouse gas conduits

    Frozen rivers in the eastern SIberian Arctic. Photo credit @JoshuaFDean
    Frozen rivers in the eastern SIberian Arctic. Photo credit @JoshuaFDean

    Rivers emit ~2-3 Pg of carbon as the greenhouse gas carbon dioxide (CO2) to the atmosphere, each year. This is equivalent to 20% of annual anthropogenic CO2 emissions and an important component of the global carbon cycle. Methane (CH4) emissions from river networks are very poorly understood. CH4 is a potent greenhouse gas, 34 times stronger than CO2 over a 100-year timeframe. Rivers are estimated to emit ~27 Tg of CH4 each year, equivalent to 8% of anthropogenic CH4 emissions. However, these CH4 emissions vary greatly both spatially and over time.

    Rivers, acting as conduits for terrestrial greenhouse gases, can thus influence ongoing climate change. Landscape disturbance, either through human activity or climate change, can enhance river carbon emissions adding substantially to an already overloaded atmospheric carbon pool. This may represent a feedback to the global climate system as river carbon emissions can be enhanced by the impact of climate change on the terrestrial carbon cycle. Characterising the magnitude and source of river carbon emissions across globally representative ecosystems is therefore urgently needed for us to understand and predict current and future climate change.

    Methane in urban waterways

    Sampling in the Amsterdam canals. Photo credit @PatrikWiniger
    Sampling in the Amsterdam canals. Photo credit @PatrikWiniger

    Methane is a greenhouse gas with 86 times the global warming potential of carbon dioxide over a 20-year period - the timescale in which global action to reduce carbon emissions and limit catastrophic climate change is needed. Roughly half the methane currently in the atmosphere comes from human activity, so addressing human-driven methane emissions is crucial to achieving international climate targets. Three key challenges stand in the way of this goal:
    1) How do we accurately measure methane emissions?
    2) Where do methane emissions originate?
    3) How do we reduce methane emissions?

    This project aims to deliver technical solutions to address these challenges. The project focuses on urban waterways because:
    a) they are potential hotspots of methane emissions, receiving inputs from leaking urban infrastructure and organic matter decomposition,
    b) this wide range of methane inputs provides a realistic testbed to apply techniques for measuring methane emissions and origins in non-perfect conditions, and
    c) the unique ecology of urban waterways is poorly studied, allowing novel exploration of how spatial and temporal methane patterns, influenced by human activity, impact microbial methane consumption (oxidation).

    The project includes fieldwork in urban waterways across the UK, mainland Europe, the USA, China and Bangladesh.

    Research Grants

    NI: CONFLUENCE – Disentangling the role of rivers as greenhouse gas conduits

    NATURAL ENVIRONMENT RESEARCH COUNCIL (NERC)

    December 2020 - December 2022

    Impact of urbanisation on river carbon emissions

    MANCHESTER GEOGRAPHICAL SOCIETY (UK)

    June 2021 - May 2022