Beavers and climate change mitigation in freshwater systems

The reintroduction of beavers has been a conservation success story repeated across
Europe and North America. By damming small rivers and creating pools, ponds and
canals, beavers have restored lost ecosystem services such as: enhanced landscape
biodiversity (Nummi et al., 2019; Willby et al., 2018), flood and drought alleviation and
improved water quality (Brazier et al., 2020). Yet, these ecosystem modifications may
also play a role in climate change as a function of the vast quantities of sediment that
accumulate in the ponds upstream of beaver dams, in addition to increased biomass of
aquatic plants (Law et al., 2016) and large volumes of dead wood comprising the beaver
dams. These rewilded landscapes may therefore also act as carbon sinks and, hence, as
a potentially valuable tool in creating resilient ecosystems in the face of a changing
climate.
However, ponds of all types are simultaneously a disproportionately large source of
greenhouse gases (GHGs), a major driver of global warming (Holgerson and Raymond,
2016), due to their shallow depths, frequent mixing, high nutrient loading and fast energy
turnover. Our understanding of GHG emissions from ponds, both in terms of magnitude
and driving processes, is lacking, even more so in beaver ponds which differ from other
freshwater systems in their fundamental physico-chemical characteristics (Cazzolla Gatti
et al., 2018). There is currently a dearth of studies that assess the full carbon mass
balance of beaver ponds, with none at the UK scale and therefore we are unable to
quantify the net effect of beaver reintroduction on carbon cycling. This limits our
understanding of the overall impact and influence of beavers in relation to climate
change.
Recognising and quantifying the role of ecosystems and individual species in carbon
cycling is essential as we work towards net-zero carbon emissions and developing
nature-based solutions. Robust evidence of the role of the beavers in carbon cycling is
now needed to identify whether carbon emitted is offset by carbon stored in beaver
ponds' sediments, vegetation and the dead wood comprising their dams. The overall aim
of this PhD project is to quantify the net effect of beavers on carbon cycling, in order to
determine their climate impact.