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.