Beavers and climate change mitigation in freshwater systems

点击翻译按钮获取中文摘要

The reintroduction of beavers has been a conservation success story repeated acrossEurope and North America. By damming small rivers and creating pools, ponds andcanals, beavers have restored lost ecosystem services such as: enhanced landscapebiodiversity (Nummi et al., 2019; Willby et al., 2018), flood and drought alleviation andimproved water quality (Brazier et al., 2020). Yet, these ecosystem modifications mayalso play a role in climate change as a function of the vast quantities of sediment thataccumulate in the ponds upstream of beaver dams, in addition to increased biomass ofaquatic plants (Law et al., 2016) and large volumes of dead wood comprising the beaverdams. These rewilded landscapes may therefore also act as carbon sinks and, hence, asa potentially valuable tool in creating resilient ecosystems in the face of a changingclimate.However, ponds of all types are simultaneously a disproportionately large source ofgreenhouse gases (GHGs), a major driver of global warming (Holgerson and Raymond,2016), due to their shallow depths, frequent mixing, high nutrient loading and fast energyturnover. Our understanding of GHG emissions from ponds, both in terms of magnitudeand driving processes, is lacking, even more so in beaver ponds which differ from otherfreshwater systems in their fundamental physico-chemical characteristics (Cazzolla Gattiet al., 2018). There is currently a dearth of studies that assess the full carbon massbalance of beaver ponds, with none at the UK scale and therefore we are unable toquantify the net effect of beaver reintroduction on carbon cycling. This limits ourunderstanding of the overall impact and influence of beavers in relation to climatechange.Recognising and quantifying the role of ecosystems and individual species in carboncycling is essential as we work towards net-zero carbon emissions and developingnature-based solutions. Robust evidence of the role of the beavers in carbon cycling isnow needed to identify whether carbon emitted is offset by carbon stored in beaverponds' sediments, vegetation and the dead wood comprising their dams. The overall aimof this PhD project is to quantify the net effect of beavers on carbon cycling, in order todetermine their climate impact.