Recovery pathways for lake ecosystems

Global water demand has increased by 600% over the past 100 years and is predicted to grow significantly over the next few decades. Under current and future scenarios, aquatic ecosystems are under threat from multiple pressures, most notably human population growth with its often-conflicting demands for water, food and energy security, leading to declining freshwater quantity and quality. More than 30% of global biodiversity loss is due to pollution of water resources and aquatic ecosystems. Here, we focus on the contribution these challenges are having on freshwater lakes, where nutrient enrichment has been recognised as the key pressure. Across the world, increasing numbers of lakes are collapsing into polluted states. For example, in 2005, all 14,000 UK lakes >1 ha in size were risk-assessed for ecological status, of which over half failed the 'good' threshold, being judged at risk and likely to require some remediation. Most recently, in 2020, new data from the Environment Agency revealed that only 14% of lakes were classed as in good ecological health in England. Concomitantly, in a study of 273 Chinese lakes, amongst those with human impacts, only 22% showed relatively stable and resilient states. It is clear that such trajectories are unsustainable in terms of global freshwater use and functioning. Many countries have recognised the urgency of the problem, and are enacting local and global policies (e.g. EU, UN) for freshwater lake restoration. Despite substantial investment, current restoration projects are often based on short-term assumptions, and hence can fail due to the lack of knowledge of mid- to long-term recovery pathways after system collapse.

Our project addresses this challenge, to deliver a step change in our understanding of pathways to lake ecosystem recovery. Much of the difficulty in restoring lake ecosystems to 'good' (resilient) clear water states is due to hysteresis (the dependence of the state of a system on its history), keeping the...