Exploring the nature, origins and ecological significance of dissolved organic matter in freshwaters: state of the science and new directions

Over 83% of freshwater habitats in the EU were classed as being in unfavourable condition in 2015, higher than any other habitat type (European Environment Agency 2015). Similarly, freshwaters in North America are reported to be losing species at a rate of 4% per annum, five times faster than in terrestrial ecosystems (Vaughn 2010). Meanwhile, more than 50% of freshwater flora and fauna have declined in the past 40 years in the UK with 13% threatened with extinction and many more are already functionally extinct, while 25% of species in ponds with statutory protection have been lost since the 1990s alone (Hayhow et al. 2016). Over 25% of all freshwater species are currently threatened with extinction globally (Tickner et al. 2020) and freshwater fauna declined globally by 83% from 1970 to 2014, compared to 60% for all habitat types (WWF 2018; Reid et al. 2019). In no other planetary domain is biodiversity declining so rapidly, despite the raft of domestic and international legislation requiring action to halt this decline. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) has called for transformative change in our approaches to management of freshwaters to meet this challenge and restore and protect nature (IPBES 2019), and the research community has proposed an emergency recovery plan to ‘bend the curve’ of freshwater biodiversity loss (Tickner et al. 2020).