Despite their limited spatial extent, freshwater ecosystems host remarkable biodiversity, including one-third of all vertebrate species. This biodiversity is declining dramatically: Globally, wetlands are vanishing three times faster than forests, and freshwater vertebrate populations have fallen more than twice as steeply as terrestrial or marine populations. Threats to freshwater biodiversity are well documented but coordinated action to reverse the decline is lacking. We present an Emergency Recovery Plan to bend the curve of freshwater biodiversity loss. Priority actions include accelerating implementation of environmental flows; improving water quality; protecting and restoring critical habitats; managing the exploitation of freshwater ecosystem resources, especially species and riverine aggregates; preventing and controlling nonnative species invasions; and safeguarding and restoring river connectivity. We recommend adjustments to targets and indicators for the Convention on Biological Diversity and the Sustainable Development Goals and roles for national and international state and nonstate actors.

Although biomonitoring approaches are being increasingly used in the measurement of stream and river health, critical assumptions about the nature of biological populations and communities that underpin them are often ignored. Many approaches based on pattern detection in plant and animal communities assume high temporal persistence in the absence of anthropogenic disturbances. However, this has been rarely tested with long-term data sets and there is evidence that this assumption is not true in some river systems. Biological processes, such as predation and recruitment, can account for considerable spatial and temporal variation in the structure of some stream communities. These processes may prevent the development of robust predictive models or indices based on pattern detection. Measurements of population or community attributes also are often used to infer ecosystem processes, yet the link between pattern and process has rarely been demonstrated. Many goals of river management relate to the maintenance of natural ecological processes and ecosystem function: direct measurement of these processes is, however, often neglected in assessment programs. Such measures are often sensitive to causal faetors that are known to affect river health and it is possible to develop simple but powerful predictive models. Perhaps more importantly, should an impact to be detected, strategies for remediation are more obvious as the causal processes are generally better known. The ultimate success of biomonitoring approaches depends on how well we understand the biophysical processes that influence the structure and dynamics of stream and river systems, and the way they function.

Stable isotope and ecological stoichiometry investigations of aquatic food webs require separate measurements of microalgae and detritus, but fine particulate matter collected as seston or scraped from biofilms typically is an unknown mixture of these two components plus other material. This paper describes an economical method to partition fine particulate matter into predominantly algal and detrital components by centrifugation in colloidal silica. Centrifugation using this density also worked well to separate algae from inorganic matter. The protocol was tested by sampling a broad range of water bodies in Queensland, Australia. Seston was concentrated using an inexpensive continuous centrifuge and organic matter was collected from surfaces of rocks, mud, or plants. Separation in colloidal silica was achieved using a standard benchtop centrifuge. When the colloidal silica was adjusted to a density of 1.27 g/cm 3 , the light fraction (supernatant) tended to be dominated by algal organic matter while the heavy fraction tended to be more detrital. Ratios of organic carbon to chlorophyll a indicated the efficacy of the separations. Stable C and N isotope ratios often differed considerably between the algal and detrital fractions, demonstrating the need to perform such separations in many aquatic environments.

Keeping the Earth system in a stable and resilient state, in order to safeguard Earth's life support systems while ensuring that Earth's benefits, risks and related responsibilities are equitably shared, constitutes the grand challenge for human development in the Anthropocene. Here, we describe a framework that the recently formed Earth Commission will use to define and quantify target ranges for a 'safe and just corridor' that meets these goals. Although 'safe' and 'just' Earth system targets are interrelated, we see safe as primarily referring to a stable Earth system and just targets as being associated with meeting human needs and reducing exposure to risks. To align safe and just dimensions, we propose to address the equity dimensions of each safe target for Earth system regulating systems and processes. The more stringent of the safe or just target ranges then defines the corridor. Identifying levers of social transformation aimed at meeting the safe and just targets and challenges associated with translating the corridor to actors at multiple scales present scope for future work.

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