More than half of Earth's rivers strongly impacted by human activity

February 18, 2021

Few of Earth's freshwater areas remain untouched by humans. More than half of the planet's freshwater river basins have been heavily impacted by human activities, according to a new study, which presents a novel, multi-faceted approach for evaluating biodiversity change at a global scale. Although rivers and lakes cover less than 1% of the planet's surface, they support a substantial component of the planet's biodiversity, including a quarter of Earth's vertebrates. Further, freshwater systems support the functioning and stability of a variety of ecosystems, including those that contribute to human wellbeing. Centuries of human activity - overfishing, non-native species introductions, on-river development, water pollution and climate change - have directly impacted freshwater biodiversity; they all threaten rivers systems and in many of these, they have altered the local species diversity. While evident, little is known about the global scale and magnitude of human impacts on freshwaters. To address this, Guohuan Su and colleagues evaluated the extent to which freshwater biodiversity has changed due to human activity over the past 200 years in a collection of 2,456 river basins worldwide. To compare each region, Su et al. developed what they call the cumulative change in biodiversity facets (CCBF) - an index that measures change in a specific area based on six key biodiversity indicators, providing a score ranging from 0 - 12. Higher scores depict greater impacts across a wider range of facets. A score of 6 or higher indicates substantial biodiversity change. The results show that 53% of the world's river basins covering 40% of the planet's surface have undergone marked changes in biodiversity - particularly in temperate regions. Those least impacted river basins were mostly small-sized, occupying only 13.4% of the world river basin surface, and supporting 3,876 species, or only 21.7% of the world fish fauna. These least impacted rivers were overrepresented in Afrotropical and Australian regions, the authors say. They note that conserving freshwater fish diversity in the least impacted rivers alone will remain below the target to protect at least 30% of Earth's surface by 2030, as proposed by a broad coalition of environmental organizations. Protection must also focus on areas where biodiversity has already been eroded by human activity, they say. According to the authors, the CCBF framework provides a method to quantify the impacts of humans on global biodiversity for other taxa and ecosystems.
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American Association for the Advancement of Science

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