Nearly half of the world’s large lakes have lost resilience, or the ability to recover after abrupt disturbance, in recent decades. According to the first global assessment in this area, lakes in eastern North America and northern Europe have been hardest hit, with dense population and pollution largely to blame, the study suggests. However, wealthier regions had healthier lakes, suggesting that costly conservation efforts can pay off. Both people and climate can gradually move lakes away from their natural, healthy state. Warmer temperatures can increase evaporation, decreased precipitation can reduce lake levels, and persistent pollution can undermine the health of the lake ecosystem. When sudden disturbances occur, such as heat waves, droughts or floods, a “resilient” lake can recover; a vulnerable one may not be able to return to its previous state. Assessing a lake’s resilience, which takes into account its structure and ecosystem functions, is crucial for scientists to predict how it will respond to climate- and human-induced changes. However, the long-term trends of changes in lake resilience on a global scale (and why they occur) remain unknown. The new study, published in Geophysical Research Letters, fills this knowledge gap. “Monitoring lake resilience is crucial because it allows us to detect early warning signs of ecosystem degradation,” Ke Zhang, an environmental scientist at the State Key Laboratory of Lake Science and Environment Academy, said in a statement. of China Sciences who led the study. “It allows us to make timely interventions and prevent the irreversible catastrophic collapse of lake ecosystems, which can have serious socio-ecological consequences.” Zhang and his colleagues analyzed comprehensive lake health and resilience and a combination of climate and human factors for 1,049 of the world’s largest and most important lakes, looking for changes between 2000 and 2018. A set of statistical tests allowed scientists Look for “flickers” and long-term changes in a lake’s color, indicating changes in its health. If at least two of the statistical tests matched, the researchers marked the lake as experiencing a change in resilience. The researchers analyzed lake area, depth, and satellite-derived color in the context of each basin’s temperature, precipitation, population density, and gross domestic product (GDP) per capita. The researchers found that almost half of the lakes studied around the world significantly lost their resilience during the study period. Most were between 30 and 60 degrees N, but the authors point out that many of the world’s lakes are located in the higher latitudes of the Northern Hemisphere, and that there is more growth there due to climate change. On the other hand, about a quarter of the lakes studied were becoming more resilient, mainly at higher altitudes and mainly due to an increase in glacial meltwater. The Tibetan Plateau and the Andes had the largest gains in resilience as a result of melting glaciers. Central North America, primarily in Canada, also saw an increase in lake resilience. The researchers then divided the study period in half to see if any trends accelerated in recent years. Between 2000 and 2009, roughly the same proportion of lakes experienced an increase and decrease in resilience, at 36% and 35%, respectively. But between 2010 and 2018, while 28% of lakes gained resilience, 39% lost it, indicating a pronounced change in lake health. In recent years, 26.8% of lakes went from being more resilient to being less resilient between the two time periods. This pattern was particularly strong in eastern North America and northern Europe. The results surprised the researchers. “While we anticipated that human activities would significantly affect the resilience of lakes, the degree of decline in resilience (nearly half of the lakes studied) was alarming,” Zhang said. The findings could indicate that many lakes are approaching irreversible ecological tipping points, the authors wrote. The study found that population density contributed most strongly to the loss of lake resilience, likely linked to having higher pollutant concentrations and greater degrees of landscape alteration. Larger lakes and lakes at higher altitudes were more likely to be more resilient. In most regions, human factors were more important than climate, but high-altitude regions such as the Tibetan Plateau were the clear exception. There, warmer air temperatures lead to melting glaciers, which in turn allows lakes to grow larger and become clearer. And in tropical and subtropical regions, climate matters because warmer temperatures increase the risk of algal blooms, which degrade water quality and lake health. However, each of these is only one association in this study and requires further research for validation, the authors say. There are good news. Many lakes in regions with higher GDPs are improving, which the authors posit is linked to efforts such as reforestation, sustainable land use and combating eutrophication. The pattern of more resilient lakes in high GDP basins suggests that continued efforts focused on lake health could help, according to the authors. “This trend is concerning and underscores the urgent need for effective management and restoration efforts to mitigate these impacts,” Zhang said. “But the positive correlation between higher GDP and greater resilience in some areas means that economic development can be leveraged to invest in environmental protection and lake management.”
