High concentrations of cyanobacterial toxins such as microcystin represent a global challenge to water quality in lakes, threatening health, economies and ecosystem stability. Lakes are sentinels of climate change but how warming will affect microcystin concentrations is still unclear. Here we examine how warming impacts the probability of exceeding microcystin water quality thresholds across 2,804 lakes in the United States and show how future warming will alter these probabilities. We find that higher temperatures consistently increase the likelihood of microcystin occurrence but that the probability of microcystin concentrations above water quality thresholds is highest for water temperatures between 20 and 25 °C. Regions with temperatures that promote microcystin will shift to higher latitudes in the coming decades, leading to relative changes in exceedance probabilities of more than 50% in many basins of the United States. High nitrogen concentrations amplify the impact of rising temperatures, calling for increased awareness of a substantial hazard to ecosystems and human health under global warming.

The availability of surface water in global drylands is essential for both human society and ecosystems. However, the long-term drivers of change in surface water storage, particularly those related to anthropogenic activities, remain unclear. Here we use multi-mission remote sensing data to construct monthly time series of water storage changes from 1985 to 2020 for 105,400 lakes and reservoirs in global drylands. An increase of 2.20 km³ per year in surface water storage is found primarily due to the construction of new reservoirs. For lakes and old reservoirs (constructed before 1983), conversely, the trend in storage is minor when aggregated globally, but they dominate surface water storage trends in 91% of individual global dryland basins. Further analysis reveals that long-term storage changes in these water bodies are primarily linked to anthropogenic factors—including human-induced warming and water-management practices—rather than to precipitation changes, as previously thought. These findings reveal a decoupling of surface water storage from precipitation in global drylands, raising concerns about societal and ecosystem sustainability.

Climate change, especially in the form of precipitation and temperature changes, can alter the transformation and delivery of nitrogen on the land surface and to aquatic systems, impacting the trophic states of downstream water bodies. While the expected impacts of changes in precipitation have been explored, a quantitative understanding of the impact of temperature on nitrogen loading is lacking at landscape scales. Here, using several decades of nitrogen loading observations, we quantify how individual and combined future changes in precipitation and temperature will affect riverine nitrogen loading. We find that, contrary to recent decades, rising temperatures are likely to offset or even reverse previously reported impacts of future increases in total and extreme precipitation on nitrogen runoff across the majority of the contiguous United States. These findings highlight the multifaceted impacts of climate change on the global nitrogen cycle.

The contribution of terrestrial dissolved organic matter (DOM) to the ocean has been an enigma for decades. Tracking terrestrial DOM in the ocean has proven challenging due to factors such as the instability of terrestrial biomarkers, indistinguishable carbon isotopes from biogeochemical fractionation, and similar chemical composition between terrestrial and oceanic DOM. Here, we show that the terrestrial contribution to oceanic organic carbon pools is 1.7 to 2.5 times higher than previously assumed, highlighting the need to adjust global carbon cycle models. We derive these estimates by bridging high-performance liquid chromatography with ultra-high resolution mass spectrometry to investigate the presence of terrestrial molecules that are transported from rivers to the ocean and estimate their contribution to oceanic DOM. We identified 269 molecular formulae (MF) that are likely transported from land to the ocean. These formulae exhibited resistance to biological and photochemical degradation in incubation experiments, and were widely distributed in global rivers, marginal seas, and open oceans, suggesting that they are ubiquitous in inland and ocean waters and have a similar source. By relating the abundances of terrestrially derived MF to dissolved organic carbon concentrations, and radiocarbon measurements, we estimated that 16.7 to 25.0% of oceanic DOM is likely derived from rivers.