Global prevalence of non-perennial rivers and streams.

Flowing waters have a unique role in supporting global biodiversity, biogeochemical cycles and human societies1-5. Although the importance of permanent watercourses is well recognized, the prevalence, value and fate of non-perennial rivers and streams that periodically cease to flow tend to be overlooked, if not ignored6-8. This oversight contributes to the degradation of the main source of water and livelihood for millions of people5. Here we predict that water ceases to flow for at least one day per year along 51-60 per cent of the world's rivers by length, demonstrating that non-perennial rivers and streams are the rule rather than the exception on Earth. Leveraging global information on the hydrology, climate, geology and surrounding land cover of the Earth's river network, we show that non-perennial rivers occur within all climates and biomes, and on every continent. Our findings challenge the assumptions underpinning foundational river concepts across scientific disciplines9. To understand and adequately manage the world's flowing waters, their biodiversity and functional integrity, a paradigm shift is needed towards a new conceptual model of rivers that includes flow intermittence. By mapping the distribution of non-perennial rivers and streams, we provide a stepping-stone towards addressing this grand challenge in freshwater science.

Intra-Lake Arcellinida (Testate Lobose Amoebae) Response to Winter De-icing Contamination in an Eastern Canada Road-Side "Salt Belt" Lake.

Salt contamination of lakes, due to the application of winter de-icing salts on roads, presents a significant environmental challenge in the "salt belt" region of eastern North America. The research reported here presents the first deployment of a previously published proxy tool based on Arcellinida (testate lobose amoebae) for monitoring road salt contamination. The research was conducted at Silver Lake in Eastern Ontario, a 4-km-long lake with the heavily traveled Trans-Canada Highway (HWY 7) transiting the entire southern shore. The lake showed elevated conductivity (297-310 µS/cm) and sub-brackish conditions (0.14-0.15 ppt). Sodium levels were also elevated near the roadside (median Na = 1020 ppm). Cluster analysis and nonmetric multidimensional scaling results revealed four distinct Arcellinida assemblages: "Stressed Cool Water Assemblage (SCWA)," "Deep Cold Water Assemblage (DCWA)," both from below the 8-m thermocline, and the shallower water "Shallow Water Assemblage 1 (SWA-1)" and "Shallow Water Assemblage 2 (SWA-2)". Redundancy analysis showed a minor response of Arcellinida to road salt contamination in shallower areas of the lake, with confounding variables significantly impacting assemblage distribution, particularly beneath the thermocline (e.g., water temperature, water depth, sediment runoff from catchment [Ti], sediment geochemistry [Ca, S]). The results of this study indicate that the trophic structure of the lake has to date only been modestly impacted by the cumulative nature of road salt contamination. Nonetheless, the Silver Lake results should be considered of concern and warrant continued arcellinidan biomonitoring to gauge the ongoing and long-term effects of road salt on its ecosystem.