River ecosystems: A tale of superlatives and hidden beauty

River ecosystems are superlatives in many respects. Their networks represent the largest biogeochemical nexus between the continents, oceans and atmosphere. River networks span multiple catchments, even biomes, and are highly dynamic in space and time. The world’s rivers contribute relatively little by areal extent, but their CO₂ emissions are of the same magnitude as the CO₂ sequestration flux by the world’s oceans. Rivers figure among the most heterotrophic ecosystems on Earth, metabolizing terrestrial organic carbon. Owing to their dendritic structure, the biodiversity that river networks host is exceptionally high. Finally, needless to emphasize how critical the ecosystem services are that rivers provide. Central to many of these river superlatives are microbial biofilms that abundantly coat the sedimentary surfaces of the river beds. A microbiome, encompassing all three domains of life, shapes, in conjunction with the turbulent nature of water flow, intriguing biofilm architectures. Biofilms, a hidden beauty emanating from the interactions between biology, physics and chemistry, regulate ecosystem energetics and are therefore an important linchpin between river biodiversity and biogeochemistry.

In my lecture, I will attempt to provide the state-of-the-art of global river carbon biogeochemistry and biofilm ecology. An emphasis will be given on the rivers that literally drain the roof of our planet, now at risk because of climate change. It is my hope, that soon we will appreciate the world’s river networks as we do appreciate the oceans and various terrestrial ecosystems.