Rivers are among the world’s most biodiverse ecosystems but also the most threatened by human activities. River networks and their constituent biological communities perform numerous ecosystem functions (e.g. decomposition) that contribute to the recycling of carbon and nutrients. Rivers also provide essential ecosystem services – such as drinking water and climate regulation – that enhance society’s well-being. However, climate change and humans’ increasing water demands are causing river networks to dry, altering river biodiversity, ecosystem functioning (EF) and the provision of key ecosystem services. Although ecological responses to drying have been intensively studied at the local river reach scale, little is known about its impacts at the river network scale, limiting our capacity to predict the far-reaching effects of drying on river biodiversity and EF.
To fill this gap, we used the meta-system approach, which considers rivers as an ensemble of interacting terrestrial-aquatic sub-ecosystems among which organisms (e.g. microorganisms and invertebrates) disperse and resources (e.g. carbon and nutrients) are exchanged and transformed through EF (Fig. 1). In river networks, these fluxes of organisms and resources link small streams to the mainstem (longitudinal dimension) and terrestrial riparian habitats to instream aquatic habitats (horizontal dimension), ultimately linking terrestrial ecosystems to flood plains and oceans. As such, the meta-system approach integrates the multiple-facets of rivers, linking resources, biodiversity and EF across terrestrial-aquatic boundaries.
In this project, we aimed to examine the effects of drying on river-network scale biodiversity and EF and their implication to carbon processing (decomposition) and emissions (CO2). More than 50% of the world’s rivers naturally dry for at least one day per year but climate and anthropogenic changes are exacerbating drying events worldwide. A better understanding of the contribution of drying rivers to carbon cycles will thus inform CO2 emission scenarios and the design of management strategies that best preserve the ecosystem services that rivers provide to our societies.
The overall objectives of this project were to:
(O1) Determine the mechanisms driving the structuring of resource (organic matter), community (invertebrates, bacteria and fungi) and EF (decomposition and CO2 emissions) across aquatic-terrestrial boundaries in river networks fragmented by drying.
(O2) Identify where, when and under which conditions drying leads to mismatches between resource availability and organism activity, affecting carbon processing and meta-ecosystem dynamics.
