The Processing of Leaves of Trees and Aquatic Macrophytes in the Network of the River Rhone

Breakdown rate of terrestrial and aquatic leaves was found to depend on leaf species and on the biotope considered. As the leaves started decaying at different dates and had different breakdown rates, consumable allochthonous or autochthonous organic matter was fed to the aquatic system throughout the year, from one summer to the next. A comparison with former results on the main channel confirms the existence of a transversal gradient in the fluvial network: under the influence of fungal and invertebrate colonization, breakdown was fastest in the channel of the river, slower in an open side‐arm, and slower still in a more lateral and closed side arm, in which organic matter accumulated in hypoxic conditions.