ABSTRACT

Energy is required to sustain all living systems. On land solar energy is converted to organic molecules by photosynthesis. In aquatic ecosystems the energy comes from two separate sources. As on land some energy is produced by primary producers by photosynthesis (autochthonous input), while the remainder comes from organic and inorganic material swept into the water from land (allochthonous input). In rivers the secondary production (i.e. biomass of invertebrates and fish) is more dependent on the primary production of the surrounding terrestrial zone than the primary production of the river itself.