Stream ecosystem metabolism

Sources of organic carbon (C) and thus energy to lotic ecosystems fall into two broad categories: autochthonous inputs by aquatic primary producers and allochthonous inputs of dead organic matter from terrestrial ecosystems. Heterotrophs – microorganisms, meiofauna, and macrofauna – decompose and consume these supplies of organic C, ultimately remineralizing some fraction of the total as carbon dioxide (CO2), but also exporting substantial quantities to downstream ecosystems (Figure 12.1). Indeed, utilization and export are the two principal fates of organic C in stream ecosystems; although some storage occurs on the timescale of months to years, storage is thought to be negligible on longer timescales.