Allochthonous Inputs

Allochthonous material, which includes all of the organic matter that a stream receives from production that occurred outside the stream channel, often makes up a large fraction of a stream's total inputs of organic matter. Coarse and fine POM derived from the terrestrial ecosystem and DOM from groundwater and adjacent terrestrial soils are important sources of nonliving organic C originating beyond the stream channel. Hetero-trophic microorganisms and other consumers utilize these C sources, and in some settings allochthonous detritus dominates stream metabolism. Instream primary production may contribute to DOM pools by extracellular release and enter both DOM and POM pools after sloughing and dieback, and so the separation of allochtho-nous versus autochthonous sources may sometimes be imperfect, but this is unlikely to be a major source of error in the estimates that follow.

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