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<br />70 <br /> <br />Detritus <br /> <br />The term detritus ,(- a product of disintegration" from the Latin <br />deterere, to wear away) refers to all the particulate organic matl:er <br />arising from the decomposition of dead organisms and .!ssentially Identifies <br />the important link between the living (organic) and the nonliving <br />(inorganic) world. ' Organisms feeding on d.!tr1tus are commonly caUed <br />detritivores. <br /> <br />Living organisms technically and by d.!finition bE!come detritus upon <br />death and rapidly become inhabited by bacteria, fungi" protozoa, and other <br />microbiota. Separation of living and dead organic matter f or analytical <br />purposes is virtually impossible with present methods and technology, <br />Therefore, quantitative and qualitative analyses of d,!trital samples do not <br />involve "pure," but "mixed" samples. <br /> <br />Instream detritus has been separated Jtnto two br()ad organic loatter <br />categories based on particle size (Table 1). Coarse particulate organic <br />matter (CPOM) identifies particles greater than 1 mm () 1 mm). Fine <br />particulate organic matter (FPOK) identifi.!s particle!l less than-l mm (( 1 <br />am). CPUM is further divided into woody and nonwoody material such as <br />leaves, needles, flowers, bud scales, etc. Woody mat,!rial is furl:her <br />divided into coarse () 10 cm diameter) and fine (( 10 cm diameter) <br />material. Coarse wood material (debris) includes branches, rootwads and <br />boles, whereas fine wood material (debris) includes small pieces of bark, <br />twigs, etc. FPOM may be further divided into ultrafine particulate organic <br />matter (UPOM) that ranges in size from 50 11m to 0.5 um. Particles smaller <br />than 0.5 um are considered dissolved organ1:c matter (DOM). <br /> <br />Organic Matter ~nputs <br /> <br />Data largely substantiate the' hypothe!lis that both allochthonous and <br />autochthonous organic matter inputs vary plredictably dong 10ng1tudillal <br />profiles of streall ecosystems. The five pdnc1pal orllanic mstter inputs <br />are: 1) coarse particulate organic matter (CPOM), 2) periphyton <br />production, 3) phytoplankton production, 4) rooted macrophytes, and 5) fine <br />particulate organic matter (FPOM) generated from withIn and without the <br />stream ecosystem. CPOM is more prevalent in small, hE!avily shaded, <br />headwater streams and is progressively les!! important as stream order <br />increases and the riparian zone influences are reduced (Cumlll1ns 1975, <br />1977). Conversely, FPOM tends to increase in importance as strea,n order <br />increases due to abiotic-biotic processing or organic inputs. Th.!refore <br />the ratio between coarse and fine particulllte organic matter tendn to <br />decrease as streams increase in size. The export of particles from <br />upstream and primary production become mor.! important in the downntream <br />direction. <br /> <br />The relative quantities of the five types of inputs were well <br />illustrated along a twelfth order continuuen by assuming a total particulate <br />matter input of about 1000 g/m2/yr to low <)rder streams and a progressively <br /> <br />~~~~lU&liiliil<~~&!/1.~iP~''t <br />