Transport of particulate organic material in streams as a function of physical processes

Those in search of fundamental properties of stream ecosystems have soughtphysical bases for comparing biological structure and function between running watersof different sizes, within basins and between basins. This endeavor has always seemedpromising because the same functional groups of organisms, from microbes to fish,but consisting of different taxa, can be found in the streams and rivers of variousterrestrial biomes (HYNEs 1970: Commis 1974; WurrroN 1975). A number of hydraulic-geomorphic parameters, such as discharge regime or stream order (STrinttLER 1957)appear promising as independent variables upon which to regress the many dependentvariables meagured by stream ecologists, such as standing crops or the ratio of primaryproduction to community respiration (P/R). To date, no physical or chemical parameter,or combination of parameters, has been demonstrated to adequately serve as a generalorganizer for lotic biotic data, although a number of classification systems have beenproposed (e. g., PENNAK 1971; I-IAWKES 1975). For the time being, stream order hasproven to be a useful "bookkeeping" device for comparing ecological informationwithin a basin (e. g., SHELDON 1968; CUMMINS 1977), but is of limited use in comparisonsbetween basins which differ hydrologically and geomorphically.
It is likely that various biological characteristics of stream ecosystem structure andfunction will regress most reliably on different combinations of physical parameters.For example, since the transport of particulate organic matter (= POM, detritus orparticles > 0.45 kim) is dependent on the work performed by moving water, streampower per unit width of channel should be a suitable dependent variable (Luorowet al. 1964; LANGBEIN & LEOPOLD 1964). Stream power which takes into account thedensity of water, rate of discharge and stream gradient, seems to be a logical unit fromwhich comparisons can be made between streams of different sizes.
Since sediment and water moving along a stream channel are the primary indepen-dent variables influencing channel morphology, quantitative relations have been estab-lished between water and sediment discharge (WousiAN & MILLER 1960). The natureand quantity of bedload and suspended sediment and all aspects of channel morphologysuch as dimension, shape, gradient, and pattern have been related to water discharge.
In this paper particulate organic material in transport in four different sized streamsand rivers in each of four different geographical-hydrological regions in the UnitedStates are examined. The objectives are to: (1) examine POM concentration and reportthe percentage size composition in all streams; and (2) relate of POM transportas a function of stream power, as well as concentration of POM as a function of power,gradient, and watershed area.