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<br />69 <br /> <br /> <br />~"> <br /> <br />I <br /> <br />Gradient analysis is a major alternative to the more tradition~l <br />approaches to stream community through classification. Its major strength <br />relates to analysis of gradients at three l,~vels: (1) environClental <br />factors - especially as they longitudinally rel!'te_to ,.t,f.el\Jll,~!=d,r, (2) <br />functional feeding group (spe~i~s ,populatiolls), and" '(3)' cOllllllunity <br />characteristics. The st ream order concept affords art' oppon'unt"ty to <br />logically divide the stream continuum into three community types based on a <br />progressive downstream change in ecological characteristics even though <br />communities are generally (but not universally) contInuous with one another <br />I (Whittaker 1975). <br /> <br />the Trophic Res')urce <br /> <br />Benthos <br /> <br />Terminology has evolved that describes the aquatic communities living <br />on or within the solid liquid interface of stream channels. Both flora and <br />fauna inhabit the substrate and in combination with dead organic matter <br />causa the customary slipperiness of fixed and rock surfaces. _C~}_lectively, <br />the flora and fauna of the bottom community is termed stream benthos. In <br />practice, the aquatic macrophytes (i.e'l large plant life including algae <br />and the seed producing plants or angiosperms) and bottom dwelling algae are <br />termed phytobenthos and the bottom dwelling animal life zoobentho~. Stream <br />benthos may also be described on the basis of size and separated into <br />macrobenthos or microbenthos depending upon whether it passes through a <br />number 40 sieve screen. <br /> <br />Periphvton <br /> <br />The microbenthic flora and fauna blend into an even more complex, <br />largely microscopic community called the ~riphyton (peri = around; phyton <br />= plant) or German equivalent aufwuchs. Originally, the terms were coined <br />to describe a large assortment of unicellular and filamentous algae th~t <br />were sessile and attached to large plants and other substrate. More <br />recently. definition of the term has been broadened to describe a vast <br />array of more or less microscopic living and dead flora and fauna that form <br />the basic food source for secondary productIon. The kinds and numbers of <br />these microscopic plants and animals 'differ according to substratE', water <br />movement, depth, and chemical composition of the water. <br /> <br />Quantitative separation of the periphyton for analytical purposes has <br />proven unsuccessful mainly because of the heterogeneity of the intermingled <br />elements. The elements include: (1) autochthonous U.ving algae, fungi, <br />bacteria, microzoans, and their secretions, (2) dead a,utochthonous organic <br />material, (3) allochthonous organic material washed or blown into the <br />stream and lodged on the substrate to form 1m integral part of thE' <br />periphyton, and (4) inorganic particles originating from the streambed and <br />from allochthonous sources. <br /> <br />~"'''''''''''''''~'''i'ap''_':''';~)..''''':''''''''.:;.}'~~'^'~"'- "v~..-,._.~,"'--;;:::-:7.'-:'~~.:,:::~_, <br />