ALGAL POPULATIONS IN FLOWING WATERS 



John L. Blum 

 Canisius College 



The problems encountered in dealing with or- 

 ganisms that inhabit a current are different in many 

 ways from those met in the study of communities of 

 standing water. The fickle, unstable nature of both 

 the surrounding medium and the solid substratum; 

 the insecurity of being unattached in a current; the 

 enhanced chances of survival bestowed by a pro- 

 tected nook wherein to live and grow; the physio- 

 logical and mechanical stress which continued 

 pulling, twisting, and abrasion provide; the linear 

 alternation of the strikingly different environments 

 of riffle and pool; the continual supply of fresh 

 nutrients, along with silt and other debris from up- 

 stream area — all these factors so influence river 

 algae as to render the problems inherent in sam-- 

 pling, counting, and even in determining them, dif- 

 ferent in certain ways, and often more difficult, 

 than those involved in working with algae from still 

 water . 



QUANTITATIVE METHODS 

 OF SAMPUNG STREAM ALGAE 



Most of the special methods of sampling river 

 algae which have been devised are intended for 

 studies of the bottom vegetation. Of course, this 

 vegetation can simply be pulled up or scraped off 

 with a knife. Other methods better suited to give 

 quantitative data on the vegetation have been de- 

 vised by many workers . Probably the best known 

 method is that of Butcher (1932) who used a sub- 

 merged photographic frame of the type used for 

 printing postcards. The frame, holding five micro- 

 scope slides, is fastened horizontally in the river 

 and held by chains which are stretched tightly on 

 iron stakes driven into the river bed . 



This method was used throughout a long 

 series of government studies of British streams, in 

 which Butcher took part. These studies provided 

 the foundation for the most extensive information 

 we have about stream vegetation of any given 

 region of the world . It permits quantitative ap- 

 praisal of the early stages of algal growth. The 

 method has not been adapted to long periods of ob- 

 servation, and no proof has apparently been given 

 that algae colonize the slides in quite the same 

 way that they colonize the river bottom. There is 

 some evidence that numerical results from slide 

 counts are not, in fact, comparable to those from 

 the river bottom, but that the species present are 

 generally similar (Reese, 1935). However, a few 

 species of algae, which are almost universally 

 present on such slides, are little known from natu- 

 ral substrata . Large algae may easily be torn off 



smooth surfaces , and some algae may colonize 

 such a glass surface very slowly or simply show 

 slow growth (Lund and Tailing 1957). This method 

 of Butcher is hence somewhat inadequate, and par- 

 ticularly so, in recording changes in the mass or 

 volume of the vegetation or its components . This 

 is a serious drawback, for such changes can be 

 spectacular, as well as inexplicable. 



Among measures designed to measure epi- 

 phytic growth may be mentioned the method of 

 Thurman and Kuehne (195 2) . They used this method 

 for epiphytes of Cladophora glomerata (L.) Kutz., 

 but it could be easily applied to those of many 

 other filamentous algae. A cylinder of algae 1 cm. 

 thick is prepared, and pieces 1 cm. in length are 

 cut from this. The individual 1 cm. X 1 cm. cylin- 

 der pieces are placed in preservative, shaken, al- 

 lowed to stand for a day; and counts of the epiphy- 

 tic algae are made from the sediment contained in 

 the liquid . 



Algae, such as Oscillatoria and various other 

 blue-greens which live unattached on sediment, are 

 difficult to collect by means which permit quantita- 

 tive comparison between different collections . Soft 

 deposits may be sampled with a suction-tube sam- 

 pler, using a hand- or foot-operated pump and 

 sucking the surface deposit through a funnel which 

 is passed over the deposit in the manner of a vac- 

 uum cleaner. The method does not permit the col- 

 lection of comparable samples from different types 

 of substrate, nor give the same ratio of mud to 

 water from any one area on each sampling (Lund and 

 Tailing 1957). 



Margalef (1949a) has devised a method for 

 stripping the algae from surfaces of rocks from the 

 stream bed. After fixing, staining, and dehydrating 

 the algal layer in situ , a collodion solution is 

 poured over it and, when dry, is removed from the 

 surface of the rock. The method, similar to the one 

 commonly used for fossil material, is claimed by 

 Margalef to permit accurate counts of the popula- 

 tions present . 



As a means of estimating algal growth on the 

 bottoms of shallow rocky streams, I employed a 

 modification of the transect method. A rope was 

 marked off into decimeter and meter units and 

 stretched across the stream at a riffle, just above 

 the water surface. Presence was recorded in alter- 

 nate decimeters of all visible algal species, an in- 

 dividual or colony of which, is crossed by the rope. 

 The importance of the species was thus determined 

 by the relative number of decimeters within which 

 that species was present. Frequency was deter- 

 mined for each visible species by estimating the 

 relative percentage of total decimeters in which it 



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