A Comparison of Gravimetric and Photographic Methods of Stream Substrate Analysis in a Study of Benthos Microdistribution

Substrate particle size and the amount of detritus were measured by standard gravimetric sieve analysis and from photographs of the substrate surface. Details of the photographic technique are presented. The effectiveness of these variables in accounting for the variation in the numbers of Gammarus pulex (L.) between samples was assessed by multiple regression analysis. Photographic variables accounted for 49.5% of the variation and gravimetric variables 26.4%. It is concluded that the photographic technique is less laborious and provides information more relevant to the microdistribution of benthic animals which do not penetrate deeply into the substrate.