The Use of Plastic Strips to Measure Leaf Retention by Riparian Vegetation in a Coastal Oregon Stream

Abstract

The feasibility of using strips of plastic instead of leaves for estimating the rate of retention of coarse particulate organic matter (CPOM; > 1 mm in diam) in streams was tested by simultaneously measuring retention of leaves and strips of plastic cut to approximately the same size as the leaves in six third- and fourth-order streams. There was no significant difference in the retention rates between the two methods when all six study reaches were considered together, nor was there a differ- ence in the location of retention of leaves and strips of plastic within a reach. How- ever, the retention rate of plastic strips was significantly higher than that of leaves in the two reaches with the highest flows. Plastic strips were used to assess the importance of shrubby riparian vegetation in retaining CPOM in a third-order stream. The density of streamside shrubs was re- duced to approximately 60 % and 0 % of naturally occurring levels, and retention was measured by releasing known quantities of plastic strips into the stream. Retention was highest in the reaches where shrub densities were not reduced, intermediate in reaches that were thinned, and lowest in reaches where shrubs had been completely removed. Riparian vegetation was directly or indirectly responsible for 68 % of the re- tention in the cleared reaches, 79 % of the retention in the thinned sections and 847o of the retention in the control reaches.