Original paper

Hydraulic dispersion and reach-averaged velocity as indicators of enhanced organic matter transport in small Puget Lowland streams across an urban gradient

Roberts, Mindy L.; Bilby, Robert E.; Booth, Derek B.

Abstract

Organic matter transport and retention were evaluated in 14 small streams representing a range of riparian vegetation disturbance and watershed development levels in the Puget Lowland of western Washington. To determine relative transport and retention, diamond-shaped acetate strips of similar size and density to leaves were released in riffles during low-flow conditions. Simultaneous dissolved tracer releases were used to measure hydraulic characteristics of each reach. Both reach-averaged velocity and hydraulic dispersion predicted median leaf-surrogate material travel distance (R2 = 0.87, p < 0.001) and characterized transport and retention over longer reach lengths than in traditional organic matter release experiments. Relative organic matter transport distance increased as the pool/riffle ratio decreased, reach-averaged velocity increased, and dispersion increased. Because urban development affects hydraulic characteristics, urbanization enhances organic matter transport in small streams, reducing the retention of organic matter available for biotic processes.

Keywords

organic mattertransportretentionstreamurbandisturbancedispersion