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.
published: May 21, 2008
ArtNo. ESP141017102005, Price: 29.00 €
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.