Local- and landscape-level controls on coarse particulate organic matter retention in urban and forested small streams of central Massachusetts

Coarse particulate organic matter (CPOM) transport and retention were evaluated in 14 small streams in central Massachusetts. Seven streams were within the greater Worcester metropolitan area, and 7 were within protected areas north of the city. Sites drained areas with a range of watershed and riparian disturbance levels. Surrogate materials (wooden dowels that simulated small branches and diamond-shaped acetate strips that simulated leaves) of similar size and density to natural CPOM particles were released into 50-m reaches during low-flow conditions to measure retention rates. Cobble and boulders were the most important retention structures at all sites, and debris dams were important at some sites. Acetate diamonds had significantly shorter travel distances than dowels because particle flexibility and surface area reduced particle travel distance. Fewer acetate diamonds were retained in urban than in forested streams, and debris-dam density was lower in urban than in forested streams. The amount of developed area in the watershed and vegetation characteristics of the riparian zone contributed to the difference in retention. My findings indicate that restoration and management efforts for improving particle retention in urban streams should include reach- (e.g., riparian tree density) and watershed- (e.g., % urban or impervious surface) scale features during mitigation and when evaluating the success of the mitigation effort.