Factors controlling streambank erosion and phosphorus loss in claypan watersheds

Although the targeting and efficacy of erosion management practices have improved, sediment and nutrients continue to degrade surface waters of North America. This study investigated the influence of land use, stream order, and season on streambank erosion and phosphorus (P) transport in the Central Claypan Region of northeast Missouri. The erosion pin method was used to measure bank erosion at 37 sites in Crooked Creek and Otter Creek watersheds from 2008 to 2011. At 18 of the sites, bank vegetation data were collected and watershed characteristics acquired. Bank erosion was highly variable with a mean linear erosion rate of 99 kg m(-1) y(-1) (66 lb ft(-1) yr(-1)) and a range of -31 to 490 kg m(-1) y(-1) (-20 to 330 lb ft(-1) yr(-1)); mean bank recession rate was 7.1 cm y(-1) (2.8 in yr(-1)) and ranged from -2.5 to 33 cm y(-1) (-1 to 13 in yr(-1)). Erosion rates were significantly greater in winter (December to March) than other seasons and were highly correlated to winter and annual stream discharge (r >= 0.95, p < 0.05). Watershed-scale estimates showed that streambanks contributed an average of 83% of annual in-stream sediment and 67% of total P loss, clearly demonstrating the impact that bank erosion has on stream water quality in this region. Regression models developed using riparian vegetation and watershed variables accounted for up to 48% of the variability in streambank recession rates, but the models were insufficient for prediction purposes. Overall, the results indicated that current land use, bank vegetation, stream order, and watershed characteristics were not the primary controls on streambank erosion rates. Other factors, such as historic land use changes, stream channelization, and the damming of the Salt River have resulted in major alterations to stream hydrology and geomorphology in these watersheds that have not yet re-equilibrated. These overarching factors, in combination with season, continue to be the main factors controlling streambank erosion in these watersheds.