The Effects of Urbanization on Leaf Breakdown Rates in a Rock Island Watershed

The ability of streams to break down leaves is widely used as an indicator of stream health. In this study, a series of six streams within the Rock Island, Ill., watershed, which were similar in discharge, order, temperature and pH, were categorized as healthy or unhealthy based on chloride levels. This study was part of a broader study of the Rock Island watershed by Augustana. Maple leaves were collected shortly after abscission, weighed, packaged in mesh bags (approximately 5g per bag) and deployed in the streams for two- and four-week periods. After each time period, the leaves were removed, dried and weighed, and the mass loss was calculated as well as overall leaf decomposition rate. The healthy streams decomposed leaves significantly faster than the unhealthy streams. These results suggest that streams in close proximity to impervious surfaces (the unhealthy streams) experienced a loss of the ecosystem service of leaf decomposition perhaps due to a loss of invertebrate shredders because of high chloride levels associated with urbanization