Roberts, Mindy. 2007. Sources, transport, and fate of terrestrial organic matter inputs to small Puget Lowland Streams. Ph.D.
Urbanization may alter the amount of leaf and needle litter falling into streams due to removal or modification of riparian vegetation. Native aquatic species have evolved based on the timing and quality of allochthonous inputs endemic to a particular area. As non-native landscaping or invasive species replace native vegetation along the riparian corridor, the volume, timing, and nutritional content of the organic matter may change. Once leaves and other litter reach streams, the lack of large wood or other retention mechanisms in urban streams could enhance the transport of that material out of the systems. Finally, changes in physical, chemical, or biological processes may alter the decomposition of whatever organic matter remains.
Anthropogenic modifications to riparian vegetation contribute to urban stream degradation in a variety of ways, and thus rehabilitation efforts that do not consider this range may not restore key functions. Clearly, vegetation removal from riparian zones can increase water temperature by increasing the amount of solar radiation reaching the water surface, and it can reduce the supply of instream wood that would have protected stream banks and created pools and other retentive channel structures that trap sediments and organic matter. We are beginning to understand the additional roles that riparian forests play in watershed-scale nutrient cycling. The present research, being conducted by Ph.D. candidate Mindy Roberts, addresses the complementary function of riparian zones providing energy sources to small streams.
The Chico Creek watershed, located on the Kitsap Peninsula in the western lowlands ecoregion, provides a gradient of development levels as well as a unique reference location where native vegetation persists with only minimal local disturbance. Study sites were selected to include two reference reaches, one lake-dominated and the other unregulated, as well as two with vegetation patterns typical of residential development and one typical of an urban park.