No.4 Special Projects Urban Effects on Waterways Studied Urbanization results in fluvial systems that contrast sharply with more pristine streams. The cycling and retention of important nutrients like nitrogen and phosphorus, which have been shown to limit rates of photosynthesis in other systems, as well as biotic variables are expected to be markedly different in urban watercourses.
Urbanization creates a patchwork of land uses resulting in an extremely heterogeneous landscape.
These patches create barriers and pathways for the flow of water, materials and energy. Lisa Dent and Nancy Grimm, Arizona State University ecologists, working in Sycamore Creek, a comparatively pristine Sonoran desert stream, have demonstrated that the concentrations of nutrients in stream water can be extremely variable in space and time. On the surface, algal uptake of nutrients causes downstream declines in nutrient concentrations. Because nitrogen is limiting in Sycamore Creek and because phosphorus tends to be controlled by physical factors, nitrate shows greater spatial variation than in Salt River Project canals. Urban fluvial systems have often been profoundly modified.