Model-based assessment of shading effect by riparian vegetation on river water quality

Shading by riparian vegetation affects incident solar radiation and water temperature in small- and moderate-size streams, and is thus an important component in the influence of forested riparian buffers on streams. The water quality effects of riparian shading are largely unknown. A simulation study was carried out to evaluate the effect of shading on six water quality variables in a moderate-size Belgian river stretch. A dynamic modelling approach making use of the River Water Quality Model No. 1 was chosen to represent the system. The scenarios developed indicate that shading may be an effective tool in controlling stream eutrophication (44% reduction in phytoplankton productivity in the simulated stretch) but has a limited effect on dissolved oxygen, chemical oxygen demand, nitrates, ammonium nitrogen, and phosphates. Results suggest that shading can effectively be implemented as a direct management strategy to improve water quality conditions in small and moderate-size watercourses that are exposed to excessive algal growth during summer periods.