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The Effects of Urbanization on Nitrogen Processing in Urban Streams

Urban stream syndrome is described as the deterioration of stream health in an urbanized watershed and is associated with the loss of ecosystem services, which in turn degrades downstream environments. One key symptom of the urban stream syndrome is reduced processing of inorganic nitrogen. Previous research suggests that as urbanization increases and water quality decreases, the uptake length (Sw) of inorganic N increases. This indicates that the stream is increasing the export of N downstream compared to in situ incorporation of N into the ecosystem. We measured uptake length (Sw) of NO3, using a pulse addition method, along 9 different reaches located within an urban watershed in Rock Island, IL that drains into the Rock River. The sites were chosen to represent varying levels of urbanization throughout the watershed. We found evidence of significant nitrogen uptake along stretches at seven of the nine sites we tested, indicating some level of ecosystem services are still being performed in this watershed in spite of the urban setting. We also wanted to see if background concentrations of nutrients or pollutants impacted nitrogen uptake. We predicted that higher background pollutant levels would increase the uptake length; however we found no such correlation. Our key finding was evidence of N uptake occurring across an urban watershed which differed from most research done on this topic.