The urban stream syndrome

Common effects of urbanization on stream ecosystems have been referred to as the "urban stream syndrome" (Walsh et al. 2005a). Table 2 lists symptoms typically associated with the urban stream syndrome. Symptoms preceded by an arrow have been observed to consistently increase (↑) or decrease (↓) in response to urbanization, while symptoms preceded by a delta (Δ) have been observed to increase, decrease, or remain unchanged with urbanization.

As the urban stream syndrome illustrates, these streams are simultaneously affected by multiple sources, resulting in multiple, co-occurring and interacting stressors. As a result, identifying specific causes of biological impairment in urban streams, or the specific stressors that should be managed to improve condition, is difficult. Some communities are approaching this challenge by managing overall urbanization, rather than the specific stressors associated with it—for example, by establishing total maximum daily loads (TMDLs) for impervious surfaces, rather than individual pollutants.

Many characteristics of urban development affect how the urban stream syndrome is expressed within a given system. These characteristics include (but are not limited to):

Location and distribution of development

• catchment vs. riparian
• upstream vs. downstream
• sprawling vs. compact

Density of development

Type of development and infrastructure

• residential vs. commercial/transportation
• stormwater systems
• wastewater treatment systems

Age of development and infrastructure

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