Variability in stream ecosystem response to urbanization

The geomorphic and ecological degradation of streams resulting from urbanization is well recognized. Recent reviews have hypothesized variability in ecological response to urbanization among stream types and among regions with varying climate and catchment soil and geology. Testing such hypotheses will be aided by the use of consistent metrics of the primary processes that drive urban-induced degradation of streams. We thus developed an urban typology distinguishing the common classes of urban land and water management that are hypothesized to have different effects on stream ecosystems. In developing the typology, we identify and emphasize the importance of step changes (thresholds) in the hydrologic consequences of urbanization, the often-unrecognized massive increase in drainage density of urban catchments, the difficulty in setting reference condition for many cities and the resulting difficulties in comparing responses to urbanization among cities. We critically assess the evidence for variability in responses to urbanization and its causes, and conclude that there are few studies demonstrating intra- or inter-regional differences in response to urbanization that have adequately accounted for the influence of potential differences in urban land and water management. We use the urban typology to propose metrics to allow such accounting, which we argue is necessary to advance management for stream protection and restoration.