Rapid urbanization threatens the biota of streams and rivers around the globe. Efforts to manage urban streams traditionally take an engineering approach focused on stormwater runoff, physical channel condition, and chemical water quality. Our objective was to use the biology of streams-measured with the multimetric benthic index of biological integrity (B-IBI) based on benthic macroinvertebrates-to assess stream health. From 1997 to 1999, we sampled invertebrates at 45 sites in second-and third-order streams in the Puget Sound lowlands of Washington State. Land cover upstream of each site was characterized by analysis of a 1998 satellite image. We evaluated associations between five land cover categories and biological condition across three spatial scales. The relationships between B-IBI (and its component metrics) and stream substrate and hydrologic features were also analyzed at a subset of sites. Across all study sites, B-IBI declined as the percentage of urban land cover increased ( r Ͻ Ϫ 0.71, p Ͻ 0.001, n Ͼ 31). Most metrics were better predicted by sub-basin rather than local-scale urbanization. Within individual basins, however, local land-cover urbanization and B-IBI were strongly correlated ( r ϭ Ϫ 0.91, p Ͻ 0.001, n ϭ 9). The biological condition of a site was also related to measures of hydrologic alteration and stream substrate. The aquatic biota is sensitive to a variety of urban effects, expressed at both large and small spatial scales. Biological assessment tools such as B-IBI can identify areas of excellent biological condition for conservation and guide the design and evaluation of efforts to restore the biota of degraded streams.Evaluación y Restauración de la Salud de Arroyos Urbanos en la Cuenca Puget Sound

Successful stream rehabilitation requires a shift from narrow analysis and management to integrated understanding of the links between human actions and changing river health. At study sites in the Puget Sound lowlands of western Washington State, landscape, hydrological, and biological conditions were evaluated for streams flowing through watersheds with varying levels of urban development. At all spatial scales, stream biological condition measured by the benthic index of biological integrity (B‐IBI) declined as impervious area increased. Impervious area alone, however, is a flawed surrogate of river health. Hydrologic metrics that reflect chronic altered streamflows, for example, provide a direct mechanistic link between the changes associated with urban development and declines in stream biological condition. These measures provide a more sensitive understanding of stream basin response to urban development than do treatment of each increment of impervious area equally. Land use in residential backyards adjacent to streams also heavily influences stream condition. Successful stream rehabilitation thus requires coordinated diagnosis of the causes of degradation and integrative management to treat the range of ecological stressors within each urban area, and it depends on remedies appropriate at scales from backyards to regional storm water systems.

INTRODUCTIONIn-stream rehabilitation projects are commonly built in response to problems that result from both local sources and diffuse watershed degradation. Local problems, such as an improperly sized culvert, are relatively easily identified and corrected. Reversing the consequences of watershed degradation, such as channel widening and incision, is much more difficult if conditions that led to stream degradation remain unchecked. Despite this challenge, large amounts of money are being spent on in-stream projects in urban or urbanizing basins, because of numerous recognized problems on these streams, the interest of local communities in restoring the amenities these streams provide (Riley 1998, MacDonald 1995, and the relative ease and economy of site-specific in-stream work.This study investigates the effectiveness of one common technique, placement of in-stream large woody debris (LWD), to reverse local effects of watershed degradation in the absence of any systematic watershed-scale rehabilitation measures. To accomplish this, six stream rehabilitation projects in western Washington state that employ LWD were examined with the objective of answering the following questions:• Does in-stream placement of LWD produce physical channel characteristics typical of

One of the desired outcomes of dam decommissioning and removal is the recovery of aquatic and riparian ecosystems. To investigate this common objective, we synthesized information from empirical studies and ecological theory into conceptual models that depict key physical and biological links driving ecological responses to removing dams. We define models for three distinct spatial domains: upstream of the former reservoir, within the reservoir, and downstream of the removed dam. Emerging from these models are response trajectories that clarify potential pathways of ecological transitions in each domain. We illustrate that the responses are controlled by multiple causal pathways and feedback loops among physical and biological components of the ecosystem, creating recovery trajectories that are dynamic and nonlinear. In most cases, short-term effects are typically followed by longer-term responses that bring ecosystems to new and frequently predictable ecological condition, which may or may not be similar to what existed prior to impoundment.