Twenty-six key research questions in urban stream ecology: an assessment of the state of the science (original) (raw)

Urbanization and stream ecology: diverse mechanisms of change

Freshwater Science, 2016

The field of urban stream ecology has evolved rapidly in the last 3 decades, and it now includes natural scientists from numerous disciplines working with social scientists, landscape planners and designers, and land and water managers to address complex, socioecological problems that have manifested in urban landscapes. Over the last decade, stream ecologists have met 3 times at the Symposium on Urbanization and Stream Ecology (SUSE) to discuss current research, identify knowledge gaps, and promote future research collaborations. The papers in this special series on urbanization and stream ecology include both primary research studies and conceptual synthesis papers spurred from discussions at SUSE in May 2014. The themes of the meeting are reflected in the papers in this series emphasizing global differences in mechanisms and responses of stream ecosystems to urbanization and management solutions in diverse urban streams. Our hope is that this series will encourage continued interdisciplinary and collaborative research to increase the global understanding of urban stream ecology toward stream protection and restoration in urban landscapes.

Hydrologic Changes in Urban Streams and Their Ecological Significance

Urban development modifies the production and delivery of runoff to streams and the resulting rate, volume, and timing of streamflow. Given that streamflow demonstrably influences the structure and composition of lotic communities, we have identified four hydrologic changes resulting from urban development that are potentially significant to stream ecosystems: increased frequency of high flows, redistribution of water from base flow to storm flow, increased daily variation in streamflow, and reduction in low flow. Previous investigations of streamflow patterns and biological assemblages provide a scale of ecological significance for each type of streamflow pattern. The scales establish the magnitude of changes in streamflow patterns that could be expected to produce biological responses in streams. Long-term streamflow records from eight streams in urbanizing areas of the United States and five additional reference streams, where land use has been relatively stable, were analyzed to assess if streamflow patterns were modified by urban development to an extent that a biological response could be expected and whether climate patterns could account for equivalent hydrologic variation in the reference streams. Changes in each type of streamflow pattern were evident in some but not all of the urban streams and were nearly absent in the reference streams. Given these results, hydrologic changes are likely significant to urban stream ecosystems, but the significance depends on the stream's physiographic context and spatial and temporal patterns of urban development. In urban streams with substantially altered hydrology, short-term goals for urban stream rehabilitation may be limited because of the difficulty and expense of restoring hydrologic processes in an urban landscape. The ecological benefits of improving physical habitat and water quality may be tempered by persistent effects of altered streamflow. In the end, the hydrologic effects of urban development must be addressed for restoration of urban streams.

Urban streams across the USA: lessons learned from studies in 9 metropolitan areas

Journal of the North American Benthological Society, 2009

Studies of the effects of urbanization on stream ecosystems have usually focused on single metropolitan areas. Synthesis of the results of such studies have been useful in developing general conceptual models of the effects of urbanization, but the strength of such generalizations is enhanced by applying consistent study designs and methods to multiple metropolitan areas across large geographic scales. We summarized the results from studies of the effects of urbanization on stream ecosystems in 9 metropolitan areas across the US (Salt Lake City, Utah; and Portland, Oregon). These studies were conducted as part of the US Geological Survey's National Water-Quality Assessment Program and were based on a common study design and used standard sample-collection and processing methods to facilitate comparisons among study areas. All studies included evaluations of hydrology, physical habitat, water quality, and biota (algae, macroinvertebrates, fish). Four major conclusions emerged from the studies. First, responses of hydrologic, physicalhabitat, water-quality, and biotic variables to urbanization varied among metropolitan areas, except that insecticide inputs consistently increased with urbanization. Second, prior land use, primarily forest and agriculture, appeared to be the most important determinant of the response of biota to urbanization in the areas we studied. Third, little evidence was found for resistance to the effects of urbanization by macroinvertebrate assemblages, even at low levels of urbanization. Fourth, benthic macroinvertebrates have important advantages for assessing the effects of urbanization on stream ecosystems relative to algae and fishes. Overall, our results demonstrate regional differences in the effects of urbanization on stream biota and suggest additional studies to elucidate the causes of these underlying differences.

Impacts of diffuse urban stressors on stream benthic communities and ecosystem functioning: A review

Limnetica

Catchment urbanisation results in urban streams being exposed to a multitude of stressors. Notably, stressors originating from diffuse sources have received less attention than stressors originating from point sources. Here, advances related to diffuse urban stressors and their consequences for stream benthic communities are summarised by reviewing 92 articles. Based on the search criteria, the number of articles dealing with diffuse urban stressors in streams has been increasing, and most of them focused on North America, Europe, and China. Land use was the most common measure used to characterize diffuse stressor sources in urban streams (70.7 % of the articles characterised land use), and chemical stressors (inorganic nutrients, xenobiotics, metals, and water properties, including pH and conductivity) were more frequently reported than physical or biological stressors. A total of 53.3 % of the articles addressed the impact of urban stressors on macroinvertebrates, while 35.9 % fo...

The urban stream syndrome: current knowledge and the search for a cure

Journal of the North American Benthological Society, 2005

The term ''urban stream syndrome'' describes the consistently observed ecological degradation of streams draining urban land. This paper reviews recent literature to describe symptoms of the syndrome, explores mechanisms driving the syndrome, and identifies appropriate goals and methods for ecological restoration of urban streams. Symptoms of the urban stream syndrome include a flashier hydrograph, elevated concentrations of nutrients and contaminants, altered channel morphology, and reduced biotic richness, with increased dominance of tolerant species. More research is needed before generalizations can be made about urban effects on stream ecosystem processes, but reduced nutrient uptake has been consistently reported. The mechanisms driving the syndrome are complex and interactive, but most impacts can be ascribed to a few major large-scale sources, primarily urban stormwater runoff delivered to streams by hydraulically efficient drainage systems. Other stressors, such as combined or sanitary sewer overflows, wastewater treatment plant effluents, and legacy pollutants (long-lived pollutants from earlier land uses) can obscure the effects of stormwater runoff. Most research on urban impacts to streams has concentrated on correlations between instream ecological metrics and total catchment imperviousness. Recent research shows that some of the variance in such relationships can be explained by the distance between the stream reach and urban land, or by the hydraulic efficiency of stormwater drainage. The mechanisms behind such patterns require experimentation at the catchment scale to identify the best management approaches to conservation and restoration of streams in urban catchments. Remediation of stormwater impacts is most likely to be achieved through widespread application of innovative approaches to drainage design. Because humans dominate urban ecosystems, research on urban stream ecology will require a broadening of stream ecological research to integrate with social, behavioral, and economic research.

STREAMS IN THE URBAN LANDSCAPE

Annual Review of Ecology and Systematics, 2001

Key Words impervious surface cover, hydrology, fluvial geomorphology, contaminants, biological assessment s Abstract The world's population is concentrated in urban areas. This change in demography has brought landscape transformations that have a number of documented effects on stream ecosystems. The most consistent and pervasive effect is an increase in impervious surface cover within urban catchments, which alters the hydrology and geomorphology of streams. This results in predictable changes in stream habitat. In addition to imperviousness, runoff from urbanized surfaces as well as municipal and industrial discharges result in increased loading of nutrients, metals, pesticides, and other contaminants to streams. These changes result in consistent declines in the richness of algal, invertebrate, and fish communities in urban streams. Although understudied in urban streams, ecosystem processes are also affected by urbanization. Urban streams represent opportunities for ecologists interested in studying disturbance and contributing to more effective landscape management.

Biological integrity in urban streams: Toward resolving multiple dimensions of urbanization

Landscape and Urban Planning, 2007

Most studies of urban streams have relied on single variables to characterize the degree of urbanization, which may not reflect interactions among features of urban landscapes adequately. We report on an approach to the characterization of urbanization effects on streams that used principal components analysis and multiple regression to explore the combined, interactive effects of land use/land cover, human population demography, and stream habitat quality on an index of biological integrity (IBI) of fish communities. Applied to a substantially urbanized region in northeast OH, USA, the analysis demonstrated the interactive nature of urbanization effects. Urban land use and stream habitat quality were significant predictors of IBI, but were no better than and, in some cases, poorer predictors than other gradients and interactions among gradients. High integrity sites were characterized by low forest cover and high grassland cover at sub-catchment scale, but high forest cover within a 500 m radius local zone of the sample point, conditions often found in protected parklands in the region. The analysis also indicated that variability in stream habitat quality was unrelated to landscape or demographic features, a result we attribute to the interaction between the geological and urbanization histories of the region.

Developing Reference Conditions and Biological Indicators for Urban Streams

2005

There are two objectives of this project: 1) developing biological indicators that characterize urban stressors, and 2) establishing reference conditions for urban systems. Our dataset was assembled from multiple, routine biological monitoring programs in Baltimore, MD/Washington, DC, Cleveland, OH, and San Jose, CA, representing data from approximately 2500 stream sites. We propose that increased sensitivity of biological indicators in urban systems can be attained only with detailed description of stressor conditions. A stressor gradient composed of multiple abiotic parameters representing landscape and instream physical, chemical, and hydrologic conditions was assembled. An ArcView and Excel-driven hydrologic model was developed that produced site-specific daily flow data which were reduced to hydrologic indicator values. These indicators showed significant correlations with urban land use (e.g., flood frequency [R2=0.36], flashiness [R2=0.37]) and were a substantial component of the gradient. Biological indicators were selected based on their responsiveness to the stressor gradient. In urban systems, restoration to pristine conditions is impossible; therefore, we developed reference conditions that represented "best attainable" conditions, given the extent of urbanization. This approach should provide an understanding of the capacity for ecological restoration in urban systems, and a basis for adaptation of urban streams to a tiered aquatic life use framework.

The biotic integrity of streams in urban and suburbanizing landscapes

Landscape and Urban Planning, 2004

The biological health of lotic communities is negatively correlated with the amount of urban land use in the surrounding watershed. This association is due, in part, to a historic lack of regard for the ecological consequences of development. Environmental considerations are increasingly being brought to the fore in land use planning, and to bear on development in the form of stormwater regulations and best management practices. The effectiveness of these practices in maintaining the biological integrity of receiving waters is assumed, though largely untested. We examined the relationship between urban land use and the biological health of streams in historically urbanized areas of Ohio, USA, and tracked the health of three streams over a decade in the rapidly suburbanizing Columbus, Ohio metropolitan area. The health of streams, as measured by the Index of Biotic Integrity, declined significantly when the amount of urban land use measured as impervious cover exceeded 13.8%, and fell below expectations consistent with Clean Water Act goals when impervious cover exceeded 27.1%. Declining biological integrity was noted in two of the three streams with suburbanizing watersheds at levels of total urban land use as low as 4%, demonstrating that poorly regulated construction practices are the first step toward declining stream health in urbanizing landscapes, and also demonstrate that the current regulatory structure is wanting. The few sites in our data set where biological integrity was maintained despite high levels of urban land use occurred in streams where the floodplain and riparian buffer was relatively undeveloped. An aggressive stream protection policy that prescribes mandatory riparian buffer widths, preserves sensitive areas and minimizes hydrologic alteration needs to be part of the larger planning and regulatory framework.