Cohesive Channel Response to Watershed Urbanization: Insights from the Sand River, Aiken SC

Stream channel degradation is among the most widely documented symptoms of urban stream syndrome arising from watershed urbanization. Nevertheless, our present understanding of space and time scales associated with channel response to urbanization is poorly constrained and largely limited to assessments of non-cohesive systems. The purpose of this study is to assess the evolution of a cohesive, ephemeral river channel in response to watershed urbanization. The assessment of historical images document the stable, pre-urbanized channel conditions from 1870 to 1930. Historical assessments revealed a 131% increase in urbanized watershed area from 1930 to 1992, and a minimal increase in urbanized extent from 1992 to 2012. A 2012 lidar dataset was used to generate the modern long-channel profile, to reconstruct cross-channel profiles observed in 2002, and to estimate the volume flux of sediment removed from the channel from 1930 to 1992, and from 1992 to 2012. The long-channel profile reveals incision of up to 35 m in response to urbanization from 1930 to 1992. Cross-channel profiles reveal incision and widening of 2.5 and 3 m, respectively, from 2002 to 2012. Volume flux estimates indicate erosion rates of 9000 m3/yr during the first 62 years of the study period, and a flux of 4000 m3/yr after installation of stormwater control measures in 1992. Collectively, our findings highlight a cohesive channel that has undergone substantial incision and widening at a rate of ~0.20 m/yr since 1930, and the channel continues to adjust. Hence, we contend that the channel has not yet attained a new equilibrium “shape” at 82 years after peak land use change within the watershed, and that the channel will continue to adjust its shape until this new balance is achieved.

Urban Stream Syndrome and Contaminant Uptake in Salamanders of Central Texas

We studied the ecological health of springs experiencing varying levels of urban development to assess impacts to rare endemic salamanders (Eurycea spp.) of Central Texas. We evaluated measures of invertebrate species richness, water quality, and contaminant uptake by salamanders to determine how springs and their inhabitants were being affected by urban growth and changing land-use patterns. The number of environmental contaminants present and concentrations of contaminants increased in both water and salamander tissues with increasing age of the developments (i.e., years postconstruction) and increasing levels of impervious cover (e.g., roads) in urban watersheds compared with nondeveloped sites. We conclude that urbanization and associated increases in pollutant loading in watersheds can result in a loss of spring biodiversity and the accumulation of persistent and potentially toxic pollutants in salamanders. Although we detected generally low levels of pollutants, the altered water quality and invertebrate composition observed at springs, coupled with the changing hydrology and chronic contaminant exposure inherent in urban landscapes, is cause for concern, with potential implications for the long-term health, survival, and recovery of salamanders.

Urban Stream and Wetland Restoration in the Global South—A DPSIR Analysis

In many countries of the Global South, aquatic ecosystems such as streams, rivers, lakes, and wetlands are severely impacted by several simultaneous environmental stressors, associated with accelerated urban development, and extreme climate. However, this problem receives little attention. Applying a DPSIR approach (Drivers, Pressures, State, Impacts, Responses), we analyzed the environmental impacts and their effects on urban hydrosystems (including stagnant waters), and suggest possible solutions from a series of case studies worldwide. We find that rivers in the Global South, with their distinctive geographical and socio-political setting, display significant differences from the Urban Stream Syndrome described so far in temperate zones. We introduce the term of ‘Southern Urban Hydrosystem Syndrome’ for the biophysical problems as well as the social interactions, including the perception of water bodies by the urbanites, the interactions of actors (e.g., top-down, bottom-up), and the motivations that drive urban hydrosystem restoration projects of the Global South. Supported by a synthesis of case studies (with a focus on Brazilian restoration projects), this paper summarizes the state of the art, highlights the currently existing lacunae for research, and delivers examples of practical solutions that may inform UNESCO’s North–South–South dialogue to solve these urgent problems. Two elements appear to be specifically important for the success of restoration projects in the Global South, namely the broad acceptance and commitment of local populations beyond merely ‘ecological’ justifications, e.g., healthy living environments and ecosystems with cultural linkages (‘River Culture’). To make it possible implementable/practical solutions must be extended to (often poor) people having settled along river banks and wetlands.

The Value and Services of Urban Stream Polygnotou, Thessaloniki

Grey, blue and green infrastructure supports socio-ecological processes the city undergoes. Yet, procedures of constructing anthropogenic habitats often undermine the value of natural landscape elements such as urban streams. Thessaloniki’s backbone comprises of urban streams that run from the suburban forest of ‘Seih-Sou’ to the Thermaikos Gulf acting as corridors of the natural urban matrix. Policies of the past have dealt with urban streams through extensive engineering drainage methods, eliminating the risk of flooding, yet resulting in rapid stormwater runoff, water quality problems, disturbed riparian ecosystems, leading to the urban stream syndrome. Furthermore, they have failed to address urban streams as an inseparable part of the landscape and thus to incorporate them in people’s mental map and everyday activities. The paper discusses the case of ‘Polygnotou stream’ which forms the beginning of the large scale engineered peripheral moat of Thessaloniki, constructed in the 60’s, and playing the role of the water recipient for six urban streams in total. It falls unknown to the majority of people living in the area, yet its services as an ecosystem ought to be acknowledged, helping inform decision makers of its socio-ecologic, perceptual and economic value. In addition, Polygnotou stream, adjacent streams and the peripheral moat overall, could be considered as a touristic product of great importance.