| With the rapid social and economic development in the past nearly four decades, cities in China have experienced dramatic changes. Rapid urbanization has brought enormous prosperity together with exploitation and pollution of natural environment to cities. Urban rivers, which used to support navigation and provide water resources to humans, now suffer from various kinds of ecosystem degradation and thus create threats to regional sustainability. Such changes are especially significant in the Pearl River Delta (PRD) region. In this study, urban river is treated as an ecosystem which closely relates to and interacts with humans. After defining urban river ecosystem health (UREH) and summarizing the evolution processes of urban river ecosystem health protection in the international context, the relationships between urban rivers and human activities in the region are analyzed on both regional and local scales and from lateral, time-longitudinal, and spatial dimensions, thus to provide suggestions for managing urban river ecosystems.;Urban river ecosystem health is defined as requirement at three levels: sensorial fitness, living water, and affinity with human, which emphasizes more on the humanoriented needs. The evolution processes of urban river ecosystem health protection can generally be divided into four phases, demonstrating the relationships between human activities and UREH status as simple balance, uncontrolled imbalance, continuous interlocking, and stable harmony.;Analysis within the DPSIR framework of all the nine cities in the PRD region shows that in the past decades, the relationships between typical urban rivers and humans have been in Phase III, which exhibits the most frequent and active interactions. All the cities have experienced rapid urban development and the urban river ecosystems have been degraded with limited service functions. Simultaneously, abundant measures have been taken with multi-level goals for urban river improvement. Differences also exist among the nine cities in development levels, types of urban river, and management agencies, based on which three typical cities -- Shenzhen, Foshan, and Zhaoqing -- were selected for further analysis.;From the perspective of political ecology, effective actors in urban river management include governmental agencies, business, multilateral institutions, ENGOs, and grassroots actors. The unequal power relations among these actors and their own interactions with urban rivers vary over time and space, causing conflicts as well as coordination among them towards urban rivers. Among these actors, government plays a pivotal role, but the urban river management functions are distributed in various engaged governmental agencies centered by Water Authority (WA), resulting into overlap and gap among their functions in practice. The discrepancy among these simultaneously existing spatial scopes of different management goals by various departments, and the formal and informal occupation of river management area (RMA) in actual practice exacerbate the management problems in spatial dimension. New practice of a coordinating organization on river improvement work has been attempted, and still needs more and effective promotions.;On the local scale, impervious cover (IC), an important indicator representing the spatial distribution and intensity of human activities, was studied to examine the spatial scale effect of IC on urban river water quality, using Shiqi River watershed in Zhongshan as a case study. To improve the accuracy of stream network and watershed delineation in urbanizing watershed, AGREE algorithm was adopted. Results show that IC at the 100 m and 200 m- wide buffer zones within sub-watershed as well as the local contributing area and its 200 m and 500 m- wide buffer zones have significantly negative effects on water quality, indicating the importance of features of both area and location. Together with the spatial discrepancy of various departments' authorities identified above, these findings provide a strong support to the necessity of adopting a unified management strategy at the buffer zone scale to protect and restore urban river ecosystem health. |
