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Increasing eutrophication and climate change have led to heavy cyanobacterial blooms in water diversion sources (e.g., lakes, reservoirs), which can potentially cause algae-bearing water to spread to downstream to an urban river network via diversion channels. Defining the extent of cyanobacterial blooms in an urban river network has become a novel concern in urban river management. In this paper, we investigated the physicochemical and algae community characteristics of a small, closed, urban river network, JiangXinZhou (JXZ), in the Lake Taihu basin. We propose a novel indicator, resource use efficiency (RUE), for defining the extent of cyanobacterial blooms in JXZ, whose recreational drinking water comes entirely from outside diversion sources. The results show that the JXZ's aquatic habitat conditions (mean water temperature, total nitrogen concentration, total phosphorus concentration, and nitrogen to phosphorus ratio) are highly suitable for the proliferation of cyanobacterial biomass during the high-water period. The RUE was used for calculation and shows a strong relationship with algae density, which means that it can be used as an index to define the degree of urban river cyanobacterial blooms. The findings indicate that the risk of cyanobacterial bloom is absent when the RUE is less than 46.81; blooms appear in the water bodies when the RUE reaches up to 106.68. This work provides theoretical support for the sustainable use of regional water resources.

Investigating the wastewater treatment efficiency (WTE) is an important component in fostering sustainable water management. This study proposes an environmental production technology framework based on eutrophication levels and heavy metal concentrations caused by wastewater discharge. The slack based measure (SBM) model with undesirable outputs and logarithmic mean Divisia index (LMDI) decomposition model are developed to quantitatively investigate the spatiotemporal distribution and driving effects in urban wastewater treatment under the context of China's River Chief system. Results showed that the distribution curve of WTE changes from double peaks to a single peak, and WTE value appears a decreasing (2001–2010)-increasing (2011–2020) trend. Provinces with high WTE are mainly distributed in eastern China, with low WTE are in western China. Overall, wastewater treatment efficiency has been generally improved through the implementation of China’s River Chief system. And provinces with low WTE are shrinking, with high WTE are extending from southeastern to northwestern China. To achieve a simultaneous improvement in wastewater treatment efficiency, it is necessary to improve the WTE in corresponding provinces that belong to barely effective development and inefficient development. Meanwhile, provinces in superiorly effective development and slightly effective development should be encouraged to maintain their high-level WTE.