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Economic development and increasing population density along the lower reaches of the Yellow river have challenged the river’s ability to meet human and ecological demand. The evaluation of the sustainability of water resources in the lower reaches of the Yellow River is of great significance for the achievement of high-quality development in the region. Based on an improved ecological footprint method considering soil water, the spatial and temporal evolution of the water resources ecological footprint and water resources carrying capacity and evaluates the utilization of water resources in the lower Yellow River are comprehensively evaluated. The results show that agricultural water consumption in the urban agglomerations in the lower reaches of the Yellow River occupies a major position in water consumption, accounting for more than 70%. In 2013–2017, the per capita water resources ecological footprint of the cities along the lower reaches of the Yellow River decreases every year, while the water resources carrying capacity is slightly fluctuating, but remains in a relatively stable state. The deficit situation has eased, falling by 54.52% in the past five years. The water use efficiency of the lower reaches of the Yellow River has increased every year, and the water resources conflict improved significantly, after the implementation of the new environmental policy in 2015. In terms of space, the cities with the smallest per capita ecological deficits include Zibo, Zhengzhou, and Laiwu City, and Dezhou, and Kaifeng and Binzhou City have the largest. Strict water resources management measures and water pollution prevention and control regulations should be formulated to improve the water use efficiency in these areas in order to solve the problem of water shortage.

The Yellow River Basin is of great significance to China’s economic and social development and ecological security. The Yellow River Basin is not only an important ecological barrier but also an important economic zone. In this article, natural hydrological conditions were taken as a reference, a habitat simulation model of the key sections of the Yellow River was constructed based on the MIKE 21 model, and an ecological water requirement assessment method for river ecological integrity combined with habitat simulation and features of the hydrological reference group was established, which took account of the survival and reproduction of indicator species. The suitable flow rates for the spawning period (i.e., April to June) of Silurus lanzhouensis in Lanzhou (LZ) and Cyprinus carpio in Longmen (LM) were 350–720 and 260–400 m3/s, respectively. Therefore, high pulse flow with a low flow peak should be guaranteed in mid- to late April. The peak flow should be at least approximately 1,000 m3/s to ensure that fish receive spawning signals, with a high pulse flow process occurring 1–2 times in May to June. The annual ecological water requirement of the Lanzhou and Longmen section was 9.1 × 109–11 × 109 and 4.7 × 109–11.3 × 109 m3. The model quantitatively simulated the changes in ecological water requirement of indicator fishes in key sections of the Yellow River, and an effective and realistic tool for ecological water requirement accounting of the Yellow River was provided.

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Water sources carry chemicals that can have a significant impact on the water environment of a river network, and understanding the contribution of different water sources to the river network can help to manage the pollution of the river network at its source. Hydrological connectivity of a river network affects the self-purification capacity and flood prevention capacity of the river. Thus an isotope tracer approach was applied to figure out the contribution rate of different water bodies to a river network and hydrological connectivity was quantified by introducing retention rate. Changzhou city was selected as the study area because it is an urbanized city with the characteristics of plain river network and it is faced with poor hydrological connectivity due to artificial constructions (dams and pumps) and human activity (urbanization). River water, well water (shallow groundwater), lake water and rainfall were collected during the flood season and nonflood season, and hydrogen and oxygen isotopes were determined. The temporal and spatial variations in hydrogen and oxygen isotopes in different water bodies and the state of the water cycle in different water bodies were analyzed. IsoSource and MixSIAR models were established to analyze the contribution rate of river network water sources in the study area, and their effectiveness was compared. Results of MixSIAR model were selected to evaluate the hydrological connectivity of the river network in the study area, providing a method to quantify the hydrological connectivity of specific river of the river network in Changzhou. This method could also be applied to other urban plain river network area to study its river connectivity.