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The Pearl River Estuary is in the geometric center of Guangdong-Hong Kong-Macao Greater Bay Area, which is one of the main battlefields to drive the high-quality development of China's economy. This paper uses seven sets of typical satellite images in Pearl River Estuary for nearly half a century (from 1973 to 2021) to analyze the changes of coastline and sea reclamation. The results show that from 1973 to 2021, the total length of the coastline of the Pearl River Estuary increased from 240.09 km to 416.00 km, and that of the continental coastline from 186.87 km to 246.21 km (but the length of natural coastline in the continental coastline decreased from 136.91 km to 15.17 km). In the same period, the total reclamation area of the Pearl River Estuary increased by 28,256.06 ha. Before 2012, the growth rate of reclamation was generally fast. After 2012, the reclamation in China has entered a period of reflection. With reclamation was strictly controlled in the new era, only the previously approved reclamation projects and national major projects have been guaranteed, which makes the average annual growth rate of the coastline length and the reclamation area in the region show a significant downward trend. The reclamation in early days was largely for agriculture and pond culture purposes, but is shifting to transportation, industrial development, and urban construction in recent decades. This study scientifically analyzes the coastline and reclamation changes of the Pearl River Estuary in the past half century, which has a very important reference value for the next step to formulate marine ecological protection and restoration strategies, and construct a new pattern of marine space development and protection. [ABSTRACT FROM AUTHOR]

As one of the world's four Greater Bay Areas, the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) faces many environmental challenges along with rapid economic development, causing significant degradation of aquatic ecosystems. However, there is limited knowledge on long-term environmental changes (i.e., >50 years), and restoration of the degraded aquatic ecosystems in the GBA has become increasingly difficult. This study selects a typical inland water body, the Miaotan Reservoir, from Huizhou City in the GBA, to explore long-term changes in water and the eco-environment over the past 70 years and to provide some restoration and management strategies for degrading aquatic ecosystems in the region. We collected a sediment core from the reservoir center and established an age–depth profile by integrating 210Pb and 137Cs dating. We then set up high-resolution diatom community succession stratigraphy and multiple indicators (grain size, element, geochemical and social indicators) as responses to environmental changes in the reservoir. Our results show that significant changes have occurred in the ecosystem and environment of the Miaotan Reservoir and its catchment over the past 70 years. The diatom community underwent a gradual transition from absolute dominance of the mesotrophic species Aulacoseira granulata to dominance of the eutrophic species Nicizschia gracilis, Nicizschia palea and Achanathes sp., indicating the onset of water quality degradation and ecosystem changes in the 1990s due to eutrophication. The RDA (Redundancy analysis) results demonstrate that exogenous pollutant inputs into the Miaotan Reservoir resulting from agricultural activities over the period led to serious environmental changes, e.g., toxic algal bloom and heavy metal pollution. This study enriches our understanding of long-term environmental changes in inland lakes and reservoirs in South China and provides insights into the restoration and management of aquatic ecosystems in the GBA. [ABSTRACT FROM AUTHOR]

Understanding the driving factors and assessing the risk of rainstorm waterlogging are crucial in the sustainable development of urban agglomerations. Few studies have focused on rainstorm waterlogging at the scale of urban agglomeration areas. We used the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) of China as a case study. Kernel density estimation (KDE) and spatial autocorrelation analysis were applied to study the spatial distribution characteristics of rainstorm waterlogging spots during 2013–2017. A geographical detector (GD) and geographically weighted regression (GWR) were used to discuss the driving mechanism of rainstorm waterlogging by considering eight driving factors: impervious surface ratio (ISR), mean shape index of impervious surface (Shape_MN), aggregation index of impervious surface (AI), fractional vegetation cover (FVC), elevation, slope, river density, and river distance. The risk of rainstorm waterlogging was assessed using GWR based on principal component analysis (PCA). The results show that the spatial distribution of rainstorm waterlogging in the GBA has the characteristics of multicenter clustering. Land cover characteristic factors are the most important factors influencing rainstorm waterlogging in the GBA and most of the cities within the GBA. The rainstorm waterlogging density increases when ISR, Shape_MN, and AI increase, while it decreases when FVC, elevation, slope, and river distance increase. There is no obvious change rule between rainstorm waterlogging and river density. All of the driving factors enhance the impacts on rainstorm waterlogging through their interactions. The relationships between rainstorm waterlogging and the driving factors have obvious spatial differences because of the differences in the dominant factors affecting rainstorm waterlogging in different spatial positions. Furthermore, the result of the risk assessment of rainstorm waterlogging indicates that the southwest area of Guangzhou and the central area of Shenzhen have the highest risks of rainstorm waterlogging in GBA. These results may provide references for rainstorm waterlogging mitigation through urban renewal planning in urban agglomeration areas. [ABSTRACT FROM AUTHOR]