Response of Water Environment to Land Reclamation in Jiaozhou Bay, China Over the Last 150 Years

Abstract

Jiaozhou Bay (JZB), located at Qingdao City, north China, is a semi-enclosed shallow bay that has undergone large-scale land reclamation and is suffering from a deteriorated water environment. Long-term evolution of JZB with respect of coastline, tidal prism, tidal dynamics, water-exchange capacity, and pollutant transport from 1863 to 2020 was investigated in this paper, using remote sensing images, historical charts, and a numerical model. The JZB was predominated by natural evolution from 1863 to 1935, during which the coastline barely changed. Thereafter, human intervention became intense and more and more natural tidal flats were replaced by salt ponds, aquaculture area, and reclamation very quickly. As a result, tidal prism, area of tidal flats, and area of JZB decreased sharply by 0.290 km3, 182 km2, and 223 km2, respectively, from 1935 to 2020, corresponding to annual decreasing rates being of 123 times, 10 times, 12 times, respectively, as that of before 1935. A numerical model showed that the residual current in JZB tended to be weaker due to the change of coastline and bathymetry, which is not favoring the water-exchange and pollutant transport, especially in the northeast of JZB. The basin residence time increased from 15.5 days in 1935 to 17.6 days in 2020, because of weaker residual tidal current and smaller tidal prism. Local residence time increased significantly near the area with large land reclamation, especially in the northeast and west of JZB. Distribution of dissolved inorganic nitrogen (DIN), in each year, which is the dominant pollutant in JZB, indicated higher DIN concentration and weaker transport along with reclamation. The research on JZB evolution over the last 150 years can provide useful suggestions for the decision-makers of the local government to improve the marine ecosystem. The systematic method to investigate long-term water environment evolution of JZB can be used to study other semi-closed bays.

Response of Sea Water Exchange Processes to Monsoons in Jiaozhou Bay, China

“…However, similar to most previous studies on bay water exchange [27][28][29][30][31][32][33], this paper is also based on numerical models and lacks the support of field-measured data. The wind stress used in the model is driven by the seasonal average wind field.…”

“…Some models did not incorporate a comprehensive range of physical processes [27,28] and some did not consider the drying and wetting processes of tidal flats [29]. In addition, most of the existing studies paid more attention to astronomical factors (tidal currents) while giving less consideration to the impact of non-astronomical factors (monsoons) on the water exchange process [30][31][32][33].…”

“…Over the past few decades, Jiaozhou Bay has witnessed dramatic transformations in its coastline morphology and topography, resulting in subsequent shifts in its hydrodynamic field and water exchange processes [33][34][35]. This study focuses on the influence of physical processes on the bay's self-purification capability.…”

Impacts of tidal flat reclamation on suspended sediment dynamics in the tidal-dominated Wenzhou Coast, China

“…Due to the differences in engineering designs and dynamic coastal environments, the coastal geomorphological responses to reclamation projects vary in different regions. The variations are related not only to the coastal morphology, geomorphological patterns, and hydrodynamic forces after reclamation, but also to the strength and persistence of the reclamation (Su et al, 2020;Xu et al, 2021).…”