Spatial distribution, source apportionment, and assessment of marine water quality parameters in the Bohai Sea, China

Composition and Distribution of Microeukaryotic Communities in the Surface Sediments of Five Geographic Regions of Bohai Sea Based on 18S rDNA Amplicon Sequencing

“…These sampling sites were distributed among the five geographic regions [1,3]: Bohai Bay (BB) including NS-24; Liaodong Bay (LB) including NS-13; Central Bohai Sea (CS) including NS-27; Yellow River Estuary (YE) including NS-29, NS-30, and NS-31; and Miaodao Archipelago (MA) including NS-33, NS-34, and NS-35 (Figure 1). At least three parallel sediments (0-5 cm) were collected from each sampling site by a box-type sediment sampler (Figure 2A).…”

“…Thalassiosira, belonging to the phylum Bacillariophyta, has a relatively high abundance at the Central Bohai Sea, Liaodong Bay, and NS29 site (Yellow River Estuary). The Yellow Sea Warm Current, Yellow River, and Liaohe River runoff bring abundant nutrients such as silicon, nitrogen, and phosphorus to these sea areas [3]. Diatoms, especially in spring and autumn, can rapidly reproduce and become dominant species in water bodies.…”

“…Although many studies have emphasized the significance of both spatial and environmental factors in microeukaryotic communities, it is still difficult to determine which mechanism predominates [3,36]. The Bohai ecosystem has undergone a transition from an N-limited oligotrophic state prior to the 1990s to a potentially P-limited eutrophic state.…”

“…It is the only semi-enclosed inland sea in China and has an area of approximately 77,000 km 2 , with an east-west width of approximately 346 km and a northeast-southwest length of about 555 km [1,2]. The Bohai Sea's coastline spans 2796 km and is composed of five parts: Liaodong Bay in the north, Bohai Bay in the west, the central shallow basin, Laizhou Bay in the south, and the Bohai Strait in the east [3]. The Bohai Sea is enclosed by land on three sides and is only adjacent to the Yellow Sea via the 109 km wide Bohai Strait.…”

“…Its high dependence on coastal habitat conditions makes the ecosystem vulnerable and highly susceptible to human activities. With the rapid growth of population and economy, nitrogen and phosphorus fertilizers from agriculture and aquaculture, industrial wastewater discharges, and urban sewage emissions produced by frequent human activities introduce a large amount of nutrients and pollutants, alter the natural balance of water bodies, and exacerbate eutrophication [3,6,7]. Although the Chinese government has implemented extensive efforts in recent years to limit land-based pollutant discharge, eutrophication continues to frequently occur in the Bohai Sea, particularly in the Bohai Bay and the Laizhou Bay [6,7].…”