Spatiotemporal evolution of nutrients and the influencing factors in Laizhou Bay over the past 40 years

The nutrient status in Laizhou Bay has changed in composition and structure as a result of anthropogenic activities and climate change, which has led to several environmental problems (e.g., eutrophication, organic pollution and red tides). To better understand the spatiotemporal variations in dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and eutrophication in the Laizhou Bay, we collected historical research data and conducted four cruises in 2021. The highest surface DIN was found to occur in autumn and predominantly concentrated in the southwestern bay. The highest surface DIP content was found in winter and distributed in the northwestern bay. Surface organic pollution showed estuaries as the most polluted areas. In the past 40–60 years, the DIN, DIP, and eutrophication have shown an inverted U-shaped trend, and the bay has changed from N limitation to P limitation. Economic development, phytoplankton absorption, and bottom mineral release are factors influencing the content and distribution of nutrient in the bay. •Spatiotemporal evolution of DIN, DIP and eutrophication were studied over the past 40 years in Laizhou Bay.•Eutrophication and organic pollution were the main environmental pollution problems in Laizhou Bay.•High DIN concentration was mainly located in the southwest of the bay, while the high DIP was mainly in the northern part of the bay.•In the last ten years, a downward trend was shown for DIN, DIP and eutrophication, which suggested that Laizhou Bay has shifted from nitrogen limit to phosphorus limit.