The nutrients are important marine environmental parameters in coastal ocean, which directly impact the health of marine ecosystems. The human activities and global climate change have significantly changed the coastal marine environment. In recent years, there are an increasing trend of eutrophication occurrence in China's coastal ocean. Haikou Bay is a important bay in the northern South China Sea, and is experiencing more and more environmental pressure due to economic development and population increase in Haikou city. However, the variations of marine environment particularly the nutrients therein are not well understood. Based on nutrient data collected from Ocean Monitoring and Forecasting Center of Hainan Province (https://www.hnocean.cn/) covering a period from 2010 to 2021, we examined the seasonal and interannual variations of nutrients in the Haikou Bay. The results show that high nutrient concentration were mostly found close to Nandu River mouth. In addition, there is an opposite pattern between dissolved inorganic nitrogen (DIN) and salinity, suggesting fresh water input from Nandu river play an important role on nutrient distributions. The ratio of DIN to dissolved inorganic phosphate (DIP) is ~100, significantly larger than traditional Redfield ratio of N:P of 16, suggesting potential phosphorus limitation. However, the seasonal variations of nutrients are no evident, DIN concentrations in spring(12.40±0.55mmol/m³) are slightly higher than that in summer (10.49±0.55mmol/m³). On interannual time scale, DIN showed a slight decline trend during our study period, which might be attributed to pollution source control measures for sea discharge of Haikou government.

Nutrients,Haikou bay,Seasonal variation