Effects of Typhoon Haikui on Nutrient Concentrations and Biological Production in the Yangtze Estuary and Its Adjacent Sea

Abstract:

Water temperature, salinity, turbidity, nutrient concentrations, and chlorophyll fluorescence were measured at four sampling stations in the Yangtze River Estuary (YRE) and its adjacent sea before and after the passage of typhoon HAIKUI. The structure of the estuarine water column and nutrient concentrations changed greatly due to the typhoon, as strong winds and heavy precipitation caused offshore water intrusion into the YRE as well as increased freshwater discharge. Vertical mixing affected the water column within a short period after the typhoon passed over the area. As the wind subsided, the Yangtze Diluted Water (YDW) had a strong effect on the surface water, whereas the offshore water intrusion primarily influenced the bottom water. Nutrient concentrations in the surface layer increased significantly after HAIKUI, whereas complicated trends were detected in the middle and bottom layers. After the typhoon, the concentrations of dissolved inorganic nitrogen, phosphate, and silicate increased by 1.14, 0.08, and 0.31 × 10⁹ mol, respectively, relative to the values before the typhoon. Moreover, we estimate that typhoons have contributed about 118.56, 8.32, and 32.24 × 10⁹ mol of these nutrients to the YRE and its adjacent sea over the past 60 years. The increased nutrient concentrations greatly accelerated the growth of phytoplankton, although the biomass started to decline rapidly in the first few days after the typhoon because of opposing conditions. These results suggest that typhoon HAIKUI had a profound influence on water cycling and biological production in the YRE and its adjacent sea.