Eutrophication of Jiangsu Coastal Water and Its Role in the Formation of Green Tide

Since 2007, the large-scale green tide caused by Ulva prolifera (U. prolifera) have occurred as a recurrent phenomenon in the southern Yellow Sea of China. Field surveys and satellite remote sensing showed that the small scattered patches of green tide algae were first observed along the Porphyra agriculture area of the Subei Shoal in late April. In this study, we attempted to identify the role of eutrophication in the origin of the green tide in the Subei Shoal and its adjacent area. Subei Shoal and its adjacent area are characterized by rich nutrients, especially NO₃⁻-N, NH₄⁺-N, PO₄³⁻-P, and other bioavailable components (such as urea-N and amino acids). In the spring of 2017, the average concentrations of NO₃⁻-N were 19.01 ± 11.01 µmol L⁻¹, accounting for 86.68% of the dissolved inorganic nitrogen (DIN). In addition, the average concentration of NH₄⁺-N was 2.51 ± 1.60 µmol L⁻¹. PO₄³⁻−P had an average concentration of 0.14±0.13 µmol L⁻¹. The average concentrations of urea-N and total hydrolyzed amino acids (THAA) were 1.73 ± 1.36 µmol L⁻¹ and 1.33±0.80 µmol L⁻¹, respectively. Rich nutritive substances play a key role in the rapid production of U. prolifera and make the Jiangsu coastal water an incubator for green tide.