2018年南黄海浒苔绿潮发展规律及氮组分的作用探究

根据2018年南黄海漂浮态浒苔(Ulva prolifera)绿潮规模卫星监测数据以及春、夏季(4月和7月，绿潮前后)水文环境要素和氮营养盐等数据，对2018年绿潮发展规律及不同氮组分在其中的作用进行分析。结果表明:浒苔于4月25日在江苏南通近海首次发现，随后其向北漂移增殖扩展在6月29日达到最大规模，8月中旬消失。绿潮漂移区域集中在122°E以西近海并呈现两个明显的发展阶段:35°N以南江苏近海绿潮快速增殖阶段和35°N以北山东半岛外海域绿潮聚积衰退阶段。各氮营养盐组分受径流输入、冷水团以及生物活动等因素影响，呈现明显的区域和季节特征。不同绿潮阶段受氮营养盐影响不同，绿潮快速增殖阶段，丰富的氮营养盐(总溶解氮(TDN)>20 μmol/L和溶解无机氮(DIN)>20 μmol/L)是浒苔藻快速繁殖生长的物质基础，此阶段为整个绿潮发展提供了主要的氮支撑且以DIN为主要形态。绿潮聚积衰退阶段，较低的可利用氮(DIN<2 μmol/L和尿素(urea-N)<1.5 μmol/L)不利于浒苔藻持续繁殖生长，此阶段内有机氮(如urea-N)在绿潮后期的氮支撑中起到重要作用。

The development of Ulva prolifera green tide and the roles of nitrogen nutrients in it in the southern Yellow Sea in 2018

Based on the daily satellite monitoring data of floating green tides, and the nitrogen nutrients and hydrological environment parameters were collected in spring (April, before green tides) and summer (July, later stage of green tides) cruises in the southern Yellow Sea (SYS) in 2018, we studied the spatio-temporal variation characteristics of the green tides, and the role of nitrogen nutrients in it. The results showed that the small U. prolifera patches were firstly observed in shallow waters off Nantong, Jiangsu Province on April 25, then floated northward and reached its maximum scale on the June 29, followed by decomposition and disappearance in the coast of Shandong Peninsula in the mid-August. The trajectory area of floating green tides was mainly located in the western of 122°E in the SYS, and showed two distinguishable development phases, the rapid growth phase in the south of 35°N, nearshore area of Jiangsu, and the decline phase in the north of 35°N, offshore area of Shandong Peninsula. The nitrogen nutrient components showed regional and seasonal variations, influenced by the freshwater influx, cold water masses, biological activity and other factors. The effects of nitrogen components were different in different development phases of green tides. The rich nitrogen nutrients from a variety of sources (total dissdved nitrogen (TDN) >20 μmol/L and dissolved inorganic nitrogen (DIN) >20 μmol/L) provided sufficient nitrogen for the development of green tides in the dominated form of DIN, and contributed to the fast reproduction and growth of U. prolifera in the rapid growth phase. While the U. prolifera showed a higher affinity for DON in the decline phase area, the urea-N become main nitrogen source for the development of green tides because of the poor bioavailable nitrogen content (DIN<2 μmol/L and urea-N<1.5 μmol/L) condition, which would limit the continuous growth of U. prolifera.