春季海南岛近岸海域尿素与浮游生物的脲酶活性

Abstract

2011年春季(4-5月),对海南岛的海口湾、澄迈湾、文昌八门湾、陵水新村湾和大东海5个海湾的尿素浓度及浮游生物的脲酶活性开展调查研究,结合其它理化环境因子,分析海南岛近岸海域尿素的可利用性及其对该海区浮游植物生长可能产生的影响。结果表明,海南岛近岸水体中尿素平均浓度为2.07-3.30 μmol/L,占总溶解态氮TDN含量的14%-38%,尿素占TDN比例由北向东、南方向递增。浮游生物脲酶活性为0.30-0.84 μmolN·L^-1·h^-1,海口湾最高,从北部向东、南部逐渐减少。各海湾较高水平的尿素和脲酶活性主要分布在排污口、养殖区或旅游区的近岸海域。 硅藻为优势种,甲藻种类少且密度低,部分甲藻密度达到10⁴-10⁵个/L的水体,尿素和脲酶活性也处于较高水平。海区浮游植物细胞密度与脲酶活性或尿素占TDN比例等因子存在相关性,表明尿素是海南海域浮游植物生长不可忽略的重要氮源。尿素在一定程度上促进春季海南岛近岸海域甲藻等浮游植物的生长,可能对浮游植物群落结构的改变产生重要影响。;Field cruises were carried out in the coastal waters of Hainan Island to survey urea concentrations and urease activities together with other environmental parameters. The bioavailability of urea for phytoplankton growth was analyzed based on these results. Results showed that the average concentrations of urea varied from 2.07 to 3.30 μmol/L, which accounted for 14%-38% of total dissolved nitrogen (TDN) and showed the trend to increase from the north to the south and the east. The urease activities of plankton were between 0.30-0.84 μmol N·L^-1·h^-1 with the maximum in the Haikou Bay. Most of the high values of urea concentrations and urease activities were detected in the nearshore waters where sewage draining exit, aquaculture area and the tourist area located. Diatoms were the dominant species in the phytoplankton communities. However, in some stations with dinoflagellates densities as high as 10⁴-10⁵ cells/L, the urea concentrations and the urease activities were also higher comparing with other sites. The phytoplankton biomass correlated well with the urease activities or urea/TDN atomic ratios which suggested the significance of urea as one nitrogen source in the coastal waters of Hainan Island. Urea and NH₄⁺ concentrations were the most important factors responsible for the distribution of dinoflagellates in the northern and the southern waters respectively. The terrestrial input of urea promoted the growth of phytoplankton, in particularly dinoflagellates, therefore urea might play an role in the competition and succession in the phytoplankton community in the coastal waters of Hainan Island during the spring period.