一次陆源降雨污水引起血红哈卡藻赤潮的成因

以2007年烟台四十里湾海域血红哈卡藻(Akashiwo sanguinea Hirasaka)赤潮为对象,研究赤潮消长与水环境因子的关系。研究发现大量陆源降雨污水输入后,海水盐度急剧下降、营养盐大幅增加,特别是活性磷酸盐浓度明显增加,促进了血红哈卡藻的生长繁殖并最终形成赤潮。赤潮发生前海区第一优势种为尖刺拟菱形藻(Pseudo-nitzschia pungens Halse),优势度0.47(0.42—0.52),多样性指数2.63(2.43—2.89);赤潮发生时血红哈卡藻密度范围1.05×105—4.10×106个/L,优势度0.92(0.83—0.99),多样性指数0.27(0.15—0.64);赤潮消退后中肋骨条藻(Skeletonema costatum Cleve)为第一优势种,优势度0.49(0.43—0.55),多样性指数2.46(2.19—2.84)。赤潮的发生、发展、消亡与化学需氧量(COD)、无机氮(DIN)、活性磷酸盐(DIP)、富营养化指数(E)呈显著正相关(P<0.05),与盐度呈显著负相关(P<0.01)。赤潮前、后该海域为贫营养、P限制、叶绿素a含量中等,赤潮期间该海域为富营养、P限制、叶绿素a含量高。通过影响力评定,活性磷酸盐、COD、盐度是此次赤潮发生的主要诱发因子,当活性磷酸盐含量低于0.3μmol/L时,硅藻逐渐取代甲藻,此次赤潮消散。

Occurrence characteristics of akashiwo sanguinea bloom caused by land source rainwater

Based on a bloom of Akashiwo sanguinea Hirasaka in Sishili Bay,Yantai in 2007,the relationship between the harmful algal bloom and environment parameters is discussed in this paper.During the red tide,surface seawater(0—0.5m deep) samples and bottom seawater(0.5 m to the sediment) samples were collected.Water samples for the phytoplankton study were treated with 4% neutral buffered formalin to fix the phytoplankton,and then concentrated,enumerated and identified with an inverted microscope(Olympus BX51,Japan) at 100—400 magnification.The temperature was measured in situ by a temperature meter(SWL1-1).The salinity of the water samples was determined with a salinity meter(SYC2-2).DO was analyzed by the iodometric method.COD was determined by the KMnO4 method.Nitrate nitrogen,ammonium nitrogen and nitrite nitrogen were measured using the cadmium-copper reduction method,the indophenol blue methods,and the Griess-Ilosvay method,respectively.DIP and DRSi was measured with the phosphomolybdenum and silicomolybdenum blue method,respectively.Chl-a was determined by UV-VIS spectrophotometry(UV-2102).Dissolved inorganic nitrogen(DIN) was calculated as the sum of ammonium nitrogen,nitrite nitrogen and nitrate nitrogen.One-way ANOVA analysis,Duncan′s comparison and Pearson correlation analysis were completed using by SPSS 17.The results showed that because of the rainfall,the salinity declined,while the nutrients,especially inorganic phosphate,increased,and therefore the red tide of A.sanguinea occurred.Before the red tide,the dominant species was Pseudo-nitzschia pungens Grunow,with a dominance index of 0.47(0.42—0.52) and a diversity index of 2.63(2.43—2.89).During the red tide,the density of A.sanguinea ranged from 1.05×105 to 4.10×106 cells/L;its dominance index was 0.92(0.83—0.99),and its diversity index was 0.27(0.15—0.64).After the red tide,Skeletonema costatum Cleve was the dominant species;its dominance index was 0.49(0.43—0.55) and its diversity index was 2.46(2.19—2.84).The occurrence of the red tide was positively correlated with COD,inorganic nitrogen,inorganic phosphate,eutrophication index(E)(P<0.05).but it was negatively correlated with salinity(P<0.01).Before and after the red tide,the seawater was oligotrophic and phosphorus-limited,and the chl-a concentration was low;but during the red tide,the seawater was eutrophic and phosphorus-limited,and chl-a concentration was high.Based on the assessment of the impact,inorganic phosphate,COD and salinity were the major inducing factors.Diatoms replaced dinoflagellates when the concentration of inorganic phosphate was less than 0.3 μmol/L.