桑沟湾春季叶绿素a浓度分布及其影响因素

Distribution of chlorophyll-a concentration and its control factors in spring in Sungo Bay

依据2014年5月走航和定点连续调查资料,分析了桑沟湾叶绿素a的空间分布及昼日变化特征,结合理、化环境因素的相关性分析,探讨影响叶绿素a浓度的主要因素。(1)走航调查的结果显示,桑沟湾春季叶绿素a浓度较低,叶绿素a浓度范围为0.11—1.40μg/L,平均为(0.64±0.36)μg/L。叶绿素a浓度从湾内向湾外逐步降低,贝类区>混养区>海带区>外海区;湾内表层叶绿素a浓度均高于底层,而湾外的非养殖区则相反(2)网箱区叶绿素a浓度最高,日平均为1.70μg/L,显著高于其它3个区;海草区最低,为0.57μg/L,与海带养殖区无显著性差异,显著低于贝类养殖区和网箱区。叶绿素a浓度的总体趋势为:网箱区>贝类区>海带区和海草区。而且,不同养殖区域,叶绿素a浓度昼夜变化规律各不相同,反映了养殖活动的影响。海草区白天表层高于底层,而夜间则相反;网箱区底层均高于表层;贝类区表层均高于底层;海带区表底层叶绿素a浓度呈现出升降交替的规律。(3)叶绿素a浓度与硅酸盐、水温显著正相关,与其他环境因子,如氨氮、亚硝酸盐、磷酸盐等无显著相关性。硅酸盐和温度可能为影响桑沟湾春季浮游植物生长的主要限制性因素。(4)桑沟湾春季浮游植物生长受多重因素的限制,湾内营养盐浓度与叶绿素a浓度并未呈现显著的规律性,营养盐的上行控制和贝类摄食的下行控制均能影响浮游植物的生长。

Chlorophyll concentration is an important indicator for assimilation capacity for photosynthesis. For shellfish farming characterizing phytoplankton biomass and organic carbon , chlorophyll concentration can reflect food quantity and quality, and it is also the key factor for the growth of shellfish and control of the maricultural carrying capacity. To understand chlorophyll concentration and spatial distribution in maricuhural regions, we need to evaluate the environmental quality and establish a healthy farming mode. Two sampling transects for chlorophyll-a between the inner bay and the mouth of the bay were used, and 4 sampling stations in 4 different maricultural areas were sampled once every 2 h during the day in May 2014 in Sungo Bay. Spatial and diurnal variation characteristics of chlorophyll, as well as the control factors, were analyzed. The results showed that： （1） For the voyage survey, chlorophyll was in the range of 0.11-1.40μg/L, and the average value was （0.64 ± 0.36）μg/L. The general trend of chlorophyll concentration was higher in the inner rather thanthe outer site of the bay： shellfish maricuhural area 〉 polycuhural area 〉 kelp maricultural area 〉 outer site of the bay. Chlorophyll-a concentration was higher in the surface water layer than in the bottom layer in the inner bay, but the reverse trend was observed in the outer bay. （2） The highest chlorophyll concentration was observed in the cage area, with an average value of 1.70μg/L, and the lowest concentration was observed in the sea grass area （cage area 〉 shellfish area 〉 kelp area 〉 sea grass area）. In different farming areas, diurnal variation in chlorophyll a concentration was different, which shows that farming activities may affect chlorophyll concentration. Chlorophyll-a concentration was higher in the surface water layer than in the bottom layer in the sea grass area during the day, but it was the reverse at night. In the cage area, chlorophyll-a concentration was higher in the bottom layer than in the surface layer, regardless of the time; a reverse trend was observed in the shellfish area. However, diurnal variation was complete in the kelp area. （3） There was a significantly positive correlation between chlorophyll-a concentration and temperature or silicate concentration. The linear equation between chlorophyll-a concentration （C1 ） in the surface layer and silicate concentration （Sl ） or temperature （T） in the lane was as follows ： C1 = 0.8222 S1-0.6965 （ n = 15, P = 0.0001, R2 = 0.6945 ）, C1 = 0.1468T- 1.4189 （ n = 15, P = 0.0009, R2= 0.6462）. However, there was no significant correlation with other environmental factors, including ammonia, nitrite, and phosphate. Silicate concentration and temperature may be the main control factors for phytoplankton growth in spring in Sungo Bay. （4） The growth of phytoplankton was limited by multiple factors in Sungo Bay in spring, and there was no significant correlation between chlorophyll-a concentration and nutrient concentrations in the inner bay. Thus, bottom -up forces of nutrients and top-down forces of shellfish feeding can affect the growth of phytoplankton