细基江蓠和真江蓠野生种群生长海域水质营养盐特征及富营养化评价

Characteristics of nutrients and eutrophication assessment in water quality of Gracilaria tenuistipitata and Gracilaria asiatica growing sea area

【目的】了解江蓠生长海域水质营养盐特征和富营养化变化规律,为海洋牧场建设及富营养化海域人工修复的藻种选择提供科学依据。【方法】以细基江蓠和真江蓠常年生长的广西北海大冠沙乌黎村和下村海域为研究对象,通过周年监测氨态氮(NH_4^+-N)、硝态氮(NO_3^--N)、亚硝态氮(NO_2^--N)、活性磷酸盐(DIP)、化学需氧量(COD)等水质指标,采用单因子污染指数法和富营养化指数评价法,并结合氮磷比(N/P)状况研究细基江蓠和真江蓠野生种群生长海域水质营养盐特征及富营养化水平。【结果】细基江蓠生长海域溶解无机氮(DIN)和DIP含量超过四类海水水质标准的月份比例为67%和83%,COD符合三类和四类海水水质标准的比例为75%;N/P周年波动范围为3.46~18.14,平均值9.05,低于Redfield系数的月份比例为92%,氮限制为营养盐结构的主要特征;富营养化指数(Ei)周年波动范围为5.62~123.25,平均值35.04,呈严重富营养化状态,不同季节的Ei平均值排序为:秋季(54.42)>夏季(41.95)>冬季(32.75)>春季(11.06)。真江蓠生长海域DIN和DIP符合一类或二类海水水质标准,COD符合三类和四类海水水质标准的月份比例为100%,N/P周年波动范围为1.22~85.45,平均值26.24,高于Redfield系数的月份比例为58%,磷限制为营养盐结构的主要特征;Ei周年波动范围为1.82~12.75,呈多种富营养化状态(贫、轻度、中度、重度和严重富营养化),不同季节的Ei平均值排序为:夏季(12.75)>秋季(4.91)>春季(2.13)>冬季(1.82)。【结论】广西北海细基江蓠和真江蓠野生种群主要以DIN和DIP为生长所需的营养盐,可生活在多种富营养化状态的海域中,二者均适宜作为海洋牧场建设及富营养化海域人工修复的藻种,但细基江蓠对富营养化水体的耐受性优于真江蓠。

【Objective】In order to provide reference for Gracilaria sellection for construction of marine ranching and artificial restoration of eutrophic sea area,the present experiment was conducted to investigate the characteristics of nutrients and the level of eutrophication in Gracilaria growing sea area.【Method】G.tenuistipitata and G.asiatica growing in sea area of Wuli Village and Xiacun Village,Daguansha,Beihai,Guangxi were research objectives.Water quality indicatorsincluding ammoniacal nitrogen(NH4+-N),nitrate nitrogen(NO3--N),nitrite nitrogen(NO2--N),labile phosphate(DIP)and chemical oxygen demand(COD)were monitored annually.Single factor pollution index method and eutrophication evaluation method were applied to investigate characteristics of nutrients and the level of eutrophication of water quality for G.tenuistipitata and G.asiatica growing sea area combining nitrogen-phosphorus ratio(N/P).【Result】67%proportion of inorganic nitrogen(DIN)in month basis and83%proportion of DIP in month basis monitoring data exceeded the fourth grade seawater quality in G.tenuistipitata growing sea area,75%proportion of COD monitoring data was in accordance with the third and fourth grade seawater quality.Annual variation of N/P ranged from3.46to18.14,and the mean value was9.05,92%proportion of N/P in month basis were lower than the Redfield value.The main characteristics of nutrients was nitrogen-limited.Eutrophication index(Ei)ranged from11.06to54.42with average of35.04,presented severe eutrophication state.The rank of aveareg Ei for various seasons was:autumn(54.42)>summer(41.95)>winter(32.75)>spring(11.06).In G.asiatica growing sea area,100%proportion of DIN and DIP in month basis monitoring data matched the first and second grade seawater quality,100%proportion of COD in month basis monitoring data was in accordance with the third and fourth grade seawater quality.Annual variation of N/P was1.22-85.45with average of26.24,58%proportion of N/P in month basis was lower than the Redfield value.The main characteristics of nutrients was phosphrouslimited.Annual change of Ei ranged from1.82to12.75,and the eutrophication states were various(poor,mild,moderate,serious and severe).The rank of average Ei for various seasons was:summer(12.75)>autumn(4.91)>spring(2.13)>winter(1.82).【Conclusion】DIN and DIP are the main nutrients for wild G.tenuistipitata and G.asiatica populations growing in Beihai,Guangxi.G.tenuistipitata and G.asiatica can grow in sea water with several eutrophication conditions.They are both suitable speices for construction of marine ranching and artificial restoration of eutrophic sea area,but resistance of G.tenuistipitata to eutrophic water is stronger than G.asiatica.