长江口疏浚土掩埋对两种贝类存活的影响

疏浚土处置产生的土丘状浮泥,会掩埋原有底质,底栖生物被掩埋后或死亡,或垂直向迁移重新获得生存机会,而使底栖生物群落得以重建.为评价疏浚土掩埋对底栖生物存活的潜在影响,采用长江口深水航道工程疏浚土模拟掩埋尖紫蛤(Sanguinolaria acuta)、文蛤(Meretrix meretrix),观测两种贝类对不同埋深的反应及其存活情况.结果表明,文蛤和尖紫蛤被掩埋后均表现出垂向迁移行为,文蛤比尖紫蛤表现出了更强的垂向迁移能力,当掩埋深度为8cm时,可100%迁移至疏浚土表层,获得存活机会,而尖紫蛤仅50%左右个体的进出水管伸出疏浚土表层;疏浚土掩埋深度与尖紫蛤死亡率之间有极其显著正相关关系(R2=0.967,P=0.007<0.01),并求得4d-LC50为6.9cm,95%置信区间5.2~8.6cm.试验所设置掩埋深度与文蛤死亡率之间没有表现出显著相关关系,难以通过统计方法获得文蛤的4d-LC50;借鉴毒理学中推定LOEC(最低有影响深度)的方法,推定文蛤的LOED为10cm.研究表明,疏浚土处置后的沉积厚度对底栖动物种群的存亡具有决定性作用,而底栖动物在被掩埋后表现出的垂向迁移能力大小也可影响自身种群及处置区整个底栖动物群落的最终重建几率,并且积极的管理策略对底栖群落重建意义重大.表4图1参22

Burial Effects of the Yangtze River Estuary Dredging Material on Macrobenthos

Dumping process of dredging material can cause floating mud and bury benthos,as the stress of bury is mortal for the benthos.Sanguinolaria acuta and Meretrix meretrix were selected to test the burying effect of the Yangtze River Estuary dredging material.The experiment results showed that the benthos,especially M.meretrix could survive by vertically migrating out of the dredging material surface.When burying depth was 8 cm,100% M.meretrix migrated out of the surface and only 50% S.Acut did.Data analysis proved there was significant correlation between burial depth and mortality of S.acuta(R2 = 0.967,P = 0.007).The 4 d-LC50 for S.acuta was 6.9 cm.Though no significant correlation was found between depth and mortality of M.meretrix,the LOED(Lowest observed effect depth)value could be inferred larger than 10 cm from experiment data.Our study proved that the burial depth was an important factor for the survival of the tested species and their migration capability.A positive strategy should be developed and implemented for the management of dredge material dumping.Tab 4,Fig 1,Ref 22