长江中游2个湖泊沉积物枝角类微化石密度的垂直变化

Vertical Variation in the Density of Cladoceran Microfossils in the Sediments of Two Lakes Located in the Middle Yangtze River

为了重现湖泊枝角类的群落演替历史,反映人类活动对湖泊生态的干扰强度,选择长江中游的龙感湖和武昌湖分别设置2个和1个采样点,每个样点采集2根沉积柱,鉴定沉积物中的枝角类卵鞍和象鼻溞属壳刺并计数,测定沉积物样品的总氮和总磷含量并鉴定沉积物年代,探究枝角类微化石组成、密度垂直变化及其人类活动的影响。结果显示,在龙感湖和武昌湖沉积物中,分别鉴定出9种和12种枝角类卵鞍。龙感湖沉积物中的枝角类总卵鞍密度(均以干重计)为2.27个/g,高于武昌湖1.63个/g;象鼻溞壳刺的平均密度459.40个/g,显著高于武昌湖1.52个/g。自20世纪60年代以来,武昌湖沉积物中枝角类的优势类群由裸腹溞属、尖额溞属种类向裸腹溞属、盘肠溞属种类转变;50年代以前,龙感湖枝角类卵鞍的优势种群为盘肠溞属种类,之后其优势类群由盘肠溞属、裸腹溞属种类向象鼻溞属种类转变。2个湖泊沉积物中枝角类卵鞍和象鼻溞壳刺密度的垂直变化与湖泊富养化过程及渔业养殖历史一致。研究表明,人类活动的干扰强度影响了长江中下游湖泊沉积物中枝角类微化石的组成和密度变化。

Cladocera microfossils preserved in lake sediments can be used to reconstruct the community succession history of cladocera,and reflect the disturbance intensity of human activities.In this study,the vertical changes of composition and density of cladoceran remains in the sediments of two lakes(Longgan Lake and Wuchang Lake)were studied,and the effects of anthropogenic disturbance on cladoceran composition and density were discussed.In June 2019,sediment samples were collected at two sites(LG1 and LG2)in Longgan Lake and one site(WC)in Wuchang Lake,and two sediment cores were collected at each site and cladoceran ephippium and genus Bosmina spines were counted and identified.The concentrations of total nitrogen and phosphorus in the sediments and the ages of the sediments were determined.Results show that LG1 and LG2 displayed 90 years and 105 years of sediment history in Longgan Lake and WC displayed 58 years of sediment history in Wuchang Lake.There were 9 species of cladoceran ephippium identified in Longgan Lake and 12 species identified in Wuchang Lake.The total density(dry weight)of cladoceran ephippium was 2.27 ind/g in Longgan Lake sediment and 1.63 ind/g in Wuchang Lake and the density of Bosmina spines(459.40 ind/g)was significantly higher than that in Wuchang Lake(1.52 ind/g).Since the 1960s,the dominant cladocerans have changed from Moina spp.and Alona sp.to Moina spp.and Chydorus sp.in the sediments of Wuchang Lake.In Longgan Lake,the dominant cladoceran was Chydorus sp.and Moina spp.before 1950 but Bosmina sp.after 1950.The changes in vertical density of cladoceran ephippium and Bosmina spines in two lakes were consistent with the process of eutrophication and the history of fish aquaculture.Our results indicate that the anthropogenic interference intensity influenced the composition and density of cladoceran microfossils in lake sediments located in the middle and lower reaches of the Yangtze River.