Temporal and spatial distribution of phytoplankton with emphasis on Skeletonema costatum in the Mathamuhuri river – estuary (Chakaria mangrove ecosystem), Bangladesh

A total of 91 species under 44 genera were identified among the phytoplankton community during the course of one year's investigation between May 1982 and April 1983. Bacillariophyta was the most dominant group with 72 specie, Chlorophyta 11 spp, Cyanophyta 6 spp and Pyrrophyta was represented by 2 species. The yearly percentage composition of 4 groups of phytoplankton in order of abundance were Bacillariophyta 50.77%, Cyanophyta 47.70%, Chlorophyta 1.5% and Pyrrophyta 0.02%. The highest densities of phytoplankton were recorded in monsoon months (June-July) with a peak in July (31550 cells/l) and the minimum in February (770 cells/1). Higher concentration of phytoplankton was recorded at station 2, nearer to the Chakaria Sundarbans (mangroves), but abundance of phytoplankton showed no significant difference in the two stations (Mann Whitney U test, P=0.64, Z=-0.642, U=64). Phytoplankton population in this area were positively correlated with rainfall (r=0.655, P=<0.5, df.22) and water temperature (r=0.523, P=<0.05). Skeletonema costatum was the dominant member of phytoplankton and occupied 35.23% of the annual population and occurred throughout the period of study except in September and January. Its abundance was recorded during the monsoon months (April- July) with a maximum density (24185 cells/l) in July. No significant correlation was found between abundance of S. costatum and the hydro-meteorological parameters recorded in the Chakaria mangrove area.

葛洲坝截流24年来中华鲟产卵群体结构的变化

以1981～2004年间捕获的中华鲟(AcipensersinensisGray)亲鲟样本为研究材料,研究葛洲坝截流24年来中华鲟繁殖季节中坝下30km范围内产卵群体结构的变化情况。测定与统计结果显示,中华鲟雌雄性比由1981～1983年的1.10∶1降低到1987～1989年的0.63∶1,而后上升到2003～2004年的5.86∶1。雌鲟平均体长由1990～1992年的263.1cm增加到1999～2001年的276.7cm,升幅为5.2%(差异极显著);平均体重由1990～1992年的202.4kg

Changes in the Phytoplankton community of Lake Donghu since the 1980s

The phytoplankton of Lake Donghu was compared between two periods (i.e., 1982-83 and 1999-2001). During 1982-1983, Lake Donghu was characterized by cyanobacterial blooms, very high summer phytoplankton biomass, and a spring clear-water phase. However, during 1999-2001, the lake was dominated by dinophytes and diatoms and had a relatively low phytoplankton biomass and a very turbid state.. Increased stocking of silver carp and bighead carp during the interim years eliminated cyanobacterial blooms and large-bodied daphnids from the lake, creating favorable conditions for growth of the small-sized algae.

黄土高原子午岭林区6个典型群落优势种的热值和养分特征

能量流动、物质循环和信息传递共同构成了生态系统三大功能。能量是维持生态系统功能与过程的动力,Jordan(1971)认为能量比干物质更能反映出群落对自然资源(特别是太阳能)的利用情况。Long(1934)率先用热值来表示植物所含能量的多少,此后关于植物热值的研究工作逐渐展开。我国的植物热值研究始于20世纪80年代(杨福囤等,1983;祖元刚等,1986),主要集中在海南(林益明等,2000)、福建(林益明等,2004)、广东(任海等,1999)和浙江(郝朝运等,2006)等热带亚热带植物群落以及内蒙古羊草草原(鲍雅静等,2003),但有关黄土高原地区的植被热值研究尚未见报道。子午岭林区是黄土高原主要的天然次生林区,其植被主要是在弃耕地基础上逐渐恢复起来的(邹厚远等,2002)。由于自然因素与人为因素的影响,子午岭的植被在恢复时间上存在较大差异,形成了处于不同演替阶段的各种植被群落类型。本研究选取的6个代表性植被群落分别是沙棘(Hippophae rhamnoides)群落、山杨(Populus davidiana)群落、白桦(Betula platyphylla)群落、油松(Pinus tabulaeform...