赣江流域浮游硅藻功能群多样性及其水期演替的驱动特征

为了摸清我国南方丰水型河流流域重要的环境指示类群——浮游硅藻的功能多样性及其环境驱动要素,以赣江流域为例,采用国际上普遍认可的雷氏(Reynolds)、博氏(Borics)和帕氏(Padisák)分类体系进行浮游硅藻类群的系统研究. 结果表明:赣江流域共发现11个浮游硅藻功能类群(包含122种硅藻),并以MP、P、D和L_O类群物种最丰富,全年以MP、P、C和D类群占优势,不同水文期浮游硅藻优势功能类群存在明显分异,表现为丰水期以MP类群占绝对优势,枯水期以C和MP类群占共优势,平水期以则以C类群占绝对优势. 多元逐步回归分析发现,与丰水期占优势的MP、P、C和D类群密度呈显著相关的主要环境因子为纬度、ρ(Hg)、ρ(Zn)、pH和ρ(S2-),与枯水期占优势的C、MP、P和D类群密度呈显著相关的主要环境因子为ρ(Pb)、ρ(Cr6+)、纬度、ρ(BOD₅)、ρ(N)、ρ(P)和ρ(CN-),与平水期占优势的C、P和MP类群密度呈显著相关的主要环境因子为ρ(BOD₅)、ρ(Pb)、ρ(Hg)、ρ(Cd)和ρ(NH₄+-N)等.除趋势对应分析(DCA)和冗余分析结果显示,影响赣江流域浮游硅藻功能多样性的主要环境因子包括流域的经纬度、ρ(FC)(FC为粪大肠杆菌)、重金属含量〔ρ(Cu)、ρ(Pb)和ρ(Cr6+)〕、水位等(解释度达77.0%~90.4%). 研究显示,赣江流域浮游硅藻功能类群多样性及结构呈明显的季节性演替特征,南-中亚热带流域的纬度差异、气温的时空差异以及水位的水期波动、污染物年内排放节律等的共同作用会引起河流流域水体物理和化学生境的改变,这是促使浮游硅藻功能类群不同水期演替的重要原因. 

Functional Group Diversity of Planktonic Diatoms and the Driving Pattern of Water-Period Guild Succession in Ganjiang River Basin

The patterns of the planktonic diatoms community were systematically studied in Ganjiang River Basin (area about 82,0 km2), to find out the diversity of functional groups (FGs) and their environmental driving factors in the wet river. Reynolds, Borics and Padisák′s classification systems were employed to understand the planktonic diatoms of Chinese rivers from a new perspective and different guild scale. The results showed that 122 species of planktonic diatoms were found in the river basin, and taxa were assigned to 11 functional groups based on the classification systems. Most species were attached to codons MP, P, D and L_O, and the dominant FGs were diatom groups with codons MP, P, C and D, and also showed clear temporal differentiation among three different hydrographic periods. Codon MP was absolutely dominant in the high-water period; codons C and MP were co-dominant in the low-water period; and codon C was back to absolute dominance in the normal-water period. The main environmental factors were selected for each FG in the different periods of the Ganjiang River Basin through stepwise multiple regression analysis. In the high-water period, latitude, ρ(Hg), ρ(Zn), pH and ρ(S2-) in the water column were the primary factors significantly affecting the densities of dominant codons MP, P, C and D; ρ(Pb), ρ(Cr6+), latitude, ρ(BOD₅), ρ(N), ρ(P) and ρ(CN-) could significantly affect the densities of dominant codons MP, P, C and D in the low-water period; and BOD₅, ρ(Pb), ρ(Hg), ρ(Cd) and ammonia significantly influenced the densities of dominant codons C, P and MP in the normal-water period. The DCA and RDA analyses were both applied to filter out the main environmental factors (e.g. latitude, longitude, ρ(FC), ρ(Pb), ρ(Cu), ρ(Cd) and water level, explaining 77.0%-90.4% of variability), which affected the composition and diversity of planktonic diatoms' FGs in this river basin. Diversity and composition of FGs of planktonic diatoms both showed clear seasonal successions. Generally, latitudinal differences, spatiotemporal dynamics of temperature and water level, and pollutants discharge regime could induce the changes of physical and chemical stabilities in the aquatic habitats of this south-central subtropical watershed, which was the reason that drives the water-period succession of diatom functional groups.