沱江浮游生物群落时空分布及相关环境因子分析

SPATIO-TEMPORAL DISTRIBUTION OF PLANKTON AND DRIVING ENVIRONMENTAL FACTORS IN THE TUOJIANG RIVER

为研究沱江浮游生物群落结构的时空特征，并探讨影响其形成的环境因子，于2013年对沱江10个采样断面按季节进行采样分析。研究期间共检出浮游甲壳动物13种，以中小型枝角类和剑水蚤为主；尽管桡足类密度与枝角类接近，但由于体型原因桡足类生物量始终占据优势地位。检出浮游植物7门95种，优势属7个，全年均以硅藻为主。两类生物在上游资阳市区的断面中总生物量最高，中游农村断面最低：其生物量季节变化也趋于一致，均在丰水季节8月取得最高值，枯水季节2月最低。与历史数据相比，呈现出浮游植物增多，浮游甲壳动物减少的趋势。根据结构方程模型（SEM）和冗余分析（RDA）的结果，浮游甲壳动物生物量在浮游植物生物量和溶氧高的环境中较大，桡足类对溶氧的要求比中小型枝角类高。浮游植物对高温、高营养和高pH较偏好，尤其是一些优势属。尽管受浮游植物生物量影响，浮游动物对浮游植物的控制力却极弱。在流速缓慢且污染较严重的城市江段浮游植物密度已高达2．7×10 7cells／L，浮游动物尽管能选择性地以部分浮游植物为食，对其控制力却极弱，如不加强污染控制，沱江可能有暴发水华的危险。

To investigate the spatio-temporal pattern of plankton in the Tuojiang River and explore the relevant environmental factors regulating it, we conducted seasonal surveys and collected samples from 10 cross sections along the Tuojiang River in 2013. We identified 13 crustacean zooplankton species mostly composed of small-sized cladocerans and cyclopoida. Although there was no significant difference between the densities of the two zooplankton groups, copedoda dominated the total biomass of the whole zooplankton community because of a larger body size than cladocera. A total of 95 species of phytoplankton were recorded, and 7 genera dominated the total biomass of the phytoplankton community. Both zooplankton and phytoplankton were abundant in the upstream Tuojiang River crossing the urban area of Ziyang City but scarce in the lower reaches flowing through rural areas. These two plankton groups had a similar seasonal pattern in total biomass that peaked in the wet season （August） and reached its lowest level in the dry season （February）. Compared with the previous studies in 1980s, there were a decline in crustacean zooplankton rich- ness and an increase in phytoplankton abundance. Phytoplankton density was up to 2.7× 10 7 cells/L dominated by dia- tom all the year round. Results from Structure Equation Modeling （SEM） and Redundancy Analysis （RDA） indicate that crustacean zooplankton was enriched in habitats with high phytoplankton production and dissolved oxygen, and that copepoda had a higher requirement for oxygen than cladocera. Phytoplankton, especially some dominant taxa, preferred to live in an environment with high temperature, nutrient concentration and pH. Phytoplankton population was at its highest level （2.7× 10 7 cells/L） in urban sections with slow flow and high contamination, and was weakly restrained by zooplankton grazers despite their selective predation. Our study suggests substantial risks of algae blooms in Tuojiang River posed by high pollutants and therefore appeals efforts to reduce pollution in this river.