珠江口磨刀门轮虫群落结构特征与水质生态学评价

Community structure of rotifers and ecological assessment of water quality in Modaomen of the Pearl River Estuary

轮虫是浮游动物群落中的重要组成部分,对水质变化反应敏感,调查轮虫群落的种类组成和丰度变化,可以获知水质变化和水体的营养状况,并可作为水质评价依据。于2009年7月至2010年1月,对珠江口磨刀门3个站点（S1滞水区、S2河道和S3水流交汇区）轮虫群落结构特征进行每月两次的调查,同时测定了水温、盐度、透明度、叶绿素、总氮、总磷等理化指标,利用非生物环境因子对水体的营养状况进行了TLIc加权综合营养状态指数评价,并通过轮虫种类组成、E/O指数、QB/T指数和生物多样性指数对水质进行了生态学评价。调查期间,水温12~29℃,盐度0.11~7.9 PSU,叶绿素a浓度0.89-9.56μg·L-1,叶绿素a与水温呈显著正相关（p〈0.0001）,与盐度呈显著负相关（p〈0.01）。磨刀门水域3个采样站点TLIc处于50~60之间,表明其水质均达到轻度富营养水平,富营养程度按S1、S2、S3依次递减。调查期间,共记录轮虫56种,S1站点轮虫种类最多,其中污染指示轮虫42种。污染指示种占轮虫总数比例表明,珠江口磨刀门达到了富营养化水平,与利用非生物环境因子作出综合营养状态指数TLIc的评价结果一致。磨刀门的优势种为广布多肢轮虫（Polyarthra vulgaris）、螺形龟甲轮虫（Keratella cochlearis）、热带龟甲轮虫（Keratella tropica）和暗小异尾轮虫（Trichocerca pusilla）。调查期间,轮虫丰度在S1、S2、S3变化范围分别为0~199 ind·L-1、1~54 ind·L-1和0~48 ind·L-1,平均丰度分别为31±54 ind·L-1、13±15 ind·L-1和11±13 ind·L-1。丰水期的8月下旬轮虫丰度达到最大值;枯水期丰度均较低。轮虫丰度与水温、总氮、叶绿素显著正相关（p〈0.05）,与盐度显著负相关（p〈0.05）。磨刀门河口理化因子变化剧烈,轮虫多样性指数波动范围较大,反映出河口水域轮虫群落结构的不稳定性。冗余分析（RDA）表明水温、盐度和叶绿素是影响轮虫群落结构季节变化的主要因子。根据水质生态学评价指标,磨刀门水体已达轻度富营养水平,与非生物环境因子营养状态综合评价结果一致。本研究表明,评价一个水体的污染程度,应将生态学指标与理化指标结合起来综合评价,可获得更为真实的评价结果。

Rotifers are a key part of the zooplankton community and react to changes in water quality. Rotifer abundance and species composition reflect the conditions and nutritional status of bodies of water, and, therefore, form a basis for the evaluation of water quality. Rotifer community structure was investigated at three different sites in the Pearl River Estuary： S1, a stagnant water district; S2, the center of the river; and S3, the confluence of rivers at the Modaomen outlet. Samples were obtained twice monthly from July 2009 to January 2010. Water temperature, salinity, transparency, chlorophylla （chla）, total nitrogen （TN）, total phosphorus （TP） and other physicochemical factors were measured simultaneously. The comprehensive trophic state index, TLIc, was evaluated using abiotic environmental factors. Also ecological assessment of water quality was carried out through not only rotifer species composition but also by theE/O,QB/T and biodiversity indices. During the survey period, water temperature ranged from 12~29℃and salinity ranged from 0.11~7.9 PSU. The concentration of Chla, which ranged from 0.89~9.56μg·L-1, was positively correlated with water temperature （p〈0.0001） and negatively correlated with salinity （p〈0.01）. The TLIc at the three sites ranged from 50-60, which suggested that water quality reached mild eutrophication. The degree of eutrophication descended in order from S1 to S2 and S3. During the survey period, 56 species of rotifer were recorded, of which 42 were pollution indicators. Rotifer species were highest at S1. The proportion of pollution indicator rotifer species of the total showed that the water in the Modaomen Estuary reached the eutrophication level, consistent with TLIc.Polyarthra vulgaris,Keratella cochlearis,K. tropica andTrichocerca pusilla were the dominant species. The rotifer abundances at S1, S2 and S3 ranged from 0~199 ind·L-1,1~54 ind·L-1and 0~48 ind·L-1, respectively, with mean abundances of 31 ± 54 ind·L-1, 13 ± 15 ind·L-1 and 11 ± 13 ind·L-1. The highest abundance was recorded at S1 in the late August; the abundances in the dry season were lower. Rotifer abundances were positively correlated with water temperature, TN, and Chla.（p〈0.05）. A significant negative correlation was detected between salinity and rotifer abundance （p〈0.05）. The physicochemical factors in the Modaomen outlet of the estuary changed dramatically and the diversity index of rotifers fluctuated widely, which indicated that the community structure of rotifers was unstable. Redundancy analysis showed that water temperature, salinity and Chla. were the most important factors influencing the seasonal variations of rotifer community structure. The ecological assessment of water quality indicated that the Modaomen outlet of the estuary had reached a level of mild eutrophication, in accordance with the comprehensive evaluation of trophic state based on abiotic environmental factors. The results show that a comprehensive evaluation combining ecological indicators and physical-chemical indicators is the most realistic way to assess water pollution.