赤水河流域秋季底栖硅藻群落结构特征及水质评价

为研究赤水河流域底栖硅藻群落特征及水质状况，2019年9月测定了赤水河流域36个代表性样点的水体理化指标，调查了底栖硅藻群落组成，并应用硅藻指数评价了赤水河流域的水质状况。结果表明：秋季赤水河流域上游的电导率和总磷、总氮浓度均高于下游；调查采集到底栖硅藻29属138种，其中扁圆卵形藻多孔变种(Cocconeis placentula var. euglypta)、变异直链藻（Melosira varians）、极细微曲壳藻（Achnanthes minutissima）和谷皮菱形藻（Nitzschia palea）等为秋季赤水河流域优势种；下游底栖硅藻群落稳定性高于中上游；CCA结果显示可溶活性磷（SRP）和总氮（TN）是影响赤水河流域底栖硅藻群落的主要环境因子。TDI和CEE硅藻指数评价结果表明，赤水河流域水质等级整体为“中等”，55.6%的样点水质等级为“中等”以上，8.3%的样点水质等级为“极差”。

Autumn Benthic Diatom Community Structure and Water Quality Assessment in the Chishui River Basin

In this study, we investigated the characteristics of the autumn benthic diatom community in the Chishui River basin, and the diatom indices were then used to evaluate the water quality. In September 2019, the determination of water environmental factors and benthic diatom sampling were carried out at 36 representative sampling sites of the upper, middle and lower Chishui River and its tributaries. Results show that the conductivity at different sampling sites fluctuated greatly in autumn, and conductivity upstream was higher than downstream. The concentrations of total nitrogen (1.56 mg/L) and total phosphorus (0.05 mg/L) in the upstream tributaries (Zhaxi River, Tongche River and Daoliu River) were significantly higher than those in the downstream tributaries (1.23 and 0.02 mg/L). A total of 138 benthic diatom species belonging to 29 genera were identified during study period. The community structure of benthic diatoms in the Chishui River basin showed obvious spatial heterogeneity. Abundances of the dominant species Cocconeis placentula var. euglypta accounted for 18.90% of the total abundance in the upper stream, and the abundance percentage of Melosira variants in the section of Weixin county was above 46.04%. The dominant species in Tongzi River of the middle reaches were Achnanthidium latecephalum and Nitzschia palea, and Achnanthes minutissima was the primary dominant species in the downstream, with an abundance of 9.18%. The Shannon-Wiener diversity and Pielou evenness indices of the benthic diatom community in the lower reaches showed higher stability than in the middle and upper reaches. Canonical correspondence analysis (CCA) showed that the primary environmental factors affecting the benthic diatom community in Chishui River basin were soluble active phosphorus and total nitrogen. The water quality grade of the all sampling sites was evaluated based on the trophic diatom index (TDI) and European Economic Community (CEE) index and the results show that 55.6% of the total sampling sites were above medium, 33.3% of the sampling sites were poor, and 11.1% of the sampling sites were bad. In conclusion, the water quality grade of the Chishui River basin was medium.