流溪河底栖硅藻群落结构的时空异质性及其影响因素

底栖硅藻能够较好地响应河流水环境变化，其群落物种组成与分布已被广泛应用于河流水质与生态状况的指示与评估。为了解流溪河底栖硅藻群落结构的时空异质性及其受河流水文与水质的影响，从上游到下游共设置了 20个样点，于2018年3月、6月、9月和12月进行季节采样和观测，采集底栖硅藻，同步测定了水体理化因子；在分析群落组成的基础上，进一步探究河流环境变量和空间变量对流溪河底栖硅藻群落的影响。结果表明，4次调查共检 出底栖硅藻276种，隶属于2纲、6目、9科、55属，底栖硅藻多样性具有明显的时空差异。在季节上，丰水期的物种丰 富度和真辛普森多样性指数高于枯水期。枯水期曲壳藻科的相对丰度超过50%，高于丰水期；而舟形藻科在丰水期 时相对丰度比枯水期高。在空间上，三级河流物种多样性最高，一级河流物种多样最低；一级河流和二级河流的优 势种主要以曲丝藻属的种类为主，三级河流的优势种主要以菱形藻属的种类为主。随着河流等级增加，曲壳藻科相 对丰度降低，而菱形藻科的相对丰度逐渐升高。冗余分析（RDA）表明，环境选择和空间要素对流溪河硅藻群落结构 均有显著影响，但营养盐水平比空间要素有更高的解释率。

Temporal and Spatial Heterogeneity of the Benthic Diatom Community and Influencing Factors in Liuxi River, South China

Benthic diatoms response to change in river environment, and their species composition and spatial distribution have been widely used to indicate and assess river water quality and ecological status. To understand the temporal and spatial heterogeneity of benthic diatoms and their responses to river hydrology and water quality, seasonal sampling and monitoring was conducted in March, June, September and December 2018 at 20 sites from upstream to downstream. Benthic diatoms were collected and physic-chemical factors were measured. Further analysis was conducted to examine the effects of environmental variables and spatial variables on the benthic diatoms in the river. In total, there were 276 species of benthic diatoms from 2 classes, 6 orders, 9 families and 55 genera detected in Liuxihe River. The species diversity of benthic diatoms changes spatially and temporally. Seasonally, richness and True Simpson index was higher in wet season than in dry season. The relative abundance of Achnanthaceae exceed 50 % in dry season, which was higher than that in wet season, but the relative abundance of Naviculaceae in wet season was higher than that in dry season. Spatially, the species diversity peaks in river order III, i.e., the downstream. Most dominant species came from Achnanthidium in river order I and river order II. In river order III, most dominant species were from Nitzschia. Along the river from headwaters to the downstream, the relative abundance of Achnanthaceae decreased, while the relative abundance of Nitzschiacea increased. RDA showed that both environmental variables and spatial variables had significant effects on diatom community in Liuxihe River. But nutrients contributed more than spatial element in explaining the temporal and spatial variation of benthic diatom community in the Liuxihe River.