流溪河底栖硅藻群落结构的时空异质性及其影响因素

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

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月进行底栖硅藻季节性采样,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。

Benthic diatoms respond quickly to changes in the river environment, and species composition and spatial distribution are widely used to indicate and assess river water quality and ecological status.Liuxi River, in northern Guangdong Province, is an important drinking water source and ecological conservation area for Guangzhou City. In this study, we explored the temporal and spatial heterogeneity of benthic diatoms and their responses to river hydrology and water quality. Further analysis was conducted to examine the effects of environmental and spatial variables on the benthic diatom community. The aim was to provide basic data and a reference for monitoring and managing Liuxi River. In March, June, September and December 2018, seasonal sampling of benthic diatoms and water quality monitoring was conducted at 20 sites from upstream to downstream representing three levels of stream order: 10 first-order river sites, 3 second-order river sites and 7 third-order river sites. A total of 276 benthic diatom species were detected during the investigation, including 55 genera, 9 families, 6 orders and 2 classes. Species diversity of benthic diatoms displayed obvious spatial and temporal heterogeneity. Seasonally, the richness and True Simpson indices of benthic diatoms were higher in wet season than in dry season. The relative abundance of Achnanthaceae exceeded 50% in dry season, higher than in wet season, but the relative abundance of Naviculaceae in wet season was higher than in dry season. Spatially, the species richness was the highest at third-order river sites and lowest at first-order river sites. Most dominant species came from Achnanthidium at first-and second-order river sites and from Nitzschia genera at third-order river sites. Along the river from the headwaters to downstream, the relative abundance of Achnanthaceae decreased, while that of Nitzschiacea increased. Redundancy analysis shows that both environmental variables and spatial variables had significant effects on the diatom community, but nutrients contributed more than spatial elements in explaining temporal and spatial variations of benthic diatom community in Liuxi River.