流溪河大型底栖动物群落的时空分布及其影响因子

流溪河位于我国热带与亚热带过渡区，其底栖动物种类丰富，群落的物种组成结构具有明显的区域性，掌握该地区的物种组成特征及与环境要素的关系是建立生态监测与评估方法的基础。于2018年的枯水期（3月、12月）和丰水期（6月、9月），自流溪河上游至下游共计20个段面对底栖动物进行了定量采样，同时测定了相应的环境因子，采用多元统计方法对流溪河水环境与群落结构及其相关关系进行了分析。共检出底栖动物76个分类单元，隶属于7纲20目50科，其中水生昆虫相对丰度最高，占69.39%。在4个优势分类单元中，摇蚊族（Chironomini）相对丰度为20.19%，河蚬（Corbicula fluminea）、短沟蜷属的一种（Semisulcospira sp.1）、双突细蜉（Caenis bicornis），相对丰度在7%-9%之间。底栖动物丰度和种类多样性均与浊度呈显著负相关；枯水期底栖动物丰度与总磷呈显著负相关，丰水期则呈显著正相关。在丰水期，不同河流级别上底栖动物群落具有明显的差异，表现较强的分布格局，而在枯水期这种分布格局不明显。典范对应分析（CCA）表明，在丰水期，影响或解释流溪河底栖动物群落变化的主要因子为pH、溶解氧、水温、电导率和硅酸盐，而在枯水期则为pH和硝态氮。受电站与采沙的影响，部分河段发生非自然断流和底质的显著改变，导致底质与水深等数据的异常变化，反映了人类活动对该河流生境与环境的重要影响。

Temporal and spatial distributions of macroinvertebrates and their influencing environmental factors

Liuxihe River, located in the transitional zone between the tropics and subtropics in southern China, is rich in macroinvertebrates that are characterized by species from both tropical and subtropical regions. Knowledge of the species richness and community structure provides useful information for rationalizing river ecological monitoring and assessment in this transitional zone. To explore species composition and the spatial distribution of macroinvertebrates and their relationships with environmental factors in the Liuxihe River, we sampled the macroinvertebrates and measured the environmental variables during the dry (March and December) and wet (June and September) seasons in 2018 at 20 upstream and downstream sites. We used multiple regression and multivariate ordination methods to analyze the relationships between environmental factors and macroinvertebrate communities. In total, we found 76 taxa (belonging to seven classes, 20 orders, and 50 families), among which the aquatic insects had the highest abundance, accounting for 69.39% of the total abundance. Chironomini was dominant with a relative abundance of 20.19%, followed by Corbicula fluminea, Semisulcospira sp. 1, and Caenis bicornis with relative abundances between 7% and 9%. The total abundance and species richness of macroinvertebrates negatively correlated with turbidity and total phosphorus during the dry season but positively correlated during the wet season. During the wet season, the macroinvertebrate communities in the three river classes significantly differed from each other, but not during the dry season. Canonical correspondence analysis (CCA) showed that water temperature, silicate, salinity, dissolved oxygen, turbidity, pH, and conductivity were the main environmental variables explaining the variation in the macroinvertebrate community in the Liuxihe River. However, habitat factors such as water depth and substrate character showed an unusual variation, which indicated that the river has been largely modified by human activity and further attention is required for ecosystem management in the watershed.