河流生态系统是人类和其它生物赖以生存的自然生态系统。目前，世界上大多数河流生态系统正遭受着气候变化和人类活动的双重威胁。浮游植物作为河流生态系统中重要的组成部分，其群落组成、细胞密度和多样性等特征与环境因子关系密切。滦河流域是中国北方典型的温带流域，是“引滦入津”工程的水源地。本论文在夏季、秋季和春季于滦河流域对浮游植物、环境因子等数据进行调查采样，分析浮游植物群落的空间分布和季节变化特征及其与环境因子的关系，明确显著影响浮游植物群落特征的环境因子，揭示不同类型环境因子对浮游植物群落特征的相对重要性和交互作用。在此基础上，确定浮游植物群落特征指标对水环境状况的指示性，为滦河流域水生态管理提供数据基础和科学支撑。

基于滦河流域中上游夏季、秋季和春季121个采样点中水环境因子数据和不同支流内社会经济、化肥施用量、土地利用数据，揭示了水环境因子时空变化特征及其与社会经济、化肥施用量、土地利用的关系。结果显示：1）五日生化需氧量、高锰酸盐指数、氨氮、硝酸盐氮、总氮、总磷和总悬浮性固体对水环境因子空间差异的贡献率大于水温、pH和叶绿素a。2）基于不同的水质因子，水质状况在不同季节和支流内的变化特征存在差异性。3）土地利用、化肥施用量和社会经济因子中只有磷肥、林地百分比和草地百分比对各支流内水环境因子影响显著（p < 0.05），解释率在夏季（83.2%）>秋季（71.6%）>春季（67.8%）。林地百分比与氮营养盐关系密切；草地百分比和磷肥施用量与水体中磷营养盐、有机物和总悬浮性固体关系密切。4）在夏季，各采样点水质综合指数与农业用地和建设用地百分比显著负相关；在秋季和春季，水质综合指数与林地和建设用地百分比显著负相关，与草地百分比显著正相关。这些结果表明河流水环境状况的空间差异主要体现在营养盐和有机物。不同水质因子的指示性和污染来源决定其时空变化特征。水环境因子的季节差异可能是受河流水文因素和农业活动强度共同影响；空间差异与人类活动（化肥施用量、农业用地、建设用地）密切相关。此外，自然用地（林地和草地）的保护对水质改善也至关重要。

基于不同季节各支流和干流中浮游植物群落组成和细胞密度数据，揭示了浮游植物群落的时空变化特征。结果显示：1）在夏季、秋季和春季分别鉴定出浮游植物6门62属、7门61属和6门44属。硅藻门和绿藻门中属类数量占比之和约为80%。浮游植物群落属类数量在干流和伊逊河中多于所有支流。2）浮游植物群落细胞密度在夏季（251.8×10⁴ cells/L）显著高于秋季（153.7×10⁴ cells/L）和春季（139.5×10⁴ cells/L）。各门类中，硅藻门细胞密度最大，其次是蓝藻门和绿藻门。浮游植物群落细胞密度在瀑河和伊逊河中显著高于其它支流。3）优势属组成中，隐藻门的类群只出现在秋季，绿藻门的类群只出现在夏季和秋季。这些结果表明浮游植物群落的组成和细胞密度存在季节差异和空间差异。季节差异性可能是受温度和水文因素共同影响。浮游植物群落中属类数量受河流中生境多样性的影响，细胞密度与人类活动强度密切相关。

基于不同季节全部采样点中浮游植物属类细胞密度、河流理化因子、营养盐和有机物数据，分析了浮游植物属类细胞密度与环境因子的关系。结果显示：1）环境因子对浮游植物群落总细胞密度的影响高于属类数量，影响因子主要为高锰酸盐指数、总磷、河宽和水温。2）河流理化因子对浮游植物属类细胞密度的影响大于营养盐和有机物；两者对浮游植物属类细胞密度的影响存在交互作用。3）以河流理化因子为控制变量，营养盐和有机物对浮游植物属类细胞密度的解释率在夏季增加，在秋季和春季降低。4）蓝藻门、绿藻门、裸藻门、甲藻门和隐藻门中属类细胞密度与河宽、氨氮、总磷、高锰酸盐指数正相关，与流速负相关。硅藻门中属类细胞密度与流速正相关，与氨氮、总磷、高锰酸盐指数负相关。这些结果表明河流理化因子与营养盐和有机物均对浮游植物属类细胞密度具有重要作用，相比而言，浮游植物群落生存的河流理化条件比其生长繁殖所需的物质基础（营养盐和有机物）更为重要。河流理化因子可以调节营养盐和有机物对浮游植物属类细胞密度的影响。以河流理化因子为控制变量，营养盐和有机物对浮游植物属类细胞密度的影响在最适生长繁殖的季节（夏季）增强，在其它季节减弱。浮游植物类群既可指示污染、富营养或污染物滞留时间较长的水体；也可指示受干扰程度较低或物质交换能力较强的水体。

基于浮游植物生物完整性指数、硅藻营养指数、Shannon-Wiener多样性指数、Margalef丰富度指数和Pielous均匀度指数评价了滦河流域中上游河流水环境状况，分析了这些指数与具有地表水环境质量标准的水质因子（溶解氧、五日生化需氧量、高锰酸盐指数、氨氮、总氮、总磷和水质综合指数）的关系。结果显示：1）基于浮游植物生物完整性指数，滦河流域中上游水环境整体状况为“良”；基于硅藻营养指数，为“中营养”；基于Shannon-Wiener多样性指数、Margalef丰富度指数和Pielous均匀度指数，均为“无污染”。2）浮游植物生物完整性指数和硅藻营养指数在人类活动干扰剧烈的区域或特定水体中（城市河流和干流）表现出明确的指示性，评价结果具有较高的区分度。浮游植物群落多样性指数对水环境状况的指示性较差，评价结果区分度较低。3）浮游植物生物完整性指数和硅藻营养指数只与高锰酸盐指数、水质综合指数、河宽和流速显著相关（p < 0.05），与其它单一水质因子的关系不显著（p > 0.05）。这些结果表明浮游植物生物完整性指数和硅藻营养指数对滦河流域中上游水环境状况具有较好的指示意义，且与水质综合状况和河流形态特征关系密切，是水体中多种影响因素的综合作用结果。

River ecosystems are natural ecosystems that humans and other livings depend on. Currently, most river ecosystems worldwide are suffering from both climate change and human activities. As an important part of river ecosystem, phytoplankton community are closely related to environmental factors. The Luanhe River Basin is a typical temperate basin in northern China. It is also the water source of the “the water diversion project from the Luanhe River to Tianjin city”. Based on the data of phytoplankton community, water quality factors, and spatial information in different seasons in the Luanhe River. The spatial distribution and seasonal variation of the characteristics of phytoplankton community and their relationship with environmental factors were analyzed. We aim to identifying the environmental factors that significantly affect the characteristics of phytoplankton community. Discussing the relative importance and interaction of different types of environmental factors. On these basis, we confirming the indicators of phytoplankton community characteristics to water quality status, and to provide data basis and scientific support for river ecosystem management in the Luanhe River Basin.

Based on the water environmental factors of 121 sampling sites, the socioeconomic factors, consumption of chemical fertilizers, and land use in tributaries of the Luanhe River Basin of July 2017 (summer), October 2017 (autumn), and April 2018 (spring), the spatial and seasonal variations of the water environmental factors and their relationship with the socioeconomic factors, chemical fertilizers, and land use were analyzed. The results show that: 1) The contribution of biochemical oxygen demand, permanganate index, ammonia nitrogen, nitrate nitrogen, total nitrogen, total phosphorus and total suspended solids to the spatial difference of water environmental factors was greater than that of water temperature, pH and chlorophyll a. 2) Based on different water quality factors, the variation characteristics of water quality in different seasons and tributaries were different. 3) Among the land use, chemical fertilizers and socioeconomic factors, only phosphorus fertilizer, the proportion of forest and grassland had significant effects on water environmental factors, and the explained variation was 83.2%, 71.6% and 67.8% in summer, autumn and spring, respectively. The proportion of forest is closely related to nitrogen nutrient. The proportion of grassland and phosphate fertilizer are closely related to phosphorus nutrient, organic pollution and total suspended solids. 4) In summer, water quality index was negatively correlated with the proportion of cultivated land and built-up land. In autumn and spring, water quality index was negatively correlated with the proportion of forest and built-up land, and positively correlated with grassland. These results show that the spatial variation of water environment was mainly reflected in nutrients and organic pullution. The indication and pollution sources of different water quality factors determine the spatiotemporal variation characteristics. The seasonal differences of water environmental factors may be influenced by river hydrological factors and agricultural activity intensity. Spatial differences are closely related to human activities (fertilizer consumption, the proportion of cultivated land and built-up land). In addition, the protection of forest and grassland is also crucial to improving water quality.

Based on the data of phytoplankton community composition and cell density in different seasons, the spatial and temporal variation characteristics of phytoplankton community were analyzed. The results show that: 1) There were 6 phyla 62 genera, 7 phyla 61 genera, and 6 phyla 44 genera identified in summer, autumn, and spring, respectively. The number of genera in Bacillariophyta and Chlorophyta was about 80% to total genera number. The genera number of phytoplankton community in the mainstream and Yixun River were higher than that in other tributaries. 2) The cell density of phytoplankton community in summer (251.8×10⁴ cells/L) was significantly higher than that in autumn (153.7×10⁴ cells/L) and spring (139.5×10⁴ cells/L). Bacillariophyta has the highest cell density, followed by Cyanophyta and Chlorophyta. The cell density of phytoplankton community in Bao River and Yixun River were significantly higher than that in other tributaries. 3) The dominant genera of Cryptophyta appeared only in autumn, the dominant genera of Chlorophyta appeared only in summer and spring. These results indicate that there were seasonal and spatial differences in phytoplankton community composition and cell density. Seasonal variation may be influenced by temperature and hydrology factors. The number of genera in phytoplankton community is affected by the habitat diversity in rivers and the cell density is closely related to the intensity of human activities.

The relationship between the cell density of phytoplankton genera and fluvial physical and chemical factors, nutrients and organics was analyzed in different seasons. The results show that: 1) The environmental factors on the total cell density of phytoplankton community were higher than that of genera compositon number, and the main influencing factors were permanganate index, total phosphorus, river width and water temperature. 2) The effect of fluvial physicochemical factors on the genera cell density of phytoplankton community was greater than that of nutrients and organics. The two interact with each other on the genera cell density of phytoplankton community. 3) After controlling for fluvial physical and chemical factors, the explained variation of nutrients and organics to the genera cell density of phytoplankton community increased in summer and decreased in autumn and spring. 4) The genera cell density of Cyanophyta, Chlorophyta, Euglenophyta, Pyrrophyta, and Cryptophyta were positively correlated with river width, ammonia nitrogen, total phosphorus, permanganate index and negatively correlated with flow velocity. The genera cell density of Bacillariophyta was positively correlated with the flow velocity and negatively correlated with the ammonia nitrogen, total phosphorus and permanganate index. These results indicate that fluvial physicochemical factors, nutrients and organics all play an important role in the genera cell density of phytoplankton community. Fluvial physicochemical factors can regulate the effects of nutrients and organics on the genera cell density of phytoplankton community. After controlling the fluvial physicochemical factors, the effects of nutrients and organics on the genera cell density of phytoplankton community were enhanced in the optimal growth and reproduction season and decreased in other seasons. Phytoplankton community can indicate water bodies with pollution, eutrophication or long retention time of pollutants. It can also indicate water body with less disturbance or strong exchange capacity.

We evaluated the water quality status of the Luanhe River based on phytoplankton index of biotic integrity (P-IBI), trophic diatom index (TDI), community diversity indexes, and analyzed their relationship with the dissolved oxygen, 5 days biochemical oxygen demand, permanganate index, ammonia nitrogen, total nitrogen, total phosphorus and water quality index. The results show that: 1) The water quality status was “good”, “mesotrophic” and “non-pollution” based on P-IBI, TDI and community diversity indexes, respectively. 2) P-IBI and TDI show specific indication in the rivers with human disturbance (urban rivers) or in specific water bodies (main streams), and the evaluation results have a high degree of differentiation. However, the community diversity indexes were the opposite. 3) P-IBI and TDI were only significantly correlated with permanganate index, water quality index, river width and flow velocity (p<0.05), but insignificantly correlated with with other factors (p>0.05). These results indicate that P-IBI and TDI provide necessary supplement for river ecological status evaluation. P-IBI and TDI are closely related to the comprehensive condition of water quality and fluvial morphology, and are the results of the comprehensive effect of various influencing factors in the water body.