基于结构方程模型的三峡库区汉丰湖叶绿素a与其关键影响因子关系识别

为明确三峡水库汉丰湖叶绿素a(Chl.a)的主要影响因素,分析了汉丰湖2018—2021年的Chl.a、pH、水温、透明度以及氮、磷营养盐等水质指标的变化情况,探讨了Chl.a与其余水质指标的相关性,并应用结构方程模型解析了Chl.a的关键影响因素。结果表明,汉丰湖水体Chl.a浓度在0.04~68.58 μg/L之间变化,水温在9.62~32.10℃之间,pH在6.75~9.81之间,总氮、溶解性氮、总磷、溶解性磷的变化范围分别为0.58~4.68、0.25~3.99、0.02~0.76、0.01~0.44 mg/L。Chl.a浓度与水温、pH、总磷和总固体悬浮物呈显著正相关,与透明度、溶解性氮、碱度、亚硝态氮、硝态氮呈极显著负相关。结构方程模型结果显示,影响Chl.a浓度的因子中理化因子的路径系数为0.68,营养物质的路径系数为0.16,这表明影响Chl.a浓度的因子以理化因子为主,营养物质的作用相对较小。同时,理化因子通过营养盐间接影响Chl.a浓度(路径系数为-0.04)。各理化因子中,水温和pH的路径系数分别为0.51和0.41,水温是理化因子的主要表征指标;在营养盐指标中,总磷和溶解性磷的路径系数分别为0.82和0.71,而总氮的路径系数为0.36,说明磷是汉丰湖的限制性营养元素。

Identification of the relationship between chlorophyll-a and its key influencing factors in Lake Hanfeng in the Three Gorges Reservoir based on structural equation model

To determine the key influence factors of chlorophyll-a (Chl.a) in the Lake Hanfeng, water temperature (T), pH, Chl.a, Secchi depth (SD), and nitrogen (N) and phosphorus (P) nutrients in Lake Hanfeng in the Three Gorges Reservoir from 2018 to 2021 were analyzed, and the correlation between Chl.a and other water quality indicators was revealed, and the key influencing factors of Chl.a were analyzed by the structural equation model. The results showed that Chl.a in Lake Hanfeng T ranged from 0.04 to 68.58 μg/L, and T ranged from 9.62 to 32.10℃, pH ranged from 6.75 to 9.81. Total nitrogen (TN), dissolved nitrogen (DN), total phosphorus (TP) and dissolved phosphorus (DP) in the Lake Hanfeng varied from 0.58 to 4.68, 0.25 to 3.99, 0.02 to 0.76 and 0.01 to 0.44 mg/L. Chl.a concentration was positively correlated with T, pH, TP and total suspended solids. Conversely, Chl.a concentration was negatively correlated with alkalinity, DN, nitrate nitrogen, nitrite nitrogen and SD. The structural equation model results showed that the path coefficient of physical factor in the factors affecting Chl.a concentration was 0.68 and nutrients 0.16, indicating that the factors affecting Chl.a concentration were mainly physical factor and the nutrients were less important. Meanwhile, physical factor indirectly affected Chl.a concentration through nutrient salts (path coefficient is -0.04). In each physical factor, the path coefficient of T and pH was 0.51 and 0.41, respectively, while T was the main characterization index of the physical factor; the path coefficients of TP and DP were 0.82 and 0.71, respectively, while the path coefficient of TN was 0.36 and P was a limiting nutrient element of Lake Hanfeng.