2022年夏季汉江中下游水华生消驱动因子及其贡献率量化研究

Summer Driving Factors and Their Quantitative Contribution to Algae Bloom Occurrence and Demise in the Middle and Lower Hanjiang River in 2022

为探究2022年夏季长江流域“汛期反枯”极端水文条件下汉江中下游首次出现的蓝藻水华成因,选取叶绿素浓度为水华表征指标,考虑各环境因子间的多重共线性关系,采用偏最小二乘回归(PLSR)量化了不同环境因子对汉江中下游仙桃、宗关断面蓝藻水华生消的贡献率。结果表明:(1)仙桃断面叶绿素a浓度与水温、pH、溶解氧和总磷均呈显著正相关关系,与氮磷比呈显著负相关关系;宗关断面叶绿素a浓度与水温、pH、溶解氧均呈显著正相关关系,与日均水位、水位日变幅、流量、总磷和氨氮均呈显著负相关关系;(2)溶解氧、pH和水温对水华生消的贡献程度较高,对仙桃断面的贡献率分别为15.18%、13.68%和14.50%,对宗关断面的贡献率分别为18.06%、15.93%和15.65%;(3)基于偏最小二乘路径模型(PLS-PM)的环境因子解析显示,气象因子是2022年夏季汉江中下游蓝藻水华暴发的诱导因子,水华“萌发”时段可能与汉江中下游涝旱急转时段重叠。建议后续研究结合准确的中长期气象预报信息,在涝旱急转时段优化汉江中下游水华防控调度的下泄流量与下泄时机,提高水华防控效果。

Under the extreme hydrological conditions of high temperature and drought in the Yangtze River basin in the summer of 2022,cyanobacteria blooms occurred for the first time in the middle and lower reaches of Hanjiang River.In this study,we identified the driving factors of algae blooms and quantified the contribution of each driving factor in the Xiantao and Zongguan sections in the Hanjiang River,aiming to provide scientific evidence and decision support for the prevention and control of al⁃gae blooms.The concentration of chlorophyll-a was selected as the indicator of algae blooms in this study,and partial least squares regression(PLSR)was used due to the multicollinearity relationship be⁃tween environmental factors.Results show that:(1)The concentration of chlorophyll-a in the Xiantao section presented a significantly positive correlation with water temperature,pH,dissolved oxygen(DO)and total phosphorus(TP),and a significantly negative correlation with the ratio of nitrogen to phosphorus.The concentration of chlorophyll-a in the Zongguan section presented a significantly posi⁃tive correlation with water temperature,pH and the DO,and a significantly negative correlation with the daily average water level,daily water level fluctuation,flow,TP and ammonia nitrogen.(2)The DO,pH and water temperature contributed most to the occurrence and demise of algae blooms,with respective contribution rates of 15.18%,13.68%,14.50%in the Xiantao section,and 18.06%,15.93%,15.65%in the Zongguan section.(3)The impact paths of various environmental factors on changes in chlorophyll-a concentration were analyzed based on Partial Least Squares Path Modeling(PLS-PM),and the results indicate that meteorological factors induced the outbreak of cyanobacteria blooms in the middle and lower reaches of the Hanjiang River in summer of 2022,and that the formation(germina⁃tion)period of summer algae blooms may overlap with"abrupt flood-drought transition"periods.Therefore,to effectively prevent and control algae blooms in the middle and lower reaches of Hanjiang River,we recommend regulating the discharge and time of water flow in combination with accurate medium and long term weather forecast information during"abrupt flood and drought transition"peri⁃ods.This study has the potential to significantly enhance the efficiency and effectiveness of algae bloom prevention and control.