西北江三角洲河网浮游植物叶绿素a粒径特征研究

Study on particle size characteristics of phytoplankton chlorophylla in theXijiang and Beijiang Delta River network

为探索浮游植物叶绿素a粒径的时空变化及其影响因素,调查研究了西北江三角洲河网水域2021年枯水期(2月份和12月份)和丰水期(5月份和8月份)的水环境和浮游植物叶绿素a粒径特征。结果显示,叶绿素a总浓度呈现明显的季节差异,最高值出现在8月份,最低值出现在5月,分析原因主要与径流量的大小、水体pH和氧化还原电位的变化有关。叶绿素a总浓度的空间特征显示,广州周边站位的叶绿素a浓度明显偏高,主要与营养盐的空间分布格局和水体的交换能力有关。粒径特征的结果显示,小型和微型浮游植物是珠三角河网水体叶绿素a的主要贡献者,呈现交替优势。季节特征显示,2-5月份微型叶绿素a占主导地位,8月份和12月份小型叶绿素a占主导地位,分析原因主要与径流量的大小、水体pH和光照有关。空间特征显示,小型叶绿素a在8月份和12月份占比的最高值往往出现在河网中部的站位,微型叶绿素a占比的最高值往往出现在远离广州市的站位点,分析原因主要与溶解氧和硝酸盐含量有关。冗余分析结果表明pH、DO、水下光度、TP和硝酸盐含量是影响浮游植物粒径分布的主要影响因子。综上,物理因子包括径流量的大小和水体pH的变化影响叶绿素a粒径特征的季节变动,而化学因素如营养盐含量影响叶绿素a粒径特征的空间分布。

The river network waters of the Xijiang and Beijiang Delta are the essential route for the two main streams of the Pearl River,Xijiang and Beijiang,to flow into the South Sea,China.To explore the relationship between phytoplankton chlorophyll a(Chla)particle size and environmental factors,the research team investigated the water environment and phytoplankton Chla particle size characteristics in this water during the dry(February and December)and wet(May and August)periods in 2021,which can provide a scientific basis for the later environmental management and restoration work.Origin visualized the spatial and temporal characteristics of environment factors and size-fractioned Chla.The relationship between environmental factors and size-fractioned Chla were analyzed by RDA analysis.The results showed that the significant temporal differences characterized WT,pH,TN and silicate concentration.Variations of DO and transparency showed significant spatial differences.The total Chla concentration showed significant seasonal differences,with the highest value occurring in August,the second highest in December,and the lowest in May,mainly related to the magnitude of runoff,water pH,and ORP changes.The spatial characteristics of the total Chla concentration showed that the Chla concentration was significantly higher at the stations around Guangzhou city,which was mainly related to the spatial distribution pattern of nutrients and the exchange capacity of the water bodies.The results of particle size characteristics showed that micro and nano phytoplankton were the main contributors to Chla in the water column of the PRD river network,showing alternating dominance.Seasonal characteristics showed that nano Chla was dominant in February and May,and micro Chla was dominant in August and December,mainly related to the magnitude of runoff,water pH and light.The spatial characteristics of the phytoplankton particle size structure showed that the phytoplankton particle size structure primarily consisted of micro and nano Chla,both of which showed alternating dominance.The highest values of micro Chla tended to occur at stations in the middle of the river network during August and December.The highest values of nano Chla dominance tended to occur at stations far from Guangzhou city,mainly related to the highest values of nano Chla tended to occur at stations far from Guangzhou,related primarily for DO and nitrate content.RDA analysis showed that pH,transparency,light,resistivity,ORP,TP,TN and silicate were the main factors affecting phytoplankton Chla concentration and pH,DO,light,TP and nitrate content were the main factors affecting the particle size distribution of phytoplankton.In summary,physical factors,including the magnitude of runoff volume and the variation of water pH affect the seasonal variation of Chla particle size characteristics.In contrast,chemical factors such as nutrient content are the key factors determining the spatial distribution of Chla particle size characteristics.