小清河专项治理对莱州湾环境和浮游植物的影响

Effects of Pollution Control of Xiaoqing River on Environment Factors and Phytoplankton Community in the Laizhou Bay

为了明确小清河流域专项治理对莱州湾环境因子和浮游植物群落结构的影响,于2018年8月(治理后丰水期)对莱州湾近海环境因子、叶绿素a(Chla)、浮游植物丰度和群落结构空间分布进行了综合调查.结果表明,小清河进行专项治理后调查海域可溶性无机氮(DIN)、可溶性无机硅(DSi)、NO_(3)^(-)和NO_(2)^(-)浓度明显降低,仅为临近2017年同期(专项治理前)的40.1%~60.4%;可溶性无机磷(DIP)和NH_(4)浓度则呈现明显上升趋势,分别是2017年同期的2.5倍和1.4倍.环境因子空间分布发生明显变化,小清河河口附近海域营养盐明显降低.浮游植物细胞丰度为21.5×10^(6) cell·m^(-3),与历史同期接近,但ρ(Chla)(2.43μg·L^(-1))明显降低;镜检法和浮游植物色素分类法均显示,莱州湾浮游植物群落结构变化明显,由硅藻占优势转变为硅、蓝藻共同占优势.小清河污染专项治理前莱州湾历史同期常见的旋链角毛藻(Chaetoceros curvisetus)、中肋骨条藻(Skeletonema costatum)和大洋角管藻(Cerataulina pelagica)等优势种占比明显降低,平裂藻(Merismopedia sp.)和针杆藻(Synedra spp.)等淡水优势种丰度明显升高.冗余分析(RDA)分析显示,小清河流域专项治理后主要浮游植物类群和优势种与氮营养盐、磷酸盐(负相关)和盐度(负相关)呈现明显的相关关系,说明河流径流输入营养盐浓度和结构的变化可能是影响浮游植物群落结构主要原因.

The spatial distribution of environmental factors,chlorophyll a(Chla),phytoplankton abundance,and community structure in the Laizhou Bay were investigated in August 2018(wet season after pollution control)to clarify the effects of the pollution control of the Xiaoqing River,which is a major source of pollution,on environmental factors and phytoplankton community structure in this area.The results showed that the environmental factors changed significantly after pollution control of the Xiaoqing River.The concentrations of dissolved inorganic nitrogen(DIN),dissolved inorganic silicon(DSi),NO_(3)^(-),and NO_(2)^(-)decreased significantly,with values only 40.1%to 60.4%of those from the same period of in 2017(the nearest year before the pollution control),whereas dissolved inorganic phosphorus(DIP)and NH_(4) increased by 2.5 and 1.4 times that of their concentrations in 2017.The spatial distribution of environmental factors changed significantly,with the nutrient concentrations around the Xiaoqing River estuary noticeably decreasing.The abundance of phytoplankton cells was 21.5×10^(6) cell·m^(-3),which was close to the results of a previous study,whereas theρ(Chla)was 2.43μg·L^(-1),which decreased obviously.Both microscopic analysis and pigment taxonomy suggested that phytoplankton community structure in the Laizhou Bay changed clearly,with the dominant community shifting from diatoms alone to the co-dominance of diatoms and cyanobacteria.Chaetoceros curvisetus,Skeletonema costatum,and Cerataulina pelagica,which were commonly observed in the Laizhou Bay before pollution control of the Xiaoqing River,decreased in 2018,whereas the abundance of common dominant freshwater species(e.g.,Merismopedia sp.and Synedra spp.)increased significantly.Redundancy analysis(RDA)showed that the phytoplankton community was significantly related to nitrogen,phosphate(negative correlation),and salinity(negative correlation)after pollution control of the Xiaoqing River,indicating that the variation in nutrient concentration and the structure of river runoff input may be the main factors affecting phytoplankton community and dominant species structure.