DataSheet2_Interactive effects of nutrients and salinity on zooplankton in subtropical plateau lakes with contrasting water depth.docx

Both eutrophication and salinization are growing global environmental problems in freshwater ecosystems, threatening the water quality and various aquatic organisms. However, little is known about their interactive effects on theses stressors and the role of lake depth on these interactions. We used field surveys to compared zooplankton assemblages over four seasons in eight Yunnan Plateau lakes with different trophic states, salinization levels, and water depths. The results showed that: 1) the species number (S), density (DZoop), and biomass (BZoop) of zooplankton exhibited strong seasonal dynamics, being overall higher in the warm seasons. 2) Data collected over four seasons and summer data both revealed highly significant positive relationships of S, DZoop, and BZoop with total nitrogen (TN), total phosphorus (TP), and phytoplankton chlorophyll a (Chl a). 3) S, DZoop, and BZoop displayed a unimodal relationship with salinity, peaking at 400–1000 μS/cm (conductivity, to reflect salinity). 4) The two large-sized taxa (cladocerans and copepods) generally increased at low-moderate levels of TN, TP, Chl a, and Cond and was constant or decreased at high levels. The average body mass (biomass/density) of crustaceans decreased with increasing TN, TP, Chl a, and conductivity. Our findings indicate that zooplankton may be more vulnerable in deep lakes than in shallow lakes when exposed to conductivity stress even under mesotrophic conditions, and the overall decrease in size in zooplankton assemblages under the combined stress of eutrophication and salinization may result in a lowered grazing effect on phytoplankton.

富营养化（eutrophication）与盐化（salinization）均为日益加剧的全球淡水生态系统环境问题，威胁着水体水质与各类水生生物。然而，目前对这两类胁迫因子的交互影响，以及湖泊深度在该交互作用中的调控作用仍知之甚少。本研究通过野外调查，对比了云南高原8个营养状态、盐化程度与水深各异的湖泊在四季中的浮游动物群落（zooplankton assemblages）组成。研究结果如下：1）浮游动物的物种数（S）、密度（DZoop）与生物量（BZoop）均呈现显著的季节动态特征，整体上暖季的各项指标更高。2）四季整合数据与夏季单独数据均显示，浮游动物的S、DZoop与BZoop与总氮（TN）、总磷（TP）及浮游植物叶绿素a（Chl a）均呈极显著正相关关系。3）S、DZoop与BZoop与盐度呈单峰关系，在400–1000 μS/cm（以电导率表征盐度）时达到峰值。4）两类大型浮游动物类群——枝角类（cladocerans）与桡足类（copepods）——在TN、TP、Chl a与电导率（Cond）处于中低水平时丰度普遍上升，而在高水平时则保持稳定或下降。甲壳动物的平均体重（生物量/密度）随TN、TP、Chl a与电导率的升高而降低。本研究结果表明，即便在中营养状态下，深水湖泊中的浮游动物在面临电导率胁迫时也比浅水湖泊更为脆弱；同时，在富营养化与盐化的联合胁迫下，浮游动物群落的整体体型减小可能会降低其对浮游植物的牧食效应。