Department of Hydrology and Water Resources, Hohai University, Nanjing 210098, China.
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
Sci Total Environ. 2019 Nov 20;692:1201-1208. doi: 10.1016/j.scitotenv.2019.07.360. Epub 2019 Jul 23.
Colloidal particles in lake waters interact inevitably with cyanobacterial extracellular polymeric substance (EPS), which will change their behavior and fate. Quantitative prediction of the effects of cyanobacterial EPS on colloidal behavior is difficult due to its variability and heterogeneity. To explore the effects of molecular weight (MW) fractions and chemical properties of cyanobacterial EPS on aggregation kinetics of colloidal particles, time-series cyanobacterial samples were collected in Lake Taihu, China, from April to November (during blooming and maintenance period), with the bulk EPS matrix fractionating into low MW (LMW-, <1 nm) and high MW (HMW-, 1 nm-0.45 μm) fractions. HMW-EPS was generally characterized with higher absorbance and predominant distribution of protein-like substances, while LMW-EPS contained mainly the humic- and fulvic-like substances. The absorbance, molecular size, and humification degree for each MW fraction consistently increased from April to November, showing obvious temporal variations from blooming period to maintenance period. As for the MW-dependent aggregation behaviors, the HMW-EPS provided better stability against aggregation than the LMW-EPS, and the bulk EPS matrix that consisted of HMW- and LMW-fractions exhibited the effects intermediate between that of each fraction alone. Regardless of MW fractions, the effects of EPS-induced stability enhancement were more evident in maintenance period than in blooming period. Further analysis showed that the colloidal stability was correlated positively with SUVA (R = 0.82-0.93) but negatively with Slope (R = 0.53-0.91) of UV-Vis absorption spectra, indicating that aromaticity and MWs were two critical parameters controlling colloidal aggregation. Therefore, cyanobacterial EPS can exhibit variable effects on colloidal stability, and characterization of MW distribution is strongly required in predicating the behavior and fate of colloidal particles in water environments.
湖水中的胶体颗粒不可避免地会与蓝藻细胞外聚合物（EPS）相互作用，这将改变胶体的行为和归宿。由于蓝藻 EPS 的可变性和异质性，定量预测其对胶体行为的影响具有一定难度。为了探究蓝藻 EPS 的分子量（MW）分数和化学性质对胶体颗粒聚集动力学的影响，本研究于 2018 年 4 月至 11 月（水华期和维持期）在太湖采集了时间序列的蓝藻样品，将 EPS 基质分为低 MW（LMW-，<1nm）和高 MW（HMW-，1nm-0.45μm）分数。HMW-EPS 通常具有较高的吸光度和以蛋白质样物质为主的优势分布，而 LMW-EPS 则主要包含腐殖质和富里酸样物质。每个 MW 分数的吸光度、分子大小和腐殖化程度均从 4 月到 11 月持续增加，表现出从水华期到维持期的明显时间变化。对于 MW 依赖的聚集行为，HMW-EPS 比 LMW-EPS 提供更好的稳定性，由 HMW 和 LMW 分数组成的 EPS 基质表现出介于各分数单独作用之间的效果。无论 MW 分数如何，EPS 诱导的稳定性增强效应在维持期比水华期更为明显。进一步分析表明，胶体稳定性与 SUVA（R=0.82-0.93）呈正相关，与 Slope（R=0.53-0.91）呈负相关，表明芳香度和 MW 是控制胶体聚集的两个关键参数。因此，蓝藻 EPS 对胶体稳定性具有可变性影响，在预测胶体颗粒在水环境中的行为和归宿时，强烈需要对 MW 分布进行特征描述。
