富营养化湖泊藻华腐解产生的溶解性有机质动态变化及其环境效应

富营养化和有害藻华是湖泊面临的主要环境问题，富营养化湖泊藻华在后期会发生衰亡和腐解并产生大量藻源溶解性有机质（DOM），影响水体DOM的质量和活性，并对关键元素的生物地球化学循环产生重要调控作用.为探究不同富营养化程度湖泊水体藻华腐解过程，对藻华腐解过程中水体DOM总量、生物有效性、相对分子质量和组分的动态变化进行分析，并探讨了藻华腐解引发的环境效应.结果表明，藻华腐解显著提高DOM浓度、生物有效性和各荧光组分强度.随着腐解的进行，DOM浓度逐渐降低，而相对分子质量逐渐增大.在分子水平上，超高分辨率质谱结果显示腐解过程中不饱和烃和脂肪族化合物优先被微生物利用，并生成木质素、缩合烃和高O/C值的单宁酸等惰性分子.藻华腐解过程中细菌群落主要优势种从变形菌门（46%）逐渐变为拟杆菌门（42%）.此外，藻华腐解还导致水体CO₂和CH₄排放显著升高1.2~5倍，且排放量可以由DOM光学指标a₂₅₄预测.该结果为全面揭示藻华腐解过程中DOM特征的动态变化，以及湖泊富营养化治理和环境效应预测提供理论依据和科学支撑.

Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO₂ and CH₄ from water, and the emission rates could be well predicted by the optical index of a₂₅₄ in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.