Hunan Engineering Research Center of Aquatic Organism Resources and Environmental Ecology, College of Life and Environmental Sciences, Hunan University of Arts and Science, Changde 415000, China; State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
Chongqing Key Laboratory of Big Data and Intelligent Computing, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China.
Sci Total Environ. 2021 Jul 10;777:146052. doi: 10.1016/j.scitotenv.2021.146052. Epub 2021 Feb 24.
Harmful algal blooms caused by cyanobacteria have been increasing in frequency worldwide. However, the main environmental drivers of this change are often difficult to identify because of the effects of the interaction between eutrophication and climate change. Recently, filamentous N-fixing cyanobacteria and non-diazotrophic Microcystis have been observed to be co-existing and undergoing succession in some eutrophic lakes. However, the succession patterns of dominant cyanobacteria and the factors driving this in mesotrophic lakes are not well understood. We hypothesized that the changes in cyanobacterial assemblages in mesotrophic lakes could result in a relatively high risks of toxic blooms, and that these changes are associated with the global climatic changes. We tested these hypotheses using data from the subtropical mesotrophic Lake Erhai. We found that the high spatiotemporal variability in the cyanobacterial community, and the increase in biomass were driven primarily by the growth of bloom-forming cyanobacterial taxa. Species-specific biomasses were related to a different environmental stressor; increases in dissolved organic carbon (DOC) concentrations were statistically associated with an increase of Microcystis biomass, whereas increases in surface water temperature favored higher biomass of Pseudanabaena at low transparency and high concentration of phosphorus. In addition, low nitrogen- to- phosphorus ratios were identified as potential determinants of the abundance of N-fixing Dolichospermum. Furthermore, changes in the concentration of DOC, total nitrogen, pH and water transparency levels were found to affect the composition of Microcystis morphotypes and genotypes mostly. This study highlights that the toxic to non-toxic Microcystis ratio might increase with the water darkening and browning (which occurs in many subtropical plateau lakes). Lake management strategies, therefore, need to consider the toxicity of cyanobacterial assemblages in mesotrophic lakes over the intensity of the cyanobacterial blooms.
蓝藻引发的有害藻华在全球范围内的发生频率正在不断增加。然而，由于富营养化和气候变化相互作用的影响，这种变化的主要环境驱动因素往往难以确定。最近，丝状固氮蓝藻和非固氮微囊藻在一些富营养化湖泊中被观察到同时存在并进行演替。然而，中营养湖泊中优势蓝藻的演替模式以及驱动这些演替的因素还不太清楚。我们假设中营养湖泊中蓝藻群落的变化可能会导致有毒藻华的风险相对较高，并且这些变化与全球气候变化有关。我们使用来自亚热带中营养洱海的数据分析来检验这些假设。我们发现，蓝藻群落的高时空变异性和生物量的增加主要是由形成水华的蓝藻分类群的生长驱动的。特定物种的生物量与不同的环境胁迫有关；溶解有机碳 (DOC) 浓度的增加与微囊藻生物量的增加呈统计学相关，而地表水温的升高有利于低透明度和高磷浓度下假鱼腥藻的生物量增加。此外，氮磷比的降低被认为是固氮 Dolichospermum 丰度的潜在决定因素。此外，DOC、总氮、pH 和水透明度水平的变化被发现主要影响微囊藻形态和基因型的组成。这项研究强调，有毒微囊藻与无毒微囊藻的比例可能会随着水的变暗和变棕色（这在许多亚热带高原湖泊中都会发生）而增加。因此，湖泊管理策略需要考虑中营养湖泊中蓝藻群落的毒性，而不仅仅是蓝藻水华的强度。
