Ecological Modelling Laboratory, Department of Physical & Environmental Sciences, University of Toronto, Toronto, ON M1C 1A4, Canada.
Environment Canada, Canada Centre for Inland Waters, Burlington, ON L7R 4A6, Canada.
Harmful Algae. 2016 May;55:121-136. doi: 10.1016/j.hal.2016.02.005. Epub 2016 Mar 19.
The Bay of Quinte, a Z-shaped embayment at the northeastern end of Lake Ontario, has a long history of eutrophication problems primarily manifested as spatially extensive algal blooms and predominance of toxic cyanobacteria. The purpose of this study was to identify the structural changes of the phytoplankton community induced by two environmental alterations: point-source phosphorus (P) loading reduction in the late 1970s and establishment of dreissenid mussels in the mid-1990s. A combination of statistical techniques was used to draw inference about compositional shifts of the phytoplankton assemblage, the consistency of the seasonal succession patterns along with the mechanisms underlying the algal biovolume variability in the Bay of Quinte over the past three decades. Based on a number of diversity and similarity indices, the algal assemblages in the upper and middle segments of the Bay are distinctly different from those typically residing in the outer segments. Our analysis also identified significant differences among the phytoplankton communities, representing the pre- and post-P control as well as the pre- and post-dreissenid invasion periods. Recent shifts in phytoplankton community composition were mainly associated with increased frequency of occurrence of toxin-producing Microcystis outbreaks and reduced biovolume of N fixers, such as Aphanizomenon and Anabaena. Bayesian hierarchical models were developed to elucidate the importance of different abiotic factors (light attenuation, water temperature, phosphorus, and ammonium) on total cyanobacteria, Microcystis, Aphanizomenon, and Anabaena relative biovolume. Our modelling exercise suggests that there is significant spatial heterogeneity with respect to the role of the factors examined, and thus total phosphorus alone cannot always explain the year-to-year variability of cyanobacteria succession patterns in the system. The lessons learned from the present analysis will be helpful to the water quality criteria setting process and could influence the management decisions in order to delist the system as an Area of Concern.
安大略湖北端的一个 Z 形海湾——安大略湾，长期以来一直存在富营养化问题，主要表现为广泛的藻类水华和有毒蓝藻的优势。本研究的目的是确定由两种环境变化引起的浮游植物群落结构变化：20 世纪 70 年代末点源磷（P）负荷减少和 20 世纪 90 年代中期双壳类贻贝的建立。本研究采用统计技术组合，推断安大略湾浮游植物组合的组成变化，以及过去三十年中藻类生物量变化的季节性演替模式的一致性及其潜在机制。基于一系列多样性和相似性指数，湾内上游和中游的藻类组合与通常存在于外部段的藻类组合明显不同。我们的分析还确定了浮游植物群落之间存在显著差异，代表了磷控制之前和之后以及双壳类贻贝入侵之前和之后的时期。浮游植物群落组成的最近变化主要与产毒微囊藻爆发的发生频率增加和固氮生物（如鱼腥藻和颤藻）的生物量减少有关。建立贝叶斯层次模型，以阐明不同非生物因素（光衰减、水温和磷、铵）对总蓝藻、微囊藻、鱼腥藻和颤藻相对生物量的重要性。我们的建模研究表明，就所研究因素的作用而言，存在显著的空间异质性，因此总磷本身并不能总是解释该系统中蓝藻演替模式的年际变化。本分析得出的经验教训将有助于水质标准制定过程，并可能影响管理决策，以便将该系统从关注区域中除名。
