Importance of ecological boundaries in aquatic ecosystem processes

在过去的几十年里，有害藻华在世界范围内的水生生态系统中增加，而不仅仅是在富营养化生态系统中。在大陆沃茨，这些水华主要是由于潜在的有毒蓝绿藻（蓝藻）。自70年代初以来，蓝绿色水华与湖泊营养物质，特别是磷（P）施肥之间的关系就已为人所知。今天的问题是，为什么水华也发生在表面沃茨中营养物质浓度低的湖泊中。在这些湖泊中的一些外部磷负荷已减少，在过去的20-30年，在其他外部人为来源是未知的。 在这些低表面营养湖泊中，水华的发生和强度每年都有变化。最近，有毒蓝绿色的增加被归因于全球变暖，这一假说的作者主张对气候变化和水华形成蓝绿色的种群动态进行更详细的研究。在我们为期5年的研究中，我们希望验证一些与气候相关的机制，这些机制可以控制小型湖泊中的藻类群落结构和蓝绿色水华。特别是，我们要衡量的重要性，风引起的物理强迫在湖泊底部（底栖边界层）的营养物质和有机体的通量从沿岸的和深栖息地的水柱（远洋栖息地）;和物理约束相邻地区（如温跃层分层湖泊）之间。我们的假设是：i）沉积物中积累的P允许具有低外部P负荷的湖泊中藻类的底部休眠阶段的生长，ii）通过边界连接不同生境（从底部到水柱和通过水柱）的营养物和生物体的物理强迫的强度，并在藻类补充中产生正反馈或负反馈。我们的研究构成了一种新的方法来解释在分层湖泊藻类群落结构的年际变化，并可能解释蓝藻水华。我们的理解的重要性，在分层的小湖泊生态过程的物理强迫应该产生更好的工具，有毒水华的管理和控制。

During recent past decades, harmful algal blooms have increased world wide in aquatic ecosystems, and not only in eutrophic ecosystems. In continental waters these blooms are mainly due to potentially toxic blue-green algae (cyanobacteria). The relationship between blue-green blooms and lake fertilisation by nutrients, particularly phosphorus (P), is known since the early 70s. The question today is why the blooms also occur in lakes with low nutrient concentrations in their surface waters. In some of these lakes external P-loading has been decreased in the last 20-30 years, in others external anthropogenic sources are unknown. In these low surface nutrient lakes the occurrence and intensity of the blooms varies between years. Recently, the increase of noxious blue-greens has been attributed to global warming, and the author of this hypothesis advocates for more detailed studies of climate change and population dynamics of bloom-forming blue-greens. In our 5-yr study we wish to verify some of the mechanisms related to climate that could control algal community structure and blue-green blooms in small lakes. In particular, we want to measure the importance of wind-induced physical forcing at the bottom of lakes (benthic boundary layer) in the fluxes of nutrients and organisms from littoral and deep habitats to the water column (pelagic habitats); and between physically constrained adjacent areas (e.g. thermocline in stratified lakes). Our hypotheses are that: i) it is the P-accumulated in the sediments that allows the growth of the bottom resting stages of algae in lakes with low external P loads and, ii) the intensity of the physical forcing of nutrients and organisms through boundaries links the different habitats (from the bottom to the water column and through the water column) and creates a positive or negative feedback in algae recruitment. Our study constitutes a novel approach to explaining the inter-annual variability in algae community structure in stratified lakes and may explain cyanobacteria blooms. Our understanding of the importance of the physical forcing on ecological processes in stratified small lakes should produce better tools for noxious bloom management and control.