Linking climate change and watershed responses to emerging cyanobacterial blooms in lakes on forested landscapes

加拿大森林景观正在发生根本性变化。五大湖--圣彼得堡。劳伦斯林区提供了世界上18%的饮用水。以前纯净的乡村清澈水域似乎正在经历蓝藻水华(蓝藻水华)的初期增加，包括具有产生强烈神经和肝脏毒素能力的潜在有害水华。最近，公众向地方政府报告的蓝藻数量大幅增加，导致公众对蓝藻的关注加剧。我们可能正处于生态临界点。在营养丰富的湖泊中，蓝藻的发生频率和强度正在增加，但大多数“新的”水华报告都是在营养贫乏的湖泊中进行的，以前没有水华的历史。根据我们目前的理解，这些湖泊不应该有支持水华的能力。现在是挑战我们理解的时候了。**我们认为，气候变化正在导致森林景观的水文和生物地球化学发生根本性变化，从而导致从陆地到湖泊的养分输送，蓝藻的兴起可能是其结果。**本提案侧重于森林景观中的营养物质来源，它们在运输路径上的转化潜力，以及它们对湖泊接收的贡献和对湖泊浮游植物群落的影响。我们的假设是，与真核竞争对手相比，气候诱导的铁(Fe)和溶解有机物(DOM)的变化为蓝藻的特殊生长创造了条件。我们将在多个尺度上检验这一假设--从对有许多湖泊的整个景观的粗尺度监测到细尺度的实验孵化。磷(P)和氮(N)在调控蓝藻中的作用已被广泛认识；然而，尽管铁已被证明调节浮游植物对P和N的利用效率，但对铁等微量营养素的作用知之甚少。我们将(1)通过对1000个湖泊浮游植物色素浓度进行为期30年的卫星调查，结合当代对蓝藻的地面调查，并确定整个地区湖泊中浮游植物的年峰值浓度是否在上升(或者如果仅限于几个湖泊)，来确认浮游植物水华是否存在上升趋势；(2)确定陆地-湖泊系统的关键特征，这些特征受到人类(普遍了解的)或气候变化(远未被了解)的影响，导致铁的储存或出口的变化-据称是与新出现的蓝藻问题相关的催化和刺激因素，(3)通过记录与DOM的结合率来表征从集水区向湖泊输送的铁的浓度和组成，以及(4)描述从集水区进入湖泊的DOM形态和铁的选择性影响，并刺激蓝藻的发育和毒性。利用湖泊的一个子集，将结合蓝藻对DOM-Fe的陆地-溪流-湖泊加工和出口进行评估。这种蓝藻形成的生物地球化学陆地-湖泊模型将在三种不同的生物测定程序中进行测试：低容量“生长”、流通式连续培养(“生态恒定器”)，使细胞能够通过生长速度的微小变化来竞争其他细胞，以及湖内多营养中生实验。**这项工作的结果将为气候驱动的森林水文和生物地球化学变化之间的机制关系、这些变化对蓝藻的后果以及由此产生的毒素生产对人类和生态系统健康的威胁提供基本的见解。

Fundamental changes are occurring on Canada's forested landscapes. The Great Lakes-St. Lawrence forest region supplies 18% of the world's drinking water. The formerly pristine clear waters of cottage country appear to be experiencing an incipient rise in cyanobacterial blooms (cyanoblooms), including potentially harmful ones that have the capacity to produce potent neural and liver toxins. Recently, there has been a significant increase in the number of cyanobloom reports by the public to regional governments, resulting in heightened public concern for cyanoblooms. We may be at an ecological tipping point. The frequency and intensity of cyanoblooms are increasing in nutrient-rich lakes, but the majority of "new" bloom reports are in nutrient-poor lakes with no prior bloom history. Based on our current understanding these lakes should not have the capacity to support blooms. It is time to challenge our understanding.* *We propose that climate change is leading to fundamental changes in the hydrology and biogeochemistry of forested landscapes, and thus nutrient delivery from land to lakes, from which the rise of cyanoblooms may be a consequence. **This proposal focuses on nutrient sources in forested landscapes, their potential for transformation along pathways of transport, and their contributions to receiving lakes and consequences on phytoplankton communities in lakes. Our hypothesis is that climate-induced changes in iron (Fe) and dissolved organic matter (DOM) create conditions for exceptional cyanobacterial growth compared with their eukaryotic competitors. We will test this hypothesis at multiple scales - from coarse-scale monitoring of entire landscapes with many lakes to fine-scale experimental incubations. The role of phosphorus (P) and nitrogen (N) in regulating cyanoblooms is widely acknowledged; however, the role of micronutrients such as Fe is less known, although Fe has been shown to regulate P and N use efficiency in phytoplankton. We will (1) confirm whether there exists a rising trend in phytoplankton blooms by constructing a 30-year satellite survey of 1,000 lake phytoplankton pigment concentrations combined with contemporary ground surveys of cyanobacteria and determining if the peak annual phytoplankton concentrations in lakes is on the rise across the region (or if it is restricted to a few lakes), (2) identify critical features of the land-lake system affected by either humans (generally well understood) or climate change (far less understood) that lead to changes in Fe storage or export - the purported catalytic and stimulatory element associated with the emerging cyanobloom problem, (3) characterize Fe concentration and composition as it is transported from the catchment to lake by documenting rates of binding to DOM, and (4) describe the selective impact of DOM form and Fe that enters lakes from catchments and stimulates the development and toxicity of cyanoblooms. Using a subset of lakes, the land-stream-lake processing and export of DOM-Fe will be assessed in conjunction with cyanoblooms. This biogeochemical land-lake model of cyanobloom formation will be tested in three different bioassay procedures: low-volume "grow outs", flow-through continuous cultures ("ecostats") that enable cells to outcompete others through small changes in growth rate, and multi-trophic within-lake mesocosm experiments. **The outcome of this work will provide fundamental insights to the mechanistic relationship between climate-driven forest hydrological and biogeochemical changes, the consequences of these changes to cyanoblooms, and the resultant threat of toxin production to human and ecosystem health.