Data for Linking Phosphorous Dynamics with Hypereutrophic Conditions on the Millennial Scale: The Paleolimnology of Shallow and Subtropical Lake Wauberg, Florida, USA

Eutrophication of aquatic ecosystems results in the proliferation of harmful algal blooms (HABs), posing a global challenge to water quality and ecosystem services. Whereas eutrophication has been linked to nutrient additions of nitrogen and phosphorus in conjunction with human activities over the last few decades, much less understanding has developed on water quality trends when nutrient additions persist for centuries or even millennia. Here, we used paleolimnological techniques to reconstruct eutrophication and cyanobacteria dynamics in Lake Wauberg, FL, USA, a lake that has experienced millennial-scale nutrient additions from natural phosphate geology. We measured photosynthetic pigments, cyanotoxins, and nutrient concentrations on a sediment core spanning the last ~6,900 years of lake history. Our primary hypothesis is that the long-term total phosphorus (TP) additions caused constant cyanobacteria dominance throughout the entire history of the lake. Results show that long-term P deposition in Lake Wauberg existed within two different hydrological conditions. Focusing on the last 5 ka BP, which represent the period of constant lake conditions, photosynthetic pigments and cyanotoxins demonstrated a strong positive relationship with TP over other nutrients. By dividing TP inputs into three levels, primary producers positively increased with low and high TP inputs but showed no change under moderate levels. Under high (2.2-3 mg g⁻¹) and extreme (>3 mg g⁻¹) TP sedimentary concentrations over the last 0.3 ka BP, substantial increases in cyanobacteria abundance, rapid production of microcystins (MCs), and a possible shift to N-fixation occurred. These data show that chronic and additive TP inputs can produce asynchronous responses in the primary producer community and MC concentrations with substantial increases occurring at higher TP thresholds. Linking the historic ecological response to TP periods with current limnological conditions could provide new directions in forecasting and managing aquatic ecosystems that experience chronic TP inputs.

水生生态系统富营养化会引发有害藻华（Harmful Algal Blooms, HABs）大规模暴发，对水质与生态系统服务构成全球性挑战。尽管近数十年来学界已将富营养化与人类活动伴随的氮、磷养分输入建立起因果关联，但对于养分输入持续数百年甚至数千年时的水质变化趋势，当前认知仍较为匮乏。本研究利用古湖沼学（Paleolimnology）技术，对美国佛罗里达州（Florida, FL）沃伯格湖（Lake Wauberg）的富营养化与蓝细菌动态开展重建——该湖长期受到自然磷酸盐地质作用带来的千年尺度养分输入影响。我们对覆盖过去约6900年湖泊演化历史的沉积物岩芯测定了光合色素、蓝细菌毒素与养分浓度。本研究的核心假设为：长期总磷（Total Phosphorus, TP）输入会使该湖泊在整个演化历史中始终维持蓝细菌优势群落状态。结果显示，沃伯格湖的长期磷沉积过程存在两种不同的水文环境背景。本研究聚焦于湖泊环境稳定的过去5000年（kilo-annum Before Present, 5 ka BP）时段，结果表明光合色素与蓝细菌毒素与总磷的相关性显著强于其与其他养分的相关性。通过将总磷输入划分为三个等级，研究发现初级生产者群落丰度随低、高等级总磷输入呈正向增长，但在中等等级输入下无显著变化。在过去300年（kilo-annum Before Present, 0.3 ka BP）的沉积物总磷高浓度（2.2~3 mg·g⁻¹）与极端浓度（>3 mg·g⁻¹）环境下，蓝细菌丰度显著升高、微囊藻毒素（Microcystins, MCs）快速生成，且可能发生了向固氮作用的群落转变。上述数据表明，长期持续的累积性总磷输入会使初级生产者群落与微囊藻毒素浓度产生异步响应，且在更高的总磷阈值下会出现显著的变化跃升。将历史时期的生态响应与总磷输入时段、当前湖沼学现状相结合，可为受长期持续总磷输入影响的水生生态系统的预测与管理提供全新研究方向。