Collaborative LTREB Proposal: Will increases in dissolved organic matter accelerate a shift in trophic status through anoxia-driven positive feedbacks in an oligotrophic lake?

湖泊为社会提供了许多服务，如清洁的饮用水和生产性渔业。然而，许多湖泊现在正经历着碳和营养物质输入增加、气温升高和冰盖减少，这可能会降低水质或导致潜在有害藻类的大量繁殖。具体来说，由于从陆地植物中浸出的大量有机物质，美国各地的许多湖泊正在经历褐变的增加。褐变降低了水的清晰度，并干扰了饮用水管理措施。此外，它还可能引起其他变化，可能导致水质长期快速下降。这项研究将检验褐变可能降低湖泊氧气浓度的假设。低氧会导致湖泊沉积物中的营养物质释放，这可能会增加藻类繁殖，导致湖泊富营养化。了解褐变的影响将增加对湖泊生态系统的认识，并改善对湖泊随周围环境变化而变化的预测。这项研究还将培养研究生和本科生，并将使公众更好地了解湖泊水质的威胁。随着人类活动迅速改变自然生态系统，生态临界点是至关重要的。溶解有机物（DOM）的变化是水生生态系统临界点的一个重要潜在驱动因素。本项目将研究陆地DOM负荷的增加是否会通过刺激低氧缺氧和沉积物DOM和磷的释放，将清水寡营养湖泊推到一个临界临界点以上，这可能会启动一个水清澈度下降、热分层增强和低氧缺氧增强的正反馈循环。这种反馈循环加速了生态变化，最终可能使湖泊的营养状况从绿色、中营养到富营养以及棕色、营养不良状态转变。该项目将扩展自20世纪80年代末以来在位于宾夕法尼亚州东北部的拉卡瓦克保护区和生物野外站内或附近的两个湖泊取样的水质变量的长期数据集。为了补充这些长期观测，将进行实验和建模，以了解与褐变有关的反馈，并加强对内陆水体更广泛变化模式的了解。该项目将支持宾夕法尼亚州的一个区域湖泊监测网络，并与全球湖泊生态观测网GLEON密切联系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Lakes provide many services to society, such as clean drinking water and productive fisheries. Many lakes, however, are now experiencing increased input of carbon and nutrients, warming temperatures, and declining ice cover, which may reduce water quality or cause blooms of potentially harmful algae. Specifically, many lakes across the United States are experiencing increased browning due to high loading of organic matter leached from land plants. Browning reduces water clarity and interferes with drinking water management practices. In addition, it can cause other changes that may lead to rapid long-term declines in water quality. This research will test the hypothesis that browning may reduce oxygen concentrations in lakes. Low oxygen can cause nutrient release from lake sediments that may increase algae blooms, leading to lake eutrophication. Understanding the effects of browning will increase knowledge of lake ecosystems, and improve forecasts of how lakes will change as their surrounding environments change. This research will also train graduate and undergraduate students, and will lead to better public understanding of threats to lake water quality.Ecological tipping points are of vital interest as anthropogenic activities rapidly transform natural ecosystems. Changes in dissolved organic matter (DOM) represent one important potential driver of tipping points in aquatic ecosystems. This project will investigate whether increases in terrestrial DOM loading can push clear-water oligotrophic lakes beyond a critical tipping point by stimulating hypolimnetic anoxia and sediment DOM and phosphorus release, which may initiate a positive feedback loop of decreasing water clarity, stronger thermal stratification, and enhanced hypolimnetic anoxia. This feedback loop accelerates ecological change and ultimately may shift lake trophic status toward greener, mesotrophic to eutrophic as well as browner, dystrophic conditions. This project will extend a long-term data set of water quality variables sampled since the late 1980s in two lakes in or near the Lacawac Sanctuary and Biological Field Station, located in northeastern Pennsylvania. Complementing these long-term observations, experiments and modeling will be carried out to understand feedbacks associated with browning and enhancing understanding of broader patterns of change in inland water bodies. The project will support a regional lake monitoring network in Pennsylvania and closely interface with GLEON, the Global Lake Ecological Observatory Network.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.