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，如清洁饮用水和生产性渔业。然而，许多湖泊现在正在经历碳和营养物质输入的增加，气温变暖，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。具体地说，美国各地的许多湖泊正经历着越来越多的褐变，这是因为从陆地植物中淋洗出的有机物质负荷很高。布朗宁降低了水的透明度，并干扰了饮用水管理实践。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会降低湖泊中氧气浓度的假设。低氧会导致湖泊沉积物释放营养物质，这可能会增加藻类的繁殖，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了解，并改善对湖泊将如何随着周围环境变化而变化的预测。这项研究还将培训研究生和本科生，并将使公众更好地了解湖泊水质面临的威胁。随着人类活动迅速改变自然生态系统，生态转折点是至关重要的。溶解有机物(DOM)的变化是水生生态系统转折点的一个重要潜在驱动因素。该项目将调查陆地DOM负荷的增加是否会通过刺激低磁缺氧和沉积物DOM和磷的释放，从而推动清水贫营养化湖泊超过临界转折点，这可能会启动一个正反馈循环，导致水透明度下降，温度层结增强，以及低磁缺氧加剧。这种反馈循环加速了生态变化，最终可能会将湖泊的营养状态向更绿色的中营养状态转变为富营养状态，以及棕色营养不良状态。该项目将扩展自20世纪80年代末以来在宾夕法尼亚州东北部拉卡瓦克保护区和生物野外站内或附近的两个湖泊中采样的水质变量的长期数据集。作为对这些长期观察的补充，将进行实验和建模，以了解与褐化有关的反馈，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络GLEON密切联系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.