Paleoecological Environmental Assessment and Research Laboratory (PEARL), Department of Biology, Queen's University, Kingston, ON, K7L 3J9, Canada.
Department of Ecology and Environmental Science, Umeå University, 90187, Umeå, Sweden.
Sci Rep. 2019 Nov 13;9(1):16676. doi: 10.1038/s41598-019-52912-0.
Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland waters across northern Europe and northeastern North America. This inland-water "browning" has profound physical, chemical and biological repercussions for aquatic ecosystems affecting water quality, biological community structures and aquatic productivity. Potential drivers of this "browning" trend are complex and include reductions in atmospheric acid deposition, changes in land use/cover, increased nitrogen deposition and climate change. However, because of the overlapping impacts of these stressors, their relative contributions to DOC dynamics remain unclear, and without appropriate long-term monitoring data, it has not been possible to determine whether the ongoing "browning" is unprecedented or simply a "re-browning" to pre-industrial DOC levels. Here, we demonstrate the long-term impacts of acid deposition and climate change on lake-water DOC concentrations in low and high acid-deposition areas using infrared spectroscopic techniques on ~200-year-long lake-sediment records from central Canada. We show that acid deposition suppressed naturally higher DOC concentrations during the 20th century, but that a "re-browning" of lakes is now occurring with emissions reductions in formerly high deposition areas. In contrast, in low deposition areas, climate change is forcing lakes towards new ecological states, as lake-water DOC concentrations now often exceed pre-industrial levels.
溶解有机碳 (DOC) 浓度和水色在北欧和北美东北部的许多内陆水域中都在增加。这种内陆水域的“褐变”对水生生态系统产生了深远的物理、化学和生物学影响，影响水质、生物群落结构和水生生产力。这种“褐变”趋势的潜在驱动因素很复杂，包括大气酸沉降减少、土地利用/覆盖变化、氮沉降增加和气候变化。然而，由于这些胁迫因素的重叠影响，它们对 DOC 动态的相对贡献仍不清楚，而且由于缺乏适当的长期监测数据，无法确定正在进行的“褐变”是否是前所未有的，还是仅仅是恢复到工业化前的 DOC 水平。在这里，我们使用来自加拿大中部约 200 年历史的湖泊沉积物记录中的红外光谱技术，展示了酸沉降和气候变化对低酸沉降和高酸沉降地区湖泊水中 DOC 浓度的长期影响。我们表明，酸沉降在 20 世纪抑制了自然状态下较高的 DOC 浓度，但在以前高沉降地区排放量减少的情况下，湖泊正在发生“再褐变”。相比之下，在低沉降地区，气候变化正在迫使湖泊进入新的生态状态，因为湖泊水中的 DOC 浓度现在经常超过工业化前的水平。
