Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, USA.
Cary Institute of Ecosystem Studies, Millbrook, NY 12545, USA.
Proc Biol Sci. 2020 Jul 8;287(1930):20200304. doi: 10.1098/rspb.2020.0304.
While deposition of reactive nitrogen (N) in the twentieth century has been strongly linked to changes in diatom assemblages in high-elevation lakes, pronounced and contemporaneous changes in other algal groups suggest additional drivers. We explored the origin and magnitude of changes in two mountain lakes from the end of the Little Ice Age at 1850, to 2010, using lake sediments. We found dramatic changes in algal community abundance and composition. While diatoms remain the most abundant photosynthetic organisms, concentrations of diatom pigments decreased while pigments representing chlorophytes increased 200-300% since 1950 and total algal biomass more than doubled. Some algal changes began 1900 but shifts in most sedimentary proxies accelerated 1950 commensurate with many human-caused changes to the Earth System. In addition to N deposition, aeolian dust deposition may have contributed phosphorus. Strong increases in summer air and surface water temperatures since 1983 have direct and indirect consequences for high-elevation ecosystems. Such warming could have directly enhanced nutrient use and primary production. Indirect consequences of warming include enhanced leaching of nutrients from geologic and cryosphere sources, particularly as glaciers ablate. While we infer causal mechanisms, changes in primary producer communities appear to be without historical precedent and are commensurate with the post-1950 acceleration of global change.
虽然在 20 世纪，活性氮 (N) 的沉积与高海拔湖泊中硅藻组合的变化密切相关，但其他藻类群体的明显和同时变化表明存在其他驱动因素。我们使用湖泊沉积物，探索了两座高山湖泊自小冰期结束（1850 年）到 2010 年的变化起源和幅度。我们发现藻类群落丰度和组成发生了巨大变化。虽然硅藻仍然是最丰富的光合生物，但自 1950 年以来，硅藻色素的浓度下降了，而代表绿藻的色素增加了 200-300%，总藻类生物量增加了一倍多。一些藻类变化始于 1900 年，但自 1950 年以来，大多数沉积物替代物的变化加速了，这与地球系统中许多人为变化是一致的。除了氮沉积，风成尘埃沉积可能也提供了磷。自 1983 年以来，夏季空气和地表水温的强烈增加对高海拔生态系统产生了直接和间接的影响。这种变暖可能直接增强了养分利用和初级生产力。变暖的间接后果包括来自地质和冰冻圈源的养分淋溶增加，特别是随着冰川消融。虽然我们推断了因果机制，但初级生产者群落的变化似乎没有历史先例，与 1950 年后全球变化的加速是相称的。
