Climate Change Forces New Ecological States in Tropical Andean Lakes

Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global average over recent decades. However, the effects of climate change on Andean lakes, which are vital to sustaining regional biodiversity and serve as an important water resource to local populations, remain largely unknown. Here, we show that recent climate changes have forced alpine lakes of the equatorial Andes towards new ecological and physical states, in close synchrony to the rapid shrinkage of glaciers regionally. Using dated sediment cores from three lakes in the southern Sierra of Ecuador, we record abrupt increases in the planktonic thalassiosiroid diatom Discostella stelligera from trace abundances to dominance within the phytoplankton. This unprecedented shift occurs against the backdrop of rising temperatures, changing atmospheric pressure fields, and declining wind speeds. Ecological restructuring in these lakes is linked to warming and/or enhanced water column stratification. In contrast to seasonally ice-covered Arctic and temperate alpine counterparts, aquatic production has not increased universally with warming, and has even declined in some lakes, possibly because enhanced thermal stability impedes the re-circulation of hypolimnetic nutrients to surface waters. Our results demonstrate that these lakes have already passed important ecological thresholds, with potentially far-reaching consequences for Andean water resources.

近数十年来，热带安第斯山脉的气温增速已超过全球平均水平。然而，气候变化对安第斯湖泊的影响仍鲜为人知——这类湖泊既是维持区域生物多样性的核心支撑，亦是当地居民赖以生存的重要水资源。本研究表明，近期的气候变化已迫使赤道安第斯山脉的高山湖泊转向全新的生态与物理状态，这一变化与区域内冰川的快速消融高度同步。本研究借助厄瓜多尔南部山脉三座湖泊的定年沉积物岩芯，观测到浮游海链藻类硅藻（thalassiosiroid diatom）星状盘形藻（Discostella stelligera）的丰度从微量水平陡然跃升至浮游植物群落中的优势类群。这一前所未有的群落转变发生在气温上升、气压场改变以及风速下降的背景之中。这些湖泊的生态系统重构与水温升高及/或水体层化作用增强密切相关。与季节性封冻的北极及温带高山湖泊不同，本研究区域的水生生产力并未随升温普遍提升，部分湖泊的生产力甚至出现下降——这可能是因为增强的热稳定性阻碍了湖下层（hypolimnetic）营养盐向表层水体的再循环。本研究结果表明，这些湖泊已越过关键生态阈值，这或将对安第斯地区的水资源产生深远影响。