Matthews-Bird Frazer, Brooks Stephen J, Gosling William D, Gulliver Pauline, Mothes Patricia, Montoya Encarni
1School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK.
2Department of Biological Sciences, Florida Institute of Technology, 150 West University Blvd, Melbourne, FL 32901 USA.
J Paleolimnol. 2017;58(4):437-453. doi: 10.1007/s10933-017-0001-0. Epub 2017 Oct 5.
Aquatic ecosystems in the tropical Andes are under increasing pressure from human modification of the landscape (deforestation and dams) and climatic change (increase of extreme events and 1.5 °C on average temperatures are projected for AD 2100). However, the resilience of these ecosystems to perturbations is poorly understood. Here we use a multi-proxy palaeoecological approach to assess the response of aquatic ecosystems to a major mechanism for natural disturbance, volcanic ash deposition. Specifically, we present data from two Neotropical lakes located on the eastern Andean flank of Ecuador. Laguna Pindo (1°27.132'S-78°04.847'W) is a tectonically formed closed basin surrounded by a dense mid-elevation forest, whereas Laguna Baños (0°19.328'S-78°09.175'W) is a glacially formed lake with an inflow and outflow in high Andean Páramo grasslands. In each lake we examined the dynamics of chironomids and other aquatic and semi-aquatic organisms to explore the effect of thick (> 5 cm) volcanic deposits on the aquatic communities in these two systems with different catchment features. In both lakes past volcanic ash deposition was evident from four large tephras dated to c.850 cal year BP (Pindo), and 4600, 3600 and 1500 cal year BP (Baños). Examination of the chironomid and aquatic assemblages before and after the ash depositions revealed no shift in composition at Pindo, but a major change at Baños occurred after the last event around 1500 cal year BP. Chironomids at Baños changed from an assemblage dominated by and -type to type-II, and such a dominance lasted for approximately 380 years. We suggest that, despite potential changes in the water chemistry, the major effect on the chironomid community resulted from the thickness of the tephra being deposited, which acted to shallow the water body beyond a depth threshold. Changes in the aquatic flora and fauna at the base of the trophic chain can promote cascade effects that may deteriorate the ecosystem, especially when already influenced by human activities, such as deforestation and dams, which is frequent in the high Andes.
热带安第斯山脉的水生生态系统正面临着越来越大的压力，这些压力来自于人类对景观的改造（森林砍伐和修建水坝）以及气候变化（极端事件增加，预计到公元2100年平均气温将上升1.5摄氏度）。然而，人们对这些生态系统抵御干扰的恢复力了解甚少。在这里，我们采用多指标古生态学方法来评估水生生态系统对自然干扰的一种主要机制——火山灰沉积的响应。具体来说，我们展示了来自厄瓜多尔安第斯山脉东侧两个新热带湖泊的数据。平多湖（南纬1°27.132′-西经78°04.847′）是一个构造形成的封闭盆地，周围环绕着茂密的中海拔森林，而巴尼奥斯湖（南纬0°19.328′-西经78°09.175′）是一个冰川形成的湖泊，在高安第斯帕拉莫草原上有入水口和出水口。在每个湖泊中，我们研究了摇蚊及其他水生和半水生生物的动态，以探究厚（>5厘米）火山沉积物对这两个具有不同集水区特征的系统中水生群落的影响。在这两个湖泊中，过去的火山灰沉积从四个大型火山灰层中清晰可见，平多湖的火山灰层年代约为公元前850年，巴尼奥斯湖的火山灰层年代为公元前4600年、3600年和1500年。对火山灰沉积前后摇蚊和水生生物群落的检查显示，平多湖的群落组成没有变化，但在公元前1500年左右的最后一次事件之后，巴尼奥斯湖发生了重大变化。巴尼奥斯湖的摇蚊从以 型和 型为主的群落转变为以II型为主，这种主导地位持续了大约380年。我们认为，尽管水化学可能发生了变化，但对摇蚊群落的主要影响来自于沉积的火山灰层厚度，它使水体变浅至超过一个深度阈值。营养链底层水生动植物的变化会引发级联效应，可能使生态系统恶化，特别是当生态系统已经受到人类活动（如森林砍伐和修建水坝，这在高安第斯地区很常见）影响时。
