Climate Change Forces New Ecological States in Tropical Andean Lakes

Abstract

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.

Assessing the effects of climate and volcanism on diatom and chironomid assemblages in an Andean lake near Quito, Ecuador

“…This depth is within the range of the unsupported/supported 210 Pb horizon recorded in other cores from the tropical Andes (Michelutti et al, 2015a(Michelutti et al, , 2015b, but should be viewed with caution.…”

“…Often the response to temperature is indirect and caused by fundamental changes to limnological variables such as thermal stability and stratification, habitat alteration, and the availability of light and nutrient resources (Rühland et al, 2015). Nonetheless, when long-term meteorological data are available to compare with paleolimnological data, the timing of biotic assemblage shifts often corresponds with the onset of temperature increases (Michelutti et al, 2015b;Rühland et al, 2013;Antoniades et al, 2005).…”

“…1). In previous paleolimnological investigations in the Andes, we recorded marked changes in diatom and chrysophyte algae in response to recent warming in the southern sierra of Ecuador near Cuenca (Michelutti et al, 2015b) and in the cordillera central of Peru, southeast of Lima (Michelutti et al, 2015a). Laguna Baños was selected for investigation as it is located near the equator from a region with little information on the response of aquatic ecosystems to recent climate change.…”

“…In the Andes, diatom assemblages have been shown to respond sensitively to recent climatic change (Michelutti et al, 2015a(Michelutti et al, , 2015b, but far less research has been done on the response of chironomids, especially in paleolimnological studies (e.g., Williams et al, 2012;Urrutia et al, 2010). The reconstruction of fossil records from both diatom and chironomid assemblages allows us to compare the timing and magnitude of responses between bio-indictors at two trophic levels.…”

Rapid decline of snow and ice in the tropical Andes – Impacts, uncertainties and challenges ahead

“…While projected future changes in Andean biomes due to climate change remain somewhat uncertain (Tovar et al, 2013), there are many impacts of climate change on Andean ecosystems that are already being felt, such as the upslope migration of the Andean timberline, ecotones and vegetation zones and increasing continental insularity (Feeley and Silman, 2010;Feeley et al, 2011;Anderson et al, 2011;Lutz et al, 2013;Anthelme et al, 2014;Morueta-Holme et al, 2015;Zimmer et al, 2017), changes in species composition of lake ecosystems (Michelutti et al, 2015) or emergence of new invasive species, pests and vectorborne disease (e.g. Seimon et al, 2007;Dangles et al, 2008;Siraj et al, 2014).…”