Aquatic community response to volcanic eruptions on the Ecuadorian Andean flank: evidence from the palaeoecological record

Frazer Matthews-Bird; Stephen J Brooks; William D Gosling; Pauline Gulliver; Patricia Mothes; Encarni Montoya

doi:10.1007/s10933-017-0001-0

Aquatic community response to volcanic eruptions on the Ecuadorian Andean flank: evidence from the palaeoecological record

J Paleolimnol. 2017;58(4):437-453. doi: 10.1007/s10933-017-0001-0. Epub 2017 Oct 5.

Authors

Frazer Matthews-Bird^{1

2}, Stephen J Brooks³, William D Gosling^{1

4}, Pauline Gulliver⁵, Patricia Mothes⁶, Encarni Montoya^{1

7}

Affiliations

¹ 1School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK.
² 2Department of Biological Sciences, Florida Institute of Technology, 150 West University Blvd, Melbourne, FL 32901 USA.
³ 3Life Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD UK.
⁴ 4Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Postbus 94248, 1090 GE Amsterdam, The Netherlands.
⁵ NERC Radiocarbon Facility (East Kilbride), SUERC, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, G75 OQF Scotland, UK.
⁶ 6Instituto Geofísico, Escuela Politécnica Nacional, Ladrón de Guevara E11-19 253, Apartado, 1701-2759 Quito, Ecuador.
⁷ 7Institute of Earth Sciences Jaume, Almera (ICTJA-CSIC), Sabaris s/n, c/Sole, 08028 Barcelona, Spain.

Abstract

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 Pseudochironomus and Polypedilum nubifer-type to Cricotopus/Paratrichocladius 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.

Keywords: Chironomids; Lake sediment burial; Long-term changes; Non-Pollen Palynomorphs (NPP); Sensitivity; Tephras.