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

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

doi:10.1007/s10933-017-0001-0

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.

Highlights

Explosive volcanic eruptions eject large amounts of silicate rock particles, known as tephra, into the Earth’s atmosphere, which can eventually be deposited within the sediments of aquatic ecosystems
Based on the X-Ray Fluorescence (XRF) data (Table 2 and ESM3), 14C dating chronology (Fig. 2) and visual examination of minerals contained in the inorganic sediments analysed (ESM4), we suggest that tephras BAN OS T1a and BAN OS T1b are from the same volcanic eruption, BAN OS T1b being the original deposition and BAN OS T1a a further input caused by either sediment collapse of the surrounding slopes or sediment arrival by inflow of upstream waters
Volcanism has been a constant feature of Quaternary environments in the tropical Andes

Summary

Introduction

Explosive volcanic eruptions eject large amounts of silicate rock particles, known as tephra, into the Earth’s atmosphere, which can eventually be deposited within the sediments of aquatic ecosystems. The environmental effects of tephra deposition, on the benthic biota of the aquatic community, are difficult to quantify and are likely location specific (Telford et al 2004). Modern monitoring studies have identified a detrimental effect of tephra on aquatic ecosystems after a volcanic eruption (Kurenkov 1966; Fazlullin et al 2000; Collier 2002), often these studies do not cover a sufficient time frame to understand the lasting longterm effects on the aquatic communities (Telford et al 2004). A more detailed understanding of the long-term effects of volcanism on aquatic habitats can help inform conservation and mitigation strategies. We use the palaeoecological record of two lakes to understand the long-term effects of volcanism in the high Andes, along the eastern Andean flank of Ecuador

Methods

Discussion

Conclusion