250-year records of mercury and trace element deposition in two lakes from Cajas National Park, SW Ecuadorian Andes

Wojciech Tylmann,Pablo V Mosquera,Henrietta Hampel,Adrien Mestrot,Hendrik Vogel,Lea Fränkl,Tobias Schneider,Moritz Bigalke,Martin Grosjean,Benjamin A Musa Bandowe,Giulia Wienhues

doi:10.1007/s11356-020-11437-0

Abstract

Historical records of trace elements in lake sediments provide source-to-sink information about potentially toxic pollutants across space and time. We investigated two lakes located at different elevations in the Ecuadorian Andes to understand how trace element fluxes are related to (i) geology, (ii) erosion in the watersheds, and (iii) local point sources and atmospheric loads. In remote Lake Fondococha (4150 m a.s.l.), total Hg fluxes stay constant between ca. 1760 and 1950 and show an approximately 4.4-fold increase between pre-1950 and post-1950 values. The post-1950 increase in fluxes of other trace elements (V, Cr, Co, Ni, Cu, Zn, As, Cd, and Pb) is lower (2.1–3.0-fold) than for Hg. Mostly lithogenic sources and enhanced soil erosion contribute to their post-1950 increase (lithogenic contribution: > 85%, Hg: ~ 58%). Average post-1950 Hg fluxes are approximately 4.3 times higher in peri-urban Lake Llaviucu (3150 m a.s.l.) than in the remote Lake Fondococha. Post-1950 fluxes of the other trace elements showed larger differences between Lakes Fondococha and Llaviucu (5.2 < 25–29.5-fold increase; Ni < Pb–Cd). The comparison of the post-1950 average trace element fluxes that are derived from point and airborne sources revealed 5–687 (Hg–Pb) times higher values in Lake Llaviucu than in Lake Fondococha suggesting that Lake Llaviucu’s proximity to the city of Cuenca strongly influences its deposition record (industrial emissions, traffic, caged fishery). Both lakes responded with temporary drops in trace element accumulations to park regulations in the 1970s and 1990s, but show again increasing trends in recent times, most likely caused by increase in vehicular traffic and openings of copper and gold mines around Cajas National Park.

Highlights

Trace elements in the environment are a global concern, due to their potential toxicity to living organisms (Tchounwou et al 2012; Beal et al 2014; Sundseth et al 2017) and their effects on environmental processes (Chojnacka 2018)
Guided by the scientific challenges mentioned above, we addressed the following questions in the present study: (i) What is the temporal pattern of Hg and other trace elements deposition in two lakes over the past approximately 250 years? Are the source patterns for Hg different from other trace elements that are mostly bound to particulate aerosols? (ii) What is the role of anthropogenic emissions and increased erosion in the catchment, and which part may be attributed to point sources, local sources from the city of Cuenca, or long-distance atmospheric transport?
The general trends compare well and both profiles do reveal a rapid mass accumulation rates (MARs) increase starting at ca. 1950, a significant MAR decrease between 1985 and ca. 1992 and thereafter again a slight MAR increase towards 2014

Summary

Introduction

Trace elements (here V, Cr, Co, Ni, Cu, Zn, As, Cd, Pb, and Hg) in the environment are a global concern, due to their potential toxicity to living organisms (Tchounwou et al 2012; Beal et al 2014; Sundseth et al 2017) and their effects on environmental processes (Chojnacka 2018). The least volatile elements can be bound to large particles and are mostly deposited close to their point sources whereas the more volatile ones (gaseous; such as Hg) may be transported over long distances in the atmosphere (Schroeder and Munthe 1998; Phillips et al 2011) This leads to pronounced spatial and temporal variability of depositional rates across the world (Selin et al 2008; Strode et al 2009; Streets et al 2011; Engstrom et al 2014; Cooke and Bindler 2015)

Methods

Results

Discussion

Conclusion