Historical anthropogenic mercury in two lakes of Central Chile: comparison between an urban and rural lake

Abstract

Mercury concentrations in the environment tend to decrease in recent years due to environmental restrictions. Lakes store mercury in their sediments, making them potential secondary contamination sources. In South America, the occurrence of mercury in lake systems has been associated mainly with volcanic emissions and only few records anthropogenic contamination in the pre-Hispanic period. The objective of this research was to study historical anthropogenic mercury concentration in two lakes in Central Chile (La Señoraza and Pillo), in order to establish background mercury levels and their variations from preindustrial to modern periods. Different background levels and mercury concentrations were found in each lake, with significantly higher concentrations in Lake La Señoraza during the last 150 years. Mining-related activities during the nineteenth century could have a negligible influence on mercury concentrations. Later on, the use of coal railroads and subsequent employment of mercury in the cellulose industry were associated with three- and fourfold increases in mercury concentration over the nineteenth century background levels, which decrease once these activities ceased. However, in the case of Lake Pillo, an important increase in mercury concentration can be observed between 1990 and the early twenty-first century, which could be related to a higher watershed/lake area ratio, extensive agriculture, and volcanic emission, being the latter that could have contributed with mercury to both systems. Nevertheless, sedimentological characteristics in Lake Pillo can be favorable to retain mercury in this aquatic system up to the present day.

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

“…The relative pattern of rural Lake Pillo is similar too, but absolute values are up to ten times higher. Peri-urban Lake Llaviucu’s post-1950 Hg flux pattern on the other hand shows similarities to the one observed in urban Lake Señoraza (south-central Chile; Álvarez et al 2018 ) with a temporary peak at around 1980 and a decrease thereafter. Absolute peak fluxes (from 160 up to 177 μg m −2 year −1 ) are comparable to those measured in Lake Señoraza, a lake which is highly influenced by urban activities.…”

“…1760 to 2014) show some differences to profiles reported from the northern hemisphere (mostly a delayed modern-era onset; Perry et al 2005 ; Engstrom et al 2014 ; Sarkar et al 2015 ; Yang et al 2016 ; Engels et al 2018 ). The delayed onset of steep increases of Hg fluxes in recent times, however, was also observed in other sites from South America (Peru: Beal et al 2013 ; Chile: Álvarez et al 2018 , Guédron et al 2019 ; Hermanns and Biester 2013 ).…”

“…The post-1950 period of Lake Fondococha resembles the profiles of Peruvian lakes (Beal et al 2013 ), Lake Chungará (northern high-altitude Chilean Andes; Guédron et al 2019 ), and rural Lake Pillo (south-central Chile, low-altitude; Álvarez et al 2018 ). For example, Lake Fondococha’s peak Hg flux values observed in the post-1950 period (from 24 to 33 μg m −2 year −1 ) correspond very well to those seen in Lake Chungará during the industrial era.…”

“…Lake sediments are very valuable environmental archives for documenting past deposition of trace elements and Hg from natural and anthropogenic activities (Smol 2008 ; Boyle et al 2015 ). Most of the high-resolution Hg records span the 210 Pb dating range of the past 150 years, and the study sites are predominantly located in the mid- and high-latitude areas of the northern hemisphere, with very few records in the southern hemisphere mid-latitudes and the inner tropics (Perry et al 2005 ; Biester et al 2007 ; Cooke et al 2009 ; Beal et al 2013 ; Beal et al 2014 ; Engstrom et al 2014 ; Álvarez et al 2018 ; Engels et al 2018 ; Guédron et al 2018 ; Guédron et al 2019 ). A majority of the sediment records from the northern hemisphere reveal an overall 2–5-fold increase of Hg deposition rates from pre-industrial to modern (1950–2000+) times (Fitzgerald et al 1998 ; Landers et al 1998 ; Perry et al 2005 ; Biester et al 2007 ; Mast et al 2010 ; Pirrone et al 2010 ; Beal et al 2013 ; Engstrom et al 2014 ) and provide critically important information about “natural” background and anthropogenic depositional rates for times long before direct measurements became available.…”