Abstract
The Atacama Desert (21–26°S) is currently one of the driest places on Earth and metal(loid)s are of special concern for this region, which hosts the largest-known porphyry copper deposits produced in Chile. Evidence of past environmental conditions is commonly preserved in natural archives, such as lacustrine sediments. Sediment records obtained from Inca Coya Lake (22°20’S-68°35’W, 2534 m.a.s.l.), a small lake located in the Atacama Desert, reflected the evolution of regional mining activity during the 20th century and sedimentation associated with decadal climate variability. We studied the aquatic community structure changes recorded in sediment records from Inca Coya Lake. By analysis of magnetic properties (susceptibility, hysteresis curves and Curie temperatures), grain size and geochemical composition of the sediments, we identified environmental periods and changes in the community of benthic and planktonic organisms (diatoms and diapausing egg bank). We identified three detrital episodes that we interpret as dry/wet phases during the last 90 years associated with the increase of flash flood events promoting hypoxia oscillations; anthropogenic (mining activity) signals were also identified. Invertebrate community structure (primary consumers) reflected the metal exposure, measured as changes in assemblage composition through species turnover. Diatom community composition was best associated with variables related to wetter/drier alternation and consequent changes in oxygen availability. Bioindicators analyzed (diatoms, diapausing egg bank and invertebrate community) demonstrated to be excellent indicators of the bioavailability of compounds in the aquatic ecosystem of Inca Coya Lake, allowing the environmental impact assessment of the water resources due to flash floods and mining activity in the driest desert of the world.
Highlights
Anthropogenic metal contamination can be an intense stressor on ecosystems and driver of biological population evolution in polluted environments [1, 2]
In previous experimental studies driven in laboratory conditions, we have shown that diapause strategies in rotifer species isolated from Inca Coya Lake are dependent on metal(oid)s exposure and that the pattern of eggs production may modulate the community structure [28]
Our results suggest that both factors, climate and metal(loid)s exposure would act as modulators of aquatic community structure, where alternation of wetter/drier events and their consequent changes in oxygen availability make a bottom-up control and the differential sensitivity to metal(loids) exposure would impact on higher trophic levels of aquatic community
Summary
Anthropogenic metal contamination can be an intense stressor on ecosystems and driver of biological population evolution in polluted environments [1, 2]. A paleoecological approach including different trophic groups as paleoindicators will contribute to a better understanding of what environmental variables have affected lake systems and how these variables have impacted the structure of ecological communities. Diapausing egg banks provide an excellent system for reconstructing conditions experienced before and during diapause, because layered deposits retain both diapausing eggs and traces of the chemical and biological conditions present in the water column at the time of deposition [9] These records allow tracking historical environmental changes by the ecological and evolutionary responses of populations and past zooplankton communities to those conditions [4, 10,11,12,13]. Studies have assessed experimentally the effects of metal(loid)s, among other toxicants, on the life cycle of rotifers [14, 15], showing that specific life history traits associated with diapausing egg production and egg bank hatchability are the most sensitive endpoints to assess metals toxicity in rotifers, and temporal changes in the structure of diapausing egg banks may be associated with changes in the metal(loid) concentrations in the environments
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