Aquatic community structure as sentinel of recent environmental changes unraveled from lake sedimentary records from the Atacama Desert, Chile

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 20 th 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. Citation: Aránguiz-Acuña A, Luque JA, Pizarro H, Cerda M, Heine-Fuster I, Valdés J, et al. (2020) Aquatic community structure as sentinel of recent environmental changes unraveled from lake sedimentary records from the Atacama Desert, Chile. PLoS ONE 15(2): e0229453. https://doi.org/ 10.

Limnological response from high-altitude wetlands to the water supply in the Andean Altiplano

“…On a millennial scale, wetter to drier periods have been identified from lake sediments using a multiproxy approach that included the analysis of isotopic and magnetic properties and the study of biological proxies such as fossil plant cover and diatom assemblages, as recorded from the Salar de Uyuni sediments 21 , 22 and Lake Titicaca 23 , 24 . For shorter timescales, decadal phenomena such as the ENSO have been identified through sedimentary records 25 , as have recent anthropic disturbances including the intensive mining activities in the Atacama Desert on lacustrine sediments and the biotic communities of the Inca Coya Lake 26 , 27 and the Ascotán salt flat 28 .…”

The role of the non‐stationary Andean Dry Diagonal in paleoclimate reconstructions

“…It is subject to both summer and winter precipitation excesses and therefore represents a critical archive of the ADD and ENSO. Cerda et al (2019) and Aránguiz‐Acuña et al (2020) interpret two sediment cores from this lake based at least in part on the Calama precipitation record suggesting that EN is the principal control, but as shown above the Calama record is largely a mirror image of that at Chiu Chiu with wet, winter El Niño precipitation more frequent in Calama and wet, summer La Niña precipitation more frequent in Chiu Chiu. Laguna Inca Coya is a sinkhole formed in Opache Formation limestones, overlain by the Chiu Chiu Formation silty clays and calcretes.…”

“…The sediments at the base of the lake show alternations between sand rich layers with increased Cl, Ca and As, and silty clay layers with increased Fe, K and Si. Cerda et al (2019) and Aránguiz‐Acuña et al (2020) interpret these layers as flood events from the east, alternating with aeolian deposition from westerly winds, whereas a more nuanced interpretation might be that these layers represent localized intense precipitation runoff with (increased) groundwater flow, alternating with low‐energy infrequent runoff and/or aeolian deposition from the Chiu Chiu Formation. Moreover, the fit between assumed flood events and the PDO and/or EN is not clear, so that the paleoclimate archive contained in cores from this lake would likely be improved by taking into account the provenance of sediment infill in relation to catchment, and the full range of potential catchment variation in EN‐LN, PDO and Atlantic SST, as well as meridional shifts in the ADD.…”

Differentiation of Diatom Guilds in Extreme Environments in the Andean Altiplano

“…Grain characteristics may be associated with the lowest abundance, diversity, and richness of motile diatoms present in Ascotán. In contrast, Carcote, dominated by finergrained sediments, such as silt and clay, is associated with precipitation of mainly authigenic material (Aránguiz-Acuña et al, 2020;Flores-Varas et al, 2021;García-Sanz et al, 2021), on which unattached diatoms are more likely to settle (Smucker and Vis, 2010). It has been suggested that depositional habitats are advantageous for motile diatoms because their raphes allow them to avoid being smothered by sediments (Stevenson and Bahls, 1999).…”