Impact of climate change and industrialization on remote Lake Bolshoe Toko, Siberia

<p>To test if recent climate change and pollution affected remote lake ecosystems without direct human influence, we used paleolimnological methods on lake sediments from a large, prestine, and deep lake in Yakutia, Russia. We compared diatoms and sediment-geochemistry from before and after the onset of industrialization in the mid-nineteenth century, at water depths between 12.1 and 68.3 m in Lake Bolshoe Toko. We analyzed diatom species changes and geochemical changes including mercury concentrations. Chronologies were established using <sup>210</sup>Pb and <sup>137</sup>Cs revealing sedimentation rates between 0.018 and 0.033 cm y<sup>-1</sup> at shallow- and deep-water sites, respectively. Increase in light planktonic diatoms (<em>Cyclotella</em>) and decrease in heavily silicified euplanktonic <em>Aulacoseira</em> through time at deep-water sites can be related to warming air temperatures and shorter periods of lake-ice cover, causing pronounced thermal stratification. Diatom beta diversity changed only significantly in shallow-water communities which can be related to the development of new habitats with macrophyte growth. Mercury concentrations increased by a factor of 1.6 as a result of atmospheric fallout. Increases in the chrysophyte <em>Mallomonas</em> indicates a trend towards acidification. We conclude that also remote boreal lakes are susceptible to human-induced long-distance pollution and recent climate change.</p>

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

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.