Holocene environments in the Middle Urals: Palaeolimnological proxies from the Lake Tavatui (Russia)

Abstract

New palaeolimnological proxies from the Lake Tavatui sediments core contributed to the reconstruction of the Middle Urals environments from over 11.9 cal ka BP and estimation of the main drivers of the lake ecosystem changes.The comparison of diatom and pollen records enables a more robust and detailed reconstruction of the Holocene Middle Urals environments than the ones previously available. In most cases, the Lake Tavatui pollen and diatom data were in a good agreement and complemented each other. The diatom and pollen records reflect cold and rather dry conditions at 11.9–11.65 cal ka BP, climate warming and slight increase in effective moisture between 11.65 and 10.35 cal ka BP. The climate got colder at 10.35–7.9 cal ka BP. The warming with a great increase in effective moisture at 7.9–6.5 cal ka BP was followed by cooling at 6.5–4.6 cal ka BP. The period from 4.6 to 3.0 cal ka BP was marked by slight warming and unstable conditions. The subsequent cooling continued from 3.0 to 1.3 cal ka BP. The pollen and diatom data reconstructions for the period between 1.3 cal ka BP and 2009 AD are controversial possibly due to human impact on the lake and catchment.The analysis of the diatom assemblages as well as diatom inferred total phosphorus (DI–TP) and electrical conductivity (DI–EC) made it possible to determine five main development stages of the Lake Tavatui. According to the quantitative reconstruction, Lake Tavatui remained in the freshwater range with DI–EC variation from 75 to 290 μS cm−1 throughout the lake development. The trophic status changed many times and varied between oligo-mesotrophic and eutrophic. The highest DI–TP values were observed for the period between 7.9 and 6.5 cal ka BP and since the 1990s. Until 1932-1943 AD, shifts in the lake ecosystem can be explained by direct and catchment-mediated natural climate change. From the mid-nineteenth century, the lake water phosphorus content changed in accordance with the main trend of increasing annual temperature. From 1932–1943 AD the main driver of DI–TP variations was the delivery of catchment-derived nutrients into the lake, which increased in periods with high precipitation. This change in the lake ecosystem response to climatic parameters could be associated with human impact which contributed to nutrients content in the catchment.