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Your search keyword '"Andreev A.A."' showing total 2 results
Start Over Author "Andreev A.A." Topic diatoms
2 results on '"Andreev A.A."'

1. The Holocene environmental history of a small coastal lake on the north-eastern Kamchatka Peninsula

Author

Solovieva, N., Klimaschewski, A., Self, A.E., Jones, V.J., Andrén, E., Andreev, A.A., Hammarlund., D., Lepskaya, E.V., and Nazarova, L.

Subjects
Diatoms, Global and Planetary Change, Chironomids, Tephra, Pollen, Total phosphorus reconstruction, Kamchatka, Oceanography, Natural eutrophication
Abstract

A radiocarbon and tephra-dated sediment core from Lifebuoy Lake, located on the north-east coast of Kamchatka Peninsula, was analysed for pollen, spores, diatoms, chironomids and tephra in order to uncover regional environmental history.The 6500-year environmental history of Lifebuoy Lake correlates with the broad regional patterns of vegetation development and climate dynamics with both diatoms and chironomids showing near-synchronous changes.Between ca. 6300 and 3900calyrBP, the lake ecosystem was naturally enriched, with several Stephanodiscus species dominating the diatom plankton. This natural eutrophication state is likely to be due to a combination of the base-rich catchment geology, the fertilisation effect of several fires in the catchment, silica input from tephra layers and, possibly, nitrogen input from seabirds. The substantial tephra deposit at about 3850calyrBP might have stopped sedimentary phosphorus from entering the lake water thus decreasing the trophic state of the lake and facilitating the shift in diatom composition to a benthic Fragiliariaceae complex.Both diatoms and chironomids showed simultaneous compositional changes, which are also reflected by statistically significant changes in their rates of change 300–400years after the arrival of Pinus pumila in the lake catchment. The rapid increase in both total diatom concentration and the percentage abundance of the large heavy species, Aulacoseira subarctica might be a response to the change in timing and intensity of lake spring turn-over due to the changes in the patterns of North Pacific atmospheric circulation, most notably westward shift of the Aleutian Low.The two highest peaks in A. subarctica abundance at Lifebouy Lake occurred during opposite summer temperature inferences: the earlier peak (3500–2900calyrBP) coincided with warm summers and the latter peak (300calyrBP–present) occurred during the cold summer period. These imply that A. subarctica shows no direct response to the changes of summer air temperature. Instead, it appears to thrive during the periods of increased winter precipitation, thicker ice and late spring turn-over periods, i.e., shows indirect response to climate.The clearest effect of tephra deposition on the lake ecosystem is above 908cm (ca. 3800calyrBP) where the tephra deposit might have caused the shift from Stephanodiscus-dominated planktonic assemblages to the Fragilariaceae complex of benthic species. Tephra deposits might have also contributed towards the development of eutrophic plankton from about 6300calyrBP. It is not certain if several tephra deposits influenced diatom and chironomid changes during the last 300years.

Published
2015
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2. The relative influences of climate and volcanic activity on Holocene lake development inferred from a mountain lake in central Kamchatka.

Author

Self, A.E., Klimaschewski, A., Solovieva, N., Jones, V.J., Andrén, E., Andreev, A.A., Hammarlund, D., and Brooks, S.J.

Subjects
*VOLCANIC eruptions, *SEDIMENTATION & deposition, *TERRESTRIAL heat flow, *CHIRONOMIDAE
Abstract

A sediment sequence was taken from a closed, high altitude lake (informal name Olive-backed Lake) in the central mountain range of Kamchatka, in the Russian Far East. The sequence was dated by radiocarbon and tephrochronology and used for multi-proxy analyses (chironomids, pollen, diatoms). Although the evolution of Beringian climate through the Holocene is primarily driven by global forcing mechanisms, regional controls, such as volcanic activity or vegetation dynamics, lead to a spatial heterogeneous response. This study aims to reconstruct past changes in the aquatic and terrestrial ecosystems and to separate the climate-driven response from a response to regional or localised environmental change. Radiocarbon dates from plant macrophytes gave a basal date of 7800 cal yr BP. Coring terminated in a tephra layer, so sedimentation at the lake started prior to this date, possibly in the early Holocene following local glacier retreat. Initially the catchment vegetation was dominated by Betula and Alnus woodland with a mosaic of open, wet, aquatic and semi-aquatic habitats. Between 7800 and 6000 cal yr BP the diatom-inferred lake water was pH 4.4–5.3 and chironomid and diatom assemblages in the lake were initially dominated by a small number of acidophilic/acid tolerant taxa. The frequency of Pinus pumila (Siberian dwarf pine) pollen increased from 5000 cal yr BP and threshold analysis indicates that P . pumila arrived in the catchment between 4200 and 3000 cal yr BP. Its range expansion was probably mediated by strengthening of the Aleutian Low pressure system and increased winter snowfall. The diatom-inferred pH reconstructions show that after an initial period of low pH, pH gradually increased from 5500 cal yr BP to pH 5.8 at 1500 cal yr BP. This trend of increasing pH through the Holocene is unusual in lake records, but the initially low pH may have resulted directly or indirectly from intense regional volcanic activity during the mid-Holocene. The chironomid-inferred July temperature reconstruction suggests cool periods between 3200–2800 cal yr BP and 1100–700 cal yr BP and a warmer period between 2800 and 1100 cal yr BP. Chironomid and diatom DCA scores decline from ca. 6000 cal yr BP, indicating compositional changes in these aquatic assemblages. In comparison declines in pollen PCA scores are delayed, starting ca. 5100 cal yr BP. The results suggest that while catchment vegetation was responding primarily to climate change, the biota within the lake and lake water chemistry were responding to localised environmental conditions. [ABSTRACT FROM AUTHOR]

Published
2015
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