A spatiotemporal investigation of varved sediments highlights the dynamics of hypolimnetic hypoxia in a large hard-water lake over the last 150 years - Archive ouverte HAL Access content directly
Journal Articles Limnology and Oceanography Year : 2013

A spatiotemporal investigation of varved sediments highlights the dynamics of hypolimnetic hypoxia in a large hard-water lake over the last 150 years

Olivier Romeyer
  • Function : Author

Abstract

The spatiotemporal distribution of biochemical varves spanning the last 150 yr was investigated using 40 cores collected over a depth gradient in a large subalpine lake--Lake Bourget--in the French Alps. Four-dimensional sedimentological, biological, and geochemical analyses show that varve preservation can be used as a reliable proxy to reconstruct annual-to-decadal oscillations of hypoxia in large lakes. The volume of hypoxic waters was calculated by integrating the volume between the lake bottom and the depth of the shallowest varve-bearing core for each year. Although Lake Bourget bottom waters have been oxic over the last 9000 yr, severe hypoxia has occurred only since 1933 ± 1. The volume of hypoxic waters showed, thereafter, a succession of pronounced fluctuations, leading to an increase of 8% of the total lake volume in the 1960s, a decline in the 1980s, and a second, ongoing increase since 1990. Whereas the initial onset of persistent hypoxic conditions could be attributed to eutrophication due to nutrient-rich inputs from sewage water and/or diffuse contamination, the later fluctuations were also driven by climatic factors, i.e., flooding, rising air temperatures, and phosphorus-independent changes in primary production. Hence, cumulative effects related to global warming seem to have driven hypolimnetic hypoxic conditions since equilibrium was initially disrupted due to a drastic shift in the trophic state.

Dates and versions

halsde-00927752 , version 1 (13-01-2014)

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Jean-Philippe Jenny, Fabien Arnaud, Jean-Marcel Dorioz, Charline Giguet-Covex, Victor Frossard, et al.. A spatiotemporal investigation of varved sediments highlights the dynamics of hypolimnetic hypoxia in a large hard-water lake over the last 150 years. Limnology and Oceanography, 2013, 58 (4), pp. 1395-1408. ⟨10.4319/lo.2013.58.4.1395⟩. ⟨halsde-00927752⟩
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