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Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

Frings, Patrick LU ; Clymans, Wim LU ; Jeppesen, Erik; Lauridsen, Torben L.; Struyf, Eric and Conley, Daniel LU (2014) In Biogeochemistry 117(2-3). p.255-277
Abstract
Weathering of silicate minerals releases dissolved silicate (DSi) to the soil-vegetation system. Accumulation and recycling of this DSi by terrestrial ecosystems creates a pool of reactive Si on the continents that buffers DSi export to the ocean. Human perturbations to the functioning of the buffer have been a recent research focus, yet a common assumption is that the continental Si cycle is at steady-state. However, we have no good idea of the timescales of ecosystem Si pool equilibration with their environments. A review of modelling and geochemical considerations suggests the modern continental Si cycle is in fact characterised in the long-term by an active accumulation of reactive Si, at least partially attributable to lakes and... (More)
Weathering of silicate minerals releases dissolved silicate (DSi) to the soil-vegetation system. Accumulation and recycling of this DSi by terrestrial ecosystems creates a pool of reactive Si on the continents that buffers DSi export to the ocean. Human perturbations to the functioning of the buffer have been a recent research focus, yet a common assumption is that the continental Si cycle is at steady-state. However, we have no good idea of the timescales of ecosystem Si pool equilibration with their environments. A review of modelling and geochemical considerations suggests the modern continental Si cycle is in fact characterised in the long-term by an active accumulation of reactive Si, at least partially attributable to lakes and reservoirs. These lentic systems accumulate Si via biological conversion of DSi to biogenic silica (BSi). An analysis of new and published data for nearly 700 systems is presented to assess their contribution to the accumulating continental pool. Surface sediment BSi concentrations (n = 692) vary between zero and > 60 % SiO2 by weight, apparently independently of lake size, location or water chemistry. Using sediment core BSi accumulation rates (n = 109), still no relationships are found with lake or catchment parameters. However, issues associated with single-core accumulation rates should in any case preclude their use in elemental accumulation calculations. Based on lake/reservoir mass-balances (n = 34), our best global-scale estimate of combined lake and reservoir Si retention is 1.53 TMol year(-1), or 21-27 % of river DSi export. Again, no scalable relationships are apparent, suggesting Si retention is a complex process that varies from catchment to catchment. The lake Si sink has implications for estimation of weathering flux generation from river chemistry. The size of the total continental Si pool is poorly constrained, as is its accumulation rate, but lakes clearly contribute substantially. A corollary to this emerging understanding is that the flux and isotopic composition of DSi delivered to the ocean has likely varied over time, partly mediated by a fluctuating continental pool, including in lakes. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Silica cycle, Biogenic silica, Lake retention, Silicon isotopes
in
Biogeochemistry
volume
117
issue
2-3
pages
255 - 277
publisher
Springer
external identifiers
  • wos:000333703400003
  • scopus:84897435262
ISSN
1573-515X
DOI
10.1007/s10533-013-9944-z
project
BECC
language
English
LU publication?
yes
id
44e564ef-a5c7-4e4e-b68c-d497fd215c72 (old id 4495831)
date added to LUP
2014-06-23 13:02:29
date last changed
2017-09-24 03:22:10
@article{44e564ef-a5c7-4e4e-b68c-d497fd215c72,
  abstract     = {Weathering of silicate minerals releases dissolved silicate (DSi) to the soil-vegetation system. Accumulation and recycling of this DSi by terrestrial ecosystems creates a pool of reactive Si on the continents that buffers DSi export to the ocean. Human perturbations to the functioning of the buffer have been a recent research focus, yet a common assumption is that the continental Si cycle is at steady-state. However, we have no good idea of the timescales of ecosystem Si pool equilibration with their environments. A review of modelling and geochemical considerations suggests the modern continental Si cycle is in fact characterised in the long-term by an active accumulation of reactive Si, at least partially attributable to lakes and reservoirs. These lentic systems accumulate Si via biological conversion of DSi to biogenic silica (BSi). An analysis of new and published data for nearly 700 systems is presented to assess their contribution to the accumulating continental pool. Surface sediment BSi concentrations (n = 692) vary between zero and > 60 % SiO2 by weight, apparently independently of lake size, location or water chemistry. Using sediment core BSi accumulation rates (n = 109), still no relationships are found with lake or catchment parameters. However, issues associated with single-core accumulation rates should in any case preclude their use in elemental accumulation calculations. Based on lake/reservoir mass-balances (n = 34), our best global-scale estimate of combined lake and reservoir Si retention is 1.53 TMol year(-1), or 21-27 % of river DSi export. Again, no scalable relationships are apparent, suggesting Si retention is a complex process that varies from catchment to catchment. The lake Si sink has implications for estimation of weathering flux generation from river chemistry. The size of the total continental Si pool is poorly constrained, as is its accumulation rate, but lakes clearly contribute substantially. A corollary to this emerging understanding is that the flux and isotopic composition of DSi delivered to the ocean has likely varied over time, partly mediated by a fluctuating continental pool, including in lakes.},
  author       = {Frings, Patrick and Clymans, Wim and Jeppesen, Erik and Lauridsen, Torben L. and Struyf, Eric and Conley, Daniel},
  issn         = {1573-515X},
  keyword      = {Silica cycle,Biogenic silica,Lake retention,Silicon isotopes},
  language     = {eng},
  number       = {2-3},
  pages        = {255--277},
  publisher    = {Springer},
  series       = {Biogeochemistry},
  title        = {Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration},
  url          = {http://dx.doi.org/10.1007/s10533-013-9944-z},
  volume       = {117},
  year         = {2014},
}