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| Titel |
Impact of long term wetting on pore water chemistry in a peat bog in Ontario, Canada |
| VerfasserIn |
Jonas Schaper, Christian Blodau, Klaus Holger Knorr |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072395
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| Zusammenfassung |
| Peatlands of the northern hemisphere store a remarkable amount of carbon but also contribute
to global methane emissions. As large areas in the boreal and subarctic zone are considered to
undergo significant climate change it is necessary to understand how these ecosystems react
to altered environmental conditions. Since not only temperatures but also precipitation
is likely to increase in these regions, it is of particular interest to understand the
impact of raised water tables and changing local hydrological flow patterns on
peatlands’ carbon cycle. We chose a pristine bog that was partly flooded by a reservoir
lake created 60 years ago in Ontario, Canada. Water management in the reservoir
resulted in seasonal flooding, shifting hydrological flow patterns and vegetation
gradients. The impact of partial flooding on pore water chemistry and DIC and CH4
concentrations were studied within surface peat layers. Samples were taken with pore water
peepers along the vegetation- and flooding gradient. Turnover rates of DIC and
methane were calculated from obtained concentration profiles and peat porosity under
the assumption that transport is dominated by diffusion. Values of pH changed
remarkably from 4 within the undisturbed bog part to almost 8 at the lake shore.
Ca2+ and Mg2+ were the only ions that showed significant distribution patterns
with readily increasing concentrations towards the lake water body. CH4 and DIC
concentrations also increased towards the lake and peaked in around 100 cm depth right at
the shore with maximum concentrations being 2766 μmol L-1 for CH4 and 7543
μmol L-1 for DIC, respectively. Turnover rates also increased towards the shore
albeit some uncertainty lies in this finding as steady state condition required for
calculations were probably not established and transport was not only dominated by
diffusion. Maximum CH4 production rates were modeled to be 36 nmol cm-3
d-1 and maximum DIC production was calculated to 64 nmol cm-3 d-1. Ca2+
and Mg2+ concentration indicate lake water intrusion into the peat. Changes in
pH are also probably due to lake water intrusion and altered plant communities.
Vascular plant roots likely increased methanotrophy in subsurface layers but fuelled
methanogenesis releasing labile carbon compounds in deeper layers. Modeling turnover
rates gets exacerbated as other forms of gas transportation than diffusion prevail in
vicinity to the lake. In addition to higher plant productivity lateral water flow is
presumably the most important factor contributing to higher DIC and methane
concentrations as it is thought to diminish the effect of end product inhibition in
deeper peat layers towards the lake. We thus hypothesize that seasonal flooding
not only affects ombrotrophic sites by nutrient inputs and subsequent changes in
vegetation, but also due to altered hydrological flow patterns which will affect pore
water chemistry and turnover rates by exchange of solutes and mineralization end
products. |
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