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Titel |
CO2, CH4 and N2O dynamics in Belgian rivers across a gradient of anthropogenic disturbance |
VerfasserIn |
Alberto V. Borges, François Darchambeau, Aurore Beulen |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250093294
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Publikation (Nr.) |
EGU/EGU2014-7894.pdf |
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Zusammenfassung |
Two rivers and two streams close to the city of Liège in Belgium (Meuse, Ourthe, Geer and
Blanc Gravier) were sampled to describe the dynamics of CO2, CH4 and N2O
(for the first time in Belgium for freshwaters). The four systems were chosen to
cover a gradient of size (stream to river) and of human influence (mainly forested to
mainly agricultural watersheds). The study covers the period from February 2011
to March 2013 with weekly sampling in surface waters. The variables were very
contrasted in the four systems, the Geer showing a strong enrichment in nitrogen
NH4+ et NO2-) and phosphorous in relation to the other three systems. The O2
concentrations were much lower, and the concentration of CH4, N2O and pCO2 were
much higher in the Geer than in other three systems. The concentrations in CH4,
N2O and pCO2 were higher in the Ourthe than in the Meuse and than in the Blanc
Gravier. Marked seasonal variations were observed in the 4 systems. In general the
concentration of CH4, N2O and pCO2 were higher in summer than in winter. This
is related on one hand to the increase of temperature in summer that stimulates
bacterial activity. Also in summer, the availability of organic matter for bacterial
activity is higher after the spring phytoplankton blooms and also from allochthnous
inputs from the watersheds. The increase of temperature and bacterial consumption
of O2 in the water column leads to a lesser O2 penetration in the sediments that
could stimulate benthic anaerobic processes among which methanogenesis and
denitrification, leading to an increase of CH4 and N2O in the water column. Also, the
production of N2O by denitrification strongly increases at low O2. During low water, the
increase of residence time of the water mass and the decrease of current (decrease
of degasing) allow an accumulation of CO2, CH4 and N2O in the water column.
On the contrary during high water, dilution and increase of current (increase of
degasing) lead to a decrease of concentrations. The four systems were over-saturated
in CH4, N2O and CO2, excepted during spring phytoplankton blooms when an
under-saturation of CO2 was observed in the Ourthe. Hence, the four systems were sources of
CH4, N2O and CO2 to the atmosphere. Diffusive CO2 fluxes varied from 24 to
607 mol m-2 yr-1 (Ourthe and Geer, respectively). Diffusive CH4 fluxes varied
from 28 to 8199 mmol m-2 an-1 (Blanc Gravier and Geer, respectively). Diffusive
N2O fluxes varied from 2 to 201 mmol m-2 an-1 (Ourthe and Geer, respectively). |
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