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| Titel |
Implications of agricultural encroachment on the carbon and greenhouse gas dynamics in tropical African wetlands. |
| VerfasserIn |
Matthew Saunders, Frank Kansiime, Michael Jones |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109337
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| Publikation (Nr.) |
 EGU/EGU2015-9240.pdf |
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| Zusammenfassung |
| Cyperus papyrus L. (papyrus) wetlands dominate the permanently inundated wetlands
of tropical East Africa and support the livelihoods of millions of people in rural
sub-Saharan Africa through the provision of multiple ecosystem services such as
the supply of drinking water, fish protein, building materials and biofuels. These
wetlands are also extremely important in local and regional scale biogeochemical
cycles due to their extensive spatial distribution, high rates of photosynthetic carbon
dioxide (CO2) assimilation, long-term carbon (C) sequestration in the form of peat
and the control of water loss through evapotranspiration. However, these wetlands
are facing significant anthropogenic pressures due to the increasing demand for
agricultural land where the papyrus plants are removed and replaced with subsistence
crops such as cocoyam (Colocasia esculenta). Eddy covariance measurements were
made on an undisturbed papyrus wetland and a cocoyam dominated wetland on the
Ugandan shoreline of Lake Victoria to better understand the impacts of agricultural
encroachment on the C sequestration potential of these wetlands. Peak rates of net
photosynthetic CO2 assimilation at the papyrus wetland were over 40 μmol CO2 m-2
s-1, even under increasing vapour pressure deficit (≥2 kPa), while maximum rates
of assimilation at the cocoyam site were 28 μmol CO2 m-2 s-1. Annual rates of
papyrus net primary productivity (NPP) were amongst the highest recorded for
wetland systems globally (3.09 kg C m-2 yr-1) and the continual regeneration of the
papyrus plants, due to an absence of pronounced seasonal climatic variability, can lead
to significant C accumulation in the above and belowground biomass (≥88 t C
ha-1). Where these wetlands remain inundated and anaerobic conditions prevail,
significant detrital and peat deposits can form further increasing the combined C sink
capacity of these ecosystems to over 700 t C ha-1. The C sink strength of these
wetlands is however offset by the production and emission of methane (CH4), and
plant-facilitated emissions of up to 32 mg CH4 m-2 h-1 were measured from mature papyrus
plants grown in a constructed wetland, suggesting that these wetlands may make
a significant contribution to regional methane emissions. The conversion of the
papyrus wetlands to agricultural land use has significant implications for the carbon
budgets of these systems, as the decomposition of detrital material in addition to the
carbon exported in the crop biomass resulted in a net loss of carbon of ~10 t C
ha-1 yr-1. The development of sustainable wetland management strategies are
therefore required to maintain and enhance the services provided by these ecosystems
especially under increasing population pressures and future climatic scenarios. |
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