Abstract
Since the Industrial Revolution, atmospheric [CO2] and temperature have increased. C is coupled with Si in many biogeochemical processes and grasses and sedges are crucial drivers in global C and Si cycles. Tropical wetlands in Africa are dominated by papyrus, a Si-accumulating sedge. The contemporary rapid increase in [CO2] and temperature may change the plants' C:Si ratio. Since tropical wetlands are a known filter between terrestrial and aquatic ecosystems, a change in plant C:Si ratio may impact the total Si flux from the wetland to the open water ecosystem where it determines phytoplankton composition and gross primary production. The aim of this project is to demonstrate the effect of increasing atmospheric [CO2] and temperature on the Si cycle in tropical wetlands. Four steps will be followed: 1) historical sampling from herbaria to demonstrate a change in C:Si ratio in the past; 2) experiment where papyrus is grown under preindustrial, present, and future [CO2] and temperature to find empirical evidence; 3) case study at Lake Mburo (Uganda) to determine the present-day Si and C mass balance in a papyrus wetland; and 4) data integration and conceptual modeling of how this mass balance may change under 3 [CO2] scenario's and which effect this may have on the phytoplankton community, as some phytoplankton groups (diatoms) are Si-dependent.
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