Spatial and Temporal Dynamics of pCO2 and CO2 Flux in Tropical Lake Malawi

Session: 27. - Emerging Partnerships, Research, and Capacity in the African Great Lakes

Maxon Ngochera, Monkey Bay Fisheries Research Station, [email protected]
Harvey Bootsma, University of Wisconsin-Milwaukee, [email protected]

Abstract

Numerous studies have documented CO₂ dynamics in temperate lakes, but only a handful of such studies exist for tropical lakes. Spatial and seasonal variation of air and water pCO₂, were measured along the north – south axis of Lake Malawi. The mean surface pCO₂ and CO₂ flux was 385.3 ± 21.9 µatm and -264.4 ± 55.6 mmol C m^-2 yr^-1 respectively. A two-way ANOVA revealed significant differences with both season and location (p < 0.001). Temporally, CO₂ under-saturated was predominant during the hot, wet season and the cool, mixing season. In contrast, CO₂ supersaturation was observed at the onset of the mixing season and the hot, stratified season. Concurrent measurements of lake temperature profiles, weather conditions, phytoplankton biomass and seston ?¹³C suggest that at the onset of the mixing season increased phytoplankton growth was not immediately accompanied by a decrease in pCO₂ because the new supplied nutrients are accompanied by CO₂-rich hypolimnetic waters. Spatially, the southernmost zone was CO₂ supersaturated compared to the central-north zones. Over an annual cycle, tropical Lake Malawi is a net sink of CO₂ from the atmosphere and areal CO₂ flux measurements indicate the lake assimilates 7.7 ± 1.6 x 10¹² mmol C yr^-1.

1. Keyword
carbon

2. Keyword
air-water interfaces

3. Keyword
Lake Malawi

4. Additional Keyword
Carbon flux

5. Additional Keyword
DIC

6. Additional Keyword
Upwelling