Seasonal differences in soil CO2 efflux and carbon storage in Ntwetwe Pan, Makgadikgadi Basin, Botswana

Abstract

The carbon cycle in salt pans is complex and poorly understood. Field-based data are needed to improve regional estimates of C storage and land-atmosphere CO 2 fluxes from dryland environments where pans are prevalent. This paper provides a first estimate of C stores and CO 2 efflux within the salt pan, grassland and woodland of Ntwetwe Pan in the Makgadikgadi Basin, Botswana. C fluxes and stores associated with cyanobacteria-salt crusts are also determined. Total C stores are approximately an order of magnitude greater than on neighbouring Kalahari Sands at 675 ± 41, 760 ± 94 and 274 ± 15 tons ha −1 to 1 m depth in the woodland, grassland and salt pan respectively. Most of the C is found as carbonate, with organic C comprising 4.6-10% of total C. CO 2 efflux increased with temperature and also increased for a few hours after flooding of the pan surface. Crusts were a small net contributor to CO 2 efflux in the dry season but could be a net CO 2 sink in the wet season. The biogeochemistry of the sediment is likely to facilitate rapid conversion of organic C from aquatic organisms, biological crusts and algal mats into inorganic carbonates. Although further work is required to improve estimates of the spatial and temporal distribution of C, our data have demonstrated the substantial C store with the Makgadikgadi environment and the important role of biological crusts in the C cycle.

Greenhouse gas emissions from natural ecosystems and agricultural lands in sub-Saharan Africa: synthesis of available data and suggestions for further research

“…(1) enhanced microbial metabolism by an increase in available substrate due to microbial death and/or destruction of soil aggregates (commonly known as the Birch effect; Birch, 1964), and (2) physical mechanisms influencing gas flux, including infiltration, reduced diffusivity, and gas displacement in the soil (e.g., Kim et al, 2012). Soil CO 2 efflux increased immediately after rainfall in a subtropical palm woodland in northern Botswana; however, the increase was short-lived (Thomas et al, 2014). Large pulses of CO 2 and N 2 O, followed by a steady decline, were also observed after the first rainfall event of the wet season in a Kenyan rainforest (Werner et al, 2007).…”

Analyses of Recent Sediment Surface Dynamic of a Namibian Kalahari Salt Pan Based on Multitemporal Landsat and Hyperspectral Hyperion Data

“…For continued advances in understanding dust sources a spatially and temporally detailed assessment of their surface sediments is necessary [11]. Salt pans are also a potential significant carbon stock in the Kalahari environment [12] and the dynamic of salt pan surfaces is of great importance for the understanding of the carbon cycle and carbon fluxes of a pan systems. Furthermore, the sensitive interrelation between regional changes in climate patterns and tectonic activity within continents is often record in the pan sedimentary deposit, and insights on current surface processes are needed for a proper interpretation of paleoenvironmental conditions [13].…”

Variations on soil carbon dioxide flux with land-use type and selected soil properties in the hardveld of Botswana

“…Despite some CO 2 flux studies conducted across the Kalahari sandveld as well as in pan environments of Botswana and neighbouring countries (Dougill and Thomas 2004;Thomas et al 2014), there is still a paucity of information on studies conducted in the hardveld of Botswana. This study will provide a preliminary understanding of soil CO 2 flux changes with land use in the hardveld of Botswana, where there is relatively intense agricultural activity that disrupts the soil and presumably produces higher CO 2 flux.…”