Thomas and Hoon, 2010. Carbon dioxide fluxes from biologically-crusted Kalahari Sands after simulated wetting.

Thomas, A.D., Hoon, S.R.,2010. Carbon dioxide fluxes from biologically-crusted Kalahari Sands after simulated wetting. J. Arid Environ. 74, 131-139.

Abstract

We report surface CO₂ efflux and subsoil CO₂ concentrations in biologically-crusted soils from the Kalahari. Fluxes were determined in-situ using a closed chamber coupled to a portable gas chromatograph on dry soils and on soils subject to simulated light and heavy rainfall. Surface efflux was measured in an artificially darkened environment in order to determine by difference, whether photosynthesis was occurring. Dry soil efflux rates were 2.8–14.8 mg C m² h⁻¹ throughout a diurnal cycle. Light rainfall led to an immediate increase in efflux to a peak of 65.6 mg C m² h⁻¹. Heavy rainfall resulted in a large pulse of CO₂ with efflux rates of 339.2 mg C m² h⁻¹ over the first hour after wetting. Peak rates remained high over the following 2 days (87.8 and 87.0 mg C m² h⁻¹). Given sufficient moisture, fluxes increased with temperature. We believe hydration of the subsoil stimulates microorganisms which repsire available C either from extracellular polysaccharide sheaths (EPS) or released into the soil through lysis of microbial cells. Higher fluxes from the soil kept in the dark suggests photosynthesis occurs in wetted crusts during the daytime but net C uptake is masked by respiration from other microorganisms.

Thomas et al. 2008. Carbon dioxide fluxes from cyanobacteria crusted soils in the Kalahari.

Thomas, A.D., Hoon, S.R., Linton, P.E., 2008. Carbon dioxide fluxes from cyanobacteria crusted soils in the Kalahari. Applied Soil Ecology 39, 254-263.

Abstract

The surface of dryland soils is frequently characterised by a biological crust comprising of various combinations of cyanobacteria, algae, moss and lichens. In the Kalahari of Botswana, soil crusts are predominantly made up of cyanobacteria, which when moist, are capable of fixing N and C. Many cyanobacteria also produce extracellular polymeric substances (EPS) which bind soil particles together and decrease erodibility. The physical integrity and metabolic activity of soil crusts is thus critical to ecological productivity, erodibility and CO₂ fluxes in dryland regions. There are, however, few studies of the magnitude and controlling factors of soil CO₂ flux within these systems.

Our aim was to quantify in situ soil CO₂ flux during contrasting antecedent moisture conditions in the south west Kalahari of Botswana. We have designed a gas exchange chamber for field deployment coupled to a portable gas chromatograph, control and data logging instrumentation. The optical and active thermal control specifications of the chamber have been designed to permit photosynthesis and cope with the temperature extremes of the Kalahari whilst minimizing disturbance to the cyanobacteria soil crust. This approach has enabled CO₂ fluxes to be monitored in situ with a high degree of precision for extended periods.

In August 2005, when the surface and subsoils were dry, the ambient CO₂ efflux was negative and low during the daytime (−6.15 mg C m² h⁻¹). When 8 mm rainfall equivalent of water was added to the surface there was an immediate uptake of CO₂ during the daytime at rates up to 75 mg C m² h⁻¹ demonstrating that rates of net photosynthesis are greatly enhanced by available moisture. In contrast, in May 2006 following a prolonged wet period when the subsoil was moist, there was a net positive efflux of CO₂ from the soil at rates of up to 60 mg C m² h⁻¹ irrespective of whether the surface soil was moist or not. This is consistent with subsoil heterotrophic bacterial respiration becoming an important contributor to soil efflux.

Thomas et al., 2012. Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO2 efflux in two semiarid grasslands in southern Botswana.

 Thomas, A.D., 2012. Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO2 efflux in two semiarid grasslands in southern Botswana. Philosophical Transactions of the Royal Society B: Biological Sciences 367, 3076-3086.

Abstract

Biological soil crusts (BSCs) are an important source of organic carbon, and affect a range of ecosystem functions in arid and semiarid environments. Yet the impact of grazing disturbance on crust properties and soil CO₂ efflux remain poorly studied, particularly in African ecosystems. The effects of burial under wind-blown sand, disaggregation and removal of BSCs on seasonal variations in soil CO₂ efflux, soil organic carbon, chlorophyll a and scytonemin were investigated at two sites in the Kalahari of southern Botswana. Field experiments were employed to isolate CO₂ efflux originating from BSCs in order to estimate the C exchange within the crust. Organic carbon was not evenly distributed through the soil profile but concentrated in the BSC. Soil CO₂ efflux was higher in Kalahari Sand than in calcrete soils, but rates varied significantly with seasonal changes in moisture and temperature. BSCs at both sites were a small net sink of C to the soil. Soil CO₂ efflux was significantly higher in sand soils where the BSC was removed, and on calcrete where the BSC was buried under sand. The BSC removal and burial under sand also significantly reduced chlorophyll a, organic carbon and scytonemin. Disaggregation of the soil crust, however, led to increases in chlorophyll a and organic carbon. The data confirm the importance of BSCs for C cycling in drylands and indicate intensive grazing, which destroys BSCs through trampling and burial, will adversely affect C sequestration and storage. Managed grazing, where soil surfaces are only lightly disturbed, would help maintain a positive carbon balance in African drylands.

Thomas et al. 2011. Soil respiration at five sites along the Kalahari Transect: Effects of temperature, precipitation pulses and biological soil crust cover.

Thomas, A.D., Hoon, S.R., Dougill, A.J., 2011. Soil respiration at five sites along the Kalahari Transect: Effects of temperature, precipitation pulses and biological soil crust cover. Geoderma 167-168, . 284-294.

Abstract

There are increasing concerns that climatic and land use changes will enhance soil respiration rates and soil organic carbon loss, compromising agricultural productivity and further elevating atmospheric CO₂. Current understanding of dryland respiration is, however, insufficient to enable prediction of the consequences of these changes for dryland soils and CO₂ fluxes. The objectives of this paper are to present in-situ respiration data from five remote sites along a climatic gradient in the Kalahari of Botswana and to determine the effects of temperature, moisture and biological crust cover on soil CO₂ fluxes. Moisture was the primary limiting factor to efflux which increased with amount of simulated rainfall. On dry soils, mean CO₂ efflux was between 1.5 and 5.9 mg C m^− 2 h^− 1. After 2 mm and 50 mm simulated wetting, mean rates increased to 4.0 to 21.8 and 8.6 to 41.5 mg C m^− 2 h^− 1 respectively. Once wet, soil CO₂ efflux increases with temperature, and sites at the hotter northern end of the transect lost more CO₂ than cooler southerly sites. Net respiration rates are, however, muted by autotrophic organisms in biological soil crusts which photosynthesise and take up CO₂. The temperature sensitivity of soil CO₂ efflux increased with moisture. Dry, 2 mm and 50 mm treated soils had a Q₁₀ of 1.1, 1.5 and 1.95 respectively. Our findings indicate that higher temperatures and a loss of biological crust cover will lead to greater soil C loss through respiration.

Thongo M'Bou et al., 2010. Growth and maintenance respiration of roots of clonal Eucalyptus cuttings: scaling to stand-level

Thongo M'Bou, A., Saint-Andre, L., Grandcourt, A.s., Nouvellon, Y., Jourdan, C., Mialoundama, F.l., Epron, D., 2010. Growth and maintenance respiration of roots of clonal Eucalyptus cuttings: scaling to stand-level. Plant Soil 332, 41-53.

Abstract

Root respiration consumes an important part of the daily assimilated carbon but the magnitude of this component of forest net ecosystem exchange and its partitioning among the different energy demanding processes in roots are still poorly documented. 5-month old Eucalyptus cuttings were grown in a greenhouse in pot filled with coarse sand. They were fertilized with three different amounts of a slow-release fertilizer with the doses of 8, 24 and 48 g of nitrogen per plant. Root respiration was measured using an infrared gas analyser by perfusing air through the pot on 9 plants per treatment on three dates 14 days apart. Measure of root respiration of the three treatments over time was made in order to obtain a large range of growth and nutrient uptake. Root respiration normalized at 22°C ranged from 0.09 to 0.23 g_C d⁻¹ for the three treatments during all the experiment. It was well predicted with a model that includes root growth rate and root nitrogen content.The nitrogen related maintenance coefficient was negatively correlated to the root nitrogen concentration suggesting a decrease in protein turnover with increasing fertility. Growth rate of fine root in a virtual stand was simulated using age-related allometric equations and further used to estimate root respiration in the field. Simulated root respiration increased over time from 0.39 to 3.14 g_C m⁻² d⁻¹ between 6 and 126 months assuming a turnover of 2 yr⁻¹ for fine roots. The major fraction of simulated root respiration in the field (78–92%) was used for the maintenance of the existing biomass.

Epron et al., 2009. Soil carbon dynamics following afforestation of a tropical savannah with Eucalyptus in Congo.

Epron, D. et al., 2009. Soil carbon dynamics following afforestation of a tropical savannah with Eucalyptus in Congo. Plant Soil 323, 309-322.

Abstract

Soil organic matter is a key factor in the global carbon cycle, but the magnitude and the direction of the change in soil carbon after afforestation with Eucalyptus in the tropics is still a matter of controversy. The objective of this work was to understand the dynamics of soil carbon in intensively managed Eucalyptus plantations after the afforestation of a native savannah. The isotopic composition (δ) of soil carbon (C) and soil CO₂ efflux (F) were measured on a four-age chronosequence of Eucalyptus and on an adjacent savannah. δ _F was used to partition F between a C3 component and a C4 component, the latter corresponding to the decomposition of a labile pool of savannah-derived soil carbon (C _SL). The mean residence time of C_SL was 4.6 years. This further allowed us to partition the savannah-derived soil carbon into a labile and a stable (C _SS) carbon pool. C _SL accounted for 30% of soil carbon in the top soil of the savannah (0–5 cm), and only 12% when the entire 0–45 cm soil layer was considered. The decrease in C _SL with time after plantation was more than compensated by an increase in Eucalyptus-derived carbon, and half of the newly incorporated Eucalyptus-derived carbon in the top soil was associated with the clay and fine silt fractions in the 14-year-old. stand. Increment in soil carbon after afforestation of tropical savannah with Eucalyptus is therefore expected despite a rapid disappearance of the labile savannah-derived carbon because a large fraction of savannah-derived carbon is stable.

Marsden et al., 2008. Relating coarse root respiration to root diameter in clonal Eucalyptus stands in the Republic of the Congo.

Marsden, C., Nouvellon, Y., Epron, D., 2008. Relating coarse root respiration to root diameter in clonal Eucalyptus stands in the Republic of the Congo. Tree Physiology 28, 1245-1254.

Abstract

Root respiration is an important component of the carbon balance of a forest ecosystem. We measured CO₂ efflux of excised fine roots and intact coarse roots in 3-, 4- and 13-year-old Eucalyptus stands in the region of Pointe-Noire, Republic of the Congo. A transportable and adaptable closed chamber gas exchange system directly measured CO₂ efflux of roots from 0.5 to 32 mm in diameter. Fluxes were corrected for measurement system leaks and normalized to a reference temperature of 30 °C. Mean fine root respiration rates at the reference temperature varied between 8.5 and 10.8 μmol CO₂ kg⁻¹ s⁻¹ depending on the stand. Coarse root respiration was strongly negatively correlated to root diameter. We propose a model based on a radial gradient of respiratory activity within the root to simulate the exponential decrease in respiration with diameter. Although many sources of uncertainty in the measurements remain, as discussed in this paper, these results provide a basis for scaling up organ-level root respiration measurements to the tree and stand levels.

Marsden et al., 2008. Two independent estimations of stand-level root respiration on clonal Eucalyptus stands in Congo: up scaling of direct measurements on roots versus the trenched-plot technique.

Marsden, C., Nouvellon, Y., M’Bou, A.T., Saint-Andre, L., Jourdan, C., Kinana, A., Epron, D., 2008. Two independent estimations of stand-level root respiration on clonal Eucalyptus stands in Congo: up scaling of direct measurements on roots versus the trenched-plot technique. New Phytol. 177, 676-687.

Summary

• • 
  Root respiration at the level of a forest stand, an important component of ecosystem carbon balance, has been estimated in the past using various methods, most of them being indirect and relying on soil respiration measurements.
• •
  On a 3-yr-old Eucalyptus stand in Congo-Brazzaville, a method involving the upscaling of direct measurements made on roots in situ, was compared with an independent approach using soil respiration measurements conducted on control and trenched plots (i.e. without living roots). The first estimation was based on the knowledge of root-diameter distribution and on a relationship between root diameter and specific respiration rates.
• •
  The direct technique involving the upscaling of direct measurements on roots resulted in an estimation of 1.53 µmol m⁻² s⁻¹, c. 50% higher than the mean estimation obtained with the indirect technique (1.05 µmol m⁻² s⁻¹).
• • 
  Monte-Carlo simulations showed that the results carried high uncertainty, but this uncertainty was no higher for the direct method than for the trenched-plot method. The reduction of the uncertainties on upscaled results requires more extensive knowledge of temperature sensitivity and more confidence and precision on the respiration rates and biomasses of fine roots.

Epron et al., 2006. Soil carbon balance in a clonal Eucalyptus plantation in Congo: effects of logging on carbon inputs and soil CO2 efflux.

Epron, D., Nouvellon, Y., Deleporte, P., Ifo, S., Kazotti, G.U.Y., Thongo M'Bou, A., Mouvondy, W., Andre, L.S., Roupsard, O., Jourdan, C., Hamel, O., 2006. Soil carbon balance in a clonal Eucalyptus plantation in Congo: effects of logging on carbon inputs and soil CO2 efflux. Global Change Biol. 12, 1021-1031.

Abstract

Soil CO₂ efflux was measured in clear-cut and intact plots in order to quantify the impact of harvest on soil respiration in an intensively managed Eucalyptus plantation, and to evaluate the increase in heterotrophic component of soil respiration because of the decomposition of harvest residues. Soil CO₂ effluxes showed a pronounced seasonal trend, which was well related to the pattern of precipitation and soil water content and were always significantly lower in the clear-cut plots than in the intact plots. On an annual basis, soil respiration represented 1.57 and 0.91 kg_C m⁻² yr⁻¹ in intact and clear-cut plots, respectively. During the first year following harvest, residues have lost 0.79 kg_C m⁻² yr⁻¹. Our estimate of heterotrophic respiration was calculated assuming that it was similar to soil respiration in the clear-cut area except that the decomposition of residues did not occur, and it was further corrected for differences in soil water content between intact and clear-cut plots and for the cessation of leaf and fine root turnover in clear cut. Heterotrophic respiration in clear-cut plots was estimated at 1.18 kg_C m⁻² yr⁻¹ whereas it was only 0.65 kg_C m⁻² yr⁻¹ in intact plots (41% of soil respiration). Assumptions and uncertainties with these calculations are discussed.

Nouvellon et al. 2012. Age-related changes in litter inputs explain annual trends in soil CO2 effluxes over a full Eucalyptus rotation after afforestation of a tropical savannah

Nouvellon, Yann, et al. 2012. Age-related changes in litter inputs explain annual trends in soil CO2 effluxes over a full Eucalyptus rotation after afforestation of a tropical savannah. Biogeochemistry 111.1-3 (2012): 515-533.

Abstract

Land use changes such as savannah afforestation with eucalypts impact the soil carbon (C) balance, therefore affecting soil CO₂ efflux (F _s ), a major flux in the global C cycle. We tested the hypothesis that F _s increases with stand age after afforestation, due to an increasing input of fresh organic matter to the forest floor. In a Eucalyptus plantation established on coastal savannahs in Congo, bimonthly measurements of F _s were carried out for 1 year on three adjacent stands aged 0.9, 4.4 and 13.7 years and presenting similar growth patterns. Litterfall and litter accumulation on the forest floor were quantified over a chronosequence. Equations were derived to estimate the contribution of litter decomposition to F _s throughout the rotation. Litterfall increased with stand age after savannah afforestation. F _s , that was strongly correlated on a seasonal basis with soil water content (SWC) in all stands, decreased between ages 0.9 year and 4.4 years due to savannah residue depletion, and increased between ages 4.4 years and 13.7 years, mainly because of an increasing amount of decomposing eucalypt litter. The aboveground litter layer therefore appeared as a major source of CO₂, whose contribution to F _s in old stands was estimated to be about four times higher than that of the eucalypt-derived soil organic C pool. The high litter contribution to F _s in older stands might explain why 13.7 years-old stand F _s was limited by moisture all year round whereas SWC did not limit F _s for large parts of the year in the youngest stands.

Epron et al., 2013. Partitioning of net primary production in Eucalyptus and Acacia stands and in mixed-species plantations: Two case-studies in contrasting tropical environments.

Epron, D., Nouvellon, Y., Mareschal, L., Moreira, R.M.e., Koutika, L.-S., Geneste, B., Delgado-Rojas, J.S., Laclau, J.-P., Sola, G., Gonçalves, J.L.d.M., Bouillet, J.-P., 2013. Partitioning of net primary production in Eucalyptus and Acacia stands and in mixed-species plantations: Two case-studies in contrasting tropical environments. For. Ecol. Manage. 301, 102-111.

Abstract

The introduction of nitrogen fixing species (NFS) in fast-growing tree plantations is an alternative option to reduce fertilizer inputs. However, the success of mixed-species plantations depends on the balance between positive interactions among species (resulting from facilitation and/or complementarity) and the negative effects of interspecific competition.

Using a carbon budget approach and coupling measurements of standing biomass, aboveground litterfall and soil CO₂ efflux, we assessed the influence of replacing half of eucalypt trees by Acacia mangium on total belowground carbon flux (TBCF), net primary production (NPP) and its partitioning between above- and belowground growth at two tropical sites in Brazil (Itatinga) and in Congo (Kissoko) exhibiting contrasting climates, edaphic conditions and wood productions.

Annual soil CO₂ efflux (F_S) was significantly lower in the acacia monocultures than in eucalypt monocultures and mixed-species stands at both sites. Annual F_S was significantly lower at Itatinga compared to Kissoko for all stands while TBCF was significantly lower in the eucalypt stands only. In the eucalypt monocultures we found a significantly lower aboveground NPP (ANPP) and wood production (wood NPP) at Kissoko compared to Itatinga that was almost fully balanced by a significantly higher belowground NPP (BNPP), leading to similar NPP. Similarly, acacia monocultures exhibited significantly higher ANPP and wood NPP at Itatinga than at Kissoko. The mixed-species stands exhibited a significantly lower wood NPP and ANPP than the eucalypt monocultures at the Brazilian site while NPP of the mixture was not significantly different than the average NPP of the two monocultures. At the Congolese site, NPP of the mixture was significantly higher than the average NPP of the two monocultures. NPP was similar in the mixed-species stand and the eucalypt monoculture with a significantly lower partitioning of NPP to belowground production, leading to a one third higher wood biomass at harvest in the mixed-species stand.

A positive effect of growing eucalypts with the nitrogen fixing acacia trees on stand wood production occurred at Kissoko but not at Itatinga. Mixed-species plantations with NFS can be advocated at sites where the productive gains resulting from nitrogen fixation are not compromised by other resource limitations.

Versini et al., 2013. The manipulation of organic residues affects tree growth and heterotrophic CO2 efflux in a tropical Eucalyptus plantation.

Versini, A., Nouvellon, Y., Laclau, J.-P., Kinana, A., Mareschal, L., Zeller, B., Ranger, J., Epron, D., 2013. The manipulation of organic residues affects tree growth and heterotrophic CO2 efflux in a tropical Eucalyptus plantation. For. Ecol. Manage. 301, 79-88.

Abstract

Fast-growing plantations are increasingly being established on tropical soils, where fertility is largely supported by soil organic matter (SOM) and where different management options of harvest organic residues is thought to impact the long-term sustainability of these plantations. The objectives of this study were: (1) to quantify the effect of contrasting methods of organic residue management on tree growth and soil CO₂ effluxes in the first 2 years after planting and (2) to evaluate the impact of organic residue manipulations on the mineralization of soil organic matter over the length of the experiment. Three treatments were setup in 0.125 ha plots and replicated in three blocks at the harvesting of a Congolese Eucalyptus stand, resulting in an aboveground organic residue mass ranging from 0 to 6.3 kg m⁻². The mineralization of SOM was deduced in each treatment by partitioning sources of soil CO₂ effluxes using decomposition experiments and by upscaling specific root respiration. Soil CO₂ effluxes were greatly affected by seasons and organic residue manipulation, although there were no significant changes in topsoil water content and topsoil temperature over most of the study period. Aboveground organic residue was the first contributor to soil CO₂ efflux in the two treatments with a litter layer. Organic residue management did not significantly influence the mineralization of SOM in our study, probably due to the low quality of Eucalyptus litter, or to the hypothetical lack of dissolved organic carbon transfers from litter to soil. A strong relationship was found between cumulative heterotrophic CO₂ efflux and tree growth, supporting the hypothesis that the early growth of Eucalyptus trees in a sandy tropical soil is largely dependent on the nutrients released by the decomposition of organic residues.

Mapanda et al., 2011. Effects of organic and mineral fertilizer nitrogen on greenhouse gas emissions and plant-captured carbon under maize cropping in Zimbabwe.

Mapanda, F., Wuta, M., Nyamangara, J., Rees, R., 2011. Effects of organic and mineral fertilizer nitrogen on greenhouse gas emissions and plant-captured carbon under maize cropping in Zimbabwe. Plant Soil 343, 67-81.

Abstract

Optimizing a three-way pact comprising crop yields, fertility inputs and greenhouse gases may minimize the contribution of croplands to global warming. Fluxes of N₂O, CO₂ and CH₄ from soil were measured under maize (Zea mays L.) grown using 0, 60 and 120 kg N hm^-2 as NH₄NO₃-N and composted manure-N in three seasons on clay (Chromic luvisol) and sandy loam (Haplic lixisol) soils in Zimbabwe. The fluxes were measured using the static chamber methodology involving gas chromatography for ample air analysis. Over an average of 122 days we estimated emissions of 0.1 to 0.5 kg N₂O-N hm⁻², 711 to 1574 kg CO₂-C hm⁻² and−2.6 to 5.8 kg CH₄-C hm⁻² from six treatments during season II with the highest fluxes. The posed hypothesis that composted manure-N may be better placed as a mitigation option against soil emissions of GHG than mineral fertilizer-N was largely supported by N₂O fluxes during the wet period of the year, but with high level of uncertainty. Nitrogen addition might have stimulated both emissions and consumption of CH₄ but the sink or source strength depended highly on soil water content. We concluded that the application of mineral-N and manure input may play an important role with reference to global warming provided the season can support substantial crop productivity that may reduce the amount of N₂O loss per unit yield. Confidence in fluxes response to agricultural management is still low due to sporadic measurements and limited observations from the southern African region.

Mapanda et al., 2012. Greenhouse gas emissions from Savanna (Miombo) woodlands: responses to clearing and cropping

Mapanda, P., Wuta, M., Nyamangara, J., Rees, R., Kitzler, B., 2012. Greenhouse gas emissions from Savanna (Miombo) woodlands: responses to clearing and cropping. African Crop Science Journal 20, 385-400.

Abstract

Natural vegetation represents an important sink for greenhouse gases (GHGs); however, there is relatively little information available on emissions from southern African savannas. The effects of clearing savanna woodlands for crop production on soil fluxes of N2O, CO2 and CH4 were studied on clay (Chromic luvisol) and loamy sand (Ferric acrisol) soils in Zimbabwe. Maize (Zea mays L.) was the test crop. Gas samples were measured from undisturbed, cleared and cultivated woodlands using the static chamber methodology involving gas chromatography for ample air analysis. Site and climatic variables were particularly important determinants of GHG emissions. Over an average of 154 days emissions of 0.8 – 2.5 kg N2O-N ha-1, 1146 – 2847 kg CO2-C ha-1 and 7.4 – 38.5 kg CH4-C ha-1 were estimated during a season that followed a relatively drier one. Fertiliser-N significantly increased GHG emissions on cropped plots (clay soil). The undisturbed woodland with a relatively higher tree density (loamy sand) was an important GHG source. The high CH4 fluxes from woodlands provide ground based validation of satellite observations of CH4 hotspots in sub-Saharan Africa, and have considerable implications on regional GHG balance.

Thomas et al., 2014. Seasonal differences in soil CO2 efflux and carbon storage in Ntwetwe Pan, Makgadikgadi Basin, Botswana.

Thomas, A.D., Dougill, A.J., Elliott, D.R., Mairs, H., 2014. Seasonal differences in soil CO2 efflux and carbon storage in Ntwetwe Pan, Makgadikgadi Basin, Botswana. Geoderma 219-220, 72-81.

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 CO₂ fluxes from dryland environments where pans are prevalent. This paper provides a first estimate of C stores and CO₂ 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. CO₂ efflux increased with temperature and also increased for a few hours after flooding of the pan surface. Crusts were a small net contributor to CO₂ efflux in the dry season but could be a net CO₂ 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.

Gondwe & Masamba, 2014. Spatial and temporal dynamics of diffusive methane emissions in the Okavango Delta, northern Botswana, Africa

Gondwe, M., Masamba, W.L., 2014. Spatial and temporal dynamics of diffusive methane emissions in the Okavango Delta, northern Botswana, Africa. Wetlands Ecol. Manage. 22, 63-78.

Abstract

Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH₄) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH₄ in the world contributing between 100 and 231 Tg year⁻¹ to the total budget of 503–610 Tg year⁻¹, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH₄ emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH₄ emission rates varied between 0.24 and 293 mg CH₄ m⁻² h⁻¹, with a mean (±SE) emission of 23.2 ± 2.2 mg CH₄ m⁻² h⁻¹ or 558 ± 53 mg CH₄ m⁻² day⁻¹. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher (P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH₄ m⁻² h⁻¹ than in floodplains (20.4 ± 2.5 mg CH₄ m⁻² h⁻¹) and lagoons (16.9 ± 2.6 mg CH₄ m⁻² h⁻¹). Diffusive CH₄ emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH₄ m⁻² h⁻¹) and lowest (0.2–3.0 mg m⁻² h⁻¹) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km², the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH₄ emission from global tropical wetlands.

Mapanda et al., 2010. A cross-ecosystem assessment of the effects of land cover and land use on soil emission of selected greenhouse gases and related soil properties in Zimbabwe.

Mapanda, F., Mupini, J., Wuta, M., Nyamangara, J., Rees, R.M., 2010. A cross-ecosystem assessment of the effects of land cover and land use on soil emission of selected greenhouse gases and related soil properties in Zimbabwe. Eur. J. Soil Sci. 61, 721-733.

Abstract
Land used for agricultural production can contribute significantly to greenhouse gas (GHG) emissions; however, there is very little information on the role of management and land use change in influencing these emissions in Africa. Thus, exploring GHG emissions that occur at the soil-atmosphere interface is an essential part of the effort to integrate land management strategies with climate change mitigation and adaptation in southern Africa. We measured soil emissions of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from rain-fed perennial tropical grassland, wastewater-irrigated perennial tropical pastureland, recently cleared woodland, miombo woodland, a Eucalyptus plantation, regular cropland and recently cleared-and-cropped land, on two contrasting soils at five sites in one cropping season in Zimbabwe. Gas samples were collected using static chambers and analysed by gas chromatography. Considerably high GHG emissions were found on sewage effluent-irrigated pastureland (means, 190 mg CO₂-C m⁻² hour⁻¹, 102 µg CH₄-C m⁻² hour⁻¹ and 6 µg N₂O-N m⁻² hour⁻¹ from sandy soil) and altered woodlands (mean ranges, 38–70 CO₂-C m⁻² hour⁻¹, 12–43 µg CH₄-C m⁻² hour⁻¹ and 20–31 µg N₂O-N m⁻² hour⁻¹ from deforested and cultivated woodland on clay and sandy soils). Relatively low and less variable emissions were found among the rain-fed perennial tropical grasslands, regular croplands and Eucalyptus plantations (mean ranges, 19–39 mg CO₂-C m⁻² hour⁻¹, −9.4–2.6 µg CH₄-C m⁻² hour⁻¹ and 1.0–4.7 µg N₂O-N m⁻² hour⁻¹). Variability in CO₂, CH₄ and N₂O emissions from soils was to the greatest extent influenced by soil temperature, but soil moisture, mineral-N and pH were also important. The increased N₂O emissions from cleared woodland on clay soil were attributed to increased mineralization and N availability when no tree could take up that N, while the N mineralized on the sandy soil could have been largely leached due to the soil's poor nutrient holding capacity, resulting in a relatively lower N₂O emission response to clearing. We concluded that the alteration of woodlands by deforestation and cultivation increased soil temperature, resulting in increased soil respiration, while the establishment of Eucalyptus plantations may provide an option for reduction in soil emissions of CO₂ and N₂O and a sink for CH₄.

Mann et al., 2014. The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin.

Mann, P.J., M Spencer, R.G., Dinga, B.J., Poulsen, J.R., Hernes, P.J., Fiske, G., Salter, M.E., Wang, Z.A., Hoering, K.A., Six, J., Holmes, R.M., The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin. Journal of Geophysical Research: Biogeosciences, DOI: 10.1002/2013JG002442

Abstract

Dissolved organic carbon (DOC) and inorganic carbon (DIC and pCO₂), lignin biomarkers and the optical properties of dissolved organic matter (DOM) were measured in a gradient of streams and rivers within the Congo Basin (Republic of Congo), with the aim of examining how vegetation cover and hydrology influences the composition and concentration of exported fluvial carbon (C). Three sampling campaigns (February 2010, November 2010 and August 2011) spanning 56 sites are compared by sub-basin watershed land cover type (savannah, tropical forest, and swamp) and hydrologic regime (high, intermediate, and low). Land cover properties predominately controlled the amount and quality of DOC, chromophoric DOM (CDOM) and lignin phenol concentrations (∑₈) exported in streams and rivers throughout the Congo Basin. Higher DIC concentrations and changing DOM composition (lower molecular weight, less aromatic C) during periods of low hydrologic flow indicated a shift from rapid overland supply pathways in wet conditions to deeper groundwater inputs during drier periods. Lower DOC concentrations in forest and swamp sub-basins were apparent with increasing catchment area, indicating enhanced DOC loss with extended water residence time. Surface water pCO₂ in savannah and tropical forest catchments ranged between 2600 and 11922 µatm, and swamp regions contained extremely high pCO₂ (10598-15802 µatm), highlighting their potential as significant pathways for water-air efflux. Our data suggest that the quantity and quality of DOM exported to streams and rivers is largely driven by terrestrial ecosystem structure and that anthropogenic land-use or climate change may impact the composition and reactivity of fluvial C, with ramifications for regional C budgets and future climate scenarios.

Wang et al., 2013. Inorganic carbon speciation and fluxes in the Congo River.

Wang, Z.A., Bienvenu, D.J., Mann, P.J., Hoering, K.A., Poulsen, J.R., Spencer, R.G.M., Holmes, R.M., 2013. Inorganic carbon speciation and fluxes in the Congo River. Geophys. Res. Lett. 40, 511-516.

Abstract
Seasonal variations in inorganic carbon chemistry and associated fluxes from the Congo River were investigated at Brazzaville-Kinshasa. Small seasonal variation in dissolved inorganic carbon (DIC) was found in contrast with discharge-correlated changes in pH, total alkalinity (TA), carbonate species, and dissolved organic carbon (DOC). DIC was almost always greater than TA due to the importance of CO₂*, the sum of dissolved CO₂ and carbonic acid, as a result of low pH. Organic acids in DOC contributed 11–61% of TA and had a strong titration effect on water pH and carbonate speciation. The CO₂* and bicarbonate fluxes accounted for ~57% and 43% of the DIC flux, respectively. Congo River surface water released CO₂ at a rate of ~109 mol m⁻² yr⁻¹. The basin-wide DIC yield was ~8.84 × 10⁴ mol km⁻² yr⁻¹. The discharge normalized DIC flux to the ocean amounted to 3.11 × 10¹¹ mol yr⁻¹. The DOC titration effect on the inorganic carbon system may also be important on a global scale for regulating carbon fluxes in rivers.

Nyasimi et al., 2013. Climate Change Adaptation and Mitigation Initiatives for Agriculture in East Africa. CCAFS Working Paper no. 60. CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS). Copenhagen, Denmark.

Nyasimi M, Radeny M, Kinyangi J. 2013. Climate Change Adaptation and Mitigation Initiatives for
Agriculture in East Africa. CCAFS Working Paper no. 60. CGIAR Research Program on Climate
Change, Agriculture and Food Security (CCAFS). Copenhagen, Denmark. Available online at:
www.ccafs.cgiar.org

Abstract

National governments across East Africa are in the process of formulating and implementing adaptation and mitigation strategies to assist farmers cope with climate change. These include formulating actions, frameworks and programs to address climate change and embedding these within the long-term national development plans. This working paper provides understanding of the current state of national climate change adaptation and mitigation efforts in Ethiopia, Kenya, Tanzania and Uganda for agriculture and provides baseline information for subsequent assessments of climate change adaptation and mitigation.

In each country, specific government departments such as Environmental Protection Authority (Ethiopia), Ministry of Environment, Water and Mineral Resources (Kenya), Vice President’s Office (Tanzania) and Ministry of Water and Environment (Uganda) are mandated to coordinate climate change initiatives. In all countries, the Ministry of Agriculture is the focal point for all climate change initiatives related to agriculture. Agricultural Sector Development Plans that provide strategies to boost agricultural productivity and spur economic growth have been prepared either as standalone plans or as part of National Development Plans (NDP). Irrigation, capacity building, enhancing private-public partnership for market development, and creating legal and regulatory environment that can attract investments are some of the priority areas identified for attention in agriculture to enhance climate resilience.

All countries have submitted draft National Adaptation Plan of Actions (NAPAs) and Nationally Appropriate Mitigation Actions (NAMAs) to UNFCCC, indicating priority interventions. Due to ineligibility to UNFCCC funding, Kenya initiated the National Climate Change Response Strategy (NCCRS) and prepared a detailed National Climate Change Adaptation Plan (NCCAP) that identified priority immediate, medium and long-term adaptation strategies in agriculture and other sectors.

Government research institutions are equally actively involved. The Kenya Agricultural Research Institute and Uganda Ministry of Water and environment have established Climate Change Units, while the Ethiopian Institute of Agricultural Research is taking pivotal role in developing livestock and crop programs geared towards contributing to a Climate Resilient Green Economy. Other initiatives include enhancing capacity of researchers and professionals in climate change in East Africa, where training is offered by universities as part of their curriculum and short courses in selected research institutions. However, the effectiveness of these initiatives is hampered by lack of a clearly defined strategy and national policy. In addition, there is lack of documentation of completed and on-going projects thus making it difficult to coordinate initiatives and avoid duplications.

To fund climate change initiatives in agriculture, all governments across the region are sourcing financing from various sources (other governments, foundations and research and development organizations). However, Kenya also seeks financing from local sources within the country such as the Local Authority Transfer Fund (LATF) and the Constituency Development Fund (CDF).

Mbow et al., 2014. Achieving mitigation and adaptation to climate change through sustainable agroforestry practices in Africa. Current Opinion in Environmental Sustainability 6, 8-14.

Mbow, C., Smith, P., Skole, D., Duguma, L., Bustamante, M., 2014. Achieving mitigation and adaptation to climate change through sustainable agroforestry practices in Africa. Current Opinion in Environmental Sustainability 6, 8-14.



Abstract
Agroforestry is one of the most conspicuous land use systems across landscapes and agroecological zones in Africa. With food shortages and increased threats of climate change, interest in agroforestry is gathering for its potential to address various on-farm adaptation needs, and fulfill many roles in AFOLU-related mitigation pathways. Agroforestry provides assets and income from carbon, wood energy, improved soil fertility and enhancement of local climate conditions; it provides ecosystem services and reduces human impacts on natural forests. Most of these benefits have direct benefits for local adaptation while contributing to global efforts to control atmospheric greenhouse gas concentrations. This paper presents recent findings on how agroforestry as a sustainable practice helps to achieve both mitigation and adaptation objectives while remaining relevant to the livelihoods of the poor smallholder farmers in Africa.