Nyamadzawo et al. 2012. The Effect of Catena Position on Greenhouse Gas Emissions from Dambo Located Termite (Odontotermes transvaalensis) Mounds from Central Zimbabwe. Atmospheric and Climate Sciences, 2(4), 502-509

Nyamadzawo, G., Gotosa, J., Muvengwi, J., Wuta, M., Nyamangara, J., Nyamugafata, P., & Smith, J. L. (2012). The Effect of Catena Position on Greenhouse Gas Emissions from Dambo Located Termite (Odontotermes transvaalensis) Mounds from Central Zimbabwe. Atmospheric and Climate Sciences, 2(4), 502-509

Abstract
Methane (CH₄), carbon dioxide (CO₂) and nitrous oxide (N₂)O) are greenhouse gases (GHGs) which cause global warming. Natural sources of GHGs include wetlands and termites. Previous studies have quantified GHG emissions from upland termites and no study has reported GHG emissions from seasonal wetlands (dambo) located termite mounds. The objective of this study was to evaluate the effect of dambo catena position on termite mound distribution and GHG emissions. It was hypothesized that mound density and GHG emissions from Odontotermes transvaalensis mounds, vary with catena position. The evaluated catena positions were margin, mid-slope, lower slope and bottom. Mound density was significantly lower in the bottom when compared to the other catena positions. The mean GHG fluxes were 88 µg m² hr^-1, 0.78 mg m² hr^-1 and 1361 mg m² hr^-1 for N₂) O, CH₄ and CO₂ respectively. Fluxes varied with catena position and were 0.48, 0.72, 1.35 and 0.79 mg m^-2 hr^-1 for CH₄ , and 1173.7, 1440.7, 1798.7 and 922.8 mg m^-2 hr^-1 for CO₂ in the margin, mid-slope, lower slope and the bottom catena position respectively. For N₂) O, there were no significant differences between catena positions. It was concluded that dambo located Odontotermes transvaalensis termite mounds are an important source of GHGs, and emissions varied with catena position for CO₂ and CH₄.

Rees et al. 2012. Nitrous oxide emissions from European agriculture; an analysis of variability and drivers of emissions from field experiments, Biogeosciences Discuss., 9, 9259-9288, doi:10.5194/bgd-9-9259-2012, 2012.

Rees, R. M., Augustin, J., Alberti, G., Ball, B. C., Boeckx, P., Cantarel, A., Castaldi, S., Chirinda, N., Chojnicki, B., Giebels, M., Gordon, H., Grosz, B., Horvath, L., Juszczak, R., Klemedtsson, Å. K., Klemedtsson, L., Medinets, S., Machon, A., Mapanda, F., Nyamangara, J., Olesen, J., Reay, D., Sanchez, L., Sanz Cobena, A., Smith, K. A., Sowerby, A., Sommer, M., Soussana, J. F., Stenberg, M., Topp, C. F. E., van Cleemput, O., Vallejo, A., Watson, C. A., and Wuta, M. 2013. Nitrous oxide emissions from European agriculture; an analysis of variability and drivers of emissions from field experiments, Biogeosciences, 10, 2671-2682, doi:10.5194/bg-10-2671-2013

Nitrous oxide emissions from a network of agricultural experiments in Europe and Zimbabwe were used to explore the relative importance of site and management controls of emissions. At each site, a selection of management interventions were compared within replicated experimental designs in plot based experiments. Arable experiments were conducted at Beano in Italy, El Encin in Spain, Foulum in Denmark, Logården in Sweden, Maulde in Belgium, Paulinenaue in Germany, Harare in Zimbabwe and Tulloch in the UK. Grassland experiments were conducted at Crichton, Nafferton and Peaknaze in the UK, Gödöllö in Hungary, Rzecin in Poland, Zarnekow in Germany and Theix in France. Nitrous oxide emissions were measured at each site over a period of at least two years using static chambers. Emissions varied widely between sites and as a result of manipulation treatments. Average site emissions (throughout the study period) varied between 0.04 and 21.21 kg N₂O-N ha⁻¹ yr⁻¹, with the largest fluxes and variability associated with the grassland sites. Total nitrogen addition was found to be the single most important determinant of emissions, accounting for 15% of the variance (using linear regression) in the data from the arable sites (p < 0.0001), and 77% in the grassland sites. The annual emissions from arable sites were significantly greater than those that would be predicted by IPCC default emission factors. Variability in N₂O within sites that occurred as a result of manipulation treatments was greater than that resulting from site to site and year to year variation, highlighting the importance of management interventions in contributing to greenhouse gas mitigation.

Gharahi Ghehi et al. 2012. Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda, Biogeosciences, 9, 1451-1463

Gharahi Ghehi, N., Werner, C., Cizungu Ntaboba, L., Mbonigaba Muhinda, J. J., Van Ranst, E., Butterbach-Bahl, K., Kiese, R., and Boeckx, P.: Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda, Biogeosciences, 9, 1451-1463, doi:10.5194/bg-9-1451-2012, 2012. 


Abstract. 
Globally, tropical forest soils represent the second largest source of N₂O and NO. However, there is still considerable uncertainty on the spatial variability and soil properties controlling N trace gas emission. Therefore, we carried out an incubation experiment with soils from 31 locations in the Nyungwe tropical mountain forest in southwestern Rwanda. All soils were incubated at three different moisture levels (50, 70 and 90 % water filled pore space (WFPS)) at 17 °C. Nitrous oxide emission varied between 4.5 and 400 μg N m⁻² h⁻¹, while NO emission varied from 6.6 to 265 μg N m⁻² h⁻¹. Mean N₂O emission at different moisture levels was 46.5 ± 11.1 (50 %WFPS), 71.7 ± 11.5 (70 %WFPS) and 98.8 ± 16.4 (90 %WFPS) μg N m⁻² h⁻¹, while mean NO emission was 69.3 ± 9.3 (50 %WFPS), 47.1 ± 5.8 (70 %WFPS) and 36.1 ± 4.2 (90 %WFPS) μg N m⁻² h⁻¹. The latter suggests that climate (i.e. dry vs. wet season) controls N₂O and NO emissions. Positive correlations with soil carbon and nitrogen indicate a biological control over N₂O and NO production. But interestingly N₂O and NO emissions also showed a positive correlation with free iron and a negative correlation with soil pH (only N₂O). The latter suggest that chemo-denitrification might, at least for N₂O, be an important production pathway. In conclusion improved understanding and process based modeling of N trace gas emission from tropical forests will benefit from spatially explicit trace gas emission estimates linked to basic soil property data and differentiating between biological and chemical pathways for N trace gas formation.

Caquet et al. 2012. Soil carbon balance in a tropical grassland: Estimation of soil respiration and its partitioning using a semi-empirical model

Caquet, B., De Grandcourt, A., Thongo M’bou, A., Epron, D., Kinana, A., Saint André, L., and Nouvellon, Y.: Soil carbon balance in a tropical grassland: Estimation of soil respiration and its partitioning using a semi-empirical model, Agricultural and Forest Meteorology, 158-159, 71-79, 2012.

Abstract

In savannah and tropical grasslands, which account for 60% of grasslands worldwide, a large share of ecosystem carbon is located below ground due to high root:shoot ratios. Temporal variations in soil CO₂ efflux (R_S) were investigated in a grassland of coastal Congo over two years. The objectives were (1) to identify the main factors controlling seasonal variations in R_S and (2) to develop a semi-empirical model describing R_S and including a heterotrophic component (R_H) and an autotrophic component (R_A). Plant above-ground activity was found to exert strong control over soil respiration since 71% of seasonal R_S variability was explained by the quantity of photosynthetically active radiation absorbed (APAR) by the grass canopy. We tested an additive model including a parameter enabling R_S partitioning into R_A and R_H. Assumptions underlying this model were that R_A mainly depended on the amount of photosynthates allocated below ground and that microbial and root activity was mostly controlled by soil temperature and soil moisture. The model provided a reasonably good prediction of seasonal variations in R_S (R² = 0.85) which varied between 5.4 μmol m⁻² s⁻¹ in the wet season and 0.9 μmol m⁻² s⁻¹ at the end of the dry season. The model was subsequently used to obtain annual estimates of R_S, R_A and R_H. In accordance with results reported for other tropical grasslands, we estimated that R_H accounted for 44% of R_S, which represented a flux similar to the amount of carbon brought annually to the soil from below-ground litter production. Overall, this study opens up prospects for simulating the carbon budget of tropical grasslands on a large scale using remotely sensed data.

Kim, D.-G., 2012. Estimation of net gain of soil carbon in a nitrogen-fixing tree and crop intercropping system in sub-Saharan Africa: results from re-examining a study.

Kim, D.-G., 2012. Estimation of net gain of soil carbon in a nitrogen-fixing tree and crop intercropping system in sub-Saharan Africa: results from re-examining a study. Agroforestry Systems, doi:10.1007/s10457-011-9477-1

 

Abstract

Nitrogen (N)-fixing tree and crop intercropping systems can be a sustainable agricultural practice in sub-Saharan Africa and can also contribute to resolving climate change through enhancing soil carbon (C) sequestration. A study conducted by Makumba et al. (Agric Ecosyst Environ 118:237–243, 2007) on the N-fixing tree gliricidia and maize intercropping system in southern Malawi provides a rare dataset of both sequestered soil C and C loss as soil carbon dioxide (CO₂) emissions. However, no soil C gain and loss estimates were made so the study failed to show the net gain of soil C. Also absent from this study was potential benefit or negative impact related to the other greenhouse gas, nitrous oxide (N₂O) and methane (CH₄) emissions from the intercropping system. Using the data provided in Makumba et al. (Agric Ecosyst Environ 118:237–243, 2007) a C loss as soil CO₂ emissions (51.2 ± 0.4 Mg C ha⁻¹) was estimated, amounting to 67.4% of the sequestered soil C (76 ± 8.6 Mg C ha⁻¹ in 0–2 m soil depth) for the first 7 years in the intercropping system. An annual net gain of soil C of 3.5 Mg C ha⁻¹ year⁻¹ was estimated from soil C sequestered and lost. Inclusion of the potential for N₂O mitigation [0.12–1.97 kg N₂O–N ha⁻¹ year⁻¹, 0.036–0.59 Mg CO₂ equivalents (eq.) ha⁻¹ year⁻¹] within this intercropping system mitigation as CO₂ eq. basis was estimated to be 3.5–4.1 Mg CO₂ eq. ha⁻¹ year⁻¹. These results suggest that reducing N₂O emission can significantly increase the overall mitigation benefit from the intercropping system. However, significant uncertainties are associated with estimating the effect of intercropping on soil N₂O and CH₄ emissions. These results stress the importance of including consideration of quantifying soil CO₂, N₂O and CH₄ emissions when quantifying the C sequestration potential in intercropping system.

Sugihara et al. 2012. Effects of land management on CO2 flux and soil C stock in two Tanzanian croplands with contrasting soil texture

Sugihara, S., Funakawa, S., Kilasara, M., and Kosaki, T.: Effects of land management on CO2 flux and soil C stock in two Tanzanian croplands with contrasting soil texture, Soil Biology and Biochemistry, 46, 1-9, 2012.

Abstract

Evaluation of carbon dynamics is of great concern worldwide in terms of climate change and soil fertility. However, the annual CO₂ flux and the effect of land management on the carbon budget are poorly understood in Sub-Saharan Africa, owing to the relative dearth of data for in situ CO₂ fluxes. Here, we evaluated seasonal variations in CO₂ efflux rate with hourly climate data in two dry tropical croplands in Tanzania at two sites with contrasting soil textures, viz. clayey or sandy, over four consecutive crop-cultivation periods of 40 months. We then: (1) estimated the annual CO₂ flux, and (2) evaluated the effect of land management (control plot, plant residue treatment plot, fertilizer treatment plot, and plant residue and fertilizer treatment plot) on the CO₂ flux and soil carbon stock at both sites. Estimated annual CO₂ fluxes were 1.0–2.2 and 0.9–1.9 Mg C ha⁻¹ yr⁻¹ for the clayey and sandy sites, respectively. At the end of the experiment, crop cultivation had decreased the surface soil carbon stocks by 2.4 and 3.0 Mg C ha⁻¹ (soil depth 0–15 cm) at the clayey and sandy sites, respectively. On the other hand, plant residue application (7.5 Mg C ha⁻¹ yr⁻¹) significantly increased the surface soil carbon stocks, i.e., 3.5–3.8 and 1.7–2.1 Mg C ha⁻¹ (soil depth 0–15 cm) at the clayey and sandy sites, respectively, while it also increased the annual CO₂ fluxes substantially, i.e., 2.5–4.0 and 2.4–3.4 Mg C ha⁻¹ yr⁻¹ for the clayey and sandy soils, respectively. Our results indicate that these dry tropical croplands at least may act as a carbon sink, though the efficiency of carbon accumulation was substantially lower in sandy soil (6.8–8.4%) compared to clayey soil (14.0–15.2%), possibly owing to higher carbon loss by leaching and macro-faunal activity.

Saunders et al. 2011. Agricultural encroachment: Implications for carbon sequestration in tropical African wetlands

Saunders, M.J., Kansiime, F., Jones, M.B., 2011. Agricultural encroachment: Implications for carbon sequestration in tropical African wetlands. Global Change Biology, 10.1111/j.1365-2486.2011.02633.x.

Abstract

Tropical wetlands have been shown to exhibit high rates of net primary productivity and may therefore play an important role in global climate change mitigation through carbon assimilation and sequestration. Many permanently flooded areas of tropical East Africa are dominated by the highly productive C₄ emergent macrophyte sedge, Cyperus papyrus L. (papyrus). However, increasing population densities around wetland margins in East Africa are reducing the extent of papyrus coverage due to the planting of subsistence crops such as Colocasia esculenta (cocoyam). In this paper we assess the impact of this land use change on the carbon cycle and in particular the impacts of land conversion on net ecosystem carbon dioxide exchange. Eddy covariance techniques were used, on a campaign basis, to measure fluxes of carbon dioxide over both papyrus and cocoyam dominated wetlands located on the Ugandan shore of Lake Victoria. Peak rates of net photosynthetic CO₂ assimilation, derived from monthly diurnal averages of net ecosystem exchange, of 28-35 μmol CO₂ m⁻² s⁻¹ and 15-20 μmol CO₂ m⁻² s⁻¹ were recorded in the papyrus and cocoyam wetlands respectively, while night time respiratory losses ranged between 10-15 μmol CO₂ m⁻² s⁻¹ at the papyrus wetland and 5-10 μmol CO₂ m⁻² s⁻¹ at the cocoyam site. The integration of the flux data suggest that papyrus wetlands have the potential to act as a sink for significant amounts of carbon, in the region of 10 t C ha⁻¹ yr⁻¹. The cocoyam vegetation assimilated ~7 t C ha⁻¹ yr⁻¹ but when carbon exports from crop biomass removal were accounted for these wetlands represent a significant net loss of carbon of similar magnitude. The development of sustainable wetland management strategies are therefore required, to promote the dual wetland function of crop production and the mitigation of greenhouse gas emissions especially under future climate change scenarios.