Reviews and syntheses: Greenhouse gas emissions in natural and agricultural lands in sub-Saharan Africa: synthesis of available data and suggestions for further studies uri icon

abstract

  • This paper summarizes currently availabledata on greenhouse gas (GHG) emissions from African natural ecosystems and agricultural lands. The avail-able data are used to synthesize current understanding of the drivers of change in GHG emissions, outline the knowledge gaps, and suggest future directions and strate- gies for GHG emission research. GHG emission data were collected from 75 studies conducted in 22 coun-tries (n=244) in sub-Saharan Africa (SSA). Carbondioxide (CO2) emissions were by far the largest con-tributor to GHG emissions and global warming potential (GWP) in SSA natural terrestrial systems. CO2 emis-sions ranged from 3.3 to 57.0 Mg CO2haâ??1yrâ??1, methane(CH4) emissions ranged fromâ??4.8 to 3.5 kg haâ??1yrâ??1(â??0.16 to 0.12 Mg CO2equivalent (eq.) haâ??1yrâ??1), and nitrous oxide (N2 O) emissions ranged fromâ??0.1 to13.7 kg haâ??1yrâ??1(â??0.03 to 4.1 Mg CO2 eq. haâ??1yrâ??1).Soil physical and chemical properties, rewetting, veg-etation type, forest management, and land-use changes were all found to be important factors affecting soil GHG emissions from natural terrestrial systems. In aquatic systems, CO 2 was the largest contributor to total GHG emissions, ranging from 5.7 to 232.0 Mg CO 2 haâ??1yrâ??1,followed by â??26.3 to 2741.9 kg CH4haâ??1yrâ??1(â??0.89 to 93.2 Mg CO2 eq. haâ??1yrâ??1) and 0.2 to 3.5 kg N 2O haâ??1yrâ??1(0.06 to 1.0 Mg CO2eq. haâ??1yrâ??1). Rates of all GHG emis-sions from aquatic systems were affected by type, location,hydrological characteristics, and water quality. In crop-lands, soil GHG emissions were also dominated by CO 2, ranging from 1.7 to 141.2 Mg CO 2 haâ??1yrâ??1, withâ??1.3 to 66.7 kg CH 4 ha â??1yrâ??1(â??0.04 to 2.3 Mg CO 2 eq. haâ??1 yrâ??1)and0.05 to112.0 kg N2 O haâ??1 yr â??1 (0.015 to 33.4 Mg CO2 eq. haâ??1 yr â??1). N2 O emission factors (EFs) ranged from 0.01 to 4.1 %. Incorporation of crop residues or manure with inorganic fertilizers invariably resulted in significant changes in GHG emissions, but results were inconsistent as the magnitude and direction of changes were differed by gas. Soil GHG emissions from vegetable gardens ranged from 73.3 to 132.0 Mg CO 2 ha â??1 yrâ??1and 53.4 to 177.6 kg N2 O haâ??1yrâ??1(15.9 to 52.9 Mg CO 2 eq. haâ??1yrâ??1)and N2 O EFs ranged from 3 to4 %. Soil CO 2 and N 2 O emissions from agroforestry were 38.6 Mg CO 2 haâ??1 yrâ??1 and 0.2 to 26.7 kg N 2 O haâ??1 yrâ??1 (0.06 to 8.0 Mg CO 2 eq. ha â??1yrâ??1), respectively. Improving fallow with nitrogen (N)-fixing trees led to increased CO 2 and N 2O emissions compared to conventional croplands.The type and quality of plant residue in the fallow is an important control on how CO 2 and N2 O emissions are affected. Throughout agricultural lands, N2 O emissions slowly increased with N inputs below 150 kg N ha â??1 yr â??1 and increased exponentially with N application rates up to 300 kg N ha â??1 yrâ??1. The lowest yield-scaled N2 O emissions were reported with N application rates ranging between 100 and 150 kg N haâ??1. Overall, total CO2eq. emissions from SSA natural ecosystems and agricultural lands were 56.9± 12.7Ã?109 Mg CO 2 eq. yrâ??1 with natural ecosystems and agricultural lands contributing 76.3 and 23.7 %, respec-tively. Additional GHG emission measurements are urgently required to reduce uncertainty on annual GHG emissions from the different land uses and identify major control fac-tors and mitigation options for low-emission development.A common strategy for addressing this data gap may includeidentifying priorities for data acquisition, utilizing appropri-ate technologies, and involving international networks andcollaboration

publication date

  • 2015
  • 2015