Abstract
Biogenic nonmethane hydrocarbon (NMHC) emissions were investigated at two field sites in the Republic of South Africa that include five important southern African savanna landscapes. Tropical savannas are a globally important biome with a high potential for biogenic emissions but no NMHC emission measurements in these regions or in any part of Africa have been reported. Landscape average hydrocarbon emissions were estimated by characterizing plant species composition and foliar density at each site, identifying and characterizing NMHC emissions of the most abundant plant species, and identifying and characterizing NMHC emissions of plant species with the highest NMHC emission rates. A hand‐held portable analyzer proved to be a useful tool for identifying plants with high emission rates. A branch enclosure system, with gas chromatography and flame ionization detector, was used to quantify isoprene and monoterpene emission rates. Emission rates were species‐specific and several genera had both high and low emitters. At least some species with high emission rates were identified in most savanna types. High and low emitters were found on both nutrient‐rich and nutrient‐poor soils. Landscape average emission capacities for the five savanna types range from 0.6 to 9 mg C m−2 h−1 for isoprene and about 0.05 to 3 mg C m−2 h−1 for monoterpenes. The savanna emission rates predicted by existing global models are within the range estimated for these five savanna types.
Highlights
Guentheret al. [1995] estimatedglobal NMHC emissionsNonmethanehydrocarbons(NMHCs) are releasedinto the atmosphere from surface sources and influence regional photochemical oxidant formation and acid deposition
Current estimatesrely on a very limited databaseof NMHC emissionratemeasurements.Existing data demonstratethat thereare large variationsin emissionrates for differentplantspeciesand for various landscapes.Most field investigationsof natural NMHC emissionshave been in North America and Europe [Guenther et al, 1995]
The HES systemconsistsof a small Trees have been the focus of most NMHC emission studies but polyethylene bag enclosureconnectedby Teflontubing to a shrubsand grassescontributesignificantlyto the total LAI in total NMHC analyzer with a photoionization detector most savannalandscapesand should be included in future (ThermoEnvironmental Instruments,model 580B)
Summary
Nonmethanehydrocarbons(NMHCs) are releasedinto the atmosphere from surface sources and influence regional photochemical oxidant formation and acid deposition. Tropical savannas are one of the ecosystemsfor which no NMHC emissions data were available. Tropical savannascover 65% of the land surfaceof Africa, 60% of Australiaand45% of South America[Huntley and Walker, 1982]. It is an important biome becauseof its potential in termsof grazing areasfor livestock and crop production, and alsobecauseof the role of savannasin the global carboncycle. The grazing and agricultural potential makes savannas susceptibleto land use change. In southern Africa the savanna biome covers 46% of all landscapes[Rutherford and Westfall, 1994]. Thetotal land dry weight weredeterminedfor the enclosedbranchso that surface in this region consists of about 30% emissionscouldbe expressedon both a foliar areaand dry Colophosperrnurnrnopane savanna, 50% Combreturn foliarmassbasis. Acacia tortilis savanna have muchhigherfoliardensitiesa,bout485 g rn', and are 4. lsoprene and Monoterpene Emission Rates comprisedof about71% A. tortilisand29% A. nilotica
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