Assessment of Soil Organic Carbon Stocks and Trace Gas Emissions from Burnt Lands Under Different Vegetation in Northern Ghana

Abstract

To determine the contributions of human activities on a changing climate do not only call for the assessment of main greenhouse gases but also trace gases emissions as well as variations of carbon sink in the soil. This study examined the dynamics of soil organic carbon stocks (SOCS) and estimated trace gas emissions using Intergovernmental Panel on Climate Change (IPCC) published guidelines. The study was conducted in the guinea savannah of Northern Region of Ghana. Six ( three on burnt and other three on unburnt lands) experimental plots of 50 m x 50 m were marked out on four different vegetation and soil samples taken from five sampling points at 0-10 cm,10-20 cm and 20-30 cm depths. Carbon concentration and bulk density were determined using Wakley Black and core method respectively. Another Five sampling plots (1m x 1m) on each vegetation cover were marked out to sample above-ground biomass for carbon content determination, before carbon release and trace gases (CH4 and CO) were further estimated. Findings of the research showed that while Carbon and bulk density differed significantly (P<0.05) across depth. A significantly strong negative correlation existed between them. Fire significantly (P<0.05) increased SOCS on burnt lands. SOCS insignificantly (P>0.05) varied under the vegetation types with close savanna woodland (CSW) recording the highest stock of organic carbon of ~16.7t/ha on unburnt sites and ~19.43 t/ha on burnt sites while Grass/herbs with scattered trees and shrubs (GHST) recoded ~7.9 t/ha and ~9.42 t/ha on unburnt and burnt sites respectively. Above-ground biomass density was highest on OSW with a density of ~4.8t/ha, while CSW recorded the least biomass density. GHST contained the highest organic carbon of 45.46% while CSW recorded 29.28% as the lowest carbon content. A significantly positive correlation existed between above-ground biomass density and carbon released. CH4 and CO emitted differs significantly (p<0.05) under all the vegetation cover types and were perfectly correlated (r=1.00) with the quantity of above ground biomass density and carbon release. Results also showed that irrespective of the vegetation type, more CO were emitted than CH4 during burning and this variation differed significantly (P<0.05) under the different vegetation types. The average amount of CH4 and CO emitted per hectare of area burnt made Open savanna woodland (OSW) the highest CH4 and CO emitter with 0.001719 tons and 0.045119 tons respectively while closed savanna woodlands (CSW ) recorded the least emission of 0.000268 tons of CH4 and 0.007043 tons of CO. The ratio of Dead and live at the time of burning on each vegetation type was the main reason for variations in emissions under the different vegetation covers. The results implies that, soils in the study area are generally low in SOCS and in the face of a changing climate(increasing temperature and unreliable rainfall) soils of this kind can barely support plant growth . Also the emissions may directly and indirectly contribute to global warming, impact negatively on both plant and animals, reduce visibility, cause health problems as well as increased human mortality especially if locally significant, especially when the release are annual, and concentrated during the dry season.