ASSESSING CARBON SEQUESTRATION AND POSSIBLE GREENHOUSE GAS EMISSION WITHIN THE DANUBE DELTA SOILS – PAST AND CURRENT ENVIRONMENTAL CONSIDERATIONS

Abstract

Soil organic carbon (SOC) sequestration generally occurs in wet ecosystems such as river flood plains and deltas. This paper deals with the carbon sequestration stock in the Danube Delta soils for various depths as based on the existing soil maps and updated materials and discusses about greenhouse gas emissions in order to enable evaluation of future evolution and possible scenarios in the light of global warming. Histosols represent about 28% of the Delta area and contribute with over 55% to the total SOC pool of this ecosystem. The histic subtypes of the Subaquatic Fluvisols, Gleysols and Arenosols also contribute much more to the total SOC pool than the non-histic subtypes. The large and significant SOC differences between mineral and organic soils is a strong reason for preservation of Histosolsʼ area and for renaturation of some less fertile soils from the lowest parts of Danube Delta in order to increase SOC and decrease atmospheric C. Only about 14.5% from the total Danube Delta area was taken for farming, mainly in its western part, where mineral soils or subtypes of organic soils occur. Histosols are especially situated in the maritime, eastern parts of the Delta ecosystem. In cropland areas the soil depth that is mobilized by plowing, disking or other works and from where the plants uptake water and nutrients is at least 0.5 m, and for some crops even from 1.0 m or below. The present paper deals with various soil depths for SOC referenced values, facilitating their use in specific estimation models. Policy makers, decision makers and opinion-formers should promote preservation of the natural landscape of the Delta under the best possible conditions to contribute to an increase in SOC stock. Maintaining the natural SOC stock at the present-day level and enhancing new organic C deposition in the renatured parts of Delta soils could contribute to global warming mitigation in the future. If global warming continues at the present rate or higher rates, the soil water regime will change reflecting the dynamics of sea level rising. This event will most probably accelerate peat formation and increase Histosol area in the lowest landforms across the Delta. Future research is needed for characteristic stationary sites specifically in the cropland area of the Danube Delta to deepen our knowledge regarding the dynamics of SOC.