Environmental modelling of use of treated organic waste on agricultural land: a comparison of existing models for life cycle assessment of waste systems.

Modelling of environmental impacts from the application of treated organic municipal solid waste (MSW) in agriculture differs widely between different models for environmental assessment of waste systems. In this comparative study five models were examined concerning quantification and impact assessment of environmental effects from land application of treated organic MSW: DST (Decision Support Tool, USA), IWM (Integrated Waste Management, U.K.), THE IFEU PROJECT (Germany), ORWARE (ORganic WAste REsearch, Sweden) and EASEWASTE (Environmental Assessment of Solid Waste Systems and Technologies, Denmark). DST and IWM are life cycle inventory (LCI) models, thus not performing actual impact assessment. The DST model includes only one water emission (biological oxygen demand) from compost leaching in the results and IWM considers only air emissions from avoided production of commercial fertilizers. THE IFEU PROJECT, ORWARE and EASEWASTE are life cycle assessment (LCA) models containing more detailed land application modules. A case study estimating the environmental impacts from land application of 1 ton of composted source sorted organic household waste was performed to compare the results from the different models and investigate the origin of any difference in type or magnitude of the results. The contributions from the LCI models were limited and did not depend on waste composition or local agricultural conditions. The three LCA models use the same overall approach for quantifying the impacts of the system. However, due to slightly different assumptions, quantification methods and environmental impact assessment, the obtained results varied clearly between the models. Furthermore, local conditions (e.g. soil type, farm type, climate and legal regulation) and waste composition strongly influenced the results of the environmental assessment.     

Sources and sinks of carbon dioxide in terrestrial ecosystems: Is the land's carbon budget balanced under the influence of man?

This contribution deals with the controversy between certain scientists on the role of terrestrial vegetation and soils in the global carbon cycle. The hypothesis of a significant net release from the vegetation, is rejected by geochemists because of the limited capacity of the ocean to take up this excess carbon dioxide. As for the man-influenced tropics, a comparison of the figures for the potential and the current phytomass, as well as plausible demographic arguments, support the assertion put forward by ecologists that the carbon budget of this zone cannot be balanced. The tropics lose about 1.7-3.9 × 10¹⁵ g/yr of carbon to the atmosphere; however, for several reasons, 0.5-2.8 × 10¹⁵ g/yr may be returned to land ecosystem, mostly in other climatic zones. Thus, a balance is achieved on combining low estimates for the losses with high estimates for the gains. From an ecological perspective, this solution is not a very probable one; nevertheless, it cannot conclusively be eliminated.