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60 4 Environmental

60 4 Environmental results: presentation, discussion and interpretation 4.2.9 Biogas versus natural gas for combined heat and power production Use of fossil fuels Greenhouse effect Acidification Eutrophication Summer smog Nitrous oxide** Human toxicity** * How to interpret the diagram Advantages for biofuel Advantages for fossil fuel -2000 -1500 -1000 -500 0 500 1000 European inhabitant equivalents* per 100 TJ The figure shows the results of comparisons between complete life cycles where natural gas is substituted by biogas for energy (heat and power) production. The unit refers to an amount of 100 TJ of energy. In this case for example the amount of fossil fuel saved is equal to the amount which about 800 European citizens would on average consume in one year (this is what is meant by “European inhabitant equivalents”). Remarks and conclusions The results show that both biogas as well as natural gas have certain ecological advantages and disadvantages. • Advantages of the biofuel: use of fossil fuels, greenhouse effect, summer smog • Advantages of the fossil fuel: acidification, eutrophication • Low or no significance: – The data for ozone depletion and human toxicity tend to have a high uncertainty. Therefore these categories should not be included in the final assessment. (**See Chapter 4.1.2 and for details on all impact categories 3.3 and 3.4) A further assessment in favour of or against biogas or natural gas cannot be carried out on a scientific basis, because for this purpose subjective value judgements regarding the individual environmental categories are required which differ from person to person.

4.2 European results: biofuels compared to fossil fuels 61 4.2.10 Results on biodiversity and soil quality As discussed in the Chapter 3.4.1, four parameters were chosen to describe biodiversity and soil quality: a) Soil compaction b) Ecosystem occupation as an indicator of loss of biodiversity c) Ecosystem occupation as a measure for life support functions of the soil d) Harmful rainfall as an indicator of erosion Of these, only the latter two yielded quantitative results, while for the other two parameters no calculations could be carried out. Furthermore, even the results for the two parameters that could be calculated were not included in the graphs of the previous sections. This is first of all due to their poor data reliability, which is a result of yet insufficiently developed assessment methodologies and secondly, because the two selected parameters do not describe biodiversity and land use issues sufficiently. However, certain results have been obtained nonetheless which will be discussed in the following sections. These results should be interpreted with care and not be used as a scientific decision base regarding the biofuels in question. Bearing these limitations in mind however, they may be regarded as a first indication of the nature of the results obtainable by means of more advanced assessment methods in the future. Results on ecosystem occupation as a measure for life support functions of the soil As explained in Chapter 3.4.1, ecosystem occupation is defined in terms of various parameters such as yield, area, growing period and others. While most of these could be assessed fairly easily (see Annex 7.5 for further information), the values for the so called free net primary production were difficult to assess for a number of crops due to a lack of data for aboveground production, root production and corresponding decomposition rates. In many cases only a mean value could be given, while in other cases values are estimates rather than hard figures. Hence the results should be interpreted with care. Because of the poor overall data quality no sensitivity analysis was made. As the examples show free net primary production values and yield data for the same crop differ between countries. Examples for free net primary production in t/(ha*a) are: Triticale: -4,0 (France) to 7,1 (Denmark) Wheat straw: 4,9 (Germany) to 8,6 (Austria) Sugar beet: -7,0 (The Netherlands) to 10,4 (France) Examples for yield in t/(ha*a) are: Rape seed : 2,7 (Austria) to 6,4 (Germany) Miscanthus: 7,5 (Denmark) to 16,8 (Netherlands) These differences indicate a level of uncertainty which prohibits a meaningful interpretation. They may partly be due to differences in management practices between regions and countries, e.g. different harvesting methods. In addition, climate and soil differences may have a substantial influence. This issue requires further investigation. Regarding the overall parameter ecosystem occupation the results can be summarised as follows: • The ranking of crops according to their result on ecosystem occupation differs between countries. For instance, sugar beet has the highest ecosystem occupation in Germany, and the lowest in the Netherlands. Similarly, triticale has the highest score in Denmark, whereas in France it has the lowest value. These differences need to be explored further in order to understand them. • In some countries, ecosystem occupation values for rape seed, triticale and wheat turn out to be negative. This implies that these crops are – with regard to those regions – better in providing free net primary production than the average one in mid-Europe. Maybe information on soil structure could explain the differences – possibly in combination with the annual addition of organic matter. • In some countries, rape seed is followed by a grass filler crop in the same year. Hence in comparison with grass fallow used here as a reference crop, the figures for ecosystem occupation by rape seed and grass filler crop would have to be summed up if they were available.

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