Figure 2From: 13C/12C composition, a novel parameter to study the downward migration of paper sludge in soils†13C/12C isotopic composition measured in 2000 of woodland and crop soils treated with paper sludge in 1992, versus non-treated soils (control). Note the 13C-enrichment of the black humic layer is due to the downward carbon transfer from the paper sludge.Back to article page