BIODEGRADABLE DISSOLVED ORGANIC-CARBON IN SEEPAGE WATERS FROM 2 FOREST SOILS

Dissolved organic carbon (DOC), biodegradable dissolved organic carbon (BDOC) and phenols were measured in water leached from two forest soils (a mottled brown soil and a podzolic pseudogley) collected during a 3-day artificial rain experiment. Different behaviours of the soils with regard to their relationships with these compounds were observed. DOC removal from brown soil decreased over the 3-day experiment following a two-step evolution (first decreasing, then stabilizing), depending on BDOC initial stock. DOC concentration from podzolic pseudogley leachates increased from day 1 to day 3 and was poor in BDOC. A major part of the DOC removed from this soil was therefore refractory carbon. A Spearman rank correlation test showed a highly significant relationship between this fraction of DOC and phenols. Differences between these two types of soil as for their organic matter are well known. Nevertheless, BDOC measurements are more satisfactory than chemical analyses because they give information on DOC quality as it directly relates to microbial populations themselves.