Mineralization of organic chemicals in soil is typically studied using large homogenized samples, but little is known about the small-scale spatial distribution of mineralization potential. We studied centimeter-scale spatial distribution of 2-methyl-4-chlorophenoxyacetic acid (MCPA) mineralization activity at different depths (8-115 cm) in a Danish agricultural soil profi le using a 96-well microplate 14C-radiorespirometric method for small-volume samples. The heterotrophic microbial population and specifi c MCPA degraders decreased 10- to 100-fold from the plow layer to a depth of 115 cm. MCPA was mineralized in all samples in the plow layer, but only about 60% in the transition zone immediately below the plow layer showed mineralization; at greater depth even fewer samples showed mineralization. A patchy spatial distribution of mineralization activity was observed from right below the plow layer and in the subsoil, with a few clearly defi ned active zones surrounded by areas devoid of mineralization activity. Due to the patchy distribution of mineralization activity at the centimeter scale just beneath the plow layer, MCPA and presumably other weakly sorbing pesticides might be at risk of leaching to the groundwater if transported from the plow layer into the subsoil.
- Programområde 2: Vandressourcer