Short-term changes in bacterial community fingerprints and potential activities in an alfisol supplemented with solid...

We investigated the effect on soil functioning of adding leachates from municipal solid waste incinerator (MSWI) ashes to laboratory columns (bare soil) and to field experimental plots (bare soil or grass cover). Leachate of MSWI-solidified air pollution control residues (SAPCr) contained more salts but less heavy metals than did MSWI-bottom ash (BA) leachate. Leachate-supplemented soils (BA soil, SAPCr soil) and control (water added) soil (W) were analyzed after 30 days. Potential denitrifying activity (PDA) and potential N2 fixation (acetylene reduction assay, ARA) were measured in controlled conditions. PDA was significantly lower in SAPCr soil than in W soil, both in the laboratory (-45%) and in bare soil in the field (-31%). ARA values were lower in bare SAPCr soil (-54%) and in bare BA (-25%) soil. Both activities remained unaffected by leachate supplementation in soil under permanent grass cover. Automated ribosomal intergenic spacer analysis (A-RISA) fingerprints and RFLP of nifH gene pools were used to assess changes in the structure of bacterial community. Multivariate analysis of these fingerprints revealed that SAPCr leachate had a stronger effect than BA leachate on the total and N2-fixing bacterial communities. Similar results were obtained for laboratory and bare soil field plots, but leachates did not affect nifH gene pools from soil under permanent grass cover. The stronger impact of SAPCr leachate on both structure of bacterial communities and activities supports the conclusion that observed effects would result from the abundance of salts rather than from heavy metal toxicity.