Microbial characteristics of the leachate contaminated soil of an informal landfill site

Abstract

Because informal landfills are not constructed in a regulated manner, they will inevitably become a source of leachate pollution to the surrounding environment over time. Microbes are an important part of the soil system, playing a vital role in maintaining the normal functionality of soil. This study investigated the microbial composition and co-occurrence pattern in the leachate contaminated soil of an informal landfill site. The landfill leachate underwent horizontal and vertical migration through the contaminated soil, resulting in significant differences in the microbial compositions of horizontal surface soil (CS) and vertical subsurface soil (DS and ES) compared to uncontaminated soil (S). The microbial diversity of CS, DS, and ES was lower than that of S. Due to the migration of landfill leachate, the microbial composition of the surface soil was substantially changed. The dominant phyla in S included Proteobacteria (26.88%), Chloroflexi (23.68%), Actinobacteroita (17.36%), and Acidobacteroita (16.86%), but in contaminated soils, Firmicutes (35.27-86.68%) were the dominant bacteria. A network analysis indicated that Bacilli, Clostridia, and Thermacetogeniazai of the Firmicutes were the keystone taxa and played a vital role in maintaining the stability of the soil ecosystem. A functional annotation of prokaryotic taxa (FAPROTAX) analysis showed that the microbes involved in the C-, N-, and S-cycles in contaminated soil were significantly different to those in uncontaminated soil. The proportion of (aerobic)-chemoheterotrophy and cellulolysis functional communities in contaminated soils was significantly reduced, while there was an increase in functional communities, such as anammox and denitrification, which are not conducive to soil nitrogen fixation. This negatively affected the maintenance of normal soil ecological functions. This study identified the microbial characteristics in leachate contaminated soil and the results will be beneficial for the remediation of contaminated soil in informal landfill sites.

Keywords: Contaminated soil; Informal landfill; Landfill leachate contamination; Soil ecological function; Soil fermentation function.