Nitrate amendment improving the stability of methane oxidation in landfill biocover soils

Cover soil has been recognized as an important strategy for reducing methane (CH₄) emissions from landfills. However, CH₄ oxidation activity often exhibits a peak followed by a decrease to a lower steady level in landfill cover soils. Herein, two types of biocover materials including compost mixture (MS) and fine-grained waste soil (BS) obtained from an excavated landfill as well as conventional landfill cover soil mixture (RS) were employed to investigate the effectiveness of nitrogen amendment to stabilize CH₄ oxidation. During the whole experiment, the average CH₄ oxidation rates of BS and MS were 292.3-308.3 μg g^-1 h^-1, which were 41.3-43.6 times higher than that of RS. As the CH₄ oxidation activity dropped to a lower level, the exogenous NO₃^--N addition of 800 mg kg^-1 could rapidly recover the CH₄ oxidation activities of BS and MS, while it did not have an obvious effect on that of RS, likely owing to the poor nutrients and low microbial abundance. Most of the nitrogen added was deposited in BS and MS, with the nitrogen loss of -1.68 %-4.21 % of total nitrogen. The microbial co-occurrence network showed that the proportion of positive correlations among microorganisms was higher in BS (73.42 %) and MS (74.52 %) than in RS (65.27 %), but the microbial community composition in the formers was weaker biome stability. These findings suggested that the environmental variables should be carefully considered to create favorable conditions for maintaining the stability of community structure, when biocover soils would be used as alternative cove soils to reduce CH₄ emissions from landfills.