Soil health indicators are compromised differently by municipal solid waste leachate under various climate conditions.

In many developing countries, landfilling is widely used as an efficient method for disposing of municipal solid waste. Literature review reveals that knowledge regarding the effects of climatic factors such as temperature and precipitation on different landfill sites is still insufficient and fragmented, especially in forest ecosystems. Therefore, this study sought to examine how waste accumulation affects soil health under different climatic conditions in the north of Iran. Soil samples were collected from four distinct sites that show a decline in precipitation alongside a rise in air temperature: Chalous, Noor, Shirgah, and Behshahr. Soil sampling across the 4 sites was performed in 2 environmental conditions (forest landfill and forest stand as a control), 4 seasons (spring, summer, fall, and winter), 3 soil depths (0-10 cm, 10-20 cm, and 20-30 cm), with 20 sampling replications taken at distances ranging from 200 to 300 m from each other. Soil sampling was done exactly at the waste dump site and after discarding the waste. Our results indicated that landfills led to a decline in litter chemical properties. In addition, landfills reduced soil porosity, aggregate stability, and soil fertility (nearly 1-2 times more in Chalous forest stand with higher precipitation and lower temperatures). Notably, the concentrations of heavy metals, such as cadmium, lead, and zinc significantly increased in landfill areas compared to the forest stand. Additionally, populations of fungi, bacteria, collembola, nematodes, acarina, protozoa have also decreased in all landfill sites. Furthermore, microbial parameters such as respiration, microbial biomass of C, N, and P, have declined following the climate pattern from Chalous to Behshahr in all the landfill sites, which were 1.5-2 times higher in Chalous forest stand with higher precipitation and lower temperatures than the other sites. Our findings highlight that unengineered landfilling had negative effects on soil health indicators at all sites studied, however, the region with the driest climate and least fertile soil suffered the most severe impacts. As a recommendation, municipalities can create targeted approaches, including waste recycling programs, that aim to mitigate risks and negative impacts while improving the overall benefits of landfills from a life-cycle perspective, addressing the needs of different stakeholders.