Adaptation of Soil Constructions of Nature-based Solutions (NbS) for Anthropogenic and Climatic Risks in the Conditions of the Moscow Megalopolis

Living in cities brings both social and economic benefits to people, but also exposes them to additional risks to life and health compared to living in the countryside. In the context of global climate change, adverse anthropogenic factors such as noise and light pollution, poor air quality, soil degradation and low biodiversity are compounded by the increased frequency of extreme weather events, ranging from heavy rainfall  to prolonged dry spells. The effects of such events are particularly pronounced in large cities in moderate climate where such hazards were uncharacteristic only a few decades ago. The megalopolis of Moscow is a prime example. The approach of systematic implementation of the principles of green infrastructure (GI) and nature-based solutions (NbS) has already proven its effectiveness in regions with southern and soft climates. However, in regions with pronounced and long winters, the implementation of NbS is limited by a number of factors: the risk of reduced soil substrate capacity due to freezing, reduced pollutant treatment efficiency at low temperatures, and the presence of de-icing chemicals in meltwater runoff. Therefore, the main objective of this work is to adapt international standards for the creation of NbS on a local scale to the natural and anthropogenic conditions of cities in moderate climate, using the Moscow megalopolis as a case study. 

The study included an experiment on de-icing salt contamination of soil for rain gardens based on a mixture of sand and loam and sand and peat under laboratory conditions. The results were focused on monitoring of agrochemical, physical and microbiological properties of soils, qualitative characteristics of leachate and the physiological state of plants. Monitoring of the experimental field rain garden was complemented by measurements of carbon dioxide emissions, field humidity, soil temperature and precipitation records, as well as analysis of the qualitative composition of snow cover and meltwater runoff. Experimental and field results related to surface runoff filtration processes were compared with modeling data obtained in Hydrus 2D. Experimentally obtained parameters of the soil-water characteristic curve (SWCC) and the results of particle size distribution analysis were used as input data for the model.  

 Model and laboratory values of filtration coefficients showed high convergence (R²=0.86) and did not exceed 300 mm/h for the proposed mixtures, but field measurements of filtration rate for identical soil mixtures were heterogeneous, with some replicates showing values almost 1.5 times higher. Soil substrates based on sand and loam were characterized by good water retention capacity and nutrient availability, which created favorable conditions for microbial communities. After salinization, the biomass and respiratory activity of microorganisms were reduced, and a low rate of recovery of viability after six months was also observed. Soils based on different types of sand and peat showed lower short-term salinity tolerance, but better long-term recovery, which can be explained by their lower water-holding capacity and better aeration.

The research was supported by the Russian Science Foundation project 23-77-01069.