Constructed Technosols as a nature-based solution for surface run-off filtration and treatment: a case study of blue-green infrastructures in Moscow

Accelerating global climate change increases the frequency of extreme meteorological events: heat waves, hurricane-force winds, and rainstorms. Sustainability of urban ecosystems to these events becomes a priority for city planning and development. Urban soils provide the basis for the sustainable development of rain gardens - urban blue-green infrastructures, performing a wide range of ecosystem services that contribute to the mitigation of global climate change, detoxification of pollutants, infiltration, and purification of surface water and, as a result, improving the quality of life in the city. Therefore, the research aimed to model and assess the potential contribution of constructed Technosols to flood mitigation and surface runoff treatment in Moscow city.

The potential of Technosols to perform these ecosystem serves depends on the materials used for Technosols’ construction, construction design (sequence and depth of layers), and vegetation type. In this study, the assessment of the relationship between soil processes and ecosystem services of blue-green infrastructures included two stages. At first, the baseline chemical (organic matter and nutrients’ content, baseline total and mobile heavy metal content, ’pH), physical (texture, water retention curve and infiltration rate) and biological (microbial activity) properties of materials (substrates) were determined. Next, water and dissolved substances’ fluxes in the soil-plant system were monitored and modelled within the framework of a vegetation experiment. At this stage, analysis of water filtrate, estimation of evapotranspiration and transpiration of plants (Hemerocallis hybrid) were studied in parallel to monitoring soil properties.

Several types of river sand of medium (predominantly from 0.5 to 2.0 mm particular sizes) and fine (up to 0.5 mm) fractions, loams and sphagnum peat were used to create soil constructions. All components of soil constructions had no exceedances of pollutants in accordance with local sanitary and hygienic standards. The ratio of components in the design was selected to provide infiltration rate of 100 to 300 mm/h and sufficient nutrient’s content for plants. The best results (237 -315 mm/h) were shown by mixtures composed from the medium sand (not less than 70%) and peat. The results of the experiment with water retention curves showed that substrates with 70% sand had total water holding capacity ranging from 37 to 68%, whereas the total water holding capacity of pure peat reached 400%. To model the real-life rainfall conditions, peat infiltration was determined for unsaturated (long period without rains) and saturated (continuous intensive rainfall) samples. The obtained difference in filtration rates was in several orders of magnitude - 7 mm/h for unsaturated samples and over 1400 mm/h for the saturated samples. This outcome will be considered for further modeling the water-conducting capacity of peat-containing constructed Technosols in the HYDRUS 3D software. Subsequent phases of the project will include monitoring of leachate contamination with lead and zinc salts and evaluation of ecosystem service performance indicators in a real rain garden.

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