The impact of urban park reconstruction on the aggregate structure of soil

In urban park reconstruction, one of the target management functions is soil quality. The aggregate structure provides the ability to efficiently perform soil ecosystem functions. The study examined the impact of park reconstruction on soil aggregate structure. The study was conducted in the recreational area of the Botanical Garden of the Oles Honchar Dnipro National University (Ukraine), where a 2.8-hectare section of the park has been reconstructed. Reconstruction work on the park included such processes as restoring pedestrian paths, removing shrubs and old damaged trees, and trimming tree crowns. Young trees were planted in places of distant old trees. Old outbuildings that had impaired the aesthetics of the park were also removed. Transport and construction equipment was involved in the reconstruction. There was found that there is an opposite dependence between the size of the fractions and their representation in the structure: the larger the size of the aggregate fraction, the smaller weight this fraction has. According to the index values, the state of the aggregate structure can be defined as good in a predominant number of cases. In a small number of cases, the condition can be assessed as satisfactory or excellent. The distribution of the aggregate fractions can be described by gamma law, the normal law, or a mixture of Gauss laws. The impact of reconstruction and the spatial aspect of variability can explain 15–69% of the variation in the content of aggregate fractions. In the condition of reconstruction, the content of larger fractions decreases, while the content of smaller fractions, on the contrary, increases. As a result of the reconstruction, the average size of aggregate fractions and structure coefficient (ratio of 1–10 mm fractions to dust particles) decreased. After reconstruction, the content of 3–5 mm aggregate fractions in the park's soil does not exceed 10.8% and/or the content of 2–3 mm aggregate fractions does not exceed 15.1%. The exposure of the area to wind combined with the increase in the content of the dust fraction is a very dangerous phenomenon induced by the reconstruction of the park. Decrease in the coefficient of soil structure indicates deterioration of the conditions of soil biota. The deterioration is due to a decrease in the specific weight of mesoaggregates and an increase in the proportion of microaggregates in the structure. Such a trend can lead to colmatage, that is, the space between meso- and macroaggregates can be densely filled with microaggregates, resulting in deterioration of the water and air regime of soils. Also, an increase in the dust fraction increases the risk of crust formation. The soil crust slows the gas exchange and also inhibits the infiltration of water that reaches the ground surface with precipitation, changing the vertical flow of water that replenishes soil moisture to lateral flow, which can accelerate water erosion of the soil. Reconstruction of the park should include alkalization of soil with sod grasses to restore soil structure and protect the soil cover from aerial erosion.