# Influence of Phosphogypsum Dump on the Soil Ecosystem in the Sumy region (Ukraine)
## 3 Results and Discussion
### The Study of Biochemical Transformations of the Technogenic Array of Phosphogypsum  
It has been established that for all phosphogypsum samples, irrespective of the residence time in the dump, an increased acidity is characteristic [33]. Thus, the aqueous extract of hydrolyzed phosphogypsum at a temperature of 24 \({}^{\circ}\)C had a pH of 2.3-2.8 for fresh phosphogypsum from a new dump taken from above the platform. For phosphogypsum stored in the dump, depending on the storage terrace, the pH value ranged from 3.8 to 5.8, depending on the age of the terrace [34]. The changes in the pH of the aqueous extract of phosphogypsum, depending on the terrace, and hence the residence time in the heap, are shown in Figure 8.  
The low pH level of fresh phosphogypsum samples can be due to the presence of water-soluble fluorine compounds (possibly H\({}_{2}\)SiF\({}_{6}\), Na\({}_{2}\)SiF\({}_{6}\), K\({}_{2}\)SiF\({}_{6}\), and HF), traces of non-void phosphoric acid and its salts, and sulfuric acid. The decrease in acidity in older terraces is explained by the gradual elution or evaporation of acidic compounds from the phosphogypsum stored earlier in the terrace under the influence of various natural factors. The concentration of phosphorus compounds decreases with the storage time of phosphogypsum, which is mainly due to the gradual transition of its compounds into water-soluble forms and washing  
Figure 8: The pH values of an aqueous extract of phosphogypsum samples depending on the place and time of stay in the dump. Figure 7: Infrared spectra of soil horizons (sampling point S1). out into the dump or the soil of the adjacent territories under the influence of hydraulic forces or atmospheric precipitation. It should be noted that the inclusion of silicon in the phosphogypsum structure occurs during deformation and fracture of mineral components, as the sealing load on the phosphogypsum layers increases in the dump. The change in the Sr content in the phosphogypsum samples (Table 2) can depend both on the composition of raw materials used for the production of fertilizers, and possibly the tendency to migrate its compounds. The conducted observations in the territory of the phosphogypsum dump showed that over time (more than 10 years), as a result of natural processes of soil formation and passages of succession, a vegetative crust occurred with a thickness of no more than 3-4 mm on the surface of non-cultivated phosphogypsum embankments [35]. Open areas of the phosphogypsum dump act as a substratum for settling on their surface, primarily by algae and moss, and in the future, gradually, higher herbaceous vegetation (Figures 9 and 10). The walls of the heap, after lying dormant with a mixture for reclamation, unlike open areas, are easily and quickly covered with light-responsive grassy vegetation. The surface roughness of phosphogypsum in the form of depressions and cracks, and also its significant moisture capacity, contributes to the settlement of the heap by plants, so phosphogypsum also contains a sufficient amount of residual phosphorus, sulfur, calcium, and other substances that act as macro- and micro-elements, becoming a good substratum, especially for ruderal and meadow vegetation. [PERSON] et al. [36]  
Figure 10: _Calamagrostis epigejos_, which dominates in restorative plant groups on the surface of the phosphogypsum dump. Figure 9: Surface layer of non-cultivated areas of the phosphogypsum dump with settlements of algae (**a**) and moss (**b**). revealed that wood small-reed had been proven to be extremely resistant to sulfur contamination and the relatively high salinity of soils, and occurred even on extremely sulphated soils. On the freshly formed open slopes of the phosphogypsum dump, vegetation is absent; on the slopes of the fresh loamy substratum, mosaic vegetation is observed, from single specimens to overgrowth of one-third of the projected covering of the area.