# Influence of Phosphogypsum Dump on the Soil Ecosystem in the Sumy region (Ukraine)
## 2 Materials and Methods  
### Study Area  
The phosphogypsum dump is located behind the town of Tokari in the Sumy region (Ukraine), at a distance of 800 (direct measurement)-1300 m (measured via road) from a residential area, and continues to receive new deposits of dihydrate phosphogypsum formed at the Public Joint-Stock Company (PJSC) \"Sumykhimprom\" location (Figure 1). Within the city of Sumy, dumps of phosphogypsum began in 1972, and today amount to about 15 million tons.  
Initially, the dump was organized on the site of the natural ravine \"Glubokij Yar\", at about 40 m deep. The presence of the ravine led to the formation of a dump with displacement of the terraces. As can be seen in Figure 1 terraces form a single frontal surface from the southeast side. The area of the dump is 492 m\({}^{2}\), with a sanitary protection zone of 637 m\({}^{2}\), and the perimeter of the active dump is about 1900 m. The phosphogypsum dump is conserved by loamy soil, and on the west side forms four terraces 12-15 m high, which can easily be seen. A new line of waste forms the upper phosphogypsum area. In order to protect this from drainage, a protective reservoir was built near the dump to its northwest.  
As a result of reclamation of the surface of the embankments of the dump, a layer of 20 to 40 cm of loamy soil is, to a certain extent, mixed with mineral particles of phosphogypsum.  
The body of the phosphogypsum dump also contains a waste repository of iron sulphate (copperas), which is waste from the production of titanium whitewash at Public Joint-Stock Company (PJSC) \"Sumykhimprom\" location. This waste repository promotes the sealing of iron sulphate in the body of phosphogypsum waste. However, it does not solve the problem of the accumulation of chemical waste in a given territory, which requires a solution to anthropogenic strain on the environment. The model of the geological structure of the dump is shown in Figure 2.  
Figure 1: Phosphogypsum terraces from the southeast side of the dump, Sumy region (Ukraine).  
Figure 2: Model of the phosphogypsum dump of PJSC “Sumykhimprom”.  
The phosphogypsum waste in the dump contains a certain amount of bound and free water. Part of the free water in the process of hydration of stored phosphogypsum causes the chemical-mineralogical transformation of hemihydrates into dihydrates. Part of the moisture, in conjunction with atmospheric precipitation, forms an anthropogenic aquifer, which is infiltrated into the lower layers of the body of phosphogypsum. The bottom of the dump was constructed from natural clay soil, and then built up by dried phosphogypsum, forming original terraces. An anti-filter screen with a clay base filled and compacted with sand protects the ground under the dump.  
There is no vegetation on the fresh slopes of the dump, but on the slopes that are freshly covered with loamy substrate, the mosaic of the vegetation cover is observed, from single specimens over a larger area to the overgrowth of one-third of the projected covering of the area.  
The dump is blocked by loam and soil, and its vegetation has spontaneously grown. We investigated the patterns of succession of the spontaneous population of the dump with plants and their change over time. In areas (terraces) that were built up more than 10 years ago, the vegetation cover is dense and there are tree species. Vegetation has not yet developed on fresh phosphogypsum, which has been laid more recently.  
On the old reclaimed slopes of the canopy, the covering of the grassy perennial vegetation is complete. On the lowest terrace, in addition to the herbaceous annual and perennial vegetation, young trees are found, which indicates ongoing successional changes in plant communities. On the three lower slopes of the dump, the projective covering of the vegetation is maximally complete. On the upper part of the terraces, especially the recent subjects of reclamation, the quantity and species diversity of plants decrease.