Natural reclamation of the vegetation and soil cover at the dumps of the Pavlovsk coal field of Primorskiy krai

Surface mining operations are accompanied by serious disturbance of natural ecosystems. The rationale for a reclamation method is based on both agrochemical and biological properties of the dumped rocks. For this reason, the investigation of primary succession and soil-formation processes at the dumps gains significant importance. The article is aimed to examine the characteristics of natural reclamation of the soil and vegetation cover in the dumps of the Pavlovsk coal field, which are different in composition and relief, and establish the relevance of the dump rocks for biological reclamation. The investigations were carried out on the territory of the Pavlovsk coal mine (Mikhailovsky district, Primorskiy Krai). At the North Depression section (44°05'39.5"N 132°04'47.3"E), two dumps were investigated - the 8-year-old dump is characterized by the conical form, with the slope of 25° (See Fig. 1A), while the 15-year-old dump has a terrace in the middle section of the slope (See Fig. IB). These dumps are formed by loamy rocks, with the ratio of its slopes being 12-15°. At the East Depression section (44°05'24.3"N 132°05'08.9"E), the 16-year dump with smoother slopes (up to 12°) formed by clay was investigated. To examine the characteristics of colonization by vegetation, the line transects were formed from the bases of dumps to their tops. The stages of succession of plants were identified according to Voronov (1973). The organic carbon (Corg.) was determined using the Tyurin method. The granulometric composition of rocks was determined according to Kachinsky. The content of active (mobile) forms of phosphorus and potassium was determined using the methods by Kirsanov and Maslova, respectively. The current and exchangeable acidities of soils were examined using potentiometry. The classification of soils of the technogenic landscapes by Kurachev (2002) and WRB (2022) was used. As part of this study, we revealed fragmentary vegetation cover at the 8-year-old dump of the North Depression section. Within the limits of the built transect, 11 species of plants belonging to 8 families were detected. The dump slopes were subjected to water erosion. The rocks of dump had рНН2O = 4.3-4.4, low content of active forms of phosphorus and potassium (See Table 3). Pedogenic accumulation of Corg. was not observed at this dump. The development of the vegetation cover was at the pioneer stage. The Initial Embryozems (Spolic Technosols (Loamic)) were formed. On the 15-year dump, 31 species of plants belonging to 12 families were detected. In the eluvial position, a minimum number of plant species were found (See Table 2). The rocks were weakly affected by the soil formation processes, had рНН2O = 4.7, low content of phosphorus and high of potassium, while that of carbon reached 2.5% at the expense of carbon-bearing inclusions (See Table 3). The development of vegetation cover was at the pioneer stage on the Initial Embryozems (Spolic Technosols (Loamic)). In the transit positions of the dump, the complex plant cluster (with large phytomass reserves) was formed. The active colonization by vegetation resulted in formation of sod horizon with the content of Сorg. up to 1.1%, where the Sod Embryozems (Spolic Technosols (Suprafolic, Loamic)) were formed. The environment reaction of the upper horizons changed toward neutral (рНН2O = 6.2). The content of active phosphorus was low, while that of active potassium was abundant. The role of woody vegetation increased in the accumulative position (terrace). This is a stage of closed phytocenosis with active soil-forming processes. Soils had рНН2O = 6.3 in the 0-5 cm layer, while the content of Corg. increased to 3.35%, and those of phosphorus and potassium reached high and very high values, respectively. The Humus-accumulative Embriozems (Spolic Technosols (Humic, Loamic)) were formed. At the 16-year-old clayey dump of the East section, the vegetation cover is very heterogeneous due to active erosion. In such areas, the vegetation cover development was at the pioneer stage and the soil cover was at the initial stage (Spolic Technosols (Clayic)). At the most overgrown sections of dump, the projective cover reached 80% (See Fig. 2). Within the limits of the built transect, 23 species of vascular plants were found (See Table 4). This is a stage of complex plant cluster, when the litter horizon and Organic-accumulative Embryozemes (Spolic Technosols (Protofolic, Clayic)) were formed on soil surface. The rocks of dump had рНН2O = 5.9-6.3, low content of Corg. very low of phosphorus, and very high of potassium. In this study, we found that the families of Asteraceae and Poaceae were the most abundant in the projective cover and number of species at the investigated dumps. The highest Jaccard similarity coefficient of vegetation species composition was relevant for older dumps. During the first ten years, the dumps of loamy composition, with slope of 25°, were scarcely colonized by vegetation due to strong erosion processes. The vegetation cover development was at the pioneer stage and the soil cover was at the initial stage (Spolic Technosols (Loamic)). With more favorable relief features, the full tree layer was already formed by the 15 th year after dumping and Humus-accumulative Embryozems (Spolic Technosols (Humic, Loamic)) were developed. At the same time, Sod Embryozems (Spolic Technosols (Suprafolic, Loamic)) were formed on the slopes. The development of vegetation at the clayey 16-year-old dump remained at the stage of complex plant clusters. On this dump Organic-accumulative Embryozems (Spolic Technosols (Protofolic, Clayic)) were formed. The phytocenoses in the clayey dumps of the East section were formed in the meadow type. At the dumps formed by lighter rocks, the survival ability of woody species of plants was higher. One of the basic constraining factors of developing the stable phytocenoses at the dumps was the processes of water erosion. It was found that in the early years after dumping, the rocks of dumps were hardly suitable for biological recultivation due to their high acidity. The paper contains 2 Figures, 4 Tables, and 31 References. The Authors declare no conflict of interest.

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