Mineral extraction is one of the key sources of revenue for the Russian Federation but also results in significant negative environmental impacts. More than 80 billion tons of mining waste have already accumulated in Russia, occupying a total area of 1.1 million hectares disturbed by mining activities. Each year, this number continues to increase, leading to the degradation of essential forest functions in areas located at or near mining and mineral processing sites. The establishment of such facilities is accompanied by extensive deforestation, removal of the fertile soil layer, and alterations to river channels and runoff patterns1 [1].

The condition of forest ecosystems plays a crucial role in the formation of river basins through surface runoff, particularly in mining regions [2]. M. E. Tkachenko (1952) considered the water protection role of forests in a broader context, not limiting it to the quantitative assessment of runoff. In his view, the beneficial effects of forests extend not only to surface waters (rivers, lakes, reservoirs) but also to groundwater, which often serves as the main source of water supply for both communities and industrial enterprises [3].

According to the concept of the general moisture-retaining function of forests, these ecosystems contribute to moisture accumulation within catchment areas, thereby increasing the total annual runoff [4]. However, an opposing view exists that considers forests as strong evaporators of moisture, suggesting that an increase in forest cover reduces river runoff [5]. O. I. Krestovsky, based on studies in the southern taiga, established that after clear cutting, the evaporation component decreases by 20–40%. As a result, the runoff regime deteriorates: during the high-water period, liquid runoff increases, whereas during low-water periods, rivers become shallower [6]. Anthropogenic impacts not only modify the conditions of various runoff types [7–9] but also transform the characteristics of diffuse pollution, affecting the quality of surface water bodies [10]. This is particularly significant when toxic elements such as heavy metals and arsenic are present, leading to suppression and die-off of forest vegetation due to their spread across natural and technogenic environmental components [11].

Thus, the formation of river runoff may depend on the following factors:

The tailings storage facilities of the Solnechny Mining and Processing Plant (Solnechny MPP) represent sites of ecological and technogenic hazard, acting as sources of contamination for groundwater, surface water, soils, vegetation, and the atmosphere due to dust emissions from their surfaces [14, 22, 23]. The purpose of this study is to assess the impact of mining operations on river runoff formation and the reduction of streamflow in small rivers within the Silinka River basin. The study addressed the following objectives: 1 – to analyze literature data on factors affecting the formation of river runoff in small rivers; 2 – to describe the disturbed area occupied by the tin mining enterprise; 3 – to assess the forest cover and water-protective function of forests within the influence zone of the Solnechny Mining and Processing Plant.

1 State (National) Report on the Status and Use of Lands.URL: https://rosreestr.gov.ru/activity/gosudarstvennoe-upravlenie-v-sfere-ispolzovaniya-i-okhrany-zemel/gosudarstvennyy-natsionalnyy-doklad-o-sostoyanii-i-ispolzovanii-zemel-rossiyskoy-federatsii (Accessed: 7 November 2024).

The study area comprises the disturbed lands of the former Solnechny MPP, located within the Silinka River catchment, Solnechny District, Khabarovsk Territory [13, 24]. Solnechny MPP was the district’s principal enterprise and the main economic driver of the area. Since 1969, large volumes of toxic waste have accumulated and been stored in three tailings storage facilities (TSFs).

As a result of open-pit and underground mining of cassiterite and cassiterite–sulfide deposits, large open pits and dumps of substandard ores and host rocks remain on the surface, along with numerous adits from which waste rock and mine water are discharged onto the slopes (Fig. 1).

Fig. 1. Schematic map of technogenic facilities within the Silinka River basin

The mining–technogenic system that developed in the Komsomolsk tin-ore district has intensified supergene processes due to the expanded contact area between weathering agents and exposed surfaces of sulfide ores, as well as finely ground sulfides in the tailings. These processes have progressed to a more advanced technogenic stage.

The tailings storage facilities of the Solnechny MPP are composed of gray hydraulic-fill sands, sometimes stained brownish by iron hydroxides formed through oxidation of sulfides. The grain size of the sands is predominantly less than 0.5 mm. Coarse fractions greater than 2 mm account for about 1% of the total volume (up to 3% in certain layers), while 70–83% of the material consists of particles in the 0.1–0.5 mm range, and 13–14% are finer than 0.1 mm (up to 28% in individual horizons). The vertical grain-size distribution is heterogeneous. According to previous assessments of waste hazard classes, the dried tailings belong to the highly hazardous toxicity class [25]. No land reclamation was undertaken in the disturbed area, despite the requirements of the Russian Federation’s Law on Subsoil [26].

The first tailings storage facility lies opposite the settlement of Gorny, approximately 100–500 m from the concentration plant. Its area is 44 hectares, with a total volume of 10.4 million tons (Fig. 2, a).

Fig. 2. Mining-disturbed areas of the former Solnechny Mining and Processing Plant: a – operating processing plant of JSC Tin Ore Company; b – surface of the second tailings storage facility; c – surface of the third tailings storage facility; d – surface of the settling pond at the Festivalnoye deposit

The waste material from the second tailings storage facility is currently being reprocessed by LLC Geoprominvest to produce tin and copper concentrates (Fig. 2, b).

At present, the assets of the former Solnechny MPP, including the Festivalnoye and Perevalnoye deposits, are managed by JSC Tin Ore Company, which has restarted tin and tungsten mining operations and continues to fill the third tailings storage facility (Fig. 2 c, d).

The forest cover of the Silinka River basin was assessed using the Normalized Difference Vegetation Index (NDVI) calculated from Landsat 8 satellite data processed in QGIS. According to previous research [27], NDVI values below 0.3 correspond to non-forested areas, while values above 0.3 indicate forested land.

The ecological and economic assessment of the impact of mineral exploration and mining activities is not standardized and lacks a unified methodological framework. In this study, cartographic modeling was performed using the open-source software QGIS 3.10, along with the recommended method for estimating the economic damage to river runoff based on forest cover [28]:

M = −1.02 + 0.068 × F, (1)

where M is the runoff modulus per 1 km2 of the catchment area, and F is the forest cover percentage.

The catchment area of the Silinka River is 1,016 km2 [29]. The river basin belongs to the Far Eastern taiga forest region and lies within the boundaries of two forestry districts – Komsomolsk and Solnechny. In the northwest, it borders the protected area of the regional natural monument “Amut Landslide Lake,” while the rest of the forested land is located within the green zone or classified as production forests.

Between 2012 and 2024, the total area of mining-disturbed lands within the Silinka River basin increased from 341.5 ha to 430.8 ha (Fig. 3).

Fig. 3. Schematic map of mining-disturbed areas: a – first tailings storage facility;b – second tailings storage facility; c – third tailings storage facility; d – settling pond at the Festivalnoye deposit.Note: blue – extent of the disturbed area in 2012; red – extent of the disturbed areas in 2024; purple – combined outline for 2012 and 2024.

According to GIS-based analysis using the Normalized Difference Vegetation Index (NDVI) calculated in QGIS from Landsat satellite data, the maximum NDVI value in the Silinka River basin does not exceed 0.494, which corresponds to a moderate level of forest biomass development (Fig. 4).

Fig. 4. Schematic map of the Silinka River basin with Normalized Difference Vegetation Index (NDVI). Note: boundary of the analysed river network section

Analysis of the resulting raster images (Table 1, Fig. 5) showed that forest cover in the Silinka River basin within the areas affected by the Solnechny MPP has changed in response to the expansion of mining-disturbed land (Fig. 6). NDVI-based estimation of forest cover indicated a decrease of 14.8%.

Table 1

Forest cover parameters derived from NDVI for river basins hosting technogenic facilities of the studied mining enterprises

Fig. 5. NDVI-based forest cover in river basins hosting mining facilities, 2012 (a) and 2024 (b)Note: black pixels represent non-forested areas

Fig. 6. Relationship between forest cover and the extent of disturbed land in the Silinka River basin

Based on the recommendations for estimating economic losses associated with changes in river runoff as a function of forest cover (Eq. 1), the specific runoff from 1 km2 of the catchment area was 3.978 × 103 m3 in 2012 and decreased to 2.9726 × 103 m3 by 2024.

The statutory charge for withdrawing 103 m3 of surface water from water bodies within the Amur River basin (Far Eastern region) within the approved quarterly abstraction limits is 264 rubles. For withdrawals exceeding these limits, the rate is applied at five times the standard level. In addition, a coefficient of 1.1 is applied to the water-use tax rate in 2024.

As a result, the charge for 103 m3 of water in 2012 and 2024 amounted to 5,776.05 rubles and 4,314.76 rubles, respectively.

The capitalized value of the study2 area amounted to 57,760.5 rubles in 2012 and 43,147.6 rubles in 2024.

The reduction in the value of 1 km2 of territory performing water-protection functions within the Silinka River basin can therefore be expressed as the difference between the capitalized values calculated for 2012 and 2024.

According to the calculations, the average value per 1 km2 of the study area decreased by 14,612.9 rubles, which corresponds to a reduction of about 25% as a result of mining activity.

2 Order No. 81 of February 11, 1998 "On Approval of the Methodology for Calculating the Damage from Groundwater Pollution". State Committee of the Russian Federation for Environmental Protection. 1998.

Geoinformation analysis based on the Normalized Difference Vegetation Index (NDVI) revealed a 14.8% decrease in forest cover within the section of the Silinka River basin affected by the former Solnechny Mining and Processing Plant, relative to the 2012 baseline. This confirms the degradation of the water-regulating function of the vegetation cover. The reduction in forest cover is accompanied by a decrease in specific runoff of 1.0064 × 103 m3 per km2, which is equivalent to a 25% decline in streamflow.

The calculated average value per 1 km2 of the study area in 2024 decreased by 14,612.9 rubles due to mining operations. Thus, the extraction of tin ore within the Silinka River basin (Solnechny District, Khabarovsk Territory) leads to a reduction in forest cover, which in turn causes a directly proportional decrease in the streamflow of small rivers.