Specifics of Soil Cover and Soil Property: Changes In Eastern Hovsgol Lake Area
The Hovsgol area is located at the boundary of the Siberian taiga and Central Asian steppe. It is an intersection of cold, dry climates, mountainous surface, with human impacts of intensifying overgrazing and forest fires that creates its own specific soil covers. In this case study of eastern Hovsgol region our objective has been to to identify specifics of soil cover and soil properties changes. We have used the comparative research method for evaluation of the overgrazing impacts and forest fires to the soil cover. Detailed investigation was carried out in the following valleys:
- Non grazed: Borsog and Dalbay
- Medium grazing: Sevsuul and Noyon
- Heavily grazed: Turag and Shagnuul valleys
The cold-humid climate conditions, the wide distribution of permafrost, taiga forest and peculiarities of rock sediment formed specific soil cover of Hovsgol area, different than many other parts of Mongolia. The main soil type of steppe pasture area of eastern Hovsgol lake area is Kastanozem soil. In the south-facing steppe slopes distributed Non-carbonated Dark Kastanozem soils. This soil is characterized by 25 cm thick humus horizons, low organic contents (humus-1.57 %), soil reaction slightly acid or neutral, exchangeable Calcium is - 9.58 cmol/kg, Magnesium is – 4.96 cmol/kg, nutrient elements Potassium low (12.78 mg/100 g) and Phosphorus (2.47 mg/100 g) ranges normal. By fertility levels these soils belong to the normal or low ranks. The texture content is sandy loam, dominated sand fraction up to 70-80%. The sandy texture content is the main reason for the comparatively low fertility level and Calcium carbonate leaching of Dark Kastanozem soils.
In the north lower slopes distributed Cryomorphic meadow, Cryomorphic peat and Chernozem soils. In the larch forests the soils are mainly dominated by Mountain taiga-derno soil, and in some lower places Mountain taiga-cryomorphic soils. In the valley bottoms distributed Cryomorphic peat, Cryomorphic Meadow and Alluvial peat soils. In the forest areas formed Mountain Derno-taiga and Mountain Cryomorphic-taiga soils.
Forest soils of Eastern Hovsgol lake area are characterized by a shallow top organic horizon, ranging 10-25 cm. In the Sevsuul valley occurred the most thin soil, only 5 cm top organic horizons on the sandy sediment. The short vegetation period and long lasting negative temperature conditions allows the accumulation of decomposing humus material. The very thin organic topsoil of forest areas is one of the main reasons for instability of trees growing there and a high percentage of falling trees in Eastern Hovsgol lake area. As the result of forest fires, the thickness of organic top layer of forest soils has decreased 2-3 times, from 20 cm to the 8 cm. In the low intensively fire affected areas, the soil humus content is 33.7-24.5 %, but in the high intensive forest fire areas, the humus content has decreased to 12.5-3.9%. The soil is becoming more compact as a result of fires. the soil bulk density in the more fire affected soils ranges 0.34-0.70 g/cm3, this is nearly 3 times more than low fire affected soils (0.14-0.19 g/cm3). As a result of fires, the soils are becoming more sandy.
As a result of overgrazing and pasture degradation, soil fertility is decreasing and soil chemical properties have changed. Soil humus content decreased by 30-50%, exchangeable Calcium decreased by 40-60% and nitrate nitrogen content has decreased in the northern overgrazed valleys.
Soil water physical properties have also changed. Soil temperature increases and moisture content decreases as a result of overgrazing. Topsoils are becoming more dense and compact as a result of animal pressure on the soil surface.
Soil humus content is a basic indicator of soil fertility level. From low grazing south valleys (Borsog, Dalbay), to the overgrazing north valleys soil humus content slightly decreasing (p=0.214). Possible to say, loss of soil fertility, result of overgrazing. Soil humus content decreased by 30-50% in overgrazed Turag valley relative to non-grazed Dalbay valley.
Soil Nitrate and Ammonium nitrogen content ranges completely different. Nitrate nitrogen content of soils, decreases towards the overgrazed valleys significantly (p=0.045). This is caused by basically soil organic contents. The decline of soil humus content in the overgrazed valleys, stipulated lower nitrate content. But, soil ammonium content increased in overgrazed valleys, slightly significant (p=0.118).
Ammonium is primarily a product of biological activity. Livestock dung and manure has a direct increasing impact of soil Ammonium Nitrogen content.
Overgrazing impacts on soil covers has not only changed soil fertility, and caused nutrient depletion, also influenced in soil water-physical properties. Top soil temperature increasing significantly (p=0.038) and moisture content decreases as a result of overgrazing. Soil temperature in the overgrazed Turag valleys increased by 3-5°C, comparing by non-grazed Dalbay valleys. Greater differences occurred at the 40-50 cm depths. The warming of soils has caused decreasing of moisture content, but relatively not very much. As the result of overgrazing and pasture degradation, soil fertility is decreasing and soil chemical properties have changed.