How does topography affect soil development

Thus, they may be thinner than the more nearly level soils that receive deposits from areas upslope. Deeper, darker colored soils may be expected on the bottom land.

Biological factors - Plants, animals, microorganisms, and humans affect soil formation. Animals and microorganisms mix soils and form burrows and pores. Plant roots open channels in the soils. Different types of roots have different effects on soils. Grass roots are fibrous near the soil surface and easily decompose, adding organic matter.

Taproots open pathways through deeper layers. Microorganisms affect chemical exchanges between roots and soil. Humans can mix the soil so extensively that the soil material is again considered parent material. The native vegetation depends on climate, topography, and biological factors, plus many soil factors such as soil density, depth, chemistry, temperature, and moisture. Leaves from plants fall to the surface and decompose on the soil. Organisms decompose these leaves and mix them with the upper part of the soil.

Trees and shrubs have large roots that may grow to considerable depths. Time - Time is also a component for the other factors to interact with the soil. Over time, soils exhibit features that reflect the other forming factors. Soil formation processes are continuous. Residue management becomes an important factor in maintaining high productivity. Lacustrine parent materials result from sediment deposited in lakes formed by glacial meltwater.

The lakes existed long enough that the large particles, such as rocks and sand, were deposited immediately after the lake was formed, while the smaller clay-sized particles were deposited later. Soils formed in lacustrine deposits have clay, clay loam and silty clay loam textures, poor internal drainage and no rocks. Many soils in northwestern Minnesota were formed in lacustrine material. Outwash is material deposited on the edges of fast-running rivers from the melting ice of receding glaciers.

This includes rocks, gravel, sand and other materials large enough to drop out of the water flow, as the river current continued transporting smaller particles. Soils formed in outwash are excessively well-drained and have sand and sandy loam textures. Examples of Minnesota areas with soils formed in outwash include the Anoka Sand Plain, North Central Sands and Bonanza Valley regions in east-central, north-central and central Minnesota, respectively.

Till bedrock deposits occur in northeastern Minnesota. Materials from the glacier were deposited over bedrock, similar to south-central Minnesota but with material from different glacial ice. There are also significant areas of soils formed directly from bedrock. Temperature and precipitation influence how fast parent materials weather and, thus, soil properties such as mineral composition and organic matter content. Temperature directly influences the speed of chemical reactions.

The warmer the temperature, the faster reactions occur. Temperature fluctuations increase physical weathering of rocks. Precipitation governs water movement in the soil. The amount of water the soil receives and the amount of evapotranspiration that occurs influence water movement. Normal annual precipitation in Minnesota is the least in the northwest corner at 16 inches, and increases as you go toward the southeast corner, where 34 inches is the normal annual precipitation Figure 2.

Evapotranspiration is the combination of water evaporated from the soil surface and water transpired by growing plants. As air temperatures increase, evapotranspiration increases.

High evapotranspiration relative to precipitation means less water is available to move through the soil. In Minnesota, the greatest evapotranspiration occurs in the southwestern part of the state and decreases as you go toward the northeastern corner. A leaching index or moisture index Figure 3 is calculated by subtracting evapotranspiration from precipitation. This index is an indicator of average soil moisture conditions.

The greater the index, the more soil moisture is present. Higher soil moisture increases chemical weathering and moves minerals, such as bases, deeper into the soil profile. This affects management practices such as drainage and inputs of mobile nutrients.

Biotic agents have greatly affected the soil formation process. These include organisms that live in the soil, such as bacteria and gophers, and vegetation growing on the surface.

Organisms in the soil can speed up or slow down soil formation. For example, microorganisms can facilitate chemical reactions or excrete organic substances to improve water infiltration in the soil.

Other organisms such as gophers slow soil formation by digging and mixing soil materials, and destroying soil horizons that have formed. Minnesota soils have been formed under two major types of vegetation: Forest and prairie.

Soils formed under forests tend to be more weathered older in soil terms because forests grow in higher rainfall areas. Soils formed in prairie tend to be in areas with less precipitation. Grasses tend to use the provided moisture, reducing the water movement through the soil profile. Organic matter forms in large quantities and to a deeper depth in the soil surface than forest soils. Figure 4 shows the different vegetations soils were formed in.

The soils in the southwestern, south-central and western parts of the state were formed in prairie. The soils in the northeastern part of the state were formed under forest vegetation. The savannah between the forest and prairie is a transitional area known as an ecotone. Prairie and forest vegetation existed in this area, changing between forest and prairie as climate changed over time. Forest vegetation would creep into the prairie in wetter climates, while events such as fires changed forested areas to prairie.

Slope refers to steepness in degrees or percent from horizontal, which affects how much soil material is deposited or eroded. Aspect is the direction the slope faces relative to the sun compass direction , which affects the amount of water that moves through the soil. A soil with a southern aspect tends to have grass vegetation, warmer soil temperatures and more evaporation.

The net effect is more soil aging with a northern aspect compared to soil with a southern aspect, even with the cooler soil temperatures. In a landscape, a sequence of soils with different horizons caused by differences in their depth to the water table is called a catena. A catena normally consists of four soil series, with soils located on the summit, shoulder, backslope and footslope as shown in Figure 5. The available K and rock content were the best explanatory variables compared with the other environmental variables, and they were positively correlated with tree volume.

The soil water content was also positively correlated with tree volume. The soil organic matter and total N were positively correlated with canopy density and were negatively correlated with above-ground biomass and herb coverage, and high correlations were observed between these variables. With high correlations, the available P and soil total porosity were positively correlated with above-ground biomass and herb coverage and was negatively correlated with canopy density.

The clay content was positively correlated with the herb coverage and above-ground biomass and was negatively correlated with canopy density.

The silt content and sand content were positively correlated with canopy density and were negatively correlated with herb coverage and above-ground biomass.

Although the explanatory power for the vegetation of silt content and sand content was relatively low, the soil texture also presented a high explanatory power for vegetation changes.

The second ordination axis represents the effects of the topographic variables on vegetation. The slope and slope aspect were positively correlated with above-ground coverage and herb coverage, and were negatively correlated with canopy density. This finding showed that the effects of topographic factors on vegetation restoration in an opencast coal mine dump located in a loess area were not obvious, but the relationship between the soil factors and the vegetation data was clear.

The correlation between soil factors and topographic factors obtained through the RDA is shown in Table 4. The total N was positively correlated with slope position 0. The soil water content was positively correlated with the slope. THE rock content was positively correlated with slope and slope position. In contrast, the sand content presented a significant positive correlation with the slope and slope position.

The clay content and sand content did not have any clear correlation with the topographic factors. The correlation between other soil factors and topographic factors was also not obvious Table 4. The results indicated that variations in the slope, slope position, and slope aspect affected the soil variables.

The correlation analysis between the soil variables is shown in Table 4. The silt content showed a positive correlation with the soil water content 0. The sand content also showed a significant positive correlation with total N 0. These changes were consistent with previous findings. The rock content and soil organic matter showed positive correlations with the total N 0.

The total N was significantly and positively correlated with the soil organic matter 0. Furthermore, total N was positively correlated with available K 0. The available K was positively correlated with soil bulk density 0. The results indicated that the soil texture, among all of the soil physical properties, presented a clear predictive role of the soil nutrient content, and a clear correlation was detected among the soil nutrient indices.

In addition, there was a clear correlation between the soil nutrients. Vegetation restoration plays a clear, predictive role in determining the soil nutrient content 22 , and soil variables, such as the available K and total N, have a significant influence on vegetation growth and development 23 , 24 , The present study indicated that the available K was the variable with the highest explanatory power compared with the other soil nutrient variables, followed by total N and soil organic matter.

The main vegetation types in the study area were locust and pine, which supplied a high amount of litter to the soil. In addition, as the most important species in the study area, locusts have a strong nitrogen fixation function 26 ; thus, the available K and total N contents increased.

Many studies have shown that the soil organic matter presents surface accumulation and has a significant influence on vegetation growth and development 20 , In addition, different vegetation restoration types may also increase the soil organic matter to different degrees 28 , Because a high amount of litter was introduced into the soil each year, its decomposition by microorganisms resulted in a greater amount of humus, and increases in the soil organic matter. This study also found that soil organic matter was positively correlated with canopy density and negatively correlated with above-ground biomass and herb coverage, and high correlations were observed between these variables.

A possible reason for this finding was that vegetation could increase soil organic matter. In addition, the coal gangue content in the dumps may also have affected the content of the soil organic matter. During vegetation reconstruction processes, the coal gangue content may differ between different sampling plots. The coal gangue itself contains organic matter; therefore, the soil organic matter content increases with coal gangue weathering Micro-topographic factors such as slope, slope aspect and slope position exert a strong influence on plant community structure and species distribution The ordination results obtained in this study indicated that the slope was the major topographic factor that affected vegetation restoration, followed by slope aspect.

The slope and slope aspect were positively correlated with above-ground biomass and herb coverage, and were negatively correlated with canopy density. However, the effect of topographic factors on vegetation were not significant compared with soil factors. A possible reason for this finding is that vegetation development is mainly attributed to topographic factors in areas lacking in soil factors, whereas when both soil factors and topographic factors are present, soil factors were assumed to be more important 20 , In this study area, the difference between the maximum and minimum elevations in the sampling plots was Topographic factors affected not only vegetation but also soil.

Topography can partly affect the accumulation and export of soil nutrients, thereby indirectly impacting plant distribution Some studies have indicated that changes in topography have clear influences on soil physical and chemical properties and soil water characteristics 34 , In this study, the available P was negatively correlated with slope, and the total N was positively correlated with slope position and slope aspect.

The soil water content was positively correlated with the slope, and the rock content was positively correlated with slope and slope position. The results also showed that the silt content had a significant negative correlation with the slope. These changes also illustrated the function of topography on soil properties. The inter-association and mutual restriction between soil factors and vegetation restoration not only illustrated the role of soil factors during vegetation restoration, but also revealed the restorative and beneficial effects of vegetation restoration on soil.

Therefore, to improve and restore the fragile ecological system in an opencast coal mine dump located in a loess area, the co-evolution of both vegetation and soil should be considered Effective management and conservation, particularly through approaches based on the emulation of natural disturbances, should take these differences into consideration by developing site-specific management guidelines for vegetation A key strategy for ecological restoration in an opencast coal mine dump located in a loess area involves improvements in soil conditions and increases in the area of artificial vegetation.

In addition, the protection of artificial and natural vegetation under local environmental conditions should also be strengthened. One study had found that a mixed model of locusts and pines has high survival rate, and the adaptability of locust and pine in the process of vegetation restoration is strong in the Antaibao opencast coal mine dump Therefore, the mixed model of locusts and pines can be selected to conduct revegetation for dumps.

Moreover, this paper showed that the soil factors had a clear correlation with the vegetation variable, and the available K and rock content were the best explanatory variables for soil factors. The available K is usually deficient in mined soils 38 ; moreover, the surface soil was very thick in the loess area. Therefore, surface soil covering and soil improvement are necessary to increase soil fertility and reduce the rock content. Soil nutrients also can be increased by the accumulation of plant litter after vegetation restoration Vegetation restoration was strongly correlated with soil factors, such as the available K, soil organic matter, total N, rock content, and soil bulk density.

The available K and rock content were the variables that exerted the most important effects on vegetation restoration. Of the topographic factors, the slope and slope aspect had large influences on vegetation restoration. Soil particles, which represent one of the physical properties, played a clear and predictive role in determining the soil nutrients.

To improve and restore the fragile ecological system in an opencast coal mine dump located in a loess area, the co-evolution of both vegetation and soil should be considered, and the mixed model of locusts and pines can be selected to conduct vegetation restoration for dumps.

The area of the Antaibao opencast coal mine is This mining area has a typical temperate arid to semiarid continental monsoon climate and a fragile ecological environment with low coverage and high soil erosion. The annual mean temperature range is 5. The study area was once primarily a landscape of forest and grassland; however, during the past years, the primary vegetation has been damaged by long-term human disturbance and climate change, leading to chronic water and soil erosion.

The ecological environments of the three dumps have been effectively restored by a multi-level and multi-type forest—shrub—grass plant structure, which is presently composed of elms, black locusts, pines, willows and sea buckthorns. A plot survey was conducted at the three dumps of the Antaibao opencast coal mine in the summer from July 7—12 Field measurements of the vegetation in the three dumps were performed in 50 sampling plots Fig.

South Dump included 2 belt transects with 1 to 22 sampling plots. The West Dump and Internal Dump included three belt transects, with 23 to 37 and 38 to 50 sampling plots, respectively. To include different topographic factors in the different sampling plots, the belt transects were laid in the northwest-southeast and northeast-southwest directions.

Due to the limited topographic conditions, and taking into account that the selected plots should have the same or similar vegetation types, parts of the sampling plots were slightly off of the actual sampling sites.

At each tree quadrat, the species, number, height, diameter at breast height DBH , and canopy density were measured. The tree volume was calculated based on the number, height and DBH. At each herb quadrat, the herbage coverage was measured. In addition, all of the above-ground herbage was clipped, and any dead branches were removed. The remaining herbs were placed into a package. The above-ground biomass was measured in the laboratory.

Soil samples were collected at the 50 sampling plots in the three dumps after any plant litter was removed. All of the samples were serially numbered and stored in soil-bags for further analysis. The soil water content, soil bulk density and soil total porosity were determined by the oven-drying method. The rock content was measured using the gravimetric method. Soil particles of the soil samples were analysed using a Longbench Mastersizer laser particle-size analyser Malvern Instruments, Malvern, England.

The soil organic matter was determined by the thermal potassium dichromate oxidation colorimetric method The total N was determined by Kjeldahl digestion, distillation and titration The available P was determined by the molybdate colorimetric method after perchloric acid digestion and ascorbic acid reduction The available K was analysed using a flame atomic absorption spectrophotometer The slope position and slope aspect were converted into a coded scale though the establishment of a membership function according to an empirical formula The slope aspect was classified as follows: a platform was given a value of 0, a sunny slope was given a value of 0.

The slope position was classified as follows: a platform was given a value of 0. Descriptive statistical analyses, including the calculations of mean, median, coefficient of variation CV , maximum values, and minimum values, were performed to analyse the soil data. Tree volume was used to indicate the vegetation restoration in this study. To determine whether a linear or unimodal-based numerical method should be used, DCA with detrending by segments was first conducted to analyse the vegetation data in order to evaluate the gradient length of the first axis.

For intermediate lengths, both models can be useful 20 , The Monte Carlo permutation test was conducted to test the significance of the eigenvalues of the first canonical axis. Inter-set correlations from the ordination analysis were evaluated to assess the importance of various soil and topographic variables According to the obtained ordination plot, the correlation between the environmental factors topographic and soil variables and vegetation were analysed.

Fourteen environmental variables topographic and soil properties were included in this analysis: slope, slope position, slope aspect, soil bulk density, soil total porosity, soil water content, rock content, total N, soil organic matter, available P, available K, clay content, silt content and sand content.

The four vegetation variables included were tree volume, canopy density, above-ground biomass and herb coverage. How to cite this article : Wang, J. Effects of soil and topographic factors on vegetation restoration in opencast coal mine dumps located in a loess area. Li, H. Improving soil enzyme activities and related quality properties of reclaimed soil by applying weathered coal in opencast-mining areas of the Chinese Loess Plateau. Clean-Soil Air Water 40 , —, doi: Wang, J.

Assessment of the potential ecological risk of heavy metals in reclaimed soils at an opencast coal mine. Disaster Adv.

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