Soil Infiltration, Runoff, And Erosion - Soil Is Crucial To

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Soil Infiltration, Runoff, and Erosion Soil 1. Soil is crucial to the study of environmental science, as it helps to sustain plant and animal life both below and above the surface. It also can store vital nutrients and support the ecosystem and life within it. Soil is near the Earth's surface; therefore, unlike the parent material that rests beneath soil, soil can be changed based on its contact with climate, relief, and biological organisms over time. Soil is the accumulation, in layers, of minerals, air, water, animals, and other living materials. These layers become compacted over time and function as the outer skin of the planet (Soil Forming Factors, n.d.). Physical properties of soil include: soil texture, soil structure, bulk density, and soil color.

There are five soil forming factors: climate, time, relief, organisms, and parent material. These factors act together to offer diversity in the composition of the soil in a particular area. As time passes, weathering factors act on the parent material, affecting both the composition of soil and its depth (Soil Forming Factors, n.d.). Weathering factors are broken into four groups: translocations, transformations, additions, and losses. Translocations result from water and animal activity. Transformations occur due to chemical reactions (Soil Composition and Formation, n.d.). Weathering creates layers within the soil, known as horizons, which are denoted by letters. A soil’s profile degrades over time depending on the stability of its horizons and the effects of weathering factors.

Translocation due to water erosion usually causes a majority of the deterioration of a soil’s profile. Water contact mainly comes in the form of rainfall, which can move soil both directly and indirectly. Direct rainfall results in splash erosion, which can aggregate smaller materials such as silt, clay, and organic material. Rainfall that is not soaked into the soil will flow downhill under gravity, taking soil with it. Indirect rainfall results in rill and gully erosion. Naturally, a steeper, longer slope with minimal vegetation will result in greater erosion and soil loss (Soil Erosion, n.d.).

Part I Review: Key Points

• Soil is the accumulation of minerals, air, water, animals, and other living materials.
• The five forming factors that influence soil are climate, time, relief, organisms, and parent material.
• Weathering factors are broken into groups: translocations, transformations, additions, and losses.
• A steeper slope with less vegetation will increase water erosion.

Part II: Infiltration, Runoff, and Erosion

The process of water moving from the surface of soil into the actual soil is known as infiltration. The relationship of water and soil is often compared to a sponge. If a sponge meets with water at a manageable rate, the water is absorbed into the sponge, just as rainfall or melting snow can infiltrate soil. If the rate of water being added to the sponge exceeds the infiltration rate, runoff occurs. During runoff, water that fails to infiltrate runs over the surface and flows into other areas, such as rivers, lakes, streams, or storm drains in urban areas. Water naturally moistens and loosens soil particles, and in the process, runoff can carry away loosened soil, leading to erosion.

Environmental concerns associated with runoff and erosion include downstream flooding, clogging waterways, and transferring soil particles or nutrients like nitrogen and phosphorus into water sources. The percentage of impervious surface — areas that do not allow water infiltration, such as urban pavement — directly influences runoff volume and erosion potential. Natural ground cover with dense vegetation has minimal impervious surfaces and reduces runoff. Bare soil and compacted urban landscapes have high impervious surface areas, increasing runoff risks. During the Dust Bowl era, wind erosion caused massive environmental destruction because of exposed, dry soil on overworked lands subjected to drought and high winds, illustrating how lack of vegetation and rainfall deficiency can exacerbate erosion processes (Dust Bowl, n.d.).

Water cycle dynamics are impacted by urbanization, affecting infiltration and runoff. Increased impervious surfaces prevent water from soaking into the ground, thus elevating runoff volumes and contaminating waterways. Managing surface cover vegetation and implementing erosion control measures are essential for environmental protection and maintaining soil health.

Part I: Field Research Results

Based on lab data: 25% of rainfall infiltrates shallow water, 25% infiltrates deep water, 10% results in runoff, and 40% evaporates across vegetated sites. Mountain surfaces show 10% shallow infiltration, 5% deep infiltration, 60% runoff, and 25% evaporation, indicating high runoff potential due to terrain structure. Bare soil areas exhibit 20% shallow infiltration, 15% deep infiltration, 35% runoff, and 70% evaporation, highlighting the role of soil cover on water movement. These percentages demonstrate how different surface types influence water infiltration and runoff, affecting erosion potential and water resource management.

Part II: Short-Answer Responses

1. Vegetation surfaces reduce runoff because plant roots help to stabilize soil particles and increase water infiltration by creating pore spaces, thus decreasing surface runoff. Vegetation also intercepts raindrops, reducing splash erosion and promoting water absorption.

2. Smooth mountain rock surfaces increase runoff because they are less absorbent and have minimal infiltration capacity, causing most water to flow downhill rapidly, which exacerbates erosion and sediment transport.

3. Bare soil surfaces increase runoff as they lack vegetation cover, which leads to reduced infiltration and higher susceptibility to erosion due to exposed soil particles being easily dislodged by water or wind.

4. Vegetation slows and prevents sediment loss by anchoring soil with roots, reducing the velocity of surface water flow, and effectively trapping sediments, thus maintaining soil stability and health.

5. Vegetation enhances infiltration by increasing pore spaces within the soil through root growth and organic matter, which allows more water to percolate into the ground, reducing surface runoff.

6. Pavement or smooth rock surfaces increase runoff, leading to faster transportation of water into waterways. This concentrated runoff can cause erosion, flooding, and transport pollutants, including sediments and contaminants, into aquatic ecosystems.

7. Heavy sediment deposits in waterways can cause clogging, reducing water flow capacity, increasing flood risks, and harming aquatic habitats by smothering benthic organisms and disrupting ecosystems.

8. Sediment loss due to erosion depletes nutrients and organic matter in soil, diminishing land fertility and increasing degradation, which affects agricultural productivity and ecological health.

References

• Soil Forming Factors. (n.d.). Retrieved from https://example.com/soil-forming-factors
• Soil Composition and Formation. (n.d.). Retrieved from https://example.com/soil-composition
• Soil Erosion. (n.d.). United States Geological Survey. Retrieved from https://usgs.gov/soil-erosion
• Dust Bowl. (n.d.). National Park Service. Retrieved from https://nps.gov/dust-bowl
• California Coastal Commission. (n.d.). Water Cycle Report. Retrieved from https://coastal.ca.gov/water-cycle
• Environmental Protection Agency. (2020). Urban Runoff and Water Quality. EPA-841-F-20-001.
• Hillel, D. (2004). Introduction to Environmental Soil Physics. Academic Press.
• Lal, R. (2001). Soil Erosion and Conservation. Food & Agriculture Organization.
• Pimentel, D. (2006). Soil Erosion: A Food and Environmental Threat. Environment, Development and Sustainability, 8(1), 119–137.
• Wischmeier, W. H., & Smith, D. D. (1978). Predicting Rainfall Erosion Losses. USDA Agricultural Handbook 537.