What do the foundation under your house, the salad you ate for lunch and the plants at your favorite park have in common? They all depend on soil! Soil, in its simplest form, is a combination of eroded rock (sand, silt and clay), organic matter (decomposed plants and organisms) and tiny organisms (earthworms and bacteria). While soil is generally considered to be an inanimate object, soil is actually a living thing. A single handful of soil contains millions of individual living organisms, including single celled bacteria, protozoa and fungi. In a process known as nutrient cycling, these microorganisms break down animal waste, leaves, dead animals and plants and release carbon and nutrients back into the soil to be used by future plants and animals. These nutrients act like a sticky glue that helps the individual particles of sand, silt and clay stick together, creating clusters of soil particles called aggregates.
Soil is a renewable resource, but it is not renewed quickly. In 2006, a study from Cornell university estimated soil in the United States is being lost at a rate ten times greater than it is being created. Soil is lost through erosion, a process in which it is worn away and transported by natural forces like wind and water. Although natural, soil erosion is accelerated by certain human activities. Physical disturbances to the soil can break apart these aggregates, causing the soil to erode. Here we will explore the process of soil erosion, the problems soil erosion creates, the leading causes of soil erosion and the ways we can all help slow soil erosion.
When soil erodes, it produces sediment, or loose particles of sand, silt and clay. If soil erodes into a lake or river, this sediment ends up in the water, causing it to become murky and cloudy. Cloudy conditions make it harder for marine creatures to find food. Sediment can also intercept sunlight, decreasing the growth of aquatic plants. Additionally, sediment can carry pollutants into bodies of water. For example, the phosphorus fertilizers used on lawns, golf courses and farms bind to soil particles. Erosion in these areas can cause the soil particles and the bound phosphorus fertilizer to wash into waterways. The fertilizer can then cause harmful algae blooms that make the water unsafe for consumption and recreation. Furthermore, sediment can cause flooding in the event of a storm. Over time, sediment transported through rainwater accumulates in storm drains and catch basins. The presence of sediment in these vessels decreases their storage capacity, displacing the excess water and causing it to flood roads and buildings.
While the sediment that is created when soil erodes can cause problems, the soil that is lost is an even bigger issue. Erosion of the soil that makes up shorelines creates dynamic shorelines, in which the boundary between the water and the land shifts over time. Dynamic shorelines can cause damage to property and infrastructure and other safety concerns. Finally, but most importantly, soil erosion contributes to increased food insecurity at a global scale. Erosion leads to poor soil quality and fertility and lower crop yields.
One of the major sources of soil erosion is farming. Conventional farming activities, such as plowing and tilling of fields, physically disturb the soil and break up soil aggregates. Fortunately, farmers have developed practices that reduce soil disturbance by mimicking natural processes. For example, no-till is a farming practice in which farmers leave plant material left over from crop growth in place rather than clearing it from the soil. They can then plant seeds for the next round of crops directly into this plant residue. Leaving plant residue in place reduces disturbance and protects the soil structure. Reduced soil erosion resulting from the use of no-till farming has been well documented– studies have shown up to 99% reduction in sediment loss with no-till practices compared to traditional tillage systems. Cover cropping is another practice in which crops are grown between traditional planting seasons instead of leaving the soil bare. When soil is left bare and exposed, it is much more susceptible to wind and water erosion. Cover cropping keeps the soil covered with vegetation throughout the year, protecting it from erosion.
While farming is arguably the largest contributor to soil erosion nationally, cities are not off the hook either. Construction and land-clearing activities common in cities can disturb the soil and make it prone to erosion. Additionally, the surfaces in urban environments (roads, sidewalks, driveways and parking lots) are typically made up of concrete and other materials that do not absorb water. As a result, there is more runoff water available to carry the disturbed soil away. In fact, the average acre under construction in an urban setting produces 60,000 pounds of sediment in downstream waters each year. Furthermore, industrial areas typically do not feature much vegetation along their shorelines, increasing their risk of shoreline soil erosion. The presence of a diverse plant community on the shore reduces erosion because the plants physically hold the soil in place with their roots and capture sediment. Without this protective vegetation, shorelines in many cities have endured severe soil erosion– examples can be found in recent news stories from Chicago and around the Great Lakes. Luckily, planting native vegetation on urban shorelines is a simple and visually-pleasing way to stabilize the soil. Referred to as “living shorelines”, these plant-heavy interfaces between land and water are the biological solution to slowing soil erosion.
Even if you’re not a farmer or a city planner, there are things you can do to help mitigate soil erosion. Try to maintain a vegetative cover over the soil in your yard or garden to prevent wind and water erosion. Shallow-rooted lawn grass is not typically very effective, so consider planting a diverse combination of species. If possible, avoid displacing native species that can grow deep roots into the soil to keep it in place. Lastly, try to minimize the amount of soil left bare during home construction projects. Soil is essential for life on earth, and we all have a responsibility to protect it.