City of Plymouth, Minnesota

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Soil Types

Reducing Runoff: Soils Affect Water Quality
Air, water, and soil are basic to human survival. Because we depend on these elements, we have learned to recognize what makes them good or bad - at least in regard to water and air. Generally, we know less about soil. What makes soil good? How can we recognize a good soil versus a bad one? Are all soils the same? How does urbanization affect soil? How does soil affect water quality?

Soil Primer
Soil is made up of many other substances. The composition of these substances is influenced by the local environment. It is the combination of these substances that gives a particular soil its unique characteristics. Whether a soil is "good" depends on whether its characteristics fulfill our particular needs. In Plymouth, we are interested in soils that help promote good water quality. Soil attributes such as structure, texture (sandy, loam, and clay), and compaction determine the movement of water in soil. How fast water drains off an area or how fast it percolates into the ground has great consequences. For instance, flooding occurs when the ground is saturated and can no longer absorb water. The rate water soaks into soil indicates:

The soil's condition;
Its ability to control run off; and
How well it can support plant growth.

Soils & Water Quality
As communities develop, the landscape changes. This change includes significant changes to the soil. Typically, development involves removing and stockpiling the top soil (the organic layer) and then redistributing it to the desired grade. During this process, what was once water-absorbing ground is transformed into a compacted surface which allows little or no water infiltration. In addition, the top soil is often replaced with either a hard surface (usually roads and roofs) or a thin layer of vegetation such as sod. Gradually, the soil has been transformed from a sponge-like surface that moves water slowly and filters nutrients to a fast-moving surface water drainage system.

With little water infiltrating the ground, there is more water on the surface (runoff) moving faster downstream. This can cause soil erosion. This nutrient-rich run off also picks up any pollutants in its path before reaching lakes and ponds. Run-off containing plant nutrients and pollutants degrades the quality of our waterways.

One of the most common examples of this is phosphorus from fertilizer running off lawns and into the streets to our lakes. Phosphorus, an ingredient in most fertilizers, promotes algae growth and turns clear water into green water. This is why the City and State restrict the use of fertilizer containing phosphorus (most soil in Minnesota does not need added phosphorus). In addition, to avoiding fertilizer containing phosphorus, you can go a step farther. You can take steps to make your yard's soil more absorbent and reduce runoff.

Reducing Runoff
As property owners, we can reduce the runoff caused by development. To do so, we need to increase the soil's organic content, increase water absorption and cultivate plants with deep, penetrating roots. Together, these will help transform compacted soil into water-absorbing ground.

One way to accomplish this, is to reintroduce native grasses into our landscape. Although, native grasses are not a silver bullet that will solve all problems, they do eliminate or minimize many. Native grasses and many of their companion wild and native flowers:

Provide a significant increase in ground water infiltration as they develop very deep root systems. The deep roots provide a network for water to infiltrate the ground. This significantly decreases the amount of surface water runoff. Less surface water run off translates into less erosion and fewer pollutants transported into our lakes and ponds.

Require no or very little fertilizer. The deep roots of these plants allow them to tap into nutrients and water that shallow rooted sod grasses or weeds cannot reach. The deep roots also allow the native grasses to out-compete other plants and weeds.

Environmental : Your Role : Soil Types


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