Background - Soil
Soil erosion is the #1 source of pollution threatening water quality in Maine. Every year, rainstorms and snowmelt wash away tons of dirt, sand, and silt. But where does it go? A significant portion of it gets deposited into the state's thousands of lakes, rivers, streams and miles of coastline.
How, you ask, can something as natural as dirt be considered a pollutant? After all, soil erosion is a natural process.
Maine's natural ecosystem is forest. The forest canopy intercepts rain drops, slowing and reducing the energy they have. Slowly, rain drips down through the vegetation. Slowly, the rain reaches the forest floor, which is covered in a thick duff layer made up of decaying leaves and branches. The duff layer acts as a large sponge soaking up rain and snowmelt and slowly releasing it. In addition, the forest floor is not "smooth" like our lawns. There are small dips and depressions that capture and hold rain water.
When we build roads, parking lots, shopping centers, housing developments, lawns, roads, and driveways, we lose forested areas. Now, the rain drops do not have anything to slow them down. When they reach the ground, they hit it with a lot of energy which loosens and washes away the soil. Increased development also results in more impervious surfaces which cannot absorb or hold water, so the stormwater runs off more quickly, eroding more soil.
Sources of soil pollution include dirt roads, driveways, agricultural fields, forestry operations, construction sites, poorly constructed culverts and ditches, and sand used during the winter.
Direct Impacts Cause by Soil
Eroded soil, including sand, silt and clay, can do serious harm to waterways and the organisms that live there. We've all seen a stream in our community turn brown during a rainstorm. This suspended soil acts like sand paper and can damage the gills of a fish, which makes breathing difficult. Cloudy water also makes it hard for fish, like trout, to see and feed.
In streams and rivers, excess soil fills in the spaces between the rocks on the gravelly bottom. These spaces are important spawning areas for many fish as they provide protection for their eggs, and young fish (fry) use them as hiding places. They are also an important habitat for small aquatic insects that fish eat.
Another problem in streams and rivers is that the soil tends to fill in the "pool" stretches of streams. Streams consist of stretches of pools and riffles. In riffle stretches, water moves quickly and sediment remains suspended. In the pool, the water moves slowly and the soil drops out to the bottom. Pools are important summer habitats for Maine's cold water fish, like Brook Trout. Reducing or eliminating the pools harms fish populations.
Cloudy water and abundant bottom sediment may also harm boating and fishing. Boaters may not be able to see hazards in the water that their propellers, rudders or keels may hit. Fishing enthusiasts are going to see a decrease in the fish population or a shift in the type of fish they'll be catching, as mentioned above.
Side-effects of Soil
The impacts discussed above are direct affects soil can have on our water resources. However, soil particles carry lots of nasty hitchhike<
Soil contains lots of nutrients, like phosphorus, that plants need to grow. Fertilizers and pesticides are often the source of the nutrients adhering to soil particles. Unfortunately, when extra nutrients are carried to the water by eroded soil, tiny plants called algae use the nutrients and grow rapidly. The result is called an algae bloom, causing the water to appear green.
Toxic materials, like those found in oil, gas, pesticides, and landfill seepage, can also hitch a ride on soil particles which have a negative impact on water quality.
To learn more about how soil effects water quality:
Soil Erosion
Why are rocks, sand, and dirt considered pollutants?
In Our Back Yard - "It's a dirty little secret"
In Our Back Yard - "A dirty tale"
In Our Back Yard - "The pollutant that gets no respect"
In Our Back Yard - "Tread lightly to protect Maine's waters"
Go to: Bacteria, Nutrients, Thermal, Toxics
