The Natural Evolution of a Lake
Lakes in nature evolve. A young lake has very clear water and is usually surrounded by rocks. As time passes, erosion brings soil and organic matter into the lake, and it gradually becomes richer in nutrients. It supports a rich diversity of aquatic plants and the fish that feed on them. The runoff contains sand and clay and soil, some of which is not washed downstream and settles on the bottom as silt. It also contains increasing amounts of organic content, decayed plants and animals and animal waste. Eventually – after many thousands of years – this sediment will fill in the lake, and it will become a marsh then a swamp then a field or forest.
One way that scientists classify lakes is by their trophic states [LINK]. A lake’s trophic classification is determined by the amount of nutrients in the lake, which in turn determine the amount of plant growth the lake can support. Lake Fairlee is in its mesotrophic phase, a mature lake growing into middle age. As additional nutrients run into the lake it will naturally become eutrophic, a state characterized by dense plant growth and algal blooms. While this is an excellent habitat for waterfowl, swimmers and boaters find it less enjoyable.
A eutrophic lake, characterized by algal blooms
Nutrients: Nitrogen and Phosphorous
Nitrogen (nitrates) and phosphorous (phosphates) are the primary nutrients needed by all plants to flourish. Increased levels of these nutrients accelerate the natural process of maturation/degradation of a lake.
Of course nitrogen and phosphorous are found in fertilizer and plant food, which are used for their beneficial effect on lawns, gardens, and farms. When excess is washed into the lake, it fertilizes plant growth there. Every type of aquatic plant is affected, from single celled algae to beautiful water lilies. Fast growing weeds, like Eurasian milfoil, absorb these nutrients rapidly with corresponding growth.
These nutrients are also found in all plant matter. So trees, leaves, and needles that fall in the lake contribute to its nutrient load. More importantly, plants die and decompose on land, and become the rich soil in our forests and fields. These plants have spent their lives (literally) pulling nitrogen out of the air and binding it in their cells. When the land is disturbed, by natural erosion or human disturbance, this soil most often ends up in the lake, and increases its nutrient level.
These nutrients are also found in animal waste. Farmers and gardeners have long taken advantage of this. Manure that is spread on fields can run off to the lake, especially after a heavy rain. An aging or poorly constructed septic system might also leak into the lake.
Pollutants: Oils, Chemicals, and Drugs
While excess nutrients can be too much of a good thing for our lake, other substances are just plain noxious. Among the most problematic are oil, paint, and solvents. This includes nail polish remover! Unused pharmaceuticals or over-the-counter medications can also cause real problems. Fortunately a properly constructed and maintained septic system will keep most of these from the lake.
But wait! Because paint and oils can be ruinous for a septic system, some people would rather dispose of them by pouring them in the woods behind the garage. Eventually some of this waste will find its way into the lake. (Our problems are actually less than municipalities with community waste processing. People throw just about anything down a garbage disposal . . . )
Because of the nature of drugs and hydrophobic (oily) contaminants, just a very small amount can have a detrimental effect on plants and animals in the lake. We will probably never know just what human waste is in the lake.
The Whole Watershed
Lake Fairlee itself covers about 450 acres, but its watershed is more than 25 times as large. All the runoff from within this 20 square mile area eventually finds its way into Lake Fairlee. This means that when a farmer up Middlebrook Road spreads manure, some will flow down to the lake. (and that is good, nutrient rich, fertilizer) It means that when a home builder half way to Bradford breaks ground for a new building, the soil unearthed will find its way into the lake. Likewise, when the road maintenance crew of one of our three towns does routine grading on one of our many gravel roads it will likely affect our lake.
It may be helpful to think of the watershed as being like a sponge, just soaking up nutrients and pollutants. The more slowly they are released into the lake, the better (from our point of view). So let’s do what we can to avoid forest fires, earthquakes, clear cutting, and massive excavation. And when we must disturb the earth anywhere near the lake, lets do so in such a way as to minimize the inevitable runoff.
What Can We Do?
We cannot stop the gradual maturation and filling-in of our lake. We can, however, take steps to reduce our contribution to the process. We can also stop allowing the introduction of hazardous chemicals.
To minimize the increase in nutrient levels:
- When doing farming, construction, landscaping, road repair: MINIMIZE disturbance (to the extent possible, NO DIGGING)
- Do not use chemical fertilizer nor herbicides
- Plant a buffer zone — this prevents erosion and filters pollution from runoff
- Work with your builder, architect, and town to make decisions that are healthy for the lake. Little changes.
- Road maintenance matters. Work with town road departments.
To protect against other pollutants:
- Dispose of paint, solvents, drugs, and the like properly
- Inspect and maintain your septic systems
- Educate the community
Remember, even clearing a lot three miles upstream has an impact. Think of the whole watershed!
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