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A Brief History of Lakes
The secret life of New Hampshire’s lakes
Lakes Through Time
New Hampshire is fortunate to be blessed with so many
beautiful lakes. There are approximately 1000 lakes in
the state — each with its own unique character. These lakes
all have something in common, though — they are all aging.
The process is called eutrophication, which means that they
are slowly filling in; becoming wetlands that will eventually
turn into meadows and ultimately forests.
The good news is that this should not happen for thousands
of years. The bad news is that we are making our lakes old
before their time. Many of New Hampshire’s lakes have shown
more aging in the last 30 years than over the prior 10,000
years!
Lake Age Groups?
All of New Hampshire’s lakes can be generally classified into 3 types: Oligotrophic, Mesotrophic or Eutrophic. Oligotrophic means “little nourishment”. This describes a lake that does not have excessive nutrients, such as phosphorus, that feed growth of algae and weeds. Eutrophic means “good or well-nourished”. These lakes are “productive” or have an abundance of algae and weed growth. Mesotrophic means “middle nourishment”. These lakes have characteristics of both Oligotrophic and Eutrophic lakes.
Most of New Hampshire’s glacial lakes are classified as Oligotrophic. They comprise approximately 30% of our lakes. These lakes are characterized by cold, deep waters with rocky or sandy shores and bottoms with virtually no silt or sediment. While plants and algae are present in some of their shallow areas, generally the lake bottom is not weedy. With their high oxygen content, these waters support trout and salmon.
Mesotrophic lakes have some plant and algae growth with accumulation of silt, soil and other sediment on the bottom. Both cold and warm water fish species may be present. Over 47% of New Hampshire’s lakes are classified as Mesotrophic.
Eutrophic is the classification given to “older” lakes (23% of the state’s lakes) and often includes those that are man-made by damming. These ponds and lakes have an over-abundance of plants and algae. Oxygen content of the water is generally low with only warm water fish species present such as bass, pickerel and perch.
Cultural Influences
Although eutrophication is the natural aging process of all lakes, cultural eutrophication is an immediate threat to our lakes and ponds. Cultural influences accelerate this geologic process. Erosion from unvegetated soils can quickly cover a lake bottom. Polluted runoff from non-absorbent surfaces such as driveways and building roofs carries nutrients which act as fertilizer, promoting the growth of plants and algae. Improper fertilization of lawns and gardens as well as failed septic systems also contribute these nutrients.
The Cycle Continues
Accelerated eutrophication increases when shore areas are cleared of trees and other natural vegetation. This allows sunlight to penetrate shallow water and when mixed with eroded soils and nutrients, plant and algae growth flourishes. When plants and algae die each year, they sink to the bottom of the lake and decay. Their decay creates additional nutrients to fertilize even more growth.
How do lakes age?
There is no “Fountain of Youth” for our lakes. To help keep your lake from aging before its time, lower cultural impacts by:
- Keeping shore areas naturally vegetated and shaded
- Assuring that all soils are covered with growth such as groundcovers, shrubs and trees
- Using proper fertilization near shore areas or better yet, no fertilizer (see NH LAKES brochure Shoreland Protection).
- Nutrients, including phosphates, nitrates and bicarbonates, are found in many sources including soil, sand, gravel, motor oil, gasoline and road salt. The gravel or sand that you bring in for your driveway can wash into the lake and foster weed growth (see NH LAKES brochure Phosphorus Pollution). Beach sand in particular can contribute to this cycle. A NH Department of Environmental Services Wetlands Bureau Permit must be obtained before building or replenishing beaches.
- Those who live away from shore areas also have the responsibility to keep New Hampshire’s lakes clean. All land in New England is part of one watershed or another. Nutrients run from land, down roads and into storm drains. From there, nutrient-laden water flows through culverts and discharges into streams, rivers, and lakes.
Here’s More That You Can Do to Help Your Lake Stay Young!
Follow the philosophy of “think globally, act locally”. What you do in and around your home really does make a difference!
- Keep shoreland areas vegetated — this will help retain soils and filter out pollutants.
- Join your local lake association — support their efforts to protect your lake.
- Volunteer to be a water quality monitor — there are two programs in New Hampshire that assist volunteers in monitoring the health of their lakes (see NH LAKES brochure WaterQuality).
- Become a volunteer weed watcher —In addition to our native weeds, exotic species are aggressive invaders and can quickly infest a lake (see NH LAKES brochure ExoticAquatics).
- Join the New Hampshire Lakes Association — NH LAKES supports the efforts of local lake associations and statewide initiatives to protect the “lake experience” for everyone.
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