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Summertime in the BelgradesContentsfor Printing Article Summaries |
Lake ProcessesBy Peter Kallin The Belgrade Lakes area is a special place, dominated by the seven large lakes of the Belgrade Lakes chain (East Pond, North Pond, Salmon Lake-McGrath Pond, Great Pond, Long Pond, and Messalonskee Lake) but also containing numerous smaller ponds, especially in the Kennebec Highlands. The State of Maine has over 6000 "great ponds" of over 10 acres. As Ship Bright of the Maine Lakes Conservancy Institute pointed out last week, these lakes bring in over $3 billion dollars per year to Maine's economy. It is incumbent on all of us to understand and protect these lakes. This week I will begin discussing how these lakes came into being and how they are evolving. Maine residents take lakes for granted — we've always had lakes as part of our landscape. These lakes are here because of the last ice age when large masses of ice were moving across Maine in a southwesterly direction, gouging out the earth's surface and piling up rocks ahead of the ice. About 20,000 years ago, when the glaciers began to melt and recede, they left behind large chunks of ice in low points in the landscape. These ice chunks melted and formed Maine's lakes and ponds, most of which are elongated north to south along the glaciers' direction of movement at the peak of the ice age. In terms of geological time, lakes are transient phenomena. Once lakes are formed, Mother Nature begins to fill them back in. As water goes through the hydrologic cycle, it is evaporated from the lakes, becomes water vapor in the atmosphere, and then condenses first into clouds and then cloud droplets combining to form precipitation. This precipitation falls back to earth, eroding the earth's surface as it flows downhill, sometimes after melting in the spring. Over geological time scales, these erosion processes turn rock into soil but they also eventually fill in low points in the landscape including lakes and ponds. This is why the southern states have very few lakes. Without the glaciers to reform large numbers of lakes every 50 thousand years or so, there are very few natural processes that form lakes. Beavers will dam streams or rivers to form ponds; volcanoes will form caldera lakes (e.g., Crater Lake, OR); meandering rivers will occasionally split off an "oxbow" lake; and sometimes meteors will crash into the earth forming depressions (kettle lakes of NC) or tectonic plates will rise from the sea (Lake Okeechobee) or collide (Lake Tanganyika). But these are uncommon events. Generally speaking lakes in the southern U.S. are actually impoundments formed by damming a river or stream. This is why southerners are especially fascinated by Maine's natural lakes. Newly formed glacial lakes contain nothing but water. They are what limnologists (people who study lakes) call "oligotrophic" or nutrient poor (think Lake Superior). Water flowing towards the lake dissolves minerals from the rocks and picks up soil particles including nutrients such as nitrogen and phosphorous. Over time, as this water enters the lakes, the water in the lakes becomes enriched and can support aquatic plants and animals including fish. This natural enrichment process is known as "eutrophication." A little eutrophication is a natural and necessary part of a lake's life cycle. But like many things in life, too much of a good thing can be disastrous and lead to premature death or illness. I will be discussing how this process affects the health of the lakes in more detail in the next few columns. Peter Kallin, Executive Director of the Belgrade Regional Conservation Alliance (BRCA), can be contacted at | ||