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Walden Pond
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The geology of Walden Pond in Concord MA is glacial—that's not unusual in New England—but the details of its formation, and its present ecology are unusual. |
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Walden Pond was formed when a huge iceberg-like chunk of glacial ice, buried in the glacial moraine, melted. The bottom of Walden still has the shape of the chunk of ice that melted here thousands of years ago. Walden is very deep: over 100 feet (30.5 meters) in the middle. Because waters filter into it from surrounding sandy soils, the pond is essentially oligotrophic, that is, it has few organic nutrients, so few plants grow in it, keeping the water pure and clear. However, nitella algae, over 10,000 pounds of it, grows naturally in Walden's depths, as does rate lake quillwort, a plant that grows nowhere else in Massachusetts, and these growths help to give it its special character. But with thousands of swimmers adding "nutrients" to the pond annually, not to mention visiting ducks and geese (fed by humans), and seepage from the park's toilets, its delicate balance may turn it eutrophic and contribute to the growth of algae and water plants, upsetting its unique ecology. Today Walden is a mecca for Thoreau and nature lovers, as well as a state park with a swimming beach, round-the-pond hiking trail, and a replica of Thoreau's cabin. Official efforts to control the number of visitors and their impact on the pond have been going on for over a century, with some success. The problem is, quite simply, that Walden is beautiful and historic, and a lot of people want to enjoy its magic. |
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Spring thaws the thick cover of ice on Walden Pond in Concord MA.
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