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Hartley Nature Center
Natural History. Stewardship. Sustainablility.

Acidity and Alkalinity around Hartley Park

ph in vernal ponds

CHART 1: PH Values in Vernal Ponds
PH values from 0 to 6.9 are measurments of acidity or sourness of fluids like vinegar and lemon juice. 7 is neutral, and 7.1-14 are alkaline values, like water solutions of baking soda and lye have. The pH data shown here were taken by CITIZEN SCIENTIST volunteers. Except for the aciditiy of the Sphagnum moss above, all of the pH’s in these ponds and streams are not limiting to the biodiversity and productivity of the life in these waters.

The above vernal ponds are a little acid due to the pH of the organic matter and salts that are dissolved in them.  The carbon dioxide in the water itself causes some acidity. The increasing carbon dioxide in the air dissolves in the ocean and makes the ocean increasingly acid. Tamarack Pond is quite acid due to the Sphagnum moss that is in the edges of the pond. Sphagnum in wetlands cause acid bogs to develop over long periods of time. Tamarack Pond may have the potential for becoming an acid bog. Bogs have plants and animals in them that are different from other wetlands. Some of these are carnivorous pitcher plants and sundew. Apparently there are no other wetlands in the park that are bogs, and that are this acid.  Some distance north of the park are boggy areas of much older organic wetlands. 


CHART 2: PH Values in Hartley Pond and Tischer Creek

The source of the alkalinity in Tischer Creek that feeds into Hartley Pond (as well as of most of the streams on the North Shore on up to Two Harbors) is the bedrock and glacial deposits that the streams flow through. They are not strongly alkaline.

This project was funded in part by the Coastal Zone Management Act, by NOAA's Office of Ocean and Coastal Resource Management, in conjunction with Minnesota's Lake Superior Coastal Program.


PH Duluth area

MAP 1 and 2: PH, Oxygen and Chloride Levels
The streams also flow through or out of various amounts of acid bogs. Apparently there is not enough acidity picked up to compensate for the slightly alkaline bedrock and glacial deposits. In alkaline Hartley Pond, only the water in the cattail zone is acidified by the living and dead organic material in the cattails. The pH of Midhartley Pond shows some
alkalinity in the first chart in spite of the water coming into it from all the plant material in the shrub swamp that it is located in. There are no large areas of peat in the Tischer Creek watershed. 


Hartley Nature Center, 3001 Woodland Ave. Duluth, MN 55803       location map
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