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Hartley Nature Center
Natural History. Stewardship. Sustainablility.

Dissolved Solids and Conductivity

Conductivity Flow Map

MAP 1: Shows the conditions discovered by CITIZEN SCIENCE monitoring of electrical conductivity in 2007.

Continued stream monitoring of Tischer Creek in 2008, 2009 & 2010 show that salt pollution in the northeastern part of the park continues.  The yearly pattern follows that of the Twin Cities area, where the surface water and it’s subterranean water reservoir have salt concentrations spiking up in winter and spring, and then decrease to lower values, for the rest of the year. These lower values are still too high for healthy life in soils and waters.  

Hartley Pond and Tischer Creek, upstream from where it receives the polluted water flow, have conductivities and chloride ion concentrations that are well below toxic levels, all year around.

Measuring water’s ability to conduct electrical current is a way of measuring the amounts of dissolved ions (electrically charged material) in the water and its ability to support the life in the water and soil.  High conductivities are due to larger amounts of ionic material in the water. Too many ions of sodium, potassium, chloride and nitrate, etc. can inhibit the life in the water and soil. You probably have noticed how road salt and too much fertilizer can “burn” and kill grass and other plants. High concentrations of these materials suck the water out of plants right through their roots and leaves.


Normal ConductivitiesSnow melt Conductivities

CHARTS 1 & 2:

The charts to the left show the very low concentrations of ionic solids in some of our vernal ponds when they are full of  water in spring. They have little or no input of surface waters; their water sheds are a narrow zone around them, that don’t extend beyond the surrounding forest soils that are rich in organic material. They have much less ionic material from bedrock, boulders, sand, silt and clay.
Most of their dissolved solids are organic material that is much less ionized.

Tischer Creek in contrast, has naturally eroded down into sources of the ionic source material
listed above. Also its watershed is very much greater and doesn’t all flow out of protected
organic forested surfaces. A lot of fast snow melt dilutes its dissolved ionic material, and slower
flows-low water levels concentrate the dissolved ions by loss of water by evaporation.

Mid Hartley Pond shows conductivities that are intermediate between vernal ponds and Tischer Creek. It has considerable surface flows from its large watershed, much of which is in the large
shrub swamp instead of forest. For that reason, it is the last pond to dry up in summer.

For chloride values and other information, click here


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.


Hartley Nature Center, 3001 Woodland Ave. Duluth, MN 55803       location map
Phone: 218-724-6735    email:

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