Natural History. Stewardship. Sustainablility.
2006 HARTLEY POND TRANSPARENCY
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The pond’s clarity increased as the summer progressed. If more readings had been done we may have seen the transparency of the water change with rain events. The color of the water was also recorded this year and was brownish yellow all summer. Thick stands of pondweed developed this summer, and 1997 and 2004 aerial photos of the pond show that this has been the case for a number of years |
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Lake and pond transparency is determined by use of a standard white "Secchi Disk" that is lowered into the water by a connected rope marked in feet. The depth at which the disk is no longer visible from the surface is measured by looking at the distance marked on the rope. This value is a standard measure of transparency.
The transparency of the water is created by the intensity of the color of dissolved matter in the water and the amount and kind of material suspended in the water. The latter includes silt and clay from exposed eroding soils, fine non-living organic particles, and microscopic algae and aquatic animals.
The good transparency of the pond allows more sunlight to penetrate the water to greater depths and encourages oxygen production by photosynthesis by algae and aquatic plants like pondweed. As they grow in the water, they provide cover and food for the aquatic animals.
Brownish water color is a sign that the pond’s water has varying amounts of dissolved organic material in it from the biological growth and death of various organisms in the pond and also in its watershed (Tischer Creek's watershed, because the pond is formed by the damming of the creek).
The lack of green color in the water of Hartley Pond indicates that the pond is not undergoing algal " blooms", a situation of too much algal growth due to excess nutrients in the water coming in from fertilizers from lawns and golf courses up stream. "Too much" means that when the algae and aquatic plants die back in autumn and winter, the decay of the material by bacteria will use up all the oxygen in the water and a fish kill will result. The much fewer algae in the water in autumn and winter will not be producing much oxygen in the darker and colder water conditions: low short-lived sun and snow cover over the ice. A large part of the summers oxygen production is not stored in the pond but is released into the air above the pond. So far only some very occasional dead fish have been seen in or along the shore of the pond.
Converting the pond’s foot depth measurements to centimeters showed a close correspondence to the transparency values as measured in the Tischer Creek water flowing out of the pond over the dam that was measured in centimeters. The pond transparencies except the lowest one, yielded values greater than 100 centimeters, which is the value most of the Tischer Creek readings were. See Tischer Creek Conditions 2006.