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Bill Simpkins, a professor of geological and atmospheric sciences at ISU, has been monitoring groundwater flow and quality from 10 testing wells at the lake site. He described the lake as being dominated by groundwater, with about 85 percent of its inflow from groundwater sources underlying the lake.
"It's one big aquifer with a hole in it," he said.
Wells from the inflow or west side of the lake tested high for phosphorus at deeper well levels.
John Downing, a professor of ecology, evolution and organismal biology at ISU, echoed Simpkins' assessment of lake health. Saying his research provided an "annual physical" of the lake's health, Downing reported the surface water quality of the lake was good, bottom water quality was poor and monitoring showed no improving trend in that assessment.
"The main element we worry about is phosphorus," Downing said.
Tim Stewart, a professor of natural resource ecology and management at ISU, discussed the performance of the wetlands that had been constructed around the lake in 2003 to filter sediment and nutrients from water inflowing to the lake. Stewart said common carp have invaded the south complex of wetlands. A non-native species, the carp overfeed, reducing the amount of healthy organic matter and insect life in the wetlands. This, in turn, reduces the wetlands' ability to filter nutrients and sediment out of the water.
Phosphorus levels are higher going out of the south wetlands into the lake than coming in, he said.
"Here we have a source of pollution rather than a mitigation of pollution," Stewart said.
The panel concurred that though sources of phosphorus were not discovered in the research, it likely was coming from both urban development and agricultural fields in the watershed. The panel said changes in the philosophy of storm water management, from rapid run-off to gradual infiltration, would help control contamination levels in the lake.
"We need to make modern hydrology behave as historic hydrology would have behaved," said Wayne Petersen, an urban conservationist for the Iowa Department of Agriculture and Land Stewardship.
The lake is formed from a sand and gravel quarry that operated until the 1990s and became part of Ada Hayden Heritage Park in 2001. The lake is about 130 acres, holds about 1 billion gallons of water and is the emergency water supply for the city.
The council requested the panel's opinion on water quality at the lake following the failure of an amendment to the city's growth strategy that would have made annexation north of the lake possible.
Annexation is considered by some citizens as the ideal way to protect the ecological health of the lake through connection to the municipal sewer.
Minutes of the council's panel discussion will be available on the city clerk's Web site at www.cityofames.org Friday, Sept. 19.
Laura Millsaps can be reached at 232-2161, Ext. 342, or lmillsaps@amestrib.com.
