Kent Park Lake might need to be dredged

TIFFIN - Radical remedies may be required to restore good water quality in the lake at Johnson County's flagship park.

It seems likely that the 27-acre lake at F.W. Kent Park, on the state's long list of impaired waters, will have to be dredged to remove phosphorus-laden sediment in the lake bed, said Johnson County Conservation Director Larry Gullett, who is leading the effort to formulate a plan to rehabilitate the polluted lake.

It also may be necessary - though counterintuitive - to cut hundreds, perhaps thousands of mature trees in the lake's watershed to stem the soil erosion that has been compromising the quality of the lake's water, Gullett said.

'When you walk around our lake and look at it - it's aesthetically objectionable, loaded with algae - you understand that something needs to be done to clean it up,” said Gullett, who encouraged the Department of Natural Resources to develop a water quality improvement plan for the lake.

That plan, released in August, found that poor water transparency caused by algae blooms is the primary reason for the unpleasing appearance of the lake, which was constructed in 1968.

The Conservation Department continues to work with members of the public, the DNR and other agencies to develop a rehabilitation plan - a prerequisite for applying for state and federal grants - that Gullett hopes will be completed by November.

'Kent Park Lake is on our short list of lakes under consideration for funding,” said George Antoniou, coordinator of the DNR's highly successful lake restoration program.

Lab tests show high levels of suspended algae in the water, poor water transparency, suspended inorganic particles and high levels of phosphorus in the water column, according to the DNR report, which defines the allowable total minimum daily load of pollutants. It also found the lake's pH, a measure of acidity and alkalinity, often exceeded the water quality standard of 9.0.

Those impairments make the lake unfit for the primary contact recreation it should be able to support, the DNR report stated.

In seven of 14 weeks this summer, the water in the lake tested higher than allowed for E. coli and other potential health hazards, prompting staffers to post 'swimming not recommended” signs.

'Although reducing phosphorus loads entering the lake is a step in the right direction, it does not directly address phosphorus previously accumulated within the lake, which can lead to algal blooms, even if external loads are reduced,” the DNR's remedial plan said.

To improve Kent Park Lake water quality in the short term, a physical mechanism (such as dredging) that removes phosphorus from the lake, especially in the shallower portions, must be considered in addition to reductions from watershed sources, according to the remedial plan.

Although more than 70 percent of the lake's 672.5 acre watershed lies within park boundaries, much of the soil erosion also comes from the county-managed land - a situation that may have been inadvertently exacerbated by reforestation efforts.

Gullett said the Conservation Department, in the past 50 years, has planted more than 200,000 trees in the park, in effect converting the landscape from an open savanna to a shaded forest.

'Our hypothesis is that in doing so we destabilized the soil and accelerated erosion,” he said.

The shading out of herbaceous species whose roots help hold soil in place also opened the door to invasive species such as honeysuckle and autumn olive, Gullett said.

'Before we came, the landscape was in equilibrium. We can upset that even with good intentions,” he said.

Gullett said the University of Iowa Hydraulics Lab is measuring the extent of erosion on different soil and land-use types within the watershed. If the lab findings confirm the hypothesis, parts of the forest will be thinned to re-create less-erosion-prone savannas, he said. Department of Natural Resources spokesman Kevin Baskins said a similar situation prevailed at Nine Eagles State Park in south-central Iowa.

Erosion there was excessive, he said, even though the entire watershed of the park's lake was owned by the state.

Though conservation staffers believe angling success has declined, DNR fisheries biologist Paul Sleeper said the lake still provides fair fishing for bass, bluegill, crappie and catfish.

From 2008 through 2012, the park has averaged 123,000 visitors per year. 'But we know there are people who are not coming as often or going elsewhere because of the quality of our water,” Gullett said.

'The bottom line is we have to decrease the volume of phosphorus entering Kent Park Lake by 55 percent just to get off the impaired waters list,” Gullett said.

'But we're not just looking for a passing grade. Our approach is to provide the best water quality possible,” he said.