2009-04-23_Minutes - Laserfiche WebLink

Home

GRASS LAKE WATER MANAGEMENT ORGANIZATION -APRIL 23, 2009 • In-Lake Water Quality - 2007 and 2008 • Watershed Pond Discharge Survey - 2008 Westerberg noted that iron content is a critical component. If iron is found, phosphorous is easily released from sediments. In 2007, the monitoring sites were Galtier Street, West Owasso Boulevard for the north end, and County Road C for the southern portion of the watershed. In 2008, a monitoring site was done at Dale Street rather than Galtier Street to find out if there is any impact from the compost site. Calibrations for the lake level were from December 2007 through December 2008. Outcomes include ice off the lake. Flux models were used in conjunction with the P8 model to estimate internal phosphorous loading. The flux model shows a significantly higher load because the base flow samples showed significantly higher phosphorous concentrations. The difference is due to internal loading sources within the wetland complex. Sources contributing to the phosphorous concentrations found at County Road C at the southern basin of the lake were tracked. External sources are from watershed runoff, atmospheric deposition and ground water. Internal sources are curly leaf pondweed, phosphorous release from sediments and rough fish (carp). The internal load in the northern part of the lake is relatively small. Curly leaf pondweed is dominant representing approximately 50%. Watershed runoff is about 18%. Under wet conditions, the watershed runoff is the dominant source. Potential sources that need additional investigation include carp activity, sediment release, wind mixing, and other biological activity. A four-year plan is recommended for curly leaf pondweed management. It could be MDNR treatment, which would require a permit, variance and permission of the homeowners. It could also be an herbicide treatment targeting curly leaf pondweed. There are 12 untreated discharges under public jurisdiction into Lake Owasso. Optimal treatment would be a water quality pond sized to N URP standards, but this is not feasible due to the lack of space. Kelsey asked how many years it takes for curly leaf pondweed to impact phosphorous content. Aichinger stated that one year does not carry over to the next year. Sobiech recommended a four-year plan of treatment with follow-up spot treatments to decrease the phosphorous concentrations and improve water clarity significantly. Also, infiltrating 50% of runoff from all impervious surfaces of the South and east drainage districts would cut phosphorous concentrations. Alum treatment would prevent phosphorous from being released from sediments. Westerberg noted that an iron mesh filter is being used at the University of