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<br />. <br /> <br />9 <br /> <br />Dual outlets were recommended to benefit the downstream fishery by <br />discharging reservoir surface water which is warmer and contains fewer metals. <br />It was unknown at the time that dual outlets would actually aggravate the <br />heavy metals and dissolved oxygen problem by reducing the amount of phosphorus <br />flushing through the reservoir. Phosphorus is directly related to heavy <br />metals through the food chain; i.e., as phosphorus ~e~els rise, algae grows. <br />As the phosphorus is consumed, algae die and settle to the reservoir bottom. <br />Decomposition requires oxygen and continues until the reservoir supply is <br />depleted. When this happens, heavy metals at the water/sediment interface <br />are chemically changed by the lack of oxygen and redissolve into reservoir <br />water. If these metals circulate through the reservoir at times of turnover, <br />they may be absorbed into the food chain and concentrate in fish flesh or be <br />discharged downstream to impact the fishery and M&I water supply. <br /> <br />The low-level outlet would flush out additional amounts of phos- <br />phorus (released from decomposing algae) and thereby lessen available nutri- <br />ents for algae production in the reservoir. The aeration option would prevent <br />metals from reentering the water column by maintaining an oxygen level of <br />4 mg/L at the water/sediment interface. In summary, the low-level outlet <br />would reduce reservoir concentrations of phosphorus and heavy metals, algae <br />blooms would be less, stagnation would be reduced as warmer, aerated water <br />gravitated downward, and with aeration, metals would be trapped. None of the <br />benefits created by the single outlet alternatives would have significant <br />impacts to reservoir or stream temperatures (see discussion under Fish and <br />Wildlife, page 10). <br /> <br />1. Dual and multilevel impacts <br /> <br />Under alternatives that include dual or multilevel <br />outlets, phosphorous accumulation and summer stagnation in the reservoir <br />are accelerated because surface releases do not permit mixing of the deeper <br />water. Thus, as mentioned in the previous paragraph, high-level releases <br />appear to increase the likelihood that heavy metals will reenter the water <br />column from the sediments as oxygen is depleted. <br /> <br />The dual and multilevel outlets would provide optimum <br />stream temperatures for trout if a significantly high reservoir elevation <br />could be maintained throughout the year. Unfortunately, this is not possible <br />in a fluctuating reservoir, and in dry years or periods preceding fall <br />turnover, releases would have to be switched from the better quality surface <br />or middle water column to the low-level stagnant water outlet. Since late <br />summer represents the period of peak stagnation, this switch could cause <br />extreme changes in temperature, dissolved oxygen, heavy metals, and a resultant <br />potential for fish kills immediately below the dam. The multilevel outlet is <br />somewhat more flexible in water column selection, but the accompanying high <br />costs provide only marginally improved water quality conditions. <br /> <br />2. Single-level impacts <br /> <br />The single-level outlet alternatives would produce similar <br />water quality effects "since all water except spillway spills would be released <br />through the bottom outlet. May and June stream terperatures would be cooler <br />