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Chapter III Affected Environment and Environmental Consequences 29 compliance with this standard. The standard is for long-term trends. The salinity program is designed to offset any long-term effects including those created by Glen Canyon Dam and Lake Powell (or any other project in the Basin). Under the No-Action Alternative, the goal of the salinity program would be to continue to fmd cost-effective ways to maintain water quality standards. The Proposed Action alternative would increase the variability of the salinity released from the dam but would not change the long-term discharge of salinity. Salinity is routed conservatively in the reservoir (USDI 1997). Salinity in the Colorado River varies more from changes in hydrologic conditions (e.g., runoff) than from any other single factor. Any change in the operation of the outlets may influence the salinity of the river, but only in temporary ways. Salinities in the Grand Canyon may vary, but mixing in Lake Mead would continue to remove most of the seasonal variation in the system. Selenium - Water quality data in the reservoir near the dam show that selenium levels are fairly uniform with depth. Values are typically 2 ug/L in summer and may vary +1- I ug/L through the year. The USDI (1997) reported average selenium levels below Glen Canyon Dam were 2.5 ug/L. The action alternative would have little or no effect on the value. Nutrients and Their Effects on Primary Productivity - A balance of nutrients is critical to the ecology of any aquatic ecosystem. Low levels of nutrients generally limit productivity higher in the food chain (fisheries). High levels of nutrients cause systems to strangle on their own wastes, depressing dissolved oxygen levels. Large, long reservoirs like Lake Powell are very efficient at retaining nutrients in the reservoir through biological processes and settling. Nutrients discharged from Glen Canyon Dam under existing conditions are extremely low. In 1981-1982, an intensive study was jointly conducted by Reclamation and the Lake Mead Limnological Research Center, University of Nevada (Paulson and Baker 1983). The study was conducted to survey nutrient bioavailability, algae productivity, and limnological characteristics of the Lake Powell and Lake Mead. The study found that total phosphorus concentrations are relatively high coming into Lake Powell. However, a major portion of the total phosphorus load settles out of the water column with sediments in the inflow zone of the reservoirs. This phosphorus is not readily available to biological processes downstream. The high iron oxide content of the Colorado River water gives it the distinguishing red color (for which the basin is famous) and reduces phosphorus concentrations via ion adsorption. Thus, when the sediment settles out, it also removes large quantities of phosphorus, Lake Powell can retain nearly 98 percent of the inflowing total phosphorus (Paulson and Baker 1983; Miller et al. 1983). A similar storage effect is repeated in Lake Mead. The entire mainstem Colorado River Basin remains very phosphorus limited throughout most of the system. Tributaries inflows (example: Paria River, Little Colorado River, and Las Vegas Wash) are an important sources of phosphorus in the river below Glen Canyon Dam. This settling process can be reversed in Lakes Powell and Mead when the reservoirs are drawn down and the sediment deltas are resuspended. Beneath the water-sediment interface