Agenda 11-02-23; 4-a - Resolution Endorsing Consensus Principles II for Revised Falls Lake Rules

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=29 watershed-lake system to inform and support the concepts and principles for the revised nutrient management strategy. While the UNRBA's complete effort includes comprehensive modeling and the development of tools that can assess the effectiveness of potential management approaches,the data, special studies, and information developed to support the modeling provides an excellent reference and basis for understanding this lake and watershed. The data itself is a "model" by conveying the status of water quality, spatial and temporal variation, and correlations among data sets. A large and extensive database provides important graphical and statistical information that informs further analysis and decision-making. The UNRBA's comprehensive monitoring report, which includes historic data, provides essential insight into the Falls Lake system and documents conditions that must be considered in the regulatory decision-making process. As a result of the UNRBA's evaluation of the data, one critical finding is that nutrient loading is not the only driver of algal growth in the lake. At times, algal growth and changes in algal activity are independent of short-term changes in nutrient loading and nutrient concentrations in the lake. Other influences such as lake sediment nutrient release, hydrology, and hydraulics in the lake and watershed can be more important in determining the trophic conditions in the lake than nutrient concentrations or loading. Physical conditions in the lake as well as chemical and biological variation are important drivers of algal growth. The amount of time the water remains in Falls Lake is controlled by the tributary inflows to the lake and releases from the dam which are controlled by the USACE. The release protocol for the dam is directed first at flood control and then, under low-flow situations, water supply and minimum releases to support downstream aquatic life. The longer the water remains in the lake,the more algal activity and growth. Other environmental issues arise during long detention periods including temperature increases and more pronounced fluctuations in dissolved oxygen and pH. This hydrologic condition also impacts lake stratification and the quality of The release protocol for the dam is directed water just above the lake sediment-water first at flood control and then, under low- interface, impacting the rate of nutrient cycling in flow situations, water supply and minimum bottom sediments. Algal species distribution is releases to support downstream aquatic impacted as well. Changes in detention time life. The longer the water remains in the and environmental, chemical, and other physical lake, the more algal activity and growth. characteristics impact the function of the arms of the lake including denitrification and settling of suspended materials. High-flow events impact algal conditions in the lake, particularly in the upper portion of the reservoir where the five major tributaries provide more than 60 percent of the flow to Falls Lake. Nutrient inputs in terms of tributary loading are driven by stream flows. 10