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

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�n=36 period (2014 to 2018), approximately 1.65 million pounds of total nitrogen were delivered to Falls Lake each year. Thus,the watershed processes and crop harvesting reduce the total nitrogen applied to the watershed by approximately 81 percent prior to delivery to Falls Lake. For total phosphorus,the watershed processes reduced the amounts applied, deposited, or released to the watershed by approximately 84 percent. These reductions due to watershed processes and crop harvesting are important considerations for the revised nutrient management strategy. Reducing one pound of nutrients in the watershed does not translate to reducing one pound delivered to Falls Lake. On average, depending on the project location, a one-pound reduction of input may result in 0.2 pounds reduction delivered to Falls Lake. The 770 square-mile watershed is processing a significant amount of nutrients before they reach Falls Lake. The UNRBA's watershed modeling has also improved understanding of the importance of soil chemistry on the transport, retention, and release of nutrients in the watershed. Soils in the watershed contain iron and aluminum that bind nutrients and release them slowly over time. This understanding must be factored into the revised strategy in terms of compliance dates and to moderate expectations about the length of time it will take for actions that reduce nutrients to impact water quality in the lake. The Chesapeake Bay STAC reported similar findings: realized nutrient load reductions had not translated to expected improvements in water quality. The modeling also demonstrates that the significant efforts to reduce point and non-point source nutrient loading have had an important impact on delivered loads to Falls Lake. Because most of the land in the watershed is unmanaged (forests, wetlands, etc.) and extensive efforts have already reduced loading from human activities, approximately one-half of the delivered nutrient and carbon load to Falls Lake originates from unmanaged lands (Figure 8). Natural areas, including forests, cycle and provide important nutrients to waters that sustain aquatic life. Land preservation is a critical safeguard for keeping the watershed as Total Phosphorus(pounds per year) natural as possible. These mostly natural 250,oao areas dominate the drainage area and are 200,000 important to the health of the watershed and .• the lake. Even watersheds that are 150,000 100 percent forested contribute flow, 100,000 nutrients, and carbon to downstream waters - a 51.3 10,000 inches 45.6 healthy ecosystems require nutrients and ML inches carbon to support life. Throughout UNRBA 0 meetings, discussions, and document reviews, TR(lblyr) multiple stakeholders and experts have w 201 ■2018 2017 02018 expressed that conservation must be a component of a revised nutrient management Total Nitrogen(pounds per year) strategy. The scientific work supports this 2,000,000 conclusion. The UNRBA's efforts and implementation of the IAIA support this activity 1,500,000 as a critical component of future management. '" 1,aoa,0oo As noted above, another important finding is the importance of precipitation and flow on 500,000 51.3 inches 45-6 delivered loading to Falls Lake (Figure 9). inches During an average rainfall year like 2017 0 w_� (approximately 45 inches of rain at Raleigh ■2015 2018 2017 ■2018 Durham International Airport, RDU), delivered total phosphorus and total nitrogen loads were Figure 9.Annual Nutrient Loads Delivered to Falls Lake from the Watershed 17