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memo 3of14 Table 1. Phosphorus Budget to Lake Owasso (Source: Lake Owasso Use Attainability Analysis, 2009) TP Load (lbs) Phosphor us Budget Wet D Ave rage Watershed Runoff 252 51% 102 36% 87 29% External Internal Loading from Watershed Waterbodies 89 18% 29 10% 60 20% Load Atmospheric Deposition 90 18% 88 31% 91 30% Sources Groundwater 62 13% 62 22% 62 21% TOTAL EXTERNAL LOAD 493 46% 281 51% 300 43% Internal Curl leaf Pondweed 184 32% 184 67% 184 45% Load Internal Sediment Release 398 68% 91 33% 221 55% Sources TOTAL INTERNAL LOAD 582 54% 275 49% 405 57% TOTAL PHOSPHOROUS LOAD 1076 556 705 To summarize this table, external phosphorus loads to Lake Owasso range from 43% to 51% of the total phosphorus loads to the lake, and the internal phosphorus loads range from 49% to 57 %. For a wet year and an average year, the internal load is the greatest contribution to the phosphorus budget and for a dry year, the internal load is two percent below the external phosphorus load to the lake (or basically equal to internal load for a wet and average year). As a result, it must be understood that solving the water quality issues in Lake Owasso will require addressing both the external and the internal loads to the resource. Of the external load sources to Lake Owasso, two of the four are sources the GLWMO can address: watershed runoff and internal loading from watershed waterbodies. Depending upon the climatic conditions (wet year, dry year or average year), watershed runoff accounts for 29% to 51% of the external load whereas internal loading from watershed waterbodies accounts for 10% to 20% of the external load. There are multiple Implementation Activities in the DRAFT 2011 Watershed Management Plan addressing these external sources of phosphorus (see Table 4). Of the internal load sources to Lake Owasso, both are sources that the GLWMO can work to address: curlyleaf pondweed and internal sediment release. Depending upon the climatic conditions (wet year, dry year or average year) curlyleaf pondweed accounts for 32% to 67% of the internal load and internal sediment release accounts for 33% to 68% of the internal load. According to the Lake Owasso Use Attainability Analysis "anecdotal evidence indicates that motorboat activity results in the resuspension of bottom sediments in shallow areas of the lake" (page xxii). However, "it is unclear what role mixing and resuspension in the shallow areas of the lake have on the overall water quality in Lake Owasso' (page xliv). Table 2 is a summary of the annual water budget to Lake Owasso. Table 3 summarizes the percent contribution of the drainage districts in the Lake Owasso watershed. As Table 3 illustrates, the south drainage district has the greatest contribution to Lake Owasso comprising 51.6% of the Lake Owasso Watershed, followed by the direct drainage district (23.8 %), the west drainage district (11.8 %) and the east drainage district (7.0 %). Table 2. Annual Water Budget to Lake Owasso (Source: Lake Owasso Use Attainability Analysis, 2009) Water Budget Wet (2002) Dry (2008) Average (2005) Volume (acre -feet) Volume (acre -feet) Volume (acre -feet) Direct Precipitation 1286 644 987 Watershed Runoff 1150 509 401 Groundwater 913 913 913 Total Water Load 3348 2066 2300 Emmons & Olivier Resources, Inc. 651 Hale Ave N, Oakdale, MN 55128 p: 651.770.8448 f: 651.770.2552 www.eorinc.com