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70 r60 s'A 8 aVi so 40 30 � to memo 10 of 14 reviews already exist that summarize this body of literature (e.g., Mosisch and Arthington 1998, Asplund 2000, and Osgood 2000). Fewer studies have focused on the specific effect of motor boat activity on phosphorus release from the sediment, and those studies are summarized below. There is no disagreement in the literature over the fact that motor boat activity negatively impacts lake water quality and health. The focus of most recent studies has been on determining which speeds, motor size, and water depths motor boat activity has the most affect. Beachler, M. M. and D. F. Hill. 2003. Stirring up trouble? Resuspension of bottom sediments by recreational watercraft. Lake and Reservoir Management 19(1): 15 -25. For this study, the authors developed a theoretical model relating boat speed, maximum lake bed velocity, and water depth. This model was verified by field measurements of sediment bed velocity and resuspended sediment concentrations from outboard, inboard, and jet motor activity over sediments at different water depths during a two -week period in July 2001 on Franklin and Butternut Lakes in Wisconsin (respectively with surface areas of 892 and 1292 acres, maximum depths of 46 and 42 feet, and an average depth of around 13 to 16 feet). Results from a theoretical model for an 150 hp outboard motor showed that the greatest impact of motor activity on sediment re- suspension occurred at `near- plane' speeds (around lOmph), with idle and high speeds having similar effects on sediment resuspension (Figure 7 below). In addition, boat speeds between 3 and 20 mph for 4 feet water depths and between 5 and 13 mph for 6 feet water depths resulted in sediment resuspension (Figure 11 below). At water depths greater than 8 feet, motor boat activity did not have a significant effect on sediment resuspension for all boat speeds. The authors recommend no -wake zones instead of motor boat speed limits because the critical speed at which sediment resuspension occurs varies with boat size and water depth. Therefore, a speed limit that minimizes sediment resuspension for one boat type might actually place another boat type in its critical speed ranee for maximum sediment resuspension. At idle speeds (no- wake), water movement above the sediments is lowest for all boat types and water depths resulting in little to no sediment resuspension 10 20 3 Boat Sneed (mph) Figure 7.- Observed and predict d values ofmaximum bed velocity, as functions of water depth and boat speed, for the outboard boat. so 70 8 60 so 40 W' O 30 20 10 depth. In em — — — dep& ■ 183 en — depth s 244 e'e depm -345 co ladpdat modes S 10 15 20 25 Boat Speed (mph) Figure 11. -Model predictions of V,..variatiouwith boatspeed for several water depths for the outboard boat Nedohin, D. N. and P. Elefsiniotis. 1997. The effects of motor boats on water quality in shallow lakes. Environmental Toxicology and Chemistry 16(1): 127 -133. Emmons & Olivier Resources, Inc. 651 Hale Ave N, Oakdale, MN 55128 p: 651.770.8448 f: 651.770.2552 www.eorinc.com ■ Oheeeeed (148 UO p OWrwd(137CM) • Obeeved 027 co) — — — Poilded (157 an) Podded (127 to) T/ \ \ 1i \ 10 20 3 Boat Sneed (mph) Figure 7.- Observed and predict d values ofmaximum bed velocity, as functions of water depth and boat speed, for the outboard boat. so 70 8 60 so 40 W' O 30 20 10 depth. In em — — — dep& ■ 183 en — depth s 244 e'e depm -345 co ladpdat modes S 10 15 20 25 Boat Speed (mph) Figure 11. -Model predictions of V,..variatiouwith boatspeed for several water depths for the outboard boat Nedohin, D. N. and P. Elefsiniotis. 1997. The effects of motor boats on water quality in shallow lakes. Environmental Toxicology and Chemistry 16(1): 127 -133. Emmons & Olivier Resources, Inc. 651 Hale Ave N, Oakdale, MN 55128 p: 651.770.8448 f: 651.770.2552 www.eorinc.com