1997-05-01_AgendaPacket - Laserfiche WebLink

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bass like clearer eater. Owasso is current{} managed for ~+alle~e and muskie. Relati~ e to similar lakes, the walleye population is in the 2~-~Oth percentile. There is a 40" minimum for muskie and Owasso is used as an egg source.. Early-season turbidity favors algae and hurts habitat. Fish need clear water for egg germination and will nest in the best habitat available; daylength and temperature are factors in which species are spawning. Turbidit}' or boat traffic is a problem for most fish nests due to disturbance, loss of cover, and loss of hard bottoms on which nests are made: males maintain nests by fanning away soft sediments even where sediments are a few feet deep, but will leave if the disturbance is too great. The DNR's past practice of posting spawning areas had little effect on fish populations. Good habitats are 1/2' to 6' deep, under lilies and sparse cattails. - (DZ) 3. Various publications (EPA, A~VSA, MPCA) discourage boating in shallo++ ++~aters to reduce sediment resuspension and bottom scouring. Define "shallrn~"and comment on this. Biologically, shallow (littoral) zones are s l5'. It could be defined for boating as s 6', possibl}• 34" (see Asplund and Cook, Effects of motor boats on submerged aquattc macroph}~tes. Lake and Reservoir Management. in press). A 90 to ]50-hp outboard motor operating at full speed can easil}~ mix down to 6'; a 24hp motor might only mix to 34" (JSch). A 175-hp bass boat aught mix to only 30" (DA). Activities such as accelerating boats onto trailers at the launch can increase scouring of lake bottoms; the bottom in Owasso's launch area Lacks vegetation (JSch). Most surface use restraints are to prevent erosion and increase safet}~ rather than to protect lake bottom. Rooted plants at/near shore would help to protect shorelines (DZ). 4. What is the significance of annual +s. monthly trends in Secchi disc readings for O+casso? Will the reason for excess turbidity in Oti also be discrn Bred (ho+r)? The MPCA identified Owasso as a lake with improving clarit}', sa SEH. Engineering examined monthly Secchi data (1973-1994) including that from Don Meyer. The only statistically significant increase in clarity occurred in June and clarity in other months was not significantly improved. With respect to Owasso's "excess turbidit}'" (beyond that due to algae), SEH hoped to clarify if the source was external (watershed] or internal (in-lake), but the cause is still unknown. Fine particles not removed by ponding might contribute, but particle size data are lacking. The proportion of total lake P (phosphorous) due to external sources (i.e. the watershed) is not as large as expected. and there appears to be a high internal P load. Continued improvement of the external load is still desirable. The SW end is more turbid than other regions, but tt is not clear if it is the only source of mid- and E-basin turbidity. Procedures such as mechanical weed harvesting or aluminum sulfate treatment (done in an Eagan lake) do not address the source of the problem. Aluminum sulfate both precipitates P and adsorbs suspended particles, removing them to the lake bottom. It is expensive and not justified unless the majority of nutrient load is from a known group of sources. Owasso's turbidity is "higher than ideal". -(JSch) The main management focus is nutrients, not turbidity. GLWMD has rightly gone after external sources first. However, lake P levels indicate the tnternal load is also important. Sources include plant decay and sediment resuspension. This is harder to address: it is cntical to kno~;' when (seasonally) and where (in the water column) P is found. On Owasso, plant-bound P increases through September (TN). The lack of significant improvement in clarity does not negate the value of watershed projects, since beneficial effects will appear only slowly. However, if internal sources are the main problem, controlling external sources will not help (JSch). The P load is fundamentally important to productivity (e.g. algae) and the natural trend over [geological] time is to increase. Our understanding of the lake quality improvement may be too simplistic (TN). Road projects such as those on W. Owasso and N. and S. McCarrons offer Roseville opportunities for better stormwater management and lake improvement; the LOTF could support this cause (TN). 2