8.1. SR 06-17-2019 - Laserfiche WebLink

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wildlife habitat. The LID should work with the DNR's Aquatic Plant Management Program to survey aquatic and wetland plants in the areas under consideration for dredging and come up with a strategy to avoid or minimize destruction of desirable native vegetation due to dredging activity, and to design restoration projects in dredged areas where harm to native vegetation cannot be avoided. Lake Orono has several complex and interrelated problems, and measures taken to address these problems will have impacts on the lake's native vegetation. These include impacts from dredging, drawdowns, and herbicide treatment or mechanical removal of CLP. Balancing all of these measures while protecting the integrity of the aquatic vegetation community will be very challenging, but necessary. The DNR strongly encourages the LID to include consideration of the impacts of all of these problems and their proposed solutions on the vegetation, and propose a viable strategy to protect or restore the native vegetation community from the consequences of these solutions, in any Lake Vegetation Management Plan that it adopts. Water Quality Lake Orono is eutrophic, with elevated total phosphorus concentrations and low water transparency. Mean summertime TP is around 100-111 µg/L, and mean Secchi depth is about 3.1 feet. Threshold values for lakes similar to Lake Orono in the same ecoregion (North Central Hardwood Forest Shallow Lakes) are considerably less: <60 µg/L TP, <20 pg/L chi -a, and >3.3 feet Secchi depth. According to the MPCA, internal nutrient recycling and nutrients from stormwater runoff are a small part of the lake's water quality problems. Four sediment cores collected and analyzed for phosphorus in 2018 showed one sample slightly above the median for Minnesota lakes; one within the lower 25% of values expected for Minnesota lakes; and two with no phosphorus release. These results support the hypothesis that most of the excess phosphorus comes from the watershed. Lake Orono has a very large watershed:lake ratio, most of which is agricultural or otherwise developed in some fashion. The watershed is itself considered impaired for water quality characteristics in numerous stretches. These characteristics increase the lake's vulnerability to pollution from the watershed. Because these phosphorus sources are largely outside the boundaries of the proposed LID, it will be challenging for the LID to remediate them; nevertheless, reducing phosphorus inputs from the watershed is the most effective way to help Lake Orono with its eutrophication problems. To achieve this goal, the DNR strongly encourages the LID to pursue any erosion control, landscaping and ecosystem restoration projects within the boundary of the LID, and to pursue partnerships and collaborations with private property owners, Sherburne County, the Sherburne County SWCD, BWSR, the Elk River Watershed Association, and the MPCA to indirectly influence those sources of phosphorus outside the LID's boundaries. According to the Orono Lake Management Plan, the Lake Orono Water Quality Committee (LOWQC) already has a long history of working with many of these groups to pursue water quality enhancement projects in the Elk River Watershed. The DNR also suggests that the LID undertake a survey to determine whether any septic systems on the lake are noncompliant and, if so, bring them into compliance. Noncompliant septic systems can be a significant contributor of nutrients to the lake. The high mercury concentration in fish tissue is being addressed with the Statewide Mercury TMDL. DNR Advisory Report on Lake Orono Lake Improvement District Page 7