REPORT from POND and LAKE CONNECTION
Phosphorus Testing Results
Nick McMahon and Zach Davis reported on PLC’s testing for Phosphorus levels as contracted by MLIF. PLC tested lake water and sediment in 5 locations representative of different parts of the lake, with respect to location and depth to provide data on Phosphorus within the lake. These results give insight into our issues with excessive algae. Data given is below:
Water samples (amount of Phosphorus in lake water) given in micrograms/ml of Phosphorus:
Site 1 – 20.9
Site 2 — 25.6
Site 3 — 23.5R
Site 4 – 22.9
Site 5 – 18.4
Sediment core samples (amount of Phosphorus in solids) given in micrograms/ml:
Site 1 – 395
Site 2 — 629
Site 3 – 385
Site 4 — 547
Site 5 – 513
Internal loading was suspected in the 2016 state lake study as a main contributor to algae and these results prove this is the case. Our lake has too many nutrients that have built up over time and have become concentrated in the sediment. Nutrients are generally locked in the lake bottom for much of the year until the lake bottom becomes anoxic generally June, July, and August. When no oxygen is present the sediment liberates Phosphorus and fuels algae blooms.
Dredging lake bottom – exytremely costly
Lock up the Phosphorus with products like Phoslock/Alum. Cost estimate for one time application of Phoslock to reset the Phosphorus levels in the lake $238,000. This could be applied over time to spread the cost. For every lb. of Phoslock added, an exact amount of Phosphorus is locked up. Treatment could be broken up over 4, 8 or 12 years.
Introduce oxygen to the lake bottom to keep nutrients locked up in the sediment using an aeration system. There are two types:
1) Diffused air using a compressor to pump air to diffusers at lake bottom. As bubbles rise to the surface, they bring low oxygen bottom water to surface where it is replaced by high oxygen surface water.
2) Nano-bubble system that sits on shore and pulls in lake water, adds oxygen and sends out into lake. Bubbles are very small and don’t rise to surface giving them enough contact time to diffuse their oxygen into the water. Bubbles stay in suspension for weeks. Case studies of similar lakes were successful with reduced Phosphorus and more clarity. The company has a website “Moleaer”
In 2019, PLC performed 8 treatments from 4/24 – 9/26. All visits included some type of algae treatment with chelated copper. The lake experienced a brown algae or Diatom bloom that spanned several weeks through July. The increase in Diatom effectively locked up much Phosphorus so that it was not available for more problematic algae species.
Herbicide was applied to beds of Curly-Leaf Pondweed during the first treatment. This aquatic perennial weed is an aggressive invader that has no value as a non-native plant. Native plants (great benefit) were seen at their highest biovolume to date in 2019. Coontail was a nuisance in some areas of the lake. Coontail does not require a root to thrive and can form a floating mat when it becomes dense. PLC treated these areas with an herbicide meant to burn down the foliage and reduce the biomass.
Our regular monthly meeting then commenced.
Pond and Lake Connection Contract
A motion to approve the proposed 2020 contract by Pond and Lake Connection was unanimously approved by the Board.
The Board discussed the options for phosphorus removal. It was decided to invite a representative of the AirMax Diffuser Aeration system to gain further information regarding this system for our lake. Timing for grant proposals suggests this meeting and a Board decision should be by late January.
The final fundraising letter will be going out in mid-November.
It was noted that upcoming grant proposals are due in late January and late February. The Board will need to decide what projects to apply for.