I would like to recap what we have done so far which started with the installation of 4 nanobubble generators in December.  We installed the nanobubble generators because of their ability to increase dissolved oxygen concentrations, which if too low can lead to other poor water quality issues including, in this case, large scale harmful algal blooms.  In addition to the install of the nanobubble units, Solitude began a monthly water quality monitoring program to monitor the progress of the site.  After beginning water quality monitoring, we realized the site conditions were worse than we expected, and we discovered the lake already had a layer of anoxia and high BOD prior to the install.  Fortunately, because of our monitoring, we were able to help make educated adjustments to help deliver results.

Even though results with just nanobubbles cannot always be expected so soon after startup, we decided to utilize a peroxide treatment to help immediately address the Microcystis population.  This harmful algal bloom can be contributed to the constant influx of nutrient rich runoff from the communities reclaimed water use.  This treatment took place in March and proved to be very effective on the bloom and continued monitoring by DEP showed a significant decrease in toxins produced by Microcystis within the lake.  

Solitude performed an alum application in the first week of May in order to quell some of the nutrient pollution caused by the reclaimed water use.  Monitoring post treatment showed a significant reduction of Total Phosphorus in the site, which is the limiting nutrient that can drive algal blooms.  Additionally, monitoring showed that while the nanobubbles are effectively delivering oxygen to the site, the high BOD and strong thermocline is keeping the lake stratified.

Based off the data and information we have gathered over the past 5 months, Solitude believes that by continuing to inject oxygen into the lake by way of the nanobubble units and mixing the water with bottom diffused aeration, we should be able to reach the goal of increasing dissolved oxygen throughout the water column while eliminating the anoxic layer.  Nanobubbles alone may have been able to get this lake where we would like it to be but due to the high internal load the addition of bottom diffused aeration will greatly accelerate the process.

The addition of aeration at Harbor Isle Lake will come at no additional cost and we are hoping to have this install take place on June 11th.  Attached you will find a map outlining the location of the aeration cabinets and diffusers in and around the lake.

Thank you for entrusting Solitude with the care of your lake out at Harbor Isle.  We appreciate the opportunity to continue monitoring and working with the City of St. Petersburg to optimize the techniques being used to achieve the community’s goals.

If you have any additional questions, please do not hesitate to reach out.

 

Matt Kramer Senior Project Manager Aquatic Biologist