This has been a frustrating and disappointing year for water quality. My last posting on August 12 was somewhat positive about the potential for a good summer, hoping the alum treatment later in the month would stave off a serious cyanobacteria bloom. However, that is not how things turned out, with cyanobacteria still active in mid-October.
Historically our phytoplankton starts with a large population of diatoms in early summer, usually peaking some time in July. This year the peak happened during the third week of June. Our phytoplankton population then shifts to cyanobacteria in early August as the water warms, and that did happen this year. However, in past years cyanobacteria would peak in mid-September before shifting back to diatoms in early October, but this year the cyanobacteria were still quite active the end of September with no reduction in volume.
Oddly, I saw relatively clear water on the West End a few weeks ago, which made us think we were on track for a declining population. But I think it may have been during a period of cloudy weather when we had the headgate closed, leading to an optimistic outlook for October. However, we are still experiencing daytime high temperatures in the 80’s and sunshine from dawn to dusk. Our everlasting summer is providing ample sunlight for sustaining cyanobacteria, which will not decline until the water cools and we get cloudy days.
Next year
We are experiencing the effects of climate change and can expect summers like this year will be more frequent. As a result, our historical playbook for cyanobacteria control will have to be modified. What exactly this means will take some analysis, but short term we will be continuing our phosphorus control program and starting aeration again next year to see if that will help.
We have not used aeration for the past two summers and the phosphorus concentration near the surface has stayed within our target level, only exceeding it this year right before our alum treatment. Aeration works primarily to keep phosphorus in the sediment at depths greater than 16 feet, and although the phosphorus concentration at these depths gets high without aeration, it is dark down there so not much can take advantage of the nutrients. However, since cyanobacteria can adjust their buoyancy, they may be able to migrate to those depths and take advantage of available phosphorus.
We are going to throw everything we have at the lake next summer to see if we can manage phosphorus and cyanobacteria. This means limiting our use of river water, treating what we do use with alum, operating aeration as soon as the lake starts to warm, and doing a surface alum application when phosphorus gets too high.
For the remainder of this year It looks like the weather is not going to change much in the next 10 days. The lake will continue to cool since the air temperature will be dropping to the 50’s at night, but we are still going to see a lot of sunshine and no rain. The forecast shows dry weather for the next ten days, but it won’t last forever and we will be back into the rainy season soon.
