Lake Notes… Water Advisor Board Meeting
By Lionel Robbins
It is the intent of YOUR Water Advisory Board to provide Lake Holden residents information as to how and why the Board spends YOUR money. The name of this series was suggested by Caroline St Clair. The WAB members unanimously agreed to adopt the name, What’s In Your Water? Below is the first of the sequence.
What’s In Your Water?
Residence time of a drop water in a lake begins from the moment the drop enters the lake and ends the moment that the same drop leaves the lake. According to the ERD’s Lake Holden 1992 study, the average residence time of water in Central Florida lakes is 3-6 months. For Lake Holden, the residence time is 17 months.
Residence time is important to Lake Holden because when a large amount of nutrients enters the lake, the longer it will take for the nutrients to leave the lake, resulting in a longer residence time. We know the only inflow is rain (stormwater runoff) and no “outflow” because the lake is landlocked. Because the lake cannot expel these nutrients they are continually recycled or reintroduced into the water column. The nutrients provide food for the algae to grow that in turn keeps the water column clouded which prevents light to penetrate to the plants that need to grow in the lake to absorb the nutrients that the algae uses to grow….well you get the idea.
For lakes having longer residence times (a year or more), long-term average pollutant loadings become more important to overall lake water quality. As an ideal example, a lake having a water residence time of one year will still retain 50% of its original water after a year of average inflow. The second year, 25% of the original water will still remain. In the third year, the lake will have 12.5% of the original water, and so on. This characteristic requires that the longer the water residence time, the longer the time frame needed for in-lake observations to detect any response to loading reduction. (ERD 1992) With a residence time like Lake Holden, the lack of inflow and outflow the challenge was to find a way to clear the water column.
The extreme residence time for Lake Holden was a significant factor for the decision to begin the surface alum treatment program. The nutrients and other suspended particles that restrict sunlight and promote algae growth are now bonded to the alum and now contained on the lake bottom. The absence of the algae and suspended particles is the cause of the clarity of the water we enjoy today.
You are welcome and encouraged to attend any and all WAB meetings held on the third Wednesday of each month at 5:30PM. The location is 2010 East Michigan St, Facilities Training Room.
