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Bahia Del Mar Lake Restoration Case Study

Bahia Del Mar is a 14 acre lake located in St. Petersburg, FL. In January, 2012, the Home Owners Association contacted a local lake management company to request assistance with multiple lake issues. They experienced foul odors, ongoing fish kills and recurring algae blooms. Together, these signs pointed to the need for a full lake restoration including aeration.

Testing showed the to be severely stratified, with high biological oxygen demand and very low oxygen levels. The lake of oxygen greatly increased organic material in bottom waters, leading to high nutrient levels and high concentrations of hydrogen sulfide causing a “rotten egg” odor.

Assessing the Problems

Field and Lab Testing

Both field and lab tests where used to determine the existing chemical and biological conditions of the lake. Tests included levels of oxygen, redox, conductivity, pH, hydrogen sulfide, biochemical oxygen demand, salinity, turbidity, phosphorus, nitrogen and chlorophyll a.

Results showed that the lake was unsuitable for fish and other aquatic organisms; and posed a health risk to residents due to the intense noxious fumes being emitted from the lake. The main problems and the underlying causes identified were:

Intense odor causes

Hydrogen sulfide (the source of the “rotten egg” odor) permeated the lake and surrounding area due to:

Fish kills

Major fish kills that were likely due to rapid mixing of stratified layers by an existing aeration system that was undersized and installed only in the shallower areas. This undersized system was only strong enough to churn up water from the bottom of the lake without properly mixing and adding oxygen to the entire water column. This rapid mixing of bottom layer waters into the upper water levels depleted all the oxygen in the surface water and brought up high levels of hydrogen sulfide, methane and ammonia from the bottom waters up to the surface causing the death of fish, crabs, shrimp, snails and some birds in the lake.

Algal blooms

The breakdown of large amounts of organic matter in the lower water column over time caused the buildup of high concentrations of nutrients, primarily phosphorus and nitrogen. These high nutrient levels fed algal growth in the lake, which made the water look like “pea soup”.

Bathymetric Mapping

The lake management company had been told that the lake was only 18’ at it deepest point. To confirm this,  bathymetric mapping was conducted  to determine accurate depths throughout the lake, the total water volume and the location of vegetation in the lake. Contrary to what everyone thought, mapping showed areas within the lake that were actually over 50’ deep. This information showed why the existing aeration was not effective and allowed us to determine exactly how much aeration was needed to circulate the entire water body each day; and to identify the best locations in the lake for placement of the aeration.

Solutions: Lake Restoration Using Aeration and Alum Together

bahia del marThe lake did not support fish and other aquatic organisms, and it posed a health risk to residents. To correct this, a two-pronged approach brought the lake back to a healthy state quickly.

Aquatic Aeration
According to a bathymetric map the total lake volume is far higher than their existing aeration could handle. With this in mind, two Vertex Aeration Systems, an LL 4XL5 Aeration System and a HF 4XL5 Aeration System with sound kits were installed in April, 2012 to provide effective turnover rates.

Alum application
Two treatments of Alum at a rate of 60ppm were applied to quickly improve water clarity and reduce water phosphorus levels.

Results:

The lake restoration was complete: Oxygen at bottom of the lake went from 0 mg/L to 8 mg/L


If Your Lake is Showing Symptoms of Low Oxygen, Get expert Help Now.

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