Algae Removal: Holly Pond

Project Location:  Sheridan, Wyoming, USA
The goal of this project is to utilize BioHaven Floating Island (Floating Treatment Wetland / FTW) technology to reduce nutrient concentrations and improve water quality in the Holly Ponds complex located on the west side of Sheridan, Wyoming.  Specific goals are to reduce concentrations of total phosphorus (TP) and total nitrogen (TN) that are causing an annual algal bloom, using minnow growth and harvest as a complementary strategy.  In less than one year, pond water quality and aesthetics were dramatically improved.  

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Overview
Big Horn Environmental Consultants of Sheridan, Wyoming, a local distributor for Floating Island International (FII), installed BioHaven Floating Islands and Floating Streambed in Holly Pond #1 in June 2016.  Objectives were to address algal blooms by reducing TP and TN concentrations, and to also control mosquitoes through larvae-consuming fathead minnows.

Location:    Sheridan, Wyoming, USA
Parameters Studied:    TN, TP, dissolved oxygen, Secchi depth, pH
Environment:    Housing subdivision pond
BioHaven Size:    Area of 500 ft2 (46 m2), thickness of 8 inches (20 cm)
Water Source:    Groundwater
Installation Date:    June 2016
Flow Rate:    About 10 gpm
Water Body Depth:    5 ft (1.5 m) average, 7.7 ft (2.3 m) maximum
Water Body Area:    13,000 ft2 (1,200 m2) or 0.3 acre
% Coverage:    3.8% of pond covered by BioHavens

To create a “brush park,” which is a well-known aquacultural technique used to increase fish growth and harvest, 200-250 pounds of cottonwood and sandbar willow saplings were dried for 90 days, then weighted and positioned in loose bundles, and submerged in Pond #1.  The brush park provides food (microbes and periphyton) and cover for minnows, which will consume mosquito larvae and simultaneously remove TN (about 0.8% of minnow live weight) and TP (about 0.1% by weight) when they are harvested from the pond.  

It is planned to transfer minnows periodically from Pond #1 to other nearby ponds, to also remove TN, TP and mosquito larvae from those waterways.  Minnow transfer requires state agency approval, which is expected later in 2017.  It may be economical to sell the minnows, which have a retail value of about $3/dozen.  Minnows provide biological control of mosquitoes in contrast to typical chemical control via larvicides and adulticides.  Chemical treatment has been stopped at Holly Pond #1 and it is hoped to also reduce or stop it at nearby ponds after minnow transfer.

​One Floating Streambed (providing active circulation and aeration) composed of three islands was installed, and surrounded by an archipelago of seven BioHavens (passive islands without circulation).  The islands were nearly decimated by heavy waterfowl usage during the first winter but recovered without replanting.  To discourage waterfowl use in future winters, the streambed will be turned off to allow most of the pond to freeze.

Pre-FTW monitoring data are not available for Pond #1, so is it believed that the FTW effect is best shown by comparing Pond #1 to a nearby control pond.  Our proprietary data show a dramatically lower TN level in Pond #1, along with improvements in DO, Secchi depth and wildlife (turtles) compared to the control.  In order to measure TP removal by the floating islands, it will be analyzed to a lower detection limit in future sampling events.

Please submit the form to see the Holly Pond data.
The higher dissolved oxygen (DO) is probably due to the Floating Streambed aeration and circulation.  More data are required to ascertain the improvement in TN levels.

A homeowner on Pond #1 has continued to physically remove some algae in 2017.  Algae removal mass has not been quantified but anecdotally, the amount removed has been far less in 2017 than in 2016 and previous years.
 
BioHavens were under siege from active duck population, winter 2016-17 but fully recovered in spring 2017. Polyurethane “armoring” of the islands prevented long-term waterfowl damage.  Plants and microbes on the islands digest the duck guano and prevent its release to the water. 

Conclusions
Less than a year after installation of floating islands, Holly Pond #1 water quality was dramatically improved and algae growth was greatly reduced.  The total nitrogen concentration was substantially lowered and the total phosphorus concentration was also presumably reduced.   The City of Sheridan has also been able to eliminate chemical addition for mosquito control from Pond #1, which now has a thriving minnow population.

"The Floating Islands and Streambed that were installed at the Holly Ponds site have been a fantastic study. What once was a pond completely covered and choked out by algae growth is now a haven for wildlife, has improved water clarity and completely enhanced the overall aesthetics and quality of water at this site.  By using the "Nature as Model" approach promoted by Floating Island International, I have witnessed first-hand the results, without the use of chemicals, to re-create what was intended to be in the first place."

Chad Franklin
Weed & Pest Technician
City of Sheridan

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