Algal Mat Blues

This spring we have seen the return of the floating algal mats in our "new" irrigation pond on the 12th hole. Though totally natural, these mats are ugly and surely compromise the aesthetics of the green and tee complexes in the vicinity. The local watershed district wrote an article on these algal mats in 2014 that offers more information on the topic.

 

12 pond in May, 2015

So why is this pond that is replenished with low-nutrient ground water affected? The obvious culprit is direct runoff from surrounding areas. This may be a contributing factor but the main source of phosphorous can be found on the bottom of this water feature. During construction, the liner membrane was covered with one to two feet of soil to hold it down in place and protect it from UV sunlight. These soils are most likely releasing phosphorous into the water column causing the algae to flourish.

What are our options to get this visual eyesore under control? We can physically attempt to remove it but that will require many man hours of messy work. More importantly, this is only a short term fix as the plants will return. Aquatic herbicides and algaecides are a chemical option but, remember, this is the water with which we irrigate the golf course and these herbicides can cause problems with the grasses on the golf course. In addition, many native plants are being established in the shoreline area and herbicides could be detrimental to their survival.

Bill Bartodziej, District Biologist with the local watershed district, began experimenting with another chemical option last week. Because the algal mats are generally restricted to the littoral shelf of the pond, Bill began spraying alum (aluminum sulfate) from the shore on a localized basis.

 

Shoreline alum application below 13 tee. Note flocculation clouds in the water. The pH of the water was checked during and after application to assure the safety of all pond life.

 

Alum product

 

How does the alum work and what does it do? The alum chemically binds or flocculates the phosphorous and very fine sediments in the water column and these "flocs" settle to the bottom. On the bottom, this material is inert and no longer available as a nutrient source for plant growth. The cost to completely treat all 4+ million gallons of water in this 1.5 acre pond is cost prohibitive for our current budget cycle. The effectiveness of this localized treatment remains to be seen.