Field Studies

PRx Phosphate Control Study

PRx Phosphate Control Study

Application: Rochester, Michigan
Airmax® PRx Phosphate Control

Trevor Henderson, Airmax Aquatic Biologist

Harmful Algal Blooms (HABs) occur when colonies of microscopic algae grow out of control. These blooms can have a severe impact on health, natural ecosystems, and the economy of affected areas. HABs are a result of nutrient pollution, and the blooms are becoming more of a threat worldwide and in the southeast corner of Michigan. In this developed corner of the state, some of these blooms are so notoriously large they can be seen from space (the Lake Erie HAB). The most common cause of HABs is excessive nutrients (nitrogen and phosphorus), typically originating from fertilizers and traveling downstream in the form of phosphate. The nutrient-laden water travels to ponds, lakes, and other small water bodies, where the stagnant, warm, shallow water becomes a breeding ground for HABs and smaller algae growths. Airmax Inc. was approached by lake owners afflicted by algae blooms. Airmax PRx Phosphate Control (PRx) was chosen to reduce the problem-causing phosphates. The Free Reactive Phosphorus (FRP) was reduced by nearly 98% over the 16 weeks of treatment with PRx, increasing clarity and decreasing algae problems in the lake.

Through the Clinton Watershed in southeast Michigan, millions of gallons of water flow into the Great Lakes every day. With that water comes thousands of pounds of organics, inorganic pollutants, inorganic substrates, and raw nutrients. These additions to the water both decrease the water clarity and increase the overall nutrient load, leading to Harmful Algal Blooms (HABs). These HABs close beaches, close fisheries, and limit recreational water activities. In the Great Lake State, these closures have major health and economic implications, and there is a priority on finding a solution that is environmentally and economically sound. Drastic large-scale chemical treatments of HABs could have disastrous effects including releasing harmful chemicals into the environment, creating treatment-resistant algae strains, and depleting already low oxygen levels in the water.

HABs must be addressed from their source, which is the excessive nutrient load coming from upstream in watersheds, starting in the streams, rivers, retention ponds, ditches, lakes, etc. Ponds and lakes are the most affected by the excessive nutrients because of the high residence time, which often results in algae blooms. The long residence time, however, does provide the opportunity for treatment.

When Rochester, Michigan, pond owners approached Airmax at the end of 2019 requesting help with their historical cyanobacteria-ridden pond, Airmax began with water analysis. Water samples were taken to a nearby independent laboratory, where it was discovered that Free Reactive Phosphorus (FRP) levels were over 0.45 mg/L, or over 4.5x the 'Eutrophication Limit' which dictates when a waterbody is over-productive through excessive nutrients. With high phosphorus levels being confirmed as the root issue of the 1.2-acre pond, Airmax moved forward with a plan for biweekly seasonal treatments with the phosphate binder PRx.

PRx is an all-natural, permanent phosphate binder utilizing a high-surface particle with a naturally high concentration of Magnesium Oxide. With this product, the goal was to lower the concentration of the FRP molecules in the pond.

PRx was provided as a fine gray powder and was applied to a waterbody through a venturi-style high-volume sprayer used directly over the water's surface, deployed from a boat. By applying PRx biweekly the hope was to use the PRx to bind the nutrients being released, limiting the chance of reoccurring blooms. At the beginning and end of the study, representative water samples were collected and taken to an independent laboratory for testing. To have a control pond with similar environmental influences and weather, a pond of 0.5 acres was found nearby and testing was performed concurrently with the treated pond.

Upon the completion of eight applications of PRx spanning the 16 weeks from the beginning of June to the end of September, Free Reactive Phosphorus in the treated pond was recorded at 0.01 mg/L. This figure is nearly a 98% reduction from the 0.46 mg/L levels at the beginning of the study, and even lower than the control pond final values which started much lower than the treated pond. Despite a relatively low initial FRP in the control pond, the treated pond still easily surpassed the control in FRP reduction.

Figure 1.1 Figure 1.2

With the highly significant reduction in Free Reactive Phosphorus in the treated pond, it can be deemed highly probable that the reduction occurred because of the PRx applications by Airmax. These results, if treatments continue, have both long-term and short-term effects. In the short term, the treated pond can expect to see a reduction in bioaccumulation, which occurs on the pond sediment through the natural HAB/die-off cycle, which normally results in a substantial amount of organic waste accumulation. Without this high amount of additional muck, native bacteria can have more advantage in digesting the internal nutrients and reducing what is currently plaguing the pond. In addition, by restabilizing the Phosphorus-Nitrogen ratio in the pond, the algae community population will shift more towards non-harmful green algae, increasing recreational potential and overall fish health and population in the pond. Further studies can investigate the ability of PRx as a Biostimulant, as with its over 80 vitamins and minerals it can provide rare minerals to the native bacteria allowing for enhanced bacterial activity.

After a successful season of treatment, the pond owners decided to continue a yearly regimen of PRx treatments. As PRx is a safe, all-natural product with no side effects on the health of the pond, applying it long-term to combat heavy external loading through inlets and runoff is a viable option.

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