Phosphorus and septic

Phosphorous, toxic algal blooms and septics

Scientists established the link between phosphorous levels in lakes and toxic algal blooms decades ago. An understanding of how an increase in phosphorous in our lake-water directly impacts the number and frequency of toxic algal blooms can help every shoreline property owner make small changes to their daily routine which will help keep blooms to a minimum.

Ontario Ministry of Environment logo

For many years, the definitive study into the relationship between phosphorous and toxic blooms was the Ministry of the Environment’s Lakeshore Capacity Handbook

Warning sign reading Blue Green Algae

“High levels of phosphorus in lake-water will promote eutrophication — excessive plant and algae growth, resulting in a loss of water clarity, depletion of dissolved oxygen and a loss of habitat for species of cold-water fish such as lake trout. While shoreline clearing, fertilizer use, erosion and overland runoff can all contribute phosphorus to an inland lake, the primary human sources of phosphorus are septic systems — from cottages, year- round residences, camps and other shoreline facilities.”

Dialing the problem up or down

As scientific knowledge grew, so did the understanding of the real complexity of the issue and the number of factors involved in blooms. To help everyone get a clear understanding, a simple analogy - based on the workings of a radio - was developed by Dr. Andrew Paterson of the Dorset Environmental Science Centre. The graphic shows that phosphorous is usually the critical factor, as it directly controls the volume of algae:

Until recently, lakes were deemed safe if the phosphorous level in their water column was below an established threshold. However Environment Canada announced in 2013 that they no longer knew what a safe level was.

So, what are the key sources of lake-water phosphorous and what can we do to reduce the amount getting into our lakes? In addition to septic systems (we’ll come to the role they play shortly), here are the likely sources of phosphorous in Haliburton County’s lakes:

Graphic depicting rainfall

Contains three times as much phosphorous as lake water

Graphic depicting phosphorous runoff

From roads, driveways, goose poop, pet waste and fertilizers

Graphic depicting heavy rainfall

Events are becoming more frequent with climate change. Conservation authorities have discovered that these rainfall events have become a major source of phosphorous in lakes

Graphic depicting airborne phosphorous

Pollen and other material in the air can carry phosphorous

Aren’t our septic systems the worst offenders?

Algonquin Highlands 2020 results found that 32% of the systems inspected needed remediation.

Interestingly, no.

A recent study sponsored by the University of Waterloo in partnership with Environment and Climate Change Canada found that well-constructed septic systems which use the right type of fill soil for the tile beds, absorbed more phosphorous than previously thought.

However, the full impact of failing septic systems remains unknown and requires further research.

High quality (‘Level 4’) septic re-inspection programs typically show that 30% or more of inspected systems need repair. The Level 1 re-inspection program in Highlands East has found that 35% of the systems inspected so far are already at moderate to high risk. The Algonquin Highlands 2020 results found that 32% of the systems inspected needed remediation.

While an inspection program will uncover physical faults, it may not find the less obvious problems caused by people overloading their septics: this can happen when a home or cottage is occupied by more than 2 people per bedroom, or anti-bacterials such as bleach, drain cleaners, rinse aids and detergents are flushed or drained into the system. These chemicals kill the healthy bacteria in our septic tanks whose job it is to help purify water before it’s returned into our environment.

Whatever the source, the best way to avoid, intercept and absorb all of these sources of phosphorous is a natural shoreline buffer of deep-rooted vegetation around the lake. The wider the buffer, the better.