What Happens to the Phosphate?

Last week I wrote about the need to respect nature's phosphate cycle. After all, the world supply of accessible phosphate is limited. Phosphate is a scarce resource. It ought to be used carefully and sparingly.

But phosphate also can be a pollutant. We see this in Lake Winnipeg today. When the phosphate in a water body exceeds a threshold concentration, the result is excessive algal growth. When these algae die, their decomposition uses up oxygen in the water. When that happens, other living organisms, such as fish, suffocate and die.

All of us ingest plants. We call this eating. The carbon and hydrogen component of the food we eat is converted to energy as we live and work. Our body expels the food components our body does not need. What our body expels, either as feces or as urine, we call human waste, but that is a misuse of the word “waste”. Plants do not consider this waste. For plants, this is food. There are only two possibilities for this excrement: either it nurtures plants, or it pollutes our environment. These are the only two options.

Have you ever considered what happens to the stuff you flush down the toilet? If you are at all thoughtful (most of us are not), you realize it does not disappear with the flush. It goes somewhere. If you live in Steinbach, it goes first to the treatment centre and from there to the lagoon. The treatment centre deals with pathogens and fats, but does nothing with the phosphorus. You cannot get rid of it. It needs to go somewhere. It is my understanding that most of it remains as sludge at the bottom of the lagoon. The sludge has a potential as plant nutrient for the cropland around the lagoon, but the quality is seriously compromised because of contamination by the other products we flush down the sewer; products such as cleaning agents, paint and petroleum products. The Steinbach city lagoon is rarely de-sludged. So what happens to the phosphorous ingested by the 13,000 Steinbach residents? Believe me, it does not disappear.

In 1995, I was involved in the start of a manure management company. The focus of this company was the management of manure coming from the industrialized hog farms springing up in this area. At the time of our formation, there had been no effort to apply science to the way manure was applied to cropland. Our focus then was nitrogen, and our goal was to match nitrogen application with nitrogen uptake by the crop. We quickly noticed that as we were optimizing nitrogen, we were over-applying phosphate by a factor of two. “No problem”, everyone said, “our Manitoba soils can handle that.” I spoke to many people about this over-application of phosphate, and no one I talked to foresaw a problem.

In 2002, just a few years later, we began hearing about the eutrophication of Lake Winnipeg, the result of precious phosphate flushed down the toilets of our cities, and the over-application of livestock manure. We pretend phosphorous disappears when we flush at our peril. It does not disappear.

Eric Rempel