A world first: North American research has reportedly determined the “tipping point” for the safe concentration of phosphorus in a water shed.

Scientists at the Université de Montréal have found for the first time that they can calculate a maximum amount of phosphorus that can be added to a watershed before it becomes an environmental problem.

The research was led by a doctoral student Jean-Olivier Goyette. The research team looked at data from 23 watersheds near the St. Lawrence River basin in Quebec.  “Goyette estimated accumulated phosphorus levels over the past century and compared this data to phosphorus levels measured in the water over the past 26 years to determine when, exactly, local watersheds had overloaded”.

In fact, the results from the study are thought to be so groundbreaking that they have been published in Nature Geoscience. The results showed that “watersheds retain an average of 2.1 tonnes of phosphorus per square kilometre before significant leaching into surface waters occurs”.  “Goyette notes this “surprisingly low” threshold value is reached relatively quickly. By the 1950s, when mass agriculture began in Quebec, over half of the 23 watersheds had already surpassed their phosphorus limits”. 

“And despite technological advances and land-use changes to better contain fertilizer applied to farm fields, contamination of land and water systems by agricultural runoff remains a big problem for freshwater systems in North America”.

The article highlighted the problem with the overuse of fertilisers in modern agriculture. “As crops grow, they uptake phosphorus from the soil, though any phosphorus not used by the plant stays locked in the soil”. However, the phosphorus also enters waterways through farm runoff, as well as animal and human waste. Various sources of phosphorus entering water bodies mean that the concentration can accumulate very rapidly.

Phoslock is one of the products that is used by Phoslock Environmental Technologies (PET) to reduce the concentration of nutrients in water. Phoslock binds excess dissolved phosphorus in the water column and phosphate that is released from phosphate stores in sediments. Phoslock is used by water body managers as a tool to control the phosphorus that fuels harmful and persistent algal blooms.

The complete article can be read at https://www.alternativesjournal.ca/community/blogs/sustainable-aj/our-land-sponge-can-hold-no-more