Phosphorus inputs and fertilizers

Phosphorous (P) is the determining element for cyanobacteria proliferation. To avoid water degradation, it is essential to diminish the content of phosphorous.
Nature does an efficient job with the limited amount of phosphorous it naturally contains. The contribution is essential to the growth of living organisms such as nitrogen  (N) and potassium (K).
Unfortunately, human activity perturbs the natural phosphorous cycle with the result that too much phosphorous finds itself in the water courses, modifying the natural balance  and creating a situation where the biomass (aquatic plants, cyanobacteria, etc.) finds itself abnormally stimulated (we frequently speak of a ratio of 1 for 500, that is to say 1 kg of phosphorous can bring on the production of 500 kg of biomass). We could say that the lake is too productive and that its ageing process is accelerating (eutrophication).
Figure 1 shows the principal sources of phosphorous which contaminate the water bodies and lakes.

Figure 1 was adapted from: Parent, J.-E., Le flux et la dynamique du P dans les sols agricoles québécois, Colloque sur le phosphore, une gestion éclairée, novembre 2002.


An examination of this figure shows the following:


  • The phosphorous may be particular or soluble (dissolved). Most of the time (70% to 90%), it is particular and attached to fine soil particles which are brought in by run-off water heading toward the water bodies; 
  • The sources of phosphorous production are numerous and most of the time they are anthropic (man made).

Figure 2 shows the principal sources of entry of phosphorous into the lake. Let us add that the sediments already present in the lake contain large quantities of phosphorus due to carelessness and neglect in the past. This phosphorous, according to certain conditions, can be released into the water column and become available again for plants and algae. This important source in Brome Lake could eventually diminish if the amount flowing in from the drainage basin are radically reduced and if the lake manages to get  “the upper hand” (through the water renewal process which we know takes 10 months on Brome Lake and by outlet evacuation).

RBL has a strategic target to reduce by 50% the phosphorous flow into the lake over the next five years, or 10% annually. The RBL action plan to reduce phosphorous

Figure 2 : Origin of phosphorous

Fertilizers, FORBIDDEN

All municipalities in the drainage basin, Ville Lac Brome at the top of the list, should announce that since 2009 it has been forbidden to spread fertilizers on lawns. In 2011, all golf courses  became subject to the same law.


To find out more

Sources of phosphorous, article by Peter F. Wade

Comparative table on phosphorous concentrations by principal brand of dishwater soap .

Fertilizers, lake water and its tributaries, RLB, 2008 

Dossier de CAA-Québec "Infestations d’algues toxiques : comment les éviter?"