Fertilizers: The River a Little Too Well Nourished

Nitrogen and phosphorus are natural fertilizers, and so are normal parts of a healthy river.

Nevertheless, too much fertilizer causes explosive growth of plants and algae. While algae are an important food for many invertebrates, fish and ducks, too many algae can clog the waterway. Also, masses of decomposing algae reduce the amount of oxygen in the water that is available to the animals of the river.

Phosphorus is used in fertilizers for agriculture, lawns and gardens, as well as in detergents (in the form of polyphosphate). Phosphorus finds its way into the River in runoff.

Massed algae.

More precisely, phosphorus levels exceeded the guidelines during the summer months in the stretch of the River that lies within the City of Ottawa. The River is "a little too well nourished", according to Paul Hamilton, a researcher who specializes in the study of algae at the Canadian Museum of Nature.

Two causes have contributed to the situation there. In one, agricultural fertilizers and urban discharge are naturally carried downstream by the River's current. In the other, the large number of paved roads, parking lots and buildings found in urban areas reduces the surface area that will permit water to be absorbed into the ground, and as a result, runoff is not adequately filtered before it reaches the River.

Green frog, Rana clamitans.

In some towns, storm sewers have the shape of a fish built into its design, in order to signify to citizens that the sewers lead directly to the River and so their contents is not treated.