I can't seem to find the article I'm looking for, but here's something similar from The Alaska Department of Fish and Game. If you don't want to read the whole thing, the key point is this . . .
When they return to spawn, salmon become a veritable conveyor belt for nutrients. For example, an adult chum salmon returning to spawn contains an average of 130 grams of nitrogen, 20 grams of phosphorus and more than 20,000 kilojoules of energy in the form of protein and fat; a 250-meter reach of salmon stream in southeast Alaska receives more than 80 kilograms of nitrogen and 11 kilograms of phosphorous in the form of chum salmon tissue in just over one month.