• Phytoplankton are microscopic, free-floating algae which live in all surface waters.
• Algae are plants which utilize sunlight together with soluble nutrients extracted from the water for their growth and reproduction .
• Algae require primarily carbon, nitrogen and phosphorus to grow.
• In most temperate fresh waters, phosphorus is the limiting nutrient even though algal cells are less than 1% phosphorus.
• The rate of algal growth is proportional to the supply or input of phosphorus.
• One pound of phosphorus can grow 700 pounds of algae.
• Fertilizer and phosphates in septics can work their way into our aquifer and on into our river.
• A 50 pound bag of fertilizer, say Turf Gro, contains 3 pounds of phosphates.
  

What about nitrogen? Nitrogen is not usually a limiting factor in growth. Certain blue-green algae can, at times, use dissolved nitrogen gas as a source of nitrogen, through nitrogen fixation reactions. Thus, these nitrogen-fixing algae, which tend to cause severe water quality problems, have a limitless source of nitrogen.

THE CUMULATIVE EFFECTS OF PHOSPHORUS
There are 500,000 residents in Kootenai and Spokane County. Assuming 2.4 residents per household, and 60 percent having dishwashers, that is 120,000 dishwashers.
There is a range of assumptions on dishwasher use – from 90-180 times per year, or 9-36 pounds per year of dishwasher detergent. At 6% phosphorus content, the range of phosphorus entering the system is 0.5 to 2 pounds per year, per dishwasher.
120,000 dishwashers gives a range of 72,000 to 240,000 pounds per year of phosphorus entering treatment plants or septic tanks every year, or 166 to 667 pounds per day. If we assume one pound per year per dishwasher that is 330 pounds per day into the system, which is consistent with the following two studies.
Between 9% and 34% of the phosphorus load going to wastewater treatment plants from domestic sewage comes from automatic dishwashing detergents. (N.B. Pickering, CRWA, 2001) from the Organization for the Assabet River.
A recent study done in Lolo, MT, on the impact of dishwasher detergents on water quality showed that these detergents contribute from 15-20% of the phosphorus entering the wastewater treatment plant from the Tri-State Water Quality Council
When our entire phosphorus load is limited to less than 20 pounds per day, 330 pounds per day becomes a very significant part of the wasteload.
No one source of phosphate is responsible for all the problems of phosphate loading. Actions at many levels will be necessary. Limiting phosphates in laundry detergents and auto dish detergents is an easy, low cost step toward the control needed.
If a quarter of 120,000 residents used a bag per year, that would equate to 90,000 pounds of phosphates available to the aquifer and stormwater system during the summer months. Depending on application, watering, proximity to aquifer and river, this can be another significant impact.

LINKS

The Washington State Department of Ecology has developed a comprehensive website that details information on the Spokane River Phosphorus Clean-Up Plan. If you are interested in the detailed information of this process, we recommend checking out their website.

For more information, please contact Brian Walker, Watershed Program Director at bwalker@landscouncil.org or 509-209-2408