Why are Selenium and Nitrogen a problem?
Selenium is a naturally occurring element that is necessary for life, but it is toxic at high levels and is unusual in that the difference between essential and toxic levels is relatively small. Selenium is a bioaccumulative pollutant, meaning that it accumulates in the food chain through uptake and consumption by plants and wildlife, and can cause adverse effects on fish and birds. There are different forms of selenium, some more harmful than others. Similar to selenium, nitrogen is an essential nutrient, but it can cause harmful algal blooms when nitrogen levels are excessive. Excessive algal blooms decrease dissolved oxygen in surface waters (referred to as eutrophication) and can result in fish kills.
