Phosphorus is a limiting nutrient in Everglades water quality. Natural levels between 4 and 10 ppb characterized the original system, although it is thought that incoming waters from Lake Okeechobee, prior to agricultural development of its watershed, were naturally higher—at least 20 ppb. The northern Everglades acted as a natural nutrient-removal system as it grew and laid down peat soils. Considerable research has attempted to quantify the level of phosphorus that the natural Everglades could assimilate without causing an imbalance in natural populations of flora or fauna—the legal definition of allowable change. Consensus among most scientists is that the maximum level for sustainability in the Everglades is 10 ppb, which is now the center of a complex standard for waters in the Everglades Protection Area, basically the water conservation areas and Everglades National Park.
With its conversion into the EAA, the northern Everglades became a nutrient source instead of its historic role as a “sink.” Without treatment, EAA stormwater contained high phosphorus levels from the fertilizer applications, often in excess of 500 ppb. As the entire EAA became fully developed in the 1970s, the problem of where to put excess stormwater was increasingly solved by backpumping to Lake Okeechobee. It was recognized, however, that Lake Okeechobee was suffering from eutrophication from intensely used agricultural lands in its watershed. A water management decision in 1979 protected the lake from EAA nutrients, redirecting stormwater to the water conservation areas, including WCA-1, the Loxahatchee National Wildlife Refuge.