WHERE IS THE NITRATE COMING FROM? OUR OWN BACKYARDS....

Over the last few decades, nitrate, a common chemical compound found in fertilizers and human 

and animal waste, has been steadily increasing in concentration in many of the springs in the 

Southwest Florida Water Management District (SWFWMD).  Current levels range from 0.2 mg/l in 

the King's Bay Springs, the source of the Crystal River in Citrus County, to 3.1 mg/l at 

Lithia Springs on the Alafia River in Hillsborough County.  Although these concentrations

are well below Florida's primary Drinking Water Standard (10 mg/l NO3 as N), the levels

are significantly elevated above background levels (0.01 mg/l NO3 as N) measured statewide

in the Floridan aquifer by the Department of Environmental Protection's Ground-Water 

Quality Monitoring Program. Historically, regulatory agencies have shown little 

concern for nitrate as long as concentrations remain below 10 mg/l.  However, simple

calculations show that first magnitude springs with lownitrate concentrations can 

discharge hundreds to thousands of tons of nitrate annually.  Currently 3.3 million

pounds (1,660 tons) of nitrate is discharged annually from the major spring complexes

in the SWFWMD. Such quantities of a limiting nutrient discharged into rivers and 

estuaries may have a significant negative effect on the health of an aquatic system. 


On average the daily flow of ground water from the major spring complexes in the SWFWMD 

amounts to 1.6 billion gallons.  This tremendous amount of water is derived solely from

the Floridan aquifer.  Much of the spring water first fell as rain in areas near the springs

(typically within 5 - 10 miles) before seeping into the ground and into the Floridan aquifer.

Once in the Floridan, the ground water travels rapidly through the upper-most portion of the

aquifer to the springs.  Water quality, as measured at the springs, therefore, reflects the

overall degree of contamination of the aquifer over a large portion of the recharge area.



Between 1991 and 1998 approximately 70 springs and 400 monitor wells in the central and 

northern portions of the SWFWMD were sampled in an effort to determine the sources of 

nitrate discharging at the springs.  Research conducted at Rainbow, Homosassa, Chassahowitzka,

Weeki Wachee and Lithia Springs revealed that the nitrate in the ground water mostly 

originated from the use of inorganic fertilizers.  This fertilizer was applied to a variety

of land uses including pasture grasses, residential lawns, golf-courses and citrus groves. 

Nitrate loading from septic tanks and waste water was less important but still significant. 

The research also revealed that the source of the nitrate discharging at the springs was

located in the portion of the recharge area that was within 5 to 10 miles of the springs and 

probably entered the Floridan aquifer within the last 20 years.