washout process, i.e., scavenging of 

 particulate TPO4 by falling rain 

 and as dry fallout year round. In 

 contrast, nitrogen as N0 X occurs 

 primarily in the solute form and is 

 therefore removed in the rainout 

 process. Total atmospheric fallout, 

 wet plus dry, is commonly reported 

 as bulk precipitation. It consists 

 of three fractions: (1) dissolved 

 materials in aqueous precipitation, 

 (2) the water-soluble component of 

 dry precipitation, and (3) the 

 water-insoluble component of either 

 wet or dry precipitation (Irwin and 

 Kirkland 1980). Irwin and Kirkland 

 (1980) summarized qualitative rain- 

 fall characteristics at selected 

 USCS study sites in Florida includ- 



ing six sites within or adjacent to 

 the Everglades/Bay/Keys basin. Fig- 

 ure 19 illustrates the mean chemical 

 composition of the more common inor- 

 ganic ions in rainfall. Within the 

 basin, particularly at stations 3 

 and 4, calcium (Ca) and bicarbonate 

 (HCO3) are dominant ions while 

 magnesium (Mg) and sulfate (SO4) 

 are least significant. At Station 5 

 (40 Mile Bend Tamiami Trail) sodium 

 plus potassium (Na + K) and chloride 

 (CI) dominate and continue to do so 

 up to Lake Okeechobee. Waller and 

 Earle (1975) suggest that the ele- 

 vated sodium and chloride concentra- 

 tions are a function of the proxi- 

 mity of ocean waters, although a 

 decrease observed in stations within 



EXPLANATION 

 >4 Station location and number 



Na+K 



MILLIEQUIVALENTS PER 

 LITER 



Diagrams show general chemical 

 character of bulk precipitation. 

 The ionic concentrations are 

 plotted for sodium and potassium 

 (Na+K), calcium (Ca), magnesium 

 (Mg), chloride (CI), bicarbonate 

 (HCO3), and sulfate (SO4). Anions 

 are plotted to the right of the 

 centerline and cations to the left. 

 The area of a diagram is an in- 

 dication of the dissolved-solids 

 concentration—larger areas reflect 

 greater dissolved solids concentration 



N 



20 40 60 Miles 



l 1 1 l 



Figure 19. Location of precipitation sampling sites in study area, and 

 average chemical concentrations (adapted from Irwin and 

 Kirland 1980). 



43 



