fragmentary and often contradictory, we 

 can outline several generalizations: 



(1) Mangroves can grow on a wide 

 variety of substrates including mud, sand, 

 rock, and peat. 



(2) Mangrove ecosystems appear to 

 flourish on fine-grained sediments which 

 are usually anaerobic and may have a high 

 organic content. 



(3) Mangrove ecosystems which per- 

 sist for some time may modify the under- 

 lying substrate through peat formation. 

 This appears to occur only in the absence 

 of strong physical forces. 



(4) Mangrove peat is formed pri- 

 marily by red mangroves and consists pre- 

 dominantly of root material. 



(5) Red mangrove peats may reach 

 thicknesses of several meters, have a 

 relatively low pH, and may be capable of 

 dissolving underlying layers of limestone. 



(6) When drained, dried, and 

 aerated, mangrove soils usually experience 

 dramatic increases in acidity due to the 

 oxidation of reduced sulfur compounds. 

 This greatly complicates their conversion 

 to agricul ture. 



1.7 WATER QUALITY 



from virtually fresh water to above 40 ppt 

 (discussed in section 2.2), (2) low macro- 

 nutrient concentrations (particularly 

 phosphorous), (3) relatively low dissolved 

 oxygen concentrations, and (4) frequently 

 increased water color and turbidity. The 

 last three characteristics are most pro- 

 nounced in extensive mangrove ecosystems 

 such as those adjacent to the Everglades 

 and least pronounced in small, scattered 

 forests such as the overwash islands in 

 the Florida Keys. 



In general, the surface waters 

 associated with mangroves are charac- 

 terized by (1) a wide range of salinities 



The results of oxygen depletion and 

 nutrient removal are (1) dissolved oxygen 

 concentrations below saturation, typically 

 2 to 4 ppm and often near zero in stagnant 

 locations and after heavy, storm-generated 

 runoff, (2) very low total phosphorus 

 values, frequently below detection limits, 

 and (3) moderate total nitrogen values 

 (0.5 to 1.5 mg/1). In addition, TOC 

 (total organic carbon) may range from 4 to 

 50 ppm or even higher after rain; Eric 

 Heald (personal communication 1981) has 

 measured DOC (dissolved organic carbon) 

 values as high as 110 ppm in water flowing 

 from mangroves to adjacent bays. Tur- 

 bidity usually falls in the 1 to 15 JTU 

 (Jackson turbity units) range. The pH of 

 the water column in Florida swamps is 

 usually between 6.5 and 8.0 and alkalinity 

 between 100 to 300 mg/1. Obviously, ex- 

 ceptions to all of these trends can occur. 

 Both natural and human disturbance can 

 raise macronutrient levels markedly. 



11 



