suggested that the black mangrove peats 

 identified by Davis (1946) were probably 

 mixtures of peat from several sources. 



Throughout south Florida the sub- 

 strate underlying mangrove forests may 

 consist of complicated patterns of 

 calcareous muds, marls, shell, and sand 

 interspersed and overlain by layers of 

 mangrove peat and with limestone bedrock 

 at the bottom. Detailed descriptions of 

 this complex matrix and its spatial varia- 

 tion were given by Davis (1940, 1943, 

 1946), Egler (1952), Craighead (1964), 

 Zieman (1972) and Cohen and Spackman 

 (1974) among others. Scoffin (1970) dis- 

 cussed the ability of red mangrove to 

 trap and hold sediments about its prop 

 roots. So called "land-building" by man- 

 groves is discussed in section 3.2. 



The long-term effect of mangrove peat 

 on mangrove distribution is not entirely 

 clear. Certainly, if there is no change 

 in sea level or if erosion is limited, the 

 accumulation of peat under stands of red 

 mangroves combined with deposition and 

 accumulation of suspended sediments will 

 raise the forest floor sufficiently to 

 lead to domination by black or white man- 

 groves and, ultimately, more terrestrial 

 species. Whether this is a common se- 

 quence of events in contemporary south 

 Florida is not clear. It is clear that 

 peat formtion is a passive process and 

 occurs primarily where and when physical 

 processes such as erosion and sea level 

 rise are of minimal importance (Wanless 

 1974). 



Zieman (1972) presented an inter- 

 esting argument suggesting that mangrove 

 peat may be capable of dissolving under- 

 lying limestone rock, since carbonates may 

 dissolve at pH 7.8. Through this process, 

 shallow depressions might become deeper 

 and the overlying peat layer thicker 

 without raising the surface of the forest 

 floor. 



Data on chemical characteristics of 

 Florida mangrove soils and peat are 

 limited. Most investigators have found 

 mangrove substrates to be almost totally 

 anaerobic. Lee (1969) recorded typical Eh 



values of -100 to -400 mv in mangrove 

 peats. Such evidence of strongly reducing 

 conditions are not surprising considering 

 the fine-grained, high organic nature of 

 most mangrove sediments. Although man- 

 groves occur in low organic sediments 

 (less than 1% organic matter), typical 

 values for mangrove sediments are 10% to 

 20% organic matter. 



Lee (1969) analyzed 3,000- to 3,500- 

 year-old mangrove peat layers underlying 

 Little Black Water Sound in Florida Bay 

 for lipid carbon content. Peat lipid 

 content varied between 0.6 and 2.7 mg 

 lipid-C/gram of peat (dry wt ) or about 3% 

 of the total organic carbon total. These 

 values usually increased with depth. Long 

 chain fatty acids (C-16 and C-18) were the 

 dominant fatty acids found. 



Florida mangrove peats are usually 

 acidic, although the presence of carbonate 

 materials can raise the pH above 7.0. 

 Zieman (1972) found red mangrove peats to 

 range from pH 4.9 to 6.8; the most acid 

 conditions were usually found in the cen- 

 ter of the peat layer. Lee (1969) re- 

 corded a pH range from 5.8 to 6.8 in red 

 mangrove peat at the bottom of a shallow 

 embayment. Although Davis (1940) found a 

 difference between red mangrove peat (5.0 

 to 5.5) and black mangrove peat (6.9 to 

 7.2), this observation has not been con- 

 firmed because of the previously mentioned 

 difficulty in finding pure black mangrove 

 peat. 



Presumably, the acidic character of 

 mangrove peat results from release of 

 organic acids during anaerobic decomposi- 

 tion and from the oxidation of reduced 

 sulfur compounds if the peat is dried in 

 the presence of oxygen. This last point 

 explains why "reclaimed" mangrove areas 

 often develop highly acidic soils (pH 3.5 

 to 5.0) shortly after reclamation. This 

 "cat clay" problem has greatly complicated 

 the conversion of mangrove regions to 

 agricultural land in Africa and southeast 

 Asia (Hesse 1961; Hart 1962, 1963; Macnae 

 1968). 



In summary, although current under- 

 standing of mangrove peats and soils is 



10 



