Table 7. Comparison of some floodplain soil nutrients 

 to those of Coastal Plain, Piedmont, and mountain soils. 

 Floodplain values are averages from Zones II-V (blackwater 

 and alluvial). Samples are from top 6 inches below litter 

 layer. Upland soil samples are from the A horizon. 



Another consequence of prolonged 

 anaerobic conditions is pH change. Under 

 waterlogged conditions, acid soils in- 

 crease their pH while basic soils decrease 

 in pH. The pH of swamp soils in particu- 

 lar tends to remain acid throughout the 

 period of saturation (Kennedy 1970). 

 Flooding and resultant pH changes increase 

 the "mobilization" (or availability to 

 plants) of the macronutrients phosphorus 

 (P), nitrogen (N), magnesium (Mg), and 

 sulfur (S), and the micro-nutrients iron 

 (Fe), manaanese (Mn), boron (Bo), copper 

 (Cu), and" zinc (Zn) (Teskey and Hinckley 

 1977). This may offset nutrient limita- 

 tion by anoxia. 



Further, pH controls the amount of 

 DOM leaching out of leaves, the amount 

 precipitated as particles, and the size of 

 these particles (Kaushik 1975). Acid pH 

 delays precipitation of aggregated parti- 

 cles from DOM leachates. 



Organic Matter 



Organic matter concentrations of 

 floodplain soils are intermediate between 

 those of bogs and pocosins and those of 

 uplands (Table 8). jjl situ deposition is 

 the primary fate of organic detritus in 

 peat-forming and internally draining bogs 

 and pocosins. Decomposition and reminer- 

 alization are the major pathways of litter 



in the upland forest. The floodplain 

 swamp receives large inputs of organic 

 matter through leaf fall, and some decom- 

 position and incorporation of this matter 

 occur. Organic matter decomposition under 

 anaerobic conditions, however, is slow 

 (2%-5% per year) in contrast to that of 

 oxygenated waters or aerobic soils (>10%). 



The highest soil organic matter 

 occurs on floodplains draining vast, acid 

 bogs along rivers such as the Sopchoppy 

 and New (FL), and on floodplains along 

 spring-fed rivers (32%), tidal forests 

 (40%), and on peat systems (up to 44%). 

 Percent organic matter of Zone II soils in 

 spring-fed river floodplains and Zone II 

 backswamps with swamp tupelo is also quite 

 high (about 36%). Alluvial river flood- 

 plains have the lowest organic matter, 

 averaging <5%, a good working figure to 

 separate blackwater and alluvial flood- 

 plains (Wharton et al. 1977). 



Soil Characteristics of NWTC Zones 



Overall, macronutrient concentrations 

 on floodplains differ markedly from those 

 of the uplands (Table 7 and Appendix). Ex- 

 cept for phosphorus, nutrients (especially 

 calcium and magnesium) are generally 

 higher in floodplain soils than in up- 

 lands. Unusually high concentrations 

 occur in spring-fed and tidal systems in 

 particular. 



29 



