Figure 17. Many bottomland hardwoods have a dense surface mat of minute rootlets which 



may extract essential minerals from the water following mineralization of bacteria, 



hyphomycete fungi, algae, or organic detritus and may exchange nutrients with the 

 surfaces of silts, clays and organic matter. 



iods. The high clay content of floodplain 

 sediments contributes to the impermeabil- 

 ity of the sediments to water movement and 

 oxygen saturation. Retention of surface 

 water and restriction of oxygenation 

 result in anaerobic conditions usually 

 within 3 days of flooding (Phung and 

 Knipling 1976). This condition is main- 

 tained until the soils de-water during 

 drydown periods. 



A consequence of floodplain soil 

 anoxia is that it severely limits nutrient 

 uptake by plant roots. Plant species 

 which thrive in zones that are flooded 

 throughout most of the growing season 

 often have adapted to anoxic conditions by 



developing efficient methods of transport- 

 ing oxygen to the roots (see Chapter 4). 

 Oxygen diffusion through the roots creates 

 an aerobic microlayer in the surrounding 

 sediments which facilitates nutrient 

 uptake. Penetration of roots into swamp 

 soils is, however, hampered by the imper- 

 meability of soils due to waterlogging and 

 settling out of fine-grained silts and 

 clays during flooding. As a result, con- 

 ditions of nutrient unavailability exist 

 over large portions of the swamp flood- 

 plain despite soil nutrient concentrations 

 that are equal to or higher than those in 

 Coastal Plain, Piedmont, or mountain soils 

 (Table 7). 



28 



