WATER-TABLE EFFECTS ON HISTOSOL DRAINAGE WATER CARBON, NITROGEN, AND PHOSPHORUS

Water table (WT) levels in Histosols may influence release of nutrient s such as C, N, and P into drainage water. This study examined the eff ects of water table level on redox potential; C, N, and P release; and inorganic and organic P concentrations in soil columns from an Evergl ades Histosol. Soils were from two fields of Pahokee muck (euic, hyper thermic, lithic Medisaprists) in the Everglades Nutrient Removal Proje ct in Florida . Soil columns were subjected to four WT levels: 0 (floo ded), 10, 20, and 35 cm below the soil surface. Each 30 d for 5 mo, po rewater was drained and columns were leached with deionized water, fol lowed by reestablishment of water table levels. Redox potential tended to stabilize 6 to 10 d after onset of each flooding-drainage cycle an d displayed substantial spacial heterogeneity below WTs. Release of NH 4+-N and TKN were not influenced by WT depth, but release of NO3 subst antially increased with increasing WT depth in both soils. In soil fro m a previously flooded field, total P release increased with increasin g WT depth. With soil from a previously drained field, total P release response appeared to be related to previous flooding-drainage history of the site fields. Fractionation of soil P following the study revea led that labile pools of P were influenced by WT depth but sizes of bu lk inorganic and organic P pools were not. From <0.7 to 2.3% of total soil P was leached.