Water Table Effects on Histosol Drainage Water Carbon, Nitrogen, and Phosphorus

Abstract

Water table (WT) levels in Histosols may influence release of nutrients such as C, N, and P into drainage water. This study examined the effects of water table level on redox potential; C, N, and P release; and inorganic and organic P concentrations in soil columns from an Everglades Histosol. Soils were from two fields of Pahokee muck (euic, hyperthermic, lithic Medisaprists) in the Everglades Nutrient Removal Project in Florida. Soil columns were subjected to four WT levels: 0 (flooded), 10, 20, and 35 cm below the soil surface. Each 30 d for 5 mo, porewater was drained and columns were leached with deionized water, followed by reestablishment of water table levels. Redox potential tended to stabilize 6 to 10 d after onset of each flooding-drainage cycle and displayed substantial spacial heterogeneity below WTs. Release of NH 4 + -N and TKN were not influenced by WT depth, but release of NO 3 substantially increased with increasing WT depth in both soils. In soil from a previously flooded field, total P release increased with increasing WT depth. With soil from a previously drained field, total P release decreased with increasing WT depth. Differences in P release response appeared to be related to previous flooding-drainage history of the site fields. Fractionation of soil P following the study revealed that labile pools of P were influenced by WT depth but sizes of bulk inorganic and organic P pools were not. From <0.7 to 2.3% of total soil P was leached.