Soil Phosphorus and Vegetation Influence on Wetland Phosphorus Release after Simulated Drought

Abstract

Phosphorus enrichment of marsh soils can act as an internal source of nutrients to the water column, continuing to drive existing wetland eutrophic conditions even after external sources have been terminated. The goal of this study were to determine the effects of soil P concentration and flood intolerant vegetation presence on initial (1–10 d) and extended (10–38 d) P release rates from the soils after reflooding. Intact soil cores were collected from P enriched and unenriched areas of the Blue Cypress Marsh in east‐central Florida. Initial P release was greater in soils with higher soil total P concentrations and containing vegetation. Soil P enrichment resulted in the final water column P concentrations in the enriched cores to be 50% higher than those in the P unenriched cores. A single drawdown and reflood event led to ∼6% of the total soil P released to the water column from the P enriched vegetated treatment compared with a ∼1% of total P released from the P enriched non‐vegetated treatment. Initial P release rates from the enriched, vegetated treatment were five times greater than the enriched, non‐vegetated treatment. Episodic growth of flood intolerant plants under drawdown conditions was shown to be a significant mechanism for nutrient release in ephemerally flooded P enriched wetland systems. Episodic flooding and drying cycles could therefore mobilize P over the long‐term from P enriched to P unenriched areas.