Phosphate release from seasonally flooded soils: a laboratory microcosm study

Area of Science:

• Environmental Science
• Soil Science
• Water Quality

Background:

• Agricultural phosphorus is a major contributor to water quality issues in Lake Champlain.
• Mobilization of phosphorus from seasonally flooded agricultural soils is a significant concern for ecosystem health.

Purpose of the Study:

• To investigate the release of soluble phosphate from agricultural soils under flooded conditions.
• To characterize the relationship between soil properties and phosphate mobilization.

Main Methods:

• Analysis of 14 agricultural soils from New York's Champlain Valley.
• Laboratory microcosms simulating soil flooding over 60-90 days.
• Measurement of available phosphorus, extractable iron and aluminum, and phosphate concentrations in porewater and floodwater.

Main Results:

• Flooding induced significant phosphate release into soil porewater in 13 of 14 soils.
• Porewater phosphate concentrations increased 2.2 to 27.0 times, while floodwater concentrations increased up to 3.6 times.
• Ammonium-acetate phosphorus and the degree of phosphorus saturation (DPS) strongly correlated with porewater and floodwater phosphate levels.

Conclusions:

• Soil phosphorus solubility and mobility are influenced by both available phosphorus status and redox cycling.
• Redox cycling, particularly iron dynamics, plays a role in phosphate release in some soils.
• Understanding these processes is crucial for managing agricultural impacts on water quality.