DOI: 10.5061/dryad.bcc2fqzbc
title: Dataset for: Phosphorus mobilization from intact soil monoliths flooded under simulated summer versus spring snowmelt with intermittent freeze-thaw conditions

description: Enhanced phosphorus (P) release from flooded, anaerobic soils 
 have been extensively studied under summer temperatures, but not under
 cold temperatures with intermittent freeze-thaw events. We investigated
 the temperature and freeze/ thaw effects during flooding on the release of
 P to floodwater from soil monoliths (15-cm depth) collected from eight
 agricultural fields in Manitoba. Soil monoliths were flooded with reverse
 osmosis water and incubated for 56 d under simulated summer flooding (SSF,
 22±1 ℃), or snowmelt flooding with intermittent freeze thaw (IFT, 4±1 ℃
 with intermittent freezing) in triplicates. Redox potential (Eh), pore
 water and floodwater dissolved reactive P (DRP) concentrations, pH and
 concentrations of Ca, Mg, Fe and Mn were determined weekly. In seven
 soils, Eh decreased rapidly with days after flooding (DAF) under SSF to
 values &lt; 200 mV, but not under IFT. Pore water and floodwater DRP
 concentrations significantly increased with DAF in all soils under SSF,
 and in seven soils under IFT. While DRP concentrations were consistently
 greater under SSF than IFT in four soils, other soils had similar
 concentrations at certain DAFs. Significant relationships between ion
 concentrations and redox status , that fitted both  IFT and SSF
 data in most soils, suggests that similar redox-driven mechanisms are
 responsible for the P release; however, less P is released under IFT than
 SSF, since soils were not severely reduced  under IFT. 
 Substantial P release in a few soils under IFT, appeared to be unrelated
 to redox status, suggesting other P release mechanisms that are not redox
 driven.
description: Intact soil monoliths were collected from eight agricultural
 fields located in the Red River Valley of Manitoba. Soil monoliths with an
 internal diameter of 10 cm and height of 15 cm were collected using 30 cm
 length polyvinyl chloride (PVC) tubes, each with two drilled holes (3 mm)
 at 10 cm from the bottom (5 cm below the soil surface) on  opposite sides
 of the tube. The bottom of the monolith was sealed using a PVC cap . To
 extract soil pore water, two Rhizon MOM 10-cm soil solution samplers with
 an outer diameter of 2.5 mm and 0.15-µm pore size were placed horizontally
 at 5-cm depth from soil surface through the drilled holes. Soil monoliths
 were flooded to a 5-cm head. Soon after flooding, a redox potential probe
 with a platinum sensor was also installed to a 5-cm depth in each monolith
 to measure the soil redox potential (Eh). Monoliths were incubated for 56
 d under two flooding conditions; simulated summer (SSF), or simulated
 snowmelt with intermittent freeze thaw (IFT). The monoliths under SSF
 treatment were kept at 22±1 ℃ throughout the 56 d of incubation, while
 those under IFT were kept in a cooler at 4±1 ℃ with a 24-h freezing cycle
 at -18 ±1℃ every 7 d during the 56 d of incubation. Pore water (or soil solution)
 samples at 5 cm depth were extracted by applying suction using a syringe
 attached to the end of the Rhizon-MOM samplers. Overlying floodwater
 samples were collected using syringes from the center of the flooded
 monolith. Pore water and floodwater samples were collected on a weekly
 basis throughout the 56-d incubation period and coincided with the third
 day after each freeze-thaw event.  Floodwater samples were filtered
 through 0.45-mm membrane filters. Dissolved reactive P concentrations of
 pore and floodwater samples were determined immediately after sampling by
 the molybdate blue color method and pH of water samples was measured using
 a Fisher Accumet AB15 pH meter. Water samples  were acidified with 50 µL
 of conc. nitric acid and stored at 4 ℃ prior to analysis of concentrations
 of Ca, Mg, Fe and Mn using flame atomic absorption spectroscopy (AAnalyst
 400, PerkinElmer). Soil redox status (Eh) was measured at 7-d intervals
 (same day of water sampling using the pre-installed Pt redox probe and
 temporarily inserting a Ag-AgCl reference electrode with KCl electrolyte
 to the soil-floodwater interface
description: Iron and manganese concentrations were not not always detectable
 in pore water and  floodwater. The detectable limits for Fe and Mn were
 0.05 and 0.16 mg/L, respectively.