『Abstract
Hydrochemical patterns across groundwater-fed wetlands, especially
carbonate and redox gradients, can influence phosphorus (P) availability
by controlling its distribution among different soil pools. We
explored these linkages by comparing shallow (5-20 cm) soil properties
along groundwater flowpaths in two rich fens, a marl fen, and
a poor fen. Organic matter content, bulk density, and total elemental
content varied more with depth to underlying drift materials than
with water table fluctuation, but also were influenced by groundwater
discharge, which stabilized water table elevations and controlled
redox conditions. Total sulfur and calcium content increased where
pore-water chemistry indicated active iron and sulfate reduction.
Calcium mineral dynamics, however, did not appear to influence
P availability: first, calcium carbonate (CaCO3)
accounted for <2% of the soil composition, except in the marl
fen where it accounted for 20-25% of the soil composition. Second,
Ca-bound P pools, determined from hydrochloric extraction of wet
soil samples, accounted for <25% of the inorganic soil P pool.
In contrast, iron-bound P determined from bicarbonate-buffered
dithionite solution, accounted for 50-80% of the inorganic soil
P, and increased where there was evidence of groundwater mixing,
as did P release rates inferred from incubated anion resin bags.
The total carbon and phosphorus content of organic-rich soils
as well as available and labile P pools were strongly correlated
with pore-water iron and alkalinity concentrations. Groundwater
discharge and resulting hydrochemical gradients explained significant
variation in soil composition and P availability across each site.
Results highlight the importance of conducting biogeochemical
studies in the context of a site's shallow geologic setting and
suggest mechanisms supporting the diverse plant species unique
to groundwater wetlands.
Keywords: Alkalinity; Calcium carbonate; Iron; Plant nutrient
availability; Sulfate』
Introduction
Methods
Study area descriptions
Groundwater collection
Soil sample collection
Soil analyses
P release rates
Data analysis
Results
Soil composition
P release rates
Assessment of soil and pore-water effects on P-availability
Discussion
Acknowledgments
References