『Abstract
Sediment reduction is frequently proposed to increase available
phosphorus (P) but several studies found also decreases. Another
important factor for P liberation is the pH. We investigated the
relative importance of Eh and pH on P cycling in reforested mangroves.
Sediment P compounds, pH and Eh were analysed over depth along
five transects of two areas in the Saigon River Delta and compared
with leaf P levels. A three-dimensional spatial approach was used
to investigate pH and Eh effects on P compound distribution at
different sediment depth and locate layers of predominant P uptake.
along an inundation gradient, submergence durations of 254 to
2 days per year caused a large Eh gradient within the top 20 cm,
whereas Eh response was small within 20-45 cm depth. At individual
layers, a correlation between Eh and Al/Fe-P was only found in
the upper depth interval (0-20 cm). No significant effect of Eh
or Al/Fe-P on Morgan-P (available P) was detected. Minor effects
on P composition changes by the Eh were caused through generally
strongly reduced sediment at deeper layers (＞20 cm). In contrast,
pH variations produced extreme differences in both, Ca-P and available
P content at layers of apparently predominant P uptake (＞20 cm).
As available P was correlated with Ca-P (p＜0.001), leaf P (p＜0.001)
and pH (nonlinear correlation) it is likely that the pH sensitive
Ca-P fraction is a more effective source for mangrove tree growth
than Al/Fe-P. The predominant pH effect on P uptake within these
reforested mangroves differs from a proposed reduction-governed
P cycling in wetlands.
Keywords: Calcium phosphate minerals; Inundation; Phosphorus limitation
and uptake; Pyrite oxidation; sediment acidification; Sediment
redox potential』
Introduction
Materials and methods
Study area
Station selection
Sampling and preparation
Analytical methods and procedures
Data analyses
Results
Interactions among pH, Eh and inundation
Seasonal comparability
Cross sections of Eh distribution patterns
Cross sections of Al/Fe-P distribution patterns
Three-dimensional distribution patterns
P plant uptake
Discussion
Acknowledgments
Open access
References