『Abstract
The vertical distribution of various phosphorus (P) forms and
their relation to physico-chemical properties of estuary sediment
material were studied to better understand the potential release
and burial of P. Core samples were taken from two dissimilar estuaries
in the Baltic Sea: one in the Archipelago Sea (AS) and one in
the Gulf of Finland (GoF). The P reserves were characterized by
a sequential extraction procedure including the analysis of simultaneously
dissolved elements in two extraction steps. The sediment material
was also analysed for particle size distribution and total elements.
In addition, several environmental variables were determined.
The occurrence of the various forms of P varied with sediment
depth among different sites. Reductant soluble, iron (Fe) bound
P was the most dynamically changing P from in the sediment, while
P bound to other metal oxides and apatite-P were the most stable
fractions. High sedimentation rate was a dominating factor for
sediment P burial. In addition, the content of organic matter,
the amount of erosion-transported sorption components, and the
oxygen (O2) conditions in the near-bottom
water were important determinants of the behaviour of sediment
P. The results indicate that, over the long term, both estuaries
have acted as sinks for deposited P and restricted the transport
of P to the AS and the open GoF, thereby partly alleviating the
eutrophication process.
Keywords: Baltic Sea; Fractionation; Estuaries; Phosphorus; Sediment』
Introduction
Materials and methods
Research area and an overview of sediment properties
Sampling
Analytical methods
Water column and pore water samples
Sediment
P fractionation
Statistical analyses
Results
Water column and pore water
Sediments
P fractions
Total elements in NaBD- and NaOH-extracts
Statistical analyses
Discussion
Sediment properties
Vertical distribution of P and other extracted elements
Immobile P
Reactive P
Impact of sediment properties on dissolved P and N species
Burial and potential for release of sediment P
Conclusion
Acknowledgments
References
Step | Extractant | Separated P fraction |
I | 0.46 M sodium chloride (NaCl), 1 h | Pore water P, loosely sorbed P (NaCl-iP) |
II | 0.11 M sodium dithionite in sodium bicarbonate, pH 7 (NaBD), 1 h | P bound to oxides of reducible metals (Fe and Mn) (NaBD-iP) |
III | 0.1 M sodium hydroxide (NaOH), 18 h | P from Al oxides, non-reducible Fe compounds (NaOH-iP) and labile organic P (NRP) |
IV | 0.5 M hydrochloric acid (HCl), 1 h | Apatite and other inorganic P (HCl-iP) |
Ignition of the sediment residue: 2 h at 550℃ | ||
V | 1 M hydrochloric acid (HCl), 16 h | Residual, mainly refractory organic P (Res-P) |