『Abstract
We examined the effect of magnesium (Mg) on the charophyte calcite
(CaCO3) encrustation and assessed whether
charophytes, growing on non-calcareous sediments in the Myall
Lake, a poorly flushed shallow coastal lake with salinity of 2-3
PSU, could function as an effective nutrient sink for phosphorus
(P) in a similar manner to charophytes growing on calcareous sediments
of the freshwater calcium (Ca)-rich hardwater, i.e., through the
formation of Ca-bound P. Our results showed that high Mg in the
Myall Lake water reduced the calcification in charophytes. Likewise,
the addition of Mg into the tap water also produced the same effect.
The inhibition of the calcite formation decreased significantly
the percentage of Ca-bound P formation in the charophyte biomass
as well as in the sediment. However, the inability of charophytes
in Myall Lake to precipitate calcite does not reduce the plant
beds' capability to act as a P nutrient sink. Instead of Ca-bound
P, a large percentage of less bioavailable non-reactive organically
bound P (NaOH-P: 40-65％) fraction in the biomass, together with
the plant' s slow decomposition rate, will lead to burial of dead
organic matter and an incomplete mineralization process. In particular,
detritus of the charophyte plant's thalli is relatively more resistant
to mineralization. This mechanism was supported by the result
of sedimentary P fractionation in which the refractory P and non-reactive
organic P fractions accounted for at least 80％ of the total.
Keywords: Myall Lake; Charophytes; Nutrient sink; Gyttja; Refractory
phosphorus; Calcium-bound phosphorus』
Introduction
Materials and methods
Study site
Water chemistry
Plant sampling and analysis
Sediment and porewater analysis
Sediment phosphorus fractionation Plant P fractionation
Effect of Mg on charophytes calcification
Mineral saturation
Results
Overlying water and biomass
Sediment and porewater
Plant phosphorus and speciation
Phosphorus speciation of sediment
Magnesium effect on charophytes calcification
Discussion
Magnesium role in calcification
Implications for phosphorus stored in biomass and sediment
Conclusion
Acknowledgments
References