Effect of magnesium on charophytes calcification: implications for phosphorus speciation stored in biomass and sediment in Myall Lake (Australia)

Abstract

We examined the effect of magnesium (Mg) on the charophytes calcite (CaCO 3 ) 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 Cabound P, a large percentage of less bioavailable nonreactive 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 plants' 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 P.

Depth-dependence and monthly variability of charophyte biomass production: consequences for the precipitation of calcium carbonate in a shallow Chara-lake

“…However, that would only be the case if aragonite was precipitated. Second, according to the previous study in Lake Jasne (Pukacz et al 2014a), favourable conditions for calcite precipitation occurred; thus, the correlation may be the effect of the inhibiting role of magnesium ions in the process of calcification, as suggested by Siong and Asaeda (2009). …”

The mitigating effect of calcification-dependent of utilization of inorganic carbon of Chara vulgaris Linn on NH4-N toxicity

“…McConnaughey, 1991;McConnaughey and Falk, 1991), phosphorus assimilation (e.g. McConnaughey and Whelan, 1997;Siong, 2006;Siong and Asaeda, 2009b) and hyper-accumulator of heavy metals (McConnaughey, 1991;Siong and Asaeda, 2009a). In mildly alkaline water, DIC decreased by two means, either was taken up by the photosynthesis of the algae or became incorporated in the cell wall of Chara by calcification (Ray et al, 2003).…”

Characeae Biomass: Is the Subject Exhausted?

“…According to their results, besides the indirect mechanism above, P in the water column was also directly co-precipitated with encrusted calcite along the charophyte intermodal cell, and such a calcification should be regarded as a positive feedback in stabilizing Chara dominance in lakes. Siong & Asaeda (2009) studied the effect of Mg on the charophyte calcite encrustation, and assessed whether charophytes growing on the noncalcareous sediments of the Myall Lake could function as an effective nutrient sink for P in a similar manner to charophytes growing on the calcareous sediments of freshwater calciumrich hard water systems. According to the last authors, calcification of Chara fibrosa was significantly inhibited by Mg in the water column and, consequently, reduced the formation of Ca-bound P that has a potential sink for P. However, a large percentage of nonbioavailable forms of P in the lake sediments suggested that P sink was through burial of dead organic matter and subsequent mineralization process.…”