Bioavailability of phosphorus of river sediments and its effect on
growth of Selenastrum capricornutum
Increasing anthropogenic loading of phosphorus (P) threatens aquatic
ecosystems. The bioavailability of P in sediments for algal growth
depends on several physiochemical properties such as silt, clay,
mineralogy, pH, electrical conductivity (EC), and carbonate-content.
This study was aimed on selecting the best chemical extraction method to
characterize P-availability for the algae Selenastrum capricornutum.
Principal component analysis (PCA) of the data identified two components
that cover 79.3% of the total variation, and these components were
dominated by particle size distribution, active calcium carbonate
equivalence (ACCE), and EC. Many of the considered extractions were
positively correlated with each other, with the exception being Bray-II.
The sediments of some rivers had a higher Olsen-extractable P than 20 mg
kg-1, that is considered a threshold value above which the aquatic
environment may become negatively affected. The average rank order of P
extraction by single extractants was: Colwell > Mehlich III
> NaOH 0.1 M > Olsen > Morgan
> AB-DTPA > Bray II. The Colwell-extractable P
concentrations of sediments varied from 1.44 to 88.0 mg kg-1. This
extractant significantly correlated with algal growth (r2=0.92,
P<0.001) and gave a rough estimate of the amount of
bioavailable P in sediments. Therefore, the bioavailable content of P in
sediments is quite high in comparison with the soils (agronomic
requirement = 15 mg P kg-1) around the Urmia Lake basin.