Colorimetric analysis is not sufficient to estimate bioavailable phosphorus in a hypersaline aquatic environment

Colorimetric analysis is commonly used to quantify P availability in aquatic environments. However, it may not be adequate to quantify the bioavailability of dissolved organic P compounds. This study aimed to investigate to what extent the colorimetrically measurable P fractions can be utilized by algae, with a particular emphasis on organic P compounds in a hypersaline aquatic environment. In this study, the growth of the marine alga Dunaliella tertiolecta Butcher was observed in axenic hypersaline cultures prepared with different organic P forms and related to the corresponding levels of colorimetrically measured P and total P. The malachite green method was used to colorimetrically analyze the different P forms and inductively coupled plasma-optical emission spectroscopy was used to quantify the total P. The results showed that only creatine P was colorimetrically detectable, of which 87% of its total concentration was measured. The growth of algae in the culture media with organic P compounds did not reflect the colorimetrically measurable organic P compounds. The results from this study imply that colorimetric analysis may not be sufficient to assess P availability to algae in hypersaline conditions where organic P components are the main source of P.