Assessment of the content of magnesium, potassium, phosphorus and calcium in water and algae from the Black Sea in selected bays near Sevastopol

The content of macroelements such as magnesium, calcium or phosphorus in tissues of aquatic organisms is often used as an indicator of the quality of an aquatic environment. The aim of this paper was to assess the content of magnesium, potassium, calcium and phosphorus in water and in algae in selected bays of the Black Sea near Sevastopol. The samples of water and algae were collected in August 2012 from eight bays of Sevastopol (Gałubaja, Kozacha, Kamyshova, Strieletska, Kruhla, Pishchana, Pivdenna, Sevastopol Bay). One sample was obtained from the open sea near Fiolent. Cystoseira barbata and Ulva rigida algae were collected from the same sites. The collected water was conserved in situ and, after being brought to a laboratory, it underwent determinations of the content of magnesium, potassium, phosphorus and calcium. Laboratory samples of the algae were subjected to mineralization in a closed system with the use of microwave energy. The content of the elements in water and in digested algae samples was determined using the ICP-OES method. The magnesium content in water ranged between 461.6 and 638.9 mg Mg ∙ dm-3, potassium between 332.8 and 457.6 mg K ∙ dm-3, phosphorus 0.072-0.143 mg P ∙ dm-3, and the calcium content was within the range from 209.5 to 288.6 mg Ca ∙ dm-3. A higher content of calcium and phosphorus was found in Cystoseira barbata, whereas a higher level of magnesium was detected in Ulva rigida algae. No statistically significant correlation between the content of the elements in water and in algae was observed. The content of the elements in water decreased in the order Mg>K>Ca>P, whereas in algae the order was K>Ca>Mg>P. Despite the differences in amounts of the accumulated elements in algae, there was a significant relation between the content of individual elements in Cystoseira barbata and Ulva rigida, which suggests that both species of algae are suitable for biomonitoring.