⁹⁰Sr in Zostera marina from the Gulf of Gdańsk (southern Baltic Sea)

⁹⁰Sr activity was determined in Zostera marina collected in the Gulf of Gdańsk in 2008-2013. ⁹⁰Sr activity in Z. marina from Jama Kuźnicka and Klif Orłowski range from 0.83 Bq kg⁻¹ d.w. to 3.78 Bq kg⁻¹ d.w. and from 0.68 Bq kg⁻¹ d.w. to 4.95 Bq kg⁻¹ d.w., respectively. The plants collected in spring-summer showed significant differences between ⁹⁰Sr content in blades - 1.55 Bq kg⁻¹ d.w. in 2011 and 2.18 Bq kg⁻¹ d.w. in 2013, and in roots - 7.75 Bq kg⁻¹ d.w. and 11.44 Bq kg⁻¹ d.w., respectively. The reduction in ⁹⁰Sr concentrations in Z. marina roots to 1-2 Bq kg⁻¹ d.w. in summer resulted from the transport of this element to the young parts of the plant. In autumn and winter, the ⁹⁰Sr content in the blades of Z. marina was increasing and reached the maximum of 3.77 Bq kg⁻¹ d.w. This could be explained by the process opposite to dilution, related to the biomass reduction and strontium concentration in the plant tissues. Changes in ⁹⁰Sr concentration in Z. marina tissues are affected by isotope concentration in seawater as well as by salinity, which affects the concentration of Ca²⁺ - for which Sr²⁺ is a chemical analogue.