The Effect of Dissolved H2S and CO2 on Short-Term Photosynthesis of Skeletonema Costatum, a Marine Diatom

Abstract

The planktonic diatom Skeletonema costatum was exposed during 4-h periods to dissolved forms of H2S and CO2. The experimental design permitted evaluation of the acute toxicity of these gases by measuring the reduction in photosynthesis using the 14C assimilation technique. Carbon dioxide gas, measured with a CO2-specific electrode, demonstrated a EC50 value of 0.69-mM molecular CO2. The inhibition in algal photosynthesis was largely attributed to the decrease in pH with increasing exposure concentrations (from pH 8.45 to 5.73). Hydrogen sulfide, measured colorimetrically, showed no adverse effects up to 24-μM total sulfide corresponding with 1.2-μM molecular H2S. The calculated EC50 value was 3.1-μM H2S. The toxicity tests yielded results useful for the assessment of potential harmful effects to marine diatoms of discharge of these gases into ocean waters by off-shore natural gas production platforms.