Volcanic Ash as a Fertilization Agent : A Comparative Mesocosm Study of Mafic and Felsic Ash in Baltic Seawater

Sammanfattning

Volcanic ash dissolution can supply marine systems with numerous elements and compounds which can have positive or negative effects on marine biota. Many studies have been conducted but never with large mesocosms (2000 L) and Baltic seawater. This study looked at the differences in nutrient release and phytoplankton response between mafic and felsic volcanic ashes from the Fur formation in Baltic seawater over a duration of 1.5 weeks. Other chemical and physical parameters were also included. The results showed that despite an initial phosphate spike and high nitrate levels in the felsic treatment, phytoplankton biomass did not increase likely due to an acidic environment and lack of other limiting nutrients. Phytoplankton biomass increased considerably in the mafic treatment along with elevated ammonium and silica concentrations. However, the mafic ash might have supplied iron, through either mineral weathering or dissolution, to the system instigating the phytoplankton response. These findings highlight both the negative and positive effects volcanic ash may have on the biogeochemistry of Baltic seawater upon deposition. However, to draw conclusions more work is required in this field.