Possible effect of volcanic ashes from Sakurajima Volcano on material cycling in marine environment in Kagoshima Bay

活火山位于鹿儿岛县的樱岛火山连续喷发，大量火山灰降落在邻近地区，包括鹿儿岛湾的海洋环境。水下观测结果表明，火山灰在喷发过程中，表层海水中出现了大量的宏观团聚体（海洋雪），这些宏观团聚体在火山灰喷发过程中会发生大量的沉积。樱岛大颗粒物在表层水中几天内趋于消失，并在接近海底的较深层（25 m）中观察到。海洋雪的沉降速度明显大于浮游动物粪球的沉降速度。据估计，含有海洋雪的灰加速了悬浮在海水中的颗粒物质的下沉速度。此外，实验室研究表明，火山灰对海水质量有影响。首先，火山颗粒释放大量的营养物质到海水中。含有火山颗粒的实验海水在一小时内迅速增加了硝酸盐，氨和磷酸盐的浓度。然而，在一周内没有观察到硅酸盐浓度的显著增加。其次，火山颗粒将溶解在海水中的有机碳吸附到颗粒表面。火山颗粒可能对鹿儿岛湾的海洋环境产生影响。

Active volcano, Mt. Sakurajima located in Kagoshima Prefecture, has continuously erupted with heavy ash fall in the neighboring area including marine environment in Kagoshima Bay. The purpose of the present study is to evaluate possible effect of volcanic ashes on material cycling in sea water.The underwater observation showed that large abundant of macroscopic aggregates (marine snow) markedly occurred in the surface sea water during the ash falling ejected from Mt. Sakurajima. The large particles tended to disappeared in surface water in a few days and were observed in deeper layr (25m) near to the sea bottom. The measured sinking speed of marine snow was significantly larger than that of fecal pellet of zooplankton. It is estimated that ash containing marine snow accelerate the sinking speed of particulate material suspended in sea water. Further, laboratory studies indicated that volcanic ashes influenced on quality of sea water. Firstly, volcanic particles release significant amount of nutrients into sea water. The experimental sea water that were contained volcanic particles rapidly increased nitrate, ammonia, and phosphate concentration within one hour. However, significant increase of silicate concentration was not observed in a week. Secondly, the volcanic particles adsorb organic carbon dissolved in sea water into surface of the particles. It is concluded that volcanic particles possibly influenced on marine environment in Kagoshima Bay.