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

活火山，Mt.位于鹿儿岛县的樱岛火山不断喷发，周边地区包括鹿儿岛湾的海洋环境都落下了大量的火山灰。本研究的目的是评估火山灰对海水物质循环的可能影响。水下观测表明，在火山灰从山上喷出的过程中，表层海水中显着地出现了大量丰富的宏观集合体(海雪)。樱岛。这些大颗粒在几天内在表层水中趋于消失，并在靠近海底的更深层(25m)观察到。测得的海洋雪的下沉速度明显大于浮游动物粪便颗粒的下沉速度。据估计，含有海洋雪的火山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，火山颗粒向海水中释放了大量的营养物质。含有火山颗粒的实验海水在一小时内迅速增加了硝酸盐、氨和磷的浓度。然而，硅酸盐浓度在一周内没有明显增加。其次，火山颗粒将溶解在海水中的有机碳吸附到颗粒表面。由此可见，火山颗粒可能对鹿儿岛湾的海洋环境产生了影响。

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.