The material basis of the coast includes water, rock, organisms have certain effect on grain size of beach sediment. sediment and organisms. Biodetritus which come from By adding excess acid and hydrogen peroxide in the beach surface sediment samples from the Gaolong Bay, Hainan Island, the difference of their grain size distribution with and without biodetritus was discussed, and the analysis was made with the height of the beach. It can be seen from the results that (1) Biodetritus content on beach is mainly determined by marine dynamic, and the biodetritus which have coarse sizes and large mass is brought to the beach by waves during high tidal period. (2) The distribu- tion of biodetritus in the beach sediment is influenced by landform and main wave direction, biodetritus produced by beach breeding as well as coral reefs flat offcoast. (3) Biodetritus content in the beach sediment changes with the sea- sons. The biodetritus supplied by sea water would be reduced and further decomposed from winter to spring, which makes biodetritus content decrease in the north area, but the stable supply of coral debris and strong wave dynamics in spring increase the biodetritus content in the south area of the beach. (4) Coarse particles in surface beach,sediment in Gaolong Bay contain more biodetritus than that fine particles contain. Grain size of biodetritus is mostly -1 - 26, namely coarse sand to gravel. The more biodetritus sediment contains the larger changer grain size parameters have.%在热带砂质海岸,生物碎屑是海滩沉积物的重要组成部分,其分布和变化影响海滩沉积物的粒度特征。采用添加过量盐酸和双氧水的方法对海南高隆湾海滩表层沉积物进行了去生物碎屑前后粒径分布的对比,并结合海滩高程测量分析,结果表明：（1）海滩剖面上沉积物中生物碎屑的含量主要受到海水动力的影响,且生物碎屑颗粒较粗、重量较大,在高潮时由波浪流推上海滩并滞留。（2）海滩沉积物中生物碎屑的分布主要受三方面影响：一是地形及常涌浪向;二是区域中养殖业产生的生物碎屑;三是岸外发育的珊瑚礁坪。（3）海滩沉积物中生物碎屑的含量随季节变化,冬季至春季由海水供给的生物碎屑减少、进一步分解,使得北部海滩生物碎屑含量减少;而珊瑚碎屑的稳定供给和春季较强的波浪动力条件又使研究区南部断面的生物碎屑含量增加。（4）海滩沉积物中粗颗粒所含生物碎屑多于细颗粒中的生物碎屑,生物碎屑粒径主要为-1～2,即粗砂至细砾。沉积物中生物碎屑含量愈大,对粒径参数的影响也愈大。
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