| 南海诸岛土壤的形成和年龄 |
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| 引用本文： | 龚子同,刘良梧,周瑞荣.南海诸岛土壤的形成和年龄[J].第四纪研究,1996,16(1):88-95. |
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| 作者姓名： | 龚子同 刘良梧 周瑞荣 |
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| 作者单位： | 中国科学院南京土壤研究所 |
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| 基金项目： | 国家自然科学基金,南沙综合考察资助 |
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| 摘 要： | 本文在阐明南海珊瑚诸岛土壤的生物集聚过程、积盐和脱盐过程,以及有关的土壤诊断特性基础上,进一步介绍了那里的磷质石灰土和滨海盐土两大土壤类型,它们的空间分布及其与岛屿结构、地形、植被和鸟类活动之间的关系。最后,作者针对南海珊瑚岛土壤的特征,运用(１４)Ｃ方法探讨了它的年龄及其与土壤形成、发育之间的相互关系。
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| 关 键 词： | 南海诸岛 磷质石灰土 成土过程 诊断特性 土壤14C年龄 |
FORMATION OF THE SOILS IN THE SOUTH CHINA SEA ISLANDS AND THEIR AGES |
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| Institution: | Nanjing Institute of Soil Science, Chinese Academy of Sciences |
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| Abstract: | Islands in the South China Sea consist of Dongsha, Xisha, Zhongsha and Nansha Archipelagoes, including 260 small islands, of which the biggest ones are Yongxing island with 1.85 km2 and Taiping island with 0.43 km2. Many cultural relics unearthed in the islands and official written documents in the history have convincingly demonstrated that the islands had already been a part of China since the Qin and Han Dynasties (B .C.221-AD.220 ).The formation processes of the soils in the South China Sea Islands are apparently different from allitization of the tropical and subtropical soils in China.The islands soils are characterized by Ca-enriched parent materials, special biolgoical activities and salinization- desaliinization etc.1. Lithological characteristics and Ca-enrichment parent materials The soil parent materials of the South China Sea islands are mainly loose fragmentary sands of corals and shells with 95% of carbonate. Under the tropical oceanic climate, calcium carbonate affected by humic acids and abundant rainfall moves down from soil surfaces. Due to coral contribution, soil mass still contains high carbonate (62%-83%). In addition, the soils are light loam to loose sand in texture and remain lithological characteristics of obvious rock-like coral and shell fragments.2. p-enriched property and accumulation of phosphorous Diverse biological activities, especially sea birds leave large amount of guano to soils. Under humid and thermal conditions, the guano is quickly decomposed and forms phosphate. Then the phosphate moves downward and combines with Ca derived from corals and shells, finally resulting in p-enrichment property of soils with 7%-22% of P2O5.3. Accumulation of organic matter and isohumic property A great deal of organic matter accumulates on soil surfaces through decayed leaves and then increases soil organic matter content to a certain degree. This enhances further eluviation to deeper part of soil profiles, thus forming organic epipedon with dark brown color and organic subsurface horizon with brown color,i. e. isohumic property.4. Salinization-desalinization and saline property The soils infected by sea water contain high content of salt, mainly being NaCl. However, phospho-calcic soils and hardpan Phospho-calcic soils contain much less soluble salt, and chiefly in the composition of Ca2+-HCO, which resuits from desalinization with the extension of island and soil developments.5. Gley process and gleyed property.Under the condition of permanent stagnant water, abundant organic matter (> 1% ) makes anaeronic decomposition, so that Fe-Mn is reduced and accumulated in soils, resulting in occurrence of a gleyed horizon in soil profiles.Based on above-mentioned soil formation processes-and diagnostic properties,the soils of the South China Sea Islands can be divided into two great groups:phospho-caldc soils and coast salanchaks. The phospho-calcic soils are subdivided into young and fragmental phospho-calcic soils, Phospho-calcic soils,hardpan Phospho-caldc soils and gleyed phospho-calcic soils etc, in the light of thickness of soil horizons, extent of isohumic property, appearance of parent material fragment within soil, existence of phospho-hardpan and gleyed horizons.Spatial distribution of the soils in the islands is related to the structure,geomorphology of the islands and vegetation and bird activities on the islands,generally like concentrical distribution.The soils affected by human activities began to form and develop under the suitable bioclimatic conditions, shortly after carbonate islands of the South China Sea became continent. Soil age gradually increases from the coast to outside and inside of sand bar, sandy level-table and further to central depression and lagoon on the islands.14C dating of the soils shows: 1) the" apparent mean residence time" for surface horizon of coastal saline soils and fragmental phospho-calcic soils are 900-700 aB. P., while for phospho-calcic soils and hardpan phospho-calcic soils are 1200 aB .P. and 1900 aB .P., respectively. 2) the difference of ages between |
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