Characteristics and distributions of humic acids in two soil profiles of the southwest China Karst area

Characteristics and distributions of humic acid(HA) and soil organic matter(SOM) in a yellow soil profile and a limestone soil profile of the southwest China Karst area were systematically investigated to reveal their evolutions in different soils of the study area. The results showed that characteristics and distribution of SOM along the two soil profiles were notably different. Total organic carbon(TOC) contents of soil samples decreased just slightly along the limestone soil profile but sharply along the yellow soil profile. TOCs of the limestone soils were significantly higher than those of the corresponding yellow soils, and C/N ratios of SOMs showed a similar variation trend to that of TOCs, indicating that SOM can be better conserved in the limestone soil than in the yellow soil. The soil humic acids were exhaustively extracted and further fractionated according to their apparent molecular weights using ultrafiltration techniques to explore underlying conservation mechanisms. The result showed that C/N ratios of HAs from different limestone soil layers were relatively stable and that large molecular HA fractions predominated the bulk HA of the top soil, indicating that HA in the limestone profile was protected while bio and chemical degradations were retarded. Combined with organic elements contents and mineral contents of two soils, weconcluded that high calcium contents in limestone soils may play a key role in SOM conservation by forming complexation compounds with HAs or/and enclosing SOMs with hypergene CaCO_3 precipitation.

Compiling distribution of karst in Southern China and Southeast Asia

As China and Southeast Asian countries have accelerated and globalized their economic development, karst environmental problems have become increasingly prominent and studying on and compiling maps of karst geology is quite important. Therefore, based on a wide collection of data in Southeast Asian countries, a cooperative map compilation has been carried out internationally. Through comprehensive research and analysis, a unified understanding has been achieved in terms of compiling principles, contents and representing methods, Distribution of Karst in Southern China and Southeast Asia(1/5 000 000) has been compiled, which provides foundations for environmental protection and scientific studies of karst geology.

Karst Types and Their Karstification

Eighty-one karst types and their main characteristics are described in this study,including the conditions of their development,the main characteristics of their karstification and their characteristic features.The classification includes the karst types of the Earth,a concise description of each karst type and the possibilities of belonging to several types of various karst areas.The classification of types is hierarchical in terms of groups,subgroups,types and subtypes.Karst can be classified according to their momentary state(the group of static karst types)and to their development(group of dynamic karst types).The group of static karst types has the azonal and zonal subgroups.Azonal karst types may be situated under any climate.These karst types are categorized according to their geological characteristics(age of karstification,constituting rock,extent of coveredness,structure),their elevation,expansion,the morphology of their surface,hydrology and to the effects occurring on the karst.Taking the above mentioned factors into consideration,the author distinguishes various types and describes their characteristics.Zonal karst types are also described(tundra karst,temperate karst,subtropical karst,tropical karst),karst types that can be distinguished based on their geomorphic evolution are identified and their characteristics are presented.

A quantitative morphometric comparison of cockpit and doline karst landforms

This study presented a quantitative comparison of cockpit and doline karst by examining the numbers and characteristics of typical types of landform entities that are developed in Guilin（Guangxi, China）, La Alianza（PR, USA）, Avalton（KY, USA）, and Oolitic（IN, USA）. Five types of landform entities were defined： isolated hill（IH）, clustered hills（CHs）, isolated sinkhole（IS）, clustered sinkholes（CSs）, and clustered hills with sinkholes（CHSs）. An algorithm was developed to automatically identify these types of landform entities by examining the contour lines on topographic maps of two cockpit karst areas（Guilin and La Alianza） and two doline karst areas（Oolitic and Avalton）. Within each specific study area, the CHSs is the least developed type yet with a larger size and higher relief. The IH and IS entities are smaller in size, lower in relief, and outnumber their clustered counterparts. The total numbers of these types of entities are quite different in cockpit and doline karst areas. Doline karst is characterized by more negative（IS and CSs） than positive（IH and IHs） landforms and vice versa for cockpit karst. For example, the Guilin study area has 1192 positive landform entities in total, which occupy 9.81% of the total study area. It has only 622 negative landform entities occupying only 3.91% of the total study area. By contrast, the doline karst in Oolitic has 130 negative while only 10 positive landform entities. The positive and negative landforms in Oolitic occupy 12.68% and 2.61% of the total study area, respectively. Furthermore, average relief and slope of the landform entities are much higher and steeper in the cockpit karst than the doline karst areas. For instance, the average slope of CHs in Alvaton is 3.90 degrees while it is 19.78 degrees in La Alianza. The average relief of CSs is 4.07 m and 34.29 m in Oolitic and Guilin respectively. Such a difference within a specific area or between the cockpit and doline karst may reveal different controls on the development of karst landscape.