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Vol. 11 No. 1 2004 Het arseen wat vrijkomt uit pyriet kan meteen worden geadsorbeerd aan nieuwgevormde ijzerhydroxides. 3.2 Ingrepen in gebieden met "roest-type" Arseen dat aan ijzerhydroxiden is gebonden ("roesttype") komt vrij indien de omstandigheden reducerend zijn. De gehaltes in de bodem zijn vaak niet verhoogd t.o.v. de streefwaarde, terwijl onder reducerende omstandigheden ijzerhydroxiden oplossen, en het arseen dat aan de ijzerhydroxiden is gebonden vrijkomt. Hierbij valt te denken aan situaties waar de grondwaterspiegel wordt verhoogd, waardoor gereduceerde omstandigheden in de bodem kunnen ontstaan. In het freatisch grondwater kunnen, als gevolg van (natuurlijke) fluctuaties in de grondwaterstand, ijzerhydroxiden oplossen en het arseen vrijkomen. Bij een hoge grondwaterstand zullen hoge gehaltes arseen worden gemeten en bij een lage grondwaterstand lagere gehaltes. De diepere grondwaterpakketten met sterk verhoogde arseengehaltes zijn voornamelijk geconcentreerd in gebieden die in het verleden een aanvoer van ijzer en arseen hebben meegemaakt. Indien dit grondwater wordt onttrokken, zal na beluchting het ijzer en arseen onmiddellijk neerslaan als ijzerhydroxiden. Bij grote ontrekkingen in een gebied met lage arseengehaltes kan arseenrijk grondwater worden aangetrokken vanuit gebieden met een hoge gehalte as. De mate waarin dit kan gebeuren is sterk afhankelijk van het lokale grondwaterstroming. Ingeokring Newsletter 56 23
Ingeokring Newsletter ENVIRONMENT Environmental Friendly Roads in Bhutan: Providing access to rural communities while protecting the <strong>environment</strong> Hendrik Visser (Civil Engineer Delft University of Technology) Bhutan The Kingdom of Bhutan, or the land of the thunder dragon, has an area of approximately 38,394 square kilometres. It has borders with the Tibetan autonomous region of China in the north and India in the east, west and south. Geographically Bhutan lies within the latitudes 26°45' N and 28°10'N and longitudes 88°45'E and 92°10' E. The climatic conditions vary due to the mountainous nature of the country. The country is subject to the monsoon rain in summer, with relatively dry winters. About 73 percent of the land area is covered by forests of temperate and sub-tropical species that are a natural habitat of a diversity of flora and fauna. The country has one of the richest biodiversity in the world with about 3,281 plant species per 10,000 square kilometres and has been declared one of the ten global biodiversity 'hotspots'. Bhutan is one of the least populated countries in South Asia. Most of the population is concentrated in the valleys, while large areas at higher altitudes in the north of the country are virtually empty except for nomadic herders. The population was estimated to be 699,000 in 2001, with more than 40 percent of the people below 15 years. The population is probably growing at between 2.5-3.5 percent per year, putting heavy pressure on natural resources in the villages and resulting in a high rate of Figure 1: Countries within the Hindu-Kush Himalayan migration from rural to urban areas. The current rate of increase is, however, expected to decline to 1.6 percent per annum in 2011 and 1.3 percent in 2016. Approximately 80 percent of the population lives in villages in an extended family system. The average household is variously estimated to comprise between 6-8 members, with an average of 43 houses per village. There are approximately 80,000 landholdings in rural Bhutan. About 60 percent of farmers own less than 2 hectares, which is usually insufficient to feed the average size family. Only 7-8 percent of the land can be cultivated and the population pressure on land and other figure 2: equipment use figure 3: controlled blasting 24
Page 2 and 3: Table of contents Editorial .......
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Page 10 and 11: Vol. 11 No. 1 2004 ENVIRONMENT BioS
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Page 14 and 15: Vol. 11 No. 1 2004 Infrastructural
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