Karakteristik, Klasifikasi, dan Arahan Pengelolaan Tanah Terpengaruh Tsunami di Nanggroe Aceh Darussalam (Studi Kasus di Aceh Utara)

Abstract

On 26 Desember 2004 a strong earthquake in Aceh caused the tsunami wave. The wave had a kinetic energy resulting from the water movements, the characteristics of water as agent of leaching and dissolving, and mud containing organic and inorganic matter carried by the wave, all of resulted in the change of ecosystem in the major part of the coastal areas of Nangroe Aceh Darussalam, including the change of soil characteristics. This research aims to study (1) the characteristics of tsunami mud, (2) the characteristics of tsunami affected soil, (3) to classify of soil in the tsunami-affected areas, and (4) guidance for management of the tsunami-affected soil. In relation to the above research objectives, 17 soil profiles that were affecteed or not by the tsunami mud were observed. A sample of the tsunami mud materials were collected from the research location. The determination of the soil profiles (pedons) was based on the distance from the beach, land use, and the types of soil. The distance of soil profiles from the coastal line consists of less than 500 metres from the coastal line, 1000-2500 metres from the coastal line, and 3000-5000 metres from the coastal line, The type of land use consist of rice fields, ponds, gardens, and shrubs. observation in each profile focused on the morphological, mineral, physical, chemical, and biological characteristics of soil. The morphological characteristics of soil were observed on the cross section soil profile. Meanwhile the mineralogical, physical, chemical, and biological characteristics were analyzed based on the soils samples collected from the horizon of each soil profile. The results of analysis showed that the materias of tsunami mud contain clay fraction of 56.62 N; pHH2o,7.60; ca, 14.81 me/l00 g; Mg, 14.56 mellOO g; Na, 2.16 mell}0; Electric conductivity (EC), 5.67 dS/m; Fe,30.52 ppm; Mn, 66.96 ppm; N, 0.13 %; and P, 3.00 ppm. The results of analysis of mineral sand fraction show that there is the difference of mineral composition between the soil affected by tsunami rnud (<500 m and 1000-2500 m from the coastal line) and the soil not affected by tsunami mud (3000-5000 m from the coastal line). The soil affected by tsunami mud has weatherable minerals (WM) higher than the soil not affected by tsunami mud. Weatherable minerals come from the sea that will resist the weathering in the flooded condidition. When tsunami occured, this WM were carried by the sea to land which in turn increased the amount of WM in tsunami-affected soil. The dominant wetherable mineral took the forms of fragmental rock and labradorit. A side from those forms there had been found a lot of green hornblende, brown homblende, augit, hyperstine and epidot. While in the soil far from the coastal areas and not affected by tsunami mud the contents of green hornblende, brown hornblende, augit, hyperstine and epidot were not found. The soil affected by tsunami mud indicated are different from those not affected by tsunami mud term of the structure of clay minerals. The soil near the coastal areas and affected by the tsunami contains the goethite minerals, while the soil far from the coastal areas and not affected by the tsunami does not contain those minerals. The difference is due to the fact that the minerals the iron of ferromagnesian weathered and released the iron. The iron then changed to be the goethite minerals because it contacted with the atmosphere on the top soil. The soil near the coastal areas and affected by the tsunami has indistinct and undominated of peak minerals, while the soil far from the coastal areas and not affected by the tsunami showed clear and dominant forms. This condition occured because the tsunami affected soil contains the amorphous material that disturb the appearance of the crystal mineral. Generally, clay mineralogy fraction are dominated by the amorphous material and kaolinite. The amorphous material is indentified by the first temperature of the peak of endothermic betrveen 84-181"C and the second one 270-276oC, and the first exothermic temperature 335-359"C and the second one is 448'C. Kaolinite indentified by the endothermic temperature for 576-578oC. The existance of kaolinite supported by the reaction of difractogram with the first temperature 7.14 A - 7.rg A and the second one 3.56 A.

Due to its close distance from the sea and the influence of tsunami mud, soil affected by tsunami mud indicated a few different characteristics of physic, chemistry, and biology. The profiles near coastal areas and affected by tsunami mud, have a coarse soil fraction because the tsunami wave carried and increased the sand fraction to the original soil, and the hardness of soil is higher in the upper horizon than in the lower caused by the formation of Si-oxidehydroxide and Fe-oxidehydroxide to be cementation, as well as the content of these profiles, soil water is lower than that of the other profiles far from the coastal areas and not affected by tsunami mud. The pH of profiles (pedons) near the coastal line and affected by tsunami mud increases more and more in the lower layers of soil profiles because of a higher level of the cationic base. The cation exchangeable (Ca, Mg, Na) is higher in the profiles (pedons) affected by tsunami mud than the profiles not affected by tsunami mud, and profiles near the coastal areas contain ca<Mg<Na. The tsunami-affected soil indicated were higher EC (salinity) than the soil not affected by the tsunami. The EC is related to the contents of clay (0.29*), sulphate (0. 59* *), sodium (0.+0**';. The different biological characteristic of the soil affected by tsunami mud are total microorganism. The soil affected by tsunami mud has more disturbed (unstable) mikroorganism than the soil not affected by tsunam mud, because the tsunami mud contains organic matter, higher pH H2o, and higher EC (salinity). The degree of weathering of pedons was studied including at the juvenile dan virile stages. Both of these stages shows lower ratio of weathering mineral product and weatherable minerals (wMp : wM), cation exchange capacity, and higher base saturation, ratio of calsium-magnesium

, ratio of fine-sandy and silty- clay, and ApH.

The results showed that tsunami mud influenced on the pedoprocess too. This is indicated by the higher content of iron (Fe) produced by weathering iron minerals. These iron minerals then oxidized to be goethite that resulted in the broum colored soil (braunification). Salinization is a real pedoprocess caused by the tsunami wave in which has the higher content of the soils with sulphate and sodium which in tum cause the higher salinity (EC). This research is canied out twelve kinds of soil family categories, i.e. Sulfic Endoaquenfs, ashy over loamy, isohyperthermic; Typic udipsamments, mixed, isohyperthermic; Ltthic Psammaquents, mixed, ishyperthermic; suffic Endoaquepts', sandy, mixed, isohyperthermic; Aquic Eutruclepls, sandy, mixed, isohyperthermic; suffic Endoaquents, clayey over sandy, illitic, isohyperthermic; sulfic Endoaquepts, clayey over sandy, kaolinitic, isohyperthermic; Aquic udipsamments, mixed, isohypertherrnic; Typic Endoaquepts, sandy, mixed, isohiperthermic; Typic Endoaquepts, loamy, mixed, isohyperthermic; Typic Endoaquepls, clayey, mixed, isohyperthermic; oxyaquic Dystrudepts, loamy, mixed, isohyperthermic. Guidance for soil management should be based on the change of the ecosystem and soil cahracteristics, covering the following aspects: mangrove replanting around pedon near the coastal areas; a rational management of phosphate caused by higher amorphus materials; The addition of organic matter; leaching the soil with irrigation to decrease EC and werease sulphate. This research recommend that land use for paddy fields, ponds, and coconut,s plantation with irrigation and drainage systems should be preserved. Alternatavely, these areas can also be used for pasture and forages planting