Tropentag, September 19 - 21, 2012 in Göttingen "Resilience of agricultural systems against crises"

An Integrated Approach to Assess Land Use History in a Watershed in Northwest Vietnam

¹University of Hohenheim, Inst. of Plant Production and Agroecology in the Tropics and Subtropics, Germany
²Hanoi University of Agriculture, Center for Agricultural Research and Environmental Studies (CARES), Vietnam

Abstract

In the past decades, the introduction and extended cultivation of hybrid maize and hybrid cassava provided higher income for farmers but replaced traditional crops, such as upland rice and local maize and cassava varieties, in the upland area which surrounds a reservoir in Chieng Khoi, Yen Chau district in mountainous Northwest Vietnam. Furthermore, new cultivation areas are still expanding into protected forest, grazing areas and fruit tree plantations. Consequently, primary forest on the upper, steep slopes is illegally cleared for hybrid maize and cassava cultivation.
Detailed Geographic Information System (GIS) based classification of land uses is difficult when crops are planted during the same period of the year and reflect similar spectral bands. Therefore, this study aimed to reconstruct ground cover maps, to distinguish characteristic upland land uses before and after the reservoir was installed and to determine the sediment contribution of different land uses to the reservoir. Hybrid classification combining remote sensing data (aerial photograph 1954, Landsat 1973 and 1993) with farmers' information were used to obtain detailed classification of past land cover.
Compound specific stable isotope (CSSI) analysis of fatty acid methyl ester (FAME) and fallout radionuclide (FRN) measurements were chosen to support and match the data obtained by remote sensing - GIS and farmer interviews. The integration of FRNs and CSSI-FAME markers enables apportioning sediment bodies to land use specific erosion rates. This is achieved through the following steps: 1. FRN are used to distinguish sediment strata at the deposition sites. To receive an estimate of sediment volumes, a statistical analysis of sediment strata is based on spatially distributed sediment profiles. The approach is capable of converting measurements of FRN soil inventories to estimate soil erosion and deposition rates. 2. The land use specific mass accumulation represented within a stratum is estimated by multiplying the mass of the stratum (FRN) by the land use specific soil proportion (CSSI-FAME). 3. Linking the land use specific mass accumulation to land use information from GIS allows the evaluation of land use specific erosion dynamics corresponding to the sediment strata.

Keywords: Compound specific stable isotopes, fallout radionuclides, GIS, land use history, remote sensing

Contact Address: Thanh Thi Nguyen, University of Hohenheim, Inst. of Plant Production and Agroecology in the Tropics and Subtropics, Garbenstr. 13, 70599 Stuttgart, Germany, e-mail: nguyenthanh0406gmail.com