Finalprint PHD Thesis
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LAND USE/COVER CHANGE MODELLING AND LAND DEGRADATION ASSESSMENT IN THE KEISKAMMA CATCHMENT USING REMOTE SENSING AND GIS. PAIDAMWOYO MHANGARA Submitted in fulfillment of the requirement for the degree of PHILOSOPHIAE DOCTOR in the Faculty of Science at the Nelson Mandela Metropolitan University January 2011 Promoter: Professor Vincent Kakembo AUTHOR'S DECLARATION I hereby declare that the work contained in this thesis is my own original work and that I have not previously submitted it, in its entirety or in part, at any university for a degree. ii Abstract Land degradation in most communal parts of the Keiskamma catchment has reached alarming proportions. The Keiskamma catchment is particularly predisposed to severe land degradation associated with soil erosion, thicket degradation and deteriorating riparian vegetation. There is a close coupling between land use/cover dynamics and degradation trends witnessed in the catchment. Soil erosion is prevalent in most of the communal areas in the catchment. The principal aim of this study was to investigate land use/cover trends, model the spatial patterns of soil loss and predict future land use/cover scenarios as a means of assessing land degradation in the Keiskamma catchment. Multi-temporal Landsat satellite imagery from 1972 to 2006 was used for land use/cover change analyses using object-oriented post-classification comparison. Fragmentation analysis was performed by computing and analyzing landscape metrics in the riparian and adjacent hillslope areas to determine the land cover structural changes that have occurred since 1972. The landscape function analysis was used to validate the current rangeland conditions in the communal areas and the former commercial farms. The current condition of the riparian zones and proximal hillslopes was assessed using the Rapid Appraisal of Riparian Condition and future land use/cover scenarios were simulated using the Markov- cellular automata model. Spatial patterns of soil loss in the Keiskamma catchment were determined using the Sediment Assessment Tool for Effective Erosion Control (SATEEC), which is a GIS based RUSLE model that integrates sediment delivery ratios. Object oriented classification was used to map soil erosion surfaces and valley infill in ephemeral stream channels as a means of demonstrating the major sediment transfer processes operating in the Keiskamma catchment. The Mahalanobis distance method was used to compute the topographic thresholds for gully erosion. To understand the effect of soil characteristics in severe forms of erosion, laboratory analyses were undertaken to determine the physico-chemical soil properties. iii The temporal land use/cover analysis done using the post-classification change detection indicated that intact vegetation has undergone a significant decline from 1972 to 2006. The temporal changes within the intermediate years are characterized by cyclic transitions of decline and recovery of intact vegetation. An overall decline in intact vegetation cover, an increase in degraded vegetation and bare eroded soil was noted. Fragmentation analyses done in the communal villages of the central Keiskamma catchment indicated increasing vegetation fragmentation manifested by an increase in smaller and less connected vegetation patches, and a subsequent increase of bare and degraded soil patches which are much bigger and more connected. The Landscape Organisation Index revealed very low vegetation connectivity in the communal rangelands that have weak local traditional institutions. Fragmentation analyses in the riparian and proximal hillslopes revealed evidence of increasing vegetation fragmentation from 1972 to 2006. The Markov Cellular Automata simulation predicted a decline in intact vegetation and an increase in bare and degraded soil in 2019. The Keiskamma catchment was noted as experiencing high rates of soil loss that are above provincial and national averages. The classification of erosion features and valley infill showcased the vegetation enrichment in the ephemeral streams which is occurring at the expense of high soil losses from severe gully erosion on the hillslopes. This in turn has led to an inversion of grazing patterns within the catchment, such that grazing is now concentrated within the ephemeral stream channels. Soil chemical analyses revealed a high sodium content and low soluble salt concentration, which promote soil dispersion, piping and gully erosion. The presence of high amounts of illite-smectite in the catchment also accounts for the highly dispersive nature of the soil even at low SAR values. Significant amounts of swelling 2:1 silicate clays such as smectites cause cracking and contribute to the development of piping and gullying in the catchment. Given the worsening degradation trends in the communal areas, a systematic re-allocation of state land in sections of the catchment that belonged to the former commercial farms is recommended to alleviate anthropogenic pressure. Strengthening local institutions that effectively monitor and manage natural resources will be required in order to maintain iv optimum flow regimes in rivers and curb thicket degradation. Measures to curb environmental degradation in the Keiskamma catchment should encompass suitable ecological interventions that are sensitive to the socio-economic challenges facing the people in communal areas. v Acknowledgements This research was made possible through postgraduate funding from NMMU Research Office and the NRF, I value this immense contribution. The outstanding support offered by several scholars added value to this PHD; indeed I was standing on the shoulders of giants. I am greatly indebted to my promoter Professor Vincent Kakembo for this guidance and support throughout my doctoral studies. I am forever grateful for his accessibility and guidance during my research. My sincere gratitude goes to Professor Kyoung Jae Lim the SATEEC software developer at Kangwon National University, Chuncheon, and Kangwon, Korea for reviewing my work on soil erosion risk modeling. I am also grateful to Dr Courage Kamusoko of Asia Air Survey, Kanagawa, Japan for his advice on the Markov Cellular model. I owe deep gratitude to Dr Pardon Muchaonyerwa for his assistance with soil analysis. Many thanks for making arrangements for soil analysis at Dohne Soil laboratory and for reviewing my soil analysis results. I also treasure the support offered by staff at the CSIR Satellite Application Centre in providing satellite imagery, expertise and image processing software. I am greatly indebted to Dr John Odindi for his encouragement to purse this doctorate. He was willing to share his resources during difficult times. May I also extend my appreciation to the Department of Water Affairs and Forestry, South Africa and Mr. Peter Bradshaw of SANParks for providing critical digital datasets for this study. Finally, I would like to thank all my colleagues at NMMU particularly Adolf Nyamugama and Munyaradzi Manjoro for volunteering as field assistants during their own busy schedules. Many thanks go to staff in the NMMU Geosciences Department for creating an academically friendly atmosphere, which made this work worthwhile. I am much obliged to my entire family for their moral support. My deep appreciation goes to my wife Sophia and sons Tadiwanashe and Tawananyasha for their unwavering support during my studies. To God be the Glory. vi Dedication I dedicate this to my parents who worked tirelessly to ensure I reach the apex of education. vii Table of Contents Chapter 1 : Introduction ................................................................................................................. 1 1.1 Introduction.......................................................................................................................... 1 1.2 Problem Statement ............................................................................................................... 3 1.3 Research Aim....................................................................................................................... 4 1.4 Specific objectives................................................................................................................ 4 1.5 Chapter Outline.................................................................................................................... 6 Chapter 2 : A characterization of the Keiskamma catchment and review of land degradation assessment methods. ...................................................................................................................... 9 2.1 Introduction.......................................................................................................................... 9 2.2 Catchment setting................................................................................................................. 9 2.2. 1 Climate...................................................................................................................... 10 2.2. 2 Geological Setting ..................................................................................................... 11 2.2.3 Vegetation ................................................................................................................... 12 2.2.4 Land use and land tenure ............................................................................................. 13 2.2.5 Land degradation in the Keiskamma catchment............................................................ 13 2.3 Assessment of land degradation.........................................................................................