An integrated, landscape-based approach to model the formation and hydrological functioning of wetlands in semiarid headwater catchments of the Umzimvubu River, South Africa
Wetlands are very important elements of the landscape in almost every environment. Addressing the continued loss of wetland area worldwide, wetlands are recognized as highly vulnerable with regard to natural and anthropogenic system changes. Consequently, the research of their natural and socio-economical functions, importance for the water and nutrient cycles and their role as wildlife habitats received increasing scientific and public awareness in the past decades. The landscape of the semi-arid Eastern Cape Province, South Africa, is characterized by the occurrence of different types of palustrine wetlands. Intensive afforestation in the headwaters of the Umzimvubu catchment since 1989 has changed downstream wetland characteristics, but little attention was given to evaluate and quantify these impacts. Addressing this research deficit, the main objectives of this dissertation are the development of an integrated, landscape-based research approach to improve the understanding of the formation, functioning and dynamics of wetlands and the prognostic modeling and assessment of afforestation impacts on these wetland systems. The conceptual and methodological approach of this dissertation is based on three individual aspects: i) observation and data mining; ii) integrated system analysis; and iii) system modeling and assessment integrating empirical field studies, laboratory analysis, GIS and remote sensing techniques, system analysis and process-oriented, plant growth and hydrological modeling, This integrated research approach provides information regarding a generalized understanding of dominant environmental processes at wetland and catchment scale and the impact of afforestation on wetland and basin hydrology. By means of this effort three main wetland types, being different in terms of landscape position, extent and size of the tributary catchment, soils, vegetation composition and hydrological dynamics, could be identified. The hydrodynamics of plateau and slope wetlands are mainly controlled by recharge mechanisms, while larger valley bottom wetlands are driven by interlinked ground-/surface water dynamics, discharge/recharge processes and direct rainfall input. Coupling plant growth and hydrological modeling, it was found that wetland dynamics and their landscape functions will be influenced by afforestation in terms of altered recharge/discharge mechanisms; reduced base flows addressed to increased interception losses and reduced water retention capability as a result of net loss of wetland area. In addition, such changes will affect environmental functions and biodiversity due to habitat loss and alterations. Integrating the results and information of the present study, an integrated landscape model was developed aiming to characterize wetland formation and emphasizing impacts of human activities on past and recent wetland and landscape dynamics.