Analysis of the rainfall runoff processes of Andean ecosystems in Southern Ecuador : using hydrometric, tracers and modeling approaches

Abstract

The tropical Andes is one of the world s 25 most species rich and exceptional areas, and the montane forest ecosystems in particular are considered as biodiversity hotspots. Also the high altitude páramo region, between 3500 and 5000 m a.s.l., is another important Andean ecosystem. The low temperatures, high intra-day temperature variability and the tendency to be consistently humid throughout the year creates an environment ideal for wet páramo flora primarily consisting of tussock-grasses or bunch-grasses, and the home of a multitude of endemic species. Ecuador possesses the largest net wet páramo area within South America. According to SENPLADES the montane forests and páramos are two of the most important natural ecosystems that still exist. Both provide essential services to the society such as the biodiversity in flora and fauna, carbon sequestration, and water regulation and supply. These ecosystems are considered as the major water suppliers for Venezuela, Colombia and Ecuador, providing good water quality to millions of habitants of the main cities in the Andean cordillera and coastal areas.Notwithstanding the socio-economic and environmental importance of the highland ecosystems, good understanding of their functioning is still scarce hindering their conservation and management. According to several authors the geochemical, biologic and ecologic processes in tropical forest and páramo systems are controlled by the water passing through them. Therefore, most socio-economic and ecological services of these ecosystems are strongly linked to the governing hydrological processes. Logically, disturbance of the hydrology will directly affect all water dependent processes and the services provided by them. In this context, it is important and relevant to research the hydrological functioning of the highlands catchments. Good understanding of the hydrology is essential as to conserve in a more effective way these ecosystems. Where, identification of the hydrological processes governing the conversion of precipitation into runoff is one of the major challenges for hydrologists worldwide. The main objective of this dissertation was to identify the rainfall runoff processes that control the discharge generation of the study areas. The research was conducted on the south of Ecuador, between latitude 2°24´ and 3°58´, the altitude range between 1742 to 4100 m a.s.l.. The research uses multi techniques including hydrometric data analysis, tracers (isotopes and chemical constituents) and conceptual modeling. Results obtained using a variety of techniques and the detailed analysis of existing datasets and the collection of new datasets revealed that the hydrology of the study catchments is strongly controlled by the soil. This knowledge is very useful in deriving policies and regulations that best manage and protect the gamma of ecological services offered by these fragile ecosystems. For the generic use of the acquired knowledge findings were translated into a conceptual model mimicking the rainfall-runoff process, primarily based on mimicking the soil hydrology. With the tested model it will be possible to predict the impact on the runoff of future changes in climate and land use, and to test the effect of mitigation and management policies with respect to the sustainability in water delivery by this catchments for the multiple water uses in the region. The findings are representative for the area in which the study sites are located. Given the similarity in properties of the micro-basins in the Ecuadorian Andes cordillera above 2500 m a.s.l., stretching from Riobamba to the border with Peru, a bird-flight distance of 600 km, it is very likely that the modeling concept can be used for the prediction of the runoff in most, if not all, of the micro-catchments in this region.