Assessment of sustainablility of papyrus-based wetland water resources in Uganda

Abstract

Wetlands contribute up to 43.5% of the value of earthly natural biomes, yet they cover only 3% of the planet’s surface. The largest area of these wetlands, which is of international importance, is Africa, where they mainly occur as papyrus-dominated marshes. Studies on these wetlands seldom cover their flow regulation services, with none at the catchment scale. This has hindered their economic valuation and conservation. This study quantified their flow regulation service in a tropical catchment and linked its flow regime to its biologically relevant hydrologic attributes. Results show that papyrus wetlands are at least four times better at regulating quickflow than baseflow. Predictions at 2 and 4°C global warming levels (GWLs) indicate they will play critical roles in mitigating flood risks by lowering future mean flood magnitude and halving the average number of flood events in a year. However, the future mean flood duration is expected to increase. Their Environmental Flow Components (EFCs) can be broadly categorised into large floods, small floods, high flows, low (base) flows, and extreme low flows. These EFCs are significantly altered for the irrigated area to catchment area ratio greater than approximately 1:150 (i.e., irrigated area of 1,100 ha to catchment area of 1,680 km2). The result, however, is subject to uncertainty in hydrological model parameter estimation and flow simulation, mainly due to inherent errors in the satellite-based precipitation product used. Large-scale river water abstraction and land use change are mostly linked to agriculture and are the leading cause of wetland loss in the developing world. In the case of papyrus wetlands, lowland rice cultivation considerably alters the magnitude, duration, timing and rate of change of EFCs. These modified EFCs directly impact papyrus’s ability to reproduce (sexually and asexually), access groundwater during extreme low flows, and resist invasive species. In general, the findings in this study can help policymakers and authorities in papyrus-dominated catchments plan for the protection and conservation of papyri wetlands, a keystone species on which wetland biodiversity depends.