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- Senkondo, William, 1982-
(författare)
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Modelling water resources despite data limitations in Tanzania’s Kilombero Valley
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water is a vital resource for survival on the Earth. Sustainable management of water resources is therefore required for the wellbeing of present and future generations. A cornerstone of water resources management is scientific guidance supported by relevant data (in terms of quantity and quality). Most developing regions, where such guidance is crucial due to the intimate connection between natural resources and livelihoods, unfortunately face data limitations. This thesis aims to develop systematic approaches for informing water resources management in data limited regions. Specifically, this work targets Tanzania’s Kilombero Valley (KV) basin as an exemplar of a data limited region undergoing social-economic development through expansion and intensification of agriculture and other water-related interventions. Through a synthesis of lessons learned from the ongoing evolution of hydrological modelling development for water resources management in the Eastern Africa, several promising approaches were identified that could potentially be robust despite data limitations across the region. Putting these approaches into practice, recession analysis based on non-continuous discharge data in conjunction with estimations of the actual evapotranspiration (ET) using remote sensing techniques provided a basis to improve process understanding and help characterize the hydrological systems in the KV basin. This understanding translated into more-informed parameter estimation and improved accuracy when integrated into the development of a hydrological modelling framework using the Soil and Water Assessment Tool (SWAT) model. The modeling framework established for KV has potential to be used as tool for estimating impacts of water resources management strategies relative to future anthropogenic pressures and climatic changes. What is even more promising, is the possibility to derive scientific guidance to assist water resources management in a data limited region through implementation of an integrated workflow which employs state-of-the-science approaches. The methodological framework for model development adopted in this thesis could be applied in any data limited region facing similar challenges as those of the KV basin.
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| 2. |
- Yu, Qian, 1989-
(författare)
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α-Cell signalling in glucose-regulated glucagon secretion
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glucagon is a blood glucose-elevating hormone released from α-cells in the islets of Langerhans during hypoglycaemia. Glucagon is critical for glucose homeostasis and inappropriate regulation of its secretion underlies both impaired counter-regulation of hypoglycaemia and chronic hyperglycaemia in diabetes patients. The mechanisms by which glucose controls glucagon secretion are poorly understood, but have been suggested to involve both direct effects of the sugar on α-cells and indirect effects mediated by paracrine factors released within the islet, including insulin and gamma-hydroxybutyrate (GHB) from β-cells, and somatostatin from δ-cells. This thesis addresses the role of the intracellular messengers ATP, Ca2+ and cAMP in glucose-regulated glucagon secretion. Various fluorescence microscopy techniques were used to monitor changes of these messengers in single, dispersed α-cells and those in situ within intact islets, and glucagon secretion from islets was measured with an immunoassay. Glucose induced elevations of α-cell ATP, which were smaller and showed a left-shifted concentration-dependence compared to those in β-cells, consistent with α-cells being less dependent on oxidative metabolism and optimized for sensing hypoglycaemia. α-Cells showed Ca2+ oscillations with little glucose dependence. Surprisingly, these oscillations became synchronized in phase with Ca2+ oscillations in β-cells at high glucose. Since Ca2+ is a main trigger of exocytosis in both cell types, and since insulin and glucagon secretion is pulsatile in opposite phase, the results indicate that factors other than Ca2+ are more important for shaping glucagon secretion. Consistent with a key role of cAMP for the regulation of glucagon release, the concentration of the messenger was relatively high in α-cells at low glucose concentrations, and elevations of glucose suppressed cAMP in parallel with glucagon secretion. This effect was independent of paracrine signalling from insulin and somatostatin. The glucose-induced suppression of glucagon secretion was prevented by cAMP-elevating agents and mimicked by inhibitors of protein kinase A. GHB lacked effects both on Ca2+, cAMP and glucagon secretion from mouse islets, but tended to stimulate glucagon secretion by a somatostatin-receptor-dependent mechanism in human islets. The data indicate that GHB is not an inhibitor of glucagon secretion and that α-cell-intrinsic glucose sensing involves signalling via cAMP and protein kinase A.
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