Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / The study illustrates the current ecological integrity of the Diep River system, based on the recent river health assessment using the South African Scoring System version 5 (2000-2003) and the water quality data (1996-2002). Some of the major land-use impacts on the river system are highlighted.

Karst aquifers are characterized by highly conductive conduit flow paths embedded in a less conductive fissured and fractured matrix resulting in strong permeability contrasts with structured heterogeneity and anisotropy. Groundwater storage occurs predominantly in the fissured matrix. Hence, most karst models assume quasi steady-state flow in conduits neglecting conduit associated drainable storage (CADS). The concept of CADS considers storage volumes, where karst water is not part of the active flow system but rather hydraulically connected to conduits (for example karstic voids and large fractures). The disregard of conduit storage can be inappropriate when direct water abstraction from karst conduits occurs, e.g. large scale pumping. In such cases, CADS may be relevant. Furthermore, the typical fixed head boundary condition at the karst outlet can be inadequate for water abstraction scenarios because unhampered water inflow is possible. The objective of this paper is to analyze the significance of CADS and flow-limited boundary conditions on the hydraulic behavior of karst aquifers in water abstraction scenarios. To this end, the numerical hybrid model MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is enhanced to account for CADS. Additionally, a fixed-head limited-flow (FHLQ) boundary condition is added that limits inflow from constant head boundaries to a user-defined threshold. The affect and proper functioning of these modifications is demonstrated by simplified model studies. Both enhancements, CAD storage and the FHLQ boundary, are shown to be useful for water abstraction scenarios within karst aquifers. An idealized representation of a large-scale pumping test in a karst conduit is used to demonstrate that the enhanced CFPM1 is potentially able to adequately represent water abstraction processes in both the conduits and the matrix of real karst systems.

This thesis deals with the problem of water consumption in European Union and ways to overcome its excessive abstraction. The aim is to analyze whether the current abstraction in each area is sustainable in the future, and if there is any possible way how to ensure this sustainability. This work is based on the information about the development of abstraction in different sectors, changes in the amount of water that will be caused by global warming and the data on the current technical possibilities of obtaining water. The first section explains the concept of sustainable development and clarifies why the water consumption is excessive. The second chapter deals with the quantity of water and its resources, including alternative resources. The third chapter describes the water abstraction and the potential for savings. The last part focuses on policies and measures to ensure sustainable water abstraction.

Un paradigme émergent prédit que les perturbations influencent les processus qui déterminent l'organisation des communautés. L'assèchement des rivières (disparition complète d'eau de surface pour une durée déterminée) est une perturbation naturelle affectant les cours d'eau dans de nombreuses régions du monde. De plus en plus de cours d'eau pérenne s'assèchent en réponse aux changements globaux. Toutefois, l'effet de ces assèchements sur les communautés aquatiques et les processus impliqués dans leur résilience restent mal quantifié et mal compris. A travers quatre études allant de suivis de terrain à des expérimentations in-situ et des mésocosmes en laboratoire, une résilience exceptionnelle des communautés d'invertébrés a été mesurée dans huit rivières alluviales. La zone hyporhéique semble être la principale source de recolonisation expliquant la forte résilience de ces communautés. En laboratoire, l'augmentation de la température et de la compétition intra-spécifique entraine une migration de Gammarus pulex dans la zone hyporhéique. L'augmentation de la profondeur de la zone hyporhéique lors d'assèchements pourrait réduire la résilience et avoir des effets sur les fonctions de l'écosystème (décomposition de litière). Ces résultats montrent que les assèchements n'ont pas toujours des effets sévères sur les communautés d'invertébrés des rivières alluviales qui semblent même très résilientes. La zone hyporhéique joue un rôle primordial dans la résilience des communautés des cours d'eau. Un accent devrait être mis sur la protection de la zone hyporhéique dans les rivières alluviales afin de préserver cette capacité de résilience face aux changements globaux / Understanding community response to disturbance is essential to identifying processes that determine their assembly and to predicting the future effects of climate change on biodiversity and ecosystem functions. Drying (complete loss of surface water) is a natural disturbance affecting 50% of rivers worldwide and is occurring more in perennial rivers due to climate change. However, its effects on aquatic invertebrate communities and the underlying processes contributing to their resilience (i.e. return to pre-drying or undisturbed levels) have not been well quantified. Using 4 congruous field and mesocosm experiments to quantify community resilience and identify its primary sources in environmentally harsh alluvial rivers. First, I found communities in 8 alluvial rivers were highly resilient to moderate and severe drying. Second, I showed that the hyporheic zone (saturated interstitial sediments) can be the primary source of colonists, promoting high community resilience. Third, I found high water temperature and intraspecific competition caused Gammarus pulex, a common benthic detritivore, to migrate into the hyporheic zone. Fourth, I found increasing depth to the water table diminished the hyporheic zone’s role as a source of colonists by reducing survival of G. pulex. My results support an emerging concept that harsh ecosystems are highly resilient and indicate that the effects of drying on biodiversity and ecosystem functions could vary across river systems. In alluvial rivers, the hyporheic zone can contribute strongly to community resilience and management should focus on protecting and restoring vertical connectivity to maximize resilience to climate change

Karst aquifers are characterized by highly conductive conduit flow paths embedded in a less conductive fissured and fractured matrix resulting in strong permeability contrasts with structured heterogeneity and anisotropy. Groundwater storage occurs predominantly in the fissured matrix. Hence, most karst models assume quasi steady-state flow in conduits neglecting conduit associated drainable storage (CADS). The concept of CADS considers storage volumes, where karst water is not part of the active flow system but rather hydraulically connected to conduits (for example karstic voids and large fractures). The disregard of conduit storage can be inappropriate when direct water abstraction from karst conduits occurs, e.g. large scale pumping. In such cases, CADS may be relevant. Furthermore, the typical fixed head boundary condition at the karst outlet can be inadequate for water abstraction scenarios because unhampered water inflow is possible. The objective of this paper is to analyze the significance of CADS and flow-limited boundary conditions on the hydraulic behavior of karst aquifers in water abstraction scenarios. To this end, the numerical hybrid model MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is enhanced to account for CADS. Additionally, a fixed-head limited-flow (FHLQ) boundary condition is added that limits inflow from constant head boundaries to a user-defined threshold. The affect and proper functioning of these modifications is demonstrated by simplified model studies. Both enhancements, CAD storage and the FHLQ boundary, are shown to be useful for water abstraction scenarios within karst aquifers. An idealized representation of a large-scale pumping test in a karst conduit is used to demonstrate that the enhanced CFPM1 is potentially able to adequately represent water abstraction processes in both the conduits and the matrix of real karst systems.

Human related activities have influenced the rivers of the southern Western Cape since as early as the 1700’s. As there is no detailed information available on ecological status of the Holsloot River, a tributary of the Breede River, this study aimed to gain insight into the effect of impacts associated with human activities on the habitat integrity of this river. The study intended to understand how seasonal changes, catchment characteristics and events are reflected in the ecological status of habitats along the river by applying bio-monitoring and river health measurements at selected sites in the upper, middle and lower reaches of the Holsloot River and compare the results to that of an undisturbed reference site. Results obtained in this study are compared with data gathered in 2008/2009 to determine if the ecological status of the river had changed in the period between the two sampling times. The study included assessment of the ecological status of the river based on standard bio-monitoring protocol (SASS5, IHI, IHAS and VEGRAI) as well as in situ water quality analysis (pH, dissolved oxygen, electrical conductivity and total dissolved solids). The construction of the instream Stettynskloof Dam changed the configuration of the riparian zone and river channel in the upper catchment area. Agricultural- and other human related activities, with consequent water abstraction, non-point-source pollution, loss of riparian vegetation, as well as dense stands of alien invader plants influence flow patterns and affects river ecology, especially in the dry summer months. Providing sufficient stream flow and adequate water levels, human related activities can create a larger variety of habitat types available that can support larger biodiversity and higher productivity. The level of inundation and stream flow, influenced by water abstraction as well as irrigation return-flow from extensive drainage systems especially in the dry months, contribute to the loss of biodiversity in the middle and lower reaches of the river. Where the upper reaches of the river are largely natural with few modifications, the habitat integrity deteriorates in the middle reaches so much so that ecosystem functioning are collectively impaired in lower reaches due to human related impacts. Sensitive macro-invertebrates found at lower seriously impacted parts of the river however, were in all probability washed down from lower impacted upstream habitats and may expectedly be able to again occupy habitats downstream if water quality and habitat availability improves. / Environmental Sciences / M. Sc. (Environmental Science)

Human related activities have influenced the rivers of the southern Western Cape since as early as the 1700’s. As there is no detailed information available on ecological status of the Holsloot River, a tributary of the Breede River, this study aimed to gain insight into the effect of impacts associated with human activities on the habitat integrity of this river. The study intended to understand how seasonal changes, catchment characteristics and events are reflected in the ecological status of habitats along the river by applying bio-monitoring and river health measurements at selected sites in the upper, middle and lower reaches of the Holsloot River and compare the results to that of an undisturbed reference site. Results obtained in this study are compared with data gathered in 2008/2009 to determine if the ecological status of the river had changed in the period between the two sampling times. The study included assessment of the ecological status of the river based on standard bio-monitoring protocol (SASS5, IHI, IHAS and VEGRAI) as well as in situ water quality analysis (pH, dissolved oxygen, electrical conductivity and total dissolved solids). The construction of the instream Stettynskloof Dam changed the configuration of the riparian zone and river channel in the upper catchment area. Agricultural- and other human related activities, with consequent water abstraction, non-point-source pollution, loss of riparian vegetation, as well as dense stands of alien invader plants influence flow patterns and affects river ecology, especially in the dry summer months. Providing sufficient stream flow and adequate water levels, human related activities can create a larger variety of habitat types available that can support larger biodiversity and higher productivity. The level of inundation and stream flow, influenced by water abstraction as well as irrigation return-flow from extensive drainage systems especially in the dry months, contribute to the loss of biodiversity in the middle and lower reaches of the river. Where the upper reaches of the river are largely natural with few modifications, the habitat integrity deteriorates in the middle reaches so much so that ecosystem functioning are collectively impaired in lower reaches due to human related impacts. Sensitive macro-invertebrates found at lower seriously impacted parts of the river however, were in all probability washed down from lower impacted upstream habitats and may expectedly be able to again occupy habitats downstream if water quality and habitat availability improves. / Environmental Sciences / M. Sc. (Environmental Science)