Arid and semiarid river systems in Western Queensland, Australia, are characterized by the unpredictable and highly variable nature of their hydrological regimes as a result of the episodic nature of rain events in the region. These dryland rivers typically experience episodic floods and extremely low or no flow periods. During low or no flow periods, water persists only in relatively wide and deep sections of the river channels, which are called 'waterholes'. These isolated waterholes serve as refugia for aquatic species during protracted intervals between floods. In such discontinuous riverine habitat, dispersal of freshwater species may be achieved only during wet seasons, when water is flowing in rivers and the nearby floodplains. Obligate aquatic species occur in habitats that represent discrete sites surrounded by inhospitable terrestrial landscapes. Thus, movements are very much limited by the physical nature and arrangement of the riverine system. In addition, the distribution of a species may be also largely dependent on historical events. Landscape and river courses continually change over geological time, often leaving distinct phylogenetic 'signatures', useful in reconciling species' biology with population connectivity and earth history. The main aim of this study was to resolve the relative importance of contemporary and historical processes in structuring populations of two freshwater species in Western Queensland river systems. To address this aim, a comparative approach was taken in analysing patterns of genetic variation of two freshwater invertebrates: a snail (Notopala sublineata) and a prawn (Macrobrachium australiense). Mitochondrial sequences were used for both the species. In addition, allozyme and microsatellites markers were employed for N. sublineata. These species have similar distributions in Western Queensland region, although N. sublineata appears to be extinct in some catchments. M. australiense is thought to have good dispersal abilities due to a planktonic larval phase in its life cycle and good swimming capabilities, whereas N. sublineata is thought to have limited dispersal abilities, because of its benthic behaviour and because this species is viviparous. It was hypothesised that these freshwater invertebrates, would display high levels of genetic structure in populations, because physical barriers represented by terrestrial inhospitable habitat, are likely to impede gene flow between populations inhabiting isolated river pools. Genetic data for the two species targeted in this study supported this hypothesis, indicating strong population subdivision at all spatial scales investigated (i.e. between and within catchments). This suggests that contemporary dispersal between isolated waterholes is relatively restricted, despite the potential good dispersal abilities of one of the species. It was hypothesised that levels of gene flow between populations of aquatic species were higher during the Quaternary (likely movements of individuals across catchment boundaries) and that they have been isolated relatively recently. There is evidence that historically gene flow was occurring between populations, suggesting that episodic dispersal across catchment boundaries was likelier in the past. Episodic historical movements of aquatic fauna were facilitated by higher patterns of river connectivity as a result of the climate changes of the Pleistocene. Because the two species targeted in this study exhibit analogous spatial patterns of evolutionary subdivision it is likely that they have a shared biogeographic history. The unpredictable flow regime of rivers in Western Queensland is likely to have considerable effects on the genetic diversity of aquatic populations. First, if populations of obligate freshwater organisms inhabiting less persistent waterholes are more likely to experience periodic bottlenecks than those inhabiting more persistent ones, they would be expected to have lower levels of genetic diversity. Second, if populations inhabiting less persistent waterholes periodically undergo local extinction with subsequent recolonisation, there should be higher levels of genetic differentiation among them, due to the founder effects, than among those populations inhabiting more persistent waterholes. Contrary to the first prediction, the observed levels of genetic diversity in both N. sublineata and M. australiense were high in both more persistent and less persistent waterholes. There was no tendency for genetic diversity to be lower in less persistent than in more persistent waterholes. However, when Cooper waterholes were ranked in order of persistence, positive correlation between water persistence time in waterholes and genetic diversity was detected in N. sublineata but not in M. australiense. Contrary to the second prediction, highly significant genetic differentiation was found among populations from both less persistent and more persistent waterholes. This indicates that not only populations from less persistent but also those from more persistent waterholes were very dissimilar genetically. This study demonstrated the importance of both contemporary and historical processes in shaping the population structure of obligate freshwater species in Western Queensland river systems. It has indicated that contemporary movements of freshwater species generally are extremely limited across the region, whereas episodic dispersal across catchment boundaries was possible during the Pleistocene, due to different patterns of river connectivity.

One of the major problems for the implementation of water resources planning and management in arid and semi-arid environments is the scarcity of hydrological data and, consequently, research studies. In this thesis, the hydrology of dryland river systems was analyzed and a semi-distributed hydrological model and a forecasting approach were developed for flow transmission processes in river-systems with a focus on semi-arid conditions. Three different sources of hydrological data (streamflow series, groundwater level series and multi-temporal satellite data) were combined in order to analyze the channel transmission losses of a large reach of the Jaguaribe River in NE Brazil. A perceptual model of this reach was derived suggesting that the application of models, which were developed for sub-humid and temperate regions, may be more suitable for this reach than classical models, which were developed for arid and semi-arid regions. Summarily, it was shown that this river reach is hydraulically connected with groundwater and shifts from being a losing river at the dry and beginning of rainy seasons to become a losing/gaining (mostly losing) river at the middle and end of rainy seasons. A new semi-distributed channel transmission losses model was developed, which was based primarily on the capability of simulation in very different dryland environments and flexible model structures for testing hypotheses on the dominant hydrological processes of rivers. This model was successfully tested in a large reach of the Jaguaribe River in NE Brazil and a small stream in the Walnut Gulch Experimental Watershed in the SW USA. Hypotheses on the dominant processes of the channel transmission losses (different model structures) in the Jaguaribe river were evaluated, showing that both lateral (stream-)aquifer water fluxes and ground-water flow in the underlying alluvium parallel to the river course are necessary to predict streamflow and channel transmission losses, the former process being more relevant than the latter. This procedure not only reduced model structure uncertainties, but also reported modelling failures rejecting model structure hypotheses, namely streamflow without river-aquifer interaction and stream-aquifer flow without groundwater flow parallel to the river course. The application of the model to different dryland environments enabled learning about the model itself from differences in channel reach responses. For example, the parameters related to the unsaturated part of the model, which were active for the small reach in the USA, presented a much greater variation in the sensitivity coefficients than those which drove the saturated part of the model, which were active for the large reach in Brazil. Moreover, a nonparametric approach, which dealt with both deterministic evolution and inherent fluctuations in river discharge data, was developed based on a qualitative dynamical system-based criterion, which involved a learning process about the structure of the time series, instead of a fitting procedure only. This approach, which was based only on the discharge time series itself, was applied to a headwater catchment in Germany, in which runoff are induced by either convective rainfall during the summer or snow melt in the spring. The application showed the following important features: • the differences between runoff measurements were more suitable than the actual runoff measurements when using regression models; • the catchment runoff system shifted from being a possible dynamical system contaminated with noise to a linear random process when the interval time of the discharge time series increased; • and runoff underestimation can be expected for rising limbs and overestimation for falling limbs. This nonparametric approach was compared with a distributed hydrological model designed for real-time flood forecasting, with both presenting similar results on average. Finally, a benchmark for hydrological research using semi-distributed modelling was proposed, based on the aforementioned analysis, modelling and forecasting of flow transmission processes. The aim of this benchmark was not to describe a blue-print for hydrological modelling design, but rather to propose a scientific method to improve hydrological knowledge using semi-distributed hydrological modelling. Following the application of the proposed benchmark to a case study, the actual state of its hydrological knowledge and its predictive uncertainty can be determined, primarily through rejected hypotheses on the dominant hydrological processes and differences in catchment/variables responses. / Die Bewirtschaftung von Wasserressourcen in ariden und semiariden Landschaften ist mit einer Reihe besonderer Probleme konfrontiert. Eines der größten Probleme für die Maßnahmenplanung und für das operationelle Management ist der Mangel an hydrologischen Daten und damit zusammenhängend auch die relativ kleine Zahl wissenschaftlicher Arbeiten zu dieser Thematik. In dieser Arbeit wurden 1) die grundlegenden hydrologischen Bedingungen von Trockenflusssystemen analysiert, 2) ein Modellsystem für Flüsse unter semiariden Bedingungen, und 3) ein nichtparametrisches Vorhersage-verfahren für Abflussvorgänge in Flüssen entwickelt. Der Wasserverlust in einem großen Abschnitt des Jaguaribe Flusses im nordöstlichen Brasilien wurde auf Basis von Daten zu Abflussraten, Grundwasserflurabstände und mit Hilfe multitemporaler Satellitendaten analysiert. Dafür wurde zuerst ein konzeptionelles hydrologisches Modell über die Mechanismen der Transferverluste in diesem Abschnitt des Trockenflusses erstellt. Dabei ergab sich, dass der Flussabschnitt mit dem Grundwasser hydraulisch verbunden ist. Der Flussabschnitt weist in der Trockenenzeit und am Anfang der Regenzeit nur Wasserverlust (Sickerung) zum Grundwasser auf. Im Laufe der Regenzeit findet auch ein gegenseitiger Austausch vom Grundwasser mit dem Flusswasser statt. Aufgrund dieser hydraulischen Kopplung zwischen Flusswasser und Grundwasser sind für diesen Flussabschnitt hydrologische Modellansätze anzuwenden, die generell für gekoppelte Fluss-Grundwassersysteme, v.a. in feuchtgemäßigten Klimaten, entwickelt wurden. Es wurde ein neuartiges hydrologisches Simulationsmodell für Transferverluste in Trockenflüssen entwickelt. Dieses Modell ist für unterschiedliche aride und semiaride Landschaften anwendbar und hat eine flexible Modellstruktur, wodurch unterschiedliche Hypothesen zur Relevanz einzelner hydrologische Prozesse getestet werden können. Es wurde für den zuvor genannten großen Abschnitt des Jaguaribe Flusses im nordöstlichen Brasilien und für einen kleinen Flussabschnitt im „Walnut Gulch Experimental Watershed“ (WGEW) in Arizona, Südwest-USA, angewendet. Für die eine prozess-orientierte Simulation von Abflussbedingungen und Transferverlusten im Einzugsgebiet des Jaguaribe hat sich gezeigt, dass die am besten geeignete Modellstruktur sowohl den Austausch zwischen Flusswasser und Grundwasser (senkrecht zur Fließrichtung des Flusses) als auch die parallel zum Fluss verlaufende Grundwasserströmung enthält. Die Simulationsexperimente mit unterschiedlichen Modellstrukturen („Hypothesentest“) reduzierte nicht nur die Modellstrukturunsicherheit, sondern quantifizierte auch die Qualität der Modellergebnisse bei folgenden Varianten der Modellstruktur: a) Abflluss im Fluss ohne Interaktion mit dem Grundwasser (keine Transferverluste) und b) Interaktion zwischen Fluss und Grundwasser ohne parallelen Grundwasserstrom zum Flussstrom. Durch die Anwendung auf die beiden unterschiedlichen Trockenflusssysteme wurden neue Erkenntnisse über die Sensitivität des Modells unter verschiedenen Bedingungen erworben. Beispielsweise waren die Parameter der ungesättigten Zone, die von hoher Relevanz für den kleinen Flussabschnitt im WGEW waren, viel sensitiver als die Parameter der gesättigten Zone, die besonders relevant für den Jaguaribe Flussabschnitt in Brasilien waren. Die Ursache für diese sehr unterschiedliche Sensitivität liegt darin, dass beim WGEW das Flusswasser nur mit der ungesättigten Zone in Kontakt steht, da sich in diesem Gebiet, welche im Vergleich zur Jaguaribe-Region noch deutlich trockener ist, kein Grund-wasserleiter bildet. Letztlich wurde ein nicht-parametrisches Verfahren, zur Simulation der deterministischen Evolution und stochastischen Fluktuation der Abflussdynamik entwickelt. Im Unterschied zu prozessbasiertem Modellsystemen basiert dieses Verfahren nicht auf Modellkalibrierung sondern auf einem Lernprozess, basierend auf Zeitreihendaten. Als Anwendungsbeispiel wurde ein mesoskaliges Einzugsgebiet im Erzgebirge, NO-Deutschland gewählt, in dem starke Abflussereignisse entweder durch konvektive Niederschlagsereignisse oder durch Schneeschmelze generiert werden. Die folgenden wichtigsten Ergebnisse wurden erzielt: • Regressionsmodellansätze basierend auf den zeitlichen Änderungen der Abflüsse liefern bessere Ergebnisse gegenüber Ansätzen basierend auf direkten Abflussdaten; • mit zunehmendem Vorhersagehorizont wandelt sich das hydrologische System von einem mit Zufallsanteilen verrauschten dynamischen System zu einem linearen probabilistischen Zufallsprozess; • Bei zunehmendem Abfluss (ansteigenden Ganglinie) erfolgt meist eine Abflussunterschätzung, bei abnehmendem Abfluss (fallende Ganglinie) erfolgt meist eine Abflussüberschätzung. Dieses nichtparametrische Verfahren ergibt im Vergleich mit einem prozess-orientierten und flächenverteilten hydrologischen Hochwasservorhersagemodell bis zu einem Vorhersagezeitraum von 3 Stunden Ergebnisse von vergleichbar guter Qualität. Letztendlich wurde ein Vorgehen bzgl. künftiger Forschungen zu hydrologischer Modellierung vorgeschlagen. Das Ziel dabei war ein wissenschaftliches Verfahren zur Verbesserung des hydrologischen Wissens über ein Einzugsgebiet. Diese Verfahren basiert auf einem Hypothesentest zu den relevanten hydrologischen Prozessen und der Untersuchung der Sensitivitäten der hydrologischen Variablen bei unterschiedlichen Einzugsgebieten.

The savannas of southern Africa are a highly variable and globally-important biome supporting rapidly-expanding human populations, along with one of the greatest concentrations of wildlife on the continent. Savannas occupy a fifth of the earth's land surface, yet despite their ecological and economic significance, understanding of the complex couplings and feedbacks that drive spatiotemporal patterns of change are lacking. In Chapter 1 of my dissertation, I discuss some of the different theoretical frameworks used to understand complex and dynamic changes in savanna structure and composition. In Chapter 2, I evaluate spatial drivers of water quality declines in the Chobe River using spatiotemporal and geostatistical modeling of time series data collected along a transect spanning a mosaic of protected, urban, and developing urban land use. Chapter 3 explores the complex couplings and feedbacks that drive spatiotemporal patterns of land cover (LC) change across the Chobe District, with a particular focus on climate, fire, herbivory, and anthropogenic disturbance. In Chapter 4, I evaluated the utility of Distance sampling methods to: 1) derive seasonal fecal loading estimates in national park and unprotected land; 2) provide a simple, standardized method to estimate riparian fecal loading for use in distributed hydrological water quality models; 3) answer questions about complex drivers and patterns of water quality variability in a semi-arid southern African river system. Together, these findings have important implications to land use planning and water conservation in southern Africa's dryland savanna ecosystems. / Ph. D.