La prévision d'étiage à long terme est l'une des questions émergentes en hydrologie en raison de la demande croissante en eau en période sèche. Des prévisions fiables de débits à longue échéance (quelques semaines à quelques mois à l'avance) peuvent améliorer la gestion des ressources en eau et de ce fait l'économie de la société et les conditions de vie aquatique. Les études limitées sur les étiages dans la littérature nous a conduit à traiter certaines des questions existantes sur l'hydrologie des étiages, principalement sur la simulation et la prévision des étiages. Notre objectif final de développer une approche d'ensemble pour la prévision à long terme des étiages se décline en plusieurs étapes préalables, telles que la caractérisation des étiages, l'évaluation de mesures existantes d'efficacité des simulations des modèles, le développement d'une version améliorée d'un modèle de simulation des étiages, et enfin l'intégration d'une approche de prévision d'ensemble. Un ensemble de bassins distribués partout en France avec une variété de conditions hydro-météorologiques a été utilisé pour l'évaluation des modèles. Cet échantillon de données a d'abord été analysé et les étiages ont été caractérisés en utilisant divers indices. Notre objectif de mieux évaluer les simulations des étiages par les modèles a conduit à proposer un critère basé sur le critère de Nash-Sutcliffe, calculé sur l'inverse des débits pour mettre davantage de poids sur les erreurs sur les très faibles débits. Les résultats montrent que ce critère est mieux adapté à l'évaluation des simulations des étiages que d'autres critères couramment utilisés..Une analyse de sensibilité structurelle a ensuite été menée pour développer une structure de modèle améliorée pour simuler les étiages. Des modèles couramment utilisés ont été choisis ici comme modèles de base pour commencer l'analyse de sensibilité. Le modèle développé, GR6J, atteint de meilleures performances à la fois sur les faibles et les hauts débits par rapport aux autres modèles existants testés. En raison de la complexité du processus pluie-débit et de l'incertitude liée aux conditions météorologiques futures, nous avons développé une approche d'ensemble pour émettre des prévisions et quantifier les incertitudes associées. Ainsi l'approche d'ensemble fournit une gamme de valeurs futures de débits sur la plage de prévision. Ici, la climatologie a été utilisée pour fournir les scénarios météorologiques en entrée du modèle pour réaliser les prévisions. Pour réduire le niveau d'incertitude lié au modèle hydrologique, des combinaisons variées de procédures de mise à jour et de corrections de sortie ont été testées. Une approche directe, similaire à ce qui peut être fait pour la prévision des crues, a été sélectionnée comme la plus efficace. Enfin, des essais ont été réalisés pour améliorer la qualité des prévisions sur les bassins influencés par les barrages, en tenant compte des variations de stockage dans les barrages amont. Testée sur les bassins de la Seine et de la Loire, l'approche a donné des résultats mitigés, indiquant le besoin d'analyses complémentaires. / Long-term stream low-flow forecasting is one of the emerging issues in hydrology due to the escalating demand of water in dry periods. Reliable long-lead (a few weeks to months in advance) streamflow forecasts can improve the management of water resources and thereby the economy of the society and the conditions for aquatic life. The limited studies on low flows in the literature guided us to address some of the existing issues in low-flow hydrology, mainly on low-flow simulation and forecasting. Our ultimate aim to develop an ensemble approach for long-term low-flow forecasting includes several prior steps such as characterisation of low flows, evaluation of some of the existing model's simulation efficiency measures, development of a better model version for low-flow simulation, and finally the integration of an ensemble forecasting approach. A set of catchments distributed over France with various hydrometeorological conditions are used for model evaluation. This data set was first analysed and low flows were characterized using various indices. Our objective to better evaluate the models' low-flow simulation models resulted in the proposition of a criterion based on the Nash-Sutcliffe criterion, but calculated on inverse flows to put more weight on the errors on extreme low flows. The results show that this criterion is better suited to evaluate low-flow simulations than other commonly used criteria. Then a structural sensitivity analysis was carried out to develop an improved model structure to simulate stream low flows. Some widely used models were selected here as base models to initiate the sensitivity analysis. The developed model, GR6J, reaches better performance in both low- as well as high-flow conditions compared to the other tested existing models. Due to the complexity of rainfall-runoff processes and the uncertainty linked to future meteorological conditions, we developed an ensemble modelling approach to issue forecasts and quantify their associated uncertainty. Thus the ensemble approach provides a range of future flow values over the forecasting window. Here observed (climatological) rainfall and temperature were used as meteorological scenarios fed the model to issue the forecasts. To reduce the level of uncertainty linked to the hydrological model, various combinations of simple updating procedures and output corrections were tested. A straightforward approach, similar to what can be done for flood forecasting, was selected as it proved the most efficient. Last, attempts were made to improve the forecast quality on catchments influenced by dams, by accounting for the storage variations in upstream dams. Tested on the Seine and Loire basins, the approach showed mixed results, indicating the need for further investigations.

An understanding of the dominant processes controlling streamwater chemistry is critical for the development of a regional water quality model. The relative importance of a variety of catchment characteristics in determining streamwater chemistry in the English Lake District is investigated in this thesis. Fifty-five streams were sampled on a bimonthly basis over the period May 1996 through March 1997. Rock samples were analysed using X-ray fluorescence analysis. The major- and trace element geochemical data was used to classify the suite into six rock types. The geochemical data was also used to establish weathering patterns, which suggested that greywackes and lithic arenites weather the easiest, andesites and dacites exhibit heterogeneous weathering and the metamorphosed slate and granite are the most resistant to weathering. Forty-one (75%) of the streams can be considered sensitive to acidification on the basis of their alkalinity and thirty-eight (69%) can be considered sensitive to acidification on the basis of their calcium concentrations. Statistical analyses showed that flow-weighted concentrations of alkalinity and base cations were lowest in the catchments with resistant bedrock, thin or peaty soils, at high altitudes or receiving relatively high loads of sulphur and nitrogen deposition. A multiple regression model incorporating some of these factors provided a fairly good approximation of alkalinity concentrations on a spatial (R2 value of 56%) and temporal scale (R2 value of 49%). The predicted alkalinity was within 50 Ileq rl of the observed (simulated) values for 77% of the sites. Although the model has a fairly good predictive capability, its spatial and temporal applicability outside the study area is an unknown quantity. To satisfy the needs of policy makers and the hydrological community, the model needs to predict alkalinity with a high degree of accuracy in a variety of study areas. This has not been tested as yet, however, the variables used in the final model are not unique to the Lake District or the 1990's and therefore the model may prove to be an extremely useful tool indeed.

Spatial and temporal trends of dissolved organic matter (DOM) were investigated in the Lower Kinabatangan River, Sabah, Malaysia over the period 2008-2012. The objectives were to: i. quantify DOM in areas of the catchment dominated by oil palm plantations; ii. characterise DOM quantity and quality in waters draining three contrasting land use types (oil palm plantations, secondary forests and coastal swamps); iii. characterise and interpret DOM quantity and quality in the main stem of the Kinabatangan river according to depth; and iv. infer differences in water movement through the catchment. Optical parameters, including fluorescence excitation-emission matrices (EEMs) and ultraviolet absorbance spectroscopy (UV-vis); and Parallel Factor Analysis were used throughout the investigation. The research comprised a preliminary catchment-wide study (225 samples) and concentrated fieldwork campaigns (510 samples). The results indicated the dominance of peaks C and M in waters from the oil palm plantations and coastal swamps respectively. The relative loss of terrestrial derived peaks could indicate progressive DOM degradation from the upper reaches towards the estuary. Results also showed DOM was transported back to the main river, as dominated by fluorescence index peak A/peak C, particularly in the coastal swamps. DOM characterisation with depth in the river, showed the dominance of peaks C and M (relative to terrestrial and microbial and/or photo-degradation processes) in waters near the riverbed.

Lakes play an important role in biosphere carbon dynamics. Though proportionally they constitute a small surface feature on the planet, in many cases lakes are subject to significant subsidies of organic material from their catchments. This input of allochthonous organic material, in addition to autochthonous organic material, has shown that lakes, particularly in temperate and boreal zones, can be heterotrophic systems and as such are net producers of CO2. Thus, understanding the magnitude of fluxes of carbon through these limnetic systems is important if their contribution to ecosystem / global carbon dynamics is to be elucidated. In this research two separate field campaigns were undertaken with the goal of understanding if, and exactly how significant secondary (bacterial) production utilising allochthonous carbon is to overall pelagic production in Loch Lomond, Scotland. Stable isotopic composition of dissolved inorganic carbon (DIC), dissolved oxygen (DO), dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), along with their respective concentrations, were measured in a temporal and spatial survey. Range in [DIC] and δ13CDIC was consistent with that predicted by the shifting balance between autotrophic and heterotrophic pathways. [DIC] peaked in the summer / autumn (0.27 ± 0.09 and 0.17 ± 0.05 mM, south and north basins respectively), reflecting a period when bacterial processing of allochthonous material is high, and thus so is CO2 production. This effect was more pronounced in the mesotrophic south basin of the lake, compared to the oligotrophic north. Surface waters in the south, middle and north basins were generally saturated in CO2 beyond atmospheric equilibrium and thus sources of CO2 to the atmosphere. δ13CDIC and δ18ODO exhibited seasonal and spatial variability, probably also a result of changing metabolic balance and inflow characteristics. Spring / summer peaks in δ13CDIC (-5.1‰ epilimnion maximum) are indicative of photosynthetic incorporation, and vice versa in the autumn / winter (-13‰ hypolimnion minimum) points towards respiratory dominance. δ18ODO is enriched during respiratory utilisation and peaks in the autumn / winter months. Depletion in δ13CDIC coupled to concurrent enrichment in δ18ODO observed with increasing depth (particularly during lake stratification) is assumed to again be a result of a shift in metabolic process dominance from autotrophic to heterotrophic (Myrbo and Shapley 2006). Spatial variability was consistent with the varying trophic states between basins, e.g., most enriched δ13CDIC was recorded in the more productive south basin compared to the middle or north. Dissolved organic carbon concentration also changed with position in the lake. Highest concentrations in the south basin were linked to a shallow gradient catchment, draining base rich soils and agricultural land, compared to the steep sloped, base-poor catchment in the north. The greater quantities of dissolved organic carbon in the south suggested that if bacterial processing of allochthonous material was significant it would likely be most prevalent in the south. During the spatial survey consistent and significant heterogeneity in DIC, DO and DOC was recorded. Although the same degree of variability may not be associated with other, more mophometrically / hydrologically simple lakes, this work has shown consideration of this possibility is advisable. The second field campaign used direct measurements of algal and bacterial productivity, using labelled stable isotope incorporation methods, to elucidate the balance between autotrophic and heterotrophic processes. Primary production (PP) followed a predictable seasonal pattern, peaking in the spring and remaining relatively high until autumn. During this period primary production generally exceeded bacterial production (BP) per litre. During the winter this pattern was reversed. Using integrated estimates of both PP and BP this work showed that BP exceeded PP in the pelagic zone for the majority of the year, and over much of the lake’s extent. Even in the epilimnion BP was regularly the more significant process through the water column, and thus it is concluded Loch Lomond is a heterotrophic system and a likely source of CO2 to the atmosphere. The PP: BP ratio ranged from 0.6 – 0.8 in the north basin, and 0.4 to 0.6 in the south. On average for the whole lake, bacterial production exceeded primary production by between 2,700 and 4,400 kg C day-1. In total it was estimated that PP processes approximately 970 tonnes of carbon per year and BP between 2,300 and 2,800 tonnes of carbon per year. The proportion of total pelagic production fuelled by bacterial utilisation of allochthonous carbon changed throughout the year. During peaks of PP in the spring and summer much of the bacterial carbon demand was met by autochthonous supply. During the autumn / winter allochthonous carbon utilisation dominated pelagic production and regularly contributed over 90% of total pelagic production. Combining estimated quantities of allochthonous carbon utilised in the north and south basins per m2 (the middle basin taken as an intermediate between the two) and combining it with GIS data on lake volume, the total quantity of terrestrially derived carbon processed in Loch Lomond was estimated at approximately 3,300 ± 2,100 kg Callo day-1. Both spatial and temporal surveys of natural abundance stable isotope ratios, along with concurrent measurements of algal and bacterial production, have provided substantial evidence for the importance of allochthonous carbon in Loch Lomond. Even minimum estimates imply a system dominated by bacterial production, fuelled by a proportionally high quantity of terrestrial material, thus producing excess CO2, and potentially fluxing CO2 to the atmosphere.

The research outlined in this thesis is concerned with the environmental aspects of groundwater re-establishment as a consequence of surface mining. No principal effects which have been identified as being detrimental to the restored land area are as follows; i). The vertical and horizontal displacements of backfill materials following restoration, and ii). The pollution of groundwater from contact with weathered rockfill materials. The research into settlement has attempted to classify the types of movement which may occur within a backfill mass, in particular the differential movements which are of great importance to the stability of proposed structures or surface drainage. The field results from 10 opencast mine sites are presented, 3 of which were instrumented for detailed field investigations. It has been shown that backfill movements do not necessarily show similar trends under similar conditions, and reasons for this are proposed. A variety of instrumentation schemes have been devised to examine backfill displacements, both vertically and horizontally. Permeability testing has been conducted at different horizons the backfill mass in order to locate the zones of collapse settlement due to groundwater recovery. A critical review of the instrumentation utilised in the investigations is presented, with suggestions for improvement. Investigations into groundwater pollution have been devoted to examining the qualities of groundwater flowing into British surface mines and evaluating its likely reactions with fill materials. An insight into general groundwater pollution and treatment techniques is presented together with a critical analysis of their applicability, to British conditions. An investigation into water qualities in each of the six geographical regions of the opencast mining industry of Great Britain is detailed. Finally some suggestions for future research areas are indicated.

No description available.

Detailed snow surveys were carried out in the Allt a Mharcaidh catchment on the western edge of the Cairngorm mountains during the winters of 1985/86,1986/87 and 1988/89. Snowpack data collected included depth, density, areal extent and water equivalent. From these data it was possible to determine seasonal patterns in snowpack behaviour and relate these to the initial snowpack water equivalent volume and timing of the snow accumulation and ablation. Using meteorological and flow data collected in the Mharcaidh by the Institute of Hydrology as part of the SWAP project simple linear regression relationships were determined. These indicated that the availability of detailed meteorological data did not improve the ability to simulate observed flow and that a successful regression could be established using simple and readily available data. Using this data temperature index models were developed and tested on the Mharcaidh. These showed that the mean daily temperature provided a better index of melt than more complex indices and that simple changes regarding the addition of a freezing level hindered the model performance despite being closer to reality than other assumptions made in the model. This suggested that the degree of complexity in the model has to be similar for all operations to obtain optimum results; having one particularly complex sub-model reduces the performance of the others. Two other types were tested on the Mharcaidh based on the layered structure developed by Martinec (1975) and Anderson's (1968) method using temperature and windspeed as an index to the energy changes at the snowpack boundary during rain-on--snow events. These again show that simple methods using readily available data can produce acceptable results and that increasing the complexity of the model does not produce a similar increase in performance. The three different models were then run on different datasets for different catchments and years. The dependence of Anderson's method on good quality data is highlighted suggesting that it is not as widely applicable as the other models. The level of performance for all models is related to the extent and depth of the snowpack indicating that further improvements may be necessary to the hydrological components of the model rather than the melt sub-model itself. The models were tested in simulated real time conditions on one dataset and, following this, guidelines for use in real time to predict snowmelt runoff are given.

The effect of climate on the fluvial system has long been investigated due the significant impact it can have on a river’s hydrological regime and fluvial processes. In recent years this interest has increased as global changes in climate are expected to bring more frequent high magnitude flood events globally and to North West Europe in particular. Despite the knowledge that the frequency and magnitude of floods is to increase, less is known about the geomorphological implications of this for river channels and where channel instability is likely to occur at both the river network and national scale. This is certainly the case in Scotland where increased flooding is expected and large floods have been abundant over the last two decades. To manage Scottish river catchments effectively in the future, in terms of hazard mitigation and nature conservation, river managers need to be able to predict not only how climate will impact flood magnitude and frequency in Scotland but the effect these changes will have on the internal dynamics of river channels in terms of erosion, sediment transport and deposition, and morphological dynamics. Such knowledge will ensure adequate measures are implemented to reduce fluvial risks to humans and to maintain and preserve valuable river habitats and linked species. In this thesis, several novel methods incorporating field, laboratory and GIS-based analysis, have been investigated as a means of predicting how climate change will affect channel stability in Scottish rivers and the implications of this for river management and river ecology. This includes (i) analysing the potential change in the frequency of geomorphologically-active flood flows with climate change; (ii) the use of stream power thresholds to predict changes in channel stability on a national scale with climate change; and (iii) using a Digital River Network developed using geospatial data to predict changes in the rate of bedload transfer and channel stability with climate change. Studies were undertaken on 13 different rivers across Scotland from north to south and east to west. vii As a case study of ecological implications, the thesis also examines how changes in habitat and stability of freshwater pearl mussels (Margaritifera margaritifera) may be altered by increased flooding. Predictions of the frequency of geomorphic activity, channel stability, rate of bedload transfer, and the stability of freshwater pearl mussel habitat with climate change are discussed along with the methods used to obtain these outcomes. The results all suggest an increase in the frequency and rate at which bedload is transferred through the river system and an increased frequency of flood flows resulting in greater channel instability. Morphological responses vary spatially with some river reaches experiencing greater increased erosion and transport potential than others. Climate change effects on the freshwater pearl mussel are: increased occasions of disturbance and transport downstream and the importance of specific populations in more stable environments for ensuring population recovery post flooding is highlighted. It is hoped that the methodologies developed for predicting changes in channel stability with climate change will provide useful screening tools to regulatory agencies which can be developed further to assist management decisions in the future which aim to reduce fluvial hazards and maintain good quality river environments for the species that inhabit it. The approaches used in this study allow for the identification of areas at high risk of morphological and ecological change, and the pro-active planning and management of sediment-related river management issues and nature conservation.

Cryptophytes are free-living unicellular algae which are important for the productivity and food chain Dynamics of temperate lakes. This study provides fundamental information on the ecophysiology of two freshwater cryptophytes of different cell size, mainly in terms of growth and related factors. This thesis comprises of six chapters, three of which describe light or light-and-temperature experiments with small-scale batch cultures (Chapters. 2 to 4), one depicts a larger scale laboratory experiment simulating natural conditions (Chapter 5) and the two last (Chapters 6 and 7) are based on short-term investigations in situ. The effects of light and temperature on nutrient-saturated growth and cellular composition (chlorophyll a, proteins, carbohydrates) were studied in batch cultures. With the help of mathematical models, the physiological basis for interspecific differences of growth response was determined (Chapter 2). The cryptophyte strain L315 appeared to be a cold-water species as its optimum temperature was ca. 19°C. The strain L485 was more adapted to warm-water conditions with its optimum of ca. 24.5 °C. In respect of their growth response to irradiance, L485 can be said to be a stenotopic and L315 a eurytopic strain, as L485 shows photoinhibition soon after saturation point, whereas L315 tolerates a much wider range of irradiance. The role of changes in cellular composition is discussed. In order to explain the observed growth differences the effects of light and temperature on gross photosynthesis, respiration and hence net productivity were studied (Chapter 3). The observed respiration/photosynthesis ratios were high, as in L485 and L315 respiration accounted for 17-77 % and 14-81 % of gross photosynthesis, respectively. Under optimum conditions the respiration/Pmax for L485 was 17 % and for L315 58 %. The response of cryptophytes to chromatic light was studied by means of quantitative epifluorescence microscopy and it was found that in comparison to blue-green algae cryptophytes L485 and L315 do not gain such great adaptational advantages in terms of growth by chromatic adaptation (Chapter 4). The modest role of chromatic adaptation is discussed. The role of diel vertical migrations (DVM) in the growth of cryptophytes was studied in 4 m tall experimental columns (Chapter 5). Results revealed that by migrating into cooler, nutrient rich. hypolimnion flagellated cryptophytes can increase their growth rate under conditions where resources (light and nutrients) are spatially separated for prolonged time periods. This study also emphasizes the need for more detailed DVM studies in situ. Finally, the pattern and timing of nuclear and cellular division in two Cryptomonas species in situ was studied by means of mitotic index technique (Chapter 6) and DNA quantification (Chapter 7). The nuclear division of Cryptomonas L485 (Chapter 6) appeared to be well phased, but as in this division pattern mitosis and cytokinesis were totally overlapping, it was impossible to calculate in situ growth rates. Field observations (Chapter 7) revealed that DNA quantification by means of epifluorescence microscopy is possible from a natural cryptophyte population, but as the Cryptomonas sp. population under scrutiny was not well phased, growth rate calculation could not be carried out. The survival strategies of Cryptophytes L485 and L315 in terms of r vs. K strategies are discussed in Chapter 8. It is pointed out that, although the habitats occupied by these strains as well as some of their morphological and physiological features indicate that L485 is probably a r-strategist and L315 a K-strategist, it is not possible to draw final conclusions on the basis of this study. Light and temperature, i.e. the factors mostly studied in this thesis, are presumably not the environmental factors of greatest selective importance for these cryptophytes in natural competitive situations.

Ecologically, the hyporheic zone (HZ) performs numerous roles within stream ecosystems (e.g. habitat, refugia from floods and droughts, nutrient cycling, pollution attenuation) with the dominant control on these various roles sediment composition. Recently, the body of literature on the role of sediment in the HZ has grown, though these studies rarely extend beyond the reach scale with little regional scale research undertaken in England and Wales. In this thesis, meio- and macrofaunal hyporheic assemblages at two depths (20cm and 50cm) across four geological regions (chalk – fine sediment, sandstone - fine to medium sediment and limestone – coarse sediment) two seasons (summer (n = 396) and winter (n = 192)) are described. The influence of recent glaciations (Devensian) on the distribution of stygobite fauna (summer (n = 192) and winter (n = 98)) is also considered. A reach scale experimental manipulation of sediment composition in the HZ of a highly dynamic, species rich and diverse study site (limestone) was also undertaken. I found the influence of glaciation on stygobite fauna still apparent in the two limestone areas with macrofaunal sized stygobite species rare or absent in both limestone areas. Meiofaunal sized stygobite fauna Antrobathynella stammeri (Crustacea: Syncarida) were recorded from the glaciated limestone site. These results suggest large stygobite fauna are rare or absent in the limestone areas of Northern England with meiofaunal stygobites possibly surviving in sub-glacial refugia. Stygobite fauna were abundant in southern England with alternative migratory routes north discussed (e.g. River Severn catchment and chalk aquifers). Geological regions had characteristic fauna with species richness and abundance of meio- and macrofauna high in the HZ of both limestone areas. Conversely, species richness and abundance was low in the chalk and sandstone HZ. The chalk HZ had a high abundance of macrofaunal sized Crustacea (Gammarus pulex) and low abundance of meiofaunal sized Crustacea (Copepoda). This suggested mechanical properties (burrowing) rather than morphology (body size and shape) was important in fine sediments, whereas in the limestone HZ morphology rather than mechanical properties was important. In the experimental study results were more intuitive with meiofauna abundant across all sediment treatments (fine, mixed, coarse and natural) with macrofauna abundant in sediment treatments containing a high proportion of coarse material. These results suggest Copepoda assume a greater role in ecological processes in fine sediment patches within a dynamic HZ, whereas when fine sediment dominates a system (e.g. chalk HZ) then the role of Copepoda is reduced. One implication could be the use of Copepoda as indicators of colmation and hydrologic exchange in the assessment of ecosystem health and give an indication of the refugial capacity of the HZ from projected high and low flow events in light of UK climate change forecasts.