Seven streams, one of them permanent, were studied in western Oregon, USA. The research was designed to assess the value of summer-dry headwaters for conservation oriented landscape management. Streams were categorized primarily according to exposure (forest versus meadow sites) and secondarily according to flow duration (ephemeral = short-flow versus temporary = long-flow sites). Ephemeral streams have discontinuous flow and last less than three months annually. Temporary streams have continuous flow for more than five months each season. Ephemeral forest streams were highly efficient at filtering road-generated sediment. Uptake lengths for suspended sediment were short (36 m-105 m) at moderately elevated input concentrations. As a result of the filtration mechanism, filtration efficiency is expected to increase as annual flow duration decreases. Injection experiments yielded nitrate uptake rates of almost 1% per m of temporary stream channel. Exchange with subsurface flow was the most important route for nitrate removal from the water column. Biological uptake was insignificant in a light-limited forest stream, whereas a considerable amount of nitrate was retained by the biota a nutrient-limited meadow channel. At least 207 insect species were collected from the summer-dry streams. Species richness recorded from temporary forest streams exceeded that in an adjacent permanent headwater and there was high overlap between the fauna of the permanent and the temporary streams. Species richness in ephemeral channels was only 1/4 to 1/3 of that in long-flow forest streams. Multivariate analysis of community structure revealed flow duration and microhabitat pattern (riffle-pool) as the most important environmental factors determining faunal composition in temporary forest streams. Summer drought conditions at the sample sites also were important. By providing habitat and contributing to water quality in permanent downstream reaches, summer-dry streams have the potential to serve multiple purposes in conservation management. Their value from a conservation perspective is unexpectedly high. Landscape management therefore should be directed toward the preservation and protection of ephemeral and temporary streams. / Graduation date: 1993

In aquatic ecosystems, dissolved organic matter (DOM) is an important source of detrital energy on which microorganisms rely. However, its dynamics are not well understood in an ecological context. By isolating watershed sources, the work reported in this thesis has attempted to characterize the seasonal patterns of DOM in the hyporheic zone of a temperate stream and to find the likely sources that contribute to this pool of organic carbon. Hyporheic DOM characteristics described by UV spectroscopy indicated temporal rather than spatial dependence. Excitation-emission matrices (EEMs) showed that hyporheic DOM was mainly comprised of fulvic- and humic-like fluorescence with small amounts of protein-like fluorescence. Increases in dissolved organic carbon (DOC) concentrations from birch litter isolates were greater than those from cedar litter in early autumn, but less in late autumn. Although streambed biofilm was not significant in increasing DOC concentrations, it was also a source of protein-like fluorescence.

Water chemistry and bioindicators (diatoms and invertebrates) were examined for freshwater lakes, ponds and streams in two regions within Sirmilik National Park, northern Baffin Island, Nunavut. Significant differences were recorded between the water chemistry and diatom and invertebrate assemblages of the two regions. Modern diatom assemblages were explained mainly by specific conductivity, ORP, pH, temperature, elevation and distance from the coast. Paleolimnological techniques were applied to a sediment core from Lake BY14 on Bylot Island. Fossil diatom assemblages indicate increases in nutrients and temperature since 1935 AD. The diatom biostratigraphy does not show as large an increase in diversity and production since the middle 20th century as has been noted elsewhere, and this may be a reflection of the more nutrient-rich status of the lake relative to other Arctic lakes.

Water chemistry and bioindicators (diatoms and invertebrates) were examined for freshwater lakes, ponds and streams in two regions within Sirmilik National Park, northern Baffin Island, Nunavut. Significant differences were recorded between the water chemistry and diatom and invertebrate assemblages of the two regions. Modern diatom assemblages were explained mainly by specific conductivity, ORP, pH, temperature, elevation and distance from the coast. Paleolimnological techniques were applied to a sediment core from Lake BY14 on Bylot Island. Fossil diatom assemblages indicate increases in nutrients and temperature since 1935 AD. The diatom biostratigraphy does not show as large an increase in diversity and production since the middle 20th century as has been noted elsewhere, and this may be a reflection of the more nutrient-rich status of the lake relative to other Arctic lakes.

In aquatic ecosystems, dissolved organic matter (DOM) is an important source of detrital energy on which microorganisms rely. However, its dynamics are not well understood in an ecological context. By isolating watershed sources, the work reported in this thesis has attempted to characterize the seasonal patterns of DOM in the hyporheic zone of a temperate stream and to find the likely sources that contribute to this pool of organic carbon. Hyporheic DOM characteristics described by UV spectroscopy indicated temporal rather than spatial dependence. Excitation-emission matrices (EEMs) showed that hyporheic DOM was mainly comprised of fulvic- and humic-like fluorescence with small amounts of protein-like fluorescence. Increases in dissolved organic carbon (DOC) concentrations from birch litter isolates were greater than those from cedar litter in early autumn, but less in late autumn. Although streambed biofilm was not significant in increasing DOC concentrations, it was also a source of protein-like fluorescence.

L'objectiu d'aquest estudi és el d'investigar sobre l'ús de matèria orgànica per part dels fongs i bacteris que colonitzen diferents substrats bentònics en rius Mediterranis i analitzar l'efecte dels factors ambientals i antròpics sobre l'estabilitat estructural i funcional de les comunitats del biofilm. La metodologia emprada en aquest estudi consisteix en: i) anàlisi de la biomassa bacteriana i fúngica, ii) anàlisi de la composició de les comunitats bentòniques (identificació d'hifomicets aquàtics i anàlisi del 16S rDNA bacterià), i iii) anàlisi de l'activitat enzimàtica extracel·lular relacionada amb el reciclatge de matèria orgànica en rius. / This study aimed to investigate on the use of organic matter by fungi and bacteria inhabiting different benthic substrata and to analyze the effect of environmental and anthropogenic perturbations on the structural and functional stability of biofilms. The following methodologies has been used in this study: i) analysis of fungal and bacterial biomass, ii) analysis of benthic community composition (identification of hyphomycete taxa, analysis of the bacterial 16S rDNA), and iii) analysis of extracellular enzyme activities involved in organic matter recycling in rivers.

The online and data stream models of computation have recently attracted considerable research attention due to many real-world applications in various areas such as data mining, machine learning, distributed computing, and robotics. In both these models, input items arrive one at a time, and the algorithms must decide based on the partial data received so far, without any secure information about the data that will arrive in the future. In this thesis, we investigate efficient algorithms for a number of fundamental geometric optimization problems in the online and data stream models. The problems studied in this thesis can be divided into two major categories: geometric clustering and computing various extent measures of a set of points. In the online setting, we show that the basic unit clustering problem admits non-trivial algorithms even in the simplest one-dimensional case: we show that the naive upper bounds on the competitive ratio of algorithms for this problem can be beaten using randomization. In the data stream model, we propose a new streaming algorithm for maintaining "core-sets" of a set of points in fixed dimensions, and also, introduce a new simple framework for transforming a class of offline algorithms to their equivalents in the data stream model. These results together lead to improved streaming approximation algorithms for a wide variety of geometric optimization problems in fixed dimensions, including diameter, width, k-center, smallest enclosing ball, minimum-volume bounding box, minimum enclosing cylinder, minimum-width enclosing spherical shell/annulus, etc. In high-dimensional data streams, where the dimension is not a constant, we propose a simple streaming algorithm for the minimum enclosing ball (the 1-center) problem with an improved approximation factor.

The stretch from the riparian zone of a major river, through the mouth and upstream in tributaries forms a range of differing habitats. The aim of this study was to investigate the effect of these different habitats on the riparian frog community in primary rain forest in Borneo; i.e. examine whether any gradients could be demonstrated in terms of species composition, diversity and density of frogs, as well as which environmental characteristics that seem to be of most importance in forming habitats of high conservational value. A major river, Segama, and three of its tributaries were investigated. The surveys were carried out at night by searching for frogs visually and acoustically along the streams, from the shore of the Segama river and 400 metres upstream in the tributaries. In all transects 10 habitat variables were also measured. The results from the study show a significantly lower diversity and abundance of frogs along the shores of Segama and close to the mouths of the tributaries compared to further upstream, and a significant difference in species assemblage. Most species exhibited a negative correlation with the downstream transects or were not found there at all. The habitat characteristics waterfalls and boulders were found to be of most importance for the diversity and abundance of frogs, making these characteristics key components of habitats with high conservational value. Major rivers could also potentially form dispersal corridors for invasive species, which findings of the introduced species Fejervarya limnocharis along the shores of Segama shows.

The online and data stream models of computation have recently attracted considerable research attention due to many real-world applications in various areas such as data mining, machine learning, distributed computing, and robotics. In both these models, input items arrive one at a time, and the algorithms must decide based on the partial data received so far, without any secure information about the data that will arrive in the future. In this thesis, we investigate efficient algorithms for a number of fundamental geometric optimization problems in the online and data stream models. The problems studied in this thesis can be divided into two major categories: geometric clustering and computing various extent measures of a set of points. In the online setting, we show that the basic unit clustering problem admits non-trivial algorithms even in the simplest one-dimensional case: we show that the naive upper bounds on the competitive ratio of algorithms for this problem can be beaten using randomization. In the data stream model, we propose a new streaming algorithm for maintaining "core-sets" of a set of points in fixed dimensions, and also, introduce a new simple framework for transforming a class of offline algorithms to their equivalents in the data stream model. These results together lead to improved streaming approximation algorithms for a wide variety of geometric optimization problems in fixed dimensions, including diameter, width, k-center, smallest enclosing ball, minimum-volume bounding box, minimum enclosing cylinder, minimum-width enclosing spherical shell/annulus, etc. In high-dimensional data streams, where the dimension is not a constant, we propose a simple streaming algorithm for the minimum enclosing ball (the 1-center) problem with an improved approximation factor.

The Montian Kartal Formation lies in the south-west of Ankara region and overlies the Upper Cretaceous Beyobasi Formation and is overlain by Thanetian Kirkkavak Formation conformably in the studied region (Kayabasi village, NW of town of Haymana). A 283 m stratigraphic section, which is mainly composed of an alternation siliciclastic and carbonate rocks has been measured in the Kartal Formation within the Haymana-Polatli basin. The aim of this study is to carry out the sedimentological and cyclostratigraphical analyses of the upper part of the Kartal Formation within Haymana-Polatli basin which represents a well developed cyclic pattern. In this study, detailed lithofacies analyses were performed and four different facies were recognized along the measured section: sandstones, limestones, mudrocks and conglomerates. Sedimentological analyses, such as modal, provenance, palaeocurrent, grain-size and grain parameters were also performed and their relation with the depositional environment and change in depositional conditions were discussed. Interpretations of the depositional environment revealed that the deposition occurred by low sinuosity rivers and waves. Additional environmental interpretations suggested that the sediments were deposited in shallow marine and/or coastal (beach) environments. High resolution cyclostratigraphy studies based on meter scale cyclic and rhytmic occurrences of lithofacies along the measured section were performed. The whole section, which is 283 m thick, was divided into large-scale hierarchy-cycles which comprise smaller-scale fining upward and deepening upward cyclic and rhythmic beds.