As a response to the environmental degradation of many coastal areas in east Africa research have been initiated aiming towards the understanding of the coastal ecosystems and the interactions between them. The sediment of three seagrass communities were investigated with regard to nitrification, denitrification, pore water nutrient content, organic content and physical character. The aim was to estimate the magnitude and importance of nitrification and denitrification and correlate those to any difference in organic load. Total organic carbon and total nitrogen decreased while C:N ratio increased with distance from the mangroves indicating a larger organic load closer to the mangroves. There was however no significant difference between the sites regarding ammonium and nitrate + nitrite concentrations in the porewater; nor regarding denitrification. Recalculated to ambient nitrate concentrations denitrification was less than 157 nmol N m-2h-1. No trend could be seen for nitrification either. Nitrification ranged from 0-12.0 µmol N m-2h-1, but the method used may underestimate the rates. Denitrification, and especially nitrification rates, varied considerably within each site indicating an extremely patchy environment. Considering that nutrient regeneration rates in tropical environments are usually high, nitrification and denitrification seemed to be minor pathways in the nitrogen cycle irrespective of organic load. The study also suggests that nitrification and denitrification may be of less importance in Chwaka bay compared to other areas studied. / Som svar på den försämrade miljön i flera kustområden i Östafrika har forskning påbörjats inriktad på förståelsen av kustliga ekosystem samt samspelet dem emellan. Sedimentet i tre sjögräsområden undersöktes med avseende på nitrifikation, denitrifikation, näringshalt i porvattnet, organisk halt samt fysikalisk karaktär. Syftet var att uppskatta storleken och betydelsen av nitrifikation och denitrifikation samt att korrelera dessa med organisk belastning. Totala halten organiskt kol och totala halten kväve minskade medan C:N kvoten ökade med avståndet till mangroven vilket tyder på en större organisk belastning närmare mangroven. Det var däremot ingen signifikant skillnad mellan områdena beträffande ammonium- eller nitrat + nitrit koncentrationen i porvattnet; inte heller beträffande denitrifikation. Omräknad till föreliggande nitratkoncentrationer var denitrifikationen mindre än 157 nmol N m-2h-1. Nitrifikationen varierade från 0-12.0 µmol N m-2h-1, men den använda metoden kan ha underskattat hastigheterna. Någon trend i nitrifikationen syntes inte heller. Denitrifikationen och speciellt nitrifikationen varierade avsevärt inom varje område vilket tyder på en extremt omväxlande miljö. Med tanke på att regenerationen av näringsämnen ofta är hög i tropiska miljöer så verkade nitrifikationen och denitrifikationen vara mindre betydelsefulla delar i kvävecykeln oavsett organisk belastning. Denna studie tyder också på att nitrifikation och denitrifikation är mindre betydelsefulla i Chwaka bay än i andra studerade områden.

Lake evaporation from a shallow lake in central Sweden has been estimated using three independent methods from measurements during summer 1995. The applied isotope method is a combination of the water and isotope mass balance. Its main feature is that inflows need not to be measured. Only knowledge of their isotopic content is sufficient. For calculations by the bulk aerodynamic method a computer program was applied, which takes into account the different conditions of stratification. The energy balance of the lake was determined by using the short and long wave radiation, heat storage and advective heat energy. Measurements were done on a small island and at a mast in the middle of the lake. Evaporation estimated by all the methods varied from -1.1 to 5.0 mm/d during the summer months 1995. Values estimated by the energy balance method agreed well with those from the bulk aerodynamic method. Evaporation estimates from the isotope method a showed fairly good agreement with the two other methods, excepting a few periods. It was found that both the isotope as well as the energy balance method are sensitive to errors in lake volume. Both methods carry some uncertainty due to their dependence on water balance components, some of which are difficult to determine. The bulk aerodynamic method is independent of the water balance of the lake. A good accuracy can be achieved using only four variables i.e. wind speed, relative humidity, skin and air temperature. / Avdunstningen från den grunda sjön Tämnaren i centrala Sverige bestämdes med tre oberoende metoder ur mätningar från sommaren 1995. Den använda isotopmetoden är en kombination av vatten- och isotopbalansen. Dess viktigaste fördel är att inflödet inte behöver mätas, utan att kännedom om isotophalten är tillräcklig. För beräkningarna med den bulk-aerodynamiska metoden användes ett datorprogram som tar hänsyn till atmosfärens stabilitet. Energibalansen beräknades ur kort- och långvågsstrålningen, värmelagringen och den tillförda energin. Mätningarna utfördes dels på en liten ö och dels vid en mast mitt i sjön. Avdunstningen varierade mellan -1.1 mmd-1 till 5.0 mmd-1. Resultaten från energibalansmetoden överenstämde bra med resultaten från den bulk-aerodynamiska metoden. Även resultaten från isotopmetoden överenstämde bra med resultaten från de två andra metoderna, med undantag av några få perioder. Både isotop- och energibalansmetoden var känsliga för feluppskattningar av sjövolymen. Båda metoderna innehåller osäkerheter som en följd av deras beroende på vissa av vattenbalansens komponenter, som är svåra att bestämma. Den bulk-aerodynamiska metoden är oberoende av sjöns vattenbalans och en bra noggranhet kan uppnås med mätningar av endast de fyra variablerna vindhastighet, relativ fuktighet, yt- och lufttemperatur. / Die Verdunstung von einem flachen See in Zentralschweden wurde mit Hilfe von drei unabhängigen Methoden bestimmt. Die Messungen wurden im Sommer 1995 durchgeführt. Die angewandte Isotopenmethode ist eine Kombination aus Wasserbilanz and lsotop-Massenbilanz. Das besondere Merkmal dieser Methode ist es, daß Zuflüsse nicht gemessen werden müssen. Es genügt, ihre isotopische Zusammensetzung zu kennen. Für die Berechungen mit der bulk-aerodynamischen Methode wurde ein Computerprogamm verwendet, das die unterschiedlichen atmosphärischen Schichtungen berücksichtigt. Die Energiebilanz des Sees wurde mit Hilfe der kurz- und langwelligen Strahlung, der gespeicherten Energie im See und der durch Zuflüsse und Niederschlag zugeführten Energie bestimmt. Die Messungen wurden auf einer kleiner Insel und an einem Mast in der Mitte des Sees durchgeführt. Die Verdunstung reichte von -1.1 mmd-1 bis 5.0 mmd-1 während der Sommermonate 1995. Die Ergebnisse der Energiebilanz stimmten gut mit den Ergebnissen der bulk-aerodynamischen Methode überein. Die Ergebnisse der Isotopenmethode stimmten relativ gut mit den Ergebnissen der beiden anderen Methoden überein, mit Ausnahme einiger Perioden. Es wurde festgestellt, daß sowohl die Isotopenmethode als auch die Energiebilanzmethode sensibel auf Fehler im Seevolumen reagieren. Beide Methoden enthalten einige Unsicherheiten wegen ihrer Abhängikeit von Wasserbilanzkomponenten, die z.T. schwer zu bestimmen sind. Die bulk-aerodynamische Methode dagegen ist unabhängig von der Wasserbilanz des Sees. Gute Ergebnisse können mit nur vier zu messenden Variablen erreicht werden (Windgeschwindigkeit, relative Luftfeuchtigkeit, Wasseroberflächen- und Lufttemperatur). / <p>Parts of the thesis work later published as:</p><p>Saxena, R., Jaedicke, C., &amp; Lundin, L. C. (1999). Comparison of lake evaporation estimated by isotope mass-balance, bulk-aerodynamic and bowen ratio methods. <em>Phys. Chem Earth (B), </em>Vol. 24, No. 7, pp. 851–859.</p><p>and</p><p>Saxena, R., &amp; Jaedicke, C. (1997). Estimation of vapour flux from a shallow lake by oxygen -18 mass balance. <em>Isotope Techniques in the Study of Environmental Change</em>, 225–237. Vienna: IAEA-SM-349/23.</p>

In the past decade considerable research in several disciplines has been oriented toward the design of optimal capacity expansion plans for water resource systems. The emphasis of most of these efforts has been directed toward minimization total cost outlays in project planning. This focus somewhat limits the full applicability of the optimal capacity expansion solutions since it is believed that the criteria of economic efficiency is not well addressed in this mode. This study explores the merits of scheduling water resource project facilities on the basis of anticipated economic benefits provided, an approach needed only infrequently in the systems engineering literature. Using the Umatilla River Basin in Northeast Oregon as a case study example, the facilities (and their alternatives) of a previously planned federal water resource development project in that area were carefully analyzed with respect to the magnitude and timing of anticipated benefits and costs. Irrigated agriculture and fishery development/enhancement benefits were the two principal purposes of the project considered. In addition, benefits arising from flood prevention, municipal and industrial water supply, and erosion control were also integral to the original overall evaluation. The design of the research was to first implement a basic scheduling model in the context of the case study area and then to explore the ramifications of exchange-theoretic and distribution-theoretic criteria on the timing of facilities and the ultimate allocation of water among purposes. The model implemented was aimed at maximizing the present value of net benefits inherent in an optimally timed set of facilities subject to an annual budget constraint. Having designed the model along integer programming lines, three different solution techniques were explored in order to realize a desirable level of efficiency in basic model solution. It was found that reasonably efficient solutions could be obtained. By optimally timing the facilities it was found that the total present value of net benefits of the project could be significantly enhanced when compared to the original schedule proposed in the project planning documents. Of even greater interest is the issue of incorporating into the planning process (and specifically into the capacity expansion mode of planning) considerations of tradeoffs or exchanges between project beneficiaries. Such exchanges and other distributional criteria can affect and be affected by the selection and timing of project facilities within an overall project design. These interrelationships are explored paying particular attention to the way in which exchanges of water (via water rights transfers) could establish higher levels of benefits in future years. Noneconomic exchange processes such as the enforcement of extant property rights relating to water resources are another issue which complicated the process of water planning. Such distributional criteria are difficult to incorporate into the capacity expansion mode of planning analysis. However, ways are explored by which the basic model may be modified and used by decision makers in order to take account of more realistic problems in water resource planning for individual river basins. / Graduation date: 1981 / Partially funded by the U.S. Dept. of the Interior as authorized under the Water Research and Development Act of 1978. / Final technical completion report for project no. A-046-ORE to U.S. Dept. of the Interior.

Hydrological drainage/river basins constitute highly heterogeneous systems of coupled natural and anthropogenic water and pollutant flows across political, national and international boundaries. These flows need to be appropriately understood, quantified and communicated to stakeholders, in order to appropriately guide environmental water system management. In this thesis, various uncertainties about water and pollutant flows in drainage/river basins and their implications for effective and efficient water pollution abatement are investigated, in particular for mine-related heavy metal loadings in the Swedish Dalälven River basin and for nitrogen loadings in the Swedish Norrström drainage basin. Economic cost-minimization modeling is used to investigate the implications of pollutant load uncertainties for the cost-efficiency of catchment-scale abatement of water pollution. Results indicate that effective and efficient pollution abatement requires explicit consideration of uncertainties about pollution sources, diffuse contributions of the subsurface water system to downstream pollutant observations in surface waters, and downstream effects of different possible measures to reduce water pollution. In many cases, downstream load abatement measures must be used, in addition to source abatement, in order to reduce not only expected, but also uncertainties around expected pollutant loads. Effective and efficient environmental management of water systems must generally also consider the entire catchments of these systems, rather than focusing only on discrete pollutant sources. The thesis presents some relatively simple, catchment-scale pollutant flow analysis tools that may be used to decrease uncertainties about unmonitored water and pollutant flows and subsurface pollutant accumulation-depletion and diffuse loading to downstream waters.

Snowfall interception is particularly important to the hydrology of forested cold regions. Unloading of intercepted snow controls the snow available for interception loss due to sublimation from that held in the canopy. This thesis seeks to determine the factors that affect the magnitude and timing of unloading at the forest-stand scale. A field program was established that measured interception and unloading at a forest-stand scale using a series of hanging lysimeters and a 7 m tall spruce tree suspended, in-situ, on a load-cell.<p> Meteorological conditions including snowfall, wind speed, air temperature, and incoming radiation were recorded above and below the forest canopy. Unloading did not behave as described by current unloading models. It was observed to be triggered by occurrences of wind gusts or melt conditions within the canopy but no trends were found in the measurements that could be used to predict the onset of unloading from gusts or air temperature alone. An association between intercepted snow sublimation and unloading was found and this relationship was further found to be an exponential function of air temperature. An expression based on this empirical model can be used to calculate unloading as a function of sublimation rate in hydrological models or to calculate unloading directly as a function of canopy snow load and air temperature.

Numerical models of flow and transport are commonly applied for the sustainable management of water resources and for the selection of appropriate remediation techniques. However, these numerical models are not always accurate due to uncertain parameters and the disparity of scales across which observations are made, hydrological processes occur, and modeling is conducted. The modeling framework becomes further complex because hydrologic processes are coupled with chemical and biological processes. This dissertation focuses on the most widespread contaminants of surface and ground water, which are E. coli and nitrate, respectively. Therefore, this research investigates the linkages between bio-chemical and hydrologic processes for E. coli transport, explores the spatio-temporal variability of nitrate, quantifies uncertainty, and develops models for both E. coli and nitrate transport that better characterize these biogeochemical linkages. A probabilistic framework in the form of Bayesian Neural Networks (BNN) was used to estimate E. coli loads in surface streams and was compared with a conventional model LOADEST. This probabilistic framework is crucial when water quality data are scarce, and most models require a large number of mechanistic parameters to estimate E. coli concentrations. Results indicate that BNN provides better characterization of E. coli at higher loadings. Results also provide the physical, chemical, and biological factors that are critical in the estimation of E. coli concentrations in Plum Creek, Texas. To explore model parameters that control the transport of E. coli in the groundwater (GW) and surface water systems, research was conducted in Lake Granbury, Texas. Results highlight the importance of flow regimes and seasonal variability on E. coli transport. To explore the spatio-temporal variability of nitrate across the Trinity and Ogallala aquifers in Texas, an entropy-based method and a numerical study were employed. Results indicate that the overall mean nitrate-N has declined from 1940 to 2008 in the Trinity Aquifer as opposed to an increase in the Ogallala Aquifer. The numerical study results demonstrate the effect of different factors like GW pumping, flow parameters, hydrogeology of the site at multiple spatial scales. To quantify the uncertainty of nitrate transport in GW, an ensemble Kalman filter was used in combination with the MODFLOW-MT3DMS models. Results indicate that the EnKF notably improves the estimation of nitrate-N concentrations in GW. A conceptual modeling framework with deterministic physical processes and stochastic bio-chemical processes was devised to independently model E. coli and nitrate transport in the subsurface. Results indicate that model structural uncertainty provides useful insights to modeling E. coli and nitrate transport.

Snowfall interception is particularly important to the hydrology of forested cold regions. Unloading of intercepted snow controls the snow available for interception loss due to sublimation from that held in the canopy. This thesis seeks to determine the factors that affect the magnitude and timing of unloading at the forest-stand scale. A field program was established that measured interception and unloading at a forest-stand scale using a series of hanging lysimeters and a 7 m tall spruce tree suspended, in-situ, on a load-cell.<p> Meteorological conditions including snowfall, wind speed, air temperature, and incoming radiation were recorded above and below the forest canopy. Unloading did not behave as described by current unloading models. It was observed to be triggered by occurrences of wind gusts or melt conditions within the canopy but no trends were found in the measurements that could be used to predict the onset of unloading from gusts or air temperature alone. An association between intercepted snow sublimation and unloading was found and this relationship was further found to be an exponential function of air temperature. An expression based on this empirical model can be used to calculate unloading as a function of sublimation rate in hydrological models or to calculate unloading directly as a function of canopy snow load and air temperature.

<p>Hydrological drainage/river basins constitute highly heterogeneous systems of coupled natural and anthropogenic water and pollutant flows across political, national and international boundaries. These flows need to be appropriately understood, quantified and communicated to stakeholders, in order to appropriately guide environmental water system management. In this thesis, various uncertainties about water and pollutant flows in drainage/river basins and their implications for effective and efficient water pollution abatement are investigated, in particular for mine-related heavy metal loadings in the Swedish Dalälven River basin and for nitrogen loadings in the Swedish Norrström drainage basin. Economic cost-minimization modeling is used to investigate the implications of pollutant load uncertainties for the cost-efficiency of catchment-scale abatement of water pollution.</p><p>Results indicate that effective and efficient pollution abatement requires explicit consideration of uncertainties about pollution sources, diffuse contributions of the subsurface water system to downstream pollutant observations in surface waters, and downstream effects of different possible measures to reduce water pollution. In many cases, downstream load abatement measures must be used, in addition to source abatement, in order to reduce not only expected, but also uncertainties around expected pollutant loads. Effective and efficient environmental management of water systems must generally also consider the entire catchments of these systems, rather than focusing only on discrete pollutant sources. The thesis presents some relatively simple, catchment-scale pollutant flow analysis tools that may be used to decrease uncertainties about unmonitored water and pollutant flows and subsurface pollutant accumulation-depletion and diffuse loading to downstream waters.</p>

"A thesis submitted to Oregon State University." / Includes appendices. Photocopy of original. Includes bibliographical references (leaves 126-132). Also available on the World Wide Web.

<p> California Department of Water Resources (DWR) Snow Surveys Section has recently explored the potential use of recently developed hydrologic models to estimate snow water equivalent (SWE) for the Sierra Nevada mountain range. DWR Snow Surveys Section&rsquo;s initial step is to determine how well these hydrologic models compare to the trusted regression equations, currently used by DWR Snow Surveys Section. A comparison scheme was ultimately developed between estimation measures for SWE by interpreting model results for the Feather River Basin from: a) National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL) gridded SWE reconstruction product, b) United States Geological Survey (USGS) Precipitation-Runoff Modeling System (PRMS), and c) DWR Snow Surveys Section regression equations. Daily SWE estimates were extracted from gridded results by computing an average SWE based on 1,000 ft elevation band increments from 3,000 to 10,000 ft (i.e. an elevation band would be from 3,000 to 4,000 ft). The dates used for processing average SWE estimates were cloud-free satellite image dates during snow ablation months, March to August, for years 2000&ndash;2012. The average SWE for each elevation band was linearly interpolated for each snow sensor elevation. The model SWE estimates were then compared to the snow sensor readings used to produce the snow index in DWR&rsquo;s regression equations. In addition to comparing JPL&rsquo;s SWE estimate to snow sensor readings, PRMS SWE variable for select hydrologic response units (HRU) were also compared to snow sensor readings. Research concluded with the application of statistical methods to determine the reliability in the JPL products and PRMS simulated SWE variable, with results varying depending on time duration being analyzed and elevation range.</p>