Groundwater is an important water resource that must be protected from potential contamination due to anthropogenic activities such as industrial production and agriculture. It is necessary to understand the presence, movement, and persistence of contaminants in aquifers to develop adequate protection plans. Fractured bedrock aquifers with thin overburden cover are very sensitive to contamination, and little is known about transport processes from the ground surface to depth in this setting. Thus, this research was undertaken to improve the understanding of anthropogenic impacts on water quality in a natural fractured bedrock aquifer with minimal overburden protection. This was accomplished through a field-based investigation conducted in an agricultural setting near Perth, Ontario, Canada. The temporal and spatial variations of several contaminants and indicators (including nitrate, E. coli and polybrominated diphenyl ethers) were examined. A unique infiltration tracer experiment was also conducted to simulate the transport of solutes from the ground surface to wells. Results showed that nitrate concentrations were consistent on a daily scale, but varied monthly. In contrast to nitrate, greater bacterial (E. coli) variability was observed daily. E. coli was not identified in some locations for several months. The temporal variability of concentrations is an important consideration for those consuming groundwater in this setting, as concentrations may be acceptable one month while unsuitable another month (or even another day for fecal bacteria). Annual groundwater monitoring will likely not capture maximum concentrations and thus may not protect human health. Polybrominated diphenyl ethers (flame retardants), which had not been previously measured in groundwater, were detected in the study aquifer at concentrations greater than observed in surface water bodies. It is evident that additional surveys of PBDE concentrations in groundwater are warranted. The infiltration tracer experiment showed that solute transport from the ground surface through thin soil to wells in fractured bedrock can be extremely rapid (on the order of hours) although very complex. This is an important consideration for private and municipally owned drinking water systems that draw water from shallow bedrock aquifers. The results of this research demonstrate that protecting water at the source is imperative in order to preserve water quality in sensitive fractured bedrock aquifers with minimal overburden cover. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2009-10-25 21:37:21.418

Nitrate (NO⁻3) export can vary widely among forested watersheds with similar nitrogen loading, geology, and vegetation, which suggests the importance of understanding differing internal retention mechanisms. Transport should be studied at the hillslope scale because the hillslope is the smallest unit with spatial and temporal resolution to reflect many relevant NO⁻3 retention and transport (flow-generation) processes, and headwater forested watersheds are largely comprised of sections of hillslopes. I conducted two experiments to elucidate subsurface flow dynamics and NO⁻3 transport and retention mechanisms on a constructed experimental hillslope model. In the first experiment, I tested whether decadal pedogenetic changes in soil properties in the experimental hillslope used by Hewlett and Hibbert (1963) would lead to changes in recession flow. I repeated (twice) their seminal experiment, whose results led to the development of the Variable Source Area paradigm, by also saturating, covering, and allowing the experimental hillslope to drain until it no longer yielded water. In the historical experiment there was fast drainage for 1.5 d, followed by slow drainage for ~140 d, which led the authors to conclude that recession flow in unsaturated soil could sustain baseflow throughout droughts. This long, slow drainage period was not reproduced in my experiments. Shapes of the drainage curves in my experiments were similar to the historical curve, but slow drainage was truncated, ending after 17 and 12 d, due likely to a leak in the boundary conditions, rather than to pedogenetic changes since the historical experiment. Leakage to bedrock, analogous to the leak in the hillslope model, is a commonly observed phenomenon and this study highlights how that can reduce drainage duration and the contribution of moisture from soils to support baseflow. In the second experiment, I tested whether movement of NO⁻3, which is considered a mobile ion, would be delayed relative to movement of water through a hillslope. I added concentrated pulses of ¹⁵NO⁻3 and a conservative tracer (²H₂O) on the same experimental hillslope, which was devegetated and irrigated at hydrologic steady state. Retention of the ¹⁵NO⁻3 tracer was high in the soil surface (0–10 cm) layer directly where the tracer was added. The portion of the ¹⁵NO⁻3 tracer that passed through this surface layer was further retained/removed in deeper soil. The reduction in the peaks in δ¹⁵N breakthrough was an order of magnitude larger than in δ₂H breakthrough at the outlet 5 m downslope of the tracer addition. The peaks in δ¹⁵N were also delayed relative to the peaks in δ₂H by 1, 6, 9 and 18.5 d for slope distances of 0, 2, 4, and 5 m, respectively, from tracer addition to the outlet. The excess mass of ¹⁵NO⁻3 recovered at the outlet was less than 3% of the original tracer mass injected. Nitrification and denitrification were estimated to be roughly 1:1 and were large fluxes relative to lateral transport into and out of the riparian zone. This tracer experiment shows that bedrock leakage, coupled with multiple retention/removal mechanisms can significantly delay export of added NO⁻3 with implications of additional NO⁻3 sink strength at the watershed scale. / Ph. D. / Nitrate (NO₃⁻) export can vary widely among forested watersheds with similar nitrogen loading, geology, and vegetation, which suggests the importance of understanding differing internal process mechanisms. I conducted two experiments to illustrate how water and NO₃⁻ moved on a constructed hillslope model. In the first experiment, I quantified differences in soil properties in the hillslope model used by Hewlett and Hibbert (1963). Then I repeated (twice) the seminal drainage experiment described in Hewlett and Hibbert (1963). The same hillslope (21.8°; 40%) was wetted up, covered, and allowed to drain until water stopped exiting at the outlet. In the historical experiment there was fast drainage for 1.5 d, followed by slow drainage for ~140 d, which led the authors to hypothesize that slow drainage in surface soil could continually contribute water to streams even during droughts. This long, slow drainage period was not reproduced in my experiments. Drainage was similar at the beginning of drainage between my experiments and the historical experiment, but in my experiment the slow drainage ended earlier (after 17 and 12 d) due likely to a leak in the constructed hillslope model, rather than to significant changes that occurred in the soil itself since the original experiment. This leak in the hillslope model is similar to leakage to bedrock, which is commonly observed in natural hillslopes. In the second experiment, I tested whether NO₃⁻ and water would move through a hillslope at the same rate. I added concentrated pulses of NO₃⁻ (as ¹⁵NO₃⁻ and water (as ²H₂O) on the same devegetated experimental hillslope. Retention of the ¹⁵NO₃⁻ tracer was high in the surface (0–10 cm) where the tracer was added, with little change in the immediately surrounding soil, despite high rates of water input immediately after tracer addition and throughout the experiment. The portion of the ¹⁵NO₃⁻ tracer that passed through the surface layer was further processed by microbes in deeper soil as it traveled downslope. This body of work shows that bedrock leakage, coupled with multiple retention mechanisms throughout the soil profile, can significantly delay export of added NO₃⁻ at the watershed scale.

<p>When protection zones for wells are delineated, it is important to acquire good knowledge about possible travel time from different points in the catchment area to the well. Often, simple analytical methods are used for estimating travel times and the assumption is made that the hydraulic conductivity is relatively homogenous within the aquifer. Nevertheless, many aquifers are strongly heterogeneous which may lead to differences between estimates and actual travel times. As a part of the process to develop improved methods for delineating protection zones for groundwater supply wells, a tracer experiment was performed in a glaciofluvial esker formation in Järlåsa. On the basis of the experiment, a numerical flow model was created for the test site.</p><p>The purpose of this master’s thesis was to apply the flow model to an aquifer where the hydraulic conductivity shows great variability and should be described by a stochastic distribution. The purpose was also to determine the statistical properties of the hydraulic conductivity and to simulate the transport times and their variation from different locations in the aquifer to the pumping well.</p><p>The hydraulic conductivity was estimated from grain size distributions in soil samples that were taken at various locations within the test site. The analysis of the hydraulic conductivity showed a large variation and confirmed the hypothesis that the aquifer is heterogeneous. Using the statistics, a large number of stochastic conductivity fields were created and flow simulation was performed for each realization. From the simulation result, frequency distributions of the transport times were produced describing the probability for the transit time for a water particle between a certain location in the aquifer and the pumping well. A comparison with the tracer experiment shows higher simulated transport times implying the need for improved model calibration. The conclusion is that the method used in this project is suitable for glaciofluvial esker aquifers. When protection zones are delineated, stochastic modeling can be used to express the zone boundaries in statistical terms.</p> / <p>När skyddsområden för grundvattentäkter skapas är det viktigt att ha god kännedom om vattnets transporttider från olika delar i tillrinningsområdet till uttagsplatsen av grundvattnet. Metoderna för att bestämma dessa tider är ofta enkla och vanligen görs antagandet att områdets hydrauliska konduktivitet är relativt homogen. Många akviferer är dock kraftigt heterogena och de verkliga transporttiderna kan då skilja sig från de uppskattade. Som ett led i metodutvecklingen för bättre avgränsning av skyddsområden genomfördes ett spårämnesförsök i en isälvsavlagring i Järlåsa. Med utgångspunkt från försöket har en numerisk flödesmodell konstruerats över försöksområdet.</p><p>Syftet med examensarbetet var att tillämpa flödesmodellen i en akvifer där den hydrauliska konduktiviteten visar sådana variationer att den beskrivs bäst av en stokastisk fördelning. Vidare var syftet att bestämma den hydrauliska konduktivitetens statistiska egenskaper och att simulera transporttiderna och deras variation från olika punkter i akviferen till pumpbrunnen.</p><p>Den hydrauliska konduktiviteten uppskattades utifrån kornstorleksfördelningar i jordprover som togs på en mängd platser i försöksområdet. Analysen av den hydrauliska konduktiviteten visar stora variationer i området vilket bekräftar att akviferen är heterogen.</p><p>Utifrån konduktivitetens statistik genererades ett stort antal stokastiska konduktivitetsfält och transporttiderna beräknades för varje realisering. Resultatet från simuleringarna gav frekvensfördelningar för transporttiderna som beskriver sannolikheten för hur lång uppehållstid en vattenpartikel har i marken mellan en startpunkt och pumpbrunnen. Jämfört med spårämnesförsöket blev de simulerade transporttiderna något större vilket tyder på att flödesmodellen kräver en bättre kalibrering mot fältmätningar. Slutsatsen är att metodiken är lämplig för att studera vattnets transporttider i isälvsavlagringen och när ett skyddsområde skapas för den här typen av akvifer kan stokastisk modellering användas för att beskriva skyddszoner i form av statistiska termer.</p>

<p>The euthropthication of the Baltic Sea is a threat that is beginning to be taken seriously by the governments concerned. In Sweden, regulations concerning the allowed nitrogen (N) concentration in the effluent water from wastewater treatment plants are being tightened up. The Rimbo wastewater treatment plant has been imposed to reduce the annual mean concentration of total N in the effluent water to levels below 15 mg l-1. A more and more common way to reduce the nitrogen level in wastewater is to let the water pass through a wetland. This study investigates the possibility to build this kind of wetland at the outlet of the Rimbo wastewater treatment plant.</p><p>A prestudy of the topography, soil characteristics and groundwater flow indicates that the land area in question is well suited for the construction of a wetland. A proposal for the design has been made by using a physically based computer model developed in the PRIMROSE project (PRocess based Integrated Management of constructed and Riverine wetlands for Optimal control of wastewater at catchment ScalE), which is financed by the EU. Analysis of the residence time distribution (RTD) is a tool for understanding wetland design characteristics and can be used for wetland engineering such as optimizing design for best possibleefficiency in nitrogen removal. In order to characterize the performance of a wetland, it is useful to translate the RTD to a key figure representing the treatment efficiency. In this work, two types of such key figures have been used. Key figure 1 gives the hydraulic efficiency and Key figure 2 gives an estimation of the nitrogen retention by an integration of hydraulic characteristics and the chemical transformation of nitrogen.</p><p>The results of this study show that constructing a wetland in Rimbo probably would be an efficient way to reduce the nitrogen level at the effluent of the wastewater plant below the limits of the regulations. In addition, a wetland would form a nice place of recreation for the people in Rimbo and also make a good habitat for birds.</p> / <p>Övergödningen i Östersjön är ett problem som uppmärksammas alltmer. Ett led i att minska kvävebelastningen på Östersjön är ökade krav på rening i de svenska kommunala reningsverken. Rimbo avloppsreningsanläggning har blivit ålagd ett riktvärde för totalkväve på 15 mg l-1 i utgående vatten, vilket motsvarar en reningsgrad som inte uppnås idag. Ett alltmer vanligt sätt att minska föroreningshalterna är att anlägga våtmarker i anslutning till reningsverken för att efterpolera spillvattnet. Det här arbetet är en del av en förstudie till en sådan våtmark i Rimbo.</p><p>En förundersökning av topografi, jordart och grundvattenflöden indikerar att det område som föreslagits i anslutning till reningsverket i Rimbo lämpar sig väl för ett våtmarksbygge. Förslag till utformning har tagits fram med hjälp av en fysikaliskt baserad modell över vattenströmning, utvecklad inom det EU-finansierade projektet PRIMROSE (PRocess based Integrated Management of constructed and Riverine wetlands for Optimal control of wastewater at catchment ScalE). Analys av vattnets uppehållstidsfördelning ger förståelse för våtmarkens egenskaper och kan därför användas vid t ex optimering av våtmarksdesign med avseende på kväverening. För att på ett enkelt sätt kunna jämföra olika våtmarkers effektivitet är det praktiskt att översätta uppehållstidsfördelningen till ett nyckeltal för reningseffekten. I det här arbetet har två olika sådana nyckeltal beräknats. Det första ger den hydrauliska effektiviteten och det andra bygger på en metod där våtmarkens interna hydraulik integreras med den kemiska omvandlingen av kväve. Nyckeltal 1 ger ett mått på hur stor del av volymen i våtmarken som används för kväverening, medan Nyckeltal 2 ger ett mått på den procentuella kväveavskiljningen.</p><p>Den här förstudien visar att en våtmark sannolikt skulle vara ett utmärkt sätt att klara riktvärdet för kvävehalten vid reningsverket i Rimbo. Därutöver skulle en våtmark kunna utgöra ett positivt inslag i landskapet och öka den biologiska mångfalden, inte minst vad gäller fågelliv.</p>

Des écoulements matriciels et des flux préférentiels peuvent se produire concurremment dans le même sol. Ces deux régimes d’écoulements se manifestent par des empreintes de flux caractéristiques qu’on peut visualiser par des essais de traçage. Afin d’extraire l’information quantitative des essais de traçage un grand nombre de méthodes existe. On peut, entre autre, décrire les empreintes de traceur par ce qu’on appelle la fonction de couverture, c’est à dire le pourcentage de région teintée par un traceur coloré en fonction de la profondeur du sol. En utilisant la statistique des valeurs extrêmes cette fonction peut être réinterprétée comme une fonction exprimant la probabilité de trouver le traceur à une profondeur donnée. Ainsi, la fonction de probabilité à deux paramètres 1 – H, H étant la distribution de Pareto généralisée, peut être ajustée. Le paramètre de forme de cette fonction est utilisé comme indice de risque de propagation verticale des solutés. Nous avons effectué des essais de traçage au Bleu Brillant FCF sur trois sites différents : dans une forêt d’épicéa dans le sud-est de l’Allemagne, dans une forêt tropicale humide montagnarde en Équateur et sur un champ agricole au sud de la France. Nous avons examiné la capacité de l’indice de risque à rassembler l’information principale des essais de traçage et à caractériser les empreintes de flux dans des sols différents, sous conditions aux limites diverses. Nos résultats indiquent que l’indice de risque est, dans une certaine mesure insensible aux changements des conditions aux limites (comme l’intensité d’irrigation). Par contre, l’humidité initiale du sol semble influencer cet indice de façon importante. L’ajustement des paramètres de la fonction Pareto généralisée s’avère difficile si la fonction de couverture fluctue ou ne décroît pas de manière monotone. Ceci peut être dû à la tortuosité des chemins d’écoulement, à la variation des mécanismes de flux ou aux changements de propriétés physiques du sol (stratification). Ainsi, dans des sols stratifiés nous avons restreint l’analyse à la partie inférieure du profil de sol. En effet, étant donné que la théorie de l’indice de risque est basée sur les valeurs extrêmes de propagation verticale de solutés c’est la partie inférieure qui est la plus intéressante. Nous proposons de combiner les deux paramètres de la fonction Pareto généralisée et d’utiliser la distribution 1 – H complète afin d’estimer le risque de propagation verticale des solutés dans le sol. Bien que l’indice de risque montre une certaine invariance vis-à-vis du changement des conditions aux limites il n’est pas un paramètre intrinsèque de sol. Comme le régime d’écoulement dans un même sol peut être dominé soit par le flux matriciel soit par le flux préférentiel le risque de propagation verticale des solutés change. Ceci est une réalité physique et non un défaut dans la théorie de l’indice de risque. Les paramètres de la fonction de Pareto généralisée capturent le régime d’écoulement dominant représenté par les empreintes du traceur. En prenant en compte les conditions aux limites de l’essai de traçage comme l’intensité d’irrigation, le traceur utilisé, l’humidité initiale du sol ou la nature de la végétation (pérenne ou saisonnière, type d’enracinement) il est ainsi possible de comparer des sites différents ou des résultats obtenus sur le même site sous conditions aux limites différentes et d’estimer le risque de propagation verticale de solutés. L’analyse d’image d’empreintes de flux basée sur le risque de propagation verticale de solutés a révélé l’existence d’écoulements préférentiels sur le site allemand. Afin de comprendre les mécanismes de flux ainsi que les impacts éventuels des flux préférentiels sur la chimie du sol nous avons analysé la texture du sol, la densité racinaire, la densité du sol, la concentration des cations échangeables, le pH, et les teneurs en C et N total dans les chemins préférentiels et la matrice du sol. Les résultats de la modélisation indiquent que sur ce site les racines constituent les chemins préférentiels et créent les écoulements le long des macropores, surtout dans la partie supérieure du sol. Dans la partie inférieure la densité racinaire diminue et l’infiltration hétérogène à partir des chemins préférentiels dans la matrice provoque un écoulement non-uniforme. Nous n’avons constaté aucune différence significative de texture, mais des différences de densité du sol dans les chemins préférentiels par rapport à celle de la matrice. Ceci est probablement dû à la quantité de matière organique plus élevée dans les chemins préférentiels. Nous avons également trouvé des pH plus acides, plus de Ca, plus de Mg, et plus de C et de N dans les chemins préférentiels. Comparé à la matrice, des quantités plus importantes d’Al et de Fe (mais de petites quantités absolues) ont été trouvés dans la partie inférieure du sol où l’écoulement préférentiel le long des macropores créés par les racines diminue et le flux matriciel hétérogène domine. Ces propriétés chimiques distinctes peuvent s’expliquer par l’activité racinaire et la translocation de solutés et du carbone organique dissous (COD) le long des chemins préférentiels. Le temps de contact entre le COD et le sol étant réduit il est transporté plus bas dans le profil où il peut potentiellement créer des complexes organo-minéraux. Ainsi, l’écoulement préférentiel est un mécanisme qui peut promouvoir la séquestration de C en sous-sol et n’influence pas uniquement son environnent immédiat, mais aussi les horizons sous-jacents. Un des acquis majeurs de cette thèse est le nombre important d’images d’empreintes de flux issues des sols différents. Dans les études qui suivront les méthodes récentes de réduction de dimensionnalité peuvent être employées afin de trouver d’éventuelles structures de basse dimensionnalité dans ces images / Matrix flow and preferential flow can occur concurrently in the same soil. Both flow regimes produce typical flow patterns that can be visualised in dye tracer experiments. To extract quantitative information from dye tracer studies a vast variability of approaches exists. One of them is to describe dye patterns by the so called dye coverage function, i.e. the percentage of stained area per soil depth. Based on extreme value statistics the dye coverage function can be reinterpreted as a probability function to find the tracer in a certain depth. Therefore, the two-parametric probability distribution 1 – H, H being the generalised Pareto distribution, can be fitted to the dye coverage function. The form parameter of this distribution serves as a risk index for vertical solute propagation. We did tracer experiments with Brilliant Blue FCF at three different study sites: in a Norway spruce forest in southeast Germany, in a tropical mountain rainforest in southern Ecuador and on an agricultural field in southern France. We tested the ability of the risk index to summarise main information obtained in dye tracer studies and characterise flow patterns in different soils under varying boundary conditions. Our results suggest that the risk index is to some degree invariant to changing experimental conditions (such as irrigation rate). The initial soil moisture, however, seems to have a large influence on the risk index. It is difficult to adjust the parameters of the generalised Pareto distribution when the dye coverage function fluctuates or does not decrease monotonically. This might be due to tortuosity of paths, varying flow mechanism or changing soil physical properties (stratification). Thus, in stratified soil, we restricted the analysis to the lowest part of the profile. Since the theory of the risk index is based on extreme values of vertical solute propagation it is the lowest part of the profile that is the most interesting. We propose to combine the two parameters of the generalized Pareto distribution and to use the complete distribution 1 - H to estimate the risk of vertical solute propagation in soils. Despite a certain resistance to changes of experimental conditions, the risk index is not an intrinsic soil parameter. Since the flow regime in the same soil can be dominated either by preferential flow or by uniform matrix flow, the risk of vertical solute propagation will change. It is a physical reality and not a default in the risk index theory. The adjusted parameters of the generalised Pareto distribution will capture the dominant flow regime as reflected by tracer flow patterns. Bearing in mind the boundary conditions of the tracer experiment like irrigation rate, the tracer employed, soil initial moisture or type of vegetation (permanent or seasonal, deep rooted or shallow rooted) it is possible to compare different study sites or to consider the same site at different boundary conditions and to access the risk of vertical solute propagation. Pattern analysis based on the risk index for vertical solute propagation revealed the occurrence of preferential flow at the German study site. To gain insight in flow mechanisms and possible impacts of preferential flow on soil chemistry we analysed soil texture, fine root density, soil bulk density, exchangeable cations, pH and total C and N contents in preferential flow paths and soil matrix. Results from linear mixed-effects models suggested that at this study site roots constituted main preferential flow paths and induced macropore flow, especially in the topsoil. In the subsoil root density decreased and inhomogeneous infiltration from preferential flow paths into the soil matrix caused non-uniform flow. There were no textural differences between the flow domains, but smaller bulk densities in preferential flow paths. This is probably due to a higher soil organic matter content in preferential flow paths. We found smaller pH values, more Ca, more Mg, more C and more N in preferential flow paths. Compared to the adjacent soil matrix, more Al and more Fe (but small absolute amounts) were found in the subsoil where macropore flow along root channels decreases and heterogeneous matrix flow dominates. These distinct chemical properties can be explained by root activity and translocation of solutes and DOC (dissolved organic carbon) via preferential flow paths. During transport along preferential flow paths contact time between DOC and soil is reduced so that DOC is transported to greater depth where it potentially forms organo-mineral associations. If this holds true, preferential flow is a mechanism that promotes C sequestration in subsoil and does not only influence its immediate environment around paths, but also underlying subsoil horizons. A major outcome of this thesis is the large number of images of flow patterns from different soils. Further studies could employ recent dimensionality reduction techniques to investigate whether there is a low dimensional structure underlying these images / Matrixfluss und präferentieller Fluss können in ein und demselben Boden gleichzeitig auftreten. Beide Fließregime erzeugen charakteristische Fließmuster, die in Versuchen mit Farbtracern sichtbar gemacht werden können. Es existiert eine Reihe von Methoden, um Tracerversuche quantitativ auszuwerten. Eine davon ist die Beschreibung der Fließmuster durch die so genannte Deckungsgradfunktion, den Anteil der gefärbten Fläche pro Tiefe. Die Methoden der Extremwertstatistik erlauben eine Neuinterpretation der Deckungsgradfunktion als eine Wahrscheinlichkeitsfunktion, den Tracer in einer bestimmten Tiefe anzutreffen. Demzufolge kann die zweiparametrige Wahrscheinlichkeitsfunktion 1 – H (H: verallgemeinerte Paretoverteilung) an die Deckungsgradfunktion angepasst werden. Der Formparameter dieser Verteilung dient als Risikoindex für vertikale Ausbreitung von gelösten Substanzen. Tracerversuche mit Brilliant Blue FCF wurden an drei unterschiedlichen Standorten durchgeführt: in einem Fichtenwald in Südostdeutschland, einem Bergregenwald in Südostecuador und an einem landwirtschaftlichen Standort in Südfrankreich. Es wurde überprüft, ob die wichtigsten Ergebnisse aus Tracerversuchen auf unterschiedlichen Böden und bei verschiedenen Randbedingungen mithilfe des Risikoindex beschrieben werden können. Die Ergebnisse zeigen eine gewisse Unabhängigkeit des Risikoindex von experimentellen Randbedingungen (wie z. B. Beregnungsintensität). Dagegen scheint die Bodenfeuchte eine zentrale Rolle zu spielen. Schwierigkeiten bei der Anpassung der Parameter der verallgemeinerten Paretoverteilung ergeben sich, wenn die Deckungsfunktion fluktuiert oder nicht monoton fallend ist. Dies kann möglicherweise auf die Tortuosität von Fließpfaden, variierenden Fließmechanismen oder sich verändernden bodenphysikalischen Eigenschaften (Stratifikation) zurückgeführt werden. Daher wurde die Musteranalyse in stratifizierten Böden auf den Unterboden begrenzt. Da die dem Risikoindex zugrunde liegende Theorie auf den Extremwerten der vertikalen Ausbreitung von gelösten Stoffen basiert, gilt das Hauptinteresse dem untersten Teil des Bodenprofils. Wir schlagen vor, die beiden Parameter der verallgemeinerten Wahrscheinlichkeitsverteilung zu nutzen, um das Risiko der vertikalen Ausbreitung von gelösten Stoffen in Böden abzuschätzen. Obwohl der Risikoindex eine gewisse Toleranz gegenüber sich ändernden Randbedingungen zeigt, ist er kein intrinsischer Bodenparameter. Da das Fließgeschehen in ein und demselben Boden sowohl vom Matrix- als auch vom präferentiellen Fluss dominiert werden kann, ändert sich das Risiko der vertikalen Ausbreitung von gelösten Stoffen. Dies ist physikalische Realität und kein Fehler in der Theorie des Risikoindex. Die angepassten Parameter der verallgemeinerten Paretoverteilung erfassen das durch den Tracer sichtbar gemachte dominante Fließregime. Unter der Berücksichtigung der Randbedingungen des Tracerexperiments wie Beregnungsintensität, des verwendeten Tracers, Bodenfeuchte oder Art der Vegetation (einjährig, mehrjährig oder perennierend, tiefwurzelnd oder flachwurzelnd) ist es möglich, unterschiedliche Standorte zu vergleichen oder denselben Standort unter verschiedenen Randbedingungen zu betrachten und das Risiko der vertikalen Ausbreitung von gelösten Stoffen abzuschätzen. Extremwertstatistikgestützte Musteranalyse zeigte das Auftreten von präferentiellem Fluss auf dem Standort in Südostdeutschland. Um die Fließmechanismen und mögliche Auswirkungen des präferentiellen Flusses auf die Bodenchemie aufzudecken, wurden Textur, Feinwurzeldichte, Trockenraumdichte, austauschbare Kationen, pH, Gehalt an totalem C und N in präferentiellen Fließwegen und Bodenmatrix analysiert. Ergebnisse aus gemischten Modellen zeigen, dass auf diesem Standort präferentielle Fließwege durch Wurzeln gebildet werden, und zwar hauptsächlich im Oberboden. Im Unterboden nimmt die Durchwurzelung ab, und heterogene Infiltration aus den präferentiellen Fließpfaden in die Bodenmatrix führt zu ungleichmäßigem Matrixfluss. Es wurden keine signifikanten Unterschiede in der Textur gefunden. Allerdings ist die Trockenraumdichte in den präferentiellen Fließwegen geringer als in der Bodenmatrix, wahrscheinlich bedingt durch den erhöhten Gehalt an organischer Materie. Weiterhin wurden in den präferentiellen Fließwegen niedrigere pH-Werte, höherer Gehalt an Ca, Mg, C und N gemessen. Im Vergleich zur umgebenden Bodenmatrix wurde im weniger durchwurzelten und von heterogenem Matrixfluss dominierten Unterboden höherer Gehalt an Al und Fe (allerdings kleine absolute Mengen) festgestellt. Diese klar unterschiedlichen chemischen Eigenschaften lassen sich durch Wurzelaktivitäten und den Transport von gelösten Substanzen (darunter auch DOC: gelöster organischer Kohlenstoff) durch präferentielle Fließwege erklären. Während des Transports ist die Kontaktzeit zwischen dem DOC und dem Boden verkürzt, so dass der Kohlenstoff in tiefere Bodenhorizonte transportiert wird, in denen er eventuell organo-mineralische Komplexe bilden kann. Dies würde bedeuten, dass präferentieller Fluss unter Umständen die Kohlenstoff-Sequestration im Unterboden begünstigen könnte, und nicht nur seine unmittelbare Umgebung, sondern auch die tiefer liegenden Bodenhorizonte beeinflusst. Ein wichtiges Ergebnis dieser Untersuchungen ist die große Anzahl an Bildern der Fließmuster in verschiedenen Böden. In nachfolgenden Arbeiten könnte mit den neuesten Methoden der Reduktion der Dimension untersucht werden, ob diesen Bildern eine niedrigdimensionale Struktur zugrunde liegt

<p>Understanding of the processes affecting solute transport in flowing water is important for the possibility to predict the evolution with time of polluted stream systems. </p><p>This thesis presents tracer experiment methodology and model developments for solute transport in streams, with special focus on retention processes and their effect on solute stream transport. Results are presented from a tracer experiment in the Säva Stream, Uppland County, Sweden, where both a conservative (³H as tritiated water) and a reactive (⁵¹Cr as trivalent chromium ion) tracer were injected simultaneously. The time and length scales of the experiment were prolonged compared to previous studies, which allowed for new critical tests of different model concepts. </p><p>It was found that the hyporheic exchange greatly affected the solute transport of both tracers. However, the retention of chromium was significantly more pronounced. About 76% of the injected chromium was lost from the stream water phase directly after the passage of the pulse 30 km downstream of the injection point. The inventory of chromium in the sediments indicated that the main part was retrieved in the hyporheic zone. </p><p>Both a diffusive and an advective hyporheic exchange model were developed and evaluated versus independent observations in the stream water and hyporheic zone. Analytical expressions for the central temporal moments of the breakthrough curve and semi-analytical solutions for the solute concentration in the Laplace domain were derived. Both models were found useful in representing the observations.</p><p>For the transport of the reactive solute, it was found essential to consider a kinetic sorption on to particulate matter in the hyporheic zone. The time needed for a wash-out of 75% of the maximum uptake in the hyporheic zone was found to be ~85 times longer for the reactive solute, compared to the conservative solute. Neglecting the sorption kinetics in the transport model yielded significant errors in the central temporal moments, which implied an incorrect description of the wash-out process from the hyporheic zone. Independent observations in the stream water and hyporheic zone as well as choice of evaluation method are essential for a correct interpretation of the processes.</p><p>A first attempt was also made to link model parameters such as the residence time in the hyporheic zone with measurable parameters of the stream. Such a relationship offers the possibility to generalize results for other streams and stream conditions. A generic study of the transport of an inert solute in the Lule River, Sweden, using this kind of relationship, indicated that the hyporheic exchange can have a large practical implication.</p>

Understanding of the processes affecting solute transport in flowing water is important for the possibility to predict the evolution with time of polluted stream systems. This thesis presents tracer experiment methodology and model developments for solute transport in streams, with special focus on retention processes and their effect on solute stream transport. Results are presented from a tracer experiment in the Säva Stream, Uppland County, Sweden, where both a conservative (3H as tritiated water) and a reactive (51Cr as trivalent chromium ion) tracer were injected simultaneously. The time and length scales of the experiment were prolonged compared to previous studies, which allowed for new critical tests of different model concepts. It was found that the hyporheic exchange greatly affected the solute transport of both tracers. However, the retention of chromium was significantly more pronounced. About 76% of the injected chromium was lost from the stream water phase directly after the passage of the pulse 30 km downstream of the injection point. The inventory of chromium in the sediments indicated that the main part was retrieved in the hyporheic zone. Both a diffusive and an advective hyporheic exchange model were developed and evaluated versus independent observations in the stream water and hyporheic zone. Analytical expressions for the central temporal moments of the breakthrough curve and semi-analytical solutions for the solute concentration in the Laplace domain were derived. Both models were found useful in representing the observations. For the transport of the reactive solute, it was found essential to consider a kinetic sorption on to particulate matter in the hyporheic zone. The time needed for a wash-out of 75% of the maximum uptake in the hyporheic zone was found to be ~85 times longer for the reactive solute, compared to the conservative solute. Neglecting the sorption kinetics in the transport model yielded significant errors in the central temporal moments, which implied an incorrect description of the wash-out process from the hyporheic zone. Independent observations in the stream water and hyporheic zone as well as choice of evaluation method are essential for a correct interpretation of the processes. A first attempt was also made to link model parameters such as the residence time in the hyporheic zone with measurable parameters of the stream. Such a relationship offers the possibility to generalize results for other streams and stream conditions. A generic study of the transport of an inert solute in the Lule River, Sweden, using this kind of relationship, indicated that the hyporheic exchange can have a large practical implication.

The euthropthication of the Baltic Sea is a threat that is beginning to be taken seriously by the governments concerned. In Sweden, regulations concerning the allowed nitrogen (N) concentration in the effluent water from wastewater treatment plants are being tightened up. The Rimbo wastewater treatment plant has been imposed to reduce the annual mean concentration of total N in the effluent water to levels below 15 mg l-1. A more and more common way to reduce the nitrogen level in wastewater is to let the water pass through a wetland. This study investigates the possibility to build this kind of wetland at the outlet of the Rimbo wastewater treatment plant. A prestudy of the topography, soil characteristics and groundwater flow indicates that the land area in question is well suited for the construction of a wetland. A proposal for the design has been made by using a physically based computer model developed in the PRIMROSE project (PRocess based Integrated Management of constructed and Riverine wetlands for Optimal control of wastewater at catchment ScalE), which is financed by the EU. Analysis of the residence time distribution (RTD) is a tool for understanding wetland design characteristics and can be used for wetland engineering such as optimizing design for best possibleefficiency in nitrogen removal. In order to characterize the performance of a wetland, it is useful to translate the RTD to a key figure representing the treatment efficiency. In this work, two types of such key figures have been used. Key figure 1 gives the hydraulic efficiency and Key figure 2 gives an estimation of the nitrogen retention by an integration of hydraulic characteristics and the chemical transformation of nitrogen. The results of this study show that constructing a wetland in Rimbo probably would be an efficient way to reduce the nitrogen level at the effluent of the wastewater plant below the limits of the regulations. In addition, a wetland would form a nice place of recreation for the people in Rimbo and also make a good habitat for birds. / Övergödningen i Östersjön är ett problem som uppmärksammas alltmer. Ett led i att minska kvävebelastningen på Östersjön är ökade krav på rening i de svenska kommunala reningsverken. Rimbo avloppsreningsanläggning har blivit ålagd ett riktvärde för totalkväve på 15 mg l-1 i utgående vatten, vilket motsvarar en reningsgrad som inte uppnås idag. Ett alltmer vanligt sätt att minska föroreningshalterna är att anlägga våtmarker i anslutning till reningsverken för att efterpolera spillvattnet. Det här arbetet är en del av en förstudie till en sådan våtmark i Rimbo. En förundersökning av topografi, jordart och grundvattenflöden indikerar att det område som föreslagits i anslutning till reningsverket i Rimbo lämpar sig väl för ett våtmarksbygge. Förslag till utformning har tagits fram med hjälp av en fysikaliskt baserad modell över vattenströmning, utvecklad inom det EU-finansierade projektet PRIMROSE (PRocess based Integrated Management of constructed and Riverine wetlands for Optimal control of wastewater at catchment ScalE). Analys av vattnets uppehållstidsfördelning ger förståelse för våtmarkens egenskaper och kan därför användas vid t ex optimering av våtmarksdesign med avseende på kväverening. För att på ett enkelt sätt kunna jämföra olika våtmarkers effektivitet är det praktiskt att översätta uppehållstidsfördelningen till ett nyckeltal för reningseffekten. I det här arbetet har två olika sådana nyckeltal beräknats. Det första ger den hydrauliska effektiviteten och det andra bygger på en metod där våtmarkens interna hydraulik integreras med den kemiska omvandlingen av kväve. Nyckeltal 1 ger ett mått på hur stor del av volymen i våtmarken som används för kväverening, medan Nyckeltal 2 ger ett mått på den procentuella kväveavskiljningen. Den här förstudien visar att en våtmark sannolikt skulle vara ett utmärkt sätt att klara riktvärdet för kvävehalten vid reningsverket i Rimbo. Därutöver skulle en våtmark kunna utgöra ett positivt inslag i landskapet och öka den biologiska mångfalden, inte minst vad gäller fågelliv.

<p>Treatment wetlands play an important role in reducing nitrogen content in wastewater and agricultural run-off water. The main removal process is denitrification and the removal efficiency depends on the hydrological and microbiological features of the wetland, especially in terms of water residence times and denitrification rates. The aim of this thesis was to increase the understanding of the coupled hydrological and microbiological processes regulating the denitrification capacity. This was done by applying a broad spectrum of analyses methods, including tracer experiment, water flow modeling, denitrification rate measurements, and analyses of the microbial community structures. The tracer experiment and flow modeling revealed that the wetland design, especially the vegetation, largely can affect the water residence time distributions in wetlands. In the investigated wetland, vegetation dominated the water flow, explaining 60-80% of the variance in water residence times, whereas basin shape only explained about 10% of the variance, but also mixing phenomena significantly affected the residence times and could considerably delay solutes. Measured potential denitrification rates in the wetland exhibited significant spatial variations, and the variations were best described by concentration of nitrogen in sediments and water residence time. Analyses of the denitrifying bacteria populations indicated that a few key populations dominated and that the community diversity increased with decreasing nutrient levels and increasing water residence times. Moreover, it was found that denitrification rates in terms of Menten and first order kinetics can be evaluated by fitting a mathematical expression, considering denitrification and other nitrogen transforming processes to measured product formation in nitrate limited experiments.</p>

When protection zones for wells are delineated, it is important to acquire good knowledge about possible travel time from different points in the catchment area to the well. Often, simple analytical methods are used for estimating travel times and the assumption is made that the hydraulic conductivity is relatively homogenous within the aquifer. Nevertheless, many aquifers are strongly heterogeneous which may lead to differences between estimates and actual travel times. As a part of the process to develop improved methods for delineating protection zones for groundwater supply wells, a tracer experiment was performed in a glaciofluvial esker formation in Järlåsa. On the basis of the experiment, a numerical flow model was created for the test site. The purpose of this master’s thesis was to apply the flow model to an aquifer where the hydraulic conductivity shows great variability and should be described by a stochastic distribution. The purpose was also to determine the statistical properties of the hydraulic conductivity and to simulate the transport times and their variation from different locations in the aquifer to the pumping well. The hydraulic conductivity was estimated from grain size distributions in soil samples that were taken at various locations within the test site. The analysis of the hydraulic conductivity showed a large variation and confirmed the hypothesis that the aquifer is heterogeneous. Using the statistics, a large number of stochastic conductivity fields were created and flow simulation was performed for each realization. From the simulation result, frequency distributions of the transport times were produced describing the probability for the transit time for a water particle between a certain location in the aquifer and the pumping well. A comparison with the tracer experiment shows higher simulated transport times implying the need for improved model calibration. The conclusion is that the method used in this project is suitable for glaciofluvial esker aquifers. When protection zones are delineated, stochastic modeling can be used to express the zone boundaries in statistical terms. / När skyddsområden för grundvattentäkter skapas är det viktigt att ha god kännedom om vattnets transporttider från olika delar i tillrinningsområdet till uttagsplatsen av grundvattnet. Metoderna för att bestämma dessa tider är ofta enkla och vanligen görs antagandet att områdets hydrauliska konduktivitet är relativt homogen. Många akviferer är dock kraftigt heterogena och de verkliga transporttiderna kan då skilja sig från de uppskattade. Som ett led i metodutvecklingen för bättre avgränsning av skyddsområden genomfördes ett spårämnesförsök i en isälvsavlagring i Järlåsa. Med utgångspunkt från försöket har en numerisk flödesmodell konstruerats över försöksområdet. Syftet med examensarbetet var att tillämpa flödesmodellen i en akvifer där den hydrauliska konduktiviteten visar sådana variationer att den beskrivs bäst av en stokastisk fördelning. Vidare var syftet att bestämma den hydrauliska konduktivitetens statistiska egenskaper och att simulera transporttiderna och deras variation från olika punkter i akviferen till pumpbrunnen. Den hydrauliska konduktiviteten uppskattades utifrån kornstorleksfördelningar i jordprover som togs på en mängd platser i försöksområdet. Analysen av den hydrauliska konduktiviteten visar stora variationer i området vilket bekräftar att akviferen är heterogen. Utifrån konduktivitetens statistik genererades ett stort antal stokastiska konduktivitetsfält och transporttiderna beräknades för varje realisering. Resultatet från simuleringarna gav frekvensfördelningar för transporttiderna som beskriver sannolikheten för hur lång uppehållstid en vattenpartikel har i marken mellan en startpunkt och pumpbrunnen. Jämfört med spårämnesförsöket blev de simulerade transporttiderna något större vilket tyder på att flödesmodellen kräver en bättre kalibrering mot fältmätningar. Slutsatsen är att metodiken är lämplig för att studera vattnets transporttider i isälvsavlagringen och när ett skyddsområde skapas för den här typen av akvifer kan stokastisk modellering användas för att beskriva skyddszoner i form av statistiska termer.