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Flow Dynamics and Reactivity in the Transition Zone Between Streams and Riparian Aquifers.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Flow Dynamics and Reactivity in the Transition Zone Between Streams and Riparian Aquifers./
作者:	Nogueira, Guilherme Emidio Horta.
面頁冊數:	1 online resource (194 pages)
附註:	Source: Dissertations Abstracts International, Volume: 84-05, Section: B.
Contained By:	Dissertations Abstracts International84-05B.
標題:	Water quality. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=29805393click for full text (PQDT)
ISBN:	9798352983751

Flow Dynamics and Reactivity in the Transition Zone Between Streams and Riparian Aquifers.
Nogueira, Guilherme Emidio Horta.

Flow Dynamics and Reactivity in the Transition Zone Between Streams and Riparian Aquifers. - 1 online resource (194 pages)

Source: Dissertations Abstracts International, Volume: 84-05, Section: B.

Thesis (Ph.D.)--Universitaet Bayreuth (Germany), 2022.

Includes bibliographical references

The stream water (SW) and groundwater (GW) domains are two parts of one hydrologic continuum. The riparian zone (RZ) is a transition zone between both domains, which connects the aquatic and terrestrial ecosystems. The RZ has been shown to have a potential for regulating water quality in stream-corridors. This potential is mainly related to SW-GW interactions and the associated hydrological and biogeochemical processes occurring at different spatio-temporal scales within RZ. Mixing of different solutes, and high microbial activities are only some of the factors responsible for the high potential for contaminant attenuation and general solutes turnover within RZ. However, an adequate representation of these coupled processes, and their variations in space and time is challenging due to the multiple interactions between the hydrological and biogeochemical processes. This PhD addresses this challenge by aiming at an evaluation of the effects of flow dynamics on riparian reactive potential at different scales. The three consecutive studies comprising this thesis were carried out in a well-instrumented RZ located at the low-land portion of the Selke River catchment, a 4th-order stream, central Germany. The location is well suited for this type of research since it is well instrumented and has a long history of agricultural activity within the riparian corridor with associated inputs of nitrate (NO3-) into the riparian aquifer. This thesis combines data-driven and numerical modelling in order to explore and disentangle the different factors and processes shaping water quality at the different scales within the RZ.As dissolved oxygen (DO) is a key-component regulating the redox state of the system, in the data-driven analyses (Study 1), a suite of tracer-tests were carried out and combined with high-resolution hydrological and chemical data to characterize the near stream system (appx. 20m from stream bank) for aerobic respiration. For that, Damkohler numbers for DO (DADO) were employed. Results showed that seasonal and short-term variations in temperature are major controls shaping the reactive state of the system. Seasonal temperature variations in GW induce a shift on reactive state from transport-limited (DADO>1) in summer to reaction-limited conditions (DADO<1) in winter. On the other hand, short-term events had only minor impacts on the system, resulting in slightly less transport-limited conditions due to decreasing temperature and transit-times associated with the events. The study also shows that assuming a constant water temperature along a SW infiltration flowpath could lead to an over- or underestimation of reaction rates by a factor of 2-3 due to different infiltrating water temperature at the SW-GW interface. Also assuming constant water transit-times throughout the hydrological year results in an underestimation of NO3- removal (40%-50% difference).The numerical modelling of Study 2 focused on the simulation of water flow and mass (DO and NO3-) transport using the measured data from Study 1 but extended the spatial scale. The modelling concept combined a fully-integrated 3D transient numerical flow model with a temperature-dependent reactive transport along subsurface flow paths. Results revealed that temperature variations shift the reactive zone for NO3-, whereas this zone is near the stream under warmer conditions. Even under limited carbon availability (as an electron donor) and low-temperatures, NO3- removal fractions (RNO3) were greater further from the stream than along short hyporheic flow paths (RNO3=0.4 and RNO3=0.1, respectively). Conversely, transit-times and DO concentrations constrained nitrate removal at the near stream region. Additionally, with increasing temperature, the effects of stream flow and solute concentrations on biogeochemical turnover and the redox zonation around the stream strongly decreased. The modelling concept of this study provides an adaptive framework to quantify reach-scale biogeochemical turnover around hydrological dynamic streams.In Study 3, the flow model is coupled with a Hydraulic Mixing Cell method for mapping the source composition of water and tracking their spatio-temporal evolution within RZ. This allowed the identification of mixing hotspots which can be defined to have nearly equal fractions of SW and GW per aquifer volume. These mixing hotspots can facilitate mixing-dependent reactions and solute turnover. Only about 9% of the total simulated domain could be identified as mixing hot-spots (mainly at the fringe of the geochemical hyporheic zone), but this value could be 1.5x higher following large discharge events. Such events increase mixing further away from the stream, whereas near the stream the rapid increase of SW influx shifts the ratio between the water fractions to SW, reducing the potential for mixing and the associated reactions. The study also provides an easy-to-transfer approach to assess spatio-temporal patterns of mixing processes and mixing-dependent turnover reactions in riparian zones.In summary, findings from the three studies elucidated the relationships and controls among hydrology and biogeochemistry at different scales in the RZ. By combining innovative methods and using coupled, mechanistic models, this thesis advanced the understanding of reactive potentials within the RZ, which can be useful to devise further research and actions for integrated aquatic ecosystem management and recovery.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798352983751Subjects--Topical Terms:

556913
Water quality.
Index Terms--Genre/Form:

542853
Electronic books.

Flow Dynamics and Reactivity in the Transition Zone Between Streams and Riparian Aquifers.
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245 1 0 $a Flow Dynamics and Reactivity in the Transition Zone Between Streams and Riparian Aquifers.
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500 $a Source: Dissertations Abstracts International, Volume: 84-05, Section: B.
500 $a Advisor: Fleckenstein, Jan H.; Frei, Sven.
502 $a Thesis (Ph.D.)--Universitaet Bayreuth (Germany), 2022.
504 $a Includes bibliographical references
520 $a The stream water (SW) and groundwater (GW) domains are two parts of one hydrologic continuum. The riparian zone (RZ) is a transition zone between both domains, which connects the aquatic and terrestrial ecosystems. The RZ has been shown to have a potential for regulating water quality in stream-corridors. This potential is mainly related to SW-GW interactions and the associated hydrological and biogeochemical processes occurring at different spatio-temporal scales within RZ. Mixing of different solutes, and high microbial activities are only some of the factors responsible for the high potential for contaminant attenuation and general solutes turnover within RZ. However, an adequate representation of these coupled processes, and their variations in space and time is challenging due to the multiple interactions between the hydrological and biogeochemical processes. This PhD addresses this challenge by aiming at an evaluation of the effects of flow dynamics on riparian reactive potential at different scales. The three consecutive studies comprising this thesis were carried out in a well-instrumented RZ located at the low-land portion of the Selke River catchment, a 4th-order stream, central Germany. The location is well suited for this type of research since it is well instrumented and has a long history of agricultural activity within the riparian corridor with associated inputs of nitrate (NO3-) into the riparian aquifer. This thesis combines data-driven and numerical modelling in order to explore and disentangle the different factors and processes shaping water quality at the different scales within the RZ.As dissolved oxygen (DO) is a key-component regulating the redox state of the system, in the data-driven analyses (Study 1), a suite of tracer-tests were carried out and combined with high-resolution hydrological and chemical data to characterize the near stream system (appx. 20m from stream bank) for aerobic respiration. For that, Damkohler numbers for DO (DADO) were employed. Results showed that seasonal and short-term variations in temperature are major controls shaping the reactive state of the system. Seasonal temperature variations in GW induce a shift on reactive state from transport-limited (DADO>1) in summer to reaction-limited conditions (DADO<1) in winter. On the other hand, short-term events had only minor impacts on the system, resulting in slightly less transport-limited conditions due to decreasing temperature and transit-times associated with the events. The study also shows that assuming a constant water temperature along a SW infiltration flowpath could lead to an over- or underestimation of reaction rates by a factor of 2-3 due to different infiltrating water temperature at the SW-GW interface. Also assuming constant water transit-times throughout the hydrological year results in an underestimation of NO3- removal (40%-50% difference).The numerical modelling of Study 2 focused on the simulation of water flow and mass (DO and NO3-) transport using the measured data from Study 1 but extended the spatial scale. The modelling concept combined a fully-integrated 3D transient numerical flow model with a temperature-dependent reactive transport along subsurface flow paths. Results revealed that temperature variations shift the reactive zone for NO3-, whereas this zone is near the stream under warmer conditions. Even under limited carbon availability (as an electron donor) and low-temperatures, NO3- removal fractions (RNO3) were greater further from the stream than along short hyporheic flow paths (RNO3=0.4 and RNO3=0.1, respectively). Conversely, transit-times and DO concentrations constrained nitrate removal at the near stream region. Additionally, with increasing temperature, the effects of stream flow and solute concentrations on biogeochemical turnover and the redox zonation around the stream strongly decreased. The modelling concept of this study provides an adaptive framework to quantify reach-scale biogeochemical turnover around hydrological dynamic streams.In Study 3, the flow model is coupled with a Hydraulic Mixing Cell method for mapping the source composition of water and tracking their spatio-temporal evolution within RZ. This allowed the identification of mixing hotspots which can be defined to have nearly equal fractions of SW and GW per aquifer volume. These mixing hotspots can facilitate mixing-dependent reactions and solute turnover. Only about 9% of the total simulated domain could be identified as mixing hot-spots (mainly at the fringe of the geochemical hyporheic zone), but this value could be 1.5x higher following large discharge events. Such events increase mixing further away from the stream, whereas near the stream the rapid increase of SW influx shifts the ratio between the water fractions to SW, reducing the potential for mixing and the associated reactions. The study also provides an easy-to-transfer approach to assess spatio-temporal patterns of mixing processes and mixing-dependent turnover reactions in riparian zones.In summary, findings from the three studies elucidated the relationships and controls among hydrology and biogeochemistry at different scales in the RZ. By combining innovative methods and using coupled, mechanistic models, this thesis advanced the understanding of reactive potentials within the RZ, which can be useful to devise further research and actions for integrated aquatic ecosystem management and recovery.
520 $a Die Bereiche Fliesgewasser (SW) und Grundwasser (GW) sind Teile eine hydrologischen Kontinuums, das durch eine Ubergangszone verbunden ist. Die Flussauen (RZ), als Ubergangszone zwischen aquatischen und terrestrischen Okosystemen, ist fur ihr groses Potenzial zur Regulierung der Wasserqualitat in Flusskorridoren bekannt. Dieses Potenzial hangt hauptsachlich mit den Wechselwirkungen zwischen hydrologischen und biogeochemischen Prozessen zusammen, die auf verschiedenen raumlichen und zeitlichen Skalen innerhalb der RZ stattfinden. SW-GW-Austauschprozesse, die Durchmischung verschiedener geloster Stoffe und hohe mikrobielle Aktivitat sind nur einige der Faktoren, die fur das hohe Potenzial zur Schadstoffabschwachung und zum weiteren Stoffumsatz in den Flussauen verantwortlich sind. Die Darstellung solcher gekoppelter Prozesse sowie ihrer raumlichen und zeitlichen Variationen ist jedoch aufgrund der vielfaltigen Wechselwirkungen zwischen den hydrologischen und biogeochemischen Prozessen, die beim Durchfluss des Wassers durch die Ufersedimente berucksichtigt werden mussen, schwierig. Daher ist die Bewertung der Auswirkungen der Abflussdynamik auf das reaktive Potenzial von RZ auf verschiedenen Ebenen ein anspruchsvolles Ziel, zu dem dieses Dissertationsprojekt beitragen soll. Die drei verschiedenen Studien, die diese Dissertation umfassen, wurden in einer RZ im unteren Einzugsgebiets der Selke, einem Fluss vierter Ordnung in Mitteldeutschland durchgefuhrt. Der Standort ist fur die Untersuchung sehr gut geeignet, da er gut instrumentiert ist und das Gebiet durch eine langjahrige landwirtschaftliche Nutzung und eine damit verbundene Verschmutzung des Grundwassers mit Nitrat (NO3-) gepragt ist. In dieser Arbeit werden datengestutzte und numerische Modellierung kombiniert, um die verschiedenen Faktoren und Prozesse, die die Wasserqualitat auf den verschiedenen Skalen innerhalb der RZ pragen, zu untersuchen und zu verstehen.Da geloster Sauerstoff (DO) eine Schlusselkomponente ist, die den Redox-Zustand des Systems reguliert, wurden in den datengestutzten Analysen (Studie 1) eine Reihe von Tracer-Tests durchgefuhrt und mit hochauflosenden hydrologischen und chemischen Daten kombiniert, um das flussnahe System (ca. 20 m vom Flussufer entfernt) hinsichtlich des DO-Umsatzpotenzials zu charakterisieren. Dazu wurden Damkohler-Zahlen fur den DO-Verbrauch (DADO) verwendet. Die Ergebnisse zeigen, dass saisonale und kurzfristige Temperaturschwankungen den reaktiven Zustand des Systems masgeblich beeinflussen. Saisonale Temperaturschwankungen im Grundwasser verschieben den reaktiven Zustand des Systems von transportlimitierten (DADO>1) im Sommer zu reaktionslimitierten Bedingungen (DADO<1) im Winter. Andererseits hatten kurzfristige Ereignisse nur geringfugige Auswirkungen auf das System. Da hydrologische Ereignisse durch verminderte Wassertemperatur und kurzere Aufenthaltszeiten charakterisiert sind, reduzierte sich die Transportlimitierung des Systems leicht, Die Studie zeigt auch, dass die Annahme einer konstanten Wassertemperatur entlang eines SW-Infiltrationspfades zu einer Uber- oder Unterschatzung der Reaktionsraten um den Faktor 2-3 fuhren kann, wenn sich die Temperatur des infiltrierenden Wassers von der in der Flussaue unterscheidet. Auch die Annahme konstanter Verweilzeiten des Wassers wahrend des gesamten hydrologischen Jahres fuhrt zu einer Unterschatzung des NO3- Abbaus (40-50% Unterschied).Die numerische Modellierung in Studie 2 konzentrierte sich auf die Simulation des Wasserflusses und des Stofftransports (DO und NO3-) unter Verwendung der Messdaten aus Studie 1, wobei die raumliche Skala erweitert wurde. Diese Modellierung kombinierte ein vollstandig integriertes instationares, numerisches 3D-Stromungsmodell mit einem temperaturabhangigen reaktiven Transport entlang Grundwasserfliespfaden. Die Ergebnisse zeigen, dass Temperaturschwankungen die reaktive Zone fur NO3- verschieben, wahrend diese Zone unter warmeren Bedingungen in der Nahe des Flusses liegt. Sogar bei begrenzter Kohlenstoffverfugbarkeit (als Elektronendonor) und niedrigen Temperaturen waren die Anteile der NO3- Entfernung (RNO3) weiter entfernt vom Fluss groser als entlang kurzer hyporheischer Fliespfade (RNO3=0,4 bzw. RNO3=0,1). Umgekehrt schrankten Transitzeiten und DO-Konzentrationen den Nitratabbau in der stromnahen Region ein. Mit zunehmender Temperatur verringerten sich die Auswirkungen der Stromungmuster und der Konzentration geloster Stoffe auf den biogeochemischen Umsatz und die Redoxzonierung in der Umgebung des Flusses stark. Daruber hinaus bietet diese Studie einen anpassungsfahigen Rahmen zur Quantifizierung des biogeochemischen Umsatzes auf Reichweitenbasis in hydrologisch dynamischen Fliesgewassern.In Studie 3 wurde das Stromungsmodell mit einer Hydraulic Mixing Cell Methode gekoppelt, um die Quellzusammensetzung der Wasser zu kartieren und ihre raumlich-zeitliche Entwicklung in der Flussaue zu verfolgen. Dies ermoglichte die Identifizierung von Zonen mit ahnlichen Anteilen von SW und GW pro Aquifervolumen (d. h. "Mischungs-Hotspots"), die mischungsabhangige Reaktionen ermoglichen. Nur etwa 9% des gesamten simulierten Bereichs wurden als Mischungs-Hotspots identifiziert (hauptsachlich am Rande der geochemischen hyporheischen Zone), aber dieser Wert konnte nach grosen Abflussereignissen bis zu 1,5-mal hohere Werte erreichen. Solche Ereignisse verstarken die Durchmischung von Fluss- und Grundwasser in groserer Entfernung vom Fluss, wohingegegen in der Nahe des Flusses der rasche Anstieg des SW-Zuflusses das Verhaltnis zwischen den Wasserfraktionen zu SW verschiebt, wodurch das Potenzial fur die Durchmischung und die damit verbundenen Reaktionen verringert wird. Die Studie bietet einen leicht ubertragbaren Ansatz zur Bewertung der raumlich-zeitlichen Muster des Durchmischungsprozesses und dessen Auswirkungen auf die Biogeochemie der Auenzone in Bezug auf mischungsabhangige Umsatzprozesse. Zusammenfassend.verdeutlichen die Ergebnisse der drei Studien die Beziehungen zwischen hydrologischen und biogeochemischen Prozessen auf verschiedenen Raumskalen in der RZ. Durch die Kombination von innovativer Methoden und gekoppelten, mechanistichen Modellen hat diese Arbeit das Verstandnis des reaktiven Potenzials von Falussauen verbessert, was eine Grundlage fur weitere Forschung sowie Masnahmen fur eine integrierte Bewirtschaftung zur Wiederherstellung aquatischer Okosysteme in Flussauen bieten kann.
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538 $a Mode of access: World Wide Web
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