Estimates of water partitioning in complex urban landscapes with isotope‐aided ecohydrological modelling

Urban green space is increasingly viewed as essential infrastructure to build resilience to climate change by retaining water in the city landscape and balancing ecohydrological partitioning into evapotranspiration for cooling and groundwater recharge. Quantifying how different vegetation types affect water partitioning is essential for future management, but paucity of data and the complex heterogeneity of urban areas make water balance estimates challenging. Here, we provide a preliminary assessment of water partitioning from different sized patches of trees and grass as well as from sealed surfaces. To do this, we used limited field observations together with an advanced, process-based tracer-aided ecohydrological model at a meso-scale (5 km2) in central Berlin, Germany. Transpiration was the dominant green water flux accounting for over 50% of evapotranspiration in the modelled area. Green water fluxes were in general greater from trees compared with grass, but grass in large parks transpired more water compared with grass in small parks that were intensively used for recreation. Interception evaporation was larger for trees compared with grass, but soil water evaporation was greater for grass compared with trees. We also show that evapotranspiration from tree-covered areas comprise almost 80% of the total evapotranspiration from the whole model domain while making up less than 30% of the surface cover. The results form an important stepping-stone towards further upscaling over larger areas and highlights the importance of continuous high-resolution hydrological measurements in the urban landscape, as well as the need for improvements to ecohydrological models to capture important urban processes.Berlin University Alliance / Einstein Stiftung Berlin, Climate and Water under ChangeDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Einstein Stiftung Berlin http://dx.doi.org/10.13039/501100006188Leverhulme Trust http://dx.doi.org/10.13039/501100000275Urban Climate Observatory (UCO) BerlinPeer Reviewe

Quantifying the effects of urban green space on water partitioning and ages using an isotope-based ecohydrological model

Funding Information: Einstein Stiftung Berlin (grant no. EVF-2018-425), the Deutsche Forschungsgemeinschaft (grant no. GRK 2032/2), the Bundesmin-isterium für Bildung und Forschung (grant no. 01LP1602) and the Leverhulme Trust (grant no. RPG-2018-375). This open-access publication was funded by Technische Universität Berlin. Acknowledgements. The authors wish to thank the Einstein Foundation for financing the MOSAIC project, in which this study was performed. Contributions from Chris Soulsby were also funded by the Leverhulme Trust’s ISOLAND project. The German Federal Ministry of Education and Research (BMBF) funded instrumentation of the Urban Climate Observatory (UCO) Berlin under grant 01LP1602 within the framework of Research for Sustainable Development (FONA; https://www.fona.de, last access: 21 June 2021). We also acknowledge support by the German Research Foundation and the Open Access Publication Fund of TU Berlin. The majority of the simulations were performed on the High Performance Computing cluster of TU Berlin. We thank Christian Marx for regular input during the modelling process, Lukas Kleine for help with figures and Ralf Duda for indispensable help with technical issues throughout the modelling process.Peer reviewedPublisher PD

Response of Submerged Macrophyte Communities to External and Internal Restoration Measures in North Temperate Shallow Lakes

Submerged macrophytes play a key role in north temperate shallow lakes by stabilising clear-water conditions. Eutrophication has resulted in macrophyte loss and shifts to turbid conditions in many lakes. Considerable efforts have been devoted to shallow lake restoration in many countries, but long-term success depends on a stable recovery of submerged macrophytes. However, recovery patterns vary widely and remain to be fully understood. We hypothesize that reduced external nutrient loading leads to an intermediate recovery state with clear spring and turbid summer conditions similar to the pattern described for eutrophication. In contrast, lake internal restoration measures can result in transient clear-water conditions both in spring and summer and reversals to turbid conditions. Furthermore, we hypothesize that these contrasting restoration measures result in different macrophyte species composition, with added implications for seasonal dynamics due to differences in plant traits. To test these hypotheses, we analysed data on water quality and submerged macrophytes from 49 north temperate shallow lakes that were in a turbid state and subjected to restoration measures. To study the dynamics of macrophytes during nutrient load reduction, we adapted the ecosystem model PCLake. Our survey and model simulations revealed the existence of an intermediate recovery state upon reduced external nutrient loading, characterised by spring clear-water phases and turbid summers, whereas internal lake restoration measures often resulted in clear-water conditions in spring and summer with returns to turbid conditions after some years. External and internal lake restoration measures resulted in different macrophyte communities. The intermediate recovery state following reduced nutrient loading is characterised by a few macrophyte species (mainly pondweeds) that can resist wave action allowing survival in shallow areas, germinate early in spring, have energy-rich vegetative propagules facilitating rapid initial growth and that can complete their life cycle by early summer. Later in the growing season these plants are, according to our simulations, outcompeted by periphyton, leading to late-summer phytoplankton blooms. Internal lake restoration measures often coincide with a rapid but transient colonisation by hornworts, waterweeds or charophytes. Stable clear-water conditions and a diverse macrophyte flora only occurred decades after external nutrient load reduction or when measures were combined.Additional co-authors: Wolf M. Mooij, Ruurd Noordhuis, Geoff Phillips, Jacqueline Rücker, Hans-Heinrich Schuster, Martin Søndergaard, Sven Teurlincx, Klaus van de Weyer, Ellen van Donk, Arno Waterstraat and Carl D. Saye

Där Åkerströmmen svämmar över.

Det går att hävda att Sverige är förskonat från katastrofala översvämningar och med största sannolikhet kommer vi inte behöva uppleva en förödelse såsom den i Pakistan år 2010. Samtidigt finns det belägg för att översvämningar kommer inträffa oftare och bli allt allvarligare i takt med att klimatförändringarna fortgår. I framtiden kommer vi kanske uppleva händelser  såsom den i Arvika år 2000 som mindre extraordinära. I alla lägen behöver vi veta mer om det nuvarande läget för att kunna göra förutsägelser om framtiden. Den här studien syftar till att kartlägga det rådande vattenföringsläget i avrinningsområdet Åkerströmmen, norr om Stockholm. Detta genom att undersöka kulvertar och genom att analysera flödesfrekvenser. Resultatet visar att det definitivt finns en problematik kring höga vattenflöden och -nivåer som behöver adresseras. På flera platser hotar vattnet järnväg, enskilda hus, vägar och åkermark. Åtgärder behöver sättas in och ytterligare studier som kopplar samman vattennivåer med konsekvenser är nödvändiga. Samtidigt behöver frågor kring biologisk mångfald utredas parallellt då hög flödeskapacitet och förutsättningar för biologisk mångfald står i konflikt med varandra. En väl upplyst samhällsplanering är viktigt för att ta hänsyn till både ekologiska och hydrologiska effekter av åtgärder i vattendrag

Effekte von Uferfiltration auf See-Ökosysteme

With ongoing population growth and increasing urbanisation the pressure on urban water bodies increases. In 2015 four billion people, more than half of the world’s population, lived in cities. The task to provide them with safe drinking water is massive. In case of severe pollution the production of drinking water using surface water can be risky and expensive. The preferred raw water source is therefore groundwater. But groundwater resources are often scarce; groundwater depletion is increasing every year with consequences like salt water intrusion, soil surface subsidies and loss of wetlands. Many methods therefore exist to recharge the groundwater aquifer, each of them with advantages and disadvantages. One of the techniques is induced bank filtration (IBF), used worldwide for more than a century. When installing and operating groundwater wells close to a surface water body, the groundwater level drops below the surface water level and infiltration is induced. The water passage through the sediment and the subsurface provides a cost-efficient pre-treatment step for drinking water production. IBF is therefore widespread and expected to increase in the future. Existing research has focussed on the purification efficiency and abstraction capacity of IBF, while no studies investigated the ecological effects of IBF on surface water bodies. The aim of this thesis was to analyse the potential effects of IBF on surface water bodies, primarily lakes, by (1) developing a concept based on an extensive literature review, (2) a modelling study testing different scenarios of IBF effects on shallow lake ecosystems and (3) a field and laboratory study of the sediment quality in an urban lake affected by IBF and its effects on benthic primary producers. The model study was performed using the shallow lake ecosystem model PCLake and investigated the effects of IBF by focussing on five mechanisms: 1) Loss of CO2 inflow via groundwater, 2) Loss of nutrient inflow via groundwater, 3) Increase in seasonal temperature variation, 4) Increase in sedimentation rate and 5) Increase in sediment oxygen penetration depth. In addition, the impact of lake size and depth on the effect size was investigated. For the field and laboratory study sediment cores were collected from the urban Lake Müggelsee, at six locations with expected high impact of IBF and six locations with expected low impact of IBF. The sediments were analysed for grainsize distribution, organic matter content, phosphorus availability, total phosphorus and heavy metals. They were also used in a growth experiment to study if changes to the sediment characteristics by IBF would affect the growth of periphyton and submerged macrophytes. Numerous potential effects of IBF, categorized into physical, chemical and biological effects, were identified from available literature. Effects on very large rivers were thought to be small or negligible while effects on lakes and slow flowing lowland rivers were expected to be potentially adverse. By interrupting the groundwater seepage, IBF would at the same time interrupt CO2 and nutrient inflow via groundwater, increase seasonal temperature variation and the retention times in lakes. In extreme cases, extensive pumping could significantly lower lake water tables and streamflow. Many of the potential effects identified during the literature study could be tested in the modelling study. The results showed that the impact of IBF on shallow lake ecosystems was mainly caused by interrupting groundwater seepage. Increased summer water temperatures promoted cyanobacteria blooms and the loss of CO2 inflow via groundwater reduced macrophyte growth and promoted turbid states in lakes. This was true for most of the tested scenarios. In a few cases, when in the initial state groundwater CO2 concentrations were low and nutrient concentrations were high, IBF interrupted nutrient loading via groundwater, reduced phytoplankton growth and promoted a clear-water state. The net effect of IBF impact on sedimentation rate and oxygen penetration depth resulted in higher phosphorus binding in the sediment, but the effect was small. The field and laboratory study revealed that sediments from locations with a high impact of IBF had higher phosphorus availability and iron content. Submerged macrophytes grew slower in those sediments while no significant difference in periphyton growth could be observed. It can be concluded that IBF can have significant effects on lake ecosystems that need to be taken into account when applying the technique. The thesis helps to identify which water bodies are suitable for IBF and when alternatives should be considered. One such alternative is aquifer storage transfer and recovery that has the ability to provide groundwater recharge for drinking water production while still maintaining groundwater seepage into water bodies. Future research should expand to effects of IBF on rivers and deep lakes, and empirical studies should include effects of the loss of CO2 inflow in littoral zones and changing redox conditions in littoral sediments. Ultimately, this knowledge will ensure a sustainable use of IBF, economically as well as ecologically.Mit dem anhaltenden Bevölkerungswachstum und der zunehmenden Urbanisierung nimmt der Druck auf urbane Gewässer zu. Im Jahr 2015 lebten vier Milliarden Menschen, mehr als die Hälfte der Weltbevölkerung, in Städten. Die Aufgabe, sie mit sauberem Trinkwasser zu versorgen, ist gewaltig. Die Trinkwassergewinnung mit Oberflächenwasser kann, besonders bei starker Verschmutzung, riskant und teuer sein. Die bevorzugte Rohwasserquelle ist daher das Grundwasser. Die Grundwasser-ressourcen sind jedoch oft begrenzt und die Grundwasserverarmung nimmt von Jahr zu Jahr zu, mit weitreichenden Folgen wie Salzwassereinbrüchen, Landsenkungen und Verlust von Feuchtgebieten. Zur Wiederauffüllung des Grundwasserleiters stehen verschiedene Methoden zur Verfügung, die jedoch diverse Vor- und Nachteile aufweisen. Eine seit mehr als einem Jahrhundert weltweit eingesetzte Technik ist die induzierte Uferfiltration (IBF). Durch den Betrieb von Grundwasserbrunnen in der Nähe eines Oberflächenwasserkörpers wird der Grundwasserspiegel unter den Oberflächenwasserspiegel gesenkt und eine Infiltration ausgelöst. Der Wasserdurchgang durch das Sediment und den Untergrund stellt einen kostengünstigen Vorbehandlungsschritt für die Trinkwassergewinnung dar. Zahlreiche Studien befassen sich mit der Effektivität dieser Technik, für die in Zukunft eine weiter verbreitete Anwendung erwartet wird. Untersuchungen zu den ökologischen Auswirkungen von IBF auf Oberflächengewässer fehlten jedoch bisher. Ziel dieser Arbeit war es, die potenziellen Auswirkungen von IBF auf Oberflächen-gewässer, vor allem auf Seen, zu analysieren. Dazu wurden 1) ein Konzept auf Basis einer umfangreichen Literaturrecherche entwickelt, 2) verschiedene Szenarien mithilfe eines adaptierten Ökosystemmodells für Flachseen gemäßigter Breiten getestet sowie 3) Feld- und Laboruntersuchungen zum Einfluss von IBF auf die Sediment-Qualität und das Wachstum benthischer Primärproduzenten am Beispiel eines seit 100 Jahren für IBF genutzten Sees durchgeführt. Mithilfe des etablierten Ökosystemmodells PCLake, das für Flachseen entwickelt und validiert wurde, konnten verschiedene Kombinationen von fünf Mechanismen getestet werden: 1) Verringerung der Verfügbarkeit an freiem CO2 durch verringerten Grundwasserzufluss, 2) Verringerung des Nährstoffeintrags über das Grundwasser, 3) Erhöhung saisonaler Temperaturschwankungen durch verringerten Grundwasserzufluss, 4) Erhöhung der Sedimentationsrate von Partikeln und 5) Erhöhung der Eindringtiefe von Sauerstoff in das Sediment. Darüber hinaus wurde der Einfluss von Seegröße und -tiefe auf den IBF Effekt untersucht. Im Rahmen der Feld- und Laboruntersuchung wurden Sedimentkerne aus dem Müggelsee (Berlin) mit und ohne Einfluss von IBF auf Korngrößenverteilung, Gehalt an organischer Substanz, Phosphorverfügbarkeit, Gesamtphosphor und Schwermetallen analysiert. Anschließend wurde in einem Wachstumsexperiment untersucht, ob Änderungen der Sedimentmerkmale durch IBF das Wachstum von Periphyton und submersen Makrophyten beeinflussen. Die Auswirkungen von IBF auf große Flüsse wurden als klein oder vernachlässigbar angesehen, während Seen und langsam fließende Tieflandflüsse negativ beeinflusst werden können. Die Auswirkungen von IBF auf Flachseen sind hauptsächlich auf die Unterbrechung des Grundwasserzuflusses zurückzuführen. Diese führen zu erhöhten Wassertemperaturen im Sommer und fördern damit das Auftreten von Cyanobakterien-Blüten. Der Verlust des Zuflusses an freiem CO2 über das Grundwasser reduziert das Makrophytenwachstum und fördert den trüben, Phytoplankton-dominierten Zustand in Flachseen. Dies galt für die meisten der getesteten Szenarien. In einigen Fällen, wenn die CO2-Konzentration des Grundwassers niedrig und die Nährstoffkonzentrationen hoch waren, trug IBF dazu bei, die Nährstoffbelastung und das Phytoplanktonwachstum zu reduzieren und den klaren Zustand zu fördern. Der Nettoeffekt der IBF-Auswirkung auf die Sedimentationsrate und die Sauerstoffeindringtiefe führte zu einer höheren Phosphorbindung im Sediment, aber der Effekt war gering. Die Feld- und Laborstudien zeigten, dass Sedimente von Standorten mit hohem Einfluss von IBF eine höhere Phosphorverfügbarkeit und einen höheren Eisengehalt aufweisen. Das Wachstum submerser Makrophyten auf diesen Sedimenten war verringert, während kein signifikanter Unterschied im Periphyton-Wachstum auftrat. Es wird geschlussfolgert, dass IBF signifikante Effekte auf Gewässer-Ökosysteme haben kann, die bei der Anwendung der Technik berücksichtigt werden müssen. Die Studien helfen zu ermitteln, welche Gewässer für IBF geeignet sind und wann Alternativen in Betracht gezogen werden sollten. Eine dieser Alternativen ist Grundwasser-anreicherung, die in der Lage ist, die Grundwasserneubildung für die Trinkwasser-gewinnung bereitzustellen und gleichzeitig das Eindringen von Grundwasser in die Gewässer zu erhalten. Die zukünftige Forschung sollte auf die Wirkung von IBF auf Flüsse und tiefe Seen ausgedehnt werden sowie empirische Untersuchungen zum CO2-Verlust im Litoral und veränderte Redoxbedingungen in Sedimenten umfassen. Langfristig sollte das Wissen eine nachhaltige Nutzung von IBF, sowohl wirtschaftlich als auch ökologisch, ermöglichen.DFG, GRK 2032/1, Urban Water Interfaces (UWI

Phosphorus Availability and Growth of Benthic Primary Producers in Littoral Lake Sediments: Are Differences Linked to Induced Bank Filtration?

Submerged macrophytes and periphyton are benthic primary producers that play an important role for several ecosystem functions of lakes. Their growth often depends on the availability of phosphorus (P) in sediments and overlying water. This P availability is assumed to potentially be affected by induced bank filtration (IBF), a cost-effective method for drinking water production. In this study, we tested whether littoral sediments sampled at sites with high and low influence of IBF in a temperate eutrophic lake used for bank filtration since more than 100 years affects periphyton and macrophyte growth. Sediments differed in aerobic desorbed water-soluble phosphorus (PH2O) and iron (Fe) content and the growth of macrophytes in sediments with a high impact of IBF was lower compared to sediments with low impact of IBF. We also found that P addition to the nutrient solution increased periphyton growth and that periphyton limited macrophyte growth. While these results point to a potential impact of IBF on P availability in sediments that can cascade to benthic primary producers, we could not prove mechanistic links between high rates of IBF and the lower macrophyte growth. Additional research to assure a sustainable application of this valuable drinking water production method is therefore needed

Моделирование, оптимизация и управление теплотехническими системами

The Bîc River in the Republic of Moldova is a heavily polluted water body. Along the river stretch, from a small creek in Sipoteni close to the river mouth at Gura Bîcului, sediment samples were taken using a very cost-effective method and analyzed for a number of pollutants. The results showed very high levels of petroleum products in and downstream of the city of Chişinău, situated in the middle of the river basin, ex-ceeding even the guideline value for cleanup of industrial land. Concentrations of heavy metals were detected at all sample points, exceeding the Lowest Effect Level (LEL) in 37 out of 48 samples and the Probable Effect Level (PEL) in four of them. High concentrations of nutrients (N and P) were detected, especially outside of the city, where concentrations exceeded even the Severe Effect Level (SEL) for both N and P at one site. DDT concentrations were highest at the beginning of the river, the concentrations becoming lower and lower when getting closer to the river mouth. At three of the six sampling sites, DDT concentrations exceeded the LEL. PCB levels were lower than the LEL. This was attributed to unsuitable handling of the samples before analysis and therefore the PCB concentration levels requires further investiga-tion. The continued monitoring of the sediments is of great need, therefore a proposal for a monitoring program was written. It was estimated that Bîc contributes 118000 tons of suspended particles to Dniester each year, almost 60 % more per km2 than Dniester contributes to the Black Sea

Sediment State and Flow – An Investigation of Sediment Pollution and Transport in the Bîc River, Republic of Moldova. : A Minor Field Study.

The Bîc River in the Republic of Moldova is a heavily polluted water body. Along the river stretch, from a small creek in Sipoteni close to the river mouth at Gura Bîcului, sediment samples were taken using a very cost-effective method and analyzed for a number of pollutants. The results showed very high levels of petroleum products in and downstream of the city of Chişinău, situated in the middle of the river basin, ex-ceeding even the guideline value for cleanup of industrial land. Concentrations of heavy metals were detected at all sample points, exceeding the Lowest Effect Level (LEL) in 37 out of 48 samples and the Probable Effect Level (PEL) in four of them. High concentrations of nutrients (N and P) were detected, especially outside of the city, where concentrations exceeded even the Severe Effect Level (SEL) for both N and P at one site. DDT concentrations were highest at the beginning of the river, the concentrations becoming lower and lower when getting closer to the river mouth. At three of the six sampling sites, DDT concentrations exceeded the LEL. PCB levels were lower than the LEL. This was attributed to unsuitable handling of the samples before analysis and therefore the PCB concentration levels requires further investiga-tion. The continued monitoring of the sediments is of great need, therefore a proposal for a monitoring program was written. It was estimated that Bîc contributes 118000 tons of suspended particles to Dniester each year, almost 60 % more per km2 than Dniester contributes to the Black Sea

Sediment State and Flow – An Investigation of Sediment Pollution and Transport in the Bîc River, Republic of Moldova. : A Minor Field Study.

The Bîc River in the Republic of Moldova is a heavily polluted water body. Along the river stretch, from a small creek in Sipoteni close to the river mouth at Gura Bîcului, sediment samples were taken using a very cost-effective method and analyzed for a number of pollutants. The results showed very high levels of petroleum products in and downstream of the city of Chişinău, situated in the middle of the river basin, ex-ceeding even the guideline value for cleanup of industrial land. Concentrations of heavy metals were detected at all sample points, exceeding the Lowest Effect Level (LEL) in 37 out of 48 samples and the Probable Effect Level (PEL) in four of them. High concentrations of nutrients (N and P) were detected, especially outside of the city, where concentrations exceeded even the Severe Effect Level (SEL) for both N and P at one site. DDT concentrations were highest at the beginning of the river, the concentrations becoming lower and lower when getting closer to the river mouth. At three of the six sampling sites, DDT concentrations exceeded the LEL. PCB levels were lower than the LEL. This was attributed to unsuitable handling of the samples before analysis and therefore the PCB concentration levels requires further investiga-tion. The continued monitoring of the sediments is of great need, therefore a proposal for a monitoring program was written. It was estimated that Bîc contributes 118000 tons of suspended particles to Dniester each year, almost 60 % more per km2 than Dniester contributes to the Black Sea

Phosphorus Availability and Growth of Benthic Primary Producers in Littoral Lake Sediments: Are Differences Linked to Induced Bank Filtration?

Submerged macrophytes and periphyton are benthic primary producers that play an important role for several ecosystem functions of lakes. Their growth often depends on the availability of phosphorus (P) in sediments and overlying water. This P availability is assumed to potentially be affected by induced bank filtration (IBF), a cost-effective method for drinking water production. In this study, we tested whether littoral sediments sampled at sites with high and low influence of IBF in a temperate eutrophic lake used for bank filtration since more than 100 years affects periphyton and macrophyte growth. Sediments differed in aerobic desorbed water-soluble phosphorus (PH2O) and iron (Fe) content and the growth of macrophytes in sediments with a high impact of IBF was lower compared to sediments with low impact of IBF. We also found that P addition to the nutrient solution increased periphyton growth and that periphyton limited macrophyte growth. While these results point to a potential impact of IBF on P availability in sediments that can cascade to benthic primary producers, we could not prove mechanistic links between high rates of IBF and the lower macrophyte growth. Additional research to assure a sustainable application of this valuable drinking water production method is therefore needed