More

8.6: Flumes - Geosciences


Out beyond the edge of official terminology, sedimentologists often refer to flumology—presumably meaning the science and art of gaining knowledge and understanding of physical sedimentary processes by passing water and sediment through laboratory open channels, called flumes. I will be referring to flume experiments often in coming chapters.

Dictionaries define flumes as artificial channels for transporting water. That is really not restrictive enough for our purposes, though: flumes designed for nonscientific uses are usually fairly steep and crude in structure. In the context of scientific and engineering studies, I might define a flume as a laboratory channel through which liquid is passed in order to study hydraulic processes and phenomena under controlled conditions.

Flumes are built both indoors and outdoors. One of the most famous flumes—among geologists, at least—was G.K. Gilbert’s flume, outdoors on the campus of the University of California at Berkeley. Around the turn of the twentieth century Gilbert made a pioneering study of modes and processes of sediment transport by currents, which stands to this day as a valuable source of data and ideas. But hydraulic engineers had been using flumes for decades before that.

Flumes are built of wood, metal, glass, or plastic. Each material has its advantages and disadvantages. The cross section is usually but not always rectangular. Widths usually are from several centimeters to a few meters, and lengths range from a few meters to well over a hundred meters. The largest recirculating flume in the world is at the University of Tsukuba, in Japan; it is 160 m long and 4 m wide, and it can recirculate both water and sediment. I am sure that any objective observer would consider it to be an impressive structure. (I certainly did, when I was first shown it.) I am not sure where the largest tilting flume is.

The technology of construction of all but the largest flumes is straightforward, and the problems were for the most part solved long ago. In sediment-recirculating flumes, the most critical design decision revolves around the kind of pump used and/or the arrangement for extracting sediment from the flow and delivering it to the head of the channel.

Flumes are only one kind of large-scale hydraulic equipment used for studying sediment movement. Flumes, carrying unidirectional gravity-driven free-surface flow, are distinct from closed ducts and conduits, also widely used for hydraulic studies, which have pressure-gradient-driven flow without a free surface. Closed ducts may be used for unidirectional, oscillatory, or combined flow. Also widely used are simple tanks or basins arranged mainly for oscillatory flows under surface gravity waves.

Advantages of flumes:

  • sediment transport is relatively easy to watch and measure
  • particular processes can be isolated for study

Disadvantages of flumes:

  • flow and sedimentation can be oversimplified
  • the physical scale of the flow and sediment movement is usually too small

The slope of the flume may be fixed or adjustable; most flumes, except the very largest, are tilting. But when you are working with sediment transport, your flume does not really need to be tilting, because the flow itself redistributes the sediment to produce a sediment bed with slope equal to the energy slope as uniform flow is established. If you prepare a planar and uniform bed of sediment and then set up a flow over it, if the flume slope is too steep there will be erosion near the upstream end and deposition near the downstream end until a uniform flow is attained over a sediment bed that tapers upstream (Figure (PageIndex{1})A). Conversely, if you start with a flume slope that is too gentle, the result is a bed that tapers downstream (Figure (PageIndex{1})B). You just have to make sure that the flume slope you start with is near enough the slope for uniform flow that you have a full bed of sediment everywhere in the flume once the flow stops adjusting to uniformity.

Flumes vary in their arrangements for recirculation of water and sediment. Logically there are four possible combinations of recirculation; see Figure (PageIndex {2}).

Water no, sediment no (Figure (PageIndex {2})A). This arrangement is uncommon, because it is limited by water supply. Only laboratories located near dams on large rivers can afford to run large discharges of water through flumes without recirculation. Also, water temperature cannot be controlled independently. And if you do not catch the sediment, you lose it.

Water no, sediment yes (Figure (PageIndex {2})B). The same comments apply as in the preceding case, except that you do not lose the sediment.

Water yes, sediment no (Figure (PageIndex {2})C). This arrangement is more common. Its advantages are that the sediment discharge is imposed independently upon the flow. But it can be a technical challenge to separate all the sediment from the water and then feed new sediment at the upstream end.

Water yes, sediment yes (Figure (PageIndex {2})D). This arrangement is simplest and also common. Here the flow establishes its own sediment discharge; you cannot impose sediment discharge on the system. Provided that the sediment is not too coarse, this is the easiest arrangement technologically. But it is difficult to arrange for gravels.

There are two different arrangement for water-recirculating flumes:

Overfall flumes (Figure (PageIndex{3})A). In some flumes, which I will call overfall flumes, there is a free overfall at the downstream end of the channel into a separate tailbox, from which water (and in many cases also the sediment) is pumped to the head of the channel. In such flumes, the flow depth in uniform flow is fixed by the imposed water discharge and bed roughness. You can set or adjust the slope only by fiddling with a weir or gate of some kind at the downstream end of the channel, to change the water depth and therefore the mean velocity.

Closed-circuit flumes (Figure (PageIndex{3})B). In other flumes, which I will call closed-circuit flumes, there is no overfall at the downstream end; the flow passes continuously into the tailbox, to be pumped back to the head of the channel. In closed-circuit flumes, the flow depth is fixed by the volume of water in the system. You impose the water discharge and flow depth and thereby the mean velocity, which in turn determines all aspects of the sediment transport as well as the slope.

Both overfall flumes and closed-circuit flumes are in wide use. Each has advantages and disadvantages. They are used for slightly different purposes, which I will touch upon in passing in later chapters.

You will see, in Chapter 13, on mixed-size sediment, that the differences between sediment-feed flumes and sediment-recirculating flumes has significant implications (Parker and Wilcock, 1993). In a sediment-feed flume, the sediment discharge is imposed upon the flow and the flow must become adjusted to accomplish the necessary transport of all of the size fractions in the feed mix. In sediment-recirculating flumes, there is no such constraint: the flow is free to adjust its sediment-transporting behavior without any external constraint imposed except for water discharge and bed material.

References Cited Chapter 8

Parker, G., and Wilcock, P.R., 1993, Sediment feed and recirculating flumes: A fundamental difference: Journal of Hydraulic Engineering, v. 119, p. 1192- 1204.


8.6: Flumes - Geosciences

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited.

Feature Papers represent the most advanced research with significant potential for high impact in the field. Feature Papers are submitted upon individual invitation or recommendation by the scientific editors and undergo peer review prior to publication.

The Feature Paper can be either an original research article, a substantial novel research study that often involves several techniques or approaches, or a comprehensive review paper with concise and precise updates on the latest progress in the field that systematically reviews the most exciting advances in scientific literature. This type of paper provides an outlook on future directions of research or possible applications.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.


8.6: Flumes - Geosciences

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited.

Feature Papers represent the most advanced research with significant potential for high impact in the field. Feature Papers are submitted upon individual invitation or recommendation by the scientific editors and undergo peer review prior to publication.

The Feature Paper can be either an original research article, a substantial novel research study that often involves several techniques or approaches, or a comprehensive review paper with concise and precise updates on the latest progress in the field that systematically reviews the most exciting advances in scientific literature. This type of paper provides an outlook on future directions of research or possible applications.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.


Flume for Mac 2.8.6.5

Flume brings the world of Instagram to your desktop with gorgeous edge-to-edge photography, direct messaging, upload support and much more.

Features
  • Upload photos, videos and carousel posts directly to Instagram, with support for original or square formats, tagged locations and captions.*
  • Effortlessly switch between multiple Instagram accounts.*
  • Start conversations with other users, create groups and share your favourite photos or videos together.
  • A beautiful design that focuses your attention on the photos and videos.
  • View, like, comment, follow and share all day long.
  • View photos and videos in their original aspect ratio and at full resolution.
  • Immerse yourself deeper, and enlarge photos and videos via QuickLook support.
  • View popular content based on users you are following as well as your current location.
  • See the latest activity (new likes, comments and friends that join Instagram) and respond to the latest notifications (new follower requests).
  • Swipe with your trackpad or Magic Mouse and skim through your feed.
  • Search for users, hashtags, locations and save them for quick access.
  • View photos and videos tagged at a location, with a hashtag, or with other users.
  • Read comments and captions written in a language you don't understand, with translation support.
  • 100% keyboard navigable, and 100% VoiceOver/accessibility supported.

Note: Features marked with a * require purchase of Flume Pro.


Flume | Red Rocks Amphitheatre | 8/6/19

After a year and half hiatus, Australian producer Flume ignited his 2019 world-wide tour, making a stop at Colorado’s Red Rocks Amphitheatre last night.

As his only show stop on his summer tour outside of playing festivals like Lollapalooza and Outside Lands, Flume’s first night of Red Rocks led the producer to play around and experiment with his new hip-hop music collaborations with JPEGMAFIA and slowthai.

Colorado producer Collin McKenna opened up Tuesday night’s music at 6:55 p.m., before slowthai and JPEGMAFIA played 30-minute opening sets for some alternative hip-hop.

Flume took the stage at 9:45 p.m., igniting with hard-hitting electronic waves as he whipped out a pink can of spray paint, spelling out “Hi this is Flume” holding it up the screaming crowd. A melodic beat came on, as Flume welcomed collaborator slowthai onstage in his underwear for a electronic-hip hop collaboration off his newest mixtape release, Hi This Is Flume (Mixtape).

Flume kicked started into his popular “Say It” and “Never Be Like You” as female vocalist Vera Blue sang the lyrics in substitute of Kai and Tove Lo from the original recording. An edgy, unstructured electronic beat surged around the mountainous rocks as Flume danced onstage and JPEGMAFIA strode back onstage for another R&B meets electronic collaboration.

Feeling the crowd, Flume played a new song for the crowd, twisting and turning in air and space melody before hitting it with a hard and heavy with a deep electronic beat. Another hip hop remix hit the crowd as psychedelic visuals of weapons and abstracts shapes projected behind Flume welding a sign onstage that read “Red Rocks.”

Flume teased the crowd as he layed with his back down onstage in a white suit to start up “Insane”, a male robotic voice narrating the opening lyrics “our rocks are red and so damn big” and four men in black suits surrounded around him, before jumping up and leading into an upbeat Lorde “Tennis Court” remix.

JPEGMAFIA returned onstage for an intense screaming hip-hop lyrical song, and keeping up with the heavy bass, Flume transitioned into a menacing performance of smashing objects onstage. A devilish monster transformed behind Flume as objects were smashed across the stage and a blood murder scene appeared the crowd from a bird’s eye view before getting swept away.

Picking the crowd back up into a disco house beat, the crowd got back to dancing and Vera Blue made her appearance back onstage for a lyrical light-beat. The crowd clapped along as the two danced, and Flume led into a spacey electronic take as Blue left the stage. Flume took to the piano and sang about people taking advantage of you as another hip-hop collaboration came on.

Teasing the crowd with a short reappearance of “Say It,” Flume went into his ever-most popular Disclosure original “You & Me,” inviting Vera Blue, slowthai, and JPEGMAFIA onstage for a dance party to end the night.

After about six minutes, Flume returned for a three-song encore, including his Chet Faker remix of “Drop The Game” as blooming flower visuals projected on the screen to the sold-out crowd.

Flume returns to Red Rocks Amphitheatre tonight to finish off his two-night, sold-out run and last show in the United States before heading to Hangang Park, South Korea on August 15th and Centerpoint Studio, Sukhumvit 105 in Thailand on August 21st. For a full list of show dates, head to Flume’s website.


McEwen, A. S. et al. Seasonal flows on warm Martian slopes. Science 333, 740–743 (2011).

McEwen, A. S. et al. Recurring slope lineae in equatorial regions of Mars. Nat. Geosci. 7, 53–58 (2014).

Ojha, L. et al. Spectral evidence for hydrated salts in recurring slope lineae on Mars. Nat. Geosci. 8, 829–832 (2015).

Martinez, G. M. & Renno, N. O. Water and brines on Mars: current evidence and implications for MSL. Space Sci. Rev. 175, 29–51 (2013).

Chevrier, V. F. & Rivera-Valentin, E. G. Formation of recurring slope lineae by liquid brines on present-day Mars. Geophys. Res. Lett. 39, L21202 (2012).

Stillman, D. E., Michaels, T. I., Grimm, R. E. & Hanley, J. Observations and modeling of northern mid-latitude recurring slope lineae (RSL) suggest recharge by a present-day Martian briny aquifer. Icarus 265, 125–138 (2016).

Heinz, J., Schulze‐Makuch, D. & Kounaves, S. P. Deliquescence‐induced wetting and RSL‐like darkening of a Mars analogue soil containing various perchlorate and chloride salts. Geophys. Res. Lett. 43, 4880–4884 (2016).

Massé, M. et al. Transport processes induced by metastable boiling water under Martian surface conditions. Nat. Geosci. 9, 425–428 (2016).

Schmidt, F., Andrieu, F., Costard, F., Kocifaj, M. & Meresescu, A. G. Formation of recurring slope lineae on Mars by rarefied gas-triggered granular flows. Nat. Geosci. 10, 270–273 (2017).

Heldmann, J. L. & Mellon, M. T. Observations of Martian gullies and constraints on potential formation mechanisms. Icarus 168, 285–304 (2004).

Heldmann, J. L. et al. Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions. J. Geophys. Res. 110, E05004 (2005).

Stillman, D. E., Michaels, T. I. & Grimm, R. E. Characteristics of the numerous and widespread recurring slope lineae (RSL) in Valles Marineris, Mars. Icarus 285, 195–210 (2017).

Farrell, W. M. et al. Is the Martian water table hidden from radar view? Geophys. Res. Lett. 36, L15206 (2009).

Nunes, D. C. et al. Examination of gully sites on Mars with the shallow radar. J. Geophys. Res. 115, E10004 (2010).

Heggy, E. et al. On water detection in the martian subsurface using sounding radar. Icarus 154, 244–257 (2001).

Heggy, E. et al. Ground penetrating radar sounding in mafic lava flows: Assessing attenuation and scattering losses in Mars analog volcanic terrains. J. Geophys. Res. 111, E06S04 (2006).

Orosei, R. et al. Radar evidence of subglacial liquid water on Mars. Science 361, 490–493 (2018).

Kumar, P. S. & Kring, D. A. Impact fracturing and structural modification of sedimentary rocks at Meteor Crater, Arizona. J. Geophys. Res. 113, E09009 (2008).

Kumar, P. S., Head, J. W. & Kring, D. A. Erosional modification and gully formation at Meteor Crater, Arizona: insights into crater degradation processes on Mars. Icarus 208, 608–620 (2010).

Singhal, B. B. S. & Gupta, R. P. in Applied Hydrogeology of Fractured Rocks (Springer Science & Business Media, 2010).

Andrews‐Hanna, J. C., Zuber, M. T. & Hauck, S. A. Strike‐slip faults on Mars: observations and implications for global tectonics and geodynamics. J. Geophys. Res. 113, E08002 (2008).

Montgomery, D. R. et al. Continental-scale salt tectonics on Mars and the origin of Valles Marineris and associated outflow channels. Geol. Soc. Am. Bull. 121, 117–133 (2009).

Treiman, A. H. Ancient groundwater flow in the Valles Marineris on Mars inferred from fault trace ridges. Nat. Geosci. 1, 181–183 (2008).

Montgomery, D. R. & Gillespie, A. Formation of Martian outflow channels by catastrophic dewatering of evaporite deposits. Geology 33, 625–628 (2005).

Marra, W. A., Braat, L., Baar, A. W. & Kleinhans, M. G. Valley formation by groundwater seepage, pressurized groundwater outbursts and crater-lake overflow in flume experiments with implications for Mars. Icarus 232, 97–117 (2014).

Osinski, G. R. & Lee, P. Intra‐crater sedimentary deposits at the Haughton impact structure, Devon Island, Canadian High Arctic. Meteorit. Planet. Sci. 40, 1887–1899 (2005).

Osinski, G. R. & Spray, J. G. Tectonics of complex crater formation as revealed by the Haughton impact structure, Devon Island, Canadian High Arctic. Meteorit. Planet. Sci. 40, 1813–1834 (2005).

Carr, M. H. Formation of Martian flood features by release of water from confined aquifers. J. Geophys. Res. 84, 2995–3007 (1979).

Gaidos, E. J. Cryovolcanism and the recent flow of liquid water on Mars. Icarus 153, 218–223 (2001).

Mellon, M. T. & Phillips, R. J. Recent gullies on Mars and the source of liquid water. J. Geophys. Res. 106, 23165–23179 (2001).

Hauber, E. et al. Asynchronous formation of Hesperian and Amazonian aged deltas on Mars and implications for climate. J. Geophys. Res. 118, 1529–1544 (2013).

Scheidegger, J. M., Bense, V. F. & Grasby, S. E. Transient nature of Arctic spring systems driven by subglacial meltwater. Geophys. Res. Lett. 39, L12405 (2012).

Pope, K. O., Rejmankova, E. & Paris, J. F. Spaceborne imaging radar-C (SIR-C) observations of groundwater discharge and wetlands associated with the Chicxulub impact crater, northwestern Yucatan Peninsula, Mexico. Geol. Soc. Am. Bull. 113, 403–416 (2001).

Komatsu, G. et al. Drainage systems of Lonar Crater, India: contributions to Lonar Lake hydrology and crater degradation. Planet. Space Sci. 95, 45–55 (2014).

Abotalib, A. Z., Sultan, M. & Elkadiri, R. Groundwater processes in Saharan Africa: implications for landscape evolution in arid environments. Earth Sci. Rev. 156, 108–136 (2016).

Andersen, D. T., Pollard, W. H., McKay, C. P. & Heldmann, J. Cold springs in permafrost on Earth and Mars. J. Geophys. Res. 107, 5015 (2002).

Forte, E., Dalle Fratte, M., Azzaro, M. & Guglielmin, M. Pressurized brines in continental Antarctica as a possible analogue of Mars. Sci. Rep. 6, 33158 (2016).

Goldspiel, J. M. & Squyres, S. W. Groundwater discharge and gully formation on martian slopes. Icarus 211, 238–258 (2011).

Stillman, D. E., Michaels, T. I., Grimm, R. E. & Harrison, K. P. New observations of Martian southern mid-latitude recurring slope lineae (RSL) imply formation by freshwater subsurface flows. Icarus 233, 328–341 (2014).

Chojnacki, M. et al. Geologic context of recurring slope lineae in Melas and Coprates Chasmata, Mars. J. Geophys. Res. 121, 1204–1231 (2016).

Kirk, R. L. et al. Ultrahigh resolution topographic mapping of Mars with MRO HiRISE stereo images: Meter scale slopes of candidate Phoenix landing sites. J. Geophys. Res. 113, E00A24 (2008).

Clifford, S. M. A model for the hydrologic and climatic behavior of water on Mars. J. Geophys. Res. 98, 10973–11016 (1993).

Clifford, S. M. et al. Depth of the Martian cryosphere: revised estimates and implications for the existence and detection of subpermafrost groundwater. J. Geophys. Res. 115, E07001 (2010).

Levy, J. Hydrological characteristics of recurrent slope lineae on Mars: evidence for liquid flow through regolith and comparisons with Antarctic terrestrial analogs. Icarus 219, 1–4 (2012).

Archer, D. G. & Carter, R. W. Thermodynamic properties of the NaCl H2O system. 4. Heat capacities of H2O and NaCl (aq) in cold-stable and supercooled states. J. Phys. Chem. B 104, 8563–8584 (2000).


Flume Mac

Instagram ist einer der größten Erfolgsfälle in der Welt der sozialen Netzwerke. Seit Facebook auf sein Potenzial aufmerksam wurde und eine ehemals ansprechende Plattform zum Austausch von Fotos erwarb, ist es zu einem der meistgenutzten sozialen Netzwerke weltweit geworden. Und um seine Funktionen bequem von unserem Mac-Desktop aus verwalten zu können, ohne auf die offizielle App- oder Web-Version zurückgreifen zu müssen, können wir Flume herunterladen.

Ein Instagram-Client, der sich durch sein Design auszeichnet

Dieser alternative Instagram-Client für MacOS wird mit einer Reihe interessanter Funktionen sowie einer gut gestalteten Schnittstelle geliefert. Es ist eine Alternative zum offiziellen Instagram-Desktop-Client, die sich durch ihre Benutzerfreundlichkeit auszeichnet.

Dies sind seine Hauptfunktionen und Features, die von der App angeboten werden:

  • Fotos auf Ihrem Profil teilen.Mehrere Profile auf einmal verwalten.
  • Statistiken über die Leistung Ihrer Publikationen lesen.
  • DMs versenden.
  • Ihre Aktivität überprüfen.
  • Auf Bilder und Inhalte ausgerichtetes Design.
  • Betrachten Sie die Bilder in ihrer Originalgröße.
  • Erweiterte Funktion und verbesserte Suche.
  • Erforschen Sie Inhalte und erhalten Sie Vorschläge.
  • Konfigurieren Sie Mausgesten.
  • Publikationen in Ihre Sprache übersetzen.

Natürlich erfordern einige dieser Funktionen ein kostenpflichtiges Abonnement, aber es könnte sich lohnen, einen solchen vollständigen Instagram-Client zu verwenden.


Abstract

Assessing the influence of the impact pressure exerted on surrounding rock mass by potential debris flows is one of the challenges in a mountain tunnel construction project. This paper proposes an effective mathematical model for the assessment of impact pressure exerted by debris flows on obstacles. The characteristics of the new model are analyzed, and the parameters determination method for the new model are deduced. Also, a new method for dynamic reliability analysis of the rock mass surrounding tunnels is proposed and is constituted into three key steps. First, by inputting impact pressure of debris flows generated by the aforementioned new model, the FLAC3D is used as the dynamic analysis engine to obtain the time-varying stress distribution of surrounding rock mass during the impact of debris flow. Second, the factor of safety (FOS) contours of surrounding rock mass are generated based on element states using the maximum tensile stress criterion and the Mohr-Coulomb yield criterion. Third, by using the time-varying contours of the FOS, a failure probability and a reliability index are obtained from a reliability perspective. A case study shows the complete analysis process and confirms the effectiveness of the above methodology. In sum, this paper provides new ideas, new methods, and a reference example for evaluating the influence of dynamic impact exerted by debris flows on the rock mass surrounding tunnels.


2. Materials and methods

2.1 Experimental design

Independent variables Factors Coded levels
−1 0 1
Hyporheic exchange – bedforms ( B ) Level name B0 B3 B6
Number of bedforms 0 3 6
Bacterial diversity – sediment dilution ( S ) Level name S6 S3 S1
Sediment:sand dilution ratio 1:10 6 1:10 3 1:10

(1) Bacterial diversity in sediment ( S ) was achieved by diluting river sediment with commercial sand in different proportions, based on the dilution-to-extinction method. In this method, the less abundant species are “removed” by stepwise dilutions, and this loss in species richness results in lower diversity. 33 The low dilution level (S1) had a sediment dilution of 1:10 and was expected to have the highest level of bacterial diversity, the medium level (S3) was diluted in a 1:10 3 ratio, and the high dilution level (S6) corresponding to the lowest expected bacterial diversity, was set to a 1:10 6 dilution. Bacterial diversity in S1, S3 and S6 levels was investigated through Illumina sequences of the 16S rRNA taxonomic gene (details in Chapter 2.7).

(2) Hyporheic exchange ( B ) was regulated by forming triangular-shaped stationary bedforms in the flume sediment. Bedforms cause a so-called “pumping” effect, inducing advective flow through the porous streambed by pressure differences between the upstream and downstream side of the bedform. 20 Hence, we anticipated, that higher amount of bedforms would lead to higher total exchange flux, i.e. the volume of water exchanged between sediment and surface water per day. 21 Consequently, the increasing solute transfer to the hyporheic zone leads to higher contact of solutes to bacterial communities and thus higher potential for micropollutant degradation in general. We aimed at creating three contrasting levels of hyporheic exchange by minimum, medium and maximum number of bedforms feasible within the present setting. Minimum exchange was expected for flat sediment (B0), followed by a medium level (3 bedforms, B3) and a high level (6 bedforms, B6). The amount of sediment was identical in all flumes and the shape of the individual bedforms was the same in the B3 and B6 flumes. The triangular shape was determined by practicality within the setting aiming at uniform shapes across flumes and inducing hyporheic exchange rather than mimicking shapes commonly found in the field. Differences in hyporheic exchange between levels B0, B3 and B6 were investigated through a salt tracer dilution test (performed at the end of the experiment) from which exchange flux, exchange volumes and average residence times were calculated (details in Chapter 2.8).

The response surface model explores non-linear effects of the bacterial diversity ( S ) and hyporheic exchange ( B ) on the dissipation half-lives (DT50s) by fitting the responses to a quadratic equation (eqn (1)):

DT50 = β 0 + β 1 S + β 2 B + β 3 SB + β 4 S 2 + β 5 B 2 + ε (1)

The central composite face design used here is a factorial design consisting of 20 flumes (Fig. 1a): eight flumes with the factorial variable combinations, eight flumes with axial combinations and four replicates of the center-point experiments to validate the response surface model. Central composite designs are commonly used for response surface models because they are easy to expand ( e.g. to include more variables) and flexible in terms of choosing the values of each variable at the axial and center-points.

Fig. 1 (a) Number of flumes per treatment-combination ( S and B ) in the experimental design (b) flume setup scheme showing the three levels of the bedform variable (c) the timeline of the experiment indicating the days of sampling during the attenuation phase, as well as the injection times of micropollutants and the nutrient solutions (N1, N2, N3).

2.2 Preparation of the sediment-mixtures

S1 S3 S6 Erpe sediment Sand
a n.a.: not applicable.
Sand base 21.3 kg sand 23.7 kg sand 23.7 kg sand n.a. n.a.
Inoculum 2 L Erpe sediment Inoculum 1 (2 mL Erpe sediment in 2 L deionised water) Inoculum 2 (2 mL inoculum 1 in 2 L deionised water) n.a. n.a.
TC [%] 0.007 ± 0.002 0.004 ± 0.003 0.003 ± 0.001 0.840 ± 0.066 0 ± 0
Fine gravel [%] 5 5 5 6 5
Coarse sand [%] 6 5 5 13 5
Medium sand [%] 82 83 83 68 83
Fine sand [%] 6 6 6 12 6
<0.063 mm [%] <1 <1 <1 <1 <1
K f at 10 °C [m s −1 ] 3.14 × 10 −4 ± 4% 3.37 × 10 −4 ± 14% 3.37 × 10 −4 ± 14% n.a. n.a.
Porosity [%] 35 35 35 n.a. n.a.

2.3 Flume setup and pre-incubation period

2.4 Injection of micropollutants and attenuation phase

2.5 Boundary conditions and abiotic parameters

pH in the surface water was measured two times. From day −4 to day 45, the average pH in the flumes rose from 8.1 (±0.1) to 8.5 (±0.3) (Fig. S4†). While there were no significant differences between treatments at day −4 and day 45, the sediment dilution treatment had significantly influenced pH (ANOVA p < 0.05). Treatment S1 (8.2 ± 0.3) had a significantly lower pH than S3 (8.7 ± 0.1) and S6 (8.6 ± 0.2 Tukey post hoc test, p < 0.05). Dissolved oxygen (Pro 20 DO Instrument, YSI Incorporated, Yellow Springs, OH, USA) in the surface water was measured 4 times during the attenuation phase. Average O2 saturation in all flumes ranged from 101 to 110% between days 28 and 86 (Fig. S5†). Average O2 saturation at days 28, 36, 44 and 86 was significantly influenced by the sediment dilution treatment (ANOVA p < 0.05). S1 treatments showed significantly lower O2 saturation (103% ± 0.8) than S3 (105% ± 1.7) and S6 (106% ± 1.9 Tukey post hoc test, p < 0.05).

The method for analysis of nutrients (NO3 , NO2 , NH4 + , PO4 3− and total dissolved nitrogen) and dissolved organic carbon (DOC) is detailed in the ESI.† There was little variation in surface water nutrient dynamics between the bedform treatments, but nutrient concentrations were highly impacted by the level of sediment dilution (Fig. S6†). This is why at day 0 (injection of micropollutants), nutrient concentrations differed between sediment dilution levels. Generally the depletion of nitrogen and DOC during pre-incubation (day −12 to day 0) was higher and faster in treatments with lower dilution. Accordingly, after addition of nutrient solution N2 at day 10, removal of NH4 + was especially high in the lowest dilution (S1) (see ESI† for detailed discussion on nutrient dynamics).

2.6 Chemical analyses

2.7 Bacterial diversity in sediment dilution treatments

Illumina Miseq amplicon sequencing targeting the 16S rRNA gene using the bacteria specific primer pair 341F and 806R was performed by LGC Genomics GmbH (Berlin, Germany) followed by post processing of the raw data as previously published. 42 Taxonomy was assigned using the Ribosomal Database Project (RDP) classifier. For comparative diversity index analyses, uneven sequencing depth among the samples was adjusted by rarefying each sample to an even sequencing depth. The sequence data were submitted to NCBI's sequence reads archive (http://www.ncbi.nlm.nih.gov/sra/) under accession no. PRJNA531245.

Fisher-alpha diversity index was calculated at a genus taxonomic level for all the samples and ANOVA was used to compare the diversity between bedform levels (B0, B3, B6) and sediment dilution levels (S1, S3, S6). Calculations were performed in the R software 43 using the vegan 44 and phyloseq 45 packages.

2.8 Salt tracer dilution test

2.9 Dissipation half-lives and response surface model

Fig. 2 Normalized concentrations ( C / C 0) of (a) acesulfame and (b) carbamazepine, plotted per flume, as measured in SU and EAWAG. The average normalized concentration per time point (blue stars) were used to fit the first order dissipation kinetics. The sediment dilution level (S1, S3 or S6) and bedform level (B0, B3, B6) are indicated for each flume. The concentration plots of ACS in flumes corresponding to the high sediment dilution (S6) show a clear lag-phase of 21–28 days (in yellow) in which no dissipation can be observed, followed by a period of degradation. Flumes marked with * could not be fitted to 1 st order kinetics. Note the y -axis is in log-scale.

The DT50s for CBZ and ACS were calculated assuming first order kinetics by fitting the timepoint-averaged measured concentrations to an exponential function (eqn (2a) and (2b)). If no dissipation was observed in the initial timepoints, this period was considered as lag-phase and was excluded from the DT50 calculation.

C x = C 0e − k dis t(2a)
DT50 = −ln(2)/ k dis(2b)

The goodness of fit of the first-order dissipation assumption was assessed with a one-tailed t -test of the kinetic constants ( k dis) to be significantly different from zero. Only DT50s obtained from kinetic constants ( k dis) significantly different from zero ( p ≤ 0.05), n = 20 for ACS and n = 18 for CBZ, were fitted to a quadratic response surface model (RSM eqn (1)), using the rsm package (Lenth RV, 2009) in the R software. 43

The coded levels (−1, 0 and 1) were used for the sediment dilution ( S ) and bedform ( B ) variables (Table 1). The use of the coded variables to fit the RSM is adequate for our specific goal to understand the relative size and effect of the variables, as in the present study we do not aim to predict the DT50s or optimize the attenuation of micropollutants. The model coefficients β x (eqn (1)) were first calculated using ordinary least squares, then tested to be significantly different from zero (two-tailed t -test), and finally an analysis of variance (ANOVA) was used to evaluate the significance of the first ( β 1 and β 2), second order ( β 4 and β 5) and interaction ( β 3) terms. The adjusted- R 2 , F -test and model lack-of-fit were calculated to assess goodness of fit and adequacy of the regression.


5 DATA SET CONTRIBUTORS

Heye R. Bogena is administrative and research lead of the Wüstebach catchment experiment. Michael Stockinger is a former scientist on the project and Andreas Lücke is a lead scientist and coordinates the stable isotope sampling and laboratory analysis. We thank Ferdinand Engels, Rainer Harms, Werner Küpper, Martina Krause, Sirgit Kummer and Holger Wissel for supporting the sampling, stable isotope analysis and regular maintenance of the experimental set-up.


Watch the video: Institute of Geoscience at the University of Potsdam - At the Epicenter of Earth Sciences (October 2021).