Sorption and transformation of the reactive tracers resazurin and resorufin in natural river sediments

Lemke, Dennis; González‐Pinzón, Ricardo; Liao, Zijie; Wöhling, Thomas; Osenbrück, Karsten; Haggerty, R.; Cirpka, Olaf A.

doi:10.5194/hess-18-3151-2014

Cited by 20 publications

(24 citation statements)

References 32 publications

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“…Furthermore, uptake lengths provide a suitable metric to assess ecosystem respiration, particularly if determined from resazurin‐to‐resorufin transformation. Using metrics based on the transformation rate coefficient has the advantage of capturing the process of resazurin‐to‐resorufin transformation, which is known to be linked to metabolic activity, whereas additional processes involved in single‐tracer metrics are poorly understood to date (Lemke et al, ). Likewise, our study supports the use of uptake velocities, which are one of the more popular metrics for assessing stream metabolism from resazurin processing, and are obtained by multiplying the processing rate coefficient by the stream depth.…”

Section: Discussionmentioning

confidence: 99%

A Critical Assessment of Relating Resazurin–Resorufin Experiments to Reach‐Scale Metabolism in Lowland Streams

Knapp

Cirpka

2018

JGR Biogeosciences

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The reactive tracer resazurin is frequently used to investigate metabolic processes and hyporheic exchange in streams, because its transformation to resorufin is considered a function of oxygen turnover in the presence of living cells and thus of ecosystem respiration. This has been investigated and confirmed in a number of laboratory and batch studies but so far not unanimously been verified in the field. In this study we conducted 13 tracer tests with resazurin in different small, low-gradient streams typical of lowland regions. We determined tracer processing rates and ratios based on metrics commonly used to assess reactive-tracer tests with resazurin and compared them to flow characteristics and respiration rates determined from diel-oxygen recordings following a two-station approach. We found no statistical relationship between tracer processing and parameters of transport, indicating that resazurin-to-resorufin transformation cannot be explained by hydrological parameters alone. The statistical relationship between resazurin processing and respiration rates based on diel-oxygen profiles was strongest if resazurin-to-resorufin transformation ratios were used, and uptake lengths were also found to be a good proxy. However, the relationships were not linear, and weak for individual streams, contrary to what was expected based on previous laboratory and batch studies. We attribute this finding to a lack of process understanding of resazurin reactions under field conditions, and generally insignificant hyporheic exchange fluxes in lowland streams. Our findings highlight important limitations of the tracer technique under field conditions. Plain Language SummaryResazurin is a compound that can be used to track the flow of water and metabolic processes in rivers. This has been tested in laboratory experiments before, but until now the method has not been fully verified in the field. In this study we apply resazurin to 13 different small rivers and measure its transformation. We compare our results to other, independent methods that are often used to determine metabolic processes. We find good relationships between the two different methods for all rivers together, but not for individual rivers. Also, the relationships are not linear, which makes predicting metabolic rates from the transformation of resazurin difficult.

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Section: Discussionmentioning

confidence: 99%

A Critical Assessment of Relating Resazurin–Resorufin Experiments to Reach‐Scale Metabolism in Lowland Streams

Knapp

Cirpka

2018

JGR Biogeosciences

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“…The relatively low cost and ease of use of multitracer field fluorometers has resulted in their rapid uptake by the hydrological community (Lemke et al, ; Schmadel et al, ). However, measurements by field fluorometers are susceptible to interference from environmental factors, including temperature, pH, turbidity, and background organic matter fluorescence (Flett et al, ; Flury & Wai, ; Khamis et al, ), which can exhibit greater variability in naturally dynamic in situ conditions than found in controlled laboratory environments.…”

Section: Introductionmentioning

confidence: 99%

Multitracer Field Fluorometry: Accounting for Temperature and Turbidity Variability During Stream Tracer Tests

Blaen

Brekenfeld

Comer‐Warner

et al. 2017

Water Resources Research

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The use of multitracer field fluorometry is increasing in the hydrological sciences. However, obtaining high‐quality fluorescence measurements is challenging given the variability in environmental conditions within stream ecosystems. Here, we conducted a series of stream tracer tests to examine the degree to which multitracer field fluorometry produces reliable estimates of tracer concentrations under realistic field conditions. Using frequently applied examples of conservative (Uranine) and reactive (Resazurin‐Resorufin) fluorescent tracers, we show that in situ measurements of tracer breakthrough curves can deviate markedly from corresponding samples analyzed under laboratory conditions. To investigate the effects of key environmental variables on fluorescence measurements, we characterized the response of field fluorometer measurements to changes in temperature, turbidity, and tracer concentration. Results showed pronounced negative log‐linear effects of temperature on fluorescence measurements for all tracers, with stronger effects observed typically at lower tracer concentrations. We also observed linear effects of turbidity on fluorescence measurements that varied predictably with tracer concentration. Based on our findings, we present methods to correct field fluorometer measurements for variation in these parameters. Our results show how changing environmental conditions can introduce substantial uncertainties in the analysis of fluorescent tracer breakthrough curves, and highlight the importance of accounting for these changes to prevent incorrect inferences being drawn regarding the physical and biogeochemical processes underpinning observed patterns.

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“…Since this approach assumes that local horizontal heterogeneity is negligible in the range of 20-30 cm, we recommend this type only for the use in uniform systems such as channelised river reaches. Even in those systems however, small-scale variability in streambed and sediment characteristics can cause spatially heterogeneous flow distributions (Lewandowski et al, 2011;Mendoza-Lera and Mutz, 2013). The second approach with alternating nutrient sorbents and water flux measuring segments is therefore preferable in most other cases as long as a high resolution over the vertical profile is not required.…”

Section: Discussionmentioning

confidence: 99%

“…While measurements of vertical Darcy velocities are a valuable asset, primarily horizontal fluxes are needed to assess hyporheic transport and residence time (Binley et al, 2013;Munz et al, 2016). Active heat-pulse tracing enables highly resolved in situ measurements of direction and velocity of hyporheic flow (Lewandowski et al, 2011;Angermann et al, 2012). These methods are profitable in shallow sediments (max.…”

Section: Introductionmentioning

confidence: 99%

Quantifying nutrient fluxes with a new hyporheic passive flux meter (HPFM)

et al. 2017

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Abstract. The hyporheic zone is a hotspot of biogeochemical turnover and nutrient removal in running waters. However, nutrient fluxes through the hyporheic zone are highly variable in time and locally heterogeneous. Resulting from the lack of adequate methodologies to obtain representative long-term measurements, our quantitative knowledge on transport and turnover in this important transition zone is still limited.In groundwater systems passive flux meters, devices which simultaneously detect horizontal water and solute flow through a screen well in the subsurface, are valuable tools for measuring fluxes of target solutes and water through those ecosystems. Their functioning is based on accumulation of target substances on a sorbent and concurrent displacement of a resident tracer which is previously loaded on the sorbent.Here we evaluate the applicability of this methodology for investigating water and nutrient fluxes in hyporheic zones. Based on laboratory experiments we developed hyporheic passive flux meters (HPFMs) with a length of 50 cm which were separated in 5–7 segments allowing for vertical resolution of horizontal nutrient and water transport. The HPFMs were tested in a 7 day field campaign including simultaneous measurements of oxygen and temperature profiles and manual sampling of pore water. The results highlighted the advantages of the novel method: with HPFMs, cumulative values for the average N and P flux during the complete deployment time could be captured. Thereby the two major deficits of existing methods are overcome: first, flux rates are measured within one device instead of being calculated from separate measurements of water flow and pore-water concentrations; second, time-integrated measurements are insensitive to short-term fluctuations and therefore deliver more representable values for overall hyporheic nutrient fluxes at the sampling site than snapshots from grab sampling. A remaining limitation to the HPFM is the potential susceptibility to biofilm growth on the resin, an issue which was not considered in previous passive flux meter applications. Potential techniques to inhibit biofouling are discussed based on the results of the presented work. Finally, we exemplarily demonstrate how HPFM measurements can be used to explore hyporheic nutrient dynamics, specifically nitrate uptake rates, based on the measurements from our field test. Being low in costs and labour effective, many flux meters can be installed in order to capture larger areas of river beds. This novel technique has therefore the potential to deliver quantitative data which are required to answer unsolved questions about transport and turnover of nutrients in hyporheic zones.

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Sorption and transformation of the reactive tracers resazurin and resorufin in natural river sediments

Cited by 20 publications

References 32 publications

A Critical Assessment of Relating Resazurin–Resorufin Experiments to Reach‐Scale Metabolism in Lowland Streams

A Critical Assessment of Relating Resazurin–Resorufin Experiments to Reach‐Scale Metabolism in Lowland Streams

Multitracer Field Fluorometry: Accounting for Temperature and Turbidity Variability During Stream Tracer Tests

Quantifying nutrient fluxes with a new hyporheic passive flux meter (HPFM)

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