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

Resazurin (Raz) and its reaction product resorufin (Rru) have increasingly been used as reactive tracers to quantify metabolic activity and hyporheic exchange in streams. Previous work has indicated that these compounds undergo sorption in stream sediments. We present laboratory experiments on Raz and Rru transport, sorption, and transformation, consisting of 4 column and 72 batch tests using 2 sediments with different physicochemical properties under neutral (pH=7) and alkaline (pH=9) conditions. The study aimed at identifying the key processes of reactive transport of Raz and Rru in streambed sediments and the experimental setup best suited for their determination. Data from column experiments were simulated by a travel-time-based model accounting for physical transport, equilibrium and kinetic sorption, and three first-order reactions. We derived the travel-time distributions directly from the breakthrough curve (BTC) of the conservative tracer, fluorescein, rather than from fitting an advective-dispersive transport model, and inferred from those distributions the transfer functions of Raz and Rru, which provided conclusive approximations of the measured BTCs. The most likely reactive transport parameters and their uncertainty were determined by a Markov chain–Monte Carlo approach. Sorption isotherms of both compounds were obtained from batch experiments. We found that kinetic sorption dominates sorption of both Raz and Rru, with characteristic timescales of sorption in the order of 12 to 298 min. Linear sorption models for both Raz and Rru appeared adequate for concentrations that are typically applied in field tracer tests. The proposed two-site sorption model helps to interpret transient tracer tests using the Raz–Rru system.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.hydrology-and-earth-system-sciences.net/home.html

Streambed microbial communities in the transition zone between groundwater and a first-order stream as impacted by bidirectional water exchange.

The input of nitrate and other agricultural pollutants in higher-order streams largely derives from first-order streams. The streambed as the transition zone between groundwater and stream water has a decisive impact on the attenuation of such pollutants. This reactivity is not yet well understood for lower-order agricultural streams, which are often anthropogenically altered and lack the streambed complexity allowing for extensive hyporheic exchange. Reactive hot spots in such streambeds have been hypothesized as a function of hydrology, which controls the local gaining (groundwater exfiltration) or losing (infiltration) of stream water. However, streambed microbial communities and activities associated with such reactive zones remain mostly uncharted. In this study, sediments of a first-order agriculturally impacted stream in southern Germany were investigated. Along with a hydraulic dissection of distinct gaining and losing reaches of the stream, community composition and the abundance of bacterial communities in the streambed were investigated using PacBio long-read sequencing of bacterial 16S rRNA gene amplicons, and qPCR of bacterial 16S rRNA and denitrification genes (nirK and nirS). We show that bidirectional water exchange between groundwater and the stream represents an important control for sediment microbiota, especially for nitrate-reducing populations. Typical heterotrophic denitrifiers were most abundant in a midstream net losing section, while up- and downstream net gaining sections were associated with an enrichment of sulfur-oxidizing potential nitrate reducers affiliated with Sulfuricurvum and Thiobacillus spp. Dispersal-based community assembly was found to dominate such spots of groundwater exfiltration. Our results indicate a coupling of N- and S-cycling processes in the streambed of an agricultural first-order stream, and a prominent control of microbiology by hydrology and hydrochemistry in situ. Such detailed local heterogeneities in exchange fluxes and streambed microbiomes have not been reported to date, but seem relevant for understanding the reactivity of lower-order streams

Managing collaborative research data for integrated, interdisciplinary environmental research

The consistent management of research data is crucial for the success of long-term and large-scale collaborative research. Research data management is the basis for efficiency, continuity, and quality of the research, as well as for maximum impact and outreach, including the long-term publication of data and their accessibility. Both funding agencies and publishers increasingly require this long term and open access to research data. Joint environmental studies typically take place in a fragmented research landscape of diverse disciplines; researchers involved typically show a variety of attitudes towards and previous experiences with common data policies, and the extensive variety of data types in interdisciplinary research poses particular challenges for collaborative data management. In this paper, we present organizational measures, data and metadata management concepts, and technical solutions to form a flexible research data management framework that allows for efficiently sharing the full range of data and metadata among all researchers of the project, and smooth publishing of selected data and data streams to publicly accessible sites. The concept is built upon data type-specific and hierarchical metadata using a common taxonomy agreed upon by all researchers of the project. The framework’s concept has been developed along the needs and demands of the scientists involved, and aims to minimize their effort in data management, which we illustrate from the researchers’ perspective describing their typical workflow from the generation and preparation of data and metadata to the long-term preservation of data including their metadata.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

Managing collaborative research data for integrated, interdisciplinary environmental research

<jats:title>Abstract</jats:title><jats:p>The consistent management of research data is crucial for the success of long-term and large-scale collaborative research. Research data management is the basis for efficiency, continuity, and quality of the research, as well as for maximum impact and outreach, including the long-term publication of data and their accessibility. Both funding agencies and publishers increasingly require this long term and open access to research data. Joint environmental studies typically take place in a fragmented research landscape of diverse disciplines; researchers involved typically show a variety of attitudes towards and previous experiences with common data policies, and the extensive variety of data types in interdisciplinary research poses particular challenges for collaborative data management. In this paper, we present organizational measures, data and metadata management concepts, and technical solutions to form a flexible research data management framework that allows for efficiently sharing the full range of data and metadata among all researchers of the project, and smooth publishing of selected data and data streams to publicly accessible sites. The concept is built upon data type-specific and hierarchical metadata using a common taxonomy agreed upon by all researchers of the project. The framework’s concept has been developed along the needs and demands of the scientists involved, and aims to minimize their effort in data management, which we illustrate from the researchers’ perspective describing their typical workflow from the generation and preparation of data and metadata to the long-term preservation of data including their metadata.</jats:p&gt