Marc Schwientek

BACKGROUND: Analytical constraints complicate environmental monitoring campaigns of the herbicide glyphosate and its major degradation product aminomethylphosphonic acid (AMPA): their strong sorption to soil minerals requires harsh extraction conditions. Coextracted matrix compounds impair downstream analysis and must be removed before analysis.RESULTS: A new extraction method combined with subsequent capillary electrophoresis‐mass spectrometry for derivatization‐free analysis of glyphosate and AMPA in soil and sediment was developed and applied to a suite of environmental samples. It was compared to three extraction methods from literature. We show that no extraction medium reaches 100% recovery. The new phosphate‐supported alkaline extraction method revealed (1) high recoveries of 70–90% for soils and aquatic sediments, (2) limits of detections below 20 μg kg⁻¹, and (3) a high robustness, because impairing matrix components (trivalent cations and humic acids) were precipitated prior to the analysis. Soil and sediment samples collected around Tübingen, Germany, revealed maximum glyphosate and AMPA residues of 80 and 2100 μg kg⁻¹, respectively, with residues observed along a core of lake sediments. Glyphosate and/or AMPA were found in 40% of arable soils and 57% of aquatic sediment samples.CONCLUSION: In this work, we discuss soil parameters that influence (de)sorption and thus extraction. From our results we conclude that residues of glyphosate in environmental samples are easily underestimated. With its possible high throughput, the method presented here can resolve current limitations in monitoring campaigns of glyphosate by addressing soil and aquatic sediment samples with critical sorption characteristics.

Lower‐order streams (first‐ and second‐order) define the initial, landscape‐related, chemical signature of stream water in catchments. To date, first‐order streams have been perceived as predominantly draining systems, which collect water and solutes from the surrounding groundwater and surface runoff and simply mirror the chemical composition of the inputs. In this study, the impact of stream‐groundwater exchange fluxes on water chemistry of a first order agricultural stream (Schönbrunnen) and its connected groundwater in south‐western Germany was assessed combining²²²Rn, dissolved ions (chloride, sulphate, nitrate), and salt tracer tests with investigations of stream discharge and groundwater hydraulic gradients. The findings suggest that stream‐water chemistry in lower‐order streams is governed by an intricate interplay between dynamic, bidirectional water and solute exchange between groundwater and the stream leading to a pronounced hydrologic turnover along the studied reaches. High nitrate concentrations (up to 79 mg/L as NO₃⁻) in stream water were attenuated in downstream direction (a mean value of 39 mg/L) without an increase in discharge, suggesting that redox processes occurring during sediment passage in sequential infiltration and exfiltration zones affect stream water chemistry. Nitrate in stream water infiltrating into the aquifer at distinct losing spots was subject to denitrification within the first few decimetres of the streambed, while concurrent exfiltration of low‐nitrate groundwater into the stream at gaining spots compensated for flow losses and in turn diluted instream nitrate concentrations. In summary the findings imply that (1) instream mixing resulting from the bidirectional exchange of water between groundwater and the stream (hydrologic turnover) affects instream nitrate concentrations, (2) denitrification in the streambed of losing reaches and the near‐stream aquifer significantly contributes to reactive nitrate turnover and elimination, and (3) oxidation of ammonium could be a secondary source of nitrate inputs into the stream.

Currently, the export regime of a catchment is often characterized by the relationship between compound concentration and discharge in the catchment outlet or, more specifically, by the regression slope in log-concentrations versus log-discharge plots. However, the scattered points in these plots usually do not follow a plain linear regression representation because of different processes (e.g., hysteresis effects). This work proposes a simple stochastic time-series model for simulating compound concentrations in a river based on river discharge. Our model has an explicit transition parameter that can morph the model between chemostatic behavior and chemodynamic behavior. As opposed to the typically used linear regression approach, our model has an additional parameter to account for hysteresis by including correlation over time. We demonstrate the advantages of our model using a high-frequency data series of nitrate concentrations collected with in situ analyzers in a catchment in Germany. Furthermore, we identify event-based optimal scheduling rules for sampling strategies. Overall, our results show that (i) our model is much more robust for estimating the export regime than the usually used regression approach, and (ii) sampling strategies based on extreme events (including both high and low discharge rates) are key to reducing the prediction uncertainty of the catchment behavior. Thus, the results of this study can help characterize the export regime of a catchment and manage water pollution in rivers at lower monitoring costs. We propose a simple stochastic time-series model to represent the export regime of a catchment beyond simple regression. We propose how to get the required data with the least effort when the use of high-frequency in situ analyzers is not feasible or restricted. Sampling strategies based on extreme events are essential for reducing the prediction uncertainty of the catchment behavior.

Urban areas are a leading source of polycyclic aromatic hydrocarbons (PAHs) that result from combustion processes and are emitted into rivers, especially during rain events and with particle wash-off from urban surfaces. In-stream transport of suspended particles and attached PAHs is linked strongly to sediment turnover processes. This study aimed to identify particle exchange processes that contribute to the transport of suspended particles during flood events. An urban high-flow signal was tracked in high temporal resolution at two sampling sites in the Ammer River (South-western Germany). Samples were analyzed for turbidity, total suspended solids concentrations (TSS), particle-size distribution, organic carbon, and PAH. Maximum discharge and the highest TSS occurred nearly simultaneously at the upstream sampling site, whereas a temporally shifted course was observed for downstream. The total load of particles was similar, yet a decrease of PAH mass (~28%) and an increase of the particulate organic carbon (POC) content (~3.5%-points) occurred. Coarser particles (≥26 µm) dominated at the beginning of the event at both sampling sites. The signal of remobilized riverbed sediment increases downstream and leads to well-established, robust linear correlations between TSS and PAHs. This study highlights that riverbed sediment acts as intermediate storage for contaminated particles from upstream sources that shape, together with the fresh urban input, the “particle signature” of suspensions moving through catchments during high discharge conditions.

Perennial low order streams are normally well connected to shallow groundwater and therefore, they are among the first receptors of agricultural effluents. Understanding the processes governing the water quality in agricultural areas requires identifying sources of potential pollutants (such as nitrate), hotspots of biogeochemical reactivity and defining the different hydrologic flowpaths connecting groundwater and surface water. To this end, we have equipped an agricultural drainage system (Schönbrunnen) in south-western Germany with 3 stream gauging stations along a test segment of approximately 550 m and 33 piezometers in the adjacent shallow aquifer. Hydrological, hydrochemical, isotopic and microbiological variables have been monitored between August 2017 and December 2019 to spatially and temporally identify the controls of nitrogen cycling dynamics in our stream.The Schönbrunnen generally loses water in its mid-segment and it gains in the lower part of the catchment, although this behavior showed strong seasonal variations, considering winter and summer as the two main annual seasons. The groundwater-streamwater (GW-SW) exchange flux, and the replacement of streamwater lost to the aquifer over a reach by shallow groundwater, defined as hydrologic turnover, was found to influence streamwater chemistry. The main groundwater flow directions were determined based on hydraulic head contour maps. We used them to characterize the nitrogen (N) species’ behavior along the flowpaths under two different hydrologic conditions: losing and gaining. Even though the losing condition at the midstream provides more favorable condition for N-species reduction at the GW-SW interface, reduction occurred also along gaining reaches. The isotope analyses of nitrate yielded data points plotting along the denitrification trend (slope of 0.5) in a dual isotope plot (15N-NO3- versus 18O-NO3-) for some of the sampling locations within the losing area. Comprehensive molecular approaches suggested a hotspot for denitrifying microbial communities in sediments of the losing stream reach. Along the GW flow path to the gaining area a depletion of nitrate was identified in concert with increasing sulfate and declining sulfide (H2S) concentrations. Sulfide-driven nitrate reduction was likely to occur under anoxic conditions in this part of the aquifer. In summary, the findings demonstrate, that hydrologic turnover does not only mean hydrological exchanges, but also triggers variations in water composition along the transition zone between groundwater and streamwater by linking both, mixing and reactive processes.

Hydrophobic pollutants in rivers are transported to varying degrees either in the dissolved or particle-bound phase. For either very turbid rivers or very strongly sorbing compounds, transport dynamics are closely coupled to the cascading sediment movement throught the stream network. Hence, an understanding of sediment storage and mobilisation/movement, including the interaction of suspended and bed sediment phases is the basis for properly discribing contaminant transport.Suspened sediments from the Ammer River in southwestern Germany show a gradual decrease of polycyclic aromatic hydrocarbons (PAH) loadings in a downstream direction, reflecting urban sources in the headwaters. The decrease of PAH loading is, however, only weak which we attribute to only moderate inputs of more or less clean sediments along the river profile, capable of diluting the contaminant signal. The bed sediments of the river comprise a large fraction of grain sizes < 250 µm and constitute an important storage compartment for hydrophobic contaminants. Transformation or leaching into the water phase may reduce the stored amounts. Furthermore, the particle-bound mobility of the stored contaminants clearly depends on the distribution among grain size fractions. We have, therefore, also sampled the bed sediments < 250 µm along the river profile and separated into four grain size fractions (< 19 µm, 19-54 µm, 54-100 µm, 100-250 µm) using vacuum filtration and fine stainless steel meshes. The fractions have been analyzed for urban pollutants of different origins (PAH, heavy metals and the musk fragrance galaxolide) and particulate organic carbon (POC) content. First results show that POC is enriched in the 19-54 µm fraction and that metal contents are neither correlated with POC nor with grain size. This contradicts the common assumption that compounds typically sorbing to surfaces acumulate in the finest fractions due to the large specific surface area. Final results for PAH and galaxolide concentrations as a function of POC contents and particle sizes will also be presented (analysis still pending). At least for PAH a strong affinity to organic carbon is anticipated, while not much is known to date about the sorption and storage behaviour of galoxolide.The results will give further insights into the environmental behaviour of the investigated compound groups. Comparison with data from suspended sediment sampling will enhance our understanding of mobile and immobile phase interactions and, hence, the transport dynamics of these sediment-associated pollutants.

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.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.

Commonly, chemical catchment regimes are described by a simple regression slope of log-concentrations versus log-discharges measured in the catchment outlet river. The slope value of these plots defines the chemical regime of a catchment. A slope=-1 corresponds to a constant contaminant release subject to dilution by rainfall (an unrealistic extreme but needed as a base flow); whereas a slope=0 means that there are chemostatic effects in the catchment or a washout of contaminants at a constant concentration. However, reality shows that actual time-series measurements of discharge and concentrations conflict with this naive representation since the measurements show temporal hysteresis that defies regression assumptions (i.e. that regression residuals must be uncorrelated). To represent this time interaction beyond regression, we design a simple stochastic time-series model that accounts for fluctuating concentration release and transport with memory. In this work, we also establish how to get the observation data required for a robust estimation of the slope with the least effort. To show the capability of our proposed model and method, we apply a retrospective optimal design of experiments to a high-frequency data series of nitrate concentration (collected by online probes) and discharge of a real catchment in Germany. We thin out the data by applying frequency and event-based monitoring strategies to find out the key components of the strategies that best predict the catchment behavior. Results indicate that our catchment under study (the Ammer catchment in southwestern Germany) is relatively close to a chemostatic type catchment and that our stochastic model, in fact, provides more accurate results for small data sets. Also, optimal data collection schemes for this purpose should be event-based, considering both high and low extremes of discharge that are spread out over time.

Well-established relations between concentrations of total suspended solids (TSS) and the hydrophobic polycyclic aromatic hydrocarbons (PAHs) in bulk water samples make PAH ideal tracers to understand water and solid transport in catchments during high discharge events. In the study presented here, we trace particle-bound PAH concentrations in the Ammer River, Germany (annual mean discharge of 0.87 m³ s-1), during a rain event to deepen knowledge on particle origin and hydrological processes in the catchment. High-resolution temporal monitoring of discharge, TSS, particle characteristics, and PAHs was conducted over the course of an event at two sampling sites at the Ammer River. The sampling sites are located in the upper catchment and ~ 8km downstream of the upper sampling site at the outlet of the gauged catchment (134 km²), while the downstream sampling sites integrates inflowing water from tributaries and a wastewater treatment plant. High PAH particle loading demonstrates that particles in the river originate mainly from urban areas, introduced into the stream via combined sewer systems located in the upper catchment. These particles dominate the suspended particle flux over the temporal course of the event. Despite the integral suspended particle flux being nearly constant in between both sampling sites, particle quality changes which is represented by a decreased integral PAH flux and an increasing proportion of particulate organic carbon in the suspended particles. Decrease of PAH particle loading in the downstream direction suggest dilution by ‘cleaner’ particles from either un- or less contaminated or possibly leached sediments entering into the river. This shows that particle exchange between suspended and river bed sediments is more pronounced in downstream direction, demonstrating that sediment mobilisation plays a role for the overall particle flux. These results suggest that the catchment response of the Ammer River regarding the particle flux during rainfall is mainly dominated by the combined sewer system though particle exchange processes are also relevant. Urban tracers are hence helpful for understanding solid transport in catchments.