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  • Musolff, Andreas  (13)
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  • 1
    In: Fundamental and Applied Limnology / Archiv für Hydrobiologie, June 2014, Vol.184(3), pp.173-181
    Description: Heat is increasingly used as a natural tracer to quantify water fluxes at the groundwater-surface water-interface. We present a systematic approach to monitor and evaluate stream and streambed temperatures to derive daily-updated temperature-based water exchange fluxes between the stream and the streambed. Specifically designed multi-level temperature sensors coupled with a data logger and GSM modem are used to monitor temperature in the stream and streambed and transfer this data daily to a database. A suite of MATLAB scripts with structured query language (SQL) commands is applied to extract the data for processing using an inverse numerical model to estimate water flow based on the measured temperatures. Compared to common analytical approaches, which typically require sinusoidal diurnal temperature pattern, our numerical model can utilize temperature records without daily variations. Temperature-based calculations to quantify vertical water fluxes at the stream-groundwater interface can provide a supplement to, or even a replacement of, calculations based on vertical hydraulic gradients and Darcy' law.
    Keywords: Groundwater - Surface Water - Interface
    ISSN: 1863-9135
    E-ISSN: 23637110
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  • 2
    Language: English
    In: Water Research, 01 March 2018, Vol.130, pp.185-199
    Description: Nitrate contamination in ground- and surface water is a persistent problem in countries with intense agriculture. The transition zone between rivers and their riparian aquifers, where river water and groundwater interact, may play an important role in mediating nitrate exports, as it can facilitate intensive denitrification, which permanently removes nitrate from the aquatic system. However, the in-situ factors controlling riparian denitrification are not fully understood, as they are often strongly linked and their effects superimpose each other. In this study, we present the evaluation of hydrochemical and isotopic data from a 2-year sampling period of river water and groundwater in the riparian zone along a 3rd order river in Central Germany. Based on bi- and multivariate statistics (Spearman's rank correlation and partial least squares regression) we can show, that highest rates for oxygen consumption and denitrification in the riparian aquifer occur where the fraction of infiltrated river water and at the same time groundwater temperature, are high. River discharge and depth to groundwater are additional explanatory variables for those reaction rates, but of minor importance. Our data and analyses suggest that at locations in the riparian aquifer, which show significant river water infiltration, heterotrophic microbial reactions in the riparian zone may be fueled by bioavailable organic carbon derived from the river water. We conclude that interactions between rivers and riparian groundwater are likely to be a key control of nitrate removal and should be considered as a measure to mitigate high nitrate exports from agricultural catchments.
    Keywords: Riparian Zone ; Nitrate Contamination ; Nitrate Stable Isotopes ; River-Groundwater Interaction ; Denitrification ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 3
    In: Global Change Biology, September 2017, Vol.23(9), pp.e5-e6
    Description: Increasing concentrations of dissolved iron and DOC are likely linked to decreasing nitrogen depositon.
    Keywords: Atmospheric Deposition ; Carbon Cycle ; Nitrogen Biogeochemistry ; Organic Matter ; Riparian Zone ; Water Quality
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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  • 4
    Language: English
    In: Advances in Water Resources, December 2015, Vol.86, pp.133-146
    Description: Dynamics of solute export from catchments can be classified in terms of chemostatic and chemodynamic export regimes by an analysis of concentration–discharge relationships. Previous studies hypothesized that distinct export regimes emerge from the presence of solute mass stores within the catchment and their connectivity to the stream. However, so far a direct link of solute export to identifiable catchment characteristics is missing. Here we investigate long-term time series of stream water quality and quantity of nine neighboring catchments in Central Germany ranging from relatively pristine mountain catchments to agriculturally dominated lowland catchments, spanning large gradients in land use, geology, and climatic conditions. Given the strong collinearity of catchment characteristics we used partial least square regression analysis to quantify the predictive power of these characteristics for median concentrations and the metrics of export regime. We can show that median concentrations and metrics of the export regimes of major ions and nutrients can indeed be inferred from catchment characteristics. Strongest predictors for median concentrations were the share of arable land, discharge per area, runoff coefficient and available water capacity in the root zone of the catchments. The available water capacity in the root zone, the share of arable land being artificially drained and the topographic gradient were found to be the most relevant predictors for the metrics of export regime. These catchment characteristics can represent the size of solute mass store such as the fraction of arable land being a measure for the store of nitrate. On the other hand, catchment characteristics can be a measure for the connectivity of these solute stores to the stream such as the fraction of tile drained land in the catchments. This study demonstrates the potential of data-driven, top down analyses using simple metrics to classify and better understand dominant controls of solute export from catchments.
    Keywords: Water Quality ; Catchment ; Nutrient Export ; Tile Drain ; Export Regime ; Concentration–Discharge Relationships ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 5
    Language: English
    In: Hydrology and Earth System Sciences Discussions, 10/22/2018, pp.1-36
    ISSN: Hydrology and Earth System Sciences Discussions
    E-ISSN: 1812-2116
    Source: CrossRef
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  • 6
    In: Water Resources Research, March 2018, Vol.54(3), pp.2317-2335
    Description: The analysis of transit/residence time distributions (TTDs and RTDs) provides important insights into the dynamics of stream‐water ages and subsurface mixing. These insights have significant implications for water quality. For a small agricultural catchment in central Germany, we use a 3D fully coupled surface‐subsurface hydrological model to simulate water flow and perform particle tracking to determine flow paths and transit times. The TTDs of discharge, RTDs of storage and fractional StorAge Selection (fSAS) functions are computed and analyzed on daily basis for a period of 10 years. Results show strong seasonal fluctuations of the median transit time of discharge and the median residence time, with the former being strongly related to the catchment wetness. Computed fSAS functions suggest systematic shifts of the discharge selection preference over four main periods: In the wet period, the youngest water in storage is preferentially selected, and this preference shifts gradually toward older ages of stored water when the catchment transitions into the drying, dry and wetting periods. These changes are driven by distinct shifts in the dominance of deeper flow paths and fast shallow flow paths. Changes in the shape of the fSAS functions can be captured by changes in the two parameters of the approximating Beta distributions, allowing the generation of continuous fSAS functions representing the general catchment behavior. These results improve our understanding of the seasonal dynamics of TTDs and fSAS functions for a complex real‐world catchment and are important for interpreting solute export to the stream in a spatially implicit manner. Transit times of discharge strongly related to storage Strong seasonality in discharge selection preference Seasonally changing SAS functions are well captured by Beta distributions
    Keywords: Transit Time ; Subsurface Mixing ; Sas Functions
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 7
    In: Journal of Geophysical Research: Biogeosciences, August 2016, Vol.121(8), pp.2199-2215
    Description: Aerobic respiration is an important component of in‐stream metabolism. The larger part occurs in the streambed, where it is difficult to directly determine actual respiration rates. Existing methods for determining respiration are based on indirect estimates from whole‐stream metabolism or provide time invariant results estimated from oxygen consumption measurements in enclosed chambers that do not account for the influence of hydrological changes. In this study we demonstrate a simple method for determining time‐variable hyporheic respiration. We use a windowed cross‐correlation approach for deriving time‐variable travel times from the naturally changing electrical conductivity signal that is transferred into the sediment. By combining the results with continuous in situ dissolved oxygen measurements, variable oxygen consumption rate coefficients in the streambed are obtained. An empirical temperature relationship is derived and used for standardizing the respiration rate coefficients to isothermal conditions. For demonstrating the method, we compare two independent measurement spots in the streambed, which were located upstream and downstream of an in‐stream gravel bar and thus exposed strongly diverse travel times. The derived respiration rate results are in accordance with findings of other stream studies. By comparing the travel time and respiration rate coefficient (i.e., Damköhler number) we estimate the contribution of each to the oxygen consumption in the streambed. An in situ method for estimation of streambed respiration Natural variations of EC can be used for deriving time‐variable travel times Respiration is equally influenced by temperature and hydrological dynamics
    Keywords: Respiration ; Streambed ; Oxygen ; Electrical Conductivity ; Cross Correlation
    ISSN: 2169-8953
    E-ISSN: 2169-8961
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  • 8
    Language: English
    In: Advances in Water Resources, October 2016, Vol.96, pp.95-107
    Description: Solute concentration variability is of fundamental importance for the chemical and ecological state of streams. It is often closely related to discharge variability and can be characterized in terms of a solute export regime. Previous studies, especially in lowland catchments, report that nitrate is often exported with an accretion pattern of increasing concentrations with increasing discharge. Several modeling approaches exist to predict the export regime of solutes from the spatial relationship of discharge generating zones with solute availability in the catchment. For a small agriculturally managed lowland catchment in central Germany, we show that this relationship is controlled by the depth to groundwater table and its temporal dynamics. Principal component analysis of groundwater level time series from wells distributed throughout the catchment allowed derivation of a representative groundwater level time series that explained most of the discharge variability. Groundwater sampling revealed consistently decreasing nitrate concentrations with an increasing thickness of the unsaturated zone. The relationships of depth to groundwater table to discharge and to nitrate concentration were parameterized and integrated to successfully model catchment discharge and nitrate export on the basis of groundwater level variations alone. This study shows that intensive and uniform agricultural land use likely results in a clear and consistent concentration-depth relationship of nitrate, which can be utilized in simple approaches to predict stream nitrate export dynamics at the catchment scale.
    Keywords: Water Quality ; Nitrate ; Lowland Catchment ; Export Regime ; Concentration-Discharge Relationship ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 9
    Language: English
    In: Biogeosciences Discussions, 05/10/2017, pp.1-30
    ISSN: Biogeosciences Discussions
    E-ISSN: 1810-6285
    Source: CrossRef
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  • 10
    Language: English
    In: Biogeosciences, Sept 29, 2017, Vol.14(18), p.4391
    Description: Excessive amounts of nutrients and dissolved organic matter in freshwater bodies affect aquatic ecosystems. In this study, the spatial and temporal variability in nitrate (NO.sub.3 .sup.- ), dissolved organic carbon (DOC) and soluble reactive phosphorus (SRP) was analyzed in the Selke (Germany) river continuum from three headwaters draining 1-3 km.sup.2 catchments to two downstream reaches representing spatially integrated signals from 184-456 km.sup.2 catchments. Three headwater catchments were selected as archetypes of the main landscape units (land use #xC3;#x97; lithology) present in the Selke catchment. Export regimes in headwater catchments were interpreted in terms of NO.sub.3 .sup.-, DOC and SRP land-to-stream transfer processes. Headwater signals were subtracted from downstream signals, with the differences interpreted in terms of in-stream processes and contributions from point sources. The seasonal dynamics for NO.sub.3 .sup.- were opposite those of DOC and SRP in all three headwater catchments, and spatial differences also showed NO.sub.3 .sup.- contrasting with DOC and SRP. These dynamics were interpreted as the result of the interplay of hydrological and biogeochemical processes, for which riparian zones were hypothesized to play a#xC2;#xA0;determining role. In the two downstream reaches, NO.sub.3 .sup.- was transported almost conservatively, whereas DOC was consumed and produced in the upper and lower river sections, respectively. The natural export regime of SRP in the three headwater catchments mimicked a#xC2;#xA0;point-source signal (high SRP during summer low flow), which may lead to overestimation of domestic contributions in the downstream reaches. Monitoring the river continuum from headwaters to downstream reaches proved effective to jointly investigate land-to-stream and in-stream transport, and transformation processes.
    Keywords: Embankments – Environmental Aspects ; Nitrates – Chemical Properties ; Nitrates – Environmental Aspects
    ISSN: 1726-4170
    ISSN: 17264189
    E-ISSN: 17264189
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