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  • 1
    Language: English
    In: Journal of Hydrology, October 2015, Vol.529, pp.940-950
    Description: For capturing spatial variations of runoff and nutrient fluxes attributed to catchment heterogeneity, multi-site hydrological water quality monitoring strategies are increasingly put into practice. This study aimed to investigate the impacts of spatially distributed streamflow and streamwater Inorganic Nitrogen (IN) concentration observations on the identification of a continuous time, spatially semi-distributed and process-based hydrological water quality model HYPE (HYdrological Predictions for the Environment). A Bayesian inference based approach DREAM (DiffeRential Evolution Adaptive Metrololis algorithm) was combined with HYPE to implement model optimisation and uncertainty analysis on streamflow and streamwater IN concentration simulations at a nested meso scale catchment in central Germany. To this end, a 10-year period (1994–1999 for calibration and 1999–2004 for validation) was utilised. We compared the parameters’ posterior distributions, modelling performance using the best estimated parameter set and 95% prediction confidence intervals at catchment outlet for the calibration period that were derived from single-site calibration (SSC) and multi-site calibration (MSC) modes. For SSC, streamflow and streamwater IN concentration observations at only the catchment outlet were used. While, for MSC, streamflow and streamwater IN concentration observations from both catchment outlet and two internal sites were considered. Results showed that the uncertainty intervals of hydrological water quality parameters’ posterior distributions estimated from MSC, were narrower than those obtained from SSC. In addition, it was found that the MSC outperformed SSC on streamwater IN concentration simulations at internal sites for both calibration and validation periods, while the influence on streamflow modelling performance was small. This can be explained by the “nested” nature of the catchment and high correlation between discharge observations from different sites. Results revealed, also, that 95% prediction confidence intervals of streamflow and streamwater IN concentration estimated from MSC were more credible compared with those estimated from SSC, which are reflected by narrower confidence intervals and higher percentage of observations bracketed in the estimated unit confidence intervals. The outcomes of this study pointed out the importance of spatially distributed hydrological water quality observations for improving model parameter identification and provided guidelines for choice of adequate calibration strategy and design of hydrological water quality monitoring campaign.
    Keywords: Nitrogen Modelling ; Model Identification ; Multi-Site Calibration ; Uncertainty Analysis ; Spatially Distributed Observations ; Dream(Zs) ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 2
    In: Global Change Biology, May 2017, Vol.23(5), pp.1891-1901
    Description: Reductions in emissions have successfully led to a regional decline in atmospheric nitrogen depositions over the past 20 years. By analyzing long‐term data from 110 mountainous streams draining into German drinking water reservoirs, nitrate concentrations indeed declined in the majority of catchments. Furthermore, our meta‐analysis indicates that the declining nitrate levels are linked to the release of dissolved iron to streams likely due to a reductive dissolution of iron() minerals in riparian wetland soils. This dissolution process mobilized adsorbed compounds, such as phosphate, dissolved organic carbon and arsenic, resulting in concentration increases in the streams and higher inputs to receiving drinking water reservoirs. Reductive mobilization was most significant in catchments with stream nitrate concentrations 〈6 mg L. Here, nitrate, as a competing electron acceptor, was too low in concentration to inhibit microbial iron() reduction. Consequently, observed trends were strongest in forested catchments, where nitrate concentrations were unaffected by agricultural and urban sources and which were therefore sensitive to reductions of atmospheric nitrogen depositions. We conclude that there is strong evidence that the decline in nitrogen deposition toward pre‐industrial conditions lowers the redox buffer in riparian soils, destabilizing formerly fixed problematic compounds, and results in serious implications for water quality.
    Keywords: Atmospheric Deposition ; Carbon Cycle ; Nitrogen Biogeochemistry ; Organic Matter ; Riparian Zone ; Streamwater Chemistry
    ISSN: 1354-1013
    E-ISSN: 1365-2486
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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
    In: Methods in Ecology and Evolution, September 2014, Vol.5(9), pp.971-975
    Description: The estimation of stream metabolism represents a useful technique for characterising the ecological status of natural lotic systems. The existing tools for investigating metabolism in situ demand expert knowledge, provide only a few options, ignore possible groundwater effects and often rely on modelled input data, such as gas exchange, that could be subject to error. We have developed MeCa, a user‐friendly MATLAB toolbox that contains different options – including the groundwater correction – for the calculation of metabolism. A detailed explanation of all the calculation steps and the various calculation options is given in the Appendix S1. The functions of MeCa can be tested using the test data set provided. We conducted sensitivity tests to assess the effect of certain parameters (reaeration, travel time, groundwater oxygen concentration, mean depth and width) and other measurements (oxygen, temperature, pressure) on the metabolism estimation. Uncertainties in the parameters have a greater effect than those that apply to the measurements. The parameters reaeration coefficient and mean depth are the most sensitive input data. Results from sensitivity analyses show the complexity of metabolism studies in streams and the importance of direct calculations. MeCa includes all relevant calculation options, and thus makes a contribution towards the standardisation of metabolism studies.
    Keywords: Open‐Channel Method ; Stream Metabolism ; Two‐Station Technique ; Matlab
    ISSN: 2041-210X
    E-ISSN: 2041-210X
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  • 5
    Language: English
    In: Biogeochemistry, 2013, Vol.115(1), pp.53-63
    Description: Riverine dissolved organic carbon (DOC) supports the production of estuaries and coastal ecosystems, constituting one of the most actively recycled pools of the global carbon cycle. A substantial proportion of DOC entering oceans is highly aged, but its origins remain unclear. Significant fluxes of old DOC have never been observed in temperate headwaters where terrestrial imports take place. Here, we studied the radiocarbon age of DOC in three streams draining forested headwater catchments of the river Mulde (Ore Mountains, Germany). In a 4 week summer precipitation event DOC aged at between 160 and 270 years was delivered into the watershed. In one stream, the DOC was modern but depleted in radiocarbon compared to other hydrological conditions. The yield was substantial and corresponded to 20–52 % of the annual DOC yields in wet and dry years, respectively. The analysis of long-term data suggested that the DOC export in extreme precipitation events added to the annual yield and was not compensated for by lower exports in remaining periods. We conclude that climate change, along with additional processes associated with human activities, channels old soil carbon into more rapidly cycled carbon pools of the hydrosphere.
    Keywords: DOC ; DIC ; Radiocarbon ; 14C ; Catchment ; Reservoir
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 6
    Language: English
    In: CLEAN - Soil, Air, Water, 05/2011, Vol.39(5), pp.437-443
    Keywords: Wassergüte ; Elbe;
    ISSN: CLEAN - Soil, Air, Water
    E-ISSN: 18630650
    E-ISSN: 18630669
    Source: Wiley (via CrossRef)
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  • 7
    In: Journal of Hydrology and Hydromechanics, 03/1/2013, Vol.61(1), pp.81-83
    Description: Dissolved organic carbon (DOC) transported by rivers represents an important link between carbon pools of terrestrial and oceanic ecosystems. However, it is unclear how frequent DOC must be sampled to obtain reasonable load estimates. Here, we used continuous records of the specific UV absorption coefficient (SAC) and discharge from a headwater stream at the Ore Mountains (Germany) to calculate load errors depending on DOC sampling frequency. SAC was used as a proxy for DOC. The results show that the load was underestimated by 13-19% with monthly, 10-13% with bi-weekly and 7-9% with weekly DOC samplings, respectively. We conclude that collecting additional data from high discharge events decrease the error significantly.
    Keywords: Geography;
    ISSN: 0042-790X
    E-ISSN: 13384333
    Source: CrossRef
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  • 8
    In: Journal of Plankton Research, 2012, Vol. 34(2), pp.102-112
    Description: Aquatic bacteria are considered to exhibit a paradoxical behaviour. They luxuriously consume phosphorus, the element often restricting the abundance of algae, which provide the organic substrates maintaining bacterial growth. Here, we test the hypothesis that bacteria can limit their uptake of phosphorus and increase the availability of phosphorus to algae. The physiological costs for bacteria must be compensated for by a surplus of photosynthetic exudates facilitating higher biomass production. To test the potential of such an economic behaviour, we used a new differential equation model that was parameterized by independent experiments. Model results indicate that this potential does exist. As a consequence, we conducted continuous growth chemostat experiments. Bacteria did not leave more phosphorus to, “high exudation” algae compared with algae with low release. Therefore, the hypothesis was not supported by the experiments. However, bacteria significantly increased production 1.4–1.8-fold in cultures with “high exudation” algae. This was explained by an increase in conversion of organic carbon from growth medium into bacteria biomass. Algal exudates were quantitatively negligible but could act as growth factors. The results show that biomass of algae and bacteria cannot be predicted solely by mineral nutrients and carbon as assumed by the classical theory.
    Keywords: Bacteria ; Phytoplankton ; Exudation ; Phosphorus ; Differential Equation Model
    ISSN: 0142-7873
    E-ISSN: 1464-3774
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  • 9
    Language: English
    In: Journal of Great Lakes Research, 2014, Vol.40, pp.8-18
    Description: Validation of hydrodynamic two-dimensional (2D) sediment transport models is often difficult, because of their high demands for spatially distributed sediment deposition data. Therefore, the objective of this study is to introduce a new method for the validation of distributed hydrodynamic sediment transport models, which relies on the linear relationship between sedimentation and heavy metal concentration in the topsoil of riverine floodplains. The tracer method was tested in the heavily contaminated 45 km large floodplains of River Mulde near Bitterfeld (Germany), using 129 topsoil concentrations of cadmium (Cd), zinc (Zn), and arsenic (As). Sediment deposition during flood events was simulated using the hydrodynamic and sediment transport model Telemac2D. A monotonic increase in median heavy metal concentrations with increasing sediment deposition classes was found by comparing simulated sediment deposition classes to associated heavy metal concentrations of the topsoil. These findings were confirmed for Cd, Zn, and As for more than three sediment deposition classes. Results of correlation analyses indicate highly significant linear positive relationships between heavy metal concentrations and sediment deposition. The proposed method is easy to apply, and time-consuming event-based measurements are not required, because of the use of time-integrated measurements of topsoil heavy metal concentrations. The new method enables the user to evaluate the validity of 2D sediment transport models at least in a semi-quantitative manner, by comparing given heavy metal concentrations of the topsoil of active floodplains to simulated sediment deposition.
    Keywords: Sediment Deposition ; Telemac2d ; Model Validation ; Floodplains ; River Mulde ; Germany ; Engineering ; Geography
    ISSN: 0380-1330
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  • 10
    Language: English
    In: Environmental Monitoring and Assessment, 2015, Vol.187(7), pp.1-13
    Description: As benthic biofilms mediate essential functions in stream ecosystems (e.g., carbon flux, storage of nutrients and other substances), the element-specific regulation of the biofilm composition is of great interest. We tested whether (1) the elemental composition of biofilms is related to that of the water column and (2) there are different accumulation patterns from the dissolved phase (adsorption) and the particulate phase (incorporation of suspended matter). We analysed biomass parameters, nutrients and metals in biofilms and surface waters at 28 sites within a stream network (Bode catchment, Germany). Algal biomass in biofilms was dominated by diatoms. The P/C ratio in biofilms was positively related to total phosphorus of surface water (and to the proportion of agricultural area in the catchment) indicating phosphorus limitation of biofilms, whereas the N/C ratio was not related to nitrate levels of surface water, and neither the P/C nor the N/C ratio to the concentration of dissolved organic carbon (DOC) of surface water. Biofilms were enriched in metals compared to their concentrations in water. The metals in biofilms were positively related to the concentration of dissolved metals in surface water for iron and strontium (but not for manganese, copper, zinc, arsenic or lead) and to the concentrations of particle-associated metals of surface waters for strontium and lead. Manganese and arsenic were the metals with a negative effect on the biomasses of biofilm diatoms and cyanobacteria. Overall, we observed element-specific accumulation patterns in biofilms with selected elements being related to the water column while others were probably subject to biofilm-internal processes.
    Keywords: Nutrients ; Stoichiometry ; Heavy metals ; Total reflection X-ray fluorescence spectrometry (TXRF) ; Stream biofilms ; River Bode
    ISSN: 0167-6369
    E-ISSN: 1573-2959
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