Comparing seasonal streamflow forecast systems for management of a fresh water reservoir in the Netherlands

For efficient management of the Dutch surface water reservoir Lake IJssel, (sub)seasonal forecasts of the water volumes going in and out of the reservoir are potentially of great interest. Here, streamflow forecasts were analyzed for the river Rhine at Lobith, which is partly routed through the river IJssel, the main influx into the reservoir. We analyzed multiple seasonal forecast data sets derived from EFAS, E-HYPE and HTESSEL, which differ in their underlying hydrological formulation, but are all forced with similar input from the ECMWF SEAS5 meteorological forecasts. We post-processed the streamflow forecasts using quantile matching (QM) and analyzed several forecast quality metrics. Forecast performance was assessed based on the available reforecast period, as well as on individual summer seasons. QM increased forecast skill for nearly all metrics evaluated. Particularly HTESSEL, a land surface scheme that is not optimized for hydrology, needed the largest correction. Averaged over the reforecast period, forecasts were skillful for the longest lead times in spring and early summer. For this period, E-HYPE showed the highest skill; Later in summer, however, skill deteriorated after 1–2 months. When investigating specific years with either low or high flow conditions, forecast skill increased with the extremity of the event. Although raw forecasts for both E-HYPE and EFAS were more skilful than HTESSEL, bias correction based on QM can significantly reduce the difference. In operational mode, the three forecast systems show comparable skill. In general, dry conditions can be forecasted with high success rates up to three months ahead, which is very promising for successful use of Rhine streamflow forecasts in downstream reservoir management.

The Danubian cryptic invader Theodoxus fluviatilis (Gastropoda: Neritidae) in the River Rhine: a potential indicator for metal pollution?

Metal pollution poses a major threat to aquatic systems especially in anthropogenic influenced areas, in as much as metals are persistent in the environment. The freshwater snail Theodoxus fluviatilis has often been used as an indicator species for the ecological status in river monitoring. In the River Rhine, the native Northern-European form of T. fluviatilis is nowadays extinct, whilst the Danubian form is spreading along the river. The aim of our study was to investigate if the cryptic invader is affected by metal exposure present in the River Rhine and to discuss its potential as an indicator for metal pollution. Several environmental abiotic (14 water environmental variables plus five common metal concentrations in water and biofilm) and biotic parameters (biofilm mass) were measured across 23 sites along the River Rhine. Five population and six histopathological parameters were evaluated on snails collected at all 23 sites. Aqueous chromium concentration was positively correlated to the damage of male reproductive organs of T. fluviatilis, and higher ammonium concentration was correlated to a decrease in snail size and an increase in the proportion of juveniles. None of the analysed snail parameters was negatively correlated to concentrations of other metals measured, like copper and zinc. Therefore, based on the parameters evaluated, our results indicate that the Danubian form of T. fluviatilis is only restrictedly suitable as an indicator for metal pollution in the River Rhine system. Further field and laboratory investigations including other stressors are necessary to evaluate the indicator potential of the cryptic invader holistically.

Simple modelling for a large-scale assessment of total phosphorus retention in the floodplains of large rivers

Floodplains provide a multitude of ecosystem functions and services with water purification being one of them. For this study we modelled the retention of total phosphorous (TP) in the floodplains of the river Rhine and the river Elbe, looking at sediment deposition as the main process responsible for removing TP from rivers during inundation events. We applied two different approaches: a proxy-based approach (PBA) and a one-dimensional model based approach (MBA). We used both to calculate the yearly TP retention and compared it with the annual TP load in the rivers. Compared to the transported river load the Elbe floodplains investigated retained approx. 4.9% TP resp. 1.4% (PBA vs. MBA) while in the floodplains of the river Rhine about 1.8% vs. 0.3% TP was retained. We found that the greatest difficulty in quantifying TP retention in floodplains is due to the lack of spatial detail on the hydrological connectivity between rivers and their adjacent floodplains and that a sound validation of the results is absolutely necessary. Long-term monitoring data for floodplains, especially on hydrological connectivity, are of crucial importance in this respect.

Antibiotic-Resistant Bacteria in Clams—A Study on Mussels in the River Rhine

Bacterial infections have been treated effectively by antibiotics since the discovery of penicillin in 1928. A worldwide increase in the use of antibiotics led to the emergence of antibiotic resistant strains in almost all bacterial pathogens, which complicates the treatment of infectious diseases. Antibiotic-resistant bacteria play an important role in increasing the risk associated with the usage of surface waters (e.g., irrigation, recreation) and the spread of the resistance genes. Many studies show that important pathogenic antibiotic-resistant bacteria can enter the environment by the discharge of sewage treatment plants and combined sewage overflow events. Mussels have successfully been used as bio-indicators of heavy metals, chemicals and parasites; they may also be efficient bio-indicators for viruses and bacteria. In this study an influence of the discharge of a sewage treatment plant could be shown in regard to the presence of E. coli in higher concentrations in the mussels downstream the treatment plant. Antibiotic-resistant bacteria, resistant against one or two classes of antibiotics and relevance for human health could be detected in the mussels at different sampling sites of the river Rhine. No multidrug-resistant bacteria could be isolated from the mussels, although they were found in samples of the surrounding water body.

The Ponto-Caspian parasite Plagioporus cf. skrjabini reaches the River Rhine system in Central Europe: higher infestation in the native than in the introduced Danubian form of the gastropod Theodoxus fluviatilis

The introduction of non-indigenous organisms in new areas in the context of host-parasite interactions is still poorly understood. This study aimed at a parasitological and histopathological comparison of two phylogenetically distinct forms of the freshwater snail Theodoxus fluviatilis in the River Rhine system: the native Northern-European form, which showed a decline for unknown reasons and is nowadays extinct in the River Rhine, and the non-indigenous Danubian form, which was introduced via the Main–Danube canal. We histopathologically examined populations of Northern-European T. fluviatilis from three smaller rivers of the Rhine system and of Danubian T. fluviatilis from the River Rhine, after confirming the phylogenetic background of the respective population genetically. Results showed differences in the prevalence of trematodes and histopathologic organic alterations between the two snail forms. Both were infected with an opecoelid trematode Plagioporus cf. skrjabini, whereby its prevalence was significantly higher in the Northern-European than in the Danubian form. The parasitic trematode is, to our knowledge, a new trematode species in the River Rhine system, presumably co-introduced through the invasion of its second intermediate and final hosts, i.e. Ponto-Caspian amphipods and gobies. Its impact on native populations of Northern-European T. fluviatilis needs to be subject of future studies.

Discharge of the river Rhine from multi-sensor data from empirical and physical methods

<p>River discharge is a key variable to quantify the water cycle and its flux.  This study focuses on the river Rhine, of width between 200 and 500 meters. River discharge is evaluated in this paper from the Sentinel-3 altimeter water level using various approches, which are the empirical rating curve method, the semi-empirical Bjerklie method and the physically-based method based on hydraulic equations.</p><p>The Sentinel-3 GPOD ESA products from the SAMOSA+ retracker perform better than the standard Copernicus products that use the OCOG and ocean retrackers. Root-mean-square errors (RMSEs) between altimetry and in-situ stations are between 0.10 m and 0.30 m at 10 of the 17 virtual tide gauge locations. The empirical rating curve method applied to the altimetric water level and in-situ discharge provides estimates of the water discharge with accuracy of 3-7% (expressed as RMSE normalized with the mean of the discharge).</p><p>The performance of the semi-empirical Bjerklie method and of the physically-based Manning algorithm to estimate the river discharge is assessed from water surface slope, elevation and top width data for different part of the river and flow conditions. Firstly, daily synthetic water surface slopes and elevations are generated from selected in-situ gauges and mean top river widths. Secondly the input to the discharge algorithm comes from the 1D-hydrodynamic model Sobek. Various choises for reach lengths and for number of observed time-series are considered. Different time sampling are used to study the effect of the repeat cycle of nadir altimeter and SWOT missions. The effect of the priori information on the accuracy of the flow water discharge is investigated.</p>

Multiscale bedform interactions in a lowland river

<p>Multiscale bedforms exist in diverse environments. Globally, trains of small secondary bedforms have been observed in fluvial systems, where they are superimposed on larger fluvial dunes. Yet, we understand little about the morphodynamics of these superimposed bedforms and their interaction with larger bedform scales. It is unclear what their impact is on the overall system functioning, for example in terms of sediment transport and (near-bed) flow dynamics.</p><p>Bed elevation data with a high spatiotemporal resolution, obtained during a dedicated field campaign in the river Waal, a main distributary of the river Rhine, have shed light on the morphodynamics of fluvial dunes and superimposed bedforms. Results from the study indicate that superimposed bedforms persist over low-angled lee sides, whereas they disintegrate over lee side angles steeper than . The transport of bed sediment associated with secondary bedform migration is significant. The small bedforms migrate with a celerity that is an order of magnitude larger, from which a transport rate can be inferred that equals and in some sections even exceeds the transport associated with primary river dunes. Where superimposed bedforms disintegrate at or downstream of the dune lee slope, superimposed bedforms fully contribute to the migration of the primary dune. Where they persist over the dune lee side however, the sediment transport inferred from superimposed bedforms over the dune crest might partly contribute to primary dune migration. A significant portion, however, will also be transported over the dune lee side and trough and form an additional transport component. Both the persistence of the superimposed bedforms on the primary dune lee and their size and shape, appear to depend on the primary dune morphology. This is likely related to the flow structure—i.e. the presence of flow separation and the properties of the downstream, turbulent wake—that depends on the primary lee slope angle and height.</p><p>In our current work, we build upon this study, and  analyse the morphodynamics of these two bedform scales across a much larger spatial and temporal scale. Small-scale superimposed bedforms appear to be ubiquitous in the river Waal and can be observed across a range of discharge conditions. Our analysis quantifies and predicts when secondary bedform occur and persist over primary lee sides. We further aim to understand how secondary bedform morphology depends on primary dune characteristics as well as environmental conditions such as (changes in) discharge, and the bed sediment properties. In relation to that, we question to what extent superimposed bedforms in turn affect the primary dune morphology, their migration celerity and associated bedload transport.</p><p> </p>

Temporal variability of annual suspended sediment yield estimates and their uncertainties

<p>Suspended sediment contributes to the vast majority of the annual sediment load transported by rivers to the global oceans. At the same time, this large fraction is transported just in a fraction of time. Towards achieving sustainable sediment management and healthy fluvial systems, identifying the impact of the temporal variability on annual load estimates becomes indispensable in order to reduce uncertainties.</p><p>We aim to estimate the temporal variability of suspended sediment transport and the uncertainty of annual suspended sediment loads. Our approach is based on high-resolution time series (15 min sampling interval) of discharge and suspended sediment concentration (SSC) at four monitoring stations with different degrees of discharge variability. The quantification of the variability of discharge and sediment yield is achieved through the exceedance time. The uncertainty of the annual sediment load is estimated using a bootstrap approach. We assess the impact of the sampling interval and link the optimal sampling interval to different SSC-variability. Further, the impact of rating parameters on the uncertainty of annual loads is investigated.</p><p>Our results indicate an increase in SSC-variability with decreasing discharge, leading to a negative relationship with the contributing catchment area. The 80 % exceedance times for the annual sediment load range from less than 10 % for the river Ammer (catchment area 608 km²) between 10 – 20 % for the rivers Ilz (765 km²) and Moselle (27 088 km²) to more than 40 % for the river Rhine (109 806 km²). Simultaneously, the variability increases with a decrease in sampling frequency. Our preliminary results indicate a negative exponential relationship between exceedance time and uncertainties in annual load estimates. This relationship can be used to estimate the uncertainty of annual loads estimated based on low frequency sediment sampling at the continental to global scale.</p>

Impact of seasonal variations and transient colmation layer properties on bacteria and virus transport in bank filtration

<p>Bank filtration is a sustainable source for drinking water production in urbanized regions but is increasingly at risk by contamination with pathogenic bacteria and viruses from surface water receiving wastewater discharge. While recent advances have improved our process understanding for pathogen transport on laboratory scale, simulations and predictions on field scale under transient conditions, as in bank filtration, are still highly uncertain. To improve our understanding on field scale, we performed a sampling survey over 16 months at an observation well transect in a heterogeneous sand-gravel aquifer of an active bank filtration waterworks at the river Rhine in Germany. Water samples were collected from the river, the production well, and 4 multi-level observation wells. Samples were analysed for main anions/cations, and hygienic indicators (E. coli and coliform bacteria via plate counts, coliphages via plaque assay, and adenoviruses via ddPCR). A two-dimensional reactive transport model was set up using PFLOTRAN to simulate the transport of heat and dissolved species, aerobic respiration, denitrification, and colloid-based transport of bacteria and viruses. For the latter, adsorption to and desorption from the sediment, straining, blocking, and inactivation are considered. Model parameters were estimated from prior knowledge of the site or calibrated with the obtained data using particle swarm optimization.</p><p>Field observations show a strong seasonal variation of river hydraulics with up to 8 m difference in water level, a prolonged low in the summer/fall and short-termed river level increases in the winter. Aerobic respiration was strongly controlled by the temperature variation (6-24°C in groundwater), leading to an increase in oxygen consumption and limited denitrification during the warm summer/fall. Bacteria and virus concentrations in the groundwater were elevated following a flood in the first winter (up to 500 MPN/100mL coliforms, 2 PFU/100mL coliphages, 1000 copies/100mL adenovirus). Measurable concentrations were still observed during the summer (e.g., up to 10 MPN/100mL coliforms, 0.7 PFU/100mL coliphages, 500 copies/mL adenovirus), but concentrations were below the detection limit for most of the second winter, where no significant flood occurred. In the well closest to the river (40 m distance), the concentration reduction compared to the river varied over time between 1 to ≥4 log-units for coliforms, 1.5 to ≥3 log-units for coliphages, and 0.5 to ≥3 log-units for adenoviruses. The model results suggest the main driving processes for the variation in the bacteria and virus concentrations are (i) the changing groundwater velocity (driven by river level variations and pumping rate), (ii) occurrence of low dissolved oxygen concentrations which lower inactivation, and (iii) transient colmation layer properties (permeability and effective grain size). The colmation layer is affected by reworking of riverbed sediments during floods, bio-clogging during summer, and physical clogging due to constant forced infiltration caused by the bank filtration plant. This is supported by the observation of high bacteria concentrations in the aquifer for a short duration after pumps were reactivated following a 40-day maintenance period. Overall, bacteria and virus attenuation during bank filtration was high, only a strong flood resulted in significantly higher contaminant concentrations in the aquifer.</p>