Roy M. Frings

A new approach to investigate the interactions between sediment transport and ecotoxicological processes during flood events

Extreme hydrodynamic events such as flood events or dredging activities bear the risk of eroding sediments in rivers, reservoirs, harbour basins or estuaries. One of the key concerns associated with these erosion processes is the re-mobilisation of sediment-bound pollutants in highly contaminated sediments. To date, much research has been conducted to characterise flow and sediment processes associated with hydrological events such as floods. Furthermore, there is a large body of literature describing the interaction of contaminants associated with particulate matter to aquatic biota. However, there is little knowledge regarding interactions between hydro-sedimentological and ecotoxicological processes. Understanding of the ecotoxicological consequences and associated risks to aquatic wildlife associated with hydraulic events can provide critical information to regulatory bodies or managing authorities. Specifically, it will aid in assessing risks associated with current management practices and will aid in developing more sustainable future management practices for waterways or harbours. Therefore, a combined experimental methodology between hydraulic engineers and ecotoxicologists was developed to investigate the ecological and toxicological relevance of sediment re-suspension and transport during erosion. An overview of this methodology is given in the present paper.

The veterinary antibiotic journey: comparing the behaviour of sulfadiazine, sulfamethazine, sulfamethoxazole and tetracycline in cow excrement and two soils

PurposeTo conceptualize the journey that veterinary antibiotics (VAs) follow between the animal stall and the field, two experiments were conducted. (1) The VAs sulfadiazine, sulfamethazine, sulfamethoxazole and tetracycline were mixed into cow excrement; prepared with three dry solid content variations. (2) Cow excrement containing the same VAs was mixed into sandy and clayey saturated soils. The aim was to quantify the solid-liquid partitioning and time-dependent behaviour of VAs at each stage of the journey, to enable mathematical replication of the process in the future.Materials and methodsIn each case, the mixtures were partitioned into their solid and liquid phases and the VA concentration in each was determined using liquid chromatography tandem mass spectrometry. Sorption isotherms (Kd values) and elimination constants (ks: solid form, kl: liquid form) were calculated after various incubation periods.Results and discussionSulfamethoxazole exhibits fast elimination in excrement; environmental contamination is unlikely. Sulfadiazine and sulfamethazine behave similarly in excrement and soils; tetracycline is more sorptive. Small percentages of the sulfadiazine, sulfamethazine and tetracycline masses initially found in excrement may subsequently be transported to environmental compartments in liquid form. However, the majority of these VAs are speculated to accumulate in soil or be transported to surface water systems via soil erosion.ConclusionsThe VA journey has been mathematically conceptualized for the first time and is supported by sorption isotherms and eliminations constants for four commonly detected VAs. Critical findings for sulfadiazine, sulfamethazine and tetracycline are (1) the majority of an initial VA mass resides in excrement liquid; (2) following incorporation into soil, the majority of the same initial VA mass resides in soil solid; (3) VAs found in soil liquid are assumed to be eliminated within a few months; (4) VAs found in soil solid are assumed to persist and accumulate; and (5) VAs are most likely to be transported to surface water systems in solid form (via soil erosion). Due to its rapid elimination in excrement, sulfamethoxazole that stems from veterinary medicine is not assumed to be a major environmental contaminant.

From agricultural fields to surface water systems: the overland transport of veterinary antibiotics

PurposeThe aim of this study was to assess if veterinary antibiotics, which are introduced to agricultural fields via fertilizer, are present in water systems (in both water and sediment) following overland transport via runoff and soil erosion.Materials and methodsThree water and sediment sampling schemes were conducted in Germany between June 2013 and June 2014 to examine the effects of (1) season, (2) heavy rainfall and (3) high veterinary antibiotic usage. The samples were analysed for 15 veterinary antibiotics using liquid chromatography tandem mass spectrometry.Results and discussionAntibiotics were detected in all three schemes in trace quantities. This is the first time that veterinary antibiotics have been detected in German sediment.ConclusionsIn particular, the presence of tetracycline in sediment taken from irrigation ditches in an agricultural area of high veterinary antibiotic usage offers proof that the overland transport of veterinary antibiotics is occurring. Due to the strong sorption of veterinary antibiotics (particularly tetracyclines) to soils, further research into their transport via soil erosion and assessment of their presence in sediment is advised.

Downstream fining processes in sandy lowland rivers

Downstream fining of river bed sediments is well known for gravel-bed rivers, but also occurs in sand-bed rivers. The objective of this study was to determine the effect of selective transport processes, dune sorting, overbank deposition, channel migration and river bifurcations on downstream fining in sandy lowland rivers subject to relative sea level rise, tidal water level variations and increasing river width. A numerical simulation model was built using the Delft3D software. Selective suspended-load transport appeared to be dominant over selective bed-load transport. Dune sorting and channel migration increase fining rates, but overbank deposition has an opposite effect. River bifurcations affect the fining rate because of their effect on the sediment supply to bifurcating lowland rivers. Downstream fining was found to develop within decades, but it took few centuries before the longitudinal bed profile and the fining rate attained dynamic equilibrium. A comparison of the modelled fining rates with those observed in the Rhine River shows reasonable agreement.

Fully Resolved Simulations of Dune Formation in Riverbeds

The formation and dynamics of dunes is an important phenomenon that occurs in many environmental systems, such as riverbeds. The physical interactions are complex and thus evaluating and quantifying the factors of influence is challenging. Simulation models can be used to conduct large scale parameter studies and allow a more detailed analysis of the system than laboratory experiments. Here, we present new coupled numerical models for sediment transport that are based on first principles. The lattice Boltzmann method is used in combination with a non-smooth granular dynamics model to simulate the fluid flow and the sediment particles. Numerical predictions of dune formation require a fully resolved modeling of the particulate flow which is only achieved by massively parallel simulations. For that purpose, the method employs advanced parallel grid refinement techniques and carefully designed compute kernels. The weak- and strong-scaling behavior is evaluated in detail and shows overall excellent parallel performance and efficiency.

Sand and Gravel on the Move: Human Impacts on Bed-Material Load Along the Lower Rhine River

Bed material controls the geometry and morphology of the channel bed as well as the suitability of the river to serve as habitat for aquatic organisms. Therefore, knowledge on bed-material load and the human impact thereon is essential for river managers and scientists. In this chapter, we present an overview of human impacts on bed-material load in the lower Rhine River and discuss its implications for river management. Although human activity did not significantly change the overall rate of bed-material load, it strongly changed the character of the transport: (1) the travel times of bed material decreased due to the prohibition of meander migration by bank protection, (2) the distribution of bed material over the Rhine delta changed due to the construction of barrages and the modification of river bifurcations, (3) a continuous exchange of bed material between the banks and the bed was initiated by shipping, and (4) the grain size of the bed material transport increased due to the effects of embankment, meander cut-offs, river narrowing, barrages, and sediment mining. The main morphological problem in large parts of the lower Rhine River is the erosion of bed material from the river bed. This process is probably induced by river narrowing, barrage construction, and sediment mining; and triggered by shipping and dredging. The ongoing bed erosion hinders navigation, infrastructure, ecology, and drinking water supply. River managers input large amounts of sediment to the river to supplement the natural bed-material load, to stabilize the river bed, and to prevent further erosion of bed sediments. At other locations, continuous dredging of bed sediment is necessary to allow year-round navigability. In order to predict the morphological behavior of a river and to develop management strategies, the downstream fluxes of bed material (sand, gravel) through the river and the sources and sinks of this material must be understood. This requires bed-load and suspended-load measurements in combination with sediment budget analyses. The current trend among river managers to reduce the number of transport measurements in favor of relying upon echo soundings is of concern.

Ten reasons to set up sediment budgets for river management

ABSTRACT Rivers are dynamical systems with alternating patterns of sedimentation and erosion. Both sedimentation and erosion may have negative consequences from a perspective of river management. A sediment budget is a most valuable tool for taking measures in river management that deal with sediment dynamics effectively. Drawing-up a sediment budget is time consuming and complicated, but very rewarding in that it strongly increases our understanding of the functional behaviour of a river system and the human impact thereon. The main goal of this article is to provide river managers with arguments in favour of sediment budget studies. This is done by illustrating the benefits of channel sediment budgets for river management using examples from the rivers Scheldt and Rhine. We present 10 reasons for drawing-up sediment budgets for river management: sediment budgets help to: (1) create order in the apparent chaos of data, (2) identify morphological problems, (3) find smart solutions to problems, (4) set research agendas and monitoring strategies, (5) optimize dredging and nourishment strategies, (6) coordinate river management on the basin scale, (7) assess consequences of human interventions, (8) improve numerical models, (9) explain river management to society and (10) train future generations of river managers.

A decade of fluvial morphodynamics: relocation and restoration of the Inde River (North-Rhine Westphalia, Germany)

BackgroundRelocations and restorations do not only change the ecological passability and sediment continuity of a river but also its flow behavior and fluvial morphodynamics. Sediment transport processes and morphological development can be assessed with field measurements, also taking the transport of sediment-bounded contaminants as a tracer material for fluvial morphodynamics into account. The objective of this study was to determine the morphological development of the Inde River (a tributary of the Rur River in North-Rhine Westphalia, Germany) towards its pre-defined guiding principle after a relocation and restoration in 2005 AD.MethodsThe fluvial morphodynamics of the Inde River were analyzed over a period of almost 15 years taking sediment samples, analyzing echo soundings of the river’s bathymetry and determining the heavy metal content of the sediment as a tracer material for the morphological development.ResultsThe results show that the relocation and restoration of the Inde River initiates new hydrodynamic processes, which cause morphological changes of the river widths, meander belts and channel patterns. The riverbed of the new Inde River has incised into the ground due to massive erosion, which has led to increased fine sediment transport in the downstream direction. The reasons for and consequences of this fine sediment transport are discussed and correlated to the sediment continuity of a river.ConclusionsOverall, the new Inde River has reached its goal of being a natural river as a consequence of the relocation and restoration and has adapted its new conditions towards a dynamic morphological equilibrium.