Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - HypoTRAIN (Hyporheic Zone Processes – A training network for enhancing the understanding of complex physical, chemical and biological process interactions)

Teaser

Rivers are important ecosystems under various anthropogenic pressures. One of those pressures is (treated) wastewater. Although nowadays the treatment of wastewater is very effective the water quality of the effluent is still impaired, especially by nutrients and organic...

Summary

Rivers are important ecosystems under various anthropogenic pressures. One of those pressures is (treated) wastewater. Although nowadays the treatment of wastewater is very effective the water quality of the effluent is still impaired, especially by nutrients and organic micropollutants. An example for organic micropollutants is pharmaceuticals and their daughter products which are often degraded by neither the human metabolism nor treatment processes. With the effluent they are discharged into rivers and might even be transported to groundwater. Rivers and groundwater are the most important drinking water resources in many European regions. That is why maximum attenuation or degradation of pollutants is important not only for ecosystems but also for human health. Rivers themselves have a certain self-purification capacity mainly resulting from the degradation of pollutants by (micro-)organisms and retention by sorption. These processes occur to a large extent in hyporheic zones, i.e. the sediments in the river bed. River water enters and travels through the sediment matrix of hyporheic zones. Here it might mix with groundwater since hyporheic zones are often interconnected with adjacent aquifers (Figs. 1 and 2). They are dynamic and complex transition regions between rivers and aquifers where multiple physical, biological and chemical processes occur simultaneously. They are assumed to be very effective in retaining and/or degrading pollutants. For a better understanding of the processes in hyporheic zones HypoTRAIN brings together a multi-disciplinary team from the fields of hydrology, ecology, microbiology, engineering, environmental physics, contaminant science, and modelling. Together they aim at generating new mechanistic insights into the functioning of hyporheic zones to enable a more holistic design of river management plans and restoration measures.
HypoTRAIN aims at developing new conceptual and analytical tools to quantify hyporheic exchange and residence time distributions and to identify hyporheic flow paths from local to reach scales. Another research objective is the quantification of hyporheic processing of inorganic and organic contaminants and hyporheic productivity. Furthermore, the performance of models describing hyporheic processes and the fate of pollutants will be improved as well as the quantitative prediction of these processes. At best, the results will facilitate the generation of better tools for assessing the effectiveness of restoration measures, river regulation, and the impact of climate change on hyporheic processes.

Work performed

Contaminants and nutrients are transported into the hyporheic zone with the surface water. Thus, their retention and degradation depends on water exchange between river and hyporheic zone. In order to define and quantify direction and velocity of hyporheic flow a “heat pulse sensor-system” was developed and improved. The heat pulse sensor allows measuring flow in all three dimensions by sending a heat signal into the river sediment which is captured by the sensors surrounding the heat source. The so-called breakthrough curves display the heat signal passing single temperature sensors. The heat-conduction-advection equation is used to determine the flow velocity in the hyporheic zone.
At one of the focus study sites of HypoTRAIN, the River Erpe, besides temperature also electric conductivity (EC) is used as a tracer for hyporheic flow. The river is heavily impacted by the discharge of treated wastewater which increases the background EC. Since the discharge rates vary diurnally, EC concentrations in the river and in the hyporheic zone vary accordingly. The delay and dampening of the EC signal in the hyporheic zone relative to the surface water can be used to determine hyporheic flow rates.
Sorption of molecules to the mineral or organic matrix of the river sediments plays an important role in the attenuation of micropollutants and nutrients. However, for a lot of these components their sorption characteristics are not fully understood yet. That is why batch and column experiments were conducted to determine sorption isotherms and sorption rate constants for different micropollutants on different biomass.
In addition, molecular techniques (such as qPCR, barcoded amplicon pyrosequencing) for identification and linking of microorganisms associated with some specific model micropollutants have been optimized and successfully applied. Microorganisms such as bacteria contribute to the degradation of micropollutants by using them as an energy source. By this, highly complex chemical structures are gradually degraded resulting in a variety of daughter products of which many are not even known so far. To identify them analytical methods have to be developed. During the course of the project a method for the analysis of 26 parent compounds and 35 transformation products was developed and validated.
But not only microorganisms are supposed to facilitate micropollutant transformation. Also higher organisms such as macroinvertebrates and meiofauna have the potential to contribute to degradation processes. The change in the community structure along the depth gradient in the sediments has been determined by collecting sediment-cores at the same spatial and temporal scale as thermal records which allows to link organisms with water fluxes in the hyporheic zone.
The Joint Field Experiments (JFEs) in summer 2016 provided a great opportunity for collaborations of ESRs from different disciplines by working simultaneously at a river which receives high loads of treated wastewater. A multi-disciplinary approach was applied to quantify attenuation/degradation on the reach scale: Concentration time series of organic trace pollutants and their transformation products as well as turnover rates were related to hydrological processes, such as transient storage, to identify the influence of these processes on the self-purification capacity of a lowland river. Furthermore, the influence of biogeochemical cycling on productivity of hyporheic communities with a focus on primary and secondary feeders was investigated by a collaboration of several ESRs.

Final results

The activities described above have led to new insights into the processes in the hyporheic zones of rivers which contribute to their self-purification capacity. For example, it was shown that intermediate levels of grazing resulted in significant boosting rates of bacteria density. This evidenced the positive effects of grazers on biofilms with direct implications for the transformation ability of the hyporheic zone since the microorganisms inhabiting the biofilms are key players in micropollutant degradation.
New tools and improvements of methods to quantify and sample hyporheic flow enable the quantification of transformation rates of nutrients and pollutants in rivers. The outcomes will contribute to a better understanding of the role the hyporheic flow has regarding its capability to cope with anthropogenic pollution. They can be used as a basis for the implementation of new tools in river restoration concepts specifically enhancing an in situ-diminishment of anthropogenic pollution. By that HypoTRAIN contributes to the improvement of protection measures of rivers.

Website & more info

More info: http://www.hypotrain.eu.