Transformation of organic micropollutants along hyporheic flow in bedforms of river-simulating flumes

Abstract

Urban streams receive increasing loads of organic micropollutants from treated wastewaters. A comprehensive understanding of the in-stream fate of micropollutants is thus of high interest for water quality management. Bedforms induce pumping effects considerably contributing to whole stream hyporheic exchange and are hotspots of biogeochemical turnover processes. However, little is known about the transformation of micropollutants in such structures. In the present study, we set up recirculating flumes to examine the transformation of a set of micropollutants along single flowpaths in two triangular bedforms. We sampled porewater from four locations in the bedforms over 78 days and analysed the resulting concentration curves using the results of a hydrodynamic model in combination with a reactive transport model accounting for advection, dispersion, first-order removal and retardation. The four porewater sampling locations were positioned on individual flowpaths with median solute travel times ranging from 11.5 to 43.3 h as shown in a hydrodynamic model previously. Highest stability was estimated for hydrochlorothiazide on all flowpaths. Lowest detectable half-lives were estimated for sotalol (0.7 h) and sitagliptin (0.2 h) along the shortest flowpath. Also, venlafaxine, acesulfame, bezafibrate, irbesartan, valsartan, ibuprofen and naproxen displayed lower half-lives at shorter flowpaths in the first bedform. However, the behavior of many compounds in the second bedform deviated from expectations, where particularly transformation products, e.g. valsartan acid, showed high concentrations. Flowpath-specific behavior as observed for metformin or flume-specific behavior as observed for metoprolol acid, for instance, was attributed to potential small-scale or flume-scale heterogeneity of microbial community compositions, respectively. The results of the study indicate that the shallow hyporheic flow field and the small-scale heterogeneity of the microbial community are major controlling factors for the transformation of relevant micropollutants in river sediments.

Impacts of Channel‐Spanning Log Jams on Hyporheic Flow

“…Consequently, hyporheic flow alters nutrient uptake by benthic stream organisms (Lehane et al., 2002) and plays an important role in the biogeochemical cycle (Boano et al., 2010; Li et al., 2017). In addition, hyporheic flow alters the adsorption and degradation of contaminants by sediment and microbes and thus controls the fate of contaminants in streams (Jaeger et al., 2021; McCallum et al., 2020).…”

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In addition, hyporheic flow alters the adsorption and degradation of contaminants by sediment and microbes and thus controls the fate of contaminants in streams (Jaeger et al, 2021;McCallum et al, 2020).Hyporheic flows can be induced by many factors, such as bed forms (

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Hydrobiogechemical interactions in the hyporheic zone of a sulfate-impacted, freshwater stream and riparian wetland ecosystem

“…7 Water ow is also spatially and temporally heterogeneous in the hyporheic zone [8][9][10] which inuences solute transport and further drives redox zone uctuations that alter the geochemistry as well as the microbial community composition, function and activity. 3,8,[11][12][13][14][15][16][17][18] These dynamic hydrobiogeochemical interactions drive the formation and uxes of major nutrients, 4,19,20 redox active metals, 11,21 contaminants, [22][23][24] and greenhouse gases, 15,25 having implications that reach far beyond the ecotone boundaries.…”