Response of Transport Parameters and Sediment Microbiota to Water Table Fluctuations in Laboratory Columns

Abstract

Groundwater table fluctuations create a dynamic interface between the unsaturated and saturated zone with spatially as well as temporally changing water content and water fluxes. Our objective was to investigate the impact of periodic water table fluctuations on transport parameters, geochemical gradients, and bacterial abundance and community structure in groundwater sediments. We conducted tracer experiments in one‐dimensional column systems investigating vertical flow with static or fluctuating water tables, constantly infiltrated with groundwater and model dissolved organic carbon (DOC). Pore water sampling was performed throughout the experiments, and sediment bacteria of both systems were characterized after completion of the experiment. Our results indicate that neither the longitudinal dispersivity nor column geochemistry was affected by the applied water table fluctuations. However, water content and flow velocities varied dynamically over time and depth in the fluctuation zone. Depth‐resolved bacterial community composition was clearly distinct, with additional populations detected especially in the fluctuation zone. These were absent in the static column, while overall bacterial diversity was similar over depth in both columns. We assume that spatial and temporal changes in water content and/or flow velocities were driving these microbial distinctions. This implies that complex feedback mechanisms between local hydrology and sedimentary bacterial communities in porous media exist. These results are important for the understanding of transformation and biodegradation processes at groundwater tables under increased hydraulic forcing.

Recent Developments and Applications of the HYDRUS Computer Software Packages

“…HYDRUS‐1D has been applied to scales involving very short laboratory soil columns, soil profiles of one to several meters deep (e.g., Ramos et al, 2011, 2012; Neto et al, 2016), as well as to soil profiles several hundred meters deep (Scanlon et al, 2003). HYDRUS (2D/3D) has been used similarly for transport domains ranging from <1 m wide to transects of several tens or hundreds of meters wide and for both laboratory (e.g., Rühle et al, 2013, 2015) and field‐scale applications (e.g., Yakirevitch et al, 2010; Pachepsky et al, 2014). Still, we do not recommend HYDRUS for very large 3D domains such as entire catchments (Šimůnek et al, 2012b).…”

“…The HYDRUS models were further used in a large number of studies to inversely optimize various soil hydraulic and solute transport parameters (Rühle et al, 2015; Qu et al, 2014; Lv et al, 2014; Caldwell et al, 2013; Schelle et al, 2013). Of these studies, Qu et al (2014) used HYDRUS‐1D to inversely estimate van Genuchten (1980) soil hydraulic parameters from field soil water content measurements at multiple locations to evaluate the spatial variability of the soil water content.…”

Taxonomically and metabolically distinct microbial communities with depth and across a hillslope to riparian zone transect

“…Within montainous watersheds such as studied here, rising temperatures and atmospheric CO 2 concentration, droughts and early snowmelt all have the potential to alter the riparian ecosystem [2]. These changes may alter water table elevations, and consequently depth of sub-surface anoxia, affecting vegetation [47] as well as microbial community composition and functioning [48]. Lowering of the water table could accelerate the release rate of solutes, such as nitrate, sulfate, iron, and selenate from soils, causing a deterioration of water quality both locally and downstream [49].…”

Response of soil bacterial community and geochemical parameters to cyclic groundwater‐level oscillations in laboratory columns

“…However, the effect of groundwater‐level oscillations on bacterial community composition in natural aquifers is still less known. As soils in natural aquifers are abundant in organic C (Vos et al., 2019), the leaching, dissolution, and biodegradation of organic C can have an impact on the response of soil bacterial community composition at different depths over long‐term, cyclic, groundwater‐level oscillations (Rühle, von Netzer, Lueders, & Stumpp, 2015). It is possible that an impact on response of soil bacterial community composition at different depths can also occur in natural aquifers over rapid, short‐term, cyclic, groundwater‐level oscillations, as a previous study reported that short‐term, groundwater‐level oscillations can alter geochemical processes (Farnsworth et al., 2012).…”