Search

This report describes results from the CLAYFRAC project investigating possibilities to map or rank clay localities according to their vulnerability to pesticide leaching. The project entailed a combined and multiscale experimental and modelling approach starting from the polymorphological (PM) concept for ranking the heterogeneity of clay-till deposits. The PM concept separate clay-till deposits in landforms differing by their pattern of superimposed geomorphological units. Four large excavations have been established representing different PM landforms. The Havdrup-Salløv excavation was established in a PM landform named MML meaning a landform where basement marine clay (L) is overlaid by a moraine plain (M), overlaid by another moraine plain (M). MML landforms have previously been studied in detail why the other excavations were carried out at less studied landforms. The Farum excavation was on the PM-landform DMS being an outwash plain (S), overlaid by a moraine plain, overlaid by a hummocky moraine (D); the Holbæk excavation was on the PM-form DM being a moraine plain overlaid by a hummocky moraine, and finally the Tokkekøb excavation was on the PM-form DR being a marginal moraine (R), overlaid by a hummocky moraine. The lithology and presence of preferential flow paths, including macropores (wormholes, root channels, burrows etc), tectonic and desiccation fractures, and sand lenses were characterized at each excavation. All sites were geologically highly heterogeneous with different clay units being mixed with sand lenses and sand layers. This was most pronounced at Holbæk where half of the excavation showed exposure of sandy deposits. The Havdrup-Salløv excavation was characterized by having three till units separated by sand layers. Macropores dominated in the upper till with many wormholes present down to one m depth. Grey fractures were present to a depth of 1-3 meter below surface (mbs), below which the fracture surface linings became red due to i

Drinking water resources, such as groundwater, are threatened by pollution. The pesticide metabolite 2,6-dichlorobenzamide (BAM) is one of the compounds frequently found in groundwater. Studies have attempted to add specific BAM-degrading bacteria to sand filters at drinking water treatment facilities. This biotechnology has shown great potential in removing BAM from contaminated water. However, the degradation potential was formerly lost after similar to 2-3 weeks due to a decrease of the degrader population over time. The aim of the present study was to overcome the constraints leading to loss of degraders from inoculated filters. Our approach was threefold: (1) Development of a novel inoculation strategy, (2) lowering the flowrate to reduce washout of cells, and (3) increasing the concentration of nutrients hereunder the pollutant in a smaller inlet water stream. The two latter were achieved via modifications of the inlet water by applying membrane treatment which, besides producing an ultra-pure water fraction, produced a residual water stream with nutrients including BAM concentrated in similar to ten-fold reduced volume. This was done to alleviate starvation of degrader bacteria in the otherwise oligotrophic sand filters and to enable a decreased flowrate. By this approach, we achieved 100% BAM removal over a period of 40 days in sand filter columns inoculated with the BAM-degrader Aminobacter sp. MSH1. Molecular targeting of the degrader strain showed that the population of degrader bacteria persisted at high numbers throughout the sand filter columns and over the entire timespan of the experiment. 16S rRNA gene amplicon sequencing confirmed that MSH1 dominated the bacterial communities of the inoculated sand filter columns at experimental termination. The community composition of the indigenous prokaryotes, based on beta diversity, in the sand filter columns was governed by the feed water type i.e., membrane retentate or untreated water.

Preferential flow paths in subsurface soils serve as transport routes for water, dissolved organic matter and oxygen. Little is known about bacterial communities in flow paths or in subsoils below ∼4 m. We compared communities from preferential flow paths (biopores, fractures and sand lenses) with those in adjacent matrix sediments of clayey till from the plough layer to a depth of 6 m. 16S rRNA gene-targeted community analysis showed bacterial communities of greater abundance and diversity in flow paths than in matrix sediments at all depths. Deep fracture communities contained a higher relative abundance of aerobes and plant material decomposers like Nitrospirae, Acidobacteria and Planctomycetes than adjacent matrix sediments. Similarly, analyses of the relative abundances of archaeal amoA, nirK and dsrB genes indicated transition from aerobic to anaerobic nitrogen and sulphur cycling at greater depth in preferential flow paths than in matrix sediments. Preferential flow paths in the top 260 cm contained more indicator operational taxonomic units from the plough layer community than the matrix sediments. This study indicates that the availability of oxygen and organic matter and downward transport of bacteria shape bacterial communities in preferential flow paths, and suggests that their lifestyles differ from those of bacteria in matrix communities.