BTO rapport - BTO 2020.041

Recontamination of Dune Extracted Water


Dune passage in an important barrier against pathogenic microorganisms. However, faecal indicator bacteria (FIB) are occasionally found in the extracted water from the dunes. The origin of these bacteria is not clear, though the assumption is that these bacteria reach the saturated zone from ground level. In this research we investigated whether faecal deposition at ground level is the cause of the FIB occasionally found in extracted water from Dunea. Water samples at the wells are examined for FIB and by source tracking with faecal markers from specific animal groups. The aim was to establish a direct link to bacteria at ground level in this way and the possible detection of these bacteria in the water at the well, and to determine from which animal groups these bacteria originate. Wells were monitored from a vulnerable location in the dunes for FIB over a 5 month period. Low concentration of Enterococci were found in a monitoring well in January.
In addition, a second field experiment was conducted, where faeces from dune animals (cow, horse, sheep and fox) was brought to a shallow monitoring well and a heavy rain event was simulated. The peak concentration of salt was measured 3 days after the start of raining, with an infiltration (vertical) velocity of 0.39 m/day. Based on previous experiments with approximately the same rainfall intensity and duration, the infiltrating velocity is likely homogenous and not preferential flow. The peak concentrations of E. coli and Enterococci (2.7×105 and 4.92×104 CFU/L respectively) were measured five days after the start of raining. Ruminants were the only positively measured DNA marker in the water samples, with the peak concentration (2.2×105 copies/L) measured after 4 days of raining. This research clearly demonstrates that FIB can be detected in vulnerable locations within the dunes and that FIB from animal faeces at the ground surface can be transported to groundwater relatively quickly and result in the recontamination of purified dune water close to the wells.

Duinpassage is een belangrijke barrière tegen pathogene micro-organismen. In het onttrokken water van de duinen worden echter af en toe fecale indicatorbacteriën (FIB) aangetroffen. De herkomst van deze bacteriën is niet duidelijk, hoewel de veronderstelling is dat deze bacteriën de verzadigde zone vanaf het maaiveld bereiken. Met dit onderzoek is geprobeerd een direct verband te leggen tussen bacteriën in feces op maaiveldniveau en de mogelijke detectie van deze bacteriën in het water in de put, en om vervolgens te bepalen van welke diergroepen deze bacteriën afkomstig zijn. Dit onderzoek toont aan dat uitwerpselen van dieren, zoals grazers een mogelijke bron vormen voor herbesmetting van duinwater bij onttrekkingsputten van Dunea.

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