The Chemical Properties of Pond Sediments and the Operations of River Restoration.

Abstract

In France, in the last few years, a lot of ponds have been removed during operations of river restoration, remobilizing the sediments that had been deposited behind the dam over the years. Pond sediments are complicated mixtures predominantly consisting of rocks and soils particles from the watershed, atmospheric dust brought by winds, algae and organic remains or particles that were produced by processes in the water column, such as amorphous silica or calcite. Sediments “can be dressed” with chemical elements of various kinds, including pollutants that settle on the bottom of the ponds. It is therefore important to understand what types of substances can be found in pond and to understand the effect of operations of river restoration on water quality. We applied the X-ray fluorescence spectrometry (XRF), where sample is irradiated with X-rays from a radioactive source, which excites the elements in the sample and generates secondary fluorescent X-rays. Elements emit energy of unique wavelengths, which allows their qualitative and quantitative determination. Commonly, elements from atomic number 11 (Na) to 92 (U) can be detected. Using this methodology, analyses were made on sediments samples from a pond located in the centre of France: results show that the pond is relatively free of pollutants. Starting from this reference, we will think which substances can be remobilized after operations of rivers restoration.

Keywords

• ponds
• sediments
• hydrosystems restoration
• XRF
• France.