Composition and source of the sediment in the kleine Noordwaard, Biesbosch Netherlands.

Abstract

Tidal wetlands are an important environment for natural processes as well as human activities. They are, however, are rapidly disappearing. To preserve these wetlands, their morphological processes must be comprehended. The objective of this research is to determine the source of the sediment using the composition of the sediment. This will be accomplished by using different sampling and measuring methods. A total of four sampling methods are used: jars, containers, grass mats and freshly deposited sediment samples. Firstly, suspended sediment is caught in submerged jars in the channel. Secondly, tidally submerged containers and grass mats are placed on the soil for trapping suspended sediment. Lastly, freshly deposited sediment samples, submerged and above water level, were taken with a soil auger. Two fingerprinting technique are chosen, chemical fingerprinting using x-ray fluorescence and radiometric fingerprinting using activity concentration. The x-ray fluorescence measurements are statistically analysed to determine a weighted ratio. Determined by the weighted ratio, it was discovered that of the 200 samples, 57 % of the deposited sediment which originated from the polder itself and 43 % originated from the river. The freshly deposited sediment thickness varied from 0 to 11.5 cm as did the spatial distribution on a small scale. The variance of the weighted ratio can for 86 ± 38% be accounted for by the unknown original composition of the sediment and for 14± 38% it can be accounted for by the regression analysis. The sediment composition of the area provides information about the sediment source. Only two main sources could be distinguished by composition calculations: recent sediment originating from the river Rhine or reworked sediment originating from the relatively older polder soil. When interpreted, more sources can be deduced: firstly, the sediment of the polder that was reworked. Secondly, the sediment originating from an older, more contaminated tidal creek that was found in the southern part of the area. Lastly, the sediment brought in for building activities to construct the current nature development habitat.