Determination of particle-bound nutrients and micropollutants concentrations and loads in small rivers – A novel sampling method

Abstract

Pollutants and excessive nutrient inputs into rivers pose a problem for aquatic ecosystems. Humans are also at risk when these substances enter the food chain via drinking water supplies and food. Water quality monitoring and research on pollutant transport are important components for protecting humans and endangered species. Since there are few ready and easy-to-use suspended sediment samplers for small streams and usually low pollutant concentrations, there is little information on pollutant transport in such small streams. However, research is essential to protect highly endangered species such as the freshwater pearl mussel “Margaritifera margaritifera”. This publication, therefore, aims to present a new method for collecting suspended sediments even in small rivers. The sampler presented corresponds to an adapted bed load trap, with a considerably reduced mesh size of the sampler, so that sediments smaller than 2 mm can be collected. After hydraulic pre-tests, sediment samples were collected at six sampling points with the new sampler over a time period of two weeks. In addition, sediments were taken from the river bed for a comparison between mobile sediments and deposits. The sediments were analysed for selected chemical micropollutants and phosphorus availability was checked by phosphorus fractionation. The observed mechanical-biological clogging of the mesh occurs in the first 72 h, depending on the river stretch. This effect can also be observed at other samplers and usually prevents the collection of suspended sediment. However, with this new sampler concept, clogging is advantageous. Due to the partial clogging of the mesh, water can continue to flow through, but finer sediment particles are retained in the sampler. Results show that the sampler collects sufficient sample volumes even in small rivers with low bed gradients and low flow velocities. The samplers also ensure sediment sampling over a defined time period (2 weeks in this study). The presented suspended sediment sampler method can help to understand nutrient and pollutant transport better, even in small streams. These findings can improve the knowledge on underlying processes, which will help to protect endangered species such as the freshwater pearl mussel.