Technical note: A time-integrated sediment trap to sample diatoms for hydrological tracing

Abstract. Diatoms, microscopic, single-celled algae, are present in almost all habitats containing water (e.g. streams, lakes, soil, rocks) and form one of the most common and diverse algal groups in both freshwaters and marine ecosystems. In the terrestrial environment, their diversified species distributions are mainly controlled by physiographical factors and anthropic disturbances. This makes them useful tracers in catchment hydrology. In their use as a hydrological tracer, diatoms are generally sampled in streams by means of an automated sampling method and as a result many samples are collected to cover a whole storm run-off event. As diatom analysis is labour intensive, a trade-off has to be made between the number of sites and the amount of samples per site. A potential way to reduce this number is by using a time-integrated mass-flux sampler. Here, we explored the potential for the Phillips sampler to provide a representative sample of the diatom assemblage of a whole storm run-off event. We addressed this by comparing the diatom community composition of the Phillips sampler to the composite community collected by the automatic samplers for three events. Our results indicate that during two events the Phillips sampler sampled representative samples, whereas significantly different communities were collected during the third event. However, sediment data of this event, which was sampled with automatic samplers, showed much noise meaning that we could not verify if the Phillips sampler sampled representative communities or not. Nevertheless, we believe that this sampler could not only be applied in hydrological tracing using terrestrial diatoms, but may also be a useful tool in water quality assessment.