Sediment traps

 

Online sediment trap (video courtesy: Saija Saarni)

Sediment trapping is a classical technique used to acquire time series of sediment flux rates and variations in sedimentary composition in aquatic environments (Bonk et al., 2015; Saarni et al., 2023). Sediment traps are widely used to quantify seasonal sedimentation cycles and sediment components (Ojala et al., 2013), to identify sediment sources and controls on sedimentary processes (Johansson et al., 2019; Saarni et al., 2021), and to measure sediment accumulation rates (SAR).  In the SENCE research group, we use two types of traps: conventional traps and a prototype of an online sediment trap.

• A conventional sediment trap consists of a signal buoy, flotation buoys, a directing wing, an anchor weight, and two collector tubes with bottom weights that keep the tubes upright. The collector tubes are connected to the metal trap body with an articulation that maintains their upright position regardless of currents or movement during retrieval. The tube volume is 1.7 L, the height is 51 cm, and the inner diameter is 6.6 cm (Saarni et al., 2021).
• An online sediment trap is a Finnish invention developed at the University of Eastern Finland by Markus Johansson. It is based on a conventional sediment trap design, with one of the tubes equipped with a computed tomography system. The lower part of this tube is lined on the inner surface with eight optical transmitter–receiver pairs, which perform tomographic scans of the interior of the trap tube. These scans produce images representing the volumetric structure of the material within the tube. Next to the trap buoy, a floating platform equipped with a solar panel and an internet connection is installed. The trap is connected to the floating platform by a cable (Johansson et al., 2019).

References

Bonk, A., Tylmann, W., Amann, B., Grosjean, M., & Enters, D. (2015). Modern limnology and varve-formation processes in Lake Żabińskie, northeastern Poland: Comprehensive process studies as a key to understanding the sediment record. Journal of Limnology, 74(2).

Johansson, M., Saarni, S., & Sorvari, J. (2019). Ultra-high-resolution monitoring of catchment response to changing weather conditions using online sediment trapping. Quaternary, 2(2), 18.

Ojala, A. E., Kosonen, E., Weckström, J., Korkonen, S., & Korhola, A. (2013). Seasonal formation of clastic-biogenic varves: The potential for palaeoenvironmental interpretations. GFF, 135(3–4), 237–247.

Saarni, S., Hartikainen, S., Meronen, S., Uurasjärvi, E., Kalliokoski, M., & Koistinen, A. (2021). Sediment trapping—an attempt to monitor temporal variation of microplastic flux rates in aquatic systems. Environmental Pollution, 274, 116568.

Saarni, S., Soininen, T., Uurasjärvi, E., Hartikainen, S., Meronen, S., Saarinen, T., & Koistinen, A. (2023). Seasonal variation in microplastic deposition rates in boreal lake sediments. Journal of Soils and Sediments, 23(4), 1960–1970.