Abstract
AbstractWe describe a low‐cost three‐dimensional underwater particle tracking velocimetry system to directly measure particle settling rate and flux in low‐turbulence aquatic environments. The system consists of two waterproof cameras that acquire stereoscopic videos of sinking particles at 48 frames s−1 over a tunable sampling volume of about 45 × 25 × 24 cm. A dedicated software package has been developed to allow evaluation of particle velocities, concentration and flux, but also of morphometric parameters such as particle area, sinking angle, shape irregularity, and density. Our method offers several advantages over traditional approaches, like sediment trap or expensive in situ camera systems: (1) it does not require beforehand particle collection and handling; (2) it is not subjected to sediment trap biases from turbulence, horizontal advection, or presence of swimmers, that may alter particulate load and flux; (3) the camera system enables faster data processing and flux computation at higher spatial resolution; (4) apart from the particle settling rates, the particle size distribution, and morphology is determined. We tested the camera system in Lake Stechlin (Germany) in low turbulence and mean flow, and analyzed the morphological properties and settling rates of particles to determine their sinking behavior. The particle flux assessed from conventional sediment trap measurements agreed well with that determined by our system. By this, the low‐cost approach demonstrated its reliability in low turbulence environments and a strong potential to provide new insights into particulate carbon transport in aquatic systems. Extension of the method to more turbulent and advective conditions is also discussed.
Highlights
The particles sank with an angle αi1k varying between −70 and 60 (Fig. 10d, gray and blue bars), with the majority of particles sinking with the major axis horizontal or slightly tilted
We presented a new 3D-particle tracking velocimetry (PTV) method to determine particle velocities and fluxes as a function of particle size, and tested its reliability in a low turbulence environment
The apparatus consists of equipment that can be purchased on the market, assembled, operated, and deployed, when compared to commercial PTV systems (Smith and Friedrichs 2015)
Summary
Recent studies have tried to improve estimates of F and SV by combining polyacrylamide gel traps, for precise measurements of particle size and shape, with video recorders, for high-resolution particle abundance (McDonnell and Buesseler 2010, 2012). This recent, but relatively difficult-to-handle methodology, enables semiautomatic measurements and parametrization of F into particle size classes. The algorithm code is available as a configurable MATLAB® package at URL reported in the Supporting Information
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