DOWSE, A DrOne Water Sampling SystEm

Testing water samples from large water bodies at regular intervals is an imperative yet sometimes tedious operation.  Now new unmanned aerial systems (UASs, or drones) technology may assist in collecting water samples in remote areas, hard-to-reach environments, or otherwise hazardous settings.  Such drone water-sampling systems would be useful for collecting contamination causing microorganisms. The research is titled, “Microorganisms Collected from the Surface of Freshwater Lakes Using a Drone Water Sampling System (DOWSE)”, and is published in the MDPI journal Water.

The team of researchers developed a unique system by using a 3D-printed sampling device tethered to a drone (DOWSE, DrOne Water Sampling SystEm) to collect water samples from the surface of lakes. The DOWSE was used to collect surface water samples at different distances from the shore (1, 25, and 50 m) at eight different freshwater lakes in Austria in June 2018. Water samples were filtered, and microorganisms were cultured on two different media types, TSA (a general growth medium) and KBC (a medium semi-selective for bacteria in the genus Pseudomonas).

The research team comprised of of James Benson, Regina Hanlon, Teresa M. Seifried, Philipp Baloh, Craig W. Powers Hinrich Grothe and David G. Schmale from the School of Plant and Environmental Sciences, Virginia Tech; Blacksburg, Institute of Materials Chemistry, Austria and Civil and Environmental Engineering, Virginia Tech, Blacksburg, USA.

Materials and Methods

The drone used was a Phantom 4 quadcopter (DJI) powered by a 5870 mAh Lithium-ion polymer battery. After the drone GPS established waypoints, the sampling device was loaded with a sterile 50 mL conical tube, and the drone was flown manually to each waypoint location for sample collection. On reaching the sampling location, the drone descended to the surface of the water and allowed the sampling device to rest on the surface for a few seconds during which it collected water. An overhead image of the sampling device in the water providing a precise record of the location and sampling time was also taken. Following each collection, the sample was returned to the shore containing a water sample in the 50 ml tube and was switched with a new tube while the drone remained airborne. The drone then flew to another waypoint to repeat the process  until all targeted collections had been completed.

Engineering diagram of the 3D-printed water sampler designed to hold a sterile 50 mL conical tube. The tube had a swinging bucket design (right), and was attached to the drone via a carabiner on a nylon string.

Eight different freshwater lakes were sampled in Austria including Altausseersee (ALT), Grundlsee (GRU), Toplitzsee (TOP), Vorderer Gosausee (GOS), Gosaulacke (GOL), Hinterer Gosausee (HIN), Wörthersee (WOR), and Ossiachersee (OSS).

The DrOne Water Sampling SystEm (DOWSE) preparing to collect a sample at Toplitzsee (TOP) in Austria; (b) The DOWSE returning from a sampling mission at TOP; (c) Overhead image of the sampling device in the water taken from the quadcopter. This provided a precise record of the location and sampling time which was embedded in the Exif file of each of the images.

Contour maps of the spatial distribution of bacteria (meters) cultured from each of the Austrian lakes on TSA agar media (CFU/mL). These contour maps were created using the Surfer 15 software using the concentration data for each sample site in each lake. The small area mini-lake, Gosaulacke (GOL), had an alternate sample collection grid. Sample collections were plotted on a Cartesian plane.

Discussion:

Researchers on this project hypothesized:

• Concentrations of bacteria cultured on TSA varied significantly with lake depth and within the range of temperatures measured (17.7–25.0 °C), but concentrations of bacteria cultured on KBC did not vary significantly with depth and temperature.
• Contour maps of concentrations of microbes across the drone sampling domain revealed areas of high concentrations (hot spots) in some of the lakes.
• The time of year had a significant influence on the percentage of ice+ strains that were found and altitude of the lakes sampled did not have a significant impact on the percentage of ice+ bacteria collected at the different lakes sampled.

This system allows water sampling near the shore line without any major disturbances or mixing of the sample area. Future work aims to elucidate the structure and function of entire microbial assemblages within and among the Austrian lakes.

Citation: Microorganisms Collected from the Surface of Freshwater Lakes Using a Drone Water Sampling System (DOWSE), James Benson, Regina Hanlon, Teresa M. Seifried, Philipp Baloh, Craig W. Powers, Hinrich Grotheand David G. Schmale, Water 2019, 11(1), 157; https://doi.org/10.3390/w11010157