Subsurface automated samplers (SAS) for ocean acidification research

Abstract

<jats:p> Ocean acidification (OA) is the process whereby anthropogenic carbon dioxide is absorbed into seawater, resulting in altered carbonate chemistry and a decline in pH. OA will negatively impact numerous marine organisms, altering the structure and function of entire ecosystems. The progression of OA, while faster than has occurred in recent geological history, has been subtle and detection may be complicated by high variability in shallow-water environments. Nevertheless, comprehensive monitoring and characterization is important given the scale and severity of the problem. Presently, technologies used to measure OA in the field are costly and limited by their detection of only one carbonate chemistry parameter, such as pH. Discrete water samples, by contrast, offer a means of measuring multiple components of the carbonate system, including parameters of particular explanatory value (e.g., total alkalinity, dissolved inorganic carbon), for which field-based sensors do not presently exist. Here we describe the design, use, and performance of a low-cost (&lt;$220 USD) Subsurface Automated Sampler (SAS), suitable for the collection of water for carbonate chemistry analysis. Each sampler is field-programmable using a remote control, performs in depths up to 55 m seawater, collects two separately preserved samples, and logs temperature at the time of collection. SAS are designed from the ground up to be open source with respect to physical design and sampling components, electronic hardware, and software. Build instructions, parts lists, and printable 3D files are provided along with code to ultimately lower the cost of OA monitoring, facilitate further research, and encourage application-specific customization. </jats:p>

Subsurface automated samplers for eDNA (SASe) for biological monitoring and research

“…At 30 and 50 m depth, the variability from the target volume increased to 250 mL ± 7.5. The increased variability implies some effect from depth on the target volume, but, similar to findings by Enochs et al (2020), the relationship between depth and volume pumped was inconsistent (Fig. 9B) and of insufficient magnitude to warrant further design alterations.…”

“…The electronic hardware builds upon that of the subsurface automated water sampler (SAS) designed by Enochs et al (2020). Hardware was designed using Autodesk Eagle (Autodesk, Inc., v 9.2.2, Fig.…”

“…The current draw and battery longevity were tested two separate ways. First, three SASe samplers were filled with eight fully charged NiMH AA batteries (1.2 V, 2450 mAh, Eneloop pro, Panasonic) and the current draw was measured using a handheld multimeter (EX330, Extech Instruments) during sleep mode, programming mode with the screen on, and during sampling following the method of Enochs et al (2020). To compare the battery life with real-world battery life, three SASe's with fresh batteries were programmed with an edited code to sample 1000 mL every one hour and the battery voltage was logged before and after each sampling.…”

“…Despite the numerous benefits of these technologies, submersible automated eDNA samplers are expensive to purchase (>100,000 USD [16] ), creating a significant financial-barrier for smaller research and biomonitoring groups, and making widespread adoption impractical. Existing open-source water sampling tools [17] , [18] might be adapted by the user to lower operating costs for eDNA sampling, but these require design adjustments and testing to determine effectiveness of this unintended application. Here we present the design, production, and evaluation of a purpose built open-source, low-cost (∼280 USD) subsurface automated sampler for eDNA (SASe) that filters and preserves eDNA samples in situ .…”

“…The Teensy 3.5 is USB-programmable using the freely available Arduino IDE ( www.arduino.cc ), with the Teensyduino add-on ( www.pjrc.com ). The SASe code, modified from the code for the SAS [17] , relies on several freely available libraries ( Table S1 ). The main program loop offers seven cases, covering six menu options and a sleep/operating state ( Fig.…”