H033-0002
A tough but light design of a RAD7 coastal buoy – making your measurements watertight.
Tuesday, 8 December 2020
Poster
Ferdinand J Oberle, USGS Pacific Coastal and Marine Science Center Santa Cruz, Santa Cruz, CA, United States, Cordell D Johnson, USGS Pacific Coastal and Marine Science Center, Santa Cruz, CA, United States, Gerald A Hatcher, U.S. Geological Survey, Santa Cruz, CA, United States, Robert Wyland, USGS, Santa Cruz, CA, United States, Nancy Prouty, USGS, Baltimore, MD, United States and Curt Daron Storlazzi, USGS Pacific Science Ctr, Santa Cruz, CA, United States
Abstract:
The utility of radon-222
(
222Rn) as a water-mass tracer is well-proven to study and quantify rates of submarine groundwater discharge (SGD) due to its very short half-life (3.8 d) and its multifold enrichment in groundwater relative to surface water. The industry and research standard to investigate groundwater discharge in coastal settings remains the Durridge RAD7 radon detection systems equipped with a water/air exchanger. In conjunction with a
222Rn groundwater endmember, this setup allows for a near real-time calculation of groundwater discharge flow rates by using the aqueous Rn concentration and measuring the air
222Rn concentration and knowing the temperature-dependent
222Rn partitioning coefficient. Studying SGD is important because nutrient loading to coastal waters have increasingly been recognized as a major water-borne vector for transporting nutrients into the coastal ocean.
Deployment of RAD7s in the coastal zone such as on reef flats or on the shallow shelf continue to be a challenge, as the many different parts (battery, pump, exchanger) are not waterproof and not originally intended for coastal deployment. Consequently, RAD7 coastal groundwater surveys have relied on deployments from larger boats, kayaks, or from land. These approaches, however, are limited either by water depth (most boats cannot get to a shallow reef), temporal duration (a kayak requires a person to be continuously present), or reach (land approach is limited by distance of the pumping power). Furthermore, setups between surveys often vary significantly and thus bring uncertainty into the comparability between results. We here present a replicable solution to build a RAD7 buoy that is a) capable of extracting water from ocean water depths of 0.0 m – 50 m; b) can run 72 h on a single charge; c) is waterproof; d) and easily transported (airline luggage). We show dataset examples from Ofu and Faga’alu, American Samoa, and Monterey Bay, California.
