SLODS™: slow dissolving standards for water flow measurements

Slow dissolving plaster standards (SLODS?) were developed to obtain integrated water flow measurements over a time scale of 20–30 days, and tested in giant clam farms in the Solomon Islands under steady flow environments. SLODS? are composed of a gypsum plaster formulation known as Specially Prepared Gypsum (SPG). This plaster has a considerably higher compressive strength; 10 000–13 000 psi, compared with approximately 1000 psi for more common formulations of Plaster-of-Paris. Experimental calibrations in a water motion simulator over 12 days demonstrated a highly significant relationship between fractional weight loss (FWL) of SLODS? per day, and water velocity (r²=0.96). The SLODS? simultaneously measured water flow (over a 21 day period in August 1997) at 12 giant clam grow-out sites spread across 400 km of island archipelagoes. Mean water velocity ranged from 5 to 11 cm s^?1 and significantly influenced growth of giant clams. SLODS? compared well with the established methodology of clod cards (r=0.69; P<0.01), with a clear advantage in their ability to integrate water motion over an extended time period into a single measurement. A practical application of SLODS? to aquatic research will be the development of standardized SLODS? (produced in a variety of sizes and shapes) calibrated to different factors affecting dissolution. This will require a more detailed analysis of the performance of SLODS? under different flow, salinity, dissolved solute's, and temperature environments.