Effects of surface roughness and oscillatory flow on the dissolution of plaster forms: Evidence for nutrient mass transfer to coral reef communities

We dissolved plaster forms in seawater to examine the effects of surface roughness and flow conditions on mass-transfer rates. Plaster blocks with varying roughness were dissolved under both steady and oscillatory flows between 7 and 43 cm s(-1) yielding calcium mass-transfer coefficients (S-Ca) that varied from 0.5 to 3 m d(-1). S-Ca measured in a flume was 30-40% greater under oscillatory flow than under steady flow at flow speeds < 10 cm s(-1); this difference decreased with increasing flow speed. Plaster blocks with added millimeter-, centimeter-, and decimeter-scale roughness were dissolved under oscillatory flows between 2 and 26 cm s(-1) on three different coral reef flats. Plaster dissolution rates in the field were linearly proportional to surface area regardless of the roughness scale. Variation in S-Ca across different reef environments was less affected by whether the flow was steady or oscillatory (a factor of 1.2-1.6) than it was by flow speed alone (a factor of 4.7).