Mass-transfer-limited nitrate uptake on a coral reef flat, Warraber Island, Torres Strait, Australia

Previous research has identified a relationship between the rate of dissipation of turbulent kinetic energy, ε, and the mass-transfer-limited rate of uptake by a surface, herein called the ε^1/4 law, and suggests this law may be applicable to nutrient uptake on coral reefs. To test this suggestion, nitrate uptake rate and gravitational potential energy loss have been measured for a section of Warraber Island reef flat, Torres Strait, northern Australia. The reef flat section is 3 km long, with a 3 m tidal range, and on the days measured, subject to 6m s^-1 tradewinds. The measured nitrate uptake coefficient, S, on two consecutive days during the rising tide was 1.23 ± 0.28 and 1.42 ± 0.52×10^-4 m s ^-1. The measured loss of gravitational potential energy across the reef flat, ΔGPE, on the same rising tides over a 178 m section was 208 ± 24 and 161 ± 20 kg m^-1 s^-2. Assuming the ΔGPE is dissipated as turbulent kinetic energy in the water column, and using the ε^1/4 law, the mass-transfer-limited nitrate uptake coefficient, S_MTL, on the two days was 1.57 ± 0.03 and 1.45 ± 0.04×10^-4 m s^-1. Nitrate uptake on Warraber Island reef flat is close to the mass-transfer limit, and is determined by oceanographia nitrate concentrations and energy climate.