The effect of carbohydrate production by the diatom Nitzschia curvilineata on the erodibility of sediment

The effect of growth and carbohydrate production by the diatom Nitzschia curvilineata on sediment erodibility was explored in laboratory flume experiments. Diatom cultures, incubated on sediment, were monitored daily for chlorophyll and carbohydrate concentrations and eroded in a recirculating flume at successive stages of growth. Because variations in erosion rate were far greater than variations in erosion threshold during the diatom growth period, erosion rate may be a more sensitive index of sediment stability. Erosion rate was negatively correlated with sediment chlorophyll (r(2) = 0.759; P = 0.024) and bulk carbohydrate (r(2) = 0.958; P = 0.001) concentrations. A strong negative correlation was found between the sediment bulk carbohydrate-to-chlorophyll ratio and erosion rate (r(2) = 0.996; P < 0.001), suggesting that this ratio would serve as a good indicator of sediment erodibility. The size of eroding particles or aggregates increased with the age of the biofilm, probably due to the pervasion of sediment with mucilage and changes in "stickiness" of the resulting sediment microfabric. Sediment stability increased throughout the stationary phase of growth regardless of Lift forces produced by trapped bubbles within the biofilm and progressively smaller increases in sediment carbohydrate concentrations during this period. Knowledge of the physiological status of diatom biofilms is essential for the quantitative prediction of sediment transport, since diatom growth phase alters the behavior of sediment erosion.