Fig. 5. Index (R) of resource-limitation based on the sensitivity of phytoplankton growth rate to light and nutrient changes. R = ratio of the incremental change in growth rate with change in light level or nutrient concentration; R values greater >10 indicate light-limitation, values <0.1 indicate nutrient limitation and values 0.1–10 indicate co-limitation. N = nutrient concentration, N_t = nutrient-limitation threshold concentration, I = light level, I_t = light-limitation threshold level. Modified from Cloern (1999).