The heterogeneity measure I² (%) and variance for each model run with Rt and Zr accounted for by between study and within study variance, and measurement error.

ID was included as the random effect, and the full model included moderator variables of temperature, pH, salinity and water type for the full dataset. The subset model included moderator variables of temperature, pH, salinity, water type and H-type for Rt, and temperature, pH, salinity and H-type for Zr.