2.2.16—Biomass measurement

Biomass at a trophic level can be estimated by collecting representative samples and drying them to constant mass. Removing water makes dry mass a practical approximation of organic matter because water is the main inorganic component of most living samples.

Record sampled area or volume, fresh mass and repeated dry masses until further heating causes no change. Scale the mean dry mass to the habitat only when sampling is representative. Energy content can be estimated by combusting a known dry mass and measuring heat transferred to a known mass of water.

If 2.0 g of dry plant material heats 100 g of water by 8°C, the measured heat gain is mass × specific heat capacity × temperature change; divide by 2.0 g to report energy per gram. Heat lost to apparatus and incomplete combustion make the experimental value an underestimate.

Wet mass is not directly comparable biomass because water content varies. Use dry mass per unit area for standing biomass and energy per unit dry mass for combustion results, with units and uncertainty stated.

Do not treat biomass as energy; a gram of tissue does not reveal how quickly it was produced or consumed.