The total amount of living material expressed as either grams of carbon or kilocalories (1,000 calories) for a given area of space (e.g., per square meter). Kilocalories are calculated by placing together all of the living matter collected for a defined area of riverbed and drying it. After recording the total weight, it is then placed it in a bomb calorimeter. The calorimeter is filled with pure oxygen and a spark ignites the contents. The amount of heat given off is recorded in calories per gram of dried material.

  Google Search