THE CO2 BALANCE OF UNPRODUCTIVE AQUATIC ECOSYSTEMS

Community respiration (R) rates are scaled as the two-thirds power of the gross primary production (P) rates of aquatic ecosystems, indicati ng that the role of aquatic biota as carbon dioxide sources or sinks d epends on its productivity. Unproductive aquatic ecosystems support a disproportionately higher respiration rate than that. of productive aq uatic ecosystems, tend ro be heterotrophic (R > P), and act as carbon dioxide sources. The average P required for aquatic ecosystems to beco me autotrophic (P > R) is over an order of magnitude greater For marsh es than for the open sea. Although four-fifths of the upper ocean is e xpected to be nee heterotrophic, this carbon demand can be balanced by the excess production over the remaining one-fifth of the ocean.