The CO 2 Balance of Unproductive Aquatic Ecosystems

Abstract

Community respiration ( R ) rates are scaled as the two-thirds power of the gross primary production ( P ) rates of aquatic ecosystems, indicating that the role of aquatic biota as carbon dioxide sources or sinks depends on its productivity. Unproductive aquatic ecosystems support a disproportionately higher respiration rate than that of productive aquatic ecosystems, tend to be heterotrophic ( R > P ), and act as carbon dioxide sources. The average P required for aquatic ecosystems to become autotrophic ( P > R ) is over an order of magnitude greater for marshes than for the open sea. Although four-fifths of the upper ocean is expected to be net heterotrophic, this carbon demand can be balanced by the excess production over the remaining one-fifth of the ocean.