Carbon Dioxide Exchange Between the Atmosphere and Aquatic Ecosystems Occurs

Carbon dioxide exchange between the atmosphere and aquatic ecosystems occurs

A) unidirectionally from atmosphere to aquatic ecosystems, with net gain to aquatic ecosystems.
B) unidirectionally from aquatic ecosystems to the atmosphere, with net gain to the atmosphere.
C) bidirectionally, with net gain to aquatic ecosystems.
D) bidirectionally and nearly equally.
E) bidirectionally, with net gain to the atmosphere.