A simple oxygen index for trophic state description

The trophic state of a coastal marine ecosystem can be easily described by a simple oxygen index: Euclidean distance between the oxygen surplus at the surface and the oxygen deficit at the bottom. Basically, the oxygen index measures the oxygen inbalance within the water column which is a consequence of the growth and decay of organic matter; it increases with the increasing primary production at the surface and increasing benthic respiration while decreases with the decreasing stability of the water column. An analysis of the oxygen data collected in the northern Adriatic Sea between 1911 and 1982 shows that the increasing oxygen index fairly describes the occurrence of eutrophic conditions in time and space.