Rabalais and Turner have also compared the chemistry of the river with that of other large rivers around the world. Their work has satisfied most oceanographers that there is indeed a direct link between dissolved nutrients, principally nitrogen, the hypoxia in the lower water column and the ecological changes. Few seem inclined to dissent. The ecological changes are definitely due to hypoxia, and the hypoxia is clearly due to elevated nutrients. As the amount of nitrogen has increased compared with the amount of silicate, which is slowly declining because of planktonic activity upstream, overall production of plankton in the Gulf has increased.
Hypoxia is the result.
More alarming changes could be in store. Rabalais suspects the changing nutrient balance might start to benefit noxious flagellate protozoa at the expense of the less harmful diatoms. Toxic algal blooms are indeed becoming more common in the Gulf, as they are in polluted coastal regions around the world. The Gulf hypoxic zone represents a grand challenge for environmental policy. The exact geographic origin of the excess nitrogen is a matter of contention.