Ecological Implications

Linking Terrestrial and Marine Ecosystems

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Over the last several decades, nutrient loading levels in riverine ecosystems have contributed to a substantial increase in coastal eutrophication (Justic, Rabalais and Turner, 1995). The Mississippi River system is the largest in North America and ranks sixth in the world in terms of freshwater discharge accounting for 41% of the lower forty-eight states' freshwater discharge and sedimentation (Milliman and Meade, 1983). The primary factor driving coastal eutrophication in the Gulf region is excessive nutrient loading which can be linked directly back to increased and expanded agricultural and industrial activity within the Mississippi basin.

As nutrients enter the system, productivity increases. The increased primary productivity may lead to temporary increases in fisheries production (Caddy, 1993). However, as nutrient levels become scarce or excessive, the system becomes unbalanced and the effects of stratification and hypoxia start to impact coastal community structure and energy flow. Here, the linkage between the terrestrial (agriculture, industry and population centers) and marine ecosystems is clearly seen. One can imagine and/or predict the affect the hypoxic, or sometimes referred to "Dead Zone", may have on the Gulf fishery, which in 1996 accounted for 16% of the total commercial landings in the United States with over half of this total harvested from coastal waters of the Mississippi River system (Holliday and O'Bannon, 1997).

For further information, see the online report "NOAA Gulf of Mexico Ecosystem and Hypoxia Assessment."

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