Ecological Implications

Effects of Eutrophication on the Mississippi River

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The effects of eutrophication on river systems is not a well studied area. The same dramatic effects of increased primary production and hypoxia that occur in lakes and estuaries usually do not occur in rivers because the flowing waters replenish oxygen supplies and may inhibit an increase in primary production. The nutrients that are in the river have their major effects in the estuaries where they are released, such as the Gulf of Mexico (Antweiler, Goolsby and Taylor). However, eutrophication does cause problems in river systems such as large growths of filamentous algae which clog up the river system (Kelly and Whitton, 1998). Indices of river health in terms of eutrophication are being developed in order enable scientists to monitor eutrophication in river systems. Some of these indices include: the Algal Abundance Index which looks at nutrient levels in terms of how much filamentous algae is present, the Trophic Diatom Index which evaluates phosphate levels based on the taxonomic distribution of benthic diatoms and the Mean Trophic Rank index which looks at larger vegetation such vascular plants, larger algae and bryophytes. Animals can also be used to evaluate ecosystem health especially benthic macrophytes and fish; a high diversity of these species indicates a healthy ecosystem (Kelly and Whitton, 1998). Though little is known about the effects of eutrophication in river systems research is being conducted to better understand this. High nutrient loads in rivers have a large effect downstream in the estuaries that they feed into causing hypoxic conditions.

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