Beneath the Salt Marsh Canopy: Loss of Soil Strength with Increasing Nutrient Loads |
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Authors: | R Eugene Turner |
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Institution: | (1) Coastal Ecology Institute, and, Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803, USA |
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Abstract: | Although the broadly observed increase in nutrient loading rates to coastal waters in the last 100 years may increase aboveground
biomass, it also tends to increase soil metabolism and lower root and rhizome biomass—responses that can compromise soil strength.
Fourteen different multiyear field combinations of nutrient amendments to salt marshes were made to determine the relationship
between soil strength and various nitrogen, phosphorus, and nitrogen+phosphorus loadings. There was a proportional decline
in soil strength that reached 35% in the 60- to 100-cm soil layer at the highest loadings and did not level off. These loading
rates are equivalent to those in the flow path of the Caernarvon river diversion, a major wetland restoration project near
New Orleans; 12% of the wetlands in the flow path were converted to open water in 2005. The increased nutrient loading from
the Mississippi River watershed this century has also driven the formation of the low oxygen zone (the “Dead Zone”) that forms
off the Louisiana–Texas shelf each summer. These results suggest that improving water quality in the watershed will aid the
restoration of both offshore waters and coastal wetland ecosystems. |
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