Fertilizers Not the Cause of Marsh Drowning

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Matthew Garrett
Email: matthew.garrett@yale.edu
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A five-year experiment in a Long Island Sound salt marsh has found that fertilizers do not cause marsh drowning, according to researchers at the Yale School of Forestry & Environmental Studies.
Shimon Anisfeld, a senior lecturer and research scientist in water resources and environmental chemistry, led a research team that added nitrogen and phosphorus to plots in Hoadley Creek Marsh in Guilford, Conn., from 2005 to 2009 to test the idea that too high a nutrient load would be bad for the marsh and could lead to its drowning.
“We concluded that an increase in nutrient loading is unlikely to be a significant contributing factor to marsh drowning in Long Island Sound,” said Anisfeld.
He suspects that a lack of sediment, rather than the presence of nutrients, is the primary cause of marsh drowning.
Marshes provide an important buffer for coastal communities against storms and erosion. As sea levels rise, the marsh surface can rise, too, primarily through the growth of belowground plants, the accumulation of litter from aboveground plant growth and sediment delivered by the tides. However, when marshes drown, as has been occurring recently in various locations around Long Island Sound, their surfaces are overtaken by rising sea levels and they lose the vegetation and organic material that provide food for wildlife.
“We thought that the addition of nitrogen and phosphorus, separately or in combination, could lead to less organic material in the marsh peat and could result in the degradation of the marsh,” Anisfeld said.
Previous studies had suggested that nutrient enrichment might speed up decomposition of belowground organic material or might reduce root growth as plants shifted resources away from nutrient-collecting roots.
Anisfeld’s team, including doctoral student and co-author Troy Hill, set up 24 plots in the marsh grass Spartina alterniflora that were treated with varying amounts of nitrogen and phosphorus. They found that the amount of carbon dioxide released from the soil increased in the nitrogen-fertilized plots. However, they did not see a difference in root growth or in the total amount of organic material in the peat.  
The paper, “Fertilization Effects on Elevation Change and Belowground Carbon Balance in a Long Island Sound Tidal Marsh,” appears in the journal Estuaries and Coasts.
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PUBLISHED: May 10, 2012

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