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Marine Ecology Progress Series

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MEPS 532:59-72 (2015)  -  DOI:

Ulva additions alter soil biogeochemistry and negatively impact Spartina alterniflora growth

E. B. Watson1,4,*, C. Wigand1, A. J. Oczkowski1, K. Sundberg2, D. Vendettuoli1, S. Jayaraman1, K. Saliba1, J. T. Morris3

1Atlantic Ecology Division, US Environmental Protection Agency, ORD-NHEERL, Narragansett, RI 02882, USA
2Baruch Marine Field Laboratory, University of South Carolina, Georgetown, SC 29440, USA
3Belle Baruch Institute for Marine & Coastal Sciences, University of South Carolina, Columbia, SC 29208, USA
4Present address: Department of Biodiversity, Earth & Environmental Science, Academy of Natural Sciences of Drexel University, Philadelphia, PA 19103, USA
*Corresponding author:

ABSTRACT: Decaying mats of Ulva can be washed into salt marshes by the tides as large wrack deposits, especially in eutrophic estuaries, where they can negatively impact marsh vegetation. Using field and laboratory experiments, we examined the effects of decomposing Ulva on Spartina alterniflora growth, soil biogeochemistry and nitrogen dynamics. High levels of Ulva exposure resulted in reductions in above- and belowground biomass, while lower levels of Ulva exposure resulted in reductions in only belowground biomass. Porewater ammonium in soil that contained decomposing Ulva quickly attained potentially toxic levels. In addition, amending soil with Ulva led to elevated porewater concentrations of sulfide and trithiane, an organosulfur compound and potential biocide. Use of a 15N tracer documented plant uptake of Ulva-derived nitrogen, but higher nitrogen availability did not stimulate growth. Our findings support the hypothesis that decaying Ulva mats may create hotspots of adverse physiochemical conditions in salt marshes. However, because our Ulva additions were higher than typically found in coastal marshes, additional field and laboratory studies are needed to establish more firmly whether similarly adverse responses are observed under natural conditions.

KEY WORDS: Salt marsh · Eutrophic estuary · Salt marsh loss · Allelochemicals · Allelopathy

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Cite this article as: Watson EB, Wigand C, Oczkowski AJ, Sundberg K and others (2015) Ulva additions alter soil biogeochemistry and negatively impact Spartina alterniflora growth. Mar Ecol Prog Ser 532:59-72.

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