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Ulva additions alter soil biogeochemistry and negatively impact Spartina alterniflora growth
Citation:
Watson, E., C. Wigand, A. Oczkowski, K. Sundberg, D. Vendettuoli, Saro Jayaraman, K. Saliba, AND J. Morris. Ulva additions alter soil biogeochemistry and negatively impact Spartina alterniflora growth. MARINE ECOLOGY PROGRESS SERIES. Inter-Research, Luhe, Germany, 532:59-72, (2015).
Impact/Purpose:
The original purpose of this research was to document inundation impacts on nutrient uptake by salt marsh plants. However, by using algae as our mechanism for nutrient additions, we discovered a strong, and unexpected, negative impact of Ulva additions on growth of salt marsh plants. Here, we report on a series of experiments where we confirm this impact, and discuss potential causes.
Description:
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. We report on a series of field and laboratory mesocosm experiments where we examined the effects of decomposing Ulva on Spartina alterniflora growth, soil biogeochemistry, and nitrogen dynamics. Monitoring of porewater revealed rapid mineralization of ammonium from decomposing Ulva, with porewater levels quickly attaining potentially toxic concentrations. In addition, Ulva soil amendments were associated with elevated porewater sulfide levels, and trithiane, an organosulfur compound and potential biocide. Use of a 15N label documented plant uptake of Ulva-derived nitrogen, but higher nitrogen availability did not subsidize growth. In fact, higher levels of Ulva exposure resulted in pronounced reductions in above and belowground productivity, while lower levels of Ulva exposure resulted in reductions in belowground productivity only. Our findings support the hypothesis that decaying Ulva mats may create hotspots of adverse physiochemical conditions in salt marshes, similar to those reported for benthic and tidal flat habitats. Furthermore, decaying Ulva mats may compromise the erosion resistance of salt marshes via decreases in plant belowground biomass. Additional field and laboratory studies are needed to establish more concretely which Ulva related stressors are primary, and whether similarly adverse responses are observed under natural field conditions.
