Abstract
Docks constructed over salt marsh can reduce vegetation production and associated ecosystem services. In Massachusetts, there is a 1:1 height-to-width ratio (H:W) dock design guideline to reduce such impacts, but this guideline’s efficacy is largely untested. To evaluate dock height effects on underlying marsh vegetation and light availability, we deployed 1.2-m-wide experimental docks set at three different heights (low (0.5:1 H:W), intermediate (1:1 H:W), and high (1.5:1 H:W)) in the high and low marsh zones in an estuary in Massachusetts, USA. We measured temperature, light, vegetation community composition, and stem characteristics under the docks and in unshaded control plots over three consecutive growing seasons. Temperature and light were lower under all docks compared with controls; both increased with dock height. Maximum stem height and nitrogen content decreased with available light. In the Spartina patens-dominated high marsh, stem density and biomass were significantly lower than controls under low and intermediate but not high docks. Spartina alterniflora, the dominant low marsh vegetation, expanded into the high marsh zone under docks. S. alterniflora aboveground biomass significantly differed among all treatments in the low marsh, while stem density was significantly reduced for low and intermediate docks relative to controls. Permit conditions and guidelines based on dock height can reduce dock impacts, but under the current guideline of 1:1 H:W, docks will still cause significant adverse impacts to vegetation. Such impacts may interfere with self-maintenance processes (by decreasing sediment capture) and make these marshes less resilient to other stressors (e.g., climate change).
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03 October 2018
In the original article there was an error in the reported quadrat size. Sample quadrats were described as 1/16 m2 when they should have been reported as 1/32 m2 in the text of page 16 and in the figure legend for Figs. 6 and 7.
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Acknowledgments
Charles Markos, Sara Grady, Emily Pitman, and Margo Lee provided assistance with field sampling. Mark Altabet provided laboratory space, and Jessica Drysdale assisted with elemental analysis. Vincent Manfredi provided equipment for electronic stem measurements. Linda Deegan, Robert Boeri, Jay Wennemer, and Maureen Thomas provided constructive feedback on the initial design of this study. David Burdick and an anonymous reviewer provided helpful comments on earlier drafts of this manuscript. We would like to thank the residents of Trouant’s Island, especially James Tarbox, for being accommodating neighbors to our field site. This work was funded by a grant from the Massachusetts Bays National Estuary Program (MassBays).
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Logan, J.M., Voss, S., Davis, A. et al. An Experimental Evaluation of Dock Shading Impacts on Salt Marsh Vegetation in a New England Estuary. Estuaries and Coasts 41, 13–24 (2018). https://doi.org/10.1007/s12237-017-0268-4
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DOI: https://doi.org/10.1007/s12237-017-0268-4