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Joanne Rathe/Globe StaffDavid Johnson and Kate Morkeski loaded a device that feeds fertilizer into the salt marsh on Plum Island.
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Joanne Rathe/Globe StaffFor the study, researchers hauled a ton of fertilizer to the salt marsh every four days or so in the spring and summer.
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Joanne Rathe/Globe StaffDavid Johnson checked the tank where water is mixed with fertilizer and released during the rising tide.
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Joanne Rathe/Globe StaffDavid Johnson offloaded fertilizer from a boat onto a station in the marsh.