Mesocosm experiment on fresh marsh plant community responses to salinity pulses in 2014 and 2015

We established mesocosm communities using seven freshwater species (Zizaniopsis miliacea, Pontederia cordata, Persicaria hydropiperoides, Peltandra virginica, Ludwigia peploides, Sagittaria lancifolia and Eleocharis palustris) collected in the same freshwater marsh (31°20’16”N, 81°27’52”W) between Apr 19th and Apr 22nd, 2014, and the sediments were collected from a freshwater pond (31°23'54"N, 81°16'47"W) on Sapelo Island, GA at the same time. Our experimental unit was a plastic round swimming pool (h = 18 cm, r = 122 cm) filled to the top with homogenized sediments. Each unit consisted of 2 individuals of Zizaniopsis, Pontederia, Peltandra and Sagittaria, 5 – 8 Persicaria and Ludwigia separately. Eleocharis was mixed up with other species, so there were uneven numbers in each unit. From May 22 to August 19, 2014, the mesocosm communities were treated with three salinity levels (3, 5, and 10 psu: practical salinity units) and five exposure durations (5, 10, 15, 20 and 30 days per month), relative to a freshwater control (n=3 per treatment combination). Except for 30 days treatment which equals saline press treatment, plants were watered with daily freshwater after treated with saline water for 5, 10, 15 and 20 days. Different salinities were achieved by mixing tap water with sea water. We simulated tides during the treatment, by watering the plants every morning and then pumping out the excess water through a 6-in (15 cm) slotted well (constructed of PVC pipe) in the afternoon. From August 20, 2014 to June 30, 2015, all mesocosm communities were flushed with fresh tap water to recover.