Sampling Description:
Triplicate original-style SET benchmark posts were permanently installed in the high marsh (HM) and low marsh (LM) on the marsh platform in a Spartina alterniflora-dominated marsh at Goat Island, North Inlet, Georgetown, SC. Each SET sampling site consists of a permanently installed post and a removable arm. The arm has a vertical and a horizontal component. The vertical component fits into the SET benchmark post; the horizontal component reaches out over the experimental subplot and has a square plate at the end through which 9 pins are lowered. Each SET post is associated with two adjacent plots (one control, one NP fertilized). The treated plots were fertilized with NH4NO3 and P2O5 for a final annual application rate of 26.7 mol N/m2/y and 12.3 mol P/m2/y from May 1996 (HM) or Jan 2001 (LM) until Aug 2004. Each SET benchmark post is positioned such that 27 elevation readings can be taken in a fertilized plot (9 readings in 3 subplots) and 27 elevation readings can be taken in a control plot. Plots are numbered. Subplots are lettered A-F.
To measure elevations, the SET arm is locked in place over each subplot, is leveled, and the 9 fiberglass pins are lowered to touch the sediment surface and held in place with a clip. Pin heights are measured from the top of the nut on the plate to the top of the pin, and read into a digital recorder. The recordings are transcribed into one master SET pin height data set. Surface elevations are measured approximately monthly.
The SET was manufactured by Nolan’s Machine Shop in Lafayette LA; 337-235-5261. Replacement pins or collars can be purchased from Nolan’s. Stainless steel parts (roll pins etc) come from McMaster-Carr. Measuring pins are held in place with badge clips, available at office supply stores.
Numerical Processing:
Data are reported as the mean change in elevation and standard error of the 3 replicate plots (n=81) over time. Change in marsh elevation is determined by subtracting pin height at time X from the mean pin height for the subplot at time 0. Statistics were performed using SAS (SAS System for Windows; release 9.1; SAS Institute, Inc; Cary, NC).
Elevation
LTE-MP-NIN-GIHM approx 0.5 meters NAVD88
LTE-MP-NIN-GILM approx 0.2 meters NAVD88