General:
This data set is part of an on-going LTER project at the Plum Island Ecosystem (PIE) site.   The sampling location is in a Spartina alterniflora-dominated marsh at Law's Point between the Rowley River and West Creek in Rowley MA. 

Sampling Description:
Triplicate original-style SET stations were installed in the marsh in  June 1999.  Each SET consists of a permanently installed benchmark 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 an experimental subplot and has a square plate at the end, with 9 collars through which fiberglass pins are lowered.  Each SET post is associated with two adjacent plots (one control, one NP fertilized; only the control data are included here).  Each plot has three subplots.  Therefore, each SET benchmark post is positioned such that 27 elevation readings can be taken in each plot (9 readings in 3 subplots).  Plots are numbered.  Subplots are identified as L, C, or R for left, center and right, when facing the plot (back to the SET post).  To measure elevations, the SET arm is locked in place over each subplot, is leveled, and the 9 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 that fastens the collar to 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.  Change in marsh elevation is determined by subtracting pin height at time X from the mean pin height for the subplot at time 0.  SET readings occur approximately monthly, from May-October. 

The horizontal portion of the removable part of the PIE LTER SET can be correctly installed and leveled in several positions:  the arm can be extended all the way forward, all the way back, and anywhere in between.  All SET measurements are made with the arm all the way back, i.e. with the plate being as close to the SET post as possible and the SET arm being as short as possible.

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.

Data Processing:
Data are transcribed from a digital recorder to an Excel spreadsheet.  Change in marsh elevation is determined by subtracting pin height at time X from the mean pin height for the subplot at time 0.  SAS programs are used to determine treatment means and standard error for each month.  (SAS System for Windows; release 9.1; SAS Institute, Inc; Cary, NC)

Elevation:
LTE-MP-LPA, ~ 1.1 meters NAVD88