General:
This data set is part of a study including three on-going plot-level fertilization sites.  The first (LTE-MP-LPA) is in the S. alterniflora-dominated low marsh at Law's Point between the Rowley River and West Creek.  The second (LTE-MP-LPP) is in the S. patens-dominated high marsh at Law's Point between the Rowley River and West Creek. The third (LTE-MP-ORT) is in a Typha-dominated brackish water marsh on an upstream tributary of the Parker River.  SET sampling at  LTE-MP-ORT was discontinued after May 2008.

At each site a system of boardwalks was built to incorporate 12 experimental plots (1m2 each).  There are 4 treatments (three replicates each) within the boardwalk structure.  The 4 treatments are Control, N-fertilized, P-fertilized, N+P fertilized.  Additionally, at each site there are 3 control plots and 3 N+P fertilization plots external to the boardwalk structure.  These external plots contain porewater samplers, and, in some cases, biomass census plots.  In May 2006 the control porewater plots and control census plots at all three sites were moved because of potential contamination from fertilized plots.

Fertilizer is buried at several locations within each  treated plot, approximately monthly, from May-September.  From 1999-2001 the annual fertilization rate was 30 molN/m2/y and /or 15 mol P/m2/y.  From 2002 to present the fertilization rate is 7.5 mol N/m2/y and/or 3.75 mol P/m2/y.  N fertilizer was NH4NO3 through 2008, and currently is nitrate/urea/sulfate (34-0-0).  P fertilizer is P2O5 (0-44-0).

Sampling Description:
Triplicate original-style SET benchmark posts were installed between fertilized and control plots in 1999 at LTE-MP-LPA and 2000 at LTE-MP-LPP and LTE-MP-ORT.  Each SET 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 an experimental subplot and has a square plate at the end,  with 9 collars through which fiberglass  pins are lowered.  Each SET benchmark post is positioned such that 27 elevation readings can be taken in a fertilized plot (9 readings in each of 3 subplots) and 27 elevation readings can be taken in a control plot (9 readings in each of 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 pin heights, the SET arm is locked in place over each subplot and  the plate at the end of the arm is leveled.  The 9 pins are then 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.  SET readings occur approximately monthly, from May-October at LTE-MP-LPA and LTE-MP-LPP, and in May and October only at LTE-MP-ORT. Sampling at the ORT SET was discontinued in 2008.

The horizontal portion of the removable part of the PIE LTER SET can be correctly installed and leveled in several positions:  i.e. 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.  SAS programs are used to standardize pin heights due toequipment changes  (beginning in 2014) and benchmark post movement (beginning in 2018) .  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, approx 1.1 meters NAVD88
LTE-MP-LPP, approc 1.4 meters NAVD88