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 low marsh at Law's Point along the Rowley River. The second (LTE-MP-LPP) is in the high marsh at Law's Point along the Rowley River. The third (LTE-MP-ORT) is in a brackish water marsh on an upstream tributary of the Parker River. Biomass sampling is slightly different at each site, and is accomplished non-destructively at the LTE-MP-LPA and LTE-MP-ORT sites, and destructively at the LTE-MP-LPP site. Biomass sampling at LTE-ME-ORTwas discontinued after August 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, monthly, from May-September. From 1999-2001 the annual fertilization rate was 30 molN/m2/y and 15 mol P/m2/y. From 2002 to present 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:
The plant census method at LPP is destructive. One randomly placed 10x10 cm quadrat is clipped approximately monthly from May to October from each plot. Plants are clipped to 1 cm from the marsh surface and placed into a labelled plastic bag. Live and dead plants are separated, and live plants are separated species. Plants are placed into labelled paper bags, dried at 60C and weighed.
LPP census plots were established in August 2000. From 2000-2003, biomass was estimated for all 4 treatments. It is assumed that biomass was clipped from N plots and P plots within the boardwalk even though this was destructive. Biomass was not clipped from the C plots and NP plots within the boardwalk because these were also SET plots. Instead, 3 additional Control and 3 additional NP plots were established that were external to the boardwalk. Beginning in spring 2004, biomass was collected only from the external C and NP plots; biomass collection from the N plots and P plots was discontinued.
Data processing:
All data are entered into an Excel spreadsheet where mean treatment biomass in gdw/m2 are determined.