General:
This data set is part of a study including three on-going plot-level fertilization sites and two additional monitoring 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. Porewater samplers were established at LTE-MP-LPA in Jun 1999, at LTE-MP-LPP in Aug 2000 and at LTE-MP-ORT in Jun 2000. In 2017, two new sites were established. LTE-MP-SRA is in a S.alterniflora-dominated section of the marsh at Stackyard Road, part of the Plum Island NWR. LTE-MP-SRP is in a S.patens-dominated section of the marsh at Stackyard Road, part of the Plum Island NWR.
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 plot, 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 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 porewater diffusion samplers are permanently installed in fertilized and control plots at each of the three research sites. Each sampler collects porewater from depths of 10, 25, 50, 75, and 100 cm. Samples are retrieved approximately monthly from May through October. Porewater samples are either filtered (0.2 uM) and preserved with H2SO4 (for PO4 and NH4) or preserved unfiltered with ZnAc (for sulfides) either in the field or immediately upon return from the field. The samples are then shipped to a lab in SC for analysis.
Lab Methods:
Filtered porewater samples are analyzed for PO4 and NH4 according to standard laboratory protocols (Strickland and Parsons 1972) and for chloride concentrations by coulometric titration using a Haake-Buchler chloridometer. Unfiltered, preserved porewater samples are analyzed for sulfide concentrations colorimetrically (Cline 1969). Salinity was calculated from chloride concentrations of filtered porewater samples (by coulometric titration using a Haake-Buchler chloridometer) before August 2020. Beginning in August 2020, salinity was measured using an EXTECH EC600 conductivity meter.
Elevations:
LTE-MP-LPA, ~ 1.1 meters NAVD88
LTE-MP-LPP, ~ 1.4 meters NAVD88