Tidal Marsh Surface Elevation Table Data

All of these files are Microsoft Excel format files that contain Surface Elevation Table (SET) data. We installed deep rod surface elevation tables (SETs) to quantify the relative contributions of surface and subsurface processes to present-day elevation change (i.e., root growth, decomposition, compaction, water flux), shallow subsidence (accretion – elevation), and shallow subsidence between shallow (root zone) and deeper (to >10 m) portions of the soil profile. We installed four SETs at each marsh site, following methods described by Cahoon et al. 2002 and Webb et al., 2013. We established two SETs in low marsh and two in high marsh at each site after visual assessment of vegetation composition and distance from tidal source. We deployed each SET with three feldspar marker horizon plots. When the SET instrument is attached to the installed bench mark, the SET provides a constant reference plane in space from which the distance to the sediment surface can be measured by means of pins lowered to the sediment surface. SET measurements will be taken by reading the heights of nine pins lowered to the sediment surface using the SET instrumentation at 4 directions, which are 90 degrees from each other. Repeated measurements of elevation can be made with high precision because the orientation of the table in space remains fixed for each sampling. We are conducting on-going measurements every three months at all sites. We installed surface elevation tables (SETs) at our seven study sites between September and December 2013 (n = 24) to evaluate present-day changes in marsh surface elevation. As of the time of this report, we collected two to seven baseline readings at each site (Figure 24; Table 12). Early results suggest that the magnitude of marsh surface elevation change varied within sites and between low and high tidal marsh. Net marsh surface elevation change was positive in both high and low marsh in Bolinas and Mad River. In contrast, surface elevation declined in high marsh locations at Morro, Pt. Mugu, San Pablo, and Tijuana. These initial findings should be considered inconclusive until several additional years of data have been collected.