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METHODS TO DEFINE MARSH EVALUATION AND PERCENT SUBMERGENCE
Citation:
Abdelrhman, M AND G B. Thursby. METHODS TO DEFINE MARSH EVALUATION AND PERCENT SUBMERGENCE. Presented at Society of Wetland Scientists New England Chapter 2nd Annual Conference, Worcester, MA, November 14, 2002.
Description:
Elevation can determine the percentage submergence from tides and therefore is one of the controlling factors for plant zonation within salt marshes. To make comparisons among plants from various salt marshes throughout Narragansett Bay, Rhode Island, a method was developed to establish elevation bench marks (BM) referenced to the National Geodetic Vertical Datum of 1929 (NGVD). Tidal elevations from two nearby National Oceanic and Atmospheric Administration stations (referenced to NGVD) were used to relate the BMs to NGVD. Within each marsh, three 10-cm diameter tubes with holes along the sides were partially driven into the sediment at the marsh edge. At low tide peat moss was placed inside the tubes and the height of the peat moss above the sediment surface was measured the following day. This value corresponded to the highest of the two previous high tides, which could then be related to the NGVD heights from the NOAA tide stations for the same high tide. A surveyor's level was used to transfer the elevation of the peat moss to the BM for a given marsh. The method corrects for change in water surface slope in the Bay. Elevations at various locations within each marsh were related to the BM and the percentage flooding was calculated by summing the hours throughout the year when tide elevation (calculated using NOAA hourly data) exceeded the land elevation at each location. Using this data we were able to quantify the relationship between percentage flooding and growth rate for the marsh shrub Iva frutescens.