THE EFFECT OF INUNDATION ON ECOLOGICAL ZONATION IN A SALT MARSH USING LOW-ALTITUDE BALLOON AERIAL PHOTOGRAPHY

Ecological zones in a salt marsh are controlled by a hydroperiod, elevation, soil salinity, groundwater flow, competition, and nutrient/oxygen availability. Most models of zonation only take into account elevation or hydroperiod as the primary driving factor. However, the hydroperiod remains poorly understood, and its effect on zonation, due to a lack of data at spatial scales relevant to tracking the movement of water across the marsh surface. This project is designed to gather high-resolution aerial images from a helium balloon kite (Helikite) to improve the understanding of the influence of hydroperiod on ecological zonation. The helikite captures aerial photographs of Crab Haul Creek Basin, the most landward salt marsh basin, flanked by a forest-marsh boundary and a Pliestocene beach ridge. Near-IR photographs are taken from 75-100 meter altitude to provide the detail necessary to resolve the waterline during rising tide from the headwaters to a gauging station, 150 meters north.

We used Helikite visual light images and automated classification to identify ecological zones. Photographs taken during peak primary production have distinct pixel RGB values for the 7 main groundcover types. These include Spartina alterniflora (short and tall form), Juncus roemarianus, Salicornia virginica, Spartina wrack, mud, and sand. After creating a signature file based on each groundcovers distinct pixel signature, maximum likelihood pixel-based computerized classification is applied. By quantifying the hydroperiod spatially and temporally through aerial photographs and comparing frequency of inundation to ecological zones we found that though elevation and hydroperiod are driving factors of ecological zonation they do not solely explain zonation. Other driving factors must be considered important, particularly groundwater flow and evapotranspiration, to produce more accurate models of zonation.