CONICET | Buscador de Institutos y Recursos Humanos

A digital elevation model (DEM) of the intertidal zone of Bahía Blanca Estuary was created through the assimilation of waterline observations on 10 Landsat images (TM and ETM+), acquired over the period of March 2006 to May 2007, at different tidal levels. Waterlines were extracted through detection of the water land threshold in the wetness band (after Tasseled-Cap transformation). A vegetation map was obtained through unsupervised classification, after delimiting the image to the area of interest (intertidal and shorezone). Normalised Difference Vegetation Index (NDVI) values were calculated on pixels corresponding to Spartina alterniflora marshes. Spectral response at high resolution was measured in S. alterniflora canopies under natural conditions varying standing biomass by means of successive harvestings and regressions between NDVI and green aerial biomass were obtained by using a field spectroradiometer. Mudflats and saltflats covered the largest area (578 and 302 km2), followed by halophytic shrubs (203 km2). Intertidal marshes of Sarcocornia perennis and S. alterniflora covered 174 and 131 km2, respectively. Halophytic shrubs were typically supratidal, with most of their area (186 km2) exposed more than 80% of the time, and 32% of their area (66 km2) above the level of the highest tide. S. perennis marshes and saltflats occur at similar elevations, with most of the area covered by tides during 13 to 25% of the time. Mudflats and S. alterniflora marshes occurred over the widest range of elevations, with the lowest limit of vegetation flooded 53% of the time. Most of the area covered by S. alterniflora (93%) is flooded at least 20% of the time. As a general trend, higher values of biomass appeared close to main channels, with the highest values along stream banks in the outer reaches of the Canal Principal. Obtained results suggest the coexistence of two different patterns of marsh zonation, with different communities appearing at the same elevations depending on the geomorphic settings.