Application of the shorezone concept to sea level rise in coastal wetlands of the Bahía Blanca Estuary, Argentina

PIOVÁN, M.J.; PRATOLONGO, P; MAZZON, C.; ZAPPERI, G.

Mar del Plata

Conferencia; CERF 2012-The changing coastal and estuarine environment: a comparative approach; 2012

Coastal and Estuarine Research federation

The concept of shorezone is used here to define a zone of hydrologic influence of sea level, which may extend from shallow subtidal waters to non-tidal environments at the landward edge, whose hydrology is still influenced by sea level. Under a rising relative sea level the different plant associations within the shorezone are expected to migrate upslope, but wetlands transgression largely depends on the creation of waterlogged conditions near the upland boundary. In this work, we propose a classification of coastal environments in the Bahía Blanca estuary, and we explore their potential for wetlands transgression. We developed a hierarchical classification scheme based on the geomorphic setting, hydrology (water source and hydrodynamics), and plant associations. Field characterization of the 13 classes defined was the foundation for remote sensing activities. Landsat TM and ETM+ images were processed to surface reflectance and classified to derive a vegetation map. We used masks, reclassification and NDVI levels to achieve a better discrimination between floristic classes. Images acquired at low/high tide and humid/dry periods were also processed and combined to derive a map of inundability. Mudflats dominate the intertidal zone, Spartina alterniflora and Sarcocornia perennis marshes also appear at lower and higher elevations. Spartina densiflora marshes occupy abandoned channels and topographic depressions subjected to inundation during wet periods. Salt flats and shrub steppes develop in areas affected by a shallow groundwater table and high evaporation rates building elevated soil salinities. Thickets of Allenrolfea patagonica occupy areas affected by seepage from the uplands during extremely wet years, and different brushwood associations occupy elevated and well drained areas.