Direction and magnitude of recent changes in coastal wetlands of the Bahía Blanca Estuary (Argentina)

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

Mar del Plata

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

Coastal and Estuarine Research federation

In this work we used historical aerial photographs, high resolution satellite images, and GIS to quantify changes in land cover in coastal wetlands of the Bahía Blanca Estuary between years 1967 and 2005. Polygons representing the different land cover types were digitized on screen and the resulting and cover maps were used to calculate frequency matrices for the various plant associations identified in the field. Matrices describe the area that fall within each possible combination of land cover types in 1967 and 2005. Diagonal entries tabulate the area that did not change its class from the first date to the second ,and off-diagonal elements represent changes. Based on each frequency matrix, we described the direction and magnitude of changes in land cover. The replacement of Sarcocornia perennis marshes and halophytic steppes by mudflats is a repetitive pattern through the area. We estimated a total loss of 1498 and 1200 ha of marshes and steppes, respectively, and it may reflect an increased erosion, as well as ecosystem state change in response to a rising sea level. One of the most striking changes observed is the increase of the area covered by Spartina alterniflora marshes. According to our estimations, 2660 ha of new marshes appeared on formerly bare mudflats. This type of replacement suggests the occurrence of depositional environments that, at least locally, allow bed elevation and vegetation growth. Human activities have also played a significant role in reshaping coastal landscape. For de area considered in this work, 665 ha originally covered by shrub steppes and Sarcocornia perennis marshes were replaced by human land uses. Major changes correspond to massive spoil dredge deposits and land fillings.