Department of Geography and Environmental Studies

Geography

Sarah Merrill Townsend, 2003

Avon River Mudflats

This poster presents results from a field study and GIS analysis on quantifying the extent, distribution and rate of growth of Spartina alterniflora on a section of the Avon River Mud Flats, in the Minas Basin since the construction of the Windsor-Falmouth Highway 101 causeway in 1969.  The extent and distribution of both the mature and expanding juvenile colonies of S. alterniflora were measured using differential GPS from October to November 2001.  Data were collected during the low tide and included observations of vegetation density within the colonies.  The historic spatial distribution covered by S. alterniflora was determined from aerial photographs of the study area from 1972, 1981, 1992, and 1995.  The annual rate of growth and change in total saltmarsh area from 1969 to 2001 was quantified an analyzed using a Geographic Information System (GIS).

The area and rate of growth of the marsh vegetation have been increasing since causeway construction as conditions on the mudflat surface have become more favorable; with a lower tidal inundation and lower wave energy due to an increase in sediment deposition initiated with causeway construction.  Through ice and wave rafting of rhizome material from limited shoreline marsh in the study area, and possibly other sources already in existence prior to causeway, the pattern of growth expansion is typical of other marsh study sites.  Total area of marsh in 1973, 1981, 1992 and 1995 were 1,443 m2, 4,146m2 m 14,232 m2, and 40,782 m2 respectively.  In 2001 the established only marsh area was 199,083 m2, and the juvenile only marsh area totaled 191,194m2.  The rate of growth of the total S. alterniflora on the Avon River mudflat study area was calculated to be 29% per year between 1992 and 2001.  Based on regression calculations from the GIS analysis, the predicted marsh area for 2006 is 2.5 km2.  This research demonstrates that the Highway 101 causeway has acted as an important agent of change in this marsh/mudflat system.