Ecological Studies of the Windsor Causeway and Pesaquid
Lake, 2002.
Executive Summary
An extensive study of the marsh-mudflat complex on the seaward side of the Windsor Causeway and a preliminary investigation of Pesaquid Lake were carried out during the summer and fall of 2002. The purpose of the studies was to lay the basis for an assessment of the effects of expanding the causeway to accommodate additional lanes for Highway 101, and to establish continuing monitoring of changes in the marsh and mudflat in response to the causeway and to rising sea level. Results
of the study are summarized below.
1. The sediments of the Windsor Causeway tidal flat are predominately clayey silts (~68% silt and ~23% clay), with mean grain size of 23-30 µm.
2. Water contents ranged from 29.7 to 57.3% (mean ~44-46%), and organic content from 0 to 16.9% (mean 6.68 ± 5.82%). Water contents are comparable to the high values recorded by researchers in 1976-79; organic contents are higher than
previous records from the Bay of Fundy.
3. An extensive array of stations was established for long term monitoring of changes to the marsh and mudflat. Station locations were surveyed in and an updated GIS database established.
4. Short-term (<4 months) monitoring of the 33 stations showed that elevation of most (27) exhibited a net increase, averaging 1.3 cm (± 1.96) by mid-October. Six stations exhibited a decrease in elevation; most of these were adjacent to tidal channels, where there was visible evidence of slumping and erosion. Stations in vegetated areas showed greatest consistency in terms of elevation; colonization by
Spartina alterniflora typically causes stabilization of intertidal sediments.
5. Ambient sediment concentrations in flood water in the channels and over the marsh, ranged up to 1,700 mg. L-1 in the bore or the wave front of the advancing tide. Concentrations then declined as water depth increased. Ambient sediment concentrations in floodwater over the marsh ranged from high values of ~500 mg.L-1 over muddy unvegetated sites to less than 100 mg.L-1 at stations in the
middle of the marsh. Studies of accumulation on sedimentation plates showed that an average of 7.8 mg.cm-2 (± 13.0) settled out during each flood tide.
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