3rd Bay of Fundy Science Workshop
Understanding Change in the Bay of Fundy Ecosystem
Variation in the Bay's Ecosystem
Climate Change and the Bay of Fundy
Spatial and Temporal Variation in Sediment Accumulation Rates
Along the New Brunswick Coast, Bay of Fundy
Suspended Sediment Circulation and Deposition over Single Tidal
Cycles at Allen Creek Saltmarsh, Bay of Fundy
Climate Change and the Bay of Fundy Dave Wartman, Environment Canada Atmospheric Science Division, Environment Canada, Dartmouth NS
Abstract
The Intergovernmental Panel on Climate Change states "the balance of evidence suggests a discernable human influence on global climate". This anthropogenic effect is especially important in Atlantic Canada, where ecosystems such as the Bay of Fundy exist in a delicate balance that is highly sensitive to changes in the climate system and where the economy is strongly based on natural resources.
An overview of the climate change issue is presented and a comparison of recent climate trends with global climate model projections is discussed. The regional sensitivities to a changing climate are examined, including those in the fisheries, agriculture, forestry, water resources and human health sectors. Particular emphasis is placed on those sensitivities of special relevance to the Bay of Fundy, such as the aquaculture industry. Potential changes in the frequency and intensity of winter storms and tropical cyclones are considered as well as the vulnerability of communities and habitats to accelerated sea level rise.
In addition to the absolute changes in climate, the rate of these changes are critical in determining the capability of ecosystems to adapt. The potential increased frequency of extreme events such as droughts, floods, and storms are also paramount in these early stages of assessing the impacts of climate change.
Spatial and
Temporal Variation in Sediment Accumulation Rates Along the New Brunswick Coast, Bay of
Fundy G.L. Chmura, L.L. Helmer, C.B. Beecher, A. Coffey and R.
Crago,
Dept. of Geography and Centre for Climate and Global Change Research McGill University 805
Sherbrooke St., W., Montreal QC H3A 2K6
Abstract
We are measuring surface sediment deposition at seven marshes along the New Brunswick coast, from Bocabec at the mouth to Belliveau Village and Wood Point at the head of the Bay of Fundy. Vertical sediment accretion is determined by measuring the thickness of sediment accumulated over clay feldspar marker horizons. A cryogenic coring device allows us to subsample sediments of variable water content with minimal disturbance to the marsh surface. Marker horizons were established in the spring of 1997 along multiple elevational transects in each marsh. All marshes and all elevations showed measurable sediment deposition over the summer of 1997, but sediment thickness doubled at most plots during the winter of 1997-98, which was noticeably mild. In most marshes the thickness of sediment deposits decreased with elevation and distance from the mouth of the tidal creek. Amounts range from 45 mm in low marsh at Cape Enrage to a low of 2 mm in high marsh at Bocabec. An additional control is distance from sediment sources identified in the upper Bay. An interesting exception to this pattern is our site at Belliveau Village which is downstream of the Petticodiac barrage.
Sediment deposition over the historical period has been determined at two marshes on Point Lepreau, Chance Harbour and Dipper Harbour. Using the radionuclides cesium-137 and lead-210 and palynological techniques, we can compare sediment accumulation rates over time spans of 30, 100, and 200 years. Both marshes have accumulated sediment at the rate of 1.9 mm/yr over the last 30 yrs. Considering coring locations, this rate is within the range predicted from our marker horizon study. When calculated over a 100 yr period, rates of sediment accumulation decrease slightly. The greatest decrease is demonstrated when calculated over a 200-yr time span.
Suspended
Sediment Circulation and Deposition over Single Tidal Cycles at Allen Creek Saltmarsh, Bay
of Fundy Danika van Proosdij¹, Jeff Ollerhead² and Robin
Davidson-Arnott¹,
¹Department of Geography, University of Guelph, Guelph ON N1G 2W1 ²Department of
Geography, Mount Allison University, Sackville NB E4L 1A7
Abstract
Relative sea level is rising in the upper Bay of Fundy at a rate of 0.3-0.4 m per century. Therefore, the saltmarshes in this area must grow up vertically if they are to survive. The marshes can grow vertically via the input of organic or inorganic materials where the inorganic materials, mostly coarse silts, are primarily contributed to the marsh surface by suspended sediments that settle out over high tide cycles. The purpose of this presentation is to explore suspended sediment circulation and deposition patterns over single tidal cycles at the Allen Creek saltmarsh near Sackville NB and to consider which variables appear to be necessary for the creation of a reasonable predictive model.
A field study was conducted during the summer of 1998 at the Allen Creek saltmarsh where net flow velocity, suspended sediment concentration, and sediment deposition were measured over thirteen individual tidal cycles. A vertical instrument array consisting of three electromagnetic flow meters and co-located OBS probes and a single pressure transducer was deployed in the low marsh region (van Proosdij et al., 1999). Sediment deposition was measured using full-cycle sediment traps. The temporal distribution of sediment deposition was measured using sequential sediment traps exposed at different tidal stages.
The data collected suggest that sediment deposition on the marsh surface is primarily controlled by the interaction of water flow, marsh morphology and vegetation. The highest amounts of sediment were deposited during conditions of high suspended sediment concentration and low wave activity, especially when the relative roughness of the vegetation was high. Loss of suspended sediment from the water column was shown to be correlated with the sediment trap data; however, predictions of sediment deposition based on the variation in suspended sediment concentrations were found to be valid only for conditions with wave heights of less than 0.15 m.
The results clearly show that modelling the annual or even monthly amount of sediment accretion on the marsh surface using tide data and estimates of suspended sediment concentration alone is too simplistic as an approach. At a minimum, one would need to incorporate estimates of the relative roughness of any vegetation and the wave climate into such a model for it to be successful.
Reference
van Proosdij, D., Ollerhead, J. and Davidson-Arnott, R.G.D. 1999. Use of optical backscatterance sensors in estimating sediment deposition on a macro-tidal saltmarsh surface. Proceedings of the 1999 Canadian Coastal Conference, Published by the Canadian Coastal Science and Engineering Association (CC-SEA), p. 359-370.
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