Ecomorphodynamics of Intertidal Ecosystems in Modified Estuaries

'Ecomorphodynamics' refers to the study of the interaction and adjustment of topography, vegetation, fluid and hydrodynamic processes, morphologies and sequence of change dynamics involving the movement of sediment.  These feedbacks are clearly evident within the vast intertidal ecosystems located in macrotidal systems such as the Bay of Fundy.  Salt marshes and mudflats represent delicately balanced systems between hydrodynamic forces and ecological, sedimentological and morphological responses. A key to survival for many of these coastal ecosystems in face of climate change is to maintain this delicate balance.  Changes in marsh or mudflat surface elevation within the tidal frame or changes  in edge morphology will in turn induce changes in tidal prism, hydrodynamic forces, vegetation community structure, rates of sedimentation and dissipation (marsh platform) or amplification (cliff) of wave energy. The rate of these changes can be significantly influenced by human development such as the construction of tidal barriers or installation of shore protection.  

 The purpose of this research program is to examine the spatial and temporal changes in intertidal habitats in macrotidal environments such as the Bay of Fundy and isolate the relative significance of factors controlling these changes.  It involves the integration of meso-scale (decadal/basin wide) quantification of geomorphic changes in the intertidal zone using ArcGIS and high resolution digital elevation models with micro-scale (seasonal to tidal cycle/marsh level) investigations of sedimentary processes within salt marshes and mudflats of this region.

These research projects will help to develop an understanding of the mechanisms controlling the stability and resilience of mudflat and salt marsh systems in the Bay of Fundy, identifying geomorphic triggers between erosive and progradational states and overall response to the effects of climate change.

Development of marsh/mudfalt system downstream of the Windsor causeway (van Proosdij & Townsend, 2006)

Of particular interest is the response or resiliency of intertidal ecosystems to anthropogenic activities such as dyke and causeway construction or shore protection and the potential responses of the ecosystem to removing these tidal barrier structures or modifying the tidal energy within the area (e.g. tidal power).

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Hydrodynamics and Sedimentary Processes of Intertidal Ecosystems

The purpose of this research is to examine the temporal and spatial variations in hydrodynamics and sedimentary processes of intertidal ecosystems with a particular focus on muddy macrotidal systems. The new (2008) Intertidal Coastal Sediment Transport Research Unit (In_CoaST) at Saint Mary's University will play an integral role for this research.  The research will examine the interactions and feedbacks that occur between topography, biota (e.g. vegetation and invertebrates), hydrodynamic (e.g. waves and currents) and sedimentary (e.g. suspended sediment concentration, deposition, erosion) processes and the resultant adjustment of intertidal morphology at a range of spatial and temporal scales. Of particular interest is the response of intertidal environments to changes in forcing functions (e.g. wind, waves, tides, currents, sediment, vegetation, topography) and how anthropogenic activities impact this response. 

 

Data collection at low and mid spring tide on the Avon River, Bay of Fundy (photo by A. Silver,2008)

 

Additional research is being undertaken to examine the role of ice and winter meteorological conditions on sediment transport processes and dispersal of vegetation. 

 

Ice blocks laden with sediment on Windsor marsh, Feb 2007

 

 

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Salt Marsh Restoration

For centuries, human activities have reduced the amount of salt marsh and free-flowing tidal river habitats in many areas around the world.  Conservative estimates for the Bay of Fundy put the loss of salt marsh habitat between 80 to 85% mostly associated with dyking and conversion to agricultural land.  Although these activities are of historical and social significance, it is now recognized that the significant loss of habitat, species and primary productivity that has resulted from the construction of dikes, modern tidal barriers (causeways) and coastal development has had significant ecological implications, which are preventable and repairable if tidal hydrology is appropriately restored.   

One year post dyke breaching at Walton Creek restoration site, June 2007 (photo by CBWES Inc.)

Salt marsh ecosystem function may be restored passively when a dike is breached during a storm with little to no human interference or through active means by planned removal or modification of a barrier to restore tidal flow.   Examination of passive restoration sites can provide long term records about vegetation and geomorphic recovery however provide limited information about driving and/or limiting variables within the first few years after the breach event that may influence the ultimate recovery of the system.  In addition, the European experience has shown that salt marsh re-establishment is not inevitable at all sites following a breach. Properly monitored restoration projects can sometimes provide additional information on constraints that may have caused a restoration project to proceed along successional pathways not initially anticipated.

My students and I work closely with CB Wetlands and Environmental Specialists Inc (CBWES) to examine the vegetative, sedimentary, nekton and hydrologic conditions pre-restoration and the initial five years post-restoration at salt marsh sites across the province both on the Fundy and Atlantic coasts.  Additional areas of research include tidal channel hydraulics and wetland design and biogeographical processes (e.g. vegetative community interactions, dispersal mechanisms) within these systems.  Opportunities for NSERC industrial internships with CBWES are available at the undergraduate and graduate level. 

These data will contribute to the development of long term data sets of pre-restoration, post-restoration, and reference marsh conditions to determine if a marsh is proceeding as expected and to help with models that are aimed at predicting the response of marshes to tidal restoration at the upper end of the tidal spectrum.  In addition, these results can provide insight into the ecological interrelationships between biotic and abiotic variables and contribute to the development of a set of reference marsh conditions for future restoration projects in the Bay of Fundy and Atlantic coastal areas.

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Tidal Barrier GIS Database Development

Over the last century, the majority of rivers entering into the Bay of Fundy have been highly modified through the construction of tidal barriers.  The construction of these barriers resulted in either partial or complete obstruction to tidal flow in many areas around the Bay.  Tidal barriers effectively decrease turbulent energy in the tidal system causing sediments and other particles to drop from suspension and accumulate as deposits of mud, sand and silt. In other areas, localized erosion is initiated either directly upstream or downstream of a partially restrictive barrier.  Ecosystems inhabiting this zone, such as mudflats and salt marshes, are some of the first environments to feel the effects of coastal modification.  These changes have cascading impacts on intertidal ecosystems, some negative and others positive. Overall however, the cumulative impacts of tidal barriers on intertidal ecosystems of the Bay of Fundy are unknown.  This is of particular concern with increasing interest in removing or modifying tidal barriers in an effort to 'return the tides'. Without a solid baseline of past and present 'states' of these systems, assessing or predicting the success of restoration activities is difficult. 

 Coastal systems such as mudflats and marshes are not static features, they undergo cycles of progradation and retreat that are well documented around the world.  These cycles have been linked to changes in sea level and in the tidal prism due to human activities such as tidal barrier construction or dredging, changes in wind/wave climate, sediment supply, cliff morphology, intertidal sedimentation and changes in the location of the major tidal channel.  One of the most effective ways of documenting these changes is through the analysis of rectified aerial photographs within a GIS system.   This is the preliminary stage that is required before any true questions regarding the 'why' of these changes are addressed. 

 The purpose of this collaborative research project was to integrate the Bay of Fundy Tidal Barrier Audits conducted by the Ecology Action Center (EAC) and Conservation Council of New Brunswick (CCNB) into a comprehensive digital spatial database being developed in a concurrent project with Environment Canada.  Together, they will be used as a baseline to assess the cumulative impacts of tidal barriers in the Upper Bay of Fundy and serve as a platform for future research. This portion of the project will focus on data that is of particular interest for salt marsh restoration initiatives and serve as a valuable management tool.  Baseline data currently integrated into the database include: 1:10,000 planimetric (NS,NB), property management units and type classification (NS), watershed boundaries (NS,NB), digital elevation model (NS, NB), Landsat 7 ETM - 30 m resolution imagery as well as digital orthophographs (4m resolution) for New Brunswick (NB) and orthorectified aerial photographs (1 m resolution) for portions of Nova Scotia (NS), particularly the Southern Bight of the Minas Basin.  The full GIS is available to researchers and government agencies as long as the potential users have secured appropriate licensing permission from the data providers if those data are not freely available.  The geographical coordinates of tidal barriers inventoried for both NS (216 sites) and NB (91 sites) have been integrated into the GIS. Full fact sheets and summaries of the audits were prepared in conjunction with the EAC for NS and are available on-line as downloadable PDFs.  Basic attribute information and maps for NB barriers will also be available within the GIS framework however completion of complete fact sheets available to the public is not feasible within the time frame of the project at this time.    LINK to TIDAL BARRIER DATABASE via B0FEP website.

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