Potential Effects of Water-Level Changes on Island Ecosystems: A GIS Spatiotemporal Analysis of Shoreline Configuration

Pomerdy IslandWhat: Investigation of spatiotemporal changes in island shorelines due to water-level changes using the mapping and analytical tools of a geographic information system (GIS). Study area is The Massasauga Provincial Park archipelago (Georgian Bay, Lake Huron, Ontario)

When: July 10 – August 7

Where: Wesleyan University. The project consists mainly of spatial analyses using ArcGIS but will also include training in field data collection.

Who: Three students and Kim Diver (Wesleyan University)

Project Overview and Goals

The Great Lakes have been experiencing a low-water period over the past decade but existing data on island area in The Massasauga is based on high-water stages of the lake. This project will combine aerial photo and satellite imagery interpretation with field data to examine the influence of water level changes on shoreline modifications (island area, shape, composition) and island ecosystems. This project will test two hypotheses: (1) Larger island sizes and increased connectivity during low water stages of the Georgian Bay are correlated with an increase in plant species richness and (2) Islands with a greater percentage of growth during low water stages will have a greater increase in non-native plant species.

Little is known regarding the role of feedbacks between coastal processes, coastline geomorphology, and shoreline vegetation on species richness patterns on islands. Shorelines in The Massasauga are varied (e.g. steep cliff, sandy beach, cobble shore) and therefore affect the colonization and persistence ability of plants differently. The results of this project will shed light on the applicability of the prevailing model of island biogeography in areas of changing shoreline configuration and may contribute to a contemporary theory of island biogeography. This has real-world relevance, such as the misapplication of the equilibrium model in the design of nature reserves.

Geologic Background

The Canadian Shield bedrock of The Massasauga consists of the Parry Sound Greenstone Belt (metavolcanic, metasedimentary, and igneous) and the Ontario Gneiss Belt, both of Precambrian origin (Cordiner 1977; Sly & Munawar 1988). As part of the Grenville Peneplain, the general profiles of the islands are relatively flat, ranging from a few meters below lake level in depression basins to circa 50 m above lake level. The bedrock-dominated topography with thin, discontinuous sediments of glacial till and alluvium is due to bedrock erosion and substrate removal during periods of glacial abrasion and post-glacial lake wave-washing (van Luit, 1987; Larson & Schaetzl, 2001). The Thirty Thousand Island archipelago was formed by glacial scouring of the Canadian Shield, erosion from glacial meltwater drainages, and post-glacial isolation (Hirvonen & Woods, 1978). During and following deglaciation, The Massasauga islands periodically emerged and submerged with high and low lake stands. The Massasauga islands permanently emerged as dry land 3-4 ka, following isostatic rebound and draining of the higher than present day lake levels associated with the postglacial Nipissing Great Lakes Periods (Hirvonen & Woods, 1978). Lake levels for the past 2.5 ka show a stabilized mean of 177 m asl (Eschman & Karrow, 1985).

Historic lake levels in the Great Lakes basin show marked fluctuations between approximately 175 and 178 m asl, with chart datum at 176 m asl. In 1986, the record high level was approached with annual mean water levels at 177.5 m asl (Bishop 1990). Since 1998, water levels have fallen below the long-term historic average of 177 m asl. Current lake levels (2011annual mean 176.04 m asl; August 2012 monthly mean 175.97 m asl) are below the historic average, approaching the lowest recorded annual mean water level of 175.68 m asl from 1964. (Seasonal high levels for the Georgian Bay are typically in July and seasonal low levels are during mid to late winter.) Low elevation islands (< 5 m maximum elevation) and all island shorelines emerge and submerge with these fluctuations.

Potential Student ProjectsGeogian Bay

  1. Calculate differences in island area between different field collection years. Examine lake level changes and associated land cover changes on islands previously inventoried for plant species richness using orthoimagery in ArcGIS. The fieldwork occurred during low-water intervals but the base data for the official maps and GIS were configured by the Ontario Ministry of Natural Resources during a high-water period. The student will use orthophotos (georeferenced aerial photographs) from the years of data collection (2001, 2006, and 2011) to digitize new island polygons, calculate island areas, and calculate differences in island areas among the three years. This project involves the application of ArcGIS geoprocessing tools.
  2. Calculate changes in island shape and connectivity. Determine differences in island shape and isolation/connectivity among the fieldwork years in order to discern if changing shapes or isolation relate to differences in temporal variations in plant species richness. This project involves the application of spatial analysis tools in ArcGIS.
  3. Predict island area, shape, and connectivity changes with continued declining lake levels. Although lake levels fluctuate on daily, seasonal, annual, and long-term cycles, recent studies have indicated that Great Lakes water levels will decline 1 m by 2050 (Mortsch et al. 2000). The projection is based on climate change predictions of increased temperatures in the region, increased lake surface evaporation, and extreme seasonal precipitation patterns. Implications of declining water levels on island and shoreline habitats are few (see Schwartz et al. 2007). One student can use bathymetric and elevation data with water level scenario predictions to produce shoreline models. Although the model will be useful for economic, recreation, navigation, etc purposes, the data will be used to predict habitat modifications for biodiversity conservation of the archipelago.

Logistics/Field Conditions

Students will be housed in Wesleyan University dormitory-style housing. Kitchen facilities are available and a food stipend is provided. Working conditions involve spending time in a computer lab using GIS software to analyze large data sets. Students should be well-organized and detail-oriented. Two days of field work are planned which involve riding up to 2 hours (one-way) in vans, working outdoors regardless of weather, navigating on foot through vegetation without the aid of trails, and collecting data in semi-rugged conditions. During the field component, there is the possibility of interaction with toxic plants or dangerous insects or animals.

Students should bring an external hard drive (250 GB minimum recommended), notebook, sturdy hiking shoes, water bottle, and a small backpack. If a student wishes to use a personal laptop for the project, a one-year license of ArcGIS 10.1 will be provided.

Recommended Courses/Prerequisites

No prerequisites. However, priority will be given to students who have had GIS and/or remote sensing coursework. Courses in geomorphology and introductory statistics will also be helpful.


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  • Cordiner, G.S. 1977. A Reconnaissance Earth Science Inventory of Blackstone Harbour Provincial Park Reserve. Algonquin Region: Division of Parks, Ontario Ministry of Natural Resources.
  • Eschman, D.F. & Karrow, P.F. 1985. Huron basin glacial lakes: a review. In Quaternary Evolution of the Great Lakes (ed. by P. Karrow and P. Calkin). Geological Association of Canada Special Paper 30.
  • Hirvonen, R. & Woods, R.A. 1978. Georgian Bay Islands National Park Integrated Resource Survey. Forest Management Institute, Ottawa.
  • Larson, G. & Schaetzl, R. 2001. Origin and evolution of the Great Lakes. Journal of Great Lakes Research 27:518-546.
  • Mortsch, L.D., H. Hengeveld, M. Lister, B. Lofgren, F. Quinn, M. Slivitzky and L. Wenger. 2000. Climate change impacts on the hydrology of the Great Lakes-St. Lawrence system. Canadian Water Resources Journal 25:153-179.
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  • Sly, P.G. and M. Munawar. 1988. Great Lake Manitoulin: Georgian Bay and the North Channel. Hydrobiologia 163:1-19.
  • van Luit, H. 1987. Blackstone Harbour: Management Plan Background Information Document. Ontario Ministry of Natural Resources, Division of Parks, Parry Sound, Ontario.