Sand Dune Restoration in Point Pelee National Park, Ontario, Canada

Transcription

1 Sand Dune Restoration in Point Pelee National Park, Ontario, Canada Mary-Louise Byrne, Geography and Environmental Studies, Wilfrid Laurier University and Michael Brierley, Environmental science by research MSc, Queen Mary University of London

2 Sand Dune Restoration Study Site Objectives Methods Surveying Sediment Sampling Results and Discussion Recommendations Conclusion

3 Study Locations Point Pelee National Park, located in Lake Erie, is the southernmost point of mainland Canada, about 50 km from Windsor, Ontario.

4 Sand Dune Restoration Point Pelee is a cuspate foreland on Lake Erie. Two sand beaches enclose a cattail marsh the Park is home to the greatest diversity of wildlife in Canada the endangered five lined skink makes this its home.

5 Sand supply has been curtailed by updrift shoreline development Beaches have been heavily impacted by recreational use, have a finite sediment supply and are essentially closed during the winter season. Sand Dune Restoration

6 Sand Dune Restoration Our study takes place on Northwest Beach Park removed a parking lot and washroom facilities Park seeks to naturalize the area for skink habitat

7

8 Sand Dune Restoration Although heavily used in the past 80 years, today Point Pelee is frequented more by birders and those who follow the migration of the monarch butterfly, but there are still beach users Part of a diverse Carolinean ecosystem of course I have to throw in a picture of the skink

9 Initiated field work July 2009 Research at Point Pelee in Oct 2009, and January, March 2010, January and October Collected samples of surface materials along transects a mix of snow and sand. Conducted GPS surveys. Calculated sediment moisture content and weight of sediment in snow drifts. Sand Dune Restoration

10 Parking Lot

11 Natural Dune area

12 Understand the dynamic processes that affect the development of dunes at Northwest Beach. 1. What are the factors preventing dune formation at Northwest Beach? 2. What dune restoration goal is best suited for Parks Canada? Study Objectives

13 Cause for decreased Sediment Supply Colchester to Southeast Shoal Littoral Cell Sediment Traps (Baird, 2008)

14 Dunes result from the interaction between the lake, wind, vegetation, and human pressures Dunes require large amounts of sediment to form and grow Because of coastal development updrift of Pelee, sediment supply has been reduced Supply to former parking lot dune ridge is small and previously stored sand is held permanently by relatively dense vegetation in a peaked dune form Northwest Beach natural dunes have flat topped topography, 3 to 4.5 m above the mean lake level Sand Dune Restoration...

15 Point Pelee National Park Fall and Winter Moisture Content Values Moisture content % Increasing distance from waterline m Fall NP Line Fall PL Line Winter PL Line Sand Dune Restoration

16 Overall there is an abundance of sediment in ice foot. Seasonally, this sediment is held on the beach because of moisture conditions until vegetation growth is established When transport can occur, sediment then is trapped in the vegetation, preventing transport to the former parking lot Sand Dune Restoration

17 Sediment is being trapped at Pelee by cottonwood tree line. Sand Dune Restoration

18 Seasonal distribution of sand is important There is a winter availability, but it does not reach the parking lot Sand Dune Restoration

19 In October 2011, samples were taken from along and across the beach Surface samples collected from both the active beach, dune and parking lot areas. Samples collected from both the former parking lot and the adjacent natural areas. Sand Dune Restoration

20 Former Parking lot BO Natural Beach BO-2 3 BO Sampling Locations 8

21 Grain Size Distribution Distribution of grain sizes in Figure 2. shows that find sands are being transported naturally until the dune crests parallel to parking lots Sediment migrating naturally to sample 5s Figure Figure 3. shows that grain size migration has stopped and does not resemble the natural dune area sample 6-6 to 8-6 Sediments in parking lot resemble glacial till. Unsorted, large grained skewed Figure 3.

22 Grain Size Distribution Figure 4. compares grain size between dune crest samples with natural dune area Skewed to the left Well sorted fine grained sands (2-3 ф) The altered dunes and natural dunes have very similar grain size distribution Figure 5. compares blowout samples with natural dunes Blow-out samples have identical cumulative percentage curves Encouraging sign that sediments are very similar 50 percentile 2.2 ф Figure 4. Figure 5. 14

23 Decreased Sediment Movement Blow-out samples are located at pathways from former parking lots to beach that are orientated with dominate wind direction (southwest)

24 Our study suggests that much of the landward movement of sand occurs during late winter with minimal summer transport. Sand becomes entrained within the ice foot during freeze-up. Sublimation and melt exposes the material and grain by grain movement of sand occurs in a landward direction. Sand Dune Restoration

25 Sand becomes trapped by a line of cottonwoods and the dune ridge. A former fence line acts as a barrier to sand moving back into the former parking lot except through blowouts in the ridge. If the Park wants the former parking lot to resume a natural topography, then they will have to address this capture of sand. Sand Dune Restoration

26 Elevation Differences Small elevation difference between 0ctober 2010 and October 2011 Largest increase located in altered dunes adjacent to natural dune area This is a result of decreased landward sediment movement dunes in front of former parking lots have different characteristics from the natural dunes which appear to develop over a larger area resulting in the dunes having a smaller height Altered dunes in front of parking lots have a linear distribution that is parallel to the leading edge of the parking lots Visible break in dunes which are the cause of beach patrons walking from the parking to the beach 19

27 Surveyed Beach- Dune Profiles Beach dune profiles provide good visual to altered orientation Natural Dune Profile (sample 8) 20 Sample 5 profile has a concave orientation leading to peaked dune crest limited supply and vegetation stabilized dune. Sample 5 Profile Natural dune profile (sample 8)has a rounded, convex beach curve and a wide, flat-topped dune Altered dunes are sharp and abrupt Sample 1 Profile

28 1 5 8

29 Former parking lot at the top Natural area to the bottom Dunes of former parking lot narrower and more peaked squeezed Natural area dunes are flat-topped and laterally spread Sand Dune Restoration...

30 Recommendations 1. Sand supply is limited so Park must actively manage the naturalization. 2. Find a source of sand for nourishing dunes. 3. Remove or thin out current vegetation to allow easier sediment transport. Possibly remove all vegetation and replant native dune species. 4. Reduce the height of the altered dunes, moving the excess sediment into the parking lots. 5. Widen pathways (blowouts) to allow natural aeolian processes to move sand landward of the ridge. 21

31 Conclusion Decreased sediment supply has halted natural migration of altered dunes Allowing vegetation to stabilize dunes No new sand deposits are visible over organic layer on altered dune crests Invasive vegetation management/rehabilitation measures are needed Active management must be undertaken. This case study is important for understanding naturalization in a supply, limited, seasonally constrained environment. 31

32 Parks Canada Thank you to Parks Canada for logistical assistance