Elevation (meters)

Phragmites

Overlay of Phragmites sites on lidar-derived (NCALM 2005) elevation map of northern sections of the Great Marsh

Image from Google Earth

Relationships between NCALM lidar-derived elevation data and location of emergent Phragmites in northern sections of the Great MarshJeanne Anderson University of New Hampshire, Robert Buchsbaum Massachusetts Audubon Society, Peter Phippen Merrimack Valley Planning Commission, Geoff Walker Eight Towns and the Bay & Chair, Ducks Unlimited Marsh

Committee

July 21, 1999

INTRODUCTION & DATA

D87

REFERENCES and ACKNOWLEDGEMENTS

DATA ANALYSIS, RESULTS and DISCUSSION

PIE LTER NCALM (2005) Lidar

Elevations (10 centimeter elevation

classes applied within the marsh

platform)

Contrast elevation of salt marsh areas around the ditches north and south of Pine Island causeway.

Pine Island

Elevation (meters)

Overlay of Phragmites sites on elevation map of northern sections of the Great Marsh

Phragmites

Slope of lidar elevations

(0.1 meter Z factor)Note locations of

Phragmites stands (black dots) on

areas of moderate slope change within the marsh platform.

PIE LTER NCALM (2005)

Lidar Bare Earth Elevation Classification

(25 centimeter elevation classes)

RESULTS and DISCUSSION: GPS data detailing many emergent Phragmites australis locations (N=268) in a northern area of the Great Marsh were collected over several recent growing seasons. Mean elevation of these sites was determined to be 1.33 meters with a standard deviation of 0.14 m. 87% of the sites were located at elevations ranging between 1.2 and 1.5 meters. 95% of the sites were between 1.1 and 1.6 meters. Many of the Phragmites sites show an association with areas of moderate (albeit subtle) slope change within the marsh platform, at elevations similar to those that might be encountered near the marsh edge and regions of transition into higher ecotones. The elevation of ditched areas located south of the Plum Island Turnpike and north of the Pine Island Causeway appear to be approximately 10 cm lower than ditched areas south of the Pine Island causeway. The reason for this observed difference is not understood. Relationships to restrictions in tidal flow and increasing presence of winter ice as well as gradual subsidence following the construction of causeways have been discussed as potential mechanisms (see Turner 2004). In addition to the elevation data, porewater chemistry, particularly sulfides and salinity, may be useful for explaining the patterns of Phragmites colonization of this area.

The National Center for Airborne Laser Mapping (NCALM) was contracted by the Plum Island Long Term Ecological Research (LTER) Program to collect the lidar data used in this study. Phragmites location data was provided by Merrimack Valley Planning Commission (MVPC) / Eight Towns and the Bay. MVPC data is for planning purposes only and should not be used for regulatory interpretation or boundary definition.

N = 268 Mean = 1.33 mSD = 0.14

INTRODUCTION AND DATA: Phragmites australis, the invasive reed, has been expanding rapidly in the northern section of Plum Island Sound, not only at the upland edge but also in the middle of the open marsh. We examined the relationship between the location of Phragmites patches and marsh elevations. The National Center for Airborne Laser Mapping (NCALM) acquired small footprint lidar data over a research area defined by the Plum Island Long Term Ecological Research (LTER) Program on April 18-19, 2005. A second flight was also completed in 2006. The 2005 survey area was covered by 48 flight lines. Two GPS reference stations were used during the survey; both were located in the parking lot of the Plum Island Airport. Reference station coordinate differences of less than 0.023 meters in both the horizontal and vertical positions were obtained. The bare-earth elevation classification product seen above is gridded at 1 meter cell size. Phragmites data was collected by Peter Phippen and Geoff Walker during the growing seasons of 2006-2007. GPS error is estimated at approximately 3 meters.

R. R. Turner. 2004. Coastal wetland subsidence arising from local hydrologic manipulations. Estuaries 27: 265-272

Image form Google Earth