Visualizing Wetland Health over Time:
Exploring the Imagery of Flowed Meadow Wetland in Newton, Massachusetts
Created by Deb Olstein in support of her practicum at the Antioch New England Graduate School
Introduction
Visual media and imaging techniques are powerful tools that may be used to further our understanding of wetlands.
This case study of Flowed Meadow Swamp, Newton, MA shows how three main types of visual analyses can provide
a unique story of wetland health and change over time:
Comparisons of maps and aerial photography
Site photography, and
Manipulation of satellite data
Flowed Meadow Swamp
Twenty two acre shrub and hardwood swamp
Adjacent to the Charles River in the Metro-Boston area
Once operated as a typical riparian marsh and swamp system of over 400 acres
Industrialization and urbanization (beginning in the early 1800’s) has drastically altered the swamp ecology
Historic Maps & Aerials
Depict the spatial distribution of Flowed Meadow Wetland over time.
Allow wetland area measurements and illustrate the steady expansion of streets and farmland in the upland.
Maps and aerials were analyzed using MVHimage software to calculate changes in wetland area (see example).
An analysis of the Flowed Meadow site maps and aerials show the swamp was extensively filled to accommodate urbanization over time.
Flowed Meadow swamp lost on the order of 404 acres over 170 years.
Trends in spatial distribution, size, and fragmentation of wetlands can tell us much about wetland health over time.
Historic Maps were obtained from the local historical society.
Wetland area was highlighted with green to make area pixel measurements more accurate.
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Aerial Photographs were obtained from the local planning department.
Landscape features such as the wetland and landfill were uniformly colored in each image to increase the accuracy of pixel area measurements.
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Aerials can be used to reference where site photographs were taken in the field
Field Site Photography
Document wetland functions and processes.
Example: The hydrologic fluctuations of Flowed Meadow were captured over time, making water level comparisons possible.
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Pictures made with Minus Green or Purple Filters may be used to amplify contrasting areas of plant health and other natural features.
Example: Vegetation in Flowed Meadow Swamp near landfill appears stressed.
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Example: Vegetation in Flowed Meadow Swamp near landfill appears stressed.
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Near Infrared Photography
The near infrared identifies vegetation patterns & distinguishes landscape elements.
Half of the sun’s energy is emitted in the near infrared (IR), energy that lies just beyond visible red light in the electromagnetic spectrum.
Healthy vegetation looks white in the IR because it reflects an enormous amount of IR energy; stressed plants reflect less IR.
Therefore, IR is commonly used in remote sensing to analyze patterns of vegetation health and distribution.
Infrared field photography of Flowed Meadow Swamp consistently showed the vegetation to be quite lush and healthy.
Occurrences of seed heads, trunks, and bare soil were exaggerated, so that wet areas, de-foliated trees, and snags were quickly seen and identified for further investigation.
Site Photos of Flowed Meadow Swamp: experiments with the Infrared filter.
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Indexing Satellite Data
Used to calculate percent land coverage type in wetlands and uplands.
Satellite data obtained from UNH’s EOS WEBSTER free digital library and see their new Landsat Clic 'NPic
When a Normalized Difference Vegetation Index (NDVI) is applied to satellite imagery, a mathematical formula
compares intensities of the reflected infrared and visible red light of a wetland area.
Areas of high infrared
reflectance and low reflectance of red are representative of healthy vegetation cover,
whereas areas of moderate red and infrared reflectance suggest an absence of vegetation and a high incidence
of other landscape elements such as paving, soil, or water.
MVHimage may be used to calculate
NDVI values in the Landsat color composites shown above.
LANDSAT data from 1999 showed that 34% of the Flowed Meadow area is composed of healthy vegetation (areas of open water and paving were also significant.)
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Clustering Satellite Data
Satellite data may be digitally grouped according to common spectral features. Pixels of similar light and color
intensities can be clustered or grouped together to identify landscape features such as water, soil, and lush vegetation.
The free software available through Purdue University, Multispec, will cluster satellite data in multiple levels of detail.
Clustering satellite data is a useful way to quickly map wetland habitat, compare several wetlands, and gain a preliminary
understanding of a wetland before visiting.
The resulting cluster map proved to be an accurate representation of the swamp.
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Conclusions: Learning about Place through Imagery
Comparing historic maps and aerial photographs of Flowed Meadow Swamp showed and measured wetland change over time (a loss of 404 acres).
Site Photography documented hydrologic aspects of the swamp and when combined with filters, illuminated vegetation health and landscape patterns.
The manipulation of satellite imagery identified percent land cover type, plant health, and spatial distribution of landscape elements in the Flowed Meadow
area. This data can be used as baseline information for further studies.
These types of imaging techniques inform our understanding of Flowed Meadow
Swamp history and current ecology, laying the groundwork for future restoration and protection efforts.
Find Data for Your Area
Landsat Clic 'N Pic – free satellite imagery for the United States
Additional Recommendations to Explore
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