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Visualizing Wetland Health over Time:

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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).
    (Note: MVHimage software is now AnalyzingDigitalImages, available in the DEW software bundle)
    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.
Wetland area in 1831. The total area of the wetland was 426.5 Acres.
Image of wetlands taken in 1848. The total area of the wetlands was 289.4 Acres
Image of wetlands in 1874. The size of the wetlands has decreased significantly to 120.6 Acres in 43 years.


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.
In 1952, the area of the wetlands is at 43.6 Acres, with a landfill and purgatory cove buld next to it.
By 1970, The landfill keeps increasing into the wetlands. The new size of the wetlands is a mere 24.6 Acres.
By 2001, the wetlands has decreased in size to 22.1 Acres.

    Aerials can be used to reference where site photographs were taken in the field
Aerial photograph of the wetlands. The wetlands is surrounded by Purgatory Cove in the north, the Charles River to the west, a park to the south and the landfill to the east. There is a Deciduous Wooded swamp around the periphery of the swamp and a Shrub swamp in the center.

Field Site Photography

    Document wetland functions and processes.
Example: The hydrologic fluctuations of Flowed Meadow were captured over time, making water level comparisons possible.
Image of the swamp pump house
Image of the pump outlets to the river
Image of a channel full of water with some flooding before pumping.
Same channel, but this time after pumping, and it is relatively dry.
    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. 

Picutre of a field in visible light
Same field without the green filter. You can see those that are dark (reflect little light) are healthy but those that are reflecting light aren't healthy

Example: Vegetation in Flowed Meadow Swamp near landfill appears stressed.
Another picture of a field without a filter (all visible light)
Same field, but without the green filter. You can once again identify unhealthy plants that look reflect too much light (are too light in the picture).

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.
Another picture of a field in visible light.
Same field, but this time in near infrared light. Healthy vegetation looks white and the unhealthy plants look slightly darker.



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.
1999 landsat satellite data image of Eastern MA, zoomed in to show Flower Meadow.
Better image of the Flowed Meadow that is dominated by near infrared light. The high level of infrared reflectance indicates healthy vegetation.
    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.
Image of MVHimage being used to calculate NDVI values. By comparing areas of red (high infrared light) to areas of green (high red light) and blue (high green light), we can see where vegetation is healthiest. Then you set a mask such that the program displays the infrared light as black and whites out everthing else to see the contrast between healthy and unhealthy regions.

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.)

Land cover typed in the Flowed Meadow Swamp and Upland. 34% Healthy Vegatation, 29% Water and/or wetland cover, 20% Paving, and 17% Vegetation, Soil and Rock Mix

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.
Hard to read satellite data image of Flowed Meadow Swamp. border=
Clustered satellite image (20 clusters) -- represents an accurate portrayal of the swamp.




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.

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