Description of the application:
The goal of this assignment was to calculate the loss of farmland
soils in Duxbury, Massachusetts due to an increase in impervious surfaces by
using raster data. With an increase in urban development, there are more
impervious surfaces taking over the town of Duxbury, leading to a decrease in
farmland soils that are considered “prime farmland,” “farmland of statewide
importance,” and “farmland of unique importance.” Calculations were performed to determine how much of these areas are present in Duxbury.
Table 1:
|
Count (sq
meters)
|
Square
Kilometers
|
Total
study area size
|
62,326,600
|
62.33
|
Prime
Farmland
|
4,702,600
|
4.703
|
Farmland
of statewide importance
|
9,076,600
|
9.08
|
Farmland
of unique importance
|
2,470,300
|
2.47
|
Table 2:
|
Count (sq
meters)
|
Square
Kilometers
|
Prime
farmland lost
|
484,600
|
0.48
|
Farmland
of statewide importance lost
|
803,300
|
0.80
|
Farmland
of unique importance lost
|
62,600
|
0.06
|
How it was performed:
This process was performed using ArcMap and raster data provided by
the state of Massachusetts. The study area for this process was Duxbury (the town I chose), and shapefiles were created for the study area. The
raster data provided were for Massachusetts soils, and a “Map Unit” table was
provided that describes the different types of soils, and a field called
“MUKEY.” A join was performed between the study area soil raster dataset and
the Map Unit table with the shared “MUKEY” field to determine the location of
the farmland soils. The statistics tool in the attribute table on ArcMap was
used to calculate the “count” of the MUKEY, and the count field was converted
to square kilometers from square meters (COUNT * 100 to get square meters).
Next, the impervious layer raster was used and extracted to the study area. A
combination was performed to determine the amount of farmland lost for the three
categories, while another join was performed. This combination and join allowed
me to get the COUNT for the farmland lost (Table 2).
Figure 1: A map of study area
Results and Conclusions:
Based on Table 1, Duxbury is 62. 3266 square kilometers. Of the entire
area size, 4.7026 square kilometers is considered prime farmland, 9.0766 square
kilometers is considered farmland of statewide importance, and 2.4703 square
kilometers is considered farmland of unique importance. Based on Table 2,
0.4846 square kilometers of 4.7026 (approximately 10%) of prime farmland was
lost, 0.8033 square kilometers of 9.0766 (approximately 8.9%) of statewide
important farmland was lost, and 0.0626 square kilometers of 2.4703
(approximately 2.5%) of uniquely important farmland was lost.
We were visited by Maggie Payne who works for the USDA NCRS. According to Payne's presentation, the maps were made at
different times, and the data was collected based on ground conditions. This is
a limitation for the study because the ground conditions can change every day,
and impervious surfaces are constantly being added due to rapid urban
development. It
would be interesting to determine why these farmland areas are being lost, for
example, are condominiums being built, or are new parking areas being paved,
etc. Determining how many parking areas and shopping malls are being developed
on top of prime farmland can help conservationists to stop the excessive loss
of farmland. Although 10% doesn’t seem like a high percentage of farmland lost,
it would be better if it could remain less than 2%, in my opinion.