Geoscience Reference
In-Depth Information
In earlier work the statistical association between land cover variables mapped
using high resolution satellite imagery (impervious cover, tree cover, and trees
and crops in the riparian buffer zone) and stream ecology assessments was
documented across 246 small watersheds within central Maryland (Goetz et al.
2003
; Snyder et al.
2005
). These watersheds spanned a wide range of land
uses, from predominantly agricultural to mostly residential. Stream conditions
assessed by state departments of natural resources and other groups made use
of indices of biological integrity (IBI), and stream ecological health was ranked
as excellent, good, fair, or poor, based on a combination of the IBI scores
and physical stream properties such as dissolved oxygen, pH, and temperature
(Van Ness et al.
1997
;Yetman
2002
). Related analysis of land cover variables and
landscape configuration metrics, such as mean distance from impervious areas to
the stream channel along a topographically defined flow path, and indices which
define the dispersion or aggregation of land cover within the watershed, indicated
the potential of these as independent predictors of stream biotic health (Snyder
et al.
2005
). Most recently, the research expanded that analysis to the state of
Maryland, making use of the Maryland Biological Stream Survey (MBSS) data
sets, and showed that both IBI and nEPT had a strong correlation to moderate
resolution imagery (30 mLandsat imagery) (Goetz and Fiske
2008
). Here the focus
is on extending these earlier analyses to another geographic region with quite
different geological substrate and a different set of biotic indicators, and testing the
relative utility of landscape configuration in this context.
4.2 Study Area and Data Sets
4.2.1 Study Area
The study area comprises the southern portion of New England, including the states
of Massachusetts, Rhode Island, Connecticut, and southern Vermont (Fig.
4.1
).
Weather in the region is characterized by warm and humid summers, with rainfall
generally around 90-150 cm annually. Daily winter low temperatures tend to
remain below freezing from November through March, although winter temper-
atures and snowfall have both increased in the four decades preceding 2005
(Burakowski et al.
2008
).
The watersheds we focused on cover approximately 7000 km
2
of formerly
glaciated land underlain by mostly granite and metamorphic bedrock. These
watersheds include most of the large drainage systems in the area including Narra-
gansett and Buzzard's Bays, and the Connecticut and Taunton rivers. Land cover in
this area is generally forested with small amounts of agriculture in the Connecticut
River valley, cranberry growing in Southeastern Massachusetts, and steadily
increasing exurbanization characterized by low density residential development
scattered between large urban centers like Boston, Providence, and Worcester.
