Assessment of the effects of water regimes
2000 Base Version 1 executed at a 2-mile resolution (2000B1 (2 Mile))
versus
Natural System Model Version 4.6 Final (NSM_v4.6F) on
Foraging Conditions for Short-legged Wading Birds in South Florida
by
Jane Comiskey and Louis J. Gross
The Institute for Environmental Modeling
University of Tennessee, Knoxville
Knoxville, Tennessee 37996-1610
(Copyright University of Tennessee - 2003)
Hydropattern effects on wading birds are a function of water depth,
duration and areal extent of inundation, and timing of water flows
in areas that provide suitable foraging habitat.
The ATLSS Short-legged Wading Bird Foraging Potential Index (BPI) Model
uses
SFWMM restoration scenario hydrology output to make spatially explicit
estimates of the occurrence of water in the depth ranges that restrict
wading bird foraging and express depth
effects as changes in the spatial pattern of breeding potential over
the model area. In this evaluation, output from the Natural Systems
Model (NSMv4.6F) is compared to that of the SFWMM baseline scenario
2000B1.
Because of differential spatial effects of proposed hydrologic
modifications for South Florida, when we compare the results of two
hydrologic scenarios some regions of the model area will show changes
favorable to wading bird foraging for a given year, while other regions
for the same year will reflect a deterioration of conditions. The
spatial and temporal dynamics of rookery formation involve the
interplay of many factors and are not well understood; therefore, it is
difficult to ascertain the effects of predicted foraging potentials on
breeding activity. For example, because suitable wading bird rookery sites
are not distributed uniformly across the South Florida landscape,
a direct comparison of the magnitude of suitable foraging area available
under alternative scenarios would be misleading.
Therefore, interpretation of current results should focus
on areas where most birds have traditionally
nested. Those areas are located (1) along the eastern part of WCA-3A, WCA-3B,
and Northeast Shark River Slough (the
Northeastern Rookeries), and (2) in the transition zone between Shark River
Slough and the mangrove estuaries (the
Southwestern Rookeries)
(see rookery figure).
SESI result comparisons are presented for the SFWMD Indicator Regions
as well as ATLSS 3-panel maps.
Note that the Ridge & Slough indicator regions have been subdivided
for these analyses into two groups: (1) those that fall in the WCAs
(WCA-2 and WCA-3) and (2) those in Everglades National Park.
Considering these regions as a single group
masks divergent trends in the WCAs versus the Slough system to the south.
Model years are ranked by mean
water depth (ponding) over the model area (see year ranking graph and table).
Assessment of Comparison Maps
Wet Years (as measured by ponding)
FCI values for the wet years of
1995 ,
1970 , and
1969
indicate that suitable foraging conditions are somewhat more likely to exist
under NSM in what are currently the deeper water areas of the
WCAs and in the southern portion of North Taylor Slough, while
conditions are more likely to be favorable under 2000B1 through
Shark River Slough and, as deeper water precludes foraging in the Slough
itself, along the periphery.
Dry Years (as measured by ponding)
FCI values for dry years
( 1989 ,
1990 ,
1971 )
indicate that foraging conditions become somewhat localized in
the wetter
areas of the WCAs and the Shark River Slough system in the driest years.
FCI values tend to be higher under NSM in northern and NE Shark River Slough,
and along the periphery of the Slough,
while those under 2000B1 are sometimes higher in deeper water portions of
the WCAs. However, there is variation from year to year in these effects.
Average Years (as measured by ponding)
In the average ponding years of
1972 ,
1991 , and
1984 ,
patterns of foraging conditions indicated by FCIs and patterns of
relative FCI differences are variable. More extensive areas of
positive FCIs are seen in the WCAs and in some years in the Southwestern
Rookery area under NSM, while higher values are often seen under
2000B1 in the flowway of Shark River Slough and in NE SRS.
Average of All Years
The figure showing the
average of all years masks the divergent trends seen in wet vs. dry years.
Small advantages in foraging conditions are seen in Shark River Slough and
NE SRS under 2000B1, while values are roughly equivalent to those under
NSM in most other areas where a difference is seen.
Assessment of Line Graphs For Indicator Regions
LNWR
The FCI
time series graph for the LNWR
indicator regions shows substantially higher foraging index values under NSM
for all but the driest years, when values are slightly higher under 2000B1.
Ridge & Slough (north)
The FCI
time series graph for the Ridge & Slough (north) indicator
regions shows slightly higher foraging index values under NSM
in average to wet years and roughly equivalent (low) values for the
two scenarios in dry years.
Ridge & Slough (south)
The FCI
time series graph for the Ridge & Slough (south) indicator regions
shows consistently higher foraging index values under 2000B1 in all
but the driest years.
Marl Prairie
The FCI
time series graph for the Marl Prairie indicator regions
shows a pattern of low values for both scenarios in dry
years and higher values in wetter years. FCI values for
NSM are somewhat higher than those under 2000B1 in intermediate years
and slightly higher under 2000B1 in wet years, with few differences between
scenarios.
Big Cypress National Preserve
The FCI
time series graph for Big Cypress National Preserve indicator regions
shows minimal foraging conditions under
both scenarios, improving somewhat in wet years.
Summary
In relatively dry years,
FCI values under NSM are generally greater relative to 2000B1 in
Shark River Slough and Northeast SRS, while FCI values under 2000B1
are sometimes slightly higher in wetter portions of the Water Conservation
Areas encompassing
the Northeastern Rookeries. In intermediate to wet years the pattern
is reversed,
with generally higher values under NSM in the WCAs and higher values under
2000B1 in Shark River Slough and Northeast SRS.
Considering years in a sequence of dry to wet hydrologic conditions,
as water is added to the system it can be seen that advantages diminish
for both (a)
2000B1 in deep water areas of the WCAs and (b) NSM in the flowway
and periphery of Shark River Slough. Under higher surface water
conditions, short-legged wading bird foraging is significantly
curtailed under both scenarios, but
in years when foraging is not precluded by high water
NSM produces higher FCI values relative to 2000B1 for
most of the area encompassing the Northeastern Rookeries, while
relatively higher values are seen under 2000B1 in the Southwestern
Rookery area and along the periphery of Shark River Slough
As with other index model comparisons, loss of spatial extent of
suitable foraging habitat for wading birds under 2000B1 relative to
conditions under the Natural Systems Model cannot be adequately
reflected in these comparisons.
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