Assessment of the effects of water regimes
2000 Base Version 1 executed at a 2-mile resolution (2000B1 (2 Mile))
Natural System Model Version 4.6 Final (NSM_v4.6F) on
Foraging Conditions for Long-legged Wading Birds in South Florida
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 Long-legged Wading Bird Foraging Potential Index (BPI) Model
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
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
(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
1970 , and
indicate that suitable foraging conditions are more likely to exist
under NSM in what are currently the deeper water areas of the
WCAs, 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 indicate that foraging conditions are localized in the wetter
areas of the WCAs and Shark River Slough
in dry years ( 1989 ,
FCI values are higher under NSM in Shark River Slough and NE SRS, while
those under 2000B1 are higher in LNWR and deeper water areas of WCA-2 and
Average Years (as measured by ponding)
In the average ponding years of
1991 , and
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 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 slightly higher under NSM in most other
areas where a difference is seen.
Assessment of Line Graphs For Indicator Regions
time series graph for the LNWR
indicator regions show substantially higher foraging index values under NSM
for all but the driest years, when values are higher under 2000B1.
Ridge & Slough (north)
time series graph for the Ridge & Slough (north) indicator
regions shows somewhat 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)
time series graph for the Ridge & Slough (south) indicator regions
shows considerable year-to-year variation in relative foraging index values.
However, there is a consistent trend in that in
dry years FCI values are generally higher under NSM, while higher
values are seen under 2000B1 in wetter years.
time series graph for Marl Prairie indicator regions
shows a pattern of low values for both scenarios in dry
years and higher (roughly equivalent) values in wetter years.
FCI values under NSM are
distinctly higher than those under 2000B1 in intermediate years.
Big Cypress National Preserve
time series graph for Big Cypress National Preserve
indicator regions shows minimal foraging conditions under
both scenarios, improving somewhat in wet years.
In relatively dry years,
FCI values under NSM are greater relative to 2000B1 in
areas of Shark River Slough and Northeast SRS,
while FCI values under 2000B1 are somewhat higher in the
Water Conservation Areas, encompassing the Northeastern Rookeries.
In wetter years the pattern is reversed, with 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, 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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