floodplain ecosystem response to climate variability and land-cover and land-use change in lower...
TRANSCRIPT
RESEARCH ARTICLE
Floodplain ecosystem response to climate variabilityand land-cover and land-use change in Lower MissouriRiver basin
Yuyan C. Jordan • Abduwasit Ghulam •
Robert B. Herrmann
Received: 17 November 2011 / Accepted: 17 April 2012 / Published online: 3 May 2012
� Springer Science+Business Media B.V. 2012
Abstract This contribution aims at characterizing the
extreme responses of Lower Missouri River basin
ecosystems to land use modification and climate change
over a 30-year temporal extent, using long term Landsat
data archives spanning from 1975 to 2010. The inter-
annual coefficient of variation (CoV) of normalized
difference vegetation index was used as a measure of
vegetation dynamics to address ecological conse-
quences associated with climate change and the impact
of land-cover/land-use change. The slope of a linear
regression of inter-annual CoV over the entire time span
was used as a sustainability indicator to assess the trend
of vegetation dynamics from 1975 to 2010. Deduced
vegetation dynamics were then associated with precip-
itation patterns, land surface temperature, and the
impact of levees on alluvial hydrologic partitioning
and river channelization reflecting the links between
society and natural systems. The results show, a higher
inter-annual accumulated vegetation index, and lower
inter-annual CoV distributed over the uplands remain-
ing virtually stable over the time frame investigated;
relatively low vegetation index with larger CoV was
observed over lowlands, indicating that climate change
was not the only factor affecting ecosystem alterations
in the Missouri River floodplain. We cautiously
conclude that river channelization, suburbanization and
agricultural activities were the possible potential driving
forces behind vegetation cover alteration and habitat
fragmentation on the Lower Missouri River floodplain.
Keywords Remote sensing � Coefficient of variation �Normalized difference vegetation index �Land-cover and land-use change
Introduction
Habitat degradation is a process by which natural
habitat is rendered less functionally able to support an
originally present species (Groom et al. 2006), and
habitat fragmentation that is closely associated with
climate change and human activity is the most
important cause of species extinction worldwide
(Barbault and Sastrapradja 1995). As characterized
by increasing water temperature and changes in
precipitation patterns that manifest themselves as
changes to stream flow regimes, and terrestrial and
oceanographic hydrologic cycles, climate change may
alter available environmental conditions, and thus
cause observable shifts in geographic distribution of
plant and animal species (Malmqvist and Rundle
2002; Dudgeon et al. 2006). Urbanization and agri-
cultural expansion are primary human activities at
landscape scale that account for degraded water
Y. C. Jordan � A. Ghulam (&) � R. B. Herrmann
Department of Earth and Atmospheric Sciences, Center
for Environmental Sciences, Saint Louis University,
St. Louis, MO 63103, USA
e-mail: [email protected]
123
Landscape Ecol (2012) 27:843–857
DOI 10.1007/s10980-012-9748-x
quality and natural resource over-exploitation, and
eventually will exacerbate the ecological impacts of
global climate changes (IPCC 2001; Allan 2004).
The floodplain of the Lower Missouri River, once
the habitat of supporting abundant and diverse aquatic
fauna and flora, has experienced dramatic urbanization
and river channelization in the past century. The
federal endangered species list for Missouri State
indicates that most of the habitats of the endangered
and threatened species are associated with alluvial
wetland and river floodplains (U.S. Fish & Wildlife
Service office 2009). With the dramatic expansion of
human population, the areas as suitable habitat for
wildlife have been converted into agriculture and
urban area, inducing a loss of biodiversity (Sechrest
and Brooks 2002).
The impacts of human activities on the Mississippi
River system have been explored in number of studies.
For example, Belt (1975) demonstrated that the
engineering modifications on the upper Mississippi
River coincided with several marked shifts in flood
response; Pinter and Heine (2005) indicated that the
engineering construction at the Lower Missouri River
altered the hydrodynamic and morphodynamic pro-
cesses of the fluvial system driving flood magnifica-
tion. Such a flow regime reconfiguration has the
potential to have great impact on the ecosystem on the
floodplain. River regulation and channel construction
have been shown to decrease floodplain tree growth
and productivity on some rivers (Reily and Johnson
1982; Middleton and McKee 2005). River morphol-
ogy explained by channel patterns and channel forms
is the dominant controlling factor of the availability of
shallow and slow water habitat even in reaches where
the hydrograph is more intensively altered (Jacobson
and Galat 2006). Unfortunately, such an important
sanctuary for floodplain biodiversity has been lost on
many intensively engineered rivers in the United
States. The re-configurations to channels and flood-
plains have resulted in loss of biodiversity (Committee
on Missouri River Ecosystem Science et al. 2002).
Climate change studies indicate that the central
U.S. has cooled by 0.2–0.8 K while most other major
land regions experienced a summer warming trend
over the last 25 years (Pan et al. 2004). The local
reduction of warming predicted for the next several
decades over the central U.S., including the Lower
Missouri River flood plain, is associated with changes
in low-level atmospheric circulation that leads to
replenishment of seasonally depleted soil moisture,
thereby increasing late-summer evapotranspiration
and suppressing daytime maximum temperatures
(Pan et al. 2004). Causal attribution of recent biolog-
ical trends to global climate change is complicated
since non-climatic influences dominate local, short-
term biological changes (Parmesan and Yohe 2003).
Vegetation changes, as an important component
of terrestrial ecosystems, can provide informative
index for understanding land-cover/land-use (LCLU)
dynamics, and interactions between human activities
environment and climate change via coupling the
phenologic effects and the anthropogenic impacts on a
long basis (Edwards and Richardson 2004). Remote
sensing has obvious advantages in monitoring spatio-
temporal dynamics of vegetation, water and energy
cycles at terrestrial scales. Vegetation indices using
spectral measurements have been developed to qual-
itatively and quantitatively assess vegetation cover
(Bannari et al. 1995). Chlorophyll in live plant leaves
strongly absorbs the red radiation for use in photo-
synthesis, and on the other hand the cell structure of
live green leaves strongly reflects near-infrared (NIR)
radiation. Hence, the healthy plants with more leaves
will have less reflectance for the red light and more
reflectance for the NIR light. The normalized ratio of
these two spectral regions is the well-known normal-
ized difference vegetation index (NDVI), which had
been successfully utilized to monitor and assess
regional to global-scale vegetation covers (Weier
and Herring 2011).
The goal of this paper is to evaluate the potential
causes of habitat quality alteration in the Lower
Missouri River floodplain by assessing the association
between presumed independent variables of climate,
land-use, and river engineering that may contribute to
the observed habitat degradation, and response vari-
ables NDVI and land surface temperature (LST).
Following description of the study area in second
section, data acquisitions and processing methods will
be discussed in ‘‘Data and methodology’’ section.
Terrestrial vegetation dynamics and temporal trends
will be associated with precipitation patterns, LST
changes, river channelization and urban expansion,
and the driving forces of vegetation changes on
the Lower Missouri River floodplain area, and the
subsequent potential environmental impacts to the
habitat quality alteration will be discussed in ‘‘Results
and discussions’’ section.
844 Landscape Ecol (2012) 27:843–857
123
Study area
The study area focuses on the floodplain from the town
of Portland, Missouri, downstream to St. Charles,
Missouri, a distance of 138 km along the Lower
Missouri River, and Portland is 183 km upstream of
the confluence of the Missouri and Mississippi River
(Fig. 1). The Missouri River flows from the northern
Rocky Mountains along the continental divide, and
flows generally south and eastwardly to join the
Mississippi River. The Missouri River descends at a
steady slope of about 17.16 cm/km from west to east
until it joins the Mississippi River.
The climate of Missouri is continental type with
distinct alteration of seasons characterized by wide
ranges in temperature, and irregular annual and
seasonal precipitation. In the summer time, the moist
and warm air masses blown from the Gulf of Mexico
bring abundant rainfall for this region. The elevation
in this area ranges from 93 to 300 m. The highest
elevation is located at the north of the Missouri River
channel which is primarily covered by deciduous oak-
hickory forest (upland). The southern part of the study
site is lowland agricultural fields predominantly
covered by corn and soybean cropland, growing
period ranging from April to October.
Fig. 1 Study area from Portland to St. Charles, MO (See the online version for the color version of this figure)
Landscape Ecol (2012) 27:843–857 845
123
By the late 1970s the Missouri had been totally
channelized, both federal and non-federal levees were
established along the river channel from Portland to
St. Charles, to provide protection from 20 to 5 %
probability floods to the agricultural lands (U.S. Army
Corps of Engineers 2003). The river and the floodplain
in this area are subjected to the natural physiographic
and geological character of the river, and the human
modifications.
Data and methodology
Data collection
Clear sky Landsat images including the Multispec-
tral Scanner (MSS), Thematic Mapper (TM) and
Enhanced Thematic Mapper Plus (ETM?) spanning
from 1975 to 2010 were collected. Geometric correc-
tion was performed for the MSS images collected
before 1990. The MSS data were re-sampled to have
30 m spatial resolution that is consistent with the
TM/ETM? data. The MSS, TM/ETM? sensors have
different radiometric resolutions, hence their respec-
tive digital numbers (DNs) carry different levels of
information that cannot be directly compared. Con-
verting the images to surface reflectance as described
later in this section will eliminate the problems of
comparing data with different levels of quantization.
An instrument malfunction occurred onboard ETM?
on May 31, 2003 due to the failure of the Scan Line
Corrector (SLC) designed to correct the undersam-
pling of the primary scan mirror. Consequently, the
ETM? data collected after May, 2003 has been
subject to an increased scan gap. Gap filling was
performed for the images collected after 2003 follow-
ing Scaramuzza et al. (2004) to correct the missing
strips in the data. Satisfactory results were achieved
after the gap filling processes. Radiometric calibra-
tions and atmospheric corrections were performed to
derive surface reflectance using QUick Atmospheric
Correction (QUAC) (Bernstein et al. 2005) available
with ENVI� image processing and analysis software,
from EXELIS Visual Information Solutions. Spatio-
temporal dynamics of annual precipitation were used
in this study to separate the contributions of natural
forcing from anthropogenic disturbances. Precipita-
tion data obtained from the Tropical Rainfall Measur-
ing Mission (TRMM), a joint mission between NASA
and the Japanese Space Exploration Agency (JAXA)
launched on November 27, 1997, were used in this
study. These measurements are on 0.25� 9 0.25� cell
between 50� south and 50� north of latitude (Huffman
2007). The original files in HDF format were down-
loaded from NASA’s TRMM ftp site (disc2.nas-
com.nasa.gov, product 3B43). These data showed
monthly average precipitation rate in mm/h, and were
converted to yearly total precipitation in mm in the
IDL programming environment.
The flow frequency data were obtained from The
USACE Upper Mississippi River System Flow Fre-
quency Study (U.S. Army Corps of Engineers 2003),
which calculated flood frequencies for each of the
USGS streamflow-gaging stations using standardized
methods. These calculations provided flood profiles for
the 2, 5, 10, 20, 50, 100, 200, and 500-year recurrence
floods under the 2007 channel condition. Kriging
interpolation was used to predict the potential area
subjected to flood inundation along the river channel.
We also collected field measured temperature and
precipitation data over six standard weather stations
across the study area (Fig. 1) from 1975 to 2010. The
station-average method was used to interpolate data
missing in the annual record. The purpose of these
ground data was to examine the driving forces behind
the prospective environmental change over a longer
period when TRMM data were not available, and
calibrate any existing bias or offset contained in the
TRMM derived precipitation.
Temporal changes of vegetation indices
The inter-annual coefficient of variation (CoV) of
NDVI and precipitation were used to measure the
vegetation and precipitation dynamics to understand
the potential influences that contribute to environ-
mental change. The statistics of CoV had been widely
used to determine the spatial difference of temporal
variability of the vegetation activity of the world
(Weiss et al. 2001; Sun et al. 2010). The changes in the
value of the pixel level CoV over time can be
interpreted as a measure of vegetation dynamics over
the time period. In statistics, CoV is a value calculated
from the average, or mean and the standard deviation
of the NDVI series in each pixel (Milich and Weiss
2000), that gives the slope of year by NDVI value on a
pixel by pixel basis, as shown in the following
formula.
846 Landscape Ecol (2012) 27:843–857
123
CoV ¼ rl¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1n
Pni9¼1 xi� lð Þ2
q
1n
Pni¼1 xi
where l is the temporal average or mean NDVI value
for each pixel, r is the standard deviation of the NDVI
time series from 1975 to 2010 and Xi is the NDVI
value in each pixel for a specific year. The seasonality
and phenology of vegetation and agricultural activities
may affect observed NDVI values and trends. Such
impact may be too substantial to neglect at a pixel
level measurements, especially over land cover types
subject to seasonal manipulation by agricultural
activities. Therefore, one may expect that remote
sensing images are collected at least in the same month
of the year to deduce an inter-annual times series
analysis. However, optical remote sensing data, par-
ticularly those collected during rainy season over wet
climate, are often contaminated by clouds. In our case,
there is at least one Landsat image collected during the
summer months from June to August for the period of
1975–2010. Care was taken to select the images of the
same months of the years. If more than one image were
available for the summer months, then the average
NDVI was employed as a seasonal average data. To
minimize the effects of vegetation phenology and
human activities on the temporal time-series analysis,
we employed spatially mean of total NDVI, denoted as
mean-total NDVI hereafter, which is defined as the
ratio of the sum of NDVI values for all pixels over
the total number of pixels of the whole study region. The
linear regression slope of time series mean-total NDVI
over observed time frame is used as an indicator to
assess the spatio-temporal trend of vegetation dynamics
from 1975 to 2010 (Bai et al. 2005; Sun et al. 2010). The
slope a can be derived from linear regression model
Y = aX ? b, where, Y is the yearly accumulated
NDVI, X is the time array series, and a is the slope, and
b is regression coefficient. Such vegetation dynamics
(temporal trend) then can be associated with natural
growing forest and farmland or urban areas, reflecting
the correlation between natural precipitation watering
pattern and human activity (Sun et al. 2010).
Urban expansion estimation
To explore additional impacts of human activity, on
floodplain eco-systems, spatio-temporal dynamics of
urban areas were extracted for different years. Unlike
vegetation growth that showed great fluctuation by
month and year, urbanization was a slow process over
time. Therefore, we selected a limited number of years
with almost a decade interval, namely, 1976, 1991,
2001, and 2010 for urban area extraction. Examining a
number of supervised classification techniques with
different classifiers, we found that maximum likeli-
hood classification based on the Principle Component
Transform (PCT) of original spectral dataset was the
most suitable one for extracting urban areas. PCT was
an image enhancement technique used to highlight
spectral signatures, and successfully allied in mineral
exploration (Gabr et al. 2010), burn change detection
(Koutsias et al. 2009). PCT reduces the dimensionality
of the data while retaining as much as possible of the
variation present in the dataset (Pechenizkiy et al.
2004). We subsequently used first three components of
PCT to extract the urban areas from Landsat imagery
with maximum likelihood classification.
Channelization possible influence to floodplain
Landscape elevations were used to assess how water
stages interact with the ground surface. Two landscape
elevations were used in this study. The first one was the
National Elevation Dataset (NED; U.S. Geological
Survey 1999) derived from Light Detection and Rang-
ing (LIDAR) point cloud data, which had 3 m horizontal
resolution and 15 cm vertical resolution. This model
reflected the regulated current channel form and flood-
plain landscape condition after channelization.
We also synthesized a digital elevation model
(DEM) for the floodplain prior to channelization. We
obtained levee shape file data from Missouri Spatial
Data Information Service (MSDIS); these data con-
sisted of the geo-coordinates of the levees. We
registered the levees on the current DEM based on
the levees geo-coordinate. From the MSDIS levee data
we knew that the levee heights ranged from 2 to 6 m,
so we assumed that all levees were two meters high for
modeling the no levee channel condition. Using GIS
software, we subtracted the elevation at the levee
location on the current DEM to synthesize a pre-
channelization DEM of the river channel condition
without the levees. Because this project considered
only floodplain inundation changes, we ignored the
channel depth shown on these DEM data. In this step,
we had not routed the water or we had not hydrauli-
cally modeled based on conservation of mass and
Landscape Ecol (2012) 27:843–857 847
123
energy, hence the distributions of inundation were
simply the intersections of water surface elevations
that would exist under current conditions and how they
would intersect the floodplain topography under
current and pre-channelization conditions. This sys-
tematically over-maps inundation area in the pre-
channelization condition for discharges that did not
overtop the current levees (that is for 2- to 50-year
recurrence floods peak discharges).
The flood inundation map for different recurrence
intervals and floodplain topographic DEM were
overlain separately, providing different interval flood
stages for the current channel condition and for the
synthetic pre-channelization condition. As a result of
this comparison, we observed different inundation
frequencies on the floodplain at the study area under
two groups of floodplain conditions. The detailed
results of this part are shown in the discussion section.
Results and discussions
Spatial patterns of inter-annual mean NDVI
Initial inspection of the inter-annual mean NDVI data
showed a negative skew distribution with a long tail in
the negative direction of the data histogram. We used
Natural Breaks (Jenks 1967) classification scheme for
grouping the data into different categories. Our choice
of using this classification was based on the fact that it
places the class breaks on a histogram such that breaks
fall in the troughs, and classes represent natural
clumps inherent in the data. Therefore, the features are
divided into classes that best group similar values and
maximize the differences between classes.
The inter-annual mean NDVI values ranged from
-0.3 to 0.76 during 1975 to 2010 at the study area
(Fig. 2); the spatial distribution showed obvious varia-
tions, and the NDVI values were divided into five
categories manually based on the rough land cover
types. The values \0.15 were observed in the river
channel. The relatively higher values of the inter-annual
mean NDVI (0.16–0.4) mostly occurred in the flood-
plain and urban area, whose land cover was dominated
by sporadic vegetation. The NDVI values of land cover
type dominated by farmland range from 0.41 to 0.62.
The highest values of the inter-annual mean NDVI
appeared in the upland (forested area) with indices
0.63–0.76. The spatial patterns of the vegetation cover
not only reflected the spatial characteristics in climate,
topography, but also revealed the differences in alloca-
tion of water resources in human society, i.e., reduced
vegetation over rapidly developing urban areas and
altered flood plains, and larger values over hilly areas.
Spatial patterns of inter-annual CoV
Figure 3 presented the inter-annual CoV values
divided by equal intervals method. The values reflected
the salient spatial patterns of overall vegetation
Fig. 2 Spatial distribution of inter-annual mean NDVI over the last three decades (See the online version for the color version of this
figure)
848 Landscape Ecol (2012) 27:843–857
123
dynamics from 1975 to 2010. It exhibited an obviously
different distribution when compared to the inter-
annual mean NDVI. The areas with the lowest inter-
annual CoV values from 0 to 0.2 scattered in the high
elevation hilly area, indicating the least temporal
changes in vegetation with time. Inter-annual CoV
values increased in the lowland from 0.4 to 0.6. The
areas with the highest inter-annual CoV values were
mainly located in the floodplain and urban areas with
value of 0.6–1.
Comparing Figs. 2 and 3, the spatial distribution of
inter-annual mean NDVI and inter-annual CoV val-
ues, we found that in general the areas with inter-
annual mean NDVI less than 0.52 coincides with the
inter-annual CoV values between 0.4 and 1.0; these
regions were more related to cultivated land use and
urban area. When the inter-annual mean NDVI values
were higher than 0.53, the variation of vegetation
covering over years becomes smaller, these areas were
mainly dominated by forest area. The larger CoV
observed over urban and flood plain implied that the
human activity (e.g., agricultural and housing devel-
opment) may have been the driving factor behind these
changes.
Temporal variability of inter-annual mean-total
NDVI
In order to further demonstrate the annual trend of
NDVI dynamics in the study area, the inter-annual
mean-total NDVI values from 1975 to 2010 of the
whole study area were used to reflect the overall
vegetation dynamics. The results (Fig. 4) revealed
that there had been a slightly descending trend of
Fig. 3 The spatial distribution of inter-annual CoV of NDVI (See the online version for the color version of this figure)
Fig. 4 Inter-annual mean-
total NDVI trajectory from
1975 to 2010
Landscape Ecol (2012) 27:843–857 849
123
inter-annual mean-total mean NDVI for the last
35 years with minimum value of 0.41 in 2007 and a
maximum of 0.67 in 1999. During the period of
1975–1991, there were small fluctuations in NDVI
values, ranging from 0.5 to 0.64. From 1992 to 1995
the values decreased from 0.61 to 0.48 and the values
climbed up again from 1995 to 2000. After 2000, there
were 3 years of especially low NDVI values mainly
occured in 2006, 2007 and 2010. The decreasing trend
(slope = -0.002) was noticeable, and 11.2 % of the
variation of the NDVI could be explained by time series
although the regression was marginally not statistically
significant at a = 0.05 (F1, 31 = 3.926, p = 0.056).
Slope trend in Vegetation dynamics from 1975
to 2010
The slope factor of the linear regression of the inter-
annual mean NDVI over time (i.e., from 1975 to 2010)
was shown in Fig. 5. The slope value ranged from
-0.042 to 0.042 corresponding with red to green color
showed on the map, and the slope value was divided
into four categories manually based on the land-cover
types. The slope map presented those areas with
increasing vegetation cover in green color, and areas
with declining vegetation cover in orange and red
color. Those areas with orange color represent no
vegetation change and the regression line slopes were
close to zero. Positive slope values indicating vege-
tation increase was mainly distributed at the south side
of the river channel. Over the hilly area to the north of
the Missouri River, the vegetation cover showed
virtually no change, implying a stable natural habitat
less affected by human alterations. An obvious decline
in the amount of vegetation as demonstrated by
negative slope values was found at the northeast
corner of the study area which covers St. Louis county
and St. Charles County. Other notable vegetation
slope declining areas were distributed on the flood-
plain along the river channel. In St. Charles County
there have been extensive changes since 2000.
Comparing the Figs. 2, 3 and 5, a salient phenom-
enon could be noticed that those areas with low
accumulated NDVI values, high CoV and declining
trend of vegetation were all occurred on the floodplain
and urban areas. There were some corresponding
trends between these three distribution patterns, the
lower the total accumulated NDVI values, the higher
the CoV of total accumulation NDVI and the lower the
slope trends appeared, or vice versa. What were the
possible scenarios associated with the spatio-temporal
patterns of NDVI? The driving forces behind these
observations including the climate change and human
interference will be discussed in next section.
Observational connection to climate change
We collected temperature and precipitation data from
the Hermann, Warrenton, Weldon, St. Charles, Free-
dom and Union weather stations to examine the
Fig. 5 The temporal slope of NDVI derived from a linear regression analysis of data over 1975–2010. A positive slope value represents
increasing vegetation trend or vice versa (See the online version for the color version of this figure)
850 Landscape Ecol (2012) 27:843–857
123
climatic influence to the NDVI dynamics. These
stations are distributed following a stratified sampling
in the study area (Fig. 1). Unfortunately, we had no
temperature record for the Hermann station.
Figure 6 showed the temperature trajectories of the
five weather stations for the 35 years period between
1975 and 2010. The mean annual temperatures from
the five stations were different from each other, such
as in 2008 the temperature ranged from 52.46 �F in
Freedom to 63.52 �F in Warrenton. The results indi-
cated that the temperature trajectories of Warrenton,
St. Charles and Union had slightly positive slopes
(means increasing trend), while the Weldon and
Freedom presented slightly deceasing trends. The
temperature slope values were shown in Table 1,
ranging from -0.0375 to 0.082.
Figure 7 shows the precipitation trajectories at the
six weather stations from 1975 to 2010. One could be
seen from this figure that five stations had slightly
increasing trends of the annual precipitation while
Hermann had a negative precipitation slope, therefore,
a decreasing trend. Weldon had a highest precipita-
tion slope value, 0.3375 and the slope of Hermann
precipitation was -0.0169 (Table 1). The results of
statistical significance test for all the trend lines
showed that two trend lines of precipitation and one
trend line of temperature had significance value
(Table 1).
Linear regression (OLS) was used to detect tem-
poral trend of temperature and precipitation for each
location, where Kolmogorov–Smirnov tests were used
to test the normality (a = 0.05) and Durbin Waston
tests were used to check the presence of temporal
autocorrelation (Durbin and Watson 1950, 1951;
Sargan and Bhargava 1983). Only temperature data
over St. Charles station exhibited autocorrelation, and
most of datasets follows normal distribution with
exception of Precipitation in Warrenton (p = 0.04).
Comparing the trends and spatial distributions of
temperature and precipitation with the accumulated
NDVI, NDVI CoV, and NDVI slope map, we found
that the NDVI, CoV and NDVI slope distribution
patterns did not correlate with the temperature and
precipitation patterns. The lower inter-annual mean
NDVI, the higher NDVI CoV and declining NDVI
slope trends were main observations over the urban
and floodplain areas. The stable growing NDVI areas
were mainly distributed at relatively higher elevations,
for example, hilly areas. The temperatures had been
decreasing slightly in the Weldon and Freedom areas,
but the NDVI slope map showed that the vegetation
cover condition was quite stable in these two areas
from 1975 to 2010. From the Table 1, we could also
see that the precipitation pattern in this area was
dominated by an increasing trend.
The spatial distribution of yearly total precipitation
slope over the last 11 years derived from TRMM data
also showed a lightly increasing trend overall (Fig. 8).
However, some local decreasing in the south-east part
of the study area was observed. We investigated the
trajectory of spatially averaged yearly total precipita-
tion over the time period. As shown in Fig. 9, the
Fig. 6 Temperature
(1975–2010) trajectories
from five weather stations
(See the online version for
the color version of this
figure)
Landscape Ecol (2012) 27:843–857 851
123
overall increasing trend in precipitation was further
confirmed.
Based on these observations, increasing tempera-
ture and precipitation, it is expect that total NDVI
should have increased over time. However, the total
mean NDVI demonstrated a declining trend as shown
in Fig. 4. Therefore, we deduced that temperature and
precipitation were not the primary reasons causing the
vegetation quality alteration in the study area.
Urban expansion
Since 1822, the first settlers began heading west out of
Franklin, Missouri, people started to develop and
cultivate on the fertile land. The cultivated farmland
was increased dramatically since the 1940s due to the
stimulus policies of U.S. Department of Agriculture
programs. The most important factor in farming the
floodplain was the bank stabilization and navigation
program and subsequent levee construction (Ferrell
1996). With the population increase, the floodplain
had been further developed and populated. New
communities, such as New Town in St. Charles
County Missouri, built on raised mounds surrounded
by levees, were examples of recent urbanization built
on the floodplains, which consumed large amount of
previously permeable farmland with impervious sur-
faces (Kusky et al. 2008). Figure 10a shows the urban
area in 1976, 1991, 2001, and 2010. The urban area in
1991 was 0.54 km2 less than in 1976, however,
increased by 43 % from 303.44 km2 in 1991 to
434 km2 in 2010 (Fig. 10b). Comparing the urban
expansion with the total mean NDVI trajectory, we
came to a cautious conclusion that documented trend
in decreased NDVI is related mostly to urbanization.
Therefore, ecosystem quality alteration in the study
area may be attributed to human activity, in particular,
the urbanization the last two decades.
Channelization of Missouri River
Variation in NDVI in agriculture fields may not
necessarily be an indicator of environmental quality
degradation, high variation could be due to seasonal
harvests of crops. However, temporal variation (i.e.
biomass or overage stability) is one of important
functional properties of plant ecosystems (Hooper et al.
2005), and our datasets primarily reflect the naturally
occurred vegetation at annual scale, therefore our studyTa
ble
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852 Landscape Ecol (2012) 27:843–857
123
exhibit a long-term pattern of vegetation condition in
the floodplain coupled with channelization and agri-
cultural activities. Despite that trends over time were
difficult to demonstrate given the high within-year
variation that accompanies agriculture practices river
channelization may have potential environmental
Fig. 7 Precipitation
(1975–2010) trajectories
from six weather stations
(See the online version for
the color version of this
figure)
Fig. 8 Temporal slope of precipitation derived from a linear
regression analysis of time series Tropical Rainfall Measuring
Mission (TRMM) data for each pixel. For the time period
of 2000–2010, a positive slope value represents increasing
precipitation while the negative slope value shows decreasing
precipitation trend (See the online version for the color version
of this figure)
Landscape Ecol (2012) 27:843–857 853
123
influence on the floodplain ecosystems; elsewhere this
impact have been identified (Junk et al. 1989; Poff et al.
1997; Thoms 2003; Liu and Wang 2010; Watkins et al.
2010).
During the past two centuries, the Missouri River,
along with its adjacent wetlands and floodplains, had
been dramatically modified in various attempts to
promote transportation, agriculture, and development
(Criss and Kusky 2008). From the discussions above,
we have seen that the floodplain along the river channel
was characterized as highly variable vegetation system
showing low NDVI values, high CoV and a declining
vegetation trend. In this study, we explored the potential
impact of channelization to vegetation quality alteration
on the floodplain by comparing inundation modeling
with current channel status with and without levee
construction, assuming the condition without levee was
the pre-regulation channel condition.
For both channel conditions modeled with and
without levee, all the floodplains were inundated with
the 500, 200, and 100 years flood stages. For a
50 years flood, most of the levees stand higher than the
predicted water level. No significant inundation was
observed over the flood plains. However, the levee
Fig. 9 Inter-annual mean precipitation trajectory from 2000 to
2010
Fig. 10 a Urban cover area in 1976, 1991, 2001 and 2010 (See the online version for the color version of this figure). b Urban area
comparison in 1976, 1991, 2001 and 2010
854 Landscape Ecol (2012) 27:843–857
123
system was not a connected feature all along the
channel, and, therefore, water may overflow parts of
the areas. A 20-years flood seemed completely
constrained in the channel, and showed no overflow.
In other words, under the current channel condition,
when the water stage was lower than the 50 years/2 %
chance flood stage, there was no water overflow from
the channel to the adjacent floodplain.
When the levee height was removed from the
current DEM and overlain by predicted water levels
from 50, 20 and 10 years floods, the floodplain was
completely inundated. The red circle in Fig. 11a was
the levee location. The red circle in Fig. 11b shows
that the levee was removed to construct the assuming
pre-regulation channel condition. The levees possibly
decreased the opportunity of water over-bank flow to
the floodplain, and the ecological values of hydrologic
connections between a river’s main channel, back-
waters, and floodplain was emphasized in prior
researches (Gore and Shields 1995; Ward and Stanford
1995; USGS 1999). Levees were sporadically pro-
truding out of the water surface with the 5 years flood,
and most of levees were higher than the water surface,
therefore, no water overflows the river bank when it
was overlaid with 2 years/50 % chance of flood stage.
From Fig. 11a, b we could see that the flood stage
overflows the channel bank elevation after 50 years
flood stage, but for the assuming pre-regulation
channel condition without levees, 5 years flood stage
over passed the river bank and cover the floodplain.
According to statistics, 80 % of floodplain profiles had
overflow with the 5 years/20 % chance flood, and the
most of the rest of 20 % were located at the upper area.
The modeled inundation frequency for the assum-
ing pre-channelization condition was four times more
than the frequency of inundation under the current
channel conditions. The levees possibly decreased the
frequency and duration of inundation of the flood
plain, reduced sediment and nutrient exchanges
between floodplain and main channel. Inadequate
exchange could be worse for the floodplain ecosystem
in a period of low water stage. In these areas, the
decrease of overbank flow reduces the source of water,
soil and nutrition from the main channel for the growth
of vegetation, and reduces the medium for aquatic
fauna to move into floodplain to spawn and feed. This
hypothesis is consistent to the prior research that many
native fish and avian species experienced substantial
reductions, while nonnative species—especially
fishes—thrived in some areas (Committee on Missouri
River Ecosystem Science et al. 2002).
We acknowledge that quantifying the effects of
climate change and human activity on environmental
quality is a complicated task that requires extensive
inventories of plant and animal species. However, this
is beyond the scope of this contribution, and further
studies are needed to meet a solid outcome assessment.
Conclusions
This paper investigated the vegetation cover variation
connected with the role of human activity on rapidly
altering floodplain environmental quality in the Lower
Fig. 11 a Current river channel and floodplain profile at RM
96. b Assuming pre-regulation river channel and floodplain
profile at RM 96 (See the online version for the color version of
this figure)
Landscape Ecol (2012) 27:843–857 855
123
Missouri River floodplain using vegetation variables
derived from satellite data, and predicted flood
inundation scenarios from GIS modeling.
In the Lower Missouri River basin, the Missouri
River ecosystem recovery would benefit from a better
understanding of the causes of the habitat quality
alteration from natural and social perspectives. The
results show that the there were larger CoV of NDVI
over the river channel and urban areas, indicating all of
the social and economic stressors that channelization
engineering, and all of the social and economic
stressors that created the agricultural economy, subur-
banization, and urbanization may contribute to the
unstable ecosystem of Lower Missouri River basin.
These observations were further validated by trajecto-
ries of long-term temperature, precipitation, and flood
stage modeling using GIS. Overall, the inter-annual
total mean NDVI had decreased while precipitation
and surface temperature showed noticeable increase
due to regional climate variation for the time period
investigated. We came to a conservative conclusion
that human activities including suburbanization, river
channelization and levee engineering were potential
causes of environmental degradation and habitat
quality alteration in the Lower Missouri River basin.
Acknowledgments Authors would like to thank anonymous
reviewers and Dr. Robert Jacobson from Columbia
Environmental Research Center of U.S. Geological Survey for
his constructive comments on the manuscript.
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