1. Original Research Article
Mississippi River Ecohydrology: Past, present and future
Paul J. DuBowy *
Mississippi Valley Division, U.S. Army Corps of Engineers, Vicksburg, MS 39181-0080, USA
1. Introduction
Sustainability of large river systems requires an under-
standing ofthehistoricalconditions foundinpre-settlement
ecosystems and how anthropogenic changes have altered
these systems. The restoration or rehabilitation of these
large rivers can lead to increased carrying capacity and
biological diversity with resulting resistance to stress.
Ecohydrology is the analysis of integrated biological and
hydraulic processes at the landscape level with resulting
changes to hydrological, physical, chemical and ecological
attributes of aquatic systems, river basins, and adjacent
floodplains and riparian areas (Zalewski et al., 1997;
Zalewski, 2000). By extension, the Ecohydrological process
could be employed as a tool to guide rehabilitation protocols
through a careful analysis of hydrologic drivers and
other environmental stressors (Linke et al., 2012). These
alterations to drivers and stressors result in modifications
to water quality, biodiversity, and other ecosystem goods
and services. Consequently, Goals, Objectives, Targets and
Metrics of restoration projects can emanate directly from
these same Ecohydrological principles (DuBowy, 2010). The
key to the rehabilitation of sustainable river or coastal
systems is to incorporate human dimensions and values and
find middle-ground between continued economic growth
and the preservation and conservation of natural resources
and human well-being (Weinstein, 2008; Chı´charo et al.,
2009; Dufour and Pie´gay, 2009; Lockaby, 2009; Bunch et al.,
2011).
The Mississippi River catchment is the third largest
river system in the world. The Mississippi River, itself, is
over 3700 km long and, together with the Ohio and
Missouri Rivers, drains all or parts of 31 U.S. states and two
Canadian provinces. Because the Mississippi system varies
widely in hydraulics and hydrology from source to the Gulf
of Mexico, ecosystem sustainability likewise takes differ-
ent forms in different regions along the river. The effects of
river regulation, floodplain development, watershed mod-
ifications and inputs of agricultural chemicals present
constant challenges to ecosystem rehabilitation along the
Ecohydrology & Hydrobiology 13 (2013) 73–83
A R T I C L E I N F O
Article history:
Received 28 November 2012
Accepted 27 February 2013
Available online 26 March 2013
Keywords:
Mississippi River
Hydraulics and hydrology
Navigation and flood control
Nutrients and sediment
Invasive species
A B S T R A C T
For well over 100 years the twin objectives of navigation/transportation and flood-risk
management have led to an intensively managed Mississippi River system which,
hydrologically and hydraulically, has been radically altered. Additionally, human
disturbances have led to more recent environmental impacts, including increased
agricultural chemicals and industrial toxins, altered salinity and sediment loads, and
introduction of non-native species, resulting in a riverine and riparian ecosystem far
different from its historical condition. These anthropogenic impacts, combined, have led to
reduced biodiversity, resilience and ecosystem services provided to society. The goals and
objectives of ecosystem rehabilitation must include mechanisms to reverse the physical,
chemical and biological alterations to the Mississippi River. Implementing Ecohydrology
goals through the reestablishment of the historical floodplain is paramount to successful
remediation. Likewise, the ability to measure project success is critical to evaluating the
efficacy of the entire rehabilitation program.
Published by Elsevier Urban & Partner Sp. z o.o. on behalf of European Regional Centre for
Ecohydrology.
* Tel.: +1 601 634 5930.
E-mail address: paul.j.dubowy@usace.army.mil.
Contents lists available at SciVerse ScienceDirect
Ecohydrology & Hydrobiology
journal homepage: www.elsevier.com/locate/ecohyd
1642-3593/$ – see front matter. Published by Elsevier Urban & Partner Sp. z o.o. on behalf of European Regional Centre for Ecohydrology.
http://dx.doi.org/10.1016/j.ecohyd.2013.02.003

2. Mississippi River. Moreover, the continuing negative
impacts of non-native species present additional chal-
lenges to river rehabilitation. Consequently, sustainable
river and floodplain systems must be developed within the
context of the potentially different directions that other
societal uses have taken various reaches of the river
(DuBowy, 2010). This Mississippi River case study can be
examined as a primer for utilizing innovative Ecohydro-
logical techniques and concepts in the potential rehabi-
litation of extensive and important aquatic ecosystems.
The focus of this review is an examination of the
anthropogenic causes which have resulted in the current
altered/degraded river ecosystem, ongoing remediation
efforts on the Mississippi River, and implementation of
progressive planning and evaluation protocols to facilitate
future rehabilitation efforts.
2. Historical conditions
The Mississippi River is not a single homogeneous unit
(Fig. 1). From its source in northern Minnesota to the Gulf
of Mexico one can identify at least five distinct Mississippi
Rivers based on geomorphology and hydraulics. (1) The far
upper reach, from the river’s source at Lake Itasca,
Minnesota, to St. Anthony’s Falls (Minneapolis), Minnesota
(793 km length) is characterized as a typical boreal stream
with a calcareous, cobble streambed. (2) From Minneapolis
to the confluences with the Missouri and Illinois Rivers
(near St. Louis, Missouri; 1069 km), the Upper Mississippi
River (UMR) historically was a very shallow river with a
main channel and numerous paleochannels in a braided
configuration. (3) Below St. Louis to the confluence with
the Ohio River (Cairo, Illinois; 310 km), the Middle
Mississippi River (MMR) starts to develop a deeper,
broader cross-section with finer sediments. (4) The Lower
Mississippi River (LMR) begins at Cairo; the Ohio provides
most of the water in the Mississippi system, so the LMR is
extremely broad and deep (the Mississippi Alluvial Valley)
and is characterized by a sinuous course with many
oxbows, chutes and floodplain lakes (1027 km). While
these floodplain features often appear to be disconnected
from the main channel of the river, as the river stage rises
these backwaters and chutes frequently become recon-
nected to the main river channel (Marks-Guntren et al.,
2013). (5) At the confluence with the Red and Atchafalaya
Rivers (Simmsport, Louisiana) the Mississippi River
changes from one with tributaries entering to one with
distributaries flowing out; the Mississippi system begins to
form the extensive delta in coastal Louisiana (507 km).
Interestingly, the Atchafalaya, the largest distributary, has
a much shorter length (220 km), and hydraulically would
become the new Mississippi River were it not for human
intervention (Old River Control Complex).
As with all large river systems, the primary ecological
driver is hydraulics (longitudinal flow) and hydrology
(vertical/lateral flow). The entire Mississippi River system
(including the Ohio, Missouri and other tributaries)
exhibits high flow in spring (March–June) leading to flood
pulses that provide an annual subsidy of sediment,
nutrients, and energy to drive primary, and subsequently
secondary, productivity (Ahearn et al., 2006; Preiner et al.,
2008; Roach et al., 2009; McGinness and Arthur, 2011;
Meyer et al., 2013). However, on the Mississippi, changes
to riverine hydraulics and hydrology have led to a radically
altered system. The management of stressed river and
floodplain ecosystems is a major challenge for water
managers worldwide in the near future. It is incumbent to
understand causes and effects of anthropogenic changes in
order to better these large systems. Over half of the world’s
large river systems have been impacted by dams for
navigation, flood control, and hydroelectricity (Nilsson
et al., 2005). Additionally, management approaches need
to be adaptive and embedded within a catchment-wide
concept to cope with upcoming pressures originating from
global change (Tockner et al., 2010).
3. Ecosystem alterations
3.1. Navigation and flood risk management
Perhaps the most pronounced change to the Mississippi
River system has been the extensive alterations to river
[(Fig._1)TD$FIG]
Fig. 1. The Mississippi River catchment (excluding the Ohio and Missouri
subcatchments). The Mississippi River and Tributaries Project is
highlighted in red.
P.J. DuBowy / Ecohydrology & Hydrobiology 13 (2013) 73–8374

3. hydraulics and hydrology due to navigation and flood risk
management (‘‘flood control’’). Long before there were
railroads or interstate highways, the Mississippi River was
the major avenue of commerce in the central United States.
Barges are the most efficient form of commercial shipping;
water transportation moves 16% of the nation’s freight for
2% of the freight cost (Institute for Water Resources, 2008).
Currently, barge traffic accounts for 500-million tonnes of
goods shipped annually down the Mississippi to the Gulf
(DuBowy, 2010). Additionally, deep-draft navigation
provides important international shipping opportunities
along the Louisiana Chemical Coast, and navigation
[(Fig._2)TD$FIG]
Fig. 2. The Mississippi River and Tributaries Project showing its extensive levee system (tan) and floodways and diversions (red).
P.J. DuBowy / Ecohydrology & Hydrobiology 13 (2013) 73–83 75

4. provides an important societal service. Likewise, protec-
tion of infrastructure and property from the perils of
annual river floods is a major concern of all citizens of this
region. Since 1928 the U.S. Government has funded
US$14.5 billion on the LMR toward the Mississippi River
and Tributaries (MR&T) Project (Figs. 1 and 2) alone and
has received an estimated US$478 billion return on that
investment, including savings on transportation costs and
flood damages (Camillo, 2012).
Levees play the most important role in Mississippi River
flood control by preventing or eliminating most of the
historical overbank flooding during high water events. In
MR&T 5998 km of levees designed to withstand a Project
Flood have been authorized through the Flood Control Act of
1928; this levee system is now 95% complete (Camillo,
2012). Additional levees exist on the UMR, MMR and nearly
all tributaries. However, by eliminating these periods of
extensive, shallow flooding, most of the historical floodplain
has now been eliminated by hydrologically disconnecting
the floodplain from these flood pulses (Franklin et al., 2009).
The geological Mississippi Alluvial Valley is a broad, flat
floodplain (Saucier, 1994). Between Memphis, Tennessee,
and Little Rock, Arkansas, the floodplain is more than
200 km wide; between Vicksburg, Mississippi, and Monroe,
Louisiana, it is 125 km wide. The constructed levees have
now constricted the active floodplain (the batture) to less
than 10 km and frequently much less; where once flood
pulses were wide and shallow, they are now narrow and
deep, constrained by levees.
In the Mississippi River system, navigation improve-
ments fall into two different categories. In the UMR (above
St. Louis), the Ohio River, and other important tributaries
(e.g., Red, Illinois, Arkansas, Ouachita Rivers), the principal
navigation structures are locks and dams. The dams pool
water behind them, raising the surface elevation of the
water, and allow for safe navigation for a longer portion of
the year or during other times of low water (above
Minneapolis the mainstem dams of the Mississippi Head-
water Project hold water to be released in late summer and
fall to provide additional water for downriver navigation
below the Twin Cities). The locks allow towboats and barges
to pass from one river reach to the next (from pool to pool).
The MMR and LMR (below St. Louis), the Lower Missouri
River (Sioux Falls, South Dakota – St. Louis) and the
Atchafalaya River (a principal distributary of the Mississippi
in Louisiana) are characterized as ‘‘open rivers,’’ where dams
and locks are not required to raise water levels for
navigation (there is a lock in the Old River Control Complex
at the head of the Atchafalaya to regulate the mandated
70:30 division of water between the Mississippi and
Atchafalaya Rivers and to prevent capture of the Mississippi
by the Atchafalaya, but it is not necessary for navigation). In
the MMR, LMR and Lower Missouri Rivers the principal
navigationsstructures arewingdikes,closing structuresand
revetment (articulated concrete mats [ACM] or rock).
Revetment functions to eliminate the dynamic, undulating
sinuosity of the river; locking the river channel in place
provides an established navigation channel, reduces dred-
ging, and protects adjacent riverside infrastructure, notably
flood-control levees, docks and boat launches, and barge-
loading facilities (Smith and Winkley, 1996). Every reach of
the LMR from the confluence of the Ohio River at Cairo to the
Gulf haslongstretchesofACM orrockrevetment tofacilitate
navigation and protect infrastructure.
Wing dikes are long, linear berms of large rock
constructed perpendicularly from the riverbank toward
the main channel of the river. Often dikes are constructed
in a series, known as a dike field, and are used to deflect or
direct water flows toward the navigation channel of the
river at medium to low river stages (Fig. 3). This increases
current velocity in the navigation channel, thereby
increasing transport of sediments and maintaining open
and safe navigation. Slack water between dikes also
facilitates the deposition of sand and mud, thus further
reducing sediment volume and accretion in the channel.
The equivalent of over 500 km of dikes has been
constructed along the LMR as part of MR&T; each dike
ranges from 50 to 500 m in length (DuBowy, 2010).
Additional dikes and related structures are also found in
the MMR. However, wing-dike construction severs the
hydrological connections between the main river and side
channels (in the batture) as sand and other deposits fill the
chute. Closing structures, placed within or at the lower end
of side channels, further reduce connectivity. There has
been a marked decrease in the number of side channels as
the channel improvement program has progressed and the
number of dikes has increased (Marks-Guntren et al.,
2013). These backwater habitats are important feeding,
spawning and nursery areas for many important fish
species, as well as providing habitat for other environmen-
tally sensitive wildlife and invertebrate species.
3.2. Agricultural nutrients/industrial chemicals
Another radical change that has occurred in the
Mississippi River Basin (including the Ohio and Missouri
River sub-basins) has been the conversion to intense row-
crop agriculture throughout what is commonly known as
the ‘‘Corn Belt.’’ This process has been exacerbated in recent
times due to increases in corn prices as a result of ethanol
production. Corn yields of 200 bushel/acre (12,713 kg/ha)
are not uncommon (Iowa State University, 2012) due to (in
large part) the intensive use of nitrogen-based (nitrate,
nitrite and ammonium) fertilizers. In many locales, agri-
cultural practices (e.g., tillage, drainage) allow for the loss of
[(Fig._3)TD$FIG]
Fig. 3. Aerial view of wing dikes along Mississippi River.
P.J. DuBowy / Ecohydrology & Hydrobiology 13 (2013) 73–8376

5. excess nutrients from crop fields as point-source (drain
tiles) or non-point-source runoff (McIsaac et al., 2002).
Nitrate/nitrite concentrations frequently exceed 3 mg (N)
per liter in the Mississippi River (Meade, 1995), and this
excess nitrogen (and phosphorus) eventually makes its way
into the Mississippi River drainage and ultimately into the
Gulf of Mexico. These high amounts of nitrogen are the
principle cause of the Gulf of Mexico hypoxic zone adjacent
to the coast of Louisiana and Texas (Mississippi River/Gulf of
Mexico Watershed Nutrient Task Force, 2004). Hydraulic
alterations which now decouple the floodplain from the
river have had major effects on water quality as well
(Nilsson and Reno¨fa¨lt, 2008; Schramm et al., 2009).
Industrial chemicals, including agricultural pesticides and
legacy PCBs, are likewise found in excessive concentrations
along various reaches of the Mississippi River ecosystem
(Scribner et al., 2006; National Research Council, 2008).
3.3. Sediment and salinity changes
The Mississippi River is a dynamic system that responds
to geomorphic features such as landforms, sediment loads
and stream velocities. Hydraulic changes, especially dams
on the Missouri River (flood control) and the UMR and Ohio
Rivers (navigation) and dredging on the MMR and LMR
have altered sediment dynamics throughout the river
system (National Research Council, 2010). Dams create
reservoirs or pools for water storage behind them; these
extensive areas of slack water lead to a rapid settlement of
sediment that historically flowed to the Gulf Coast where it
was the primary mechanism for land building and the
prevention of marsh loss. The historical sediment load of
the Mississippi River has been reduced by over 50%
(Meade, 1995; Smith and Winkley, 1996), leading to a
rapid subsidence of coastal marsh ecosystems (Morton
et al., 2010). In contrast, in some areas of the LMR, dredging
and other navigation remediation, such as cutoffs and
channel connections (Camillo, 2012), have led to a radical
change in the grade (slope) of the river bottom (Grenfell
et al., 2012; Marks-Guntren et al., 2013). This change in
profile has led to extensive areas of head-cutting, where
rapid and pronounced erosion attempts to bring the river
back to a more normal hydraulic grade.
The Mississippi Delta in Louisiana has experienced
pronounced reductions and shifts in flow (as well as
sediment load) due to the extensive levee system and
coastal canals which now allow salt water to extend
landward due to a reduction in the hydraulic head (Barras,
2009). These salt water incursions have been exacerbated by
hurricanes and tropical storms and have led to rapid changes
in marsh salinity with concomitant shifts from fresh-water
or brackish ecosystems to more intermediate or saline
systems. These ecosystem changes are exemplified by
extensive mortality of historical vegetation (marsh die-off)
and similar loss of sessile marsh fauna, oyster (Crassostrea
virginica) beds being the most obvious (Klinck et al., 2002).
3.4. Non-native species
Like many other ecosystems world-wide, the Missis-
sippi River system has been plagued by rapid increases in
non-native species. These invasive species run the gamut
from plants (e.g. Hydrilla and reed canary grass Phalaris
arundinacea) to fish (northern snakeheads Channa argus
and round gobies Neogobius melanstomus). Two of the more
noteworthy invasive taxa are Zebra mussels (Dreissena
polymorpha) and Asian carp (Cyprinidae). Zebra mussels
are presumed to have arrived in the Mississippi River
ecosystem after passing through the Chicago Sanitary and
Ship Canal (CSSC) which connects the Illinois River to Lake
Michigan, where it is believed the mussels became
established after arriving in bilge water from ships that
passed up the St. Lawrence Seaway and entered the Great
Lakes (Briski et al., 2012). Similar to their cousins, the
Common Carp (Cyprinus carpio), four additional species,
Grass Carp (Ctenopharyngodon idella), Silver Carp
(Hypophthalmichthys molitrix), Bighead Carp (H. nobilis),
and Black Carp (Mylopharyngodon piceus), either escaped
during flood events or were deliberately released from
aquaculture ponds in the Mississippi Alluvial Valley and
quickly became established in the Mississippi River
system. Ironically, the major concern now is the potential
for these carp species to move in the opposite direction
through the CSSC and to become established in Lake
Michigan and then the other Great Lakes. Like Zebra
mussels, the latter three carp species are filter feeders that
significantly reduce the amount of phytoplankton in
oxbow lakes and other floodplain features; phytoplankton
is the base of the food chain for many economically-
important fish species, and carp have the potential to
radically alter the aquatic fauna of the system (Kolar et al.,
2007).
3.5. Climate change
Floods and droughts have been a great concern to
civilizations and societies for thousands of years, influen-
cing the locations of cities, agricultural activities, and
transportation (Krysanova et al., 2008). Additionally,
global climate shifts have been cited as a possible cause
of increased flooding in some parts of the world (Pall et al.,
2011). The Mississippi River system has experienced
pronounced extremes in weather patterns, particularly
rainfall events, in the past few years. In 2011 UMR, MMR
and LMR all experienced record or near-record flood stages
along most reaches of the system (Camillo, 2012). In
Vicksburg the highest stage recorded was +57 LWRP (Low
Water Reference Plain – defined as the level that is
exceeded 97% of the time; 57 ft % 17.1 m) in May 2011
which was 4 m above flood stage and was the highest
recorded stage ever (the 1927 flood stage may have been
higher had the upstream levees not failed). Likewise, many
towns on the UMR, MMR and tributaries were inundated
by record levels of flood water. These record flood levels
follow on high water events in 2009 as well. These flood
events are caused by cyclonic activities that push moisture
north from the Gulf of Mexico resulting in wide-spread
heavy rainfall events. Ironically, little winter snowpack
followed by a hot summer and record drought in northern
portions of the system during the following year (2012)
resulted in some of the lowest Mississippi River stages ever
recorded. The river gage at Vicksburg recorded a reading of
P.J. DuBowy / Ecohydrology & Hydrobiology 13 (2013) 73–83 77

6. À2 LWRP (%À60 cm) during August 2012 (as LWRP is
defined as 97% exceedance, gage readings can, in fact, be
negative). This is a nearly 18 m change from the preceding
year. How global climate change will further impact future
rainfall and snowfall events is yet to be determined.
However, the possibility exists that more summer
droughts and more spring/summer rainfall events may
lead to additional record high-water or low-water events
in the future. Additionally, climate change already has had
impacts on aquatic flora and fauna; more vulnerable
communities, such as montane systems, have shown the
greatest turnover (Bush et al., 2012), but impacts on
Mississippi River catchment are also expected.
4. Ecohydrological remediation
4.1. Improved hydraulics
Mississippi River Basin ecosystem rehabilitation will
require extensivereconstructionofhistoricalhydraulicsand
hydrology. Hydrological connectivity is essential for most
riparian ecological processes, especially nutrient dynamics
(Meyer et al., 2013), plant propagule colonization (Gurnell
et al., 2008) nursery areas for many fish species (Miranda,
2005; Fullerton et al., 2010; Go´rski et al., 2011; Tonkin et al.,
2011) and biodiversity (Paillex et al., 2009). Reconnection of
historical bottomland features through the reestablishment
of historical hydrology, or the creation of floodplain habitats
de novo (Gallardo et al., 2012) is critical to developing more
resilient and dynamic ecosystems. As there are several
different sections of the Mississippi River, itself, (plus the
Missouri and Ohio and other sub-basins) the hydro-
engineering required may be radically different in different
stretches of the river system. The obvious solution to
restoring the hydraulicswould betoremove all floodcontrol
and navigation structures that impede water flow. Clearly,
this cannot happen without societal costs via threats to
human safety, infrastructure security and economic bene-
fits. Rather, improved hydraulics and hydrology must be
accomplished withinthecontextofnavigationand floodrisk
management (DuBowy, 2010; Miller and Kochel, 2010;
Radspinner et al., 2010).
In the MMR and LMR immediate hydraulic improve-
ments can be accomplished within the batture (active
floodplain). Here, navigation structures restrict flow into
side channels and other floodplain features. Engineering
features have been considered to provide flow into side
channels and other floodplain features while continuing to
provide flow in the main channel for navigation; several
engineering features (dike notches, chevrons) have been
developed and implemented. Within existing dike fields
the best environmental engineering feature found for this
has been the dike notch. A notch is a trapezoidal opening in
a dike that typically has a 30-m top width, sloping sides
and a 90-m bottom width; the bottom elevation of the
notch is typically at 0 LWRP to +5 LWRP (ft % 1.5 m)
(roughly between 4.5 and 9 m below the top elevation of
the wing dike). Some notches are larger or smaller, being
adjusted to the specific channel conditions. Notches are
made either by removing rock during maintenance work
on an existing dike or by leaving an open, low section when
a new dike is built (Fig. 4); this low section permits lower
river stages to pass through the notch and down the side
channel $90–97% of the time. Notches reduce sedimenta-
tion in old chute channels and behind sandbars and
maintain flowing water conditions at lower stages in
secondary channels. Additionally, low water stages flow-
ing through a notch result in a diversity of current
velocities at the notch that increase substrate diversity
(both in composition and topography/bathymetry),
thereby increasing aquatic habitat and aquatic species
diversity downstream of the notch. Some notches have
been constructed to elevations higher than +5 LWRP. This
is unfortunate as +10 LWRP (for example) is rated at only
80% exceedance, meaning 20% of the time (%2.4 months)
there is no flow through the side channel, usually during
the hottest time of year when conditions are physiologi-
cally most stressful for aquatic fauna.
For new construction, developing navigation structures
that divide flow, providing ample flow for navigation while
providing environmental flows for floodplain enhancement,
are being planned and implemented. Chevrons (U- or J-
shaped rock structures pointing upriver) and rootless dikes
(not tied into the riverbank thus providing flow like an
enlarged notch) have been constructed in many locations in
the MMR and LMR. Not only do chevrons divide the flow,
water flowing over the middle of the structure at high river
stages scoursthebottomand provides deep-water habitatin
the center of the chevron, creating additional habitat
diversity (Davinroy et al., 1996).
Additional floodplain hydrologic improvement by
countering the desired consequences of levees and
flood-risk management is more problematic. The key
would be to establish improved hydrology while continu-
ing to provide a similar level of safety and security for
people, property and infrastructure. One alternative would
be to adopt a strategy of levee setbacks – moving the levees
farther apart to both provide more hydrological connec-
tivity to the floodplain as well as establishing improved
flood water conveyance during critical times of year
(Opperman et al., 2009). This would require protection of
infrastructure and property with the new, wider batture,
[(Fig._4)TD$FIG]
Fig. 4. Newly notched wing dike at rising stage, Lower Mississippi River,
Robinson Crusoe dike field, Tennessee.
P.J. DuBowy / Ecohydrology & Hydrobiology 13 (2013) 73–8378

7. probably by means of ring levees around critical elements,
similar to the construction of ring levees around small
towns in the wide valley of the Red River of the North in
Manitoba, Minnesota and North Dakota. The principal
drawback to this concept is that farmsteads and personal
property would not be protected unless the landowner
took the responsibility to construct a ring levee or elevate
structures above the high-water mark; consequently,
these non-structural solutions have been met with
resistance on the part of landowners.
4.2. Nutrient reductions
Much deliberation has occurred recently concerning
the role that the Mississippi River and its floodplain could
play in water quality remediation. In particular, nitrogen
and phosphorus removal via biogeochemical processes has
been proposed as an objective for the restored Mississippi
River floodplain (Mitsch et al., 2005, 2008; Schramm et al.,
2009). The length of the LMR is almost 1600 km; the
average flow rate is about 6 km hÀ1
. Consequently,
retention time along the LMR is approximately 250 h or
more than 10 days. This would prove to be more than
adequate time for water treatment and nutrient removal.
However, with the construction of mainline levees the
cross-sectional channel profile has been radically altered.
Where once the floodplain was 100 km miles or more wide
and flooded to an average depth of <0.5 m deep (Saucier,
1994), the current configuration of the system is one where
the river is 2-3 km wide and 15 m deep at flood stage; river
velocities correspondingly increase during floods in the
modified channel. On less-regulated rivers riparian wet-
lands only reduce annual nitrogen flux by about 50%, and
nitrogen flux may be as little as 10% during peak flow
conditions (Montreuil et al., 2010). This level of nitrogen
reduction, while favorable, would not be sufficient to
eliminate the Gulf hypoxia zone.
In its current configuration, most Mississippi River water
would flow with little treatment even with the entire
revegetation of the batture. The existing LMR floodplain
system exhibits reduced channel and floodplain hydro-
logical processes due to channelization and levee construc-
tion (Franklin et al., 2009). Current nitrogen removal in
bottomland soils is estimated to be 542 kg N haÀ1
, nearly a
50% reduction from historical hydrological conditions
(Schramm et al., 2009). The highest levels of N reduction
arenormally foundon1st–3rdorder streams,i.e., headwater
streams far removed from the mainstem of the Mississippi
River (Craig et al., 2008). Moreover, hypoxic conditions even
exist in low-order streams in the Mississippi River catch-
ment during high flow events (Shields and Knight, 2012). As
most nutrient contribution is by 1st-order streams (Alex-
ander et al., 2007) efforts for water quality remediation
should, likewise, occur in headwater areas and other regions
where agricultural practices lead to high nutrient loads. For
over 25 years numerous constructed wetland studies have
shown that shallow water (<50 cm) and concomitant broad
surface area are necessary for adequate treatment (Ham-
mer, 1989; Moshiri, 1993; Etnier and Guterstam, 1997).
As much of these excess nutrients are agricultural in
nature, a far better solution would be the development of
comprehensive measures for the treatment and remedia-
tion of agricultural runoff (especially cropland and dairy
operations) at its source (DuBowy and Reaves, 1994;
DuBowy, 1999). Small constructed wetlands or other
treatment systems could be constructed onsite before the
water is released into adjacent surface waters or ground-
water. Numerous studies have shown the efficacy of these
small-scale projects, even in areas with cold winter
temperatures, especially when treatment facilities are
coupled with existing farm lagoons or other holding
facilities. Small-scale constructed wetlands employing
anoxic limestone drains particularly to remove mobile
iron, have been used to remediate acid mine drainage in
many parts of Appalachia (Ohio River drainage; Johnson
and Hallberg, 2005). For larger volumes of wastewater
(municipal or industrial), constructed wetland systems
could be scaled up to meet the necessary treatment
demands and used as tertiary treatment for water
polishing (Vermaat et al., 2012). Examples include Cattail
Marsh (municipal, Beaumont, Texas), Orlando Easterly
Wetlands Reclamation Project (municipal, Florida) and the
Amoco Oil Refinery (industrial, Mandan, North Dakota).
4.3. Sediment and freshwater diversions
Historically, the farthest downriver reaches of the LMR
in Louisiana functioned as a web of distributaries which
spread (fresh) water and sediment to maintain coastal
wetland ecosystems. Construction of flood control levees
obliterated most of this network by preventing flow
through most of these natural channels. Loss of sediment
and freshwater has resulted in marsh subsidence and salt
water intrusion (Barras, 2009). Moreover, the sediment
load in the Mississippi River has been reduced by more
than 50% due to sediment capture by large flood control
dams on the Missouri River and navigation dams on the
Upper Mississippi and Ohio Rivers (Meade, 1995).
To remediate the loss of natural crevasses and outflow
channels, a series of freshwater and sediment diversions
are in the planning, construction or operational phases.
The Old River Control Complex, which sends 30% of the
combined flow of the Mississippi and Red Rivers down the
Atchafalaya River, provides freshwater and sediments to
the western portion of the coastal Louisiana delta (Fig. 2).
Sedimentation and land building have been observed near
the Wax Lake Outlet along the Atchafalaya Waterway
(Barras et al., 2008). Additional diversions currently in
operation include Bonnet Carre´ (floodwater), Davis Pond
(freshwater), Caernarvon (freshwater), Naomi Siphon
(freshwater), West Point a la Hache (freshwater), West
Bay Sediment Diversion, and Delta Crevasses (sediment).
Numerous other diversions are proposed or planned to
replace the historical crevasses along this entire stretch of
river (Falcini et al., 2012; Kenney et al., in press).
4.4. Invasive species control
Biological control of non-native species is fraught with
controversy. While billions of dollars in economic losses
are expected with the spread of Zebra mussels and Asian
carp, control currently revolves around eliminating, or at
P.J. DuBowy / Ecohydrology & Hydrobiology 13 (2013) 73–83 79

8. least reducing, the spread of these species into new bodies
of water rather than eradication. As Zebra mussel adults
are sessile and attach to various structures, many states
have embarked upon programs to insure that boaters do
not translocate mussels when moving watercraft from one
lake or stream to another (Leung et al., 2006). This program
has been only partially successful as mussels can move
through other means – adults can attach to large ships and
barges that are not regularly taken out of the water or
inspected, and free-swimming veligers may passively
move downstream in the water column (unlike native
mussel species, Zebra mussel veligers do not attach to fish;
Bossenbroek et al., 2007; Bunnell et al., 2009).
Asian carp present a different suite of problems as they
are strong swimmers and extremely mobile. Since the early
1990s Asian carp have made their way from the southern
portions of the Mississippi River all the way north to St.
Anthony’s Falls in addition to moving into the Ohio and
Missouri Rivers and tributaries (Chick and Pegg, 2001).
Currently the greatest concern is to prevent carp moving
from the Illinois River through the Chicago Ship and Sanitary
Canal (CSSC) into Lake Michigan and eventually the other
Great Lakes (there is some evidence that Bighead Carp are
already in the Calumet River and Lake Erie notwithstand-
ing). The CSSC is an artificial channel dug to link the Great
Lakes to the Mississippi system in the late 1800s. Some
agencies and government bodies have advocated closing
this link by decommissioning the canal. Others have
objected on the grounds that prevention of shipping would
be financially ruinous. Currently, an alternate mechanism is
being developed – an electrical barrier (perhaps coupled
with bioacoustic and bubbler features) that block carp (and
other fish) from passing through the CSSC. The likelihood
that this barrier will be 100% effective in preventing carp
passage into Lake Michigan is conjectural at this point. A
similar barrier system also has been proposed on the
Mississippi River at Minneapolis.
4.5. Climate change
Like other wetlands, floodplains and bottomland
ecosystems can play an important role in the remediation
of carbon dioxide emissions by means of belowground
carbon sequestration (peat) and aboveground biomass
accumulation (timber; Schoch et al., 2009). However, by
eliminating the annual flood pulse in bottomland systems,
flood control levees also have allowed extensive land
clearing for agriculture behind the levees, thus reducing
carbon storage in these areas (Franklin et al., 2009).
Bottomland carbon sequestration should not be dis-
counted; however, it will require a major paradigm shift
to return bottomland systems to pre-development seques-
tration levels. In particular, hydrological reconnection of
the historical floodplain is a necessary first step in
meaningful carbon storage.
4.6. Hydrokinetic energy production
Besides remediating climate change through carbon
sequestration, the Mississippi River system potentially can
reduce our carbon footprint by providing for alternate
hydrokinetic energy systems (National Research Council,
2013). The promise of hydrokinetic turbines is in their
ability to produce clean, sustainable energy that takes
advantage of the river’s current (flow and velocity). Several
large-scale hydrokinetic projects have been proposed for
various reaches of the UMR, MMR, and LMR. However,
there are questions about unintended consequences on
aquatic organisms, wildlife and surrounding areas. Various
agencies including the U.S. Army Corps of Engineers, U.S.
Fish and Wildlife Service, National Park Service, state
agencies, and non-governmental entities such as naviga-
tion associations, levee boards, Trout Unlimited, American
Rivers, and others have raised concerns about specific
aspects of these projects.
Impacts on fish, mussels and recreational boating and
angling are of particular concern. Studies of fish impacts
proposed by power applicants may not be adequate to
assess true impacts, especially cumulative impacts over
time. Several threatened or endangered species, including
the pallid sturgeon (Scaphirhynchus albus) may be affected
by these structures. Impacts may multiply if multiple
hydrokinetic arrays are deployed as expected. Likewise,
mussel impacts are unknown, but of concern. Several
federally-endangered species are found in the Mississippi
River in the general areas of proposed hydrokinetic kinetic
arrays. Impacts to diving birds are also unknown, but if
turbines entrain many fish these sites will become
magnets for birds in the middle of one of North America’s
most important flyways for migratory birds.
Especially in the LMR impacts to navigation, channel
maintenance and river hydraulics are also of concern. Large
static arrays of pylons with attached turbines will
undoubtedly present logistical problems for dredging,
dredge material disposal, and revetment. As these turbines
will reduce the kinetic energy of the river impacts to river
hydraulics, sediment transport, river stages, and flood risk
management must also be considered. Additionally,
impacts on recreational boating and plans for emergency
maintenance have not been adequately addressed.
5. Planning and evaluation
Ecohydrology can be used throughout the river
restoration process, from planning, through implementa-
tion and construction, to evaluation and monitoring.
Comprehensive understanding of Ecohydrological princi-
ples is required during the planning process (Hermoso
et al., 2011, 2012a,b); without understanding the linkages
between ecology and hydrology, including the spatial
extent of hydraulic and hydrological processes project
failure is likely. Likewise, these same principles can be
employed during the evaluation process by using the
metrics developed pre-project to assess project success
(Lake et al., 2007; Bunn et al., 2010).
An inherent problem of many current ecosystem
rehabilitation projects is the inability to measure success
(Woolsey et al., 2007). While most projects conduct post-
project monitoring, such monitoring only evaluates change
(physical and biological responses) and not success; in order
to evaluate success a project must a priori develop
Objectives, Goals, Targets and Metrics to be incrementally
P.J. DuBowy / Ecohydrology & Hydrobiology 13 (2013) 73–8380

9. measured both during and after the life of the project. Such
targets and metrics allow for Adaptive Management (AM) to
get projects ‘‘back on track’’ in the event of deviations from
the prescribed project objectives (National Research Coun-
cil, 2004; King et al., 2010; Mika et al., 2010). To date, many
Mississippi River rehabilitation projects, especially most on
the LMR,do not havethe abilitytomeasuresuccessdue toan
absence of pre-defined Objectives, Goals, Targets and
Metrics (DuBowy, 2010). Oftentimes the ability to simply
measure project performance (D pre-/post-project; Miller
et al., 2010) cannot even be accomplished due to a lack of
systematic data collection.
The spending hundreds of thousands of dollars on
projects that cannot be adequately evaluated is undoubt-
edly the most egregious aspect of Mississippi River
rehabilitation. Even U.S. Army Corps of Engineers Imple-
mentation Guidance for Section 2039 of Water Resources
Development Act (WRDA) 2007 (31 AUG 2009) clearly
reads that projects include plans for monitoring the
success of ecosystem restoration projects. Yet, not one
LMR environmental project has ever had its level of success
measured; in fact, there are few data to even corroborate
change of most projects. This has led to a lack of scientific
accountability on these projects (DuBowy, 2010: 440).
Using Ecohydrology principles it would be easy to
formulate Goals, Objectives, Targets and Metrics for future
projects that comprise the rehabilitation program. Goals
would be fairly neutral, comprising the overall structure of
the Ecohydrology concept (reducing input and controlling
pathways of excess nutrients and pollutants in aquatic
ecosystems; enhancing ecosystem carrying capacity, resi-
lience, biodiversity, ecosystem services for society; etc.) and
would complement the overarching program. Objectives, on
the other hand, would be specific to each project and would
reflect the ecological and (specifically) hydrological func-
tions that describe the historical system. In contrast, Targets
would reflect expectations of the realized, rehabilitated
system, recognizing that often systems can never be
restored to a historical ‘‘pristine’’ condition. Metrics would
be the specific numerical criteria (hydrological, physical and
biological) expected from the outcome of each project. In
this way, each (linked) project would meet the overall
objectives of the program while reflecting individual site
characteristics and likelihood of success.
In the future, AM plans (i.e., contingency plans) must be
developed for all riverine (and other aquatic) ecosystem
restoration projects. Each AM plan must be appropriately
scoped to the scale of the project. If the need for a specified
adjustment is anticipated due to high uncertainty in
achieving desired outputs/results, the nature and costs of
such actions should be explicitly described in the decision
document for the project. If the results of the monitoring
program support the need for physical modifications to the
project,the costofthechangesshould becost-shared among
all sponsors and partners via established guidelines.
6. Conclusions
The Mississippi River system is not unlike other global
large-river systems which have undergone radical hydrau-
lic and hydrological alterations. As with many current river
programs, rehabilitation of the Mississippi River and its
associated floodplain is fraught with controversy as
environmental goods and services are balanced against
socioeconomic constraints such as navigation, flood
control, agriculture and water supply. It will take much
work and critical ‘‘thinking outside the box’’ to accomplish
the optimization of all these factors while creating a more
resilient dynamic ecosystem.
Ecohydrology presents a framework for the establish-
ment of evaluation metrics that link environmental
resiliency, biodiversity and ecosystem goods and services
for the goal of sustainable riverine and aquatic ecosystems.
Given that the ability to measure project success and,
consequently, to implement adaptive management is
lacking in many Mississippi River rehabilitation projects,
it is critical that agencies and organizations currently
engaged in these endeavors change their philosophy and
protocols to integrate Ecohydrology into a framework to
develop Goals, Objectives, Targets and Metrics before any
new projects are initiated. Without a clear vision of
Adaptive Management, program success, especially in the
LMR, is unlikely.
Conflict of interest
None declared.
Financial disclosure statement
The Contributing Author as no conflict of interest,
including specific financial interests and relationships and
affiliations relevant to the subject matter or materials
discussed in the manuscript.
Acknowledgements
Development of the framework for using the Ecohy-
drology concept as a platform for restoration evaluation
was refined while I was a visiting professor in the Erasmus
Mundus Master of Science Programme in Ecohydrology at
the European Regional Centre for Ecohydrology (University
of Ło´dz´, Poland) and the International Centre for Coastal
Ecohydrology (University of Algarve, Portugal) through the
Fulbright Specialists Program. I thank my colleagues, Prof.
M. Zalewski (Ło´dz´) and Prof. L. Chı´charo (Algarve), and
their respective institute associates for their hospitality
and stimulating discussions during my tenure. I also thank
Prof. Zalewski for the invitation to present at the
Ecohydrology for River Basins symposium at EcoSummit
2012 in Columbus, Ohio.
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