LETTERS
PUBLISHED ONLINE: 21 OCTOBER 2012 | DOI: 10.1038/NGEO1615
Linking the historic 2011 Mississippi River flood to
coastal wetland sedimentation
Federico Falcini1,2,3 , Nicole S. Khan1 , Leonardo Macelloni4 , Benjamin P. Horton1 , Carol B. Lutken4 ,
Karen L. McKee5 , Rosalia Santoleri2 , Simone Colella2 , Chunyan Li6 , Gianluca Volpe2 ,
Marco D’Emidio4 , Alessandro Salusti1,7 and Douglas J. Jerolmack1 *
Wetlands in the Mississippi River deltaic plain are
deteriorating1 in part because levees and control structures
starve them of sediment2–4 . In spring 2011 a record-breaking
flood brought discharge on the lower Mississippi River to
dangerous levels, forcing managers to divert up to 3,500 m3 s−1
of water to the Atchafalaya River Basin5 . Here we use fieldcalibrated satellite data to quantify differences in inundation
and sediment-plume patterns between the Mississippi and
Atchafalaya River. We assess the impact of these extreme
outflows on wetland sedimentation, and use in situ data collected during the historic flood to characterize the Mississippi
plume’s hydrodynamics and suspended sediment. We show
that a focused, high-momentum jet emerged from the leveed
Mississippi, and delivered sediment far offshore. In contrast,
the plume from the Atchafalaya was more diffuse; diverted
water inundated a large area, and sediment was trapped within
the coastal current. The largest sedimentation, of up to several
centimetres, occurred in the Atchafalaya Basin despite the
larger sediment load carried by the Mississippi. Sediment
accumulation was lowest along the shoreline between the two
river sources. We conclude that river-mouth hydrodynamics
and wetland sedimentation patterns are mechanistically linked,
providing results that are relevant for plans to restore deltaic
wetlands using artificial diversions2–4,6–8 .
Protecting and expanding coastal wetlands is vital for ecosystem
services of the Mississippi River Delta9–12 , and harnessing natural
processes of wetland building using the Mississippi River and its
sediments is an essential component of restoration plans2–4 . The
only portion of the delta experiencing significant expansion of
coastal wetland at present is at the mouth of the Atchafalaya River
(Fig. 1a), where a higher mineral (that is, non-organic) sediment
concentration3 and hydrodynamic factors8 allow sufficient sediment deposition6 to outpace subsidence and sea-level rise13 . The
recently released 2012 Coastal Master Plan14 proposes river diversions and channel realignment to divert sediment and fresh water
from the Mississippi River and Atchafalaya River into adjacent
basins, to reconnect the river to delta wetlands. Successful design
and implementation of such measures require an understanding
of diverted sediment movement and deposition, especially during
high-water events when the potential sediment load is greatest.
The Mississippi River flood of spring 2011 was one of the largest
on record5,15 . Both the Mississippi River and Atchafalaya River
exhibited elevated suspended sediment loads (Fig. 1d). Floodwater
discharge (Qw ) at the Old River Control Structure—the location
where the Mississippi River bifurcates into the Atchafalaya and Mississippi channels—crested at a value of ∼20,000 m3 s−1 for the period of 14–31 May 2011 (ref. 15). To relieve pressure on levees along
the downstream portion of the Mississippi River in Baton Rouge
and New Orleans, the Morganza Spillway (Fig. 1a) was opened on
14 May 2011 for the first time in almost 40 years. At peak flooding,
3, 500 m3 s−1 of water was being diverted to the west into the
Atchafalaya Basin15 , flooding the swamps and marshes along the entire length of the Atchafalaya River (Supplementary Information).
Although both the Mississippi River and Atchafalaya River
channels had obvious sediment-laden plumes emanating from
their mouths, the differences in plume patterns and extent of
inundation were striking (Fig. 1 and Supplementary Figs S2 and S3).
We performed time-series analysis of suspended sediment concentration (SSC) from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua satellite data, calibrated using field measurements (Supplementary Information). The Mississippi River—
whose floodwaters upstream were completely contained within artificial levees—exhibited narrow and focused jets of sediment-laden
water, especially from Southwest Pass, which penetrated the coastal
current with limited mixing16–20 for the duration of the flood (Fig. 1
and Supplementary Fig. S8). The intentionally flooded Atchafalaya
Basin inundated a ∼100-km-wide coastal zone, and sediment from
its broad plume seemed to be trapped in the nearshore zone for four
weeks, where it thoroughly mixed with marine waters (Fig. 1a–c and
Supplementary Fig. S8). The diffuse nature of the Atchafalaya River
plume may also have been enhanced by the shallow depth of the
receiving bay, which would increase bottom friction compared with
the Mississippi River. We expected greater wetland sedimentation
over a broad area in the Atchafalaya Basin, from both direct
deposition by floodwaters and indirect deposition through coastal
reworking of the plume (Fig. 1a–c; Supplementary Figs S2 and S8).
To test these ideas we conducted a sedimentation survey of
45 sites by helicopter across the Mississippi Birdsfoot, Barataria,
Terrebonne and Atchafalaya basin wetlands during 21–27 June
2011 (Fig. 2). Shallow sediment cores (5 cores per site) were
extracted from the marsh surface at a consistent distance (5 m)
from waterways. The surface sediment layer was presumed to be a
recent deposit on the basis of distinguishing features such as lack of
plant roots and different colour and consistency from underlying
1 Department
of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA, 2 Istituto di Scienze dell’ Atmosfera e
del Clima, Consiglio Nazionale delle Ricerche, Rome 00133, Italy, 3 St Anthony Falls Laboratory, and National Center for Earth-surface Dynamics, University
of Minnesota, Minneapolis, Minnesota 55414, USA, 4 Mississippi Mineral Resources Institute, University of Mississippi, University, Mississippi 38677, USA,
5 US Geological Survey, National Wetlands Research Center, Lafayette, Louisiana 70506, USA, 6 Department of Oceanography and Coastal Sciences,
School of the Coast and Environment, Louisiana State University, Baton Rouge, Louisiana 70803, USA, 7 Dipartimento Scienze Geologiche, Roma Tre,
00146 Rome, Italy. *e-mail: [email protected].
NATURE GEOSCIENCE | VOL 5 | NOVEMBER 2012 | www.nature.com/naturegeoscience
© 2012 Macmillan Publishers Limited. All rights reserved.
803
NATURE GEOSCIENCE DOI: 10.1038/NGEO1615
LETTERS
a
Louisiana
Mississippi
Morganza
Spillway
Baton Rouge
M
iss
iss
Lake Pontchartrain
ive
y
ala
iR
haf
ipp
Atc
r
New Orleans
Bonnet
Carre
aR
ive
+ 30° N
92° W
r
Belle Chasse
NE1
Mississippi River
Birdsfoot Delta
Atchafalaya Bay
NE2
NE3
SE1
SE2
SE3
SW
SE4
SE5
P2-3 Pass 1
P3-3
Pass 4
50 km
Hydrographic/current meter stations
Continuous current meter transects
continuous current meter transects
Atchafalaya River
29.6
50
Mississippi River
89.2
80
89.4
60
40
30
29.3
20
40
89.6
Distance (km)
29.4
Distance (km)
Latitude (° N)
29.5
Longitude (° W)
b
29.2
20
10
89.8
29.1
30 Apr.
16 May
31 May
5
16 Jun.
0
01 Jul
30 Apr.
75
900
31 May
d
3,500
3.6
Mississippi River
QW
3.2
Latitude
MR
AR
Longitude
90° W
89° W
Longitude
360
320
2.4
280
2.0
240
1.6
200
160
0.8
91° W
400
2.8
1.2
92° W
SSC
0.4
Apr. 15
SSC (mg l¬1)
Qw (m3 s¬1 × 104)
30° N
29° N
0
01 Jul.
16 Jun.
150
2,200
SSC (mg l¬1)
c
Atchafalaya River
16 May
120
Apr. 30
May 15
May 30
Jun. 14
Jun. 29
Figure 1 | Mississippi and Atchafalaya river plume patterns during the 2011 flood. a, MODIS ocean colour image on 1 June 2011 showing the suspended
sediment pattern along the coast; boat survey locations and points of interest are indicated. b, Hovmöller plots of SSC (mg l−1 ) from field-calibrated
MODIS Aqua (Supplementary Information) along cross-plume transects of the Atchafalaya (left) and Mississippi (right) rivers, indicated on 1 May–31 July,
2011 (c). c, Cumulative SSC over the same period as in b. Values on the top (bottom) side of the colour bar refer to b (c). d, US Geological Survey gauge
data of daily discharge (Qw (m3 s−1 ), lines) and SSC (mg l−1 ; symbols) for the Mississippi River at Belle Chasse, Louisiana and the Atchafalaya River at
Morgan City, Louisiana. SSC data for the Atchafalaya River were collected at Simmesport, Louisiana. Note that sediment load, Qs = Q∗w SSC.
804
NATURE GEOSCIENCE | VOL 5 | NOVEMBER 2012 | www.nature.com/naturegeoscience
© 2012 Macmillan Publishers Limited. All rights reserved.
NATURE GEOSCIENCE DOI: 10.1038/NGEO1615
a
LETTERS
29° 40' N
29° 20' N
Terrebonne
Atchafalaya
150
Barataria
29° N
50
< 0.5
0.5 - 2.5
> 2.5
28° 40' N 0 12.5 25
50
75
100
Mississippi River
(Birdsfoot) Delta
km
91° W
90° W
0
89° W
Longitude
Average
accumulation
(g cm¬2)
b
100
Average depth (cm)
SSC (mg l¬1)
Latitude
200
10
5
0
91.6
91.1
90.6
90.1
89.6
Longitude (decimal degrees)
89.1
Figure 2 | Spatial distribution of sediment during the 2011 flood. a, Locations, and measured recent sediment accumulation, from shallow cores along the
delta shoreline (circles), merged with a map of SSC on 1 June 2011 derived from field-calibrated MODIS Aqua data. b, Recent sediment accumulation
(±s.d.) at each sampling site, calculated using the average thickness (n = 5) and bulk density (n = 2) of the flood sediment layer.
sediments. The thickness of the surface sediment layer varied from
0.0 to 8.3 cm, with a coast-wide average of 1.5 cm. These sediments
were composed of moderately sorted fine silt (median value from
all basins, 13.4 mm) with a low organic content (10 ± 1%) and
moderate bulk density (0.60 ± 0.05 g cm−3 ), features that did not
vary significantly across basins (Supplementary Table S2). Using
sediment thickness and bulk density, we calculated that recent
sediment accumulation was greatest in the Atchafalaya (1.61 ±
0.96 g cm−2 , n = 14), supporting expectations of greater potential
contribution of sediment to wetland accretion (Fig. 2). Recent
accumulation in the Birdsfoot Delta was smaller but still substantial
(1.14±0.78 g cm−2 , n = 9), showing that Mississippi River sediment
reached some marsh areas through small channels or deposition
from its spatially restricted coastal plume (Fig. 2). Much less
sediment accumulated in the Terrebonne (0.42 ± 0.18 g cm−2 , n =
14) and Barataria (0.34±0.22 g cm−2 , n = 8) basin wetlands, located
farthest from the rivers. The correspondence between zones of
high shoreline deposition, and coastal SSC patterns identified from
satellite data (Fig. 2), suggests plume-derived wetland deposition.
Recent sediments in the Atchafalaya and Birdsfoot basins
were comparable to the underlying deposits in terms of bulk
density and grain size (Supplementary Table S2), but contained a
greater abundance of centric diatoms, which are planktonic forms
commonly found in the water column21 . Underlying sediment
was dominated by pennate taxa typical of benthic environments21
(Supplementary Fig. S9). The ratio of centric/pennate diatoms in
the surface sediment was 127% higher than in the underlying
layer in the Atchafalaya and Birdsfoot basin sites, but was
only 23% higher in the Terrebonne and Barataria basins. This
finding supports the interpretation that recent accumulation in the
Atchafalaya River and Mississippi River resulted from deposition
of suspended sediment, either from overbank flooding or an
ocean-mixed plume. The former is more likely the case for sites
farther inland, whereas the latter probably dominated for coastal
locations (Fig. 2). We also observed these sediments to be relatively
enriched in diatom species indicative of low-salinity environments
(Supplementary Information), supporting riverine influence. The
similarity in physical characteristics of recent flood sediments and
underlying deposits, and the low organic content of all samples,
indicate that mineral sediment of river origin has been a dominant
contributor to building and maintaining these coastal wetlands.
To better understand the Mississippi River plume dynamics
during this extraordinary event, and to calibrate satellite data, we
carried out oceanographic transects off the Birdsfoot Delta during
the peak of the flood (Fig. 1 and Supplementary Figs S4 and S5).
Although studies have used satellites to track Mississippi plume dynamics during floods22 , in situ hydrographic measurements during
such a large flood have not been conducted. Our transect surveys
captured vertical profiles of flow velocity, temperature, salinity,
SSC and grain-size distributions, allowing us to characterize the
hydrodynamics of the effluent plume and to construct a sediment
budget for the Mississippi River flood outflow (Fig. 3). Results
from the perimeter of the Birdsfoot Delta showed three main
freshwater outflows corresponding to the Southwest, Southeast
and Northeast passes, each distinguished by salinity < 15 PSU,
temperatures cooler than ambient (Supplementary Information)
and SSC > 40 mg l−1 . We estimated a total sediment discharge of
Qs = Q∗w SSC ∼ 3.9 × 103 kg s−1 , in agreement with values reported
from an upstream gauge (Fig. 1d).
A Southwest Pass survey showed that its jet was easily
recognized, even 50 km offshore, as a persistent core of high current
velocity and SSC (Fig. 3). To relate jet dynamics to sediment
suspension, we computed the Rouse number—essentially the ratio
of particle settling velocity (vs ) to fluid shear velocity (u∗ )—for each
measurement station. We expected sediment to be well suspended
for vs /(ku∗ ) < 2.5 (ref. 23), where k is von Kármán’s constant. Shear
velocity and particle settling velocity were estimated from current
meter and grain-size data, respectively, collected off the three
study passes. The typical range of mineral suspended sediment was
0.02–0.2 mm in diameter, corresponding to representative values of
vs /(ku∗ ) of 0.016–2.262, respectively. This ratio was constant from
the mouth of Southwest Pass up to ∼40 km offshore, confirming
that all sediments were suspended within this narrow river jet
(Supplementary Information).
The exceptionally coherent plume generated by Southwest
Pass—the largest of the Mississippi River outflows—penetrated a
∼1 m s−1 northwest-trending coastal current (Fig. 1 and Supplementary Fig. S8). The absence of a littoral sediment plume and associated sedimentation along the Terrebonne and Barataria shoreline
(Fig. 2 and Supplementary Fig. S8) corroborates that the Southwest
Pass flood plume was insensitive to coastal processes. To examine
the physical basis for these dynamics, we calculate the potential
vorticity for this plume using the bulk parameter derived in ref. 8:
5c = UC/(hW ), where U (m s−1 ) and C (mg l−1 ) are scale quantities for jet velocity and SSC, respectively, and h (m) and W (m)
are channel outlet depth and width, respectively (Supplementary
NATURE GEOSCIENCE | VOL 5 | NOVEMBER 2012 | www.nature.com/naturegeoscience
© 2012 Macmillan Publishers Limited. All rights reserved.
805
NATURE GEOSCIENCE DOI: 10.1038/NGEO1615
LETTERS
a
b
A’
SSC (mg l¬1)
A
60
29.4° N
A
89.5° W
15
20
89° W
0
Velocity contours:
1.2, 0.8, 0.4 m s¬1
29.4° N
40
5
89° W
10
15
20
20
10
SSC (mg l¬1)
0
80
Velocity contours:
1.2, 0.8, 0.4 m s¬1
60
29.4° N
40
29.2° N
29° N
15
28.8° N
28.6° N
0
C’
20
0
C
C’
89.5° W
89° W
5
Section distance (km)
10
15
Section distance (km)
20
Ocean data view
0
89.5° W
150
Ocean data view
B’
Ocean data view
28.6° N
20
B
Ocean data view
29° N
100
C
5
60
28.8° N
0
80
29.2° N
15
d
B’
h (m)
h (m)
10
50
20
Section distance (km)
SSC (mg l¬1)
B
5
40
Ocean data view
Ocean data view
0
60
NE
20
10
Longitude
c
SE
SW
28.8° N
28.6° N
40
40
29° N
80
SW
h (m)
Latitude
SE
29.2° N
80
40
20
5
NE
A’
40
0
20
0
Figure 3 | SSC (mg l−1 ) and velocity (m s−1 ) profiles around the Mississippi River Birdsfoot Delta (1 June 2011). a, Map indicating a large-scale SSC
vertical transect A–A’ around the Birdsfoot Delta; Southwest, Southeast and Northeast passes are highlighted. b, SSC vertical profile along transect A–A’;
three main sediment outflows are indicated. c, SSC and velocity profiles along transect B–B’ offshore of Southwest Pass; inset shows location. d, SSC and
velocity profiles along transect C–C’.
Information). High potential vorticity inputs to the ocean—such
as cold-wind-generated filaments24 or bottom-influenced jets25,26 —
tend to conserve their potential vorticity along the direction of
flow, producing coherent self-sharpening jets24–28 and, in the case
of sediment plumes, localized deposition at jet margins8 . We found
that offshore potential vorticity values were comparable to that
at the channel mouth (that is, potential vorticity was conserved):
5c ∼ 2.49 × 10−5 , 2.24 × 10−5 , 2.14 × 10−5 kg m−4 s−1 , for the
Southwest Pass, Pass 1 and Pass 4 transects, respectively (Figs 1a and
3 and Supplementary Table S1). Data indicate that the Southwest
Pass plume indeed behaved as a self-sharpening jet, a class of flows
known to experience limited mixing with ambient waters27,28 (Figs 1
and 3). The large momentum flux through a relatively narrow
channel outlet, and the absence of strong frictional effects, seem
to be responsible for the lack of interaction between the Southwest
Pass plume and the coastal current (Supplementary Fig. S8). This
pattern is in contrast to the Atchafalaya sediment plume that shifted
direction following ocean currents (Supplementary Fig. S8).
Our analysis suggests that river-mouth hydrodynamics influenced sediment deposition patterns during the spring 2011 flood.
The historic Morganza Spillway opening simulated a more natural
flooding scenario in the Atchafalaya River: this diffuse plume—
influenced by coastal currents and winds—delivered substantial
sediment over a broad area, both directly to wetlands through
inundation and to the nearshore zone where tides and currents
could potentially carry it onshore. Although the Mississippi River
carried a larger sediment load than the Atchafalaya River, it produced less sedimentation. Flow confinement promotes delivery of
vast quantities of sediment far offshore, where it cannot build a
land platform to support wetlands. If the Mississippi River plume
806
was diffuse, its sediments would probably have been carried shoreward with the coastal current to produce substantial deposition
at Barataria and Terrebonne. To address this problem, Mississippi
River diversions are proposed upstream of the Birdsfoot where
sediment would be delivered into shallower receiving basins3,4,29
not currently fed by the Mississippi River at present. Although
the ultimate success of such diversions will depend on a variety
of factors7,30 , our work shows how fine sediments carried in a
flood and diverted to shallow marine settings could contribute
substantially to marsh sedimentation. This finding complements
a recent study demonstrating significant sand deposition in the
Bonnet Carre Spillway resulting from diversion during the same
flood29 . Engineered diversions could harness the full spectrum of
river sediment to mitigate wetland loss in key areas.
Methods
Water discharge and SSC data were obtained from US Geological Survey
surface-water time series (National Water Information System; http://la.water.
usgs.gov/MississippiRiverFlood2011.html/, accessed 12 July 2012) over the range
from 1 April to 30 June 2011. These data were collected by automatic recorders and
manual measurements at field installations. Satellite ocean true-colour images were
obtained from the MODIS. We employed MODIS images processed by the Institute
of Marine Remote Sensing of the University of South Florida (http://imars.marine.
usf.edu/, accessed 5 October 2011). Satellite SSC data were obtained using processed
MODIS Level-1A products, by following a procedure for estimating suspended
load from remote-sensing reflectance high-resolution band 1 at 645 nm. MODIS
images were downloaded through the NASA (National Aeronautics and Space
Administration) Internet servers OceanColor Web (http://oceandata.sci.gsfc.nasa.
gov/, accessed 16 July 2012). Coastal currents were examined using nowcast results
from the South Atlantic Bight and Gulf of Mexico Circulation Model, which is
developed, operated and maintained by the Ocean Observing and Modeling Group
of the Department of Marine, Earth and Atmospheric Sciences at North Carolina
State University (http://omglnx6.meas.ncsu.edu/sabgom_nfcast/, accessed 13 July
NATURE GEOSCIENCE | VOL 5 | NOVEMBER 2012 | www.nature.com/naturegeoscience
© 2012 Macmillan Publishers Limited. All rights reserved.
NATURE GEOSCIENCE DOI: 10.1038/NGEO1615
2012). Satellite sea surface temperature data were recorded by the NOAA (National
Oceanic and Atmospheric Administration) Advanced Very High Resolution
Radiometer sensor. We used sea surface temperature maps provided by the Earth
Scan Laboratory, Coastal Studies Institute of the Louisiana State University (http://
www.esl.lsu.edu/imagery/AVHRR/, accessed 5 January 2012). For a full description
of the methods, see Supplementary Information.
Received 13 August 2012; accepted 24 September 2012;
published online 21 October 2012
References
1. Couvillion, B. R. et al. US Geological Survey Scientific Investigations Map 3164,
scale 1:265,000, 12 p. pamphlet (2011).
2. Day, J. W. et al. Restoration of the Mississippi Delta: Lessons from Hurricanes
Katrina and Rita. Science 315, 1679–1684 (2007).
3. Kim, W. et al. Is it feasible to build new land in the Mississippi River Delta?
Eos Trans. AGU 90, 373–374 (2009).
4. Paola, C. et al. Natural processes in delta restoration: Application to the
Mississippi Delta. Annu. Rev. Mar. Sci. 3, 67–91 (2011).
5. http://www.mvn.usace.army.mil/bcarre/floodfight.asp.
6. Blum, M. D. & Roberts, H. H. Drowning of the Mississippi Delta due to
insufficient sediment supply and global sea-level rise. Nature Geosci. 2,
488–491 (2009).
7. Kearney, M. S., Riter, J. C. A. & Turner, R. E. Freshwater river diversions for
marsh restoration in Louisiana: Twenty-six years of changing vegetative cover
and marsh area. Geophys. Res. Lett. 38, L16405 (2011).
8. Falcini, F. & Jerolmack, D. J. A potential vorticity theory for the formation of
elongate channels in river deltas and lakes. J. Geophys. Res. 115, F04038 (2010).
9. Batker, D. et al. Gaining Ground—Wetlands, Hurricanes and the Economy:
The Value of Restoring the Mississippi River Delta (Earth Economics Tacoma,
WA, 2010). Available at http://www.eartheconomics.org/FileLibrary/file/
Reports/Louisiana/Earth_Economics_Report_on_the_Mississippi_River_
Delta_compressed.pdf.
10. Törnqvist, T. E. et al. Mississippi Delta subsidence primarily caused by
compaction of Holocene strata. Nature Geosci. 1, 173–176 (2008).
11. Kirwan, M. L. & Murray, A. B. A coupled geomorphic and ecological model of
tidal marsh evolution. Proc. Natl Acad. Sci. USA 104, 6118–6122 (2007).
12. Kirwan, M. L. et al. Limits on adaptability of coastal marshes to rising sea level.
Geophys. Res. Lett. 37, 1–5 (2010).
13. Donoghue, J. Sea level history of the northern Gulf of Mexico coast and sea
level rise scenarios for the near future. Climatic Change 107, 17–33 (2011).
14. Coastal Protection and Restoration Authority of Louisiana Louisiana’s
Comprehensive Master Plan for a Sustainable Coast. Coastal Protection and
Restoration Authority of Louisiana. Baton Rouge, LA (2012); available at http://
www.coastalmasterplan.louisiana.gov/2012-master-plan/final-master-plan/.
15. http://la.water.usgs.gov/MississippiRiverFlood2011.html#.
16. Hu, C. et al. Mississippi River water in the Florida Straits and in the Gulf
Stream off Georgia in summer 2004. Geophys. Res. Lett. 32, L14606 (2005).
17. Shi, W. & Wang, M. Satellite observations of flood-driven Mississippi River
plume in the spring of 2008. Geophys. Res. Lett 36, L07607 (2009).
18. Peckham, S. D. A new method for estimating suspended sediment
concentrations and deposition rates from satellite imagery based on the
physics of plumes. Comput. Geosci. 34, 1198–1222 (2008).
19. Walker, N. D., Rouse, L. J. Jr, Fargion, G. S. & Biggs, D. C. The Great Flood
of summer 1993: Mississippi River discharge studied. Eos Trans. AGU 75,
414–415 (1994).
20. Schiller, R. V., Kourafalou, V. H., Hogan, P. J. & Walker, N. D. The dynamics
of the Mississippi River plume: impact of topography, wind and offshore
forcing on the fate of plume waters. J. Geophys. Res. 116, C06029 (2011).
21. Round, F. E., Crawford, R. M. & Mann, D. G. The Diatoms, Biology And
Morphology of the Genera 747 (Cambridge Univ. Press, 1990).
LETTERS
22. White, J. R. et al. Mississippi River flood of 2008: Observations of a
large freshwater diversion on physical, chemical, and biological
characteristics of a shallow estuarine lake. Environ. Sci. Technol. 43,
5599–5604 (2009).
23. Bagnold, R. An approach to the sediment transport problem from general
physics. US Geol. Surv. Prof. Paper 422-I (1966).
24. Bignami, F. et al. On the dynamics of surface cold filaments in the
Mediterranean Sea. J. Mar. Res. 74, 429–442 (2008).
25. Narimousa, S., Maxworthy, T. & Spedding, G. R. Experiments on the structure
and dynamics of forced, quasi-two-dimensional turbulence. J. Fluid Mech. 223,
113–133 (1991).
26. Stern, M. E. & Austin, J. Entrainment of shelf water by a bifurcating continental
boundary current. J. Phys. Oceanogr. 25, 3118–3131 (1995).
27. Wood, R. B. & McIntyre, M. E. A general theorem on angular-momentum
changes due to potential vorticity mixing and on potential-energy changes due
to buoyancy mixing. J. Atmos. Sci. 67, 1261–1274 (2010).
28. Dritschel, D. G. & Scott, R. K. Jet sharpening by turbulent mixing. Phil. Trans.
R. Soc. A 369, 754–770 (2011).
29. Nittrouer, J. A. et al. Mitigating land loss in coastal Louisiana by controlled
diversion of Mississippi River sand. Nature Geosci. 5, 534–537 (2012).
30. Day, J. W. et al. Vegetation death and rapid loss of surface elevation in
two contrasting Mississippi delta salt marshes: The role of sedimentation,
autocompaction and sea-level rise. Ecol. Eng. 37, 229–240 (2011).
Acknowledgements
This work was supported by NSF-RAPID awards (EAR-1140269; OCE-1140307), a
NOAA grant (NA11OAR4310101) and the University of Pennsylvania’s Benjamin
Franklin Fellowship, and received further logistical support from the Luquillo Critical
Zone Observatory (EAR-0722476). The CNR WORK was partially financially supported
by the European Commission MyOcean-2 Project grant agreement (283367). We thank
C. Vervaeke and A. Constantin for assistance with the helicopter survey and T. Touchet,
M. Enache, M. Mills and T. Dura for assistance with sediment and diatom analyses. Field
support from the crew of R/V Acadiana, C. Zhang, P. Dash, A. and A. Kolker is very
much appreciated. We also thank V. Forneris for the collection of L-1A data products.
Any use of trade, product or firm names is for descriptive purposes alone and does not
imply endorsement by the US Government. This paper is a contribution to IGCP project
588 (Preparing for coastal change) and PALSEA.
Author contributions
F.F. performed the satellite analysis, developed the potential vorticity theory for
suspended sediment and coordinated the overall study. N.S.K. contributed to collection,
analysis and presentation of the wetland sediment and diatom data. L.M. and C.B.L.
contributed to the overall study and led the boat survey. B.P.H. contributed to the overall
study approach and participated in data interpretation. M.D. and A.S. performed the
hydrographic and suspended sediment data acquisition and analysis. K.L.M. contributed
to the overall study approach and led the wetland sediment survey. R.S., S.C. and G.V.
contributed to the processing of satellite data, subsequent analysis and presentation.
C.L. contributed to the collection of river-mouth flow velocity profiles, subsequent
data analysis and presentation. D.J.J. supervised the research, participated in data
interpretation and led the writing of the main text. All authors contributed to the
writing of this manuscript.
Additional information
Supplementary information is available in the online version of the paper. Reprints and
permissions information is available online at www.nature.com/reprints. Correspondence
and requests for materials should be addressed to D.J.J.
Competing financial interests
The authors declare no competing financial interests.
NATURE GEOSCIENCE | VOL 5 | NOVEMBER 2012 | www.nature.com/naturegeoscience
© 2012 Macmillan Publishers Limited. All rights reserved.
807