MISSISSIPPI RIVER AND TRIBUTARIES SYSTEM

2011 POST-FLOOD REPORT

APPENDIX F

ENVIRONMENTAL AND CULTURAL RESOURCES

F-i

MISSISSIPPI RIVER AND TRIBUTARIES SYSTEM

2011 POST-FLOOD REPORT

APPENDIX F

ENVIRONMENTAL AND CULTURAL RESOURCES

SECTION I Environmental Team Rosters

SECTION II USGS Water Science Center’s Water Quality in the Lower Mississippi-Atchafalaya 

River Basin During the 2011 Flood, April Through July

SECTION III Water Quality Data Collection and Analyses (includes figures and tables referenced in 

SECTION II)

SECTION IV USGS Water Science Center’s Water-Quality and Phytoplankton Communities in Lake 

Pontchartrain Before, During, and After the Bonnet Carré Spillway Openings in 2008 and 2011, 

Louisiana

SECTION V Entrainment of Pallid Sturgeon Through Floodways During the 2011 Lower Mississippi 

River Flood, summarizing the efforts to enumerate and relocate sturgeon that may have been entrained by 

the various spillways and flood control efforts

SECTION VI Mississippi Department of Marine Resources report 2011 Mississippi River/Bonnet 

Carré Spillway Flood Operation describing the influence of the Bonnet Carré opening on the seafood 

industry in coastal Mississippi
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-1

SECTION II

NOTE: All figures and tables referenced in this Section are found in Section III.

Water quality in the lower Mississippi-Atchafalaya River Basin during the 2011 Flood, April 

through July. By Heather L. Welch, Brent T. Aulenbach, and Richard H. Coupe

Keywords: Surface water, floods, nutrients, water quality

Heather L. Welch, Hydrologist

U.S. Geological Survey

308 South Airport Road, Jackson, MS 39208

601-933-2924 (office); 601-933-2901 (fax)

hllott@usgs.gov

Co-authors:

Brent T. Aulenbach, Hydrologist, U.S. Geological Survey, Atlanta, GA

Richard H. Coupe, Supervisory Hydrologist, U.S. Geological Survey, Jackson, MS

Abstract

In 2011, the lower Mississippi River Basin experienced a flood of historic proportions from April 

through July. This flood marked the first time in history that all three floodways of the Mississippi 

River and Tributaries System (MR&T) Project were operated simultaneously. In order to characterize 

water quality of the River during the flood, the US Geological Survey collected samples for analysis 

of field properties, suspended sediment, nutrients, and pesticides at the Mississippi River at Thebes, 

Illinois, the Ohio River at Dam 53 near Grand Chain, Illinois, six sites located in the lower Mississippi 

River Basin, three sites on the Atchafalaya River, and the three flood-control structures. In addition, 

oil and gas samples were collected at two sites on the Atchafalaya River. Concentrations of 

constituents in water from samples collected during the flood were similar to concentrations that have 

been measured historically. Elevated streamflows associated with the floodwater appeared to dilute 

concentrations of suspended sediment, total nitrogen, and total phosphorus yet the resulting fluxes 

were still large – more often in May, the month of the highest average monthly streamflow. Opening 

two of the three flood control structures – the Bird’s Point-New Madrid Floodway and the Morganza 

Floodway– had little effect on water quality in the lower Mississippi and the Atchafalaya Rivers. 

Although total nitrogen and total phosphorus concentrations stayed relatively the same throughout the 

flood period in water from the Mississippi River, there was a decrease in total nitrogen concentrations 

and an increase in total phosphorus concentrations (primarily in the dissolved phase), from 0.16 to 

0.52 milligram per liter with the opening time in the Morganza Floodway which indicates that 

chemical processing is occurring. Approximately 1.4 million metric tons of suspended sediment, 

36,500 metric tons of total nitrogen, 3,300 metric tons of total phosphorus, and 12 metric tons of 

atrazine were diverted from the main stem of the lower Mississippi River through the Bonnet Carré 

Spillway into Lake Ponchartrain below Baton Rouge, Louisiana while the Spillway was open in May 

and June 2011. 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-2

Introduction

The Mississippi River Basin (MRB) drains approximately 41 percent of the conterminous United 

States and is the largest river basin in North America (Figure 1). Citizens of the United States use the 

river for municipal, industrial, agricultural, and recreational purposes. The majority of corn, soybeans, 

wheat, cattle, hogs, and to a lesser extent cotton and rice produced in the U.S. originate from regions 

within the MRB. In order to optimize agricultural production, pesticides and fertilizers are applied to 

the landscape, and these agricultural chemicals along with sediment from agricultural fields can be 

transported into streams that eventually flow into the Mississippi River and ultimately to the Gulf of 

Mexico. Since at least 1980, a zone of hypoxia (containing less than 2 milligram per liter (mg/L) of 

dissolved oxygen) has formed during the spring and summer in the Gulf of Mexico off the coast of 

Louisiana. The zone has increased in size since measurements began in the early 1980s, and its extent 

is positively related to the annual amount of nitrogen entering the Gulf from the Mississippi River 

(Rabalais et al., 2002). More recently, models have indicated that there is also a positive correlation 

between phosphorus flux to the Gulf of Mexico and the size of the zone of hypoxia (Scavia et al., 

2004; Donner and Scavia, 2007; Scavia and Donnelly, 2007; Turner et al., 2008; Boesch et al., 2009). 

In response to the devastating 1927 flood, the MR&T Project was authorized by the Flood Control Act 

of 1928 which called for the creation of a levee system to prevent overflow on developed alluvial 

lands, floodways to divert excess streamflow past critical reaches, channel improvements and 

stabilization, and tributary basin improvement (Mississippi River Commission, 2008). This system 

was tested in April and May 2011, when the Ohio River Basin and parts of the lower MRB received 

over 5 times more precipitation than normal (Anderson, 2011). The precipitation combined with snow 

melt from the upper MRB resulted in historic flood levels. In most areas of the lower MRB, the river 

remained above flood stage for 2 1⁄2 to 3 months. Due to high streamflows measured along the main 

stem of the river and to prevent loss of property and life, this was the first time in history that all three 

floodways were operated simultaneously (Anderson, 2011; Schneider, 2011). 

Floods by their very nature inundate lands not usually covered by water, so chemicals and sediment 

associated with the landscape can be carried by floodwaters great distances from their source area. 

The introduction of large amounts of water onto the landscape may overwhelm a surface-water 

system’s ability to process agricultural chemicals, such as nutrients and pesticides, which may result in 

large amounts of these chemicals moving downstream to larger surface-water bodies such as the Gulf 

of Mexico. The 2011 Flood, in particular, occurred at a time during the year when agricultural 

chemicals were being applied throughout the Basin, and when fields were being tilled leaving the land 

more susceptible to overland runoff of chemicals and sediment. In addition to contaminant concerns 

associated with inundation of the alluvial floodplain, there was some concern that opening the floodcontrol structures, which inundated additional agricultural acreage and lands containing oil wells and 

industrial chemicals, would carry any associated chemicals back into the main stem of the Mississippi 

River when the floodwaters receded. 

Although there has been extensive documentation on the water-quality effects of floods (such as the 

one that occurred in the summer of 1993) in the upper MRB (Horowitz, 2010; Schalk et al., 1998; 

Holmes, 1996; Taylor et al., 1994; Goolsby et al., 1993), little has been published on water-quality 

effects in the lower Mississippi-Atchafalaya River Basin (MARB). This paper (1) documents all data 

collected by the US Geological Survey in the lower MARB during the Mississippi River flood from 

April through July of 2011, (2) summarizes the water quality of the Mississippi River during the flood 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-3

and compares that quality to historical observations (3) compares nitrogen, phosphorus, pesticide, and 

sediment fluxes at stations in the lower Mississippi River (starting just above the confluence of the 

Ohio and Mississippi Rivers) for May 2011, and (4) assesses the effects of opening the Bird’s PointNew Madrid Floodway and the Morganza Floodway on water quality in the Mississippi River.

Hydrology

The Mississippi River originates in Lake Itasca, Minn., and courses over 3,770 kilometers (km) 

through the middle United States until it empties into the Gulf of Mexico. The river and its tributaries 

drain parts or all of 31 states from a basin area of approximately 3.2 million km2

, ranking 3rd in size 

behind the Amazon and Congo Rivers. The drainage area of the river has been subdivided into three 

portions: (1) the upper MRB which is the portion upriver from the confluence with the Missouri River; 

(2) the middle MRB which is inclusive of the Missouri River Basin and upriver from the confluence 

with the Ohio River; and (3) the lower MRB which is downriver from the confluence with the Ohio 

River and eventually flows into the Gulf of Mexico. This paper focuses on the response of the river to 

the 2011 Flood in the lower MRB. 

Parts of the lower MRB drain streams located in the Mississippi Alluvial Plain, a relatively flat plain 

with rich, productive soils that are used extensively for agriculture. There is also contribution from 

streams located in rangeland, urban areas, and mountainous regions. Many tributaries such as the 

White River, Arkansas River, Yazoo River, and Big Black Rivers contribute to streamflow in this 

portion of the MRB; however, only 75 percent of that streamflow enters the northern Gulf of Mexico 

through the river’s delta (Horowitz, 2010). The remaining streamflow is diverted by the Old River 

control structure downstream from Vicksburg, Miss. where it merges with the Red River to form the 

Atchafalaya about 40 km upstream from Melville, La. (Meade, 1995; Mossa, 1996). Half of the water 

discharged to the Gulf of Mexico is contributed by the Ohio River and its tributaries, which represent 

approximately one-sixth of the total area drained by the Mississippi River; whereas, the Missouri 

River drains 43 percent of the MRB, but contributes only about 12 percent of the total streamflow to 

the Gulf of Mexico (Meade, 1995). 

There are three major floodways located in the lower MRB: the Bird’s Point-New Madrid Floodway, 

Mo., the Morganza Floodway, La., and the Bonnet Carré Spillway, La. (table 1). Prior to 2011, the 

Bird’s Point-New Madrid Floodway had been operated once, the Morganza Floodway had been 

operated once, and the Bonnet Carré Spillway had been operated nine times (Schneider, 2011). On 

May 2nd, 2011 the Bird’s Point-New Madrid Floodway was activated followed on May 9th by the 

opening of the Bonnet Carré Spillway to keep streamflows passing New Orleans, La. at approximately 

35,400 m3

/s (Anderson, 2011). Lands were inundated by floodwater through the Bird’s Point-New 

Madrid Floodway through May 19, 2011. The final gates on the Bonnet Carré Spillway were closed 

on June 20, 2011. The Morganza Floodway was opened on May 14th, 2011 when streamflows in the 

Mississippi River reached approximately 42,500 m3

/s (Anderson, 2011) and remained open through 

July 7, 2011. 

Water-Quality Sampling Sites

The objective of the USGS National Stream Quality Accounting Network (NASQAN) program in the 

mid-1970s was to account for quantity and quality of water moving within and from the United States. 

Since 1995, NASQAN has monitored water quality in the MRB to provide an ongoing 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-4

characterization of the concentrations and mass fluxes of sediment and agricultural chemicals at key 

locations in the Basin, to determine regional source areas for these materials, and to assess the effect of 

human influences on observed concentrations and fluxes (Coupe and Goolsby, 1999). NASQAN 

sampling stations were selected at critical junctures within the MRB to provide the essential 

framework for understanding fluxes of materials within the Basin and to the Gulf of Mexico. An 

important consideration for station selection was the influence of varying land use, and the presence of 

major reservoirs and input from major tributaries. Generally, stations were selected where substantial 

changes in mass flux were expected, such as at confluences of major tributaries or at the downstream 

end of major reservoirs. The nine NASQAN stations sampled for water quality during the flood are 

shown in figure 1 and described in table 1. The sampling site at the Mississippi River at Thebes, Ill. 

will be referred to as the Upper Mississippi River, and the sampling site at the Ohio River at Dam 53 

near Grand Chain, Ill. will be referred to as the Ohio River. In addition to NASQAN stations, four 

additional stations were sampled to quantify the effects of the opening of the Bird’s Point-New Madrid 

Floodway. These stations were at the inlet and outlet of the Bird’s Point-New Madrid Floodway (map 

#s 3 and 4 on figure 1; table 1) and downstream of the Bird’s Point-New Madrid Floodway outlet on 

the Mississippi River at Tiptonville, Tenn. and Memphis, Tenn. Water-quality samples were collected 

in the Morganza Floodway at the Atchafalaya Floodway near Ramah, La. north of I-10 (map #10, 

figure 1; table 1), and sediment and streamflow data were collected at the Morganza Spillway at 

Highway 190 near Lottie, La. Both sites will be collectively referred to as the Morganza Floodway. 

Water-quality, sediment, and streamflow data were collected from water in the Bonnet Carré Spillway 

at U.S. Highway 61 near Norco, La. (map #14, figure 1; table 1). In this report, this site will be 

referred to as the Bonnet Carré Spillway.

Methods

Sample collection, processing, and analysis

Water quality samples are typically collected 12 to 14 times per year at NASQAN sites. From April 

through July 2011, the frequency of sample collection was increased to monitor the effects of the highflow event. Samples were collected every other week in April, then weekly starting from the second 

week in May through the end of June, and every other week in July for a total of 12 samples (Map #s 7 

– 9 and 12-14, figure 1; table 1). Exceptions to this sampling protocol were at the Mississippi River at 

Baton Rouge, La. (map #11, sampled every other week April through June for a total of 6 samples), 

the Ohio River (map #2, four samples in May, two in June), and the Upper Mississippi River (map #1, 

sampled every other week April through June and monthly in July for a total of 7 samples). Periodic 

water quality samples were taken while the Bird’s Point-New Madrid Floodway was in operation 

during the flood. Samples were collected on May 5th at both the inlet and the outlet of the Bird’s 

Point-New Madrid Floodway along with downstream Mississippi River stations at Tiptonville, Tenn. 

and Memphis, Tenn. A sample was also collected on May 18 at the Mississippi River at Memphis, 

Tenn. All samples were analyzed for major inorganics, dissolved organic carbon, alkalinity, nutrients, 

pesticides, turbidity, field parameters, and suspended sediment. Additional analysis was added for 

particle size determination of the suspended sediment. 

Streamflow was measured and sediment samples were collected on the Morganza Floodway at a 

different location than the other water-quality data. At the Morganza Spillway at Highway 190 near 

Lottie, La., streamflows were measured daily from May 14th through June 27th, and sediment samples 

were collected from May 18th through June 10th (figure 1). The Bonnet Carré Spillway was sampled 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-5

seven times in May and June, and 28 sediment samples were collected at the site during the same time 

period. Samples for oil and gasoline analysis were collected at the Atchafalaya River at Melville, La. 

and the Lower Atchafalaya River at Morgan City, La. seven times in May and June (figure 1). 

The Acoustic Doppler Current Profiler (ADCP) method described by Olson and Norris (2007) was

used by the USGS to measure instantaneous streamflow at the sampled stations, where streamflow is 

the volume of water moving down a stream or river per unit of time (m3

/s). At four stations (sites 2, 7, 

8, and 9; figure 1 and table 1), instantaneous streamflow was measured at a separate location from 

where the water-quality sample was taken. The mean daily streamflow (Q) was calculated and 

reported by the USGS according to standard procedures (Rantz, 1982). Daily streamflow at the 

Mississippi River at Tarbert Landing, Miss. Old River outflow channel near Knox Landing, La. (total 

outflow) and at the Atchafalaya River at Simmesport, La., is measured by the U.S. Army Corps of 

Engineers. 

Sediment and water-quality samples were collected using isokinetic depth-integrated samplers 

according to protocols detailed in the USGS National Field Manual for the Collection of Water 

Quality Data (US Geological Survey, variously dated). The equal-discharge increment (EDI) 

sampling method was used to collect a streamflow-weighted sample representing the entire flow 

passing through the cross section. The equal-width increment (EWI) sampling method was used to 

collect the samples at sites 8 through 15 (figure 1; table 1). Suspended sediment concentration (SSC) 

samples were analyzed at either the U.S. Geological Survey (USGS) Sedimentation Laboratory in 

Baton Rouge, La., or the Sedimentation Laboratory in Iowa City, Ia., according to the method 

described by Guy (1969). Particle size analysis was performed by the USGS Sedimentation 

Laboratory in Iowa City, Ia. 

All samples for analysis of major ions and nutrients were preserved according to standard protocols 

and those samples along with samples for pesticide analysis were shipped overnight on ice for analysis 

at the USGS National Water-Quality Laboratory (NWQL) in Denver, Co. Major ions were measured 

using atomic absorption spectrometry, and nutrient concentrations were quantified using colorimetry 

(Fishman and Friedman, 1989). Pesticides analyzed at the NWQL were quantified using gas 

chromatograph-mass spectrometry. 

Samples for hydrocarbon analysis were chilled to 4° Celsius and shipped overnight for analysis at 

TestAmerica Laboratories, Inc. in Arvada, Co. Gasoline range organics were separated using a purge 

and trap method, and then analyzed using a gas chromatograph with a flame ionization detector (GCFID) as outlined by the US Environmental Protection Agency (1986). Diesel range organics were 

extracted using a separatory funnel liquid-liquid extraction method and analyzed for using GC-FID 

(US Environmental Protection Agency, 1986). Hexane extractible compounds were separated using 

solid-phase extraction and analyzed for using a gravimetric method (US Environmental Protection 

Agency, 1999). 

Data analysis

Some concentrations of pesticides and nutrients were estimated (“E”) by the USGS NWQL. Values 

coded with a remark code of “E” were treated as detections in this report, unless the value was lower 

than the method reporting level (MRL) for that constituent. All detected values lower than an 

established MRL were “censored,” or reported as less than (<) the MRL. Table 2 lists selected 

constituents and their established MRLs. 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-6

Flux estimation methods

Streamwater constituent load, also known as mass flux, is the mass of chemical constituent or 

sediment transported past a point in a stream over a period of time. Flux () is the product of 

constituent concentration (C) and streamflow (Q) integrated over time (t):

 (1)

Flux calculations using the integral in equation 1 require a continuous record of concentration and 

streamflow. Although streamflow can be measured at a sufficiently high frequency, constituent 

concentration typically is measured less frequently due to the expense and effort of collecting and 

analyzing water-quality samples. Several flux estimation approaches have been proposed to address 

the issue of using only discrete concentrations. The approach employed is known as the regressionmodel method, also known as the rating-curve method, which is a standard statistical technique that 

can be used to estimate concentration continuously, thus enabling a direct calculation of mass flux. 

This method uses a regression model relating concentration (or load) to continuous variables such as 

streamflow and day of year (for example, Johnson, 1979; Cohn and others, 1992). Fluxes were 

estimated using a seven-parameter regression model equation of the form:

ln(Li) = a0 + a1 lnQ + a2 lnQ2 + a3 sin(2dtime) + a4 cos(2dt

 + a5 dtime +a6 dtime2 +  (2

where

ln is the natural logarithm (log base e);

Li is the calculated load for sample i; 

lnQ is ln(daily average streamflow) minus center of ln(daily average streamflow);

dtime is decimal time minus center of decimal time (as defined by Cohn and 

others, 1992); 

is error; an

a0...a6 are the fitted parameters in the multiple regression model.

Fluxes were estimated with the regression-model method using Load Estimator (LOADEST), a 

FORTRAN-based flux estimation program (Runkel and others, 2004). LOADEST allows users to 

choose from three methods to estimate fluxes based on the statistical distribution of the calibration 

data set, which includes time series of streamflow, concentration, and other variables. The method 

selected to estimate fluxes in this report was the adjusted maximum likelihood estimate (AMLE), 

which is appropriate for estimation when a dataset contains censored data (concentrations less than the 

MRL). The AMLE method corrects for first-order bias in the regression coefficients (due to the 

presence of censored data in the calibration data set) and minimizes other biases such as when 

estimated logarithms of flux are retransformed to original units (Cohn et al., 1992). LOADEST allows 

users the option to automatically select an optimal model form from the nine possible choices based on 

equation 2 (model forms include equation 2 and eight subsets of the parameters in equation 2). Autoselection involves computation of the Akaike Information Criterion (AIC) statistic as described in 

Judge et al.(1988), and then the model form with the lowest value of the AIC statistic was the one 

selected. 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-7

While AMLE fluxes are estimated by LOADEST on a daily time-step, fluxes are reported here on a 

monthly time-step because of potentially large errors in estimating fluxes for short time intervals. 

Even at a monthly time-step, fluxes can be imprecise. As a means to describe uncertainty, LOADEST 

provides lower and upper 95 percent confidence intervals for each flux estimate. The confidence 

intervals are based on the standard error of prediction which includes both the estimate of parameter 

uncertainty and the unexplained variability about the model, referred to as random error (Runkel and 

others, 2004). When describing uncertainty and errors associated with using a regression based 

approach, such as LOADEST, an assumption is made that there is negligible error in the 

measurements of daily streamflow. While potential errors in measuring streamflow are generally 

small, uncertainty estimates are likely to be somewhat understated due to this false assumption. 

Therefore, confidence intervals are included with each monthly flux estimate in the report such that 

the differences in flux estimates can be assessed appropriately.

It should be noted that flux estimates presented in this report are calculated using the same approach as 

Aulenbach et al. (2007). In their paper, dissolved nitrate plus nitrite, total nitrogen, total phosphorus, and 

other nutrient fluxes were estimated for the Mississippi-Atchafalaya River Basin (to determine delivery 

to the Gulf of Mexico) and for many smaller subbasins within the MARB for each station’s period of 

record through 2005 and are updated annually by the USGS 

(http://toxics.usgs.gov/hypoxia/mississippi/flux_ests/index.thml).

In addition to the LOADEST AMLE flux estimates, fluxes were also estimates using the composite 

method during this period (Aulenbach and Hooper, 2006). The composite method is a hybrid flux 

estimation method that combines aspects of two commonly used methods: the regression-model 

method, which is used by the composite method to predict variations in concentrations between 

collected samples; and a period-weighted approach, which is used by the composite method to apply 

the residual concentrations from the regression model over time. Residual concentrations are the 

difference between the observed and model-predicted concentrations. In this approach, on days with 

observations, the model-predicted concentrations are adjusted to observed concentrations; and on days 

between observations, the model-predicted concentrations are adjusted by applying a piece-wise linear 

function of the residual concentrations as per a period-weighted approach. This approach is useful in 

situations in which there is serial autocorrelation in the residuals – residuals are not independent and 

identically distributed – such that there is structure (or patterns) in the residuals that contain some 

meaningful information that can be used to improve flux estimates. When sampling frequency is 

increased, serial autocorrelation between samples generally increases, and the composite method 

should improve adjusting predicted regression model concentrations to observed concentrations, 

thereby improving model fit.

The composite method fluxes presented here are based on the same regression models used to estimate 

LOADEST AMLE fluxes. Composite method flux estimates have previously been reported in 

Aulenbach, et al. (2007), but only for the two lower Mississippi-Atchafalaya River Basin stations 

(Mississippi River near St. Francisville, La. and Atchafalaya River at Melville, La.). The composite 

method flux estimates may be the preferred flux estimates during the flood period because for many

constituents and stations, the sampling frequency is either weekly or bi-weekly during the April 

through July flood period. An unpublished sub-sampling analysis using a daily suspended sediment 

dataset indicated that, for flux estimation for large rivers, the composite method can improve flux 

estimates for sampling frequencies of at least 15-days while also reducing variability observed within 

the calibration period. However, for the particular sub-sampling analysis, the composite method did 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-8

not improve flux estimates over the AMLE approach for monthly sampling frequencies. Another 

consideration for using the composite method is that the regression models may be poorly constrained 

at the highest streamflows during the flood because: (1) some constituents exhibit hysteresis in which 

the concentrations on the rising limb of the flood hydrograph do not match the falling limb of the 

hydrograph (regression model will predict average response at a particular streamflow); and (2) there 

are only a few observations of water-quality at the highest flows. For this report, the composite model 

can improve flux estimation during the flood by adjusting the AMLE predicted concentrations to the 

observed concentrations. Unfortunately, there is no way to estimate uncertainty associated with the 

composite method. But, it can be reasonably assumed that for periods with sampling frequencies of at 

least 15-days, loads estimated using the composite method should compare as well to observed loads 

as do loads estimated using the LOADEST AMLE method. 

Fluxes of selected pesticides for April through July 2011 that did not have a strong concentrationstreamflow relationship necessary for use in a regression-model method approach, or had an 

insufficient long-term dataset from which to create a concentration model with LOADEST, were 

estimated using a period-weighted approach in which measured concentrations were assumed to 

represent a period around which the sample was collected. A piecewise linear function 

implementation was used in which sample concentrations were linearly interpolated through time 

between sample collections (e.g. Larson et al., 1995). The products of concentration and streamflow 

were summed through time to estimate flux. All samples collected were used in the estimation, and 

there was no preconceived model for concentration. The flux estimate was sensitive to sampling 

frequency and distribution, and there was no estimate of error. 

Flux Estimation Implementation

Fluxes were estimated for the April through July 2011 Flood period and were summarized in this 

report on a monthly basis. Fluxes were estimated for 22 constituents: dissolved nitrate plus nitrite, 

total organic nitrogen plus ammonia (total Kjeldahl nitrogen), dissolved organic nitrogen plus 

ammonia (dissolved Kjeldahl nitrogen), total particulate nitrogen, and dissolved ammonia, total 

phosphorous, dissolved orthophosphate, particulate carbon, particulate inorganic carbon, particulate 

organic carbon, dissolved organic carbon, dissolved silica, dissolved chloride, suspended sediment, 

total dissolved solids (residue on evaporation),simazine, prometon, cyanazine, metolachlor, atrazine, 

alachlor, and acetochlor. In addition to these species, total nitrogen fluxes were estimated by summing 

dissolved nitrite plus nitrate and total Kjeldahl nitrogen fluxes. Fluxes were estimated for only seven 

constituents at the Red River at Alexandria, La. This is not a NASQAN station, so the water-quality 

constituents collected there are not the same as those collected at NASQAN sites. Thirteen constituent 

fluxes were estimated for the Yazoo River near Long Lake. This was recently added as a NASQAN 

station, and there were not five-years of water-quality data to calibrate regression models for all 

constituents. LOADEST requires a minimum of 12 samples, 7 of which must be uncensored, in order 

to calibrate a regression model and estimate fluxes. The water-quality dataset was prepared and 

screened for outliers as per Aulenbach et al. (2007). A change was made to these protocols for days 

with multiple samples. In lieu of averaging all sample concentrations collected on that day (including 

replicates), concentrations were instead designated from the first available sample that had a 

concentration for that constituent by sorting all samples according to: (1) routinely collected samples; 

(2) arranging samples in decreasing order by the number of water-quality constituents each sample 

contained in the analysis; and (3) ordering the samples by collection time from earliest to latest.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-9

Regression models were calibrated using the samples collected during the 5-year period water years 

2006 through 2011. The calibration period is set such that it is long enough to contain enough sample 

concentrations to sufficiently develop the regression model while not being so long that there are 

significant changes, or drift, in the model regression over the calibration period. The calibration period 

used corresponds to the calibration period that will be used for estimating fluxes at NASQAN sites for 

the 2011 water year (water year is the same as the Federal fiscal year). Hence, the results herein should 

be consistent with results published later by the USGS for the 2011 water year. One exception to the 

5-year calibration period was for the station Mississippi River above Vicksburg, which was calibrated 

for only three years, 2009 through 2011, as water-quality sampling at this station only recently 

initiated.

The fluxes for the Mississippi River near St. Francisville (downstream of the Old River diversion 

where about, on average, 25 percent of the Mississippi River streamflow is diverted to the Atchafalaya 

River) are estimated using a more complex regression model that is used by the USGS NASQAN 

program (Aulenbach et al., 2007). The streamflow used in the regression model is not the streamflow 

of the Mississippi River at Tarbert Landing, but is the Tarbert Landing streamflow combined with the 

streamflow diverted via the Old River representing the total lower MRB flow. Furthermore, it was 

found that variations in water quality at St. Francisville were related to variations in streamflow 

contributions of the upper Mississippi plus Missouri River Basins, and the Ohio plus Tennessee River 

Basins. Therefore, flow and flow-squared terms for the Upper Mississippi River and the Ohio River at 

Metropolis, Ill. were added to the regression models. These flows were lagged by 10-days to account 

for travel times for streamwater from these upstream stations to reach St. Francisville during about 

average flow conditions. The use of a custom model form with additional variables precluded the use 

of the LOADEST feature of auto-selecting the best model by using the lowest value of the AIC 

statistic. Hence, all model terms were always included. So that flux estimates represented only fluxes 

at the Mississippi River near St. Francisville, daily flux estimates were multiplied by the ratio of the 

streamflow at the Mississippi River at Tarbert Landing, Miss. and the total lower MRB streamflow 

before summarizing fluxes at other time steps.

Fluxes were not directly estimated at the Old River Diversion, Bonnet Carré Spillway, and Morganza 

Floodway as there was insufficient long-term water quality sampling at these stations to develop 

regression models. Instead, fluxes were calculated based on fluxes estimated using the water quality at 

St. Francisville prorated on a daily basis based on comparison of streamflows of the Old River 

Diversion, Bonnet Carré Spillway, and Morganza Floodway with respect to the streamflows at Tarbert 

Landing. These flux estimates were likely reasonable for dissolved constituents as these streamflow 

diversions were in the vicinity of St. Francisville, and dissolved constituents were likely to be 

reasonably well mixed in the water column. Suspended sediment, particulate, and total constituent flux 

estimates may be over-representative of actual flux due to suspended material settling out of the water 

column before entering these diversions. It should be noted that the Morganza Floodway is upstream 

of the Mississippi River near St. Francisville water-quality station, but downstream of the Mississippi 

River at Tarbert Landing streamflow station. Therefore, the flux estimates for the Morganza 

Floodway are representative of the streamflow at Tarbert Landing as the streamflows used to estimate 

the fluxes did not take into account the streamflows diverted upstream of St. Francisville when the 

Morganza Floodway was in operation during the flood.

May flux estimates for the Yazoo River below Steele Bayou near Long Lake, Miss. were complicated 

by backwater conditions that occurred during the flood that month. Backwater conditions, in which 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-10

water from the flooding in the Mississippi River flowed upstream in the lower Yazoo River, resulted

in 20 days of negative daily average streamflow in May at the Yazoo River station. For these days, it 

was assumed the stream water-quality was similar to that of the Mississippi River above Vicksburg, 

Miss. Therefore, the flux on these days were calculated as the daily flux from Mississippi River above 

Vicksburg, prorated by a ratio of streamflow of the Yazoo River and the Mississippi River above 

Vicksburg. It should be noted that the streamflow station for the Mississippi River is at Vicksburg, 

Miss., downstream of the confluence of the Yazoo River – hence, the streamflow for the Mississippi 

River above Vicksburg is calculated as the difference between the streamflow at the Mississippi River 

at Vicksburg and streamflow of the Yazoo River. The average streamflow and all of the fluxes on the 

Yazoo River are negative in May, indicating net streamflow and fluxes going upstream from the 

Mississippi River back-flooding into the lower Yazoo River Basin (presented as a negative average 

streamflow and as negative fluxes of suspended sediment, nitrogen, and phosphorus).

The monthly fluxes for streamflow, total nitrogen, total phosphorus, atrazine, metolachlor, and 

suspended sediment are discussed for May 2011 and are compartmentalized for discussion by 

comparing inputs from the Upper Mississippi River and the Ohio River to outputs to the Gulf of 

Mexico, which are calculated by adding fluxes from the Wax Lake, Morgan City, and Tarbert Landing 

sites and then subtracting fluxes from the Morganza Floodway and Bonnet Carré Spillway. One issue 

with this approach is travel time between the sites, for example, sites located close together do not 

exhibit the same time lag in constituent travel as those located further apart. 

Results 

Streamflow 

Peak flows measured during the 2011 Flood (April through July) were 24,150 m3

/s at the Upper 

Mississippi River, 35,700 m3

/s at the Ohio River, 65,400 m3/s at Vicksburg, 45,800 m3/s at St. 

Francisville, 40,500 m3

/s at Baton Rouge, and 34,800 m3/s at Belle Chasse (table 1). In the Upper 

Mississippi River and the Ohio River, median instantaneous streamflow (at the time of water-quality 

sampling) was almost three times higher than the historical median instantaneous streamflow (figure 

2). Median instantaneous streamflow measured during the flood at the four sites on the main stem of 

the lower Mississippi River were approximately twice as high as median instantaneous streamflows 

measured for the period of record at those sites. 

Average monthly streamflow was highest for the flood period during May 2011. Approximately 

16,700 m3

/s and 25,600 m3/s contributed to streamflow in the lower MARB from the Upper 

Mississippi River and the Ohio River, respectively. Average monthly streamflow was 35 percent 

higher in the Mississippi River at Vicksburg than the streamflow of the Upper Mississippi and the 

Ohio River combined (figure 3). In fact, the highest average monthly flow for the entire flood period 

was measured in May at Vicksburg (56,900 m3

/s). Below Vicksburg, Miss., about 30 percent of the 

Mississippi River flow was diverted through the Old River Channel and about 4 percent moved 

through the gates of the Morganza Floodway. The remaining 70 percent moved past St. Francisville, 

La. and Baton Rouge, La (locations in figure 1). Below Baton Rouge, flow was further dispersed 

with approximately 14 percent of what remained diverted into Lake Pontchartrain through the Bonnet 

Carré Spillway. 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-11

Sediment

Suspended sediment concentrations measured in surface water at four sites in the lower MRB, the 

Upper Mississippi River, and the Ohio River during the 2011 Flood were within the range of 

concentrations measured historically at these sites (figure 4). In fact, median suspended sediment 

concentrations measured at Vicksburg, Miss., St. Francisville, La., Baton Rouge, La., and Belle 

Chasse, La. measured during the 4-month flood period were lower than the median suspended 

sediment concentration at each site from samples collected over the period of record. The median 

suspended sediment concentration for samples collected during the flood in the Upper Mississippi 

River was slightly higher than the historical median of samples collected at this site (figure 4). 

Higher concentrations of suspended sediment were measured in water from the Mississippi River at 

Vicksburg, Miss., and St. Francisville, La. in early March (figure 5). Sampled sites upstream and 

downstream of these two sites also had high suspended sediment concentrations in March (data not 

shown). Concentrations of suspended sediment on March 1 at Vicksburg were 5 times higher than the 

median suspended sediment concentration measured during the flood period, but streamflow at the site 

on March 1 was 45 percent less than the median streamflow measured during the flood. Suspended 

sediment concentrations measured on March 8 at St. Francisville were 7 times higher than the median 

concentration of suspended sediment during the flood. The streamflow associated with the high 

suspended sediment concentration in March at St. Francisville was 25 percent less than the median 

streamflow measured during the flood period. 

Average monthly suspended sediment fluxes were highest during May 2011 with the exception of

Tarbert Landing (flux was approximately the same in April and May) and the Upper Mississippi River 

(fluxes in June and July were about 14.3 and 15.3 million metric tons, respectively). Suspended 

sediment flux from the Upper Mississippi River was 1.7 times higher than the suspended sediment 

flux entering the lower MARB from the Ohio River. During May, the highest average flux of 

suspended sediment was measured at Vicksburg, Miss. (18.8 million metric tons). There is a 7.5 

million metric ton loss between the flux at Vicksburg and the fluxes entering the Old River Channel 

and the fluxes moving past Tarbert Landing down the main stem of the Mississippi River. 

Approximately, 171,000 metric tons of the loss is due to backwater conditions in the Yazoo River. 

Four times more suspended sediment is leaving the Atchafalaya River Basin than is entering through 

the Old River Channel. Between the entry of the water into the Old River Channel and Melville, there 

is a tripling in suspended sediment flux, and the flux again increases between Melville and the 

bifurcation of the water at Wax Lake and Morgan City (increase in suspended sediment flux of 1.3 

times). Although not quantified, the Red River may have added up to 6 million metric tons to the 

Atchafalaya system in May 2011. Comparing the inputs of suspended sediment flux (the Upper 

Mississippi River plus the Ohio River) with the outputs (Wax Lake plus Morgan City plus Tarbert 

Landing minus the Morganza Floodway and Bonnet Carré Spillway); there is a cumulative gain of 2.2 

million metric tons of suspended sediment flux in the lower MARB in the month of May. 

Nutrients

Nutrient concentrations measured during the flood were of the same magnitude as concentrations 

measured historically at the Upper Mississippi River, the Ohio River, and the four downstream sites 

along the main stem (Fig 7; a and b). Median concentrations of total nitrogen were approximately the 

same as the median concentration for the period of record, except in the Upper Mississippi River 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-12

where concentrations measured during the flood were higher than the historical median total nitrogen 

concentration (figure 7a). Median total phosphorus concentrations during the flood (figure 7b) were 

higher at the Upper Mississippi River and the Ohio River; however, median concentrations of total 

phosphorus were less than the median for the period of record at St. Francisville and Baton Rouge. 

The highest concentrations of total nitrogen measured in water from the Mississippi River at 

Vicksburg, Miss., occurred before and after the period when maximum streamflows were measured in 

the river (figure 8). On March 1st, the total nitrogen concentration was 3.3 mg/L which was the largest 

concentration measured from January through August 2011 and was 1.5 times higher than the median 

total nitrogen concentration (2.2 mg/L) during the flood period. Total nitrogen concentrations 

increased in mid-June and remained above 2 mg/L until August. The total phosphorus concentration 

measured on March 1st was almost 3 times higher than the median concentration for total phosphorus 

in water at Vicksburg during the flood (0.19 mg/L). In fact, the concentration measured on March 1st

was the highest concentration measured from January through August – measured concentrations from 

this time period ranged from 0.16 to 0.23 milligrams per liter. 

Total nitrogen fluxes in the lower MARB during the flood period were highest in May 2011 at all 

sampled sites. The flux of total N entering the lower MARB was 35 percent more from the Upper 

Mississippi River than from the Ohio River (figure 9). The maximum total N flux in May 2011 

occurred at Vicksburg (262,000 metric tons); of this flux, 6-percent was lost, 26-percent was diverted 

through the Old River outflow, and 68-percent moved along the main stem past Tarbert Landing. A 

portion of the 6-percent loss is attributed to backwater conditions in the Yazoo River where there was 

a 1,800 metric ton loss in total nitrogen. There was a 7-percent increase in total N flux leaving the 

Atchafalaya River Basin from the total N flux that entered at the Old River outflow. The gain 

occurred between the confluence of the Red River with the Atchafalaya and the sampled site at 

Melville. The majority of the total N flux leaving the lower MARB and entering the Gulf of Mexico is 

through the main stem (Approximately 143,100 metric tons from Tarbert Landing minus the 

Morganza Floodway and Bonnet Carré Spillway compared to approximately 73,000 metric tons from 

the Atchafalaya River Basin computed from the loads at Wax Lake and Morgan City). Comparing the 

inputs of total N fluxes (the Upper Mississippi River plus the Ohio River) with the outputs (Wax Lake 

plus Morgan City plus Tarbert Landing minus the Morganza Floodway and Bonnet Carré Spillway); 

there is a cumulative loss of 56,630 metric tons of total nitrogen in the lower MARB in the month of 

May. 

Total phosphorus fluxes in the lower MARB during the flood period were highest in May 2011 at all 

sampled sites except for the Upper Mississippi River where total P fluxes in June and July were about 

15,000 metric tons. The flux of total P entering the lower MARB was 18 percent more from the 

Upper Mississippi River than from the Ohio River (figure 10). The maximum total P flux in May 

2011 occurred at Vicksburg (26,200 metric tons); of this flux, 12-percent was lost, 24-percent was 

diverted through the Old River outflow, and 63-percent moved along the main stem past Tarbert 

Landing. There was a 45-percent increase in total P flux leaving the Atchafalaya River Basin from the 

total P flux that entered at the Old River outflow. The gain occurred between the confluence of the 

Red River with the Atchafalaya and the sampled site at Melville and again between Melville and the 

bifurcation at Wax Lake and Morgan City. More of the total P flux leaves the lower MARB and 

enters the Gulf of Mexico through the main stem than through the Atchafalaya River (approximately 

13,400 metric tons compared to 11,600 metric tons, respectively). Comparing the inputs of total P 

fluxes (Upper Mississippi River plus the Ohio River) with the outputs (Wax Lake plus Morgan City 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-13

plus Tarbert Landing minus the Morganza Floodway and Bonnet Carré Spillway); there is a 

cumulative loss of 320 metric tons of total phosphorus in the lower MARB in the month of May. 

Pesticides

Atrazine and metolachlor are two of the most commonly detected pesticides in water from the 

Mississippi River (Meade, 1995; Pereira and Rostad, 1990). Concentrations of pesticides are seasonal; 

thus, concentrations measured during the flood were compared to concentrations collected from April 

through July for the period of record at each site. Concentrations of both constituents were of the 

same magnitude during the flood as concentrations detected historically in April through July at the 

Upper Mississippi River, the Ohio River, and the four downstream sites (figures 11a and 11b). 

Median atrazine concentrations measured during the flood were highest in the Upper Mississippi River 

and the Ohio River (figure 11a). Lower median atrazine concentrations were measured at St. 

Francisville and Baton Rouge when compared to the median concentrations from water collected April 

through July for the period of record (figure 11a). Similar to atrazine, median metolachlor 

concentrations during the flood were highest in the Upper Mississippi River and the Ohio River 

(figure 11b). Median concentrations of metolachlor were lower than the historical April through July 

median concentrations at St. Francisville, Baton Rouge, and Belle Chasse (figure 11b). 

Concentrations of atrazine and metolachlor were at or below the MRL through early April in water 

samples from the Mississippi River at Vicksburg (figure 8). Atrazine concentrations increased as 

streamflow increased from April 20th through May 4th, but concentrations decreased and remained 

around 0.45 μg/L throughout the month of May which was the time of peak streamflow at Vicksburg 

(figure 8). As streamflow began to decrease, the atrazine concentration peaked at 0.9 μg/L. 

Metolachlor concentrations followed the same pattern with streamflow as atrazine, but peaked a week 

later on June 8th with a concentration of 0.88 μg/L. 

The highest monthly flux of atrazine, 74 metric tons, was delivered to the Gulf of Mexico in May 2011 

(figure 12). Atrazine flux increased 5 times from April to May, and the flux in June (69 metric tons) 

was nearly the same as it was in May. However, by July, the flux of atrazine had decreased by half 

from its peak. The highest monthly flux of metolachlor, 60.6 metric tons, entered the Gulf of Mexico 

in June (figure 12). This flux was almost 11 times greater than the monthly flux in April and three 

times greater than the flux in May. By July, the flux of metolachlor entering the Gulf of Mexico had 

decreased to 46.6 metric tons, and this flux was greater than the atrazine flux in July. 

Water quality of the three floodways

Bird’s Point-New Madrid Floodway

Opening the Bird’s Point-New Madrid Floodway late on May 2, 2011 inundated 53,824 hectares of 

agricultural land (Olson and Morton, 2012). The inflow and the outflow of the Floodway were 

sampled four hours apart on May 4, 2011, almost 48 hours after the first breech in the levee. Total 

nitrogen concentrations at the inflow and outflow were 3.0 mg/L and 2.65 mg/L, respectively 

(Appendix 2). The total nitrogen concentration measured upstream of the breech in the Upper 

Mississippi River on April 26, 2011 was 3.1 mg/L and in the Ohio River on May 3, 2011 was 1.6 

mg/L (Appendix 2). Total nitrogen concentrations ranged from 1.6 to 1.8 mg/L downstream at 

Vicksburg during the month of May. 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-14

Nitrate concentrations at the inflow and outflow were approximately 2 mg/L (Appendix 2). The 

nitrate concentration measured in water from the Upper Mississippi River on April 26, 2011 was about 

the same as the concentrations in the Floodway; however, the concentration in the Ohio River on May 

3, 2011 was half the measured nitrate concentration at the Upper Mississippi River and in the 

Floodway. It appears that there is incomplete mixing of water in the Floodway from the two source 

streams. The nitrate concentrations measured at Vicksburg in May ranged from 1.09 to 1.23 mg/L 

which are lower than concentrations in the Floodway and in the Upper Mississippi River. 

Atrazine concentration measured on May 4, 2011 at the inflow and outflow in the Floodway were 0.49 

μg/L and 0.60 μg/L, respectively (Appendix 4). These concentrations were about half the atrazine 

concentration measured in the Upper Mississippi River on April 26, 2011 (0.95 μg/L), but they were 

greater than the concentration measured in the Ohio River on May 3rd (0.415 μg/L). The Floodway 

concentrations were also higher than the median atrazine concentration of 0.45 μg/L for water samples 

collected in May at Vicksburg. 

Morganza Floodway

The Morganza Floodway was opened on May 14, 2011 and diverted flow from the Mississippi River 

above St. Francisville and Baton Rouge to the Atchafalaya River Basin. The decision to open the 

Floodway is made when flows are predicted to reach 42,500 m3

/s at the Red River Landing. Inundated 

land in the Basin consists of swamps, small farms, and thousands of oil and gas wells. Streamflows in 

the Floodway ranged from 100 to 5,500 m3

/s, with a median streamflow of 3,100 m3/s for the period 

that it was opened (May 14 through July 7, 2011; table 1). This median streamflow was 

approximately 14-percent of the median streamflow measured during the flood period at Vicksburg 

(located upstream of the Floodway) and 12-percent of the median streamflow measured at Tarbert 

Landing and 18-percent of the median streamflow measured at Baton Rouge (both downstream of the 

Floodway). Median streamflow in the Floodway was approximately 29-percent of the median 

streamflow measured at Melville and 84-percent of the median streamflow measured at Morgan City 

(table 1). 

Suspended sediment concentrations (Appendix 6) measured in the Floodway ranged from 8 to 31 

mg/L with a median concentration of 16.5 mg/L. There was a direct relationship between streamflow 

and suspended sediment concentrations in the Morganza Floodway– as streamflow decreased, 

suspended sediment concentrations decreased (not shown; data in Appendix 6). This decrease also 

corresponded with the length of time that the Floodway had been open. Suspended sediment 

concentrations in the Floodway were 5 to 8 times less than the concentrations that were measured at 

Vicksburg, St. Francisville, and Baton Rouge. Suspended sediment concentrations in the Floodway 

were 9 to 10 times less than concentrations measured at Melville (upstream of the Floodway’s 

confluence with the Atchafalaya River) and Morgan City (downstream of the Floodway’s confluence 

with the Atchafalaya River), respectively (Appendix 3 and Appendix 6).

Total nitrogen concentrations, which were composed of mostly nitrate, in water from the Morganza 

Floodway ranged from 0.90 to 1.6 mg/L, with a median concentration of 1.1 mg/L (Appendix 2). The 

highest concentrations were measured in May, soon after the gates to the Floodway were first opened. 

Concentrations declined steadily throughout June. The lowest total nitrogen concentrations measured 

in water from Vicksburg (upstream of the inlet to the Floodway) and St. Francisville and Baton Rouge 

(both downstream of the inlet) were higher than the highest total nitrogen concentrations measured in 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-15

the Floodway. All total nitrogen concentrations measured at Melville (upstream of the Floodway outlet 

into the Atchafalaya River) were higher than the concentration measured in the Floodway. 

Downstream of the outlet, total nitrogen concentrations at Morgan City were generally higher than 

concentrations measured in the Floodway. However, there were two sampling dates where samples 

from Morgan City had a concentration less than or about equal to the concentration in the Floodway –

May 25, 2011 and June 16, 2011. 

Total phosphorus concentrations in water from the Morganza Floodway ranged from 0.16 to 0.52 

mg/L, with a median concentration of 0.22 mg/L (Appendix 2). In contrast to total nitrogen and 

nitrate concentrations, total phosphorus increased in the Floodway with length of time that the 

Floodway was open (figure 14). Most of the increase in total phosphorus was due to an increase in 

orthophosphate concentrations (figure 14). Total phosphorus concentrations at Vicksburg, St. 

Francisville, and Baton Rouge were lower than the concentrations measured in the Floodway. 

Maximum concentrations at the main stem sites were about the same as the median concentration of 

the samples collected in the Floodway (figure 13). Highest concentrations in the Mississippi River 

were measured in late June-July as the streamflow in the river decreased. Maximum total phosphorus 

concentrations measured in water at Melville and Morgan City were 0.30 mg/L and 0.34 mg/L, 

respectively, but the median concentration at both sites was 0.19 mg/L which was lower than the 

median concentration for the Floodway (Appendix 2). 

Atrazine concentrations in water from the Morganza Floodway ranged from 0.295 to 0.67 μg/L with a 

median concentration of 0.57 μg/L (Appendix 4). The highest concentrations were measured in June. 

Median concentrations of atrazine measured at Vicksburg, St. Francisville, and Baton Rouge from 

May 14, 2011 to July 7, 2011 (period that the Floodway was open) were 0.53, 0.48, and 0.56 μg/L, 

respectively. All of these medians are less than the median concentration in the Floodway. Similarly, 

the median concentrations for atrazine at Melville and Morgan City were 0.53 and 0.49 μg/L, 

respectively, lower than the median concentration in the Floodway for the sampling period.

Water samples were analyzed for evidence of contaminants from oil and gasoline at Melville, La. 

(upstream of the Morganza Floodway outlet) and at Wax Lake (downstream of the Morganza 

Floodway outlet) from May 19 through June 29, 2011, while the Floodway was in operation. There 

was one low-level detection of diesel the week of May 23rd in water upstream of the outflow (figure 

14). Concentrations of gasoline, oil and grease, and petroleum hydrocarbons were about the same in 

the upstream and downstream samples for all weeks except the weeks of May 23rd and May 30th. 

Gasoline concentrations were twice as high in the downstream samples as in the upstream samples the 

week of the 23rd. However, the following week gasoline concentrations were twice as high in the 

upstream samples as in the downstream samples (figure 14).

Bonnet Carré Spillway

The first bays on the Bonnet Carré Spillway were opened on May 9, 2011 and diverted flow from the 

Mississippi River below Baton Rouge into Lake Ponchartrain. The decision to open the Bonnet Carré 

Spillway was made when the volume of water predicted to pass New Orleans, La. was 35,400 m3

/s. 

Streamflows in the Spillway ranged from 1,000 to 11,200 m3

/s with a median streamflow of 8,000 

m3

/s (table 1) for the period that it was opened (May 9th through June 20, 2011). This median 

streamflow was approximately 32-percent of the median streamflow measured during the flood period 

at Tarbert Landing and 47-percent of the median streamflow measured at Baton Rouge (both 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-16

downstream of the Spillway). Median streamflow in the Spillway was 51-percent of the median 

streamflow measured during the flood period at Belle Chasse (downstream of the Spillway). 

Suspended sediment concentrations in the Bonnet Carré Spillway ranged from 43 to 177 mg/L with a 

median concentration of 111 mg/L (Appendix 6). The trend in suspended sediment concentration in 

the Spillway appeared to follow closely with streamflow (figure 15). As streamflow increased with 

the opening of the bays, suspended sediment concentrations increased; however, concentrations began 

to decline in late May as streamflow started to decrease which corresponded also with the length of 

time that the bays had been opened (figure 16). In comparison to sites on the main stem above and 

below the Spillway inflow, the median suspended sediment concentration was only 1.2 times less than 

the median concentrations at Baton Rouge (upstream) and Belle Chasse (downstream) during the flood 

period. Median suspended sediment concentrations at St. Francisville were 1.3 times less than the 

median concentration measured in the Spillway. 

Total nitrogen concentrations in water from the Bonnet Carré Spillway ranged from 1.5 to 1.9 mg/L, 

with a median concentration of 1.7 mg/L (Appendix 2). Concentrations increased with increasing 

streamflow after the bays were opened. In early June, concentrations decreased slightly; however, 

there was another increase in concentration as bays in the Spillway were being closed. Total nitrogen 

concentrations in the Spillway were about the same as concentrations measured upstream at St. 

Francisville and Baton Rouge and downstream at Belle Chasse while the bays were open. 

Total phosphorus concentrations in water from the Bonnet Carré Spillway ranged from 0.11 to 0.17 

mg/L, with a median concentration of 0.16 mg/L (Appendix 2). The relationship between streamflow 

and total phosphorus was similar to the relationship observed between streamflow and total nitrogen. 

Total phosphorus concentrations initially increased as the bays were opened in May. There was a 

decrease in concentration in early June; however, concentrations began to increase until the bays were 

closed. Total phosphorus concentrations upstream of the Spillway at St. Francisville and Baton Rouge 

were about the same or lower than concentrations in the Spillway during May and early June. By midJune, the concentrations at these two sites had increased and were greater than the 0.17 mg/L 

measured in the Spillway on June 22nd. Total phosphorus concentrations downstream at Belle Chasse 

averaged about 1.5 times more than concentrations in the Spillway while it was in operation. 

Atrazine concentrations in water from the Bonnet Carré Spillway ranged from 0.14 to 0.44 μg/L, with 

a median concentration of 0.31 μg/L (Appendix 4). The highest concentration was measured in June, 

almost one month after the first bays were opened. Median atrazine concentrations measured 

upstream at St. Francisville and Baton Rouge were 0.48 and 0.46 μg/L, respectively. The median 

concentration downstream at Belle Chasse was 0.46 μg/L. All measured concentrations at the 3 main 

stem sites were higher than any detection in the Spillway. Similar to the Spillway, the highest atrazine 

concentration at the three main stem sites was detected in water collected in early June.

Discussion

Streamflow

During the 2011 Flood, most of the sampled sites remained above flood stage for 2 1⁄2 to 3 months, and 

measured instantaneous streamflows for the period were higher than historical median streamflow 

measurements. Record rainfall in the Ohio River Basin was the primary contributor to streamflow in 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-17

the MRB during the months of April and May (figure 16). Snow melt and precipitation in the Upper 

MRB during June and July composed the majority of streamflow that moved into the lower MRB. 

The Ohio River Basin is more urban and forested in land use; whereas, the Missouri River and Upper 

MRB are primarily agricultural with some rangeland. The timing and contribution of the streamflow 

from the two different source areas is important as to what chemicals and other contaminants might 

enter the lower MRB via overland runoff or recedence of water from inundated lands. 

Sediment

The low median suspended sediment concentrations measured at Vicksburg and St. Francisville are 

most likely due to a storm event in early March that diminished the supply of suspended sediment that 

was available for transport when the flood occurred (figure 5). Suspended sediment concentrations 

measured during the flood were similar to concentrations that had been measured historically in the 

lower MRB; however, fluxes were quite high due to the high streamflows. Despite the fact that the 

majority of the flow introduced into the Lower MRB was from the Ohio River and the previous 

construction of reservoirs on the Missouri and Arkansas Rivers has cut off the largest natural source of 

sediment to the Mississippi River (Meade, 1995), the majority of the suspended sediment flux 

introduced into the Basin during the flood was through the Upper MRB (Thebes; figure 6). Seventy 

percent of the sediment flux moving into the lower MRB was through the Upper Mississippi River, 

which is close to the 75-percent estimated by Pereira and Rostad (1990). Flux estimates for the month 

of May show approximately 1.5 times more suspended sediment moved into the Gulf of Mexico from 

the Atchafalaya River Basin than through the Mississippi River main stem. According to Roberts 

(1998), the Atchafalaya/Wax Lake delta is the only place in the MARB where there is sufficient 

sediment for actual delta-building to occur. In contrast, the Bird’s Foot delta of the Mississippi River 

main stem is eroding (Roberts, 1998). 

As the water moved through the Old River Outflow below Vicksburg, a gain in suspended sediment 

flux occurred before the water reached Melville. There is a depositional area at the bend in the 

Atchafalaya River and the confluence with the Red River (Barb Kleiss, personal communication), but 

high streamflows in May mostly likely resuspended the deposited sediment and moved it downstream. 

In addition, the Red River could have contributed up to 6 million metric tons to the suspended 

sediment flux measured at Melville. The further increase in flux between Melville and the outlets at 

Wax Lake and Morgan City can be explained by the resuspension of sediment by high flows. 

Suspended sediment concentrations during the flood were similar in the Bonnet Carré Spillway and 

the Mississippi River at Baton Rouge (figure 15); however, suspended sediment flux estimates in the 

Spillway were calculated based on concentrations measured at St. Francisville, which were lower than 

in the Spillway and at Baton Rouge. Flux estimates for the Bonnet Carré Spillway are most likely 

higher for the period that it was opened than was estimated by the model. 

High streamflows are effective transport mechanisms for sand-sized particles (Allison et al, 2012). 

There was a decreasing trend in sand fraction percentage in the Upper Mississippi River and the Ohio 

River during the flood period; yet, sand size fraction percentage generally increased during the flood 

period in water from sites in the Lower MRB. This suggests that the Upper Mississippi River and the 

Ohio River were not the source of the sand-size particles in the Lower MRB during the flood period. 

Allison, et al. (2012) noted that the Mississippi River and Atchafalaya distributary pathways are 

efficient at sequestering suspended sediments, particularly the sand size fraction. During the flood 

period, the sand-size fraction of the suspended sediment concentration increased in May at most sites 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-18

in the lower MRB (figure 17). Maximum streamflows in the Atchafalaya River Basin occurred in the 

first week of June, and the increase in percentage of the larger size fraction corresponds to the increase 

in streamflow. Increases in the sand-size fraction of the suspended sediment flux was most likely not 

a result of new sediment being introduced from the Upper Mississippi and Ohio Rivers, but rather a 

result of high streamflows within the lower MRB and Atchafalaya River resuspending previously 

deposited sediment. 

Nutrients

Higher total nitrogen and total phosphorus concentrations during the flood compared to historical data 

in the Upper Mississippi River (and to a lesser extent the Ohio River), might be attributed to the flood 

occurring during application of agricultural chemicals in the Missouri River Basin, the Upper MRB, 

and to a lesser extent in the Ohio River Basin (figure 7). In early March, water samples from 

Vicksburg contained higher concentrations of suspended sediment, total nitrogen, and total 

phosphorus than concentrations measured during the flood (figure 5; figure 8). This was observed in 

water from other NASQAN stations in the lower MRB also, but water-quality at Vicksburg is used as 

the example here because it represents the greatest amount of water streamflow by the river while it is 

still confined to a single channel. Lower concentrations of total nitrogen, total phosphorus, and 

suspended sediment are likely a result of dilution and a lack of available material since high 

concentrations of the three constituents were measured in surface water samples collected in March. 

The largest cumulative monthly fluxes of total nitrogen and total phosphorus occurred in water from 

most of the lower MARB sites during May, which corresponds to the highest average monthly 

streamflow. The Upper Mississippi River contributed about 60-percent of the total nitrogen flux in 

May, which is slightly higher than the 50 percent documented by Meade (1995) and Goolsby and 

Battaglin(1997). Higher suspended sediment fluxes might also be a contributor to chemical transport 

since many hydrophobic chemical compounds have a tendency to adsorb to sediments, particularly 

fine-grained silts and clays (Horowitz et al., 2008). Phosphorus has a strong tendency to bind with soil 

particles, such as clay. Total phosphorus fluxes in the Upper Mississippi River were highest in June 

and July which corresponds to suspended sediment fluxes that were also highest during these two 

months from the Upper Mississippi River. 

To assess the influence of the receding floodwaters from agricultural lands inundated by the Bird’s 

Point-New Madrid Floodway, a hypothetical calculation of contribution to the total nitrogen flux in 

the Mississippi River below the outlet was made. In this worst case scenario, 100 kg/ha of nitrogen 

fertilizer (applied amount depends on soil type and agricultural management practices, and 100 kg/ha 

is on the lower end of recommended application amounts for corn) was applied to the entire 53,824 

hectares inundated by the floodwaters. If all of the water that inundated the hectares receded back into 

the Mississippi River, the Bird’s Point-New Madrid Floodway might possibly contribute about 5,400 

metric tons of total nitrogen flux to the Mississippi River below the outlet, which is approximately 2 

percent of the total nitrogen flux for May at Vicksburg (figure 18). 

Nitrogen and phosphorus concentrations and fluxes were lower in the Morganza Floodway compared 

to water at sites in the lower Mississippi River. Total nitrogen and nitrate concentrations decreased 

with the length of time that the Floodway was open which seems to indicate that there is processing of 

nitrate in the Floodway, either by denitrification or another type of assimilation pathway (Appendix 2). 

Total phosphorus in the Floodway is likely not associated with suspended sediment since suspended 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-19

sediment concentrations are low (median of 16.5 mg/L). And in contrast to total nitrogen and nitrate 

concentrations, total phosphorus concentrations and orthophosphate concentrations in the Floodway 

increased with the length of time that the bays were opened (figure 13). This suggests that phosphorus 

transformation is occurring. 

Pesticides

Large amounts of herbicides are flushed into streams during storm runoff in late spring and summer 

each year, following herbicide application (Meade, 1995). The Missouri, Illinois, and Ohio Rivers are 

the major source of herbicides and their degradation products to the lower MRB (Pereira and Rostad, 

1990). Elevated fluxes of atrazine in May and metolachlor in June is associated with the highest 

streamflows of the flood period that promote the movement of herbicides off of agricultural lands 

through overland runoff. Median concentrations of both atrazine and metolachlor were higher in the 

Upper Mississippi River and the Ohio River than median concentrations measured at four sites 

downstream (figure 11) which is most likely due to intense rainfall occurring during the time of 

agricultural chemical application which did not allow for much processing of the herbicides before 

they were transported into the Mississippi River. Unlike concentrations of suspended sediment, total 

nitrogen, and total phosphorus, highest concentrations of herbicides were measured in May and June, 

not March (figure 8). The most likely reason is that herbicides had not yet been applied in March.

Atrazine fluxes were highest in May; whereas, metolachlor fluxes were highest in June, which most 

likely corresponds with application time and the source area for the water (figure 12). Atrazine is a 

common herbicide applied to not only agricultural crops, but has non-agricultural uses as well, such as 

weed control on lawns and highway rights-of-way. The main contributor to stream streamflow in 

April and May was the Ohio River, a more urbanized source area with atrazine use. In June and July, 

the Missouri River/Upper Mississippi River contributed the majority of the streamflow to the lower 

MRB. Metolachlor is heavily used in this Basin on soybeans and corn, which is planted later in the 

season. This correlates with the higher concentrations and fluxes of metolachlor in June. 

To assess the influence of the receding floodwaters from agricultural lands inundated by the Bird’s 

Point-New Madrid Floodway, a hypothetical calculation of contribution to the atrazine flux in the 

Mississippi River below the outlet (Vicksburg) was made. In this worst case scenario, corn was 

presumed to be the only crop planted and1 kg/ha of atrazine was applied to the entire 53,824 hectares 

inundated by the floodwaters – this is the application amount recommended for corn. If all of the 

water that inundated the hectares receded back into the Mississippi River, the Bird’s Point-New 

Madrid Floodway might possibly contribute 2.7 metric tons to the atrazine flux in the Mississippi 

River below the Spillway outlet, or approximately 3.4 percent of the monthly atrazine load measured 

at Vicksburg in May (figure 19). 

 

Summary and Conclusions

High streamflows associated with the April through July flood of 2011 forced the opening of all three 

flood-control structures in the lower MRB for the first time in history in order to manage the amount 

of water moving through the system. Concentrations of sediment, nutrients, and pesticides were 

similar to historical concentrations measured in the stream. However, time series data show surface 

water contained higher concentrations of suspended sediment, total nitrogen, and total phosphorus in 

early March than concentrations that were measured during the flood. In addition, concentrations of 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-20

these three constituents decreased during the flood which indicates that there was dilution occurring by 

the increased streamflow and that the source of material or constituents was not present during the 

flood period (i.e. a large portion had been removed or transported in March). 

Although constituent concentrations were not higher than normal, historic streamflows resulted in high 

fluxes of sediment and agricultural chemicals moving through the lower MRB and eventually into the 

Gulf of Mexico. The highest fluxes of sediment, nutrients, and pesticides occurred at most sites in the 

lower MRB during the month of May which corresponds with the month of highest streamflow. More 

suspended sediment was introduced into the lower MRB from the Upper Mississippi River than was 

introduced from the Ohio River despite the fact that the majority of streamflow in April and May came 

from the Ohio River. A larger suspended sediment flux entered the Gulf of Mexico from the 

Atchafalaya River Basin than the flux that entered from the main stem of the Mississippi River. 

Approximately 2.2 million metric tons more suspended sediment left the lower MRB than entered 

from the Upper Mississippi and the Ohio Rivers due to the high streamflows that resuspended coarsergrained bed material. In contrast with suspended sediment, the majority of the total nitrogen, total 

phosphorus, atrazine, and metolachlor fluxes entered the Gulf of Mexico through the main stem as 

opposed to the Atchafalaya River Basin. There was a loss in the fluxes of total nitrogen and total 

phosphorus with transport through the lower MRB. Atrazine and metolachlor fluxes peaked in 

different months (June for atrazine; July for metolachlor) most likely due to differing application times

and a change in the source of streamflow to the lower MRB from the Ohio River to the Upper 

Mississippi River that occurred from June to July. 

The openings of the New Madrid-Bird’s Point Floodway and the Morganza Floodway were of concern 

because of potential water-quality impacts in the Mississippi River once the water receded from lands 

that normally are not inundated by stream waters. Oil and gas samples collected upstream and 

downstream of the Morganza Floodway’s confluence with the Atchafalaya River show similar 

concentrations except for the a 2-week period in late May. Decreases in total phosphorus and total 

nitrogen concentrations with length of time that the Morganza Floodway was open indicate that there 

is processing of phosphorus and nitrate occurring in the system. Diverting flow from the Mississippi 

River through the Bonnet Carré Spillway into Lake Ponchartrain led to a slight decrease in the fluxes 

of total nitrogen, total phosphorus, atrazine, and suspended sediment that moved down the main stem 

into the Gulf of Mexico. 

References 

Allison, MA, Demas, CR, Ebersole, BA, Kleiss, BA, Little, CD, Meselhe, EA, Powell, NJ, Pratt, TC, 

Vosburg, BM (2012) A water and sediment budget for the lower Mississippi-Atchafalaya River 

in flood years 2008-2010: implications for sediment discharge to the oceans and coastal 

restoration in Louisiana. Journal of Hydrology 432-433: 84-97.

Anderson, B (2011) Operation watershed: floodfight 2011. Inland Port May/June 2011 24 p.

Aulenbach, BT, Hooper, RP (2006) The composite method: an improved method for stream-water 

solute load estimation. Hydrological Processes 20: 3029-3047.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-21

Aulenbach, BT, Buxton, HT, Battaglin, WA, Coupe, RH (2007) Streamflow and nutrient fluxes of the 

Mississippi-Atchafalaya River Basin and subbasins for the period of record through 2005. US 

Geol Surv Open-File Report 2007-1080, accessed 11/17/2011 at http://toxics.usgs.gov/pubs/of2007-1080/.

Boesch, DF, Boynton, WR, Crowder, LB, Diaz, RJ, Howarth, RW, Mee, LD, Nixon, SW, Rabalais, 

NN, Rosenberg, R, Snaders, JG, Scavia, D, Turner, RE (2009) Nutrient enrichment drives Gulf 

of Mexico hypoxia. EOS, Transactions of the American Geophysical Union 90(14): 117-118. 

Cohn, TA, Caulder, DL, Gilroy, EJ, Zynjuk, LD, Sommers, RM (1992) The validity of a simple 

statistical model for estimating fluvial constituent loads: an empirical study involving nutrient 

loads entering Chesapeake Bay. Water Resources Research 28: 2352-2363.

Coupe, RH, Goolsby, DA (1999) Monitoring the water quality of the nation’s large river: Mississippi 

River Basin NASQAN program. US Geol Surv Fact Sheet FS-055-99, 6 p.

Donner, SD, Scavia, D (2007) How climate controls the flux of nitrogen by the Mississippi River and the 

development of hypoxia in the Gulf of Mexico. Limnology and Oceanography 52(2): 856-861.

Fishman, MJ, Friedman, LC, eds. (1989) Methods for determination of inorganic substances in water 

and fluvial sediments. US Geol Surv Techniques of Water-Resources Investigations, book 5, 

chapter A1, 545 p.

Goolsby, DA, Battaglin, WA (1997) Sources and transport of nitrogen in the Mississippi River Basin. 

Presented at the American Farm Bureau Federation Workshop, St. Louis, Missouri, July 14-15, 1997. 

Goolsby, DA, Battaglin, WA, Thurman, EM (1993) Occurrence and transport of agricultural 

chemicals in the Mississippi River Basin, July through august 1993. US Geol Surv Circular 

1120-C, 22 p.

Guy HP (1969) Laboratory theory and methods for sediment analysis. Techniques of Water-Resources 

Investigations of the US Geological Survey, book 5, chap. C1.

Helsel, DR, Hirsch, RM (2002) Statistical methods in water resources. Techniques of WaterResources Investigations of the US Geological Survey, book 4, chap. A3.

Holmes, RR (1996) Sediment transport in the lower Missouri and the central Mississippi rivers, June 

26 through September 14, 1993. US Geol Surv Circular 1120-I, 23 p.

Horowitz, AJ (2010) A quarter century of declining suspended sediment fluxes in the Mississippi 

River and the effect of the 1993 flood. Hydrological Processes 24: 13-34.

Horowitz, AJ, Elrick, KA, Smith, JJ (2008) Monitoring urban impacts on suspended sediment, trace 

element, and nutrient fluxes within the City of Atlanta, Georgia, USA: program design, 

methodological considerations, and initial results. Hydrological Processes 22: 1473-1496.

Johnson, AH (1979) Estimating solute transport in streams from grab samples. Water Resources 

Research 15(5): 1224-1228.

Judge, GR, Hill, C, Griffiths, WE, Lutkepohl, H, Lee, TC (1988) Introduction to the theory and 

practice of econometrics, 2nd ed. John Wiley & Sons, Inc., New York, USA, pp. 878-882.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-22

Larson, SJ, Capel, PD, Goolsby, DA, Zaugg, SD, Sandstrom, MW (1995) Relations between pesticide 

use and riverine flux in the Mississippi River Basin. Chemosphere 31(5): 3305–3321.

Meade, RH, ed. (1995) Contaminants in the Mississippi River, 1987-1992. U.S. Geol Surv Circular 

1133, 140 p. 

Mississippi River Commission (2008) The Mississippi River & Tributaries Project: designing the 

project flood. Mississippi River Commission Information Paper April 2008, 7 p.

Mossa, J (1996) Sediment dynamics in the lowermost Mississippi River. Engineering Geology 45: 

457-479.

Olson, KR, Morton, LW (2012) The impact of 2011 induced levee breaches on agricultural lands of 

Mississippi River Valley. Journal of Soil and Water Conservation 67(1): 5A-10A. 

Olson, SA, Norris, JM (2007) US Geological Survey streamgaging from the National Streamflow 

Information Program. US Geol Surv Fact Sheet 2005-3131, 4 p.

Pereira, WE, Rostad, CE (1990) Occurrence, distributions, and transport of herbicides and their 

degradation products in the Lower Mississippi River and its tributaries. Environmental Science 

and Technology 24(9): 1400-1406.

Rabalais, NN, Turner, RE, Wiseman, Jr., WJ (2002) Gulf of Mexico hypoxia, a.k.a. “The Dead Zone”. 

Annual Review of Ecological Systems 33: 235-263.

Rantz, SE. 1982. Measurement and computation of streamflow: volume 1. Measurement of stage and 

discharge and Volume 2. Computation of discharge. US Geological Survey Water Supply Paper

2175, 681 p.

Roberts, HH (1998) Delta switching: early responses to the Atchafalaya River diversion. Journal of 

Coastal Research 14(3): 882-899.

Runkel, RL, Crawford, CG, Cohn, TA (2004) Load estimator (LOADEST) – a FORTRAN program 

for estimating constituent loads in streams and rivers. US Geol Surv Techniques and Methods 

book 4, chapter A5. Accessed online on 11/17/2011 at http://pubs.usgs.gov/tm/2005/tm4A5. 

Scavia, D, Donnelly, KA (2007) Reassessing hypoxia forecasts for the Gulf of Mexico. 

Environmental Science and Technology 41: 8111-8117. 

Scavia, D, Justic, D, Bierman, VJ (2004) Reducing hypoxia in the Gulf of Mexico – advice from three 

models. Estuaries 27(3): 419-425.

Schalk, GK, Holmes, RR, Johnson, GP (1998) Physical and chemical data on sediments deposited in 

the Missouri and the Mississippi River flood plains during the July through August 1993 flood. 

US Geol Surv Circular 1120-L, 62 p. 

Schneider, K (2011) Laying the groundwork. US Army Corps of Engineers Our Mississippi, 12 p.

Taylor, HE, Antweiler, RC, Brinton, TI, Roth, DA (1994) Major ions, nutrients, and trace elements in 

the Mississippi River near Thebes, Illinois, June through September 1993. US Geol Surv 

Circular 1120-D, 21 p.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-II-23

Turner, RE, Rabalais, NN, Justic, D (2008) Gulf of Mexico hypoxia – alternate states and a legacy. 

Environmental Science and Technology 42(7): 2322-2327, doi:10.102/es071617k.

US Environmental Protection Agency (1999) Method 1664, Revision A: n-hexane extractable 

material (HEM; oil and grease) and silica gel treated n-hexane extractable material (SGT-HEM; 

non-polar material) by extraction and gravimetry. EPA -821-R-98-002, February 1999, 28 p.

US Environmental Protection Agency (1986) Test methods for evaluating solid water, 

physical/chemical methods. SW-846, 3rd edition, various updates, available online at 

http://www.epa.gov/osw/hazard/testmethods/sw846/index.htm.

US Geological Survey (2009) USGS hypoxia in the Gulf of Mexico studies. US Geol Surv web site 

accessed on 11/17/2011 at http://toxics.usgs.gov/hypoxia/.

US Geological Survey (variously dated) National field manual for the collection of water-quality data. 

US Geol Surv Techniques of Water-Resources Investigations, book 9, chapters A1-A9, 

available online at http://water.usgs.gov/owq/Field Manual/.

Appendix

Appendix I. Field parameters and inorganic constituents collected in water samples from selected 

sites in the lower Mississippi-Atchafalaya River Basin, April through July 2011.

Appendix II. Nutrients collected in water samples from selected sites in the lower MississippiAtchafalaya River Basin, April through July 2011.

Appendix III. Suspended sediment and particle size analysis collected in water samples from selected 

sites in the lower Mississippi-Atchafalaya River Basin, April through July 2011.

Appendix IV. Pesticides collected in water samples from selected sites in the lower MississippiAtchafalaya River Basin, April through July 2011.

Appendix V. Pesticides sampled for but not-detected in water from selected sites in the lower 

Mississippi-Atchafalaya River Basin, April through July 2011.

Appendix VI. Suspended sediment and particle size analysis collected in water samples from three 

flood-control structures in the lower Mississippi River Basin, April through July 2011.

Appendix VII. Oil and gas data collected at selected sites in the Atchafalaya River Basin, May 

Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-1

SECTION III. WATER QUALITY SAMPLING

Table 1. Station Names, Station Identification Numbers, Drainage Basin Areas, Map Number, and Minimum, Maximum, and Median Flow Data

for the Period April-July, 2011 Calculated at 9 Sites on the Mississippi and Atchafalaya Rivers and Their Major Tributaries

(Site # column refers to the numbered sites identified on figure 1; km2

, square kilometers; m3/s, cubic meters per second)

Streamflow, m3/s

(April through July 2011)

Station Name Site # Station ID Basin Area (km2) Minimum Maximum Median

Mississippi River at Thebes, Ill. (Upper Mississippi River) 1 07022000 1,847,180 3,300 24,200 12,100

Ohio River at Dam 53 Near Grand Chain, Ill. A (Ohio River) 2 03612500 526,027 750 35,700 5,000

Birds Point Levee Breach Inflow (BPNM) 3 365659089073101 NA 10 11,400 4,040

New Madrid Floodway Inflow Outflow No. 2 (BPNM) 4 363618089251701 NA 500 10,800 6,800

Mississippi River At Tiptonville, Tenn. B 5 362146089301901 NA 40,200 57,400 52,300

Mississippi River At Memphis, Tenn. 6 07032000 2,415,941 51,200 62,200 51,200

Mississippi River above Vicksburg at Mile 438, Miss. C 7 322023090544500 2,964,241 8,700 66,000 22,600

Mississippi River near St. Francisville, La. D 8 07373420 2,914,514 12,500 45,800 25,200

Atchafalaya River at Melville, La. E 9 07381495 241,687* 5,400 19,600 10,800

Atchafalaya Floodway near Ramah, La. North of I-10 F (Morganza Floodway) 10 302410091305201 NA 100 5,500 3,100

Mississippi River at Baton Rouge, La. 11 07374000 2,915,835 6,100 40,500 16,900

Lower Atchafalaya River at Morgan City, La. 12 07381600 NA 1,200 13,800 3,700

Wax Lake Outlet at Calumet, La. 13 07381590 NA 1,100 8,900 3,300

Bonnet Carré Spillway at U S Hwy #61 nr Norco, La. (Bonnet Carré Spillway) 14 300115090245000 NA 1,000 11,200 8,000

Mississippi River at Belle Chasse, La. 15 07374525 2,926,687 5,700 34,800 15,700

A Flow from Ohio River at Metropolis, Ill (03611500)

B Flow from Mississippi River at Tiptonville, Tenn. (U.S. Army Corps of Engineers site MS116)

C Flow from Mississippi River at Vicksburg, Miss. (07289000)

D Flow from Mississippi River at Tarbert Landing, Miss. (U.S. Army Corps of Engineers site 01100)

E Flow from Atchafalaya River at Simmesport, La. (U.S. Army Corps of Engineers site 03045)

F Flow from Morganza Spillway at Hwy 190 near Lottie, La. (07381530)

"NA" indicates indeterminate value

* Excludes contribution from Mississippi River Basin
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-2

Table 2. Method Reporting Level for Selected Constituents Analyzed, April Through July, 2011

(mg/L, milligram per liter; μg/L, microgram per liter)

Constituent

Method 

Reporting Level

Nitrate plus nitrite, in mg/L 0.05

Total phosphorus, unfiltered, in mg/L 0.10

Orthophosphate, in mg/L 0.02

Simazine, in μg/L 0.05

Prometon, in μg/L 0.05

Deethyl atrazine, in μg/L 0.05

Metolachlor, in μg/L 0.05

Atrazine, in μg/L 0.10

Acetochlor, in μg/L 0.05
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-3

Figure 1. Map showing the Mississippi River Basin. Inset map shows the lower Mississippi-Atchafalaya River 

Basin with the location of sampled sites during the 2011 Flood (April through July). 
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-4

Figure 2. Instantaneous streamflow for the period of record at six sites in the lower Mississippi RiverAtchafalaya River Basin compared to measured streamflow during the 2011 Flood (April through July). The 

first box in each pair is the historical data, and the second box is the flood data, April through July 2011.

Upper 

Mississippi 

River

Ohio 

River

St. 

Francisville

Baton 

Rouge

Belle 

Chasse
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-5

Figure 3. Average streamflow in May 2011 for sites located in the lower Mississippi-Atchafalaya River Basin. 

The average monthly flow calculated for the Morganza Floodway and Bonnet Carré Spillways did include days 

when the structures were not open. On these days, flow was 0 m3

/s. Not to scale.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-6

Figure 4. Suspended sediment concentrations in surface water sampled during the 2011 Flood (April through 

July) compared to suspended sediment concentrations observed for the period of record at selected sites in the 

lower Mississippi River Basin. The first box in each pair is the historical data, and the second box is the flood 

data, April through July 2011.

Upper 

Mississippi 

River

Ohio 

River

Vicksburg

St. 

Francisville

Baton 

Rouge

Belle 

Chasse
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-7

Figure 5. Time series plot of suspended sediment and streamflow at the Mississippi River at Vicksburg, Miss., and the 

Mississippi River at St. Francisville, La., for January through August 2011. The blue shaded area denotes samples collected during the flood period. 

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

0

100

200

300

400

500

600

700

1/1/2011 2/1/2011 3/1/2011 4/1/2011 5/1/2011 6/1/2011 7/1/2011 8/1/2011

Streamflow,

in cubic meters per second

Concentration

in milligrams per liter

Vicksburg sediment

St. Francisville sediment

Vicksburg discharge

St. Francisville discharge
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-8

Figure 6. Cumulative suspended sediment flux for May 2011 at selected sites in the lower Mississippi RiverAtchafalaya River Basin. Fluxes at Tarbert Landing, La., in the Morganza Floodway, and in the Bonnet Carré 

Spillway are calculated based on water-quality samples collected at St. Francisville, La. Not to scale.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-9

Figure 7. Concentrations of (a) Total N and (b) Total P measured during the flood compared to concentrations 

measured at these sites in the lower Mississippi River Basin for the period of record. The first box in each pair is 

the historical data, and the second box is the flood data, April through July 2011. [ MRL = method reporting 

level
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-10

Figure 8. Time series plot of total nitrogen, total phosphorus, atrazine, metolachlor, and streamflow at the Mississippi River 

at Vicksburg, Miss., for January through August 2011. The blue shaded area denotes samples collected during the flood period.

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

0

0.5

1

1.5

2

2.5

3

3.5

1/1/2011 2/1/2011 3/1/2011 4/1/2011 5/1/2011 6/1/2011 7/1/2011 8/1/2011

Streamflow, 

in cubic meters per second

Nutrient concentration,

in milligrams per liter

Pesticide concentration, 

in micrograms per liter

Mississippi River at Vicksburg

Total N

Total P

Atrazine
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-11

Figure 9. Total nitrogen flux for May 2011 at selected sites in the lower Mississippi River-Atchafalaya River 

Basin. Fluxes at Tarbert Landing, La. ,in the Morganza Floodway, and in the Bonnet Carré Spillway are 

calculated based on water-quality samples collected at St. Francisville, La. Not to scale.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-12

Figure 10. Total phosphorus flux for May 2011 at selected sites in the lower Mississippi River-Atchafalaya

River Basin. Fluxes at Tarbert Landing, La. ,in the Morganza Floodway, and in the Bonnet Carré Spillway are 

calculated based on water-quality samples collected at St. Francisville, La. Not to scale.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-13

Figure 11. Concentrations of (a) atrazine and (b) metolachlor measured during the flood compared to 

concentrations measured at these sites in the lower Mississippi River Basin for the months of April through July 

for the period of record. The first box in each pair is the historical data, and the second box is the flood data, 

April through July 2011. [ MRL = method reporting level]

A

B
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-14

Figure 12. Cumulative monthly flux of atrazine and metolachlor delivered to the Gulf of Mexico from April through July 2011. Delivery to the Gulf of 

Mexico is determined by adding the fluxes at the Atchafalaya River at Melville, La., with the fluxes as the Mississippi River near St. Francisville, La.

0

10

20

30

40

50

60

70

80

April May June July

Flux, in metric tons

Flux of pesticides delivered to the Gulf of 

Mexico

Atrazine

Metolachlor
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-15

Figure 13. Streamflow and total phosphorus concentrations measured during the flood period at sites above and below the Morganza Floodway and the total 

phosphorus concentrations and orthophosphate concentrations measured in the Morganza Floodway. The blue-shaded area denotes the period of time that the 

Morganza Floodway was open.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-16

Figure 14. Oil and Gas Data Collected Weekly Above and Below the Outlet of the Morganza Floodway
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-17

Figure 15. Streamflow and suspended sediment concentrations measured during the flood period at sites above and below the Bonnet Carré Spillway and the 

suspended sediment concentrations and streamflow measured in the Bonnet Carré Spillway. The blue-shaded area denotes the period of time that the Bonnet 

Carré Spillway was open.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-18

Figure 16. Average Monthly Streamflow for the Flood Period at the Upper Mississippi River and the Ohio River

0

5,000

10,000

15,000

20,000

25,000

30,000

Apr-11 May-11 Jun-11 Jul-11

Streamflow, 

in cubic meters per second

Ohio River Upper Mississippi River
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-19

Figure 17. Fraction of the suspended sediment concentration that was sand-sized. Blue shaded area denotes the month with the highest average streamflow.
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-20

Figure 18. Plot of streamflow from the upper Mississippi River Basin, the Ohio River Basin, and the Mississippi River at Vicksburg and the daily total N 

flux. Inset chart shows the possible contribution from the BPNM to the May monthly total N flux at Vicksburg. The light blue box represents the time period 

that the BPNM was in operation.

0

2,000

4,000

6,000

8,000

10,000

12,000

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

4/1 4/8 4/15 4/22 4/29 5/6 5/13 5/20 5/27 6/3 6/10 6/17 6/24 7/1 7/8 7/15 7/22 7/29

Total N

flux, 

in metric ton/day

Streamflow,

in m3/s

Upper Mississippi 

Ohio River

Mississippi River 

at Vicksburg Q

Ohio River daily N flux

Upper 

Mississippi 

River daily N 

Mississippi River at 

Vicksburg daily N flux
Mississippi River and Tributaries System

2011 Post Flood Report

Appendix F

Environmental and Cultural Resources

F-III-20

Figure 19. Plot of streamflow from the upper Mississippi River Basin, the Ohio River Basin, and the Mississippi River at Vicksburg and the daily atrazine 

flux. Inset chart shows the possible contribution from the BPNM to the May monthly atrazine flux at Vicksburg. The light blue box represents the time 

period that the BPNM was in operation

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

4/1 4/8 4/15 4/22 4/29 5/6 5/13 5/20 5/27 6/3 6/10 6/17 6/24 7/1 7/8 7/15 7/22 7/29

Atrazine flux, 

in metric ton/day

Streamflow,

in m3/s

Ohio River daily 

Mississippi 

River at 

Upper MS River 

Mississippi River

Ohio River

Upper Mississippi