Prepared in cooperation with the 

U.S. Environmental Protection Agency and Environment and Climate Change Canada

Spatial Distribution of Nutrients, Chloride, and Suspended 

Sediment Concentrations and Loads Determined 

by Using Different Sampling Methods in a Cross Section 

of the Trenton Channel of the Detroit River, Michigan, 

November 2014–November 2015

Scientific Investigations Report 2018–5141

U.S. Department of the Interior

U.S. Geological Survey
Cover. Velocity map of ADCP data displayed using the Velocity Mapping Toolbox and a georeferenced background at U.S. Geological Survey 

station 041686401 Trenton Channel of Detroit River at Grosse Ile, Michigan.
Spatial Distribution of Nutrients, 

Chloride, and Suspended Sediment 

Concentrations and Loads Determined 

by Using Different Sampling Methods 

in a Cross Section of the Trenton Channel 

of the Detroit River, Michigan, 

November 2014–November 2015

By Alexander R. Totten and Joseph W. Duris

Prepared in cooperation with the 

U.S. Environmental Protection Agency and 

Environment and Climate Change Canada

Scientific Investigations Report 2018–5141

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James P. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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Suggested citation:

Totten, A.R., and Duris, J.W., 2019, Spatial distribution of nutrients, chloride, and suspended sediment concentrations 

and loads determined by using different sampling methods in a cross section of the Trenton Channel of the Detroit 

River, Michigan, November 2014–November 2015: U.S. Geological Survey Scientific Investigations Report 2018–5141, 

25 p., https://doi.org/10.3133/sir20185141.

ISSN 2328-0328 (online)
iii

Acknowledgments

We would like to acknowledge our project partners including those in the U.S. Geological 

Survey Upper Midwest Water Science Center (Lansing, Michigan), U.S. Environmental 

Protection Agency, Environment and Climate Change Canada, and others who contributed 

to the project summarized in this report. For their exceptional support, we would like to 

specifically thank Alice Dove, Environmental Scientist; Sean Backus, Manager; Greg Koltun, 

Reviewer; and Paul Terrio, Reviewer.
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Purpose and Scope .......................................................................................................................................2

Description of Study Area ............................................................................................................................2

Methods...........................................................................................................................................................4

Determination of Stream Velocity, Discharge, and Channel Bathymetry....................................4

Water-Quality Sample Collection.......................................................................................................4

Multiple-Vertical Depth-Integrated Sampling.........................................................................5

Fixed-point Sampling...................................................................................................................5

Discrete Sampling .......................................................................................................................8

Processing Water-Quality Samples...................................................................................................8

Analytical Methods...............................................................................................................................8

Quality Assurance for Water Quality.................................................................................................8

Velocity and Discharge.................................................................................................................................9

Concentrations and Loads of Nutrients, Chloride, and Suspended Sediment..................................12

Constituent Concentrations Measured in Paired MVDI and Fixed-point Samples ........12

Chemical Constituent Distribution .........................................................................................16

Constituent Loads ......................................................................................................................19

Summary........................................................................................................................................................23

References....................................................................................................................................................23
v

Figures

1. Map showing Trenton Channel of the Detroit River study area between Lake 

St. Clair and Lake Erie ..................................................................................................................3

2. Illustration showing multiple-vertical depth-integrated composite profiles, 

discrete locations, and fixed-point sample locations in the Trenton Channel 

of the Detroit River downstream from the Grosse Ile Parkway Bridge from 

November 2014 through November 2015..................................................................................6

3. Map showing fixed-point, multiple-vertical depth-integrated, and discrete 

locations on the sampling transect of Trenton Channel downstream 

from Grosse Ile Parkway Bridge ................................................................................................7

4. Plan view velocity map of ADCP data at a range of 40–100 centimers per second

displayed by using the Velocity Mapping Toolbox and a geospatial reference 

background at U.S. Geological Survey station 041686401 Trenton Channel 

of Detroit River at Grosse Ile, Michigan, November 18, 2015..............................................10

5. Cross section showing relation between streamwise velocity and secondary flow 

at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River 

at Grosse Ile, Michigan, November 18, 2015..........................................................................11

6. Graphs showing relations between multiple-vertical depth-integrate and 

fixed-point samples for selected constituent concentrations in milligrams 

per liter at U.S. Geological Survey station 041686401 Trenton Channel 

of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015...................15

7. Tile graphs of discrete constituent concentrations measured at U.S. Geological 

Survey station 041686401 Trenton Channel of Detroit River at Grosse Ile, 

Michigan, March 18, 2015 .........................................................................................................17

8. Boxplots showing selected constituent concentrations based on horizontal location 

or type of sample at U.S. Geological Survey station 041686401 Trenton Channel 

of Detroit River at Gross Ile, Michigan, November 2014 to November 2015.....................18

9. Horizontal boxplots showing selected constituent concentrations based 

on vertical location at U.S. Geological Survey station 041686401 Trenton Channel 

of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015...................20

10. Graph showing comparison of phosphorus loads computed by use of multiplevertical depth-integrated and fixed-point measurements and instantaneous 

discharge at U.S. Geological Survey station 041686401 Trenton Channel 

of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015...................22
vi

Tables

1. Average channel velocity and discharge at U.S. Geological Survey station 041686401 

Trenton Channel of Detroit River at Grosse Ile, Michigan, from November 2014 

to November 2015 .........................................................................................................................9

2. Summary statistics for constituents measured in water-quality samples collected 

by multiple-vertical depth-integrated, fixed-point, and discrete sampling methods 

at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River 

at Grosse Ile, Michigan, November 2014 to November 2015...............................................13

3. Summary statistics for physical properties measured in water-quality samples 

collected by multiple-vertical depth-integrated, fixed-point, and discrete 

sampling methods at U.S. Geological Survey station 041686401 Trenton Channel 

of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015...................14

4. Wilcoxon signed-rank test of differences in median concentrations for samples 

collected by use of multple-vertical depth-integrated and fixed-point methods 

at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River 

at Grosse Ile, Michigan..............................................................................................................14

5. Simple linear regression equations for all major constituents collected 

at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River 

at Grosse Ile, Michigan, November 2014 to November 2015...............................................16

6. Constituent load estimates from multiple-vertical depth-integrated and fixed-point 

sampling methods at U.S. Geological Survey station 041686401 Trenton Channel 

of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015...................21
vii

Conversion Factors

International System of Units to U.S. customary units

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Flow rate

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F – 32) / 1.8.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Depth, as used in this report, refers to distance below the vertical datum.

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius 

(μS/cm at 25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
viii

Abbreviations

ADCP acoustic Doppler current profiler

EDI equal-discharge-increment

EWI equal width increment 

HDPE high density polyethylene

NWIS National Water Information System

NWQL National Water Quality Lab

MVDI multiple-vertical depth integrated 

EPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey
Spatial Distribution of Nutrients, Chloride, and 

Suspended Sediment Concentrations and Loads 

Determined by Using Different Sampling Methods in a 

Cross Section of the Trenton Channel of the Detroit River, 

Michigan, November 2014–November 2015

By Alexander R. Totten and Joseph W. Duris 

Abstract

The Detroit River separates the United States and Canada 

as it flows from Lake St. Clair to Lake Erie. The Trenton 

Channel is a 13-kilometer-long branch of the Detroit River 

that flows to the west of Grosse Ile before rejoining the Detroit 

River near its mouth, just before the Detroit River flows into 

Lake Erie. The U.S. Environmental Protection Agency has 

listed both the Trenton Channel and Detroit River as Areas of 

Concern because of a list of Beneficial Use Impairments such 

as interrupted drinking-water services, loss of aquatic life, and 

reduced recreational use. Phosphorus loading from tributaries 

such as the Trenton Channel is one of the primary drivers of 

eutrophication in Lake Erie. The complex flow patterns and 

variable distribution of chemical constituents in the Trenton Channel make it difficult to accurately characterize the 

concentrations and loads of nutrients and other constituents 

conveyed through the channel to Lake Erie. 

In order to better understand the Trenton Channel’s contributions of nutrients (total phosphorus, orthophosphate, total 

nitrogen, and ammonia), chloride, and suspended sediment to 

Lake Erie and evaluate differences in results obtained by using 

different sample methodologies, the U.S. Geological Survey, 

in cooperation with the U.S. Environmental Protection Agency 

and Environment Canada, completed 12 sampling campaigns 

on the Trenton Channel in Detroit, Michigan, from November 

2014 through November 2015. 

Acoustic Doppler current profiler (ADCP) techniques 

were used to characterize the distribution of velocity components within a cross section corresponding to a transect of the 

Trenton Channel at U.S. Geological Survey station 041686401 

Trenton Channel of Detroit River at Grosse Ile, Mich. Three 

methods of collecting water-quality data at the same transect 

of the Trenton Channel were used: multiple-vertical depthintegrated (MVDI), fixed-point, and discrete samples. Horizontal and vertical variations in concentrations of nutrients, 

chloride, and suspended sediment were analyzed from discrete 

samples to better understand distributions of these constituents 

throughout the channel. Constituent loads were calculated by 

using individual sample concentrations and ADCP measurements for discharge made on the same day that the water-quality samples were collected. Constituent loads calculated from 

MVDI and fixed-point sampling methods were compared. 

The relation between MVDI and fixed-point samples helped 

quantify the differences between the sampling methods. Linear 

regression equations depicting the relation between concentrations measured by using MVDI and fixed-point samples 

were prepared.

ADCP data indicates that velocities throughout the sampled transect remain uniform except for one location around 

200 meters from the west bank of the channel. Secondary flow 

vectors suggest the presence of counter-rotating helical flow 

cells, and these helical flow cells could affect the mixing of 

constituents in transport by preventing cross-channel mixing. 

Flow discharges throughout the sampling campaign showed 

small variations, although lower flow rates were observed in 

the early winter months than in the summer months. Discrete sampling methods results displayed both heterogeneity 

throughout the channel horizontally, representing limited 

horizontal mixing in the channel, and displayed homogeneity throughout vertical transects, indicating mixing vertically. 

Comparisons between MVDI and fixed-point methods found 

consistently higher concentrations were measured in MVDI 

samples compared to concentrations measured in fixed-point 

samples. To correct for this bias between MVDI and fixedpoint sample results, simple linear-regression equations were 

developed for all major constituents to help estimate constituent concentrations from fixed-point samples equivalent to 

those measured by using MVDI sampling techniques. Instantaneous constituent loads were developed by using velocity and 

discharge data obtained from ADCPs and constituent concentrations obtained from MVDI and fixed-point samples. 
2 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

Introduction

The Detroit River separates the United States and Canada 

as it flows from Lake St. Clair to Lake Erie. The Trenton 

Channel is a 13-kilometer (km) branch of the Detroit River 

that flows between the mainland of Michigan and the eastern 

edge of Grosse Ile before rejoining the Detroit River near 

its mouth just before the Detroit River flows into Lake Erie 

(fig. 1). The Detroit River splits at the northern tip of Grosse 

Ile; the Trenton Channel conveys about 22 percent of the flow 

to Lake Erie and is thus a major contributor to water quality 

in Lake Erie (Derecki, 1984). Since 1991 The U.S. Environmental Protection Agency (EPA) has listed both the Trenton 

Channel and the Detroit River as Areas of Concern because of 

Beneficial Use Impairments such as interrupted drinking-water 

services, loss of aquatic life, and reduced recreational use 

(EPA, 2015). Since 1991, remediation has helped shorten the 

list of Beneficial Use Impairments for the Detroit River and 

the Trenton Channel in hopes of ultimately removing these 

rivers from the list of Areas of Concern. 

In the last decade, there has been intense focus on understanding eutrophication issues in Lake Erie. Persistent and 

widespread algal blooms have resulted in decreased recreational opportunities and increased human health risks (Francy 

and others, 2015). The primary eutrophication driver in Lake 

Erie is phosphorus loading to the lake from its tributaries and 

internal phosphorus loading from the lake sediment (Lake Erie 

Lakewide Management Plan , 2011). The International Joint 

Commission (IJC), EPA, Great Lakes Binational Committee 

(GLBC), and Ohio EPA (OHEPA) have recognized that estimating nutrient loads from tributaries is essential to understanding the recent changes in the lake ecosystem. 

A previous study conducted by Environment Canada 

evaluated the phosphorus loading from the Detroit River and 

the Trenton Channel into Lake Erie from August through 

November 2007 (Burniston and others, 2010). Combinations 

of automated Isco samples and grab samples collected at five 

equal width increments along a transect at U.S. Geological Survey (USGS) station 041686401 Trenton Channel of 

Detroit River at Grosse Ile, Mich. (hereinafter referred to as 

the “Trenton Channel station”), were used by Burniston and 

others (2010) to develop estimated phosphorus concentrations 

throughout 2007. A two-dimensional hydrodynamic model of 

Lake St. Clair-Detroit River was used to estimate average flow 

per day in the southern part of the Trenton Channel throughout 

2007 (Holtschlag and Koschik, 2002). The combination of 

estimated concentrations and flow was used to determine an 

annual phosphorus load. 

Advances in technology have improved the ability to 

accurately measure flow in complex systems such as the 

Detroit River and Trenton Channel. During the last 10 years, 

the USGS has transitioned from using mechanical velocity 

meters to using Acoustic Doppler Current Profilers (ADCPs) 

for collecting discharge measurements in rivers that have complex directional patterns and unsteady-flow characteristics like 

the Trenton Channel. 

The USGS uses standardized techniques to monitor water 

quality. One technique that provides scientists with a high 

level of confidence in water-quality monitoring data is the 

collection of depth- and width-integrated samples that can be 

analyzed for representative flow-weighted mean concentrations (U.S. Geological Survey, 2006). 

In order to better understand the Trenton Channel’s contributions of nutrients (total phosphorus, orthophosphate, total 

nitrogen, and ammonia), chloride, and suspended sediment to 

Lake Erie and evaluate differences in results obtained by using 

different sample methodologies, the USGS, in cooperation 

with the EPA and Environment and Climate Change Canada, 

completed 12 sampling campaigns on the Trenton Channel in 

Detroit, Mich., from November 2014 through November 2015. 

In addition to fixed-point samples, a composited multiplevertical depth-integrated (MVDI) sample was collected along 

a cross section approximately 130 meters (m) downstream 

from Grosse Ile Parkway. On 4 of the 12 sampling dates, 24 

discrete samples were collected at 4 verticals across the cross 

section using a 1–L Van Dorn sampler. An ADCP was used 

directly after sampling to measure stream velocity, discharge, 

and bathymetry within the cross section. ADCP data were 

examined using the Velocity Mapping Toolbox to evaluate 

the velocity distribution and secondary flow patterns in the 

sampling cross section. 

Purpose and Scope

This report describes the results of discharge measurements and water-quality sampling done by the USGS in 

cooperation with the EPA and Environment Climate Change 

Canada in the southern part of the Trenton Channel from 

November 2014 through November 2015 to characterize 

nutrient loads. This report (1) compares analytical results for 

nutrients (total phosphorus, orthophosphate, total nitrogen, 

and ammonia), chloride, and suspended sediment measured 

with MVDI, fixed-point, and discrete sample methods in a 

cross section of the Trenton Channel; (2) describes the spatial 

distribution of velocities and major constituent concentrations 

within the cross section; and (3) compares loading estimates 

computed with concentrations obtained from MVDI and fixedpoint samples. 

Description of Study Area

The Detroit River separates the United States and Canada 

as it flows from Lake St. Clair to Lake Erie. The Trenton 

Channel of the Detroit River is located on the eastern side 

of Michigan’s Lower Peninsula (fig. 1). Grosse Ile separates 

Trenton Channel from the main channel of the Detroit River, 

creating a 13-km channel starting near Wyandotte, Mich., 

on the American side originating in the Detroit River, and 

terminating 8 km from Lake Erie near Gibraltar, Mich. The 
Description of Study Area 3

LAKE ERIE

LAKE

ST. CLAIR

DETROIT

RIVER

RIVER ROUGE

Gibraltar

Tren ton C h ann

el

04168640

# 04165710

UNITED

STATES

CANADA

42°00'

42°05'

42°10'

42°15'

42°20'

83°20' 83°10' 83°00'

10 15

10

5

5

0

0

20 KILOMETERS

MILES

EXPLANATION

Surface water site

Study area

Water flow direction

International boundary

Map image is the intellectual property of Esri and is used herein under license. 

Copyright © 2019 Esri and its licensors. All rights reserved.

Universal Transverse Mercator, projection zone 17

North American Datum 1983, 1:350,000

Map area

Figure 1. Trenton Channel of the Detroit River study area between Lake St. Clair and Lake Erie.
4 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

Trenton Channel generally flows from north to south, although 

the direction of flow in the Trenton Channel can be reversed or 

stopped temporarily by oscillating standing waves (seiches) on 

Lake Erie caused by strong winds or changes in atmospheric 

pressure (National Oceanic and Atmospheric Administration, 

2018). The Trenton Channel is deep (average depth is 8.5 m) 

and wide (average width is 330 m), with an average discharge 

of approximately 1,370 cubic meters per second (m3/s). Urban 

and industrial land cover of Detroit and the surrounding 

areas make up a majority of the Trenton Channel’s watershed 

(Homer and others, 2015). Trenton Channel is frequently used 

by local anglers, recreationists, and commercial transport vessels. The Rogue River is one of the primary local tributaries 

contributing to the Detroit River and enters the Detroit River 

from the west, approximately 9 km upstream from the northern end of the Trenton Channel (fig. 1). 

Methods

From November 2014 through November 2015, the 

USGS collected data to characterize nutrient loads in the 

Trenton Channel. In order to accurately measure nutrient loads 

in the Trenton Channel, accurate measurements of stream 

velocity, discharge, and channel bathymetry are needed. The 

methods used to measure stream velocity and bathymetry are 

described in Mueller and Wager (2009) and Mueller and others 

(2013). The water-quality sampling techniques used to measure physical properties, nutrients, chloride, and suspended 

sediment concentrations are described. Quality assurance and 

quality control measures pertaining to the sampling techniques 

are also described. The water quality processing techniques 

that were used to ensure reproducible results are described, as 

well as the laboratory analytical methods. All of the data used 

in this assessment were collected by the USGS and are stored 

in the National Water Information System (NWIS) database 

(U.S. Geological Survey, 2018).

Determination of Stream Velocity, Discharge, 

and Channel Bathymetry

An ADCP was used to measure stream velocity, discharge, and bathymetry in a cross section of the Trenton 

Channel downstream from the Grosse Ile Parkway Bridge 

at the Trenton station. ADCPs produce beams of ultrasonic 

sound that bounce off small particles of material in the water 

and the bed of the channel before traveling back to the ADCP. 

The frequency and travel time of the reflected acoustic 

signals are measured upon arrival back at the ADCP. Velocity is calculated from the change in frequency of the acoustic 

signal reflected to the ADCP, resulting from the Doppler effect 

(Mueller and Wagner, 2009). Bathymetry is measured based 

on the two-way travel time of the signals. Stream discharge is 

computed from the product of velocity and area of the channel. ADCPs use four transducers in a Janus configuration to 

send and receive acoustic signals (Mueller and others, 2013). 

The use of four beams to detect velocity at four different 

angles gives the ADCP the ability to calculate bathymetry 

and three-dimensional velocity. The ADCP was deployed at 

a depth of approximately 0.75 m below the water surface; a 

“blank zone” in which accurate acoustic signals could be measured extended approximately 0.5 m below the depth at which 

the ADCP was deployed. The combined depth (approximately 

1.25 m) is considered the superficial zone and no velocity 

measurements could be made within this zone. Because of a 

high amount of interference produced by bed sediment, known 

as side-lobe interference, the ADCP cannot develop velocity 

measurements near the bed of the channel (Mueller and others, 

2013). Side-lobe interference affects about 6 to 13 percent of 

the measured system, and data cannot be accurately collected 

in this area. However, extrapolation of velocities and discharge 

can be calculated for this area. 

A boat-mounted ADCP was used. In order to compensate for the velocity of the moving boat while making the 

measurement, a global positioning system was mounted over 

the ADCP to determine the boat velocity. The ADCP was 

configured and calibrated onsite before every sample. Movement of near-bed sediment during the ADCP data collection 

can produce errors in the discharge measurement. A movingbed test is done at every sampling site before the discharge 

measurement begins to compensate for this possible source 

of error. For each sampling effort a measurement consisted 

of four separate ADCP transects made along the cross section for which velocity and discharge were calculated. If the 

discharge measurements from the four transects did not differ 

from each other by more than 5 percent, they were used to 

compute an average velocity and discharge (U.S. Geological Survey 2002). None of the 12 ADCP discharge measurements during sampling campaigns had differences between 

individual transects that exceeded 5 percent. Average velocity 

and total discharge data for the measurements can be found 

on the NWIS website at https://waterdata.usgs.gov/nwis/

measurements/?site_no=041686401. 

Version 4.0.9 of the Velocity Mapping Toolbox (VMT) 

was used to display and examine the data collected with the 

ADPCs (Parsons and others, 2013). VMT is a Matlab-based 

software used for processing and visualizing ADCP data. The 

software produces transverse three-dimensional flow models 

and plan-view depth-averaged flow maps (Lane and others 

2000). Velocity maps were produced for every viable ADCP 

measurement with available global positioning systems and 

complete flow data.

Water-Quality Sample Collection

Similar to the velocity and discharge measurement, all of 

the water-quality samples were collected at the Trenton station 
Methods 5

downstream from the Grosse Ile Parkway Bridge. A waterquality sonde (YSI ProPlus) (Xylem Inc., 2018) was used to 

make onsite measurements of selected physical properties of 

the water (temperature, pH, specific conductance, and dissolved oxygen). The water-quality sonde was calibrated before 

each sampling event in accordance with standard USGS 

procedures (Gibs and others, 2007). Concurrent with MVDI 

and fixed-point sample collection, the water-quality sonde 

was placed 0.5 m below the water surface to obtain point 

physical-property measurements traversing the cross section 

from which discharge data and water-quality samples were 

collected. Results were stored in the NWIS database (U.S. 

Geological Survey, 2018). Physical properties were recorded 

at each discrete location concurrent with discrete sampling. A 

weighted DH–2 sampler was used to obtain physical properties at each discrete location. The YSI ProPlus was attached 

to the DH–2 sampler with zip-ties and lowered to the depth 

corresponding to the discrete sampling location.

Three methods were used to collect water-quality 

samples: (1) a MVDI method; (2) a fixed-point sampling 

method; and (3) a discrete sampling method. The MVDI 

method consisted of 10 vertical isokinetic depth-integrated 

samples collected by using a DH–2 sampler; the 10 depthintegrated samples were subsequently composited to form a 

single sample. For the fixed-point sampling method, sequential samples were collected about 20 m from the east bank by 

using a DH–2 sampler positioned 2 m below the water surface. 

Discrete samples collected using a 1–L Van Dorn sampler at 

four locations along the transect. At three locations along the 

transect, the discrete samples were collected at increments of 

1 m of depth; at a fourth location near the west bank, discrete 

samples were collected at increments of 0.5 m of depth. USGS 

personnel carried out all three of these water-quality sampling 

techniques in a consistent manner along the same sampling 

transect at the Trenton Channel station. A total of 12 MVDI 

and 12 fixed-point samples were collected during the November 2014–November 2015 sampling period. On four dates 

within the sampling period, 24 discrete samples were collected 

in four verticals along the sampling transect of Trenton Channel (fig. 2). After all water-quality samples had been collected, 

a series of 4 boat mounted ADCP measurements were averaged to produce velocities, bathymetry, and discharge in the 

sampling cross section.

Multiple-Vertical Depth-Integrated Sampling

The USGS commonly uses MVDI sampling methods 

in water-quality analysis because MVDI sampling provides 

an accurate depth integrated isokinetic sample that spatially 

characterizes the cross section (Topping and others, 2011). 

MVDI samples were collected 12 times during the sampling 

period from a cross section about 100 m downstream from 

Grosse Ile Pkwy road (figs. 2 and 3; fixed-point and discrete 

samples were also collected from this cross section). Because 

of interference from a marina, it was not possible to collect 

MVDI samples from a small section of the channel near the 

east bank, and as a result the sampling method is better categorized as a MVDI than a common equal width increment 

(EWI) sample. The approximately 310-m-wide sampling 

cross section was subdivided into 10 approximately equalwidth intervals. Vertical sampling profiles along the sampling transect were collected at the 10 points of intersection 

between adjacent intervals. Based on the velocity of the river 

and river depth, a single vertical transit rate was calculated 

and used at each vertical (U.S. Geological Survey, 2006). At 

each MVDI vertical, a boat-mounted crane was used to lower 

the DH–2 sampler at the specified transit rate to just above 

the bed of the channel then back up. A DH–2 sampler was 

used because of the depth of the Trenton Channel exceeded 

7 m in some locations. A DH–2 bag sampler is used instead 

of a bottle sampler if the sampling depth exceeds 7 m to offset the water pressure at such deep depths (Davis, 2005). The 

sample obtained from each vertical profile was emptied into 

a 14-L polyethylene churn splitter. After all 10 verticals were 

sampled and emptied into the churn splitter, the mixture was 

homogenized using the churn paddle, and individual bottles 

for analysis were filled from the churn. 

Fixed-point Sampling

Fixed-point samples were collected from a boat using a 

DH–2 weighted bag sampler lowered by a crane to a discrete depth of 2 m. Ambient water flowed into a 1-liter (L) 

high-density polyethylene (HDPE) bag through a 5/16-inch 

diameter nozzle (7.94 millimeter) attached to the DH–2 

bag sampler. The sampling location was approximately 

20 m from the east bank and about 130 m downstream from 

Grosse Ile Pkwy Bridge (figs. 2 and 3). The DH–2 sampler 

is not a point sampler; it was quickly lowered to a depth of 

2 m below the surface so that most of the water it collected 

was from the desired sampling depth. Because the DH–2 

sampler is not a true point sampler, the samples collected 

with the DH–2 sampler are referred to herein as “fixed-point 

samples.” The water collected from each sample bag constituting a fixed-point sample was poured into a 14–L HDPE 

churn. The 5 sample bags were collected over a 5-minute 

time period. A total of 5 sample bags were composted into 

the 14–L churn and then the sample was homogenized using 

the churn paddle and decanted individual bottles for analysis. The USGS often deploys automated samplers in order to 

obtain accurate temporal water-quality results. Automated 

samplers can provide temporally accurate data, but at a cost 

of bias in spatial representation of sample area (Anderson and 

Rounds, 2010). The location and methods used for collecting 

fixed-point samples were selected for the purpose of obtaining samples similar to those obtained by using an automated 

sampler. Cross sectionally composited sampling methods like 

MVDI sampling provide a sample that represents the sample 
6 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan 0.5 meter 1.5 meters 2 meters 1 meter 2 meters 3 meters 4 meters 5 meters 6 meters 7 meters if possible 1 meter 2 meters 3 meters 4 meters 5 meters 6 meters 7 meters 1 meter 2 meters 3 meters 4 meters 5 meters 6 meters 7 meters 2 meters West bank East bank 10 meters 60 meters 170 meters 280 meters EXPLANATION Multiple-vertical depth-integrated composite

—

Profile locations throughout the cross section where vertical depth-integrated water-quality samples were taken

Discrete sampling point—Depths at which 

discrete water-quality samples were collected at each vertical profile,in meters

Fixed-point sampling point—Samples collected

from a single depth (2 meters) using DH-2 sampler

Bed of channel—Estimated and extrapolated 

depth to the bed of channel

Figure 2. Multiple-vertical depth-integrated composite profiles, discrete locations, and fixed-point sample locations in the Trenton Channel of the Detroit River downstream from the Grosse Ile Parkway Bridge from November 2014 through November 2015 (west bank is on the left). 
Methods 7

83°10'45" 83°10'40" 83°10'35" 83°10'30" 83°10'25"

42°07'40"

42°07'35"

42°07'30"

42°07'25"

Map area

LAKE

ST. CLAIR

LAKE ERIE 

DETROIT RIVER Trenton Channel

UNITED

STATES

CANADA

83°30' 83°20' 83°10' 83°00' 82°50' 42°30'

42°20'

42°10'

150

200 400

0 75

0 FEET

Map image is the intellectual property of Esri and is used herein under license. METERS

Copyright © 2019 Esri and its licensors. All rights reserved.

Universal Transverse Mercator, projection zone 17

North American Datum 1983

EXPLANATION

Multiple-vertical depth-integrated location

Discrete location

Fixed-point location

International boundary

Figure 3. Fixed-point, multiple-vertical depth-integrated, and discrete locations on the sampling transect of Trenton Channel 

downstream from Grosse Ile Parkway Bridge. 
8 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

cross section spatially (Topping and others, 2011). The 

purpose for deploying the fixed-point method was to statistically build a linear regression between the fixed-point and 

MVDI methods. 

Discrete Sampling

Multiple discrete samples were collected throughout the 

cross section to help describe the distribution of nutrients, 

chloride, and suspended sediment in the Trenton Channel. 

A total of 24 discrete samples were collected at four verticals along the sampling cross section using a 1–L Van Dorn 

sampler. These verticals were located at 10 m, 60 m, 170 m, 

and 280 m from the west bank of the channel (figs. 2 and 3). 

At most verticals, discrete samples were collected at 1-m 

intervals below the water surface to the bed of the channel 

(fig. 2). At the western-most vertical, samples were collected 

at intervals ranging from 0.5 to 1 m because of the shallow 

waters at this vertical transect. For each discrete sample, the 

open Van Dorn sampler was lowered to the indicated depth 

along with a messenger weight that follows the suspension 

line and triggers sample acquisition. The sample obtained 

from the Van Dorn sampler was then decanted into a sterile 

1-L HDPE bottle for later processing. During two of the four 

discrete sampling dates, the water was too shallow to collect 

a 7-m deep sample at the 60-m location. 

Processing Water-Quality Samples

Prior to each sample event, 500-milliliter HDPE sample 

bottles were rinsed with deionized water to condition the 

bottles for sampling. The capsule filter with 0.45 micrometer pore size used in the processing of filtered samples 

was flushed with approximately 2 L of deionized water to 

condition the filter. All sample splitting, decanting, filtering, 

and processing was done in a mobile laboratory van. Filtering was done by pumping water through the capsule filters 

using a peristaltic pump with clean tubing. One milliliter of 

1:7 sulfuric acid preservation was done after samples were 

split. Samples were shipped on ice the day of collection to 

the USGS National Water Quality Laboratory (NWQL) for 

processing and analysis for all constituents except turbidity. 

A conditioned 250-milliliter HDPE bottle was used to 

store the turbidity sample until analysis. Turbidity was measured at the USGS Water Science Center in Lansing, Mich. 

by using a Hach 2100Q turbidity meter (Hach Company, 

2018). The median value of three separate quantifications 

was entered into the NWIS database. All water-quality results 

can be obtained from the NWIS: Web Interface (NWISWeb) 

(https://nwis.waterdata.usgs.gov/usa/nwis/qwdata). To retrieve 

the water-quality data, check the box next to Site Number 

and click the Submit button. Enter 041686401 as the Site 

Number and click on the Submit button. From the resulting 

web page, a variety of options are offered for retrieving the 

water-quality data.

Analytical Methods

All water samples collected by USGS personnel were 

analyzed and processed by the NWQL located in Lakewood, Colorado, in accordance with analytical procedures 

as described in the USGS methods of analysis by the USGS 

NWQL (Fishman, 1993). All suspended sediment samples 

collected by the USGS were analyzed for suspended-sediment 

concertation by the USGS Kentucky Sediment Laboratory 

located at the Kentucky Water Science Center in Louisville. 

Suspended sediment samples analysis was conducted according to the USGS methods and procedures, as described in 

the Quality Assurance Plan for the Kentucky Water Science 

Center Sediment Laboratory (Shreve and Downs, 2005; 

Guy, 1969). 

Quality Assurance for Water Quality

 A part of producing accurate and unbiased data is 

implementing some form of quality assurance and quality 

control (QA/QC). For this study, 5 percent of all samples were 

QA/QC samples in the form of blanks or replicates. Three 

blanks and one replicate were collected during the sampling 

period to assess possible bias, as well as variability and 

reproducibility of the results. Blank sample concentrations 

were below the equipment’s observed limits or near estimated 

detection levels. The field blank collected on May 29, 2015, 

had a total phosphorus concentration of 0.0072 milligrams 

per liter (mg/L) which is above the NWQL minimum reporting level of 0.004 mg/L. The minimum reporting level is the 

smallest concentration of a substance that can be reliably 

measured by a given analytical method (Childress and others, 

1999). The field blank collected on August 26, 2015, had an 

ammonia as nitrogen concentration of 0.012 mg/L which is 

above the NWQL minimum reporting level of 0.010 mg/L. 

Blanks collected in this study demonstrated that field sample 

collection did not show evidence of gross contamination. 

Study results were not censored because of detections in field 

blanks, because the exceedance was close to NWQL detection limits. Replicate sample concentrations were found to 

be within 5 percent of concentrations in the corresponding 

environmental samples.
Velocity and Discharge 9

Velocity and Discharge

A summary of average channel velocity and discharge 

measured in a cross section of the Trenton Channel at the 

Trenton Channel station is provided (table 1). Example plots 

of depth-average velocity vectors and cross-sectional velocity 

distribution with vectors that show transverse velocity patterns 

are shown in figures 4 and 5. ADCP velocity measurements 

ranged from 20–100 centimeter per second (cm/s) as depicted 

by VMT (fig. 5).

The discharge measured at Trenton Channel for this study 

ranged from 1,200 to 1,450 m3/sec (table 1). Average channel 

velocities ranged from 0.515 to 0.640 m/sec (table 1). Flow 

velocities throughout the sampling campaign varied little with 

no seasonal pattern evident; some of highest discharge values 

of 1,450 m3/sec and 1,440 m3/sec were measured during the 

winter (December 17, 2014, and March 18, 2015, respectively). 

Some of the lowest discharge values of 1,210 m3/sec and 

1,260 m3/sec were measured in fall mid-winter (October 21, 

2015, and January 18, 2015, respectively). 

Figure 4 shows depth-averaged velocity vectors measured 

on November 18, 2015, displayed in plan view (shown with the 

western edge of the river on the left). The velocity vectors were 

superimposed onto a georeferenced tagged image file format, 

or GeoTIFF, plan-view image of the Trenton Channel. Plots for 

measurements made on the other dates looked similar to figure 4. The length and color of the vectors are indicative of the 

velocity magnitudes. It should be noted that the measurement 

cross section did not extend across the entire channel because 

of the presence of docks on the east bank, and so velocities 

were not measured throughout the entire cross section. Even 

so, discharge was computed by estimating the discharge in the 

unmeasured area using a ratio-interpolation method based on 

velocities and depths in the measured portion of the channel 

Table 1. Average channel velocity and discharge at U.S. 

Geological Survey station 041686401 Trenton Channel of 

Detroit River at Grosse Ile, Michigan, from November 2014 to 

November 2015.

[m/sec, meter per second; m3/sec, cubic meter per second]

Date Average channel 

velocity (m/sec)

Trenton Channel 

discharge (m3/sec)

December 17, 2014 0.631 1,450

March 18, 2015 0.640 1,440

April 9, 2015 0.548 1,390 

May 4, 2015 0.564 1,340

May 29, 2015 0.585 1,330

August 12, 2015 0.579 1,420 

August 26, 2015 0.582 1,420

September 1, 2015 0.554 1,330

September 23, 2015 0.557 1,350

September 30, 2015 0.600 1,450

October 21, 2015 0.515 1,210

November 18, 2015 0.542 1,260

and measurements of distance from the bank (Fulford and 

Sauer, 1986). Depth-averaged velocity vectors were fairly 

uniform in magnitude and direction along most of the cross 

section; however, a few sections had noticeably higher average 

velocity. Depth-averaged velocities in those sections ranged 

from approximately 85 to 108 centimeters per second (cm/s) 

as compared to the rest of the cross section where depth-averaged velocities typically ranged from about 45 to 65 cm/s.

VMT was used to plot streamwise velocities (that is, 

velocities perpendicular to the transect) obtained from ADCP 

data collected at the Trenton Channel station. The different 

colors indicate the streamwise velocities throughout the cross 

section of the Trenton Channel (fig. 5). The black arrows 

in figure 5 represent the magnitudes and directions of components of velocity vectors in the plane of the cross section 

referred to as secondary flow. Secondary flow is orientated 

perpendicular to the streamwise flow and plays an important 

role in sediment routing and mixing of flow (Lane and others, 

2000). The bold white line represents the bottom bathymetry 

of the cross section corresponding to the bed of the channel. 

Discrete sampling locations are shown to illustrate their depths 

and position within the cross section. Like figure 4, the streamwise velocity map shown in figure 5 was developed from data 

collected on November 18, 2015. 

This section of the Trenton Channel shares characteristic of alluvial rivers for two reasons: (1) subcritical flow can 

be seen near the edges of the transect and near the bed of the 

channel, and (2) the highest flows are at surface throughout the 

cross section of the river (Magirl and others, 2009). The plan 

and streamwise figures have many traits in common. Sections 

of higher than average velocities can be seen in both types of 

figures. One particular high-velocity section, located approximately 200 m from left bank plus or minus 10 m, stands out in 

both plan and streamwise view maps. This particular section of river had the highest velocities, accounting for about 

25 percent of the flow. Secondary flow vectors suggest the 

presence of counter-rotating helical flow cells. These helical 

flow cells could affect the mixing of constituents in transport 

by preventing cross-channel mixing. 

 Bathymetry displayed in velocity maps show a depth 

range of about 4.75 m to 8.75 m in the cross section. About 

50 percent of the cross section (east side) had an approximate depth of 8 m and the remaining portion (west side) was 

approximately 6 m in depth. Transverse velocity maps can also 

be used to help define an appropriate sampling method for this 

section of the Trenton Channel based on velocity distribution 

and presence of secondary flow. If the depth and velocities are 

highly variable along the cross section, an equal-dischargeincrement (EDI) sampling method is necessary because the 

EDI method uses varying transit rates to accommodate for 

varying of depths and velocities. If the flow and depths are 

uniform throughout the cross section, then an Equal Width 

Increment sample is appropriate (U.S. Geological Survey, 

2006). Based on the variability of the depth and velocities on 

the Trenton Channel, an EDI sampling method is most appropriate for future sampling. 
10 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

42°07’38”

83°10’39” 

42°07’36”

83°10’35”

42°07’34”

42°07’33”

42°07’31”

83°10’30” 83°10’26” 83°10’22” 83°10’17” 83°10’13” 83°10’09”

100

90

80

70

60

50

40

Depth-averaged velocities, in centimeters per second

EXPLANATION

Multiple-vertical depth-integrated location

Discrete location

Fixed-point location

Velocity measurement—Arrow head indicates

direction of flow based on true north. Size 

of arrow indicates the relative velocity 

magnitude. Arrow color indicates 

actual velocity magintude.

150

200 400

0 75

0 FEET

Map image is the intellectual property of Esri and is used herein under license. METERS

Copyright © 2019 Esri and its licensors. All rights reserved.

Universal Transverse Mercator, projection zone 17

North American Datum 1983

Figure 4. Plan view velocity map of ADCP data at a range of 40–100 centimers per second displayed by using the Velocity 

Mapping Toolbox (VMT) and a geospatial reference background at U.S. Geological Survey station 041686401 Trenton Channel of 

Detroit River at Grosse Ile, Michigan, November 18, 2015. 
Velocity and Discharge 11

Blanking zoneBlanking zone

Reference vector showing30 centimeters per secondvector magnitude

0 50 100 150 200 250 300

012345678

Distance from west bank, in meters

Depth, in meters below water surface

West bank East bank

10080604020

Velocity, in centimeters per second

EXPLANATION

Bed of channel

Water velocity, parallel and vertical

Discrete sampling location

to transect direction—Arrow headindicates direction of flow. Sizeof arrow indicates velocity, incentimeters per second

Blanking zone—Size of arrow indicates

area of no measurement due to side lobe interference or depth of ADCP

Figure 5. Relation between streamwise velocity and secondary flow at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River at Grosse Ile, Michigan, November 18, 2015.
12 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

Concentrations and Loads of Nutrients, 

Chloride, and Suspended Sediment

A summary of nutrients, chloride, suspended-sediment, 

and physical-property concentrations measured at the Trenton 

Channel cross section at various distances from the west bank 

is provided (tables 2 and 3). Statistical differences in the analytical results for nutrients (total phosphorus, orthophosphate, 

total nitrogen, and ammonia), chloride, and suspended sediment measured with MVDI, fixed-point, and discrete sample 

methods are also assessed in this section. The relation between 

concentrations of nutrients, chloride, and suspended sediment measured by using the MVDI and fixed-point sampling 

methods is determined by linear regression. Tile graphs and 

boxplots are used to depict the spatial distribution of constituent concentrations within the cross section. Estimates of the 

loads of nutrients, chloride, and suspended-sediment conveyed 

through the Trenton Channel are also provided. 

Constituent Concentrations Measured in Paired 

MVDI and Fixed-point Samples

Differences in constituent concentrations obtained from 

paired MVDI and fixed-point samples were evaluated by using 

the Wilcoxon signed-rank test (Helsel and Hirsch, 2002). The 

Wilcoxon signed-rank test was applied to the data because this 

test is not sensitive to the distributions of the data. The null 

hypothesis is that the median difference between the paired 

observations is zero. The Wilcoxon signed-rank test is used to 

evaluate for a statistically significant difference between two 

datasets based on the probability of rejecting the null hypothesis when it is true (referred to as the alpha value). An alpha 

value of 0.05 was used for tests of significance; if the probability value (p-value) is less than or equal to the alpha value, 

the difference is considered statistically significant and the 

null hypothesis is rejected (Helsel and Hirsch, 2002). The null 

hypothesis was rejected for total phosphorus, total nitrogen, 

ammonia, and chloride, but not for suspended sediment or 

orthophosphate (table 4). In this case, rejection of the null 

hypothesis implies that concentrations in the MVDI samples 

tended to be significantly larger or smaller than those in the 

corresponding fixed-point samples. The most representative 

type of future sampling would include a combination of these 

two methods or a method that is more representative of the 

sample area considering the statistically significant difference 

observed in median values for total phosphorus, total nitrogen, 

ammonia, and chloride. 

Liner regression analysis was used to determine the 

relation between constituent concentrations measured by 

using MVDI and fixed-point sampling methods. Correlations 

between methods and constituents have been fitted with a 

black 1:1 line and a red best-fit line. Sample size (n) and coefficient of determination (R2

) summary statistic information is 

provided for each regression equation (fig. 6).

Linear regressions produced from the comparison of 

MVDI and fixed-point methods represent the relation between 

the concentrations measured by the two methods. The 1:1 line 

represents line of agreement between the two methods. An 

overall pattern of higher constituent concentrations measured 

using the MVDI method compared to the constituent concentration measured using the fixed-point samples is evident in 

the regression analyses. Suspended sediment shows a pattern 

of sporadic distribution of points around the 1:1 line with 

few high MVDI concentrations. Higher concentrations from 

MVDI samples in relation to fixed-point samples likely represent the heterogeneity of constituent distributions in the Trenton Channel. MVDI samples consist of a composite of equal 

sections of the channel. Therefore, MVDI samples represent a 

much larger portion of the channel and flow in comparison to 

fixed-point samples. Higher MVDI concentrations than fixedpoint samples also indicate a distribution of higher constituent 

concentrations west of the fixed-point sampling location in 

Trenton Channel. Constituents such as chloride, phosphorus, 

and orthophosphate show a strong correlation (R2 values 

greater than 0.70) and represent a consistently higher concentration from the MVDI sampling method per those constituents. Correlations between these three particular constituents 

could provide a relation between the MVDI and fixed-point 

methods, providing data for future sampling method applications in Trenton Channel. 

A simple linear regression equation was produced for 

each major constituent measured in samples obtained from 

the Trenton Channel during the sampling campaign (table 5). 

These simple linear regressions can be used to estimate instantaneous concentrations, daily loads, or annual loads in Trenton 

Channel. All linear models were produced in R Programming language (R Core Team, 2018). Residual standard error, 

adjusted-R2, and p-values were developed to assess the fit of 

each regression equation to the major constituent concentrations. For each major constituent, the fit of the regression 

equation was statistically significant. Regression equations are 

expressed as:

yi = b + mxi (1)

where

yi is the i th observation of the response 

(dependent) variable (concentration);

xi is the independent variable (observed 

fixed-point sample);

m is the slope; and

b is the intercept.
Concentrations and Loads of Nutrients, Chloride, and Suspended Sediment 13

Table 2. Summary statistics for constituents measured in water-quality samples collected by multiple-vertical depth-integrated (MVDI), fixed-point, and discrete sampling methods at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015.[mg/L, milligram per liter; P, phosphorous; N, nitrogen; n, number of samples collected from November 2014 to November 2015; Min., minimum; Max., maximum; Avg., average; m, meter]

Sample type 

and distance 

from bank 

Total phosphorus 

(mg/L as P)

Orthophosphate 

(mg/L as P)

Total nitrogen 

(mg/L as N)

Ammonia 

(mg/L as N)

Chloride 

(mg/L)

Suspended sediment 

(mg/L) n

Min. Max. Avg. Min. Max. Avg. Min. Max. Avg. Min. Max. Avg. Min. Max. Avg. Min. Max. Avg.

MVDI–

various distances from west bank

0.01 0.032 0.017 0.004 0.011 0.005 0.52 0.82 0.64 0.12 0.26 0.18 10.6 31.8 15.1 1 27 8 12

Fixed-point–

about 20 m from east bank

0.09 0.026 0.014 0.004 0.006 0.004 0.46 0.71 0.57 0.08 0.20 0.13 9.5 25.5 13.2 2 17 6 12

Discrete–

10 m from west bank 

0.01 0.037 0.026 0.004 0.007 0.006 0.62 0.90 0.77 0.15 0.27 0.23 16.0 38.7 22.2 2 21 8 12

Discrete–

60 m from west bank

0.01 0.049 0.024 0.004 0.011 0.007 0.59 0.88 0.73 0.14 0.29 0.23 14.6 38.0 20.7 1 31 8 26

Discrete–

170 m from west bank

0.01 0.035 0.020 0.004 0.011 0.006 0.500 0.81 0.666 0.120 0.24 0.189 10.600 34.2 17.814 2 22 8.53 28

Discrete–

280 m from west bank

0.01 0.035 0.018 0.004 0.009 0.006 0.470 0.90 0.618 0.100 0.20 0.151 10.400 30.6 16.164 2 20 7.75 28
14 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

Table 3. Summary statistics for physical properties measured in water-quality samples collected by multiple-vertical depthintegrated (MVDI), fixed-point, and discrete sampling methods at U.S. Geological Survey station 041686401 Trenton Channel of Detroit 

River at Grosse Ile, Michigan, November 2014 to November 2015.

[°C, degrees Celsius; μS/cm, microsiemen per centimeter at 25°C; mg/L, milligram per liter; n; number of samples; Min., minimum; Max., maximum; 

Avg., average; m, meter]

Sample type 

and distance 

from bank 

(fig. 2)

Water temperature 

(°C)

Specific conductance 

(μS/cm)

pH

(standard units)

Dissolved oxygen 

(mg/L) n

Min. Max. Avg. Min. Max. Avg. Min. Max. Avg. Min. Max. Avg.

MVDI–

various distances 

from west bank

1.40 22.9 13.68 228.00 322 249.50 7.90 8.5 8.09 8.00 16.3 10.91 12

Fixed-point–

about 20 from 

east bank

1.00 22.7 13.55 226.00 294 243.08 7.80 8.5 8.09 8.00 16.1 10.90 12

Discrete–

10 m from west 

bank

1.90 21.7 12.38 255.00 347 281.42 7.80 8.2 7.91 7.20 14.4 10.88 12

Discrete–

60 m from west 

bank

1.30 21.7 12.50 252.00 336 270.92 7.80 8.2 7.93 7.70 14.3 11.18 26

Discrete–

170 m from west 

bank

1.40 21.5 12.16 228.00 325 260.25 7.90 8.4 8.06 8.00 14.2 11.35 28

Discrete–

280 m from west 

bank

1.30 21.5 11.94 225.00 310 253.19 7.90 8.4 8.12 8.00 14.5 11.49 8

Table 4. Wilcoxon signed-rank test of differences in median 

concentrations for samples collected by use of multple-vertical 

depth-integrated (MVDI) and fixed-point methods at U.S. 

Geological Survey station 041686401 Trenton Channel of Detroit 

River at Grosse Ile, Michigan.

[p-value, probability value, bold values are significant (p-value ≤ 0.05); 

mg/L, milligram per liter; ≤, less than or equal to]

Constituent

MVDI versus fixed-point

p-value Median difference 

(mg/L)

Phosphorus 0.020 0.001

Suspended sediment 0.355 0.5

Orthophosphate 0.056 0

Total nitrogen 0.004 0.095

Ammonia 0.008 0.05

Chloride 0.025 1.3
Concentrations and Loads of Nutrients, Chloride, and Suspended Sediment 15

Multiple-vertical depth-integrate sample concentration, in milligrams per liter 

Fixed-point sample concentration, in milligrams per liter

A. Phosphorus

R2 = 0.7339

n = 12

0.010

0.005

0.015

0.020

0.030

0.035

0.025

0.005 0.010 0.015 0.020 0.025 0.030

B. Suspended sediment

R2 = 0.5757

n = 12

0

5

10

15

20

25

30

0 5 10 15 20 25

F. Total nitrogen

R2 = 0.6627

n = 12

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

E. Ammonia

R2 = 0.4298

n = 12

0.10

0.15

0.20

0.30

0.25

0.05 0.10 0.15 0.20 0.25

C. Orthophosphate

R2 = 0.8896

0.004 n = 12

0.003

0.005

0.006

0.007

0.008

0.009

0.010

0.011

0.012

0.003 0.004 0.005 0.006 0.007

D. Chloride

R2 = 0.8998

n = 12

10

15

20

25

30

35

5 10 15 20 25 30

EXPLANATION

Best-fit regression equation (see table 5)

1:1 line

Figure 6. Relations between multiple-vertical depth-integrate (MVDI) and fixed-point samples for selected constituent 

concentrations in milligrams per liter at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River at 

Grosse Ile, Michigan, November 2014 to November 2015. (R2, coefficient of determination; n, sample size)
16 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

Table 5. Simple linear regression equations for all major constituents collected at U.S. Geological Survey station 041686401 Trenton 

Channel of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015.

[R2, coefficient of determination; p-value, probability value, bold values are significant (p-value ≤ 0.05); n, number of observations; ≤, less than or equal to]

Constituent Regression 

equation

Residual 

standard error Adjusted-R2 p-value n

Phosphorus yi

 = −0.00043 + 1.2165xi 0.003628 0.7339 2.284 × 10−4 12

Suspended sediment yi

 = −0.7215 + 1.4177xi 4.909 0.5757 2.556 × 10−3 12

Orthophosphate yi

 = −0.00833 + 3.1764xi 0.0006917 0.8896 2.619 × 10−6 12

Chloride yi

 = −2.128 + 1.3003xi 2.08 0.8998 1.604 × 10−6 12

Ammonia yi

 = 0.06924 + 0.9579xi 0.03465 0.4298 1.228 × 10−2 12

Total nitrogen yi

 = 0.0964 + 0.9579xi 0.05245 0.6627 7.745 × 10−4 12

Chemical Constituent Distribution 

Discrete samples were collected at 1-m intervals at profile 

locations 10 m, 60 m, 170 m, and 280 m from the west bank 

to help describe the distribution of nutrients, chloride, and 

suspended sediment at the Trenton Channel station. R packages were used to create tile graphs of constituent concentrations throughout the horizontal and vertical planes sampled 

in Trenton Channel (Wickham, 2009). The tile graphs display 

color-scale tiles representing observed discrete constituent 

concentrations (fig. 7). ADCP channel depth data are graphed 

in a solid black line and extrapolated depths estimated from 

initial site investigation are graphed in dashed black lines. 

Graphs display data collected on March 18, 2015. 

Tile graphs are displayed for all major constituents 

collected and represent constituent concentrations collected 

at each discrete sample location. Although concentrations 

varied between sampling dates, there are some patterns in the 

distribution of concentrations that were typical. Constituent 

concentrations where generally highest near the west bank 

of the channel. All constituents except suspended sediment 

display a distribution of higher concentrations near the west 

bank than the east bank and in some cases, concentrations 

near the west bank are three times as high (phosphorus). 

Chloride is considered a conservative ion: when ionized in the 

environment it stays in that particular ionic state and is rarely 

affected by sediment and other particles. Because chloride is 

a conservative ion, it is a good indicator of point sources of 

chemicals (Mullaney and others, 2009). The distribution of 

higher concentrations (especially chloride) near the west bank 

could indicate a source influence upstream on the Michigan 

side of the channel, but more data would need to be collected 

throughout the channel to make any determination. Tile graphs 

also show the distribution of concentrations vertically through 

the water column. There is less than 10 percent vertical 

variation of constituent concentrations and in some cases less 

than a 5 percent difference vertically among concentrations 

(orthophosphate, ammonia, and chloride). The concentration 

of suspended sediment had no consistent pattern of vertical or 

horizontal distribution across sampling dates. 

In general, the tile graphs show horizontal heterogeneity and vertical homogeneity. A distribution of higher concentrations to the west side of the channel is present for all 

major constituents except suspended sediment. This horizontal distribution could be the result of a source influence 

upstream near the west side of the channel. Discrete samples 

show little change in concentrations vertically throughout 

the transect of Trenton Channel for all major constituents. 

Patterns in horizontal and vertical distribution can provide 

insight for the application of future sampling methods in 

this part of the Trenton Channel, potentially focusing sampling efforts to capture the unique horizontal distribution of 

constituent concentrations. 

Boxplot summaries of constituent concentrations collected throughout the sampling campaign using the MVDI 

method are displayed in figures 7 and 8. Median constituent 

concentrations are shown by a bold line in the middle of the 

boxplot, the upper 75th percentile is represented by the top of 

the boxes, and the lower 25th percentile by the bottom of the 

box. Vertical lines located above the box represent samples 

within the 90th percentile. Vertical lines located below the 

box represent samples within the 10th percentile. Numbers of 

sample values indicated at the top of each boxplot represent 

sample sizes. Constituent concentrations are color-coded by 

date for reference. Constituents summarized in figures 7 and 8 

include phosphorus, suspended sediment, orthophosphate, 

total nitrogen, ammonia, and chloride. 

Discrete sampling results are depicted with boxplot 

graphs for each constituent (fig. 8). All constituents showed 

that samples collected at the 280 m transect had the lowest 

median concentrations, except suspended sediment. Suspended sediment did not exhibit the same pattern as other 

constituents, and suspended-sediment mean concentrations 

did not vary much throughout the transect. The 280 m sample 

generally represents water quality from the eastern and upper 

most parts of the channel, and the locality of the 10 m samples 

generally represent the western most part of the Trenton Channel. The highest average constituent concentrations at the 10 m 

location and the lowest concentrations at the 280 m location 

is evidence the highest constituent concentrations are near 
Concentrations and Loads of Nutrients, Chloride, and Suspended Sediment 17

A. Phosphorus

0 100 200 300

Distance from west bank, in meters

02468

Discrete sampling depth, in meters

EXPLANATION

0.0350.0300.0250.020

Concentration, 

in milligrams per liter

Bed of channel

0.0210.0360.027

0.0260.0250.0250.0240.0260.029

0.0210.0190.0210.0210.0210.0210.022

0.0170.0180.0190.0170.0180.0180.019

0.016

B. Suspended sediment

0 100 200 300

Distance from west bank, in meters

02468

Discrete sampling depth, in meters

EXPLANATION

105

Concentration, 

in milligrams per liter

Bed of channel

344464

2355555

14

433544

5

472

C. Orthphosphate

0.0070.0070.0070.0070.0060.006

0.0060.0060.0060.0050.0060.0070.007

0.0050.0050.0060.0050.0060.0060.006

0.004

0.0040.0040.004

EXPLANATION

0.0070.0060.0050.004

Concentration, 

in milligrams per liter

Bed of channel 0 100 200 300

Distance from west bank, in meters

02468

Discrete sampling depth, in meters

D. Chloride

0 100 200 300

Distance from west bank, in meters

02468

Discrete sampling depth, in meters 37.6 37.7 38 37.8 37.5 37.2 34 34.1 3434 34.2 34.1 34.1 30.4 30.4 30.4 30.3 30.6 30.3 30.3 25.5 38.7 38.5 38

EXPLANATION

3530

Concentration, 

in milligrams per liter

Bed of channel

E. Ammonia

0.270.270.290.290.290.28

0.190.19

0.2

0.18

0.20.2

0.21

0.170.170.170.170.170.170.18

0.18

0.270.270.27

EXPLANATION

0.2750.2500.2250.2000.175

Concentration, 

in milligrams per liter

Bed of channel 0 100 200 300

Distance from west bank, in meters

02468

Discrete sampling depth, in meters

F. Total nitrogen

0 100 200 300

Distance from west bank, in meters

02468

Discrete sampling depth, in meters 0.81 0.83 0.88 0.81 0.88 0.87 0.75 0.71 0.75 0.71 0.72 0.76 0.74 0.73 0.71 0.77 0.7 0.71 0.71 0.71 0.67 0.88 0.9 0.87 EXPLANATION 0.90 0.85 0.80 0.75 0.70 Concentration, in milligrams per liter

Bed of channel

Figure 7. Discrete constituent concentrations measured at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River at Grosse Ile, Michigan, March 18, 2015.
18 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

Concentration of discrete depth samples, in milligrams per liter

Distance from west bank, in meters

Date

Number of values

90th percentile75th percentileMedian25th percentile10th percentile

March 18, 2015May 29, 2015August 26, 2015November 18, 2015

12

EXPLANATION

A. Phosphorus

10 60 170 280

0.01

0

0.060.050.040.030.02

12 26 28 28

B. Suspended sediment

10 60 170 280 0

40302010

12 26 28 28

C. Orthophosphate

10 60 170 280

0.0120.0100.0080.0060.0040.002

12 26 28 28

F. Total nitrogen

10 60 170 280

1.00.90.80.70.60.50.4

12 26 28 28

E. Ammonia

10 60 170 280

0.300.250.200.150.100.05

12 26 28 28

D. Chloride

10 60 170 280

40302010

12 26 28 28

Figure 8. Selected constituent concentrations based on horizontal location or type of sample at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River at Gross Ile, Michigan, November 2014 to November 2015. Vertical-transect distances in meters from the west bank.
Concentrations and Loads of Nutrients, Chloride, and Suspended Sediment 19

the west side of the channel. Higher-than-average concentrations of nutrients, chloride, and suspended sediment at the 

10 m sampling location could be because of source influence 

upstream in the tributary, but without more data this cannot 

be confirmed. The distribution of constituent concentrations 

within the sampling period is indicative of lower concentrations for all constituents in the summer through fall period 

(May through October) and higher concentrations in the winter 

through spring period (November through April). More data (a 

longer sampling period) would need to be collected to confirm 

the seasonal distribution of constituents. Spikes of chloride 

concentrations around the March 28, 2015, sample date may 

represent road salting in the winter months. Road salting has 

increased since 1950 for deicing roads, parking lots, and other 

impervious sources (Mullaney and others, 2009). Road salt 

can directly increase the concentrations of chloride in surface 

water from runoff. 

Boxplot summaries displaying the horizontal distribution 

of constituents in this section of Trenton Channel can help to 

provide appropriate and representative methods for categorizing major nutrient, chloride, and suspended-sediment concentrations based on scope and purpose of analysis. Sample 

results obtained throughout the study were grouped by vertical 

discrete transect locations then summarized using boxplots 

(fig. 9). Boxplots of vertical discrete samples were developed 

for each constituent sampled. The boxplots display generally 

consistent vertical distribution of average concentrations for 

all constituents for each sampling date. The consistent constituent concentrations vertically indicate mixing and homogeneity throughout the water column. Differences in concentrations throughout the sampling period follow a distinct pattern 

of vertical symmetry; distribution of concentrations vertically 

by sample date is apparent for almost all major constituents. 

Higher concentrations are typical in the winter through spring 

and lower concentrations are typical in the summer through 

fall; this same pattern is seen at every discrete location 

throughout the water column. Homogeneity throughout the 

water column provides evidence for diversification of samples 

horizontally instead of vertically to capture the distribution of 

constituent concentrations more efficiently in the future.

The horizontal boxplots (fig. 8) show constituent concentrations tended to be highest near the west side of the channel 

and lowest near the east side of the channel. There was no consistent pattern of concentration varying by depth in the water 

column; vertical homogeneity was evident (fig. 9). Higherthan-average constituent concentrations were observed in the 

winter through spring and lower-than-average concentrations 

were observed in the summer through fall. Documented differences in constituent concentrations horizontally indicates 

a sampling method which captures horizontal differences in 

water quality would likely be most effective for determining 

the water chemistry of the Trenton Channel at this location. 

Cross sectional methods like EDI or Equal Width Increment 

would likely be most effective for capturing horizontal distribution of constituent concentrations in the southern part of the 

Trenton Channel. 

Constituent Loads

An estimated daily constituent load was calculated 

using all major constituent concertation values from MVDI 

and fixed-point methods, as well as discharge values from 

ADCP data collected on all 12 sampling dates. Daily loads in 

kilograms per day were aggregated by summing instantaneous 

loads throughout the course of a day. Instantaneous loads 

were calculated using equation 2.

TCLi = TCi × Qi × C (2)

where

TCLi is daily constituent load, in kilograms per 

day;

TCi is instantaneous constituent concentration, 

in milligrams per liter;

Qi is instantaneous discharge, in cubic meters 

per second; and

C is the constant 86.4 to convert units of load 

to kilograms per day. 

Table 6 lists estimated constituent loads based on MVDI 

and fixed-point concentrations and measured discharges. All 

concentrations obtained from MVDI and fixed-point sampling 

techniques were above the laboratory minimum reporting 

levels and thus represent a quantifiable value reported by 

the NWQL. 

Phosphorus load calculations in Trenton Channel were 

further analyzed because of its contribution and relation to 

eutrophication in Lake Erie (Ohio EPA, 2013). Phosphorus 

loads calculated using the MVDI method produced higher 

loads in comparison to fixed-point methods on all sampling 

dates except one (fig. 10). This pattern of higher MVDI estimated loads is likely the result of the difference in sampling 

approach between MVDI and fixed-point methods. The 

MVDI method incorporates transects from the entire channel and represents more channel area than the fixed-point 

method. Compared to the fixed-point method, the MVDI 

method is able to better represent the overall phosphorus 

concentration by incorporating the gradients in phosphorus 

concentration found in the channel (fig. 9), which results in a 

higher and more representable phosphorus load. Phosphorus 

loads obtained from both the MVDI and fixed-point methods 

are closely related to streamflow patterns because of a direct 

relation between streamflow and load. During the sampling 

interval, phosphorus loads tended to be lower during the 

summer months than the winter months, likely because of 

the high concentrations observed during these times (fig. 10). 

Overall, we can conclude from these data that fixed-point 

sampling produces results that are biased low for most of the 

sampling period.
20 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan Concentration, in milligrams per liter

Discrete sampling depth, in meters

A. Phosphorus

0.01 0 0.02 0.03 0.04 0.05 0.06

1234567

16201212121210

B. Suspended sediment

0 10 20 30 40

16201212121210

C. Orthophosphate

0.004 0.002 0.006 0.008 0.010 0.012 0.014

16201212121210

F. Total nitrogen

1234567

0.5 0.4 0.6 0.7 0.8 0.9 1.0

16201212121210

E. Ammonia

0.10 0.05 0.15 0.20 0.25 0.30 0.35

16201212121210

D. Chloride

10 0 20 30 40 50

16201212121210

Date

March 18, 2015May 29, 2015August 26, 2015November 18, 2015

Number of values90th percentile75th percentileMedian25th percentile10th percentile

12

EXPLANATION

Figure 9. Selected constituent concentrations based on vertical location at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015. Discrete samples were collected at vertical depths of 1, 2, 3, 4, 5, 6, and 7 meters (m).
Concentrations and Loads of Nutrients, Chloride, and Suspended Sediment 21

Table 6. Constituent load estimates from multiple-vertical depth-integrated and fixed-point sampling methods at U.S. Geological Survey station 041686401 Trenton Channel of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015.[m3/sec, cubic meters per second; kg/day, kilogram per day]

Date Discharge (m3/sec)

Multiple-vertical depth-integrated sampling Fixed-point sampling

Total 

phosphorus 

(kg/day)

Suspended 

sediment 

(kg/day)

Orthophosphate 

(kg/day)

Total 

nitrogen 

(kg/day)

Ammonia 

(kg/day)

Chloride 

(kg/day)

Phosphorus 

(kg/day)

Suspended 

sediment 

(kg/day)

Orthophosphate 

(kg/day)

Total 

nitrogen 

(kg/day)

Ammonia 

(kg/day)

Chloride 

(kg/day)

December 17, 2014 1,450 1,630 751,000 501 83,900 20,000 1,590,000 2,250 751,000 501 88,900 25,000 2,000,000March 18, 2015 1,440 2,740 374,000 749 102,000 32,400 3,970,000 2,000 624,000 499 83,600 22,500 3,180,000April 9, 2015 1,380 1,320 719,000 479 79,100 21,600 3,070,000 1,080 360,000 479 70,700 18,000 2,350,000May 4, 2015 1,340 1,160 116,000 463 79,800 22,000 1,680,000 1,040 463,000 463 67,100 13,900 1,420,000May 29, 2015 1,330 1,610 460,000 460 73,500 23,000 1,490,000 1,260 345,000 460 62,100 13,800 1,260,000August 12, 2015 1,420 1,720 613,000 490 67,400 14,700 1,510,000 1,590 735,000 490 58,800 9,800 1,400,000August 26, 2015 1,420 1,470 490,000 490 63,700 15,900 1,400,000 1,350 613,000 490 56,400 12,300 1,240,000September 1, 2015 1,330 1,610 804,000 575 64,400 14,900 1,420,000 1,380 230,000 460 56,300 10,300 1,280,000September 23, 2015 1,350 1,510 466,000 466 62,800 16,300 1,350,000 1,280 466,000 466 61,700 11,600 1,190,000September 30, 2015 1,350 2,750 750,000 875 76,200 27,500 1,460,000 2,370 625,000 625 68,700 20,000 1,300,000October 21, 2015 1,200 2,820 2,820,000 522 71,000 24,000 1,110,000 1,780 1,150,000 418 58,500 15,700 993,000November 18, 2015 1,260 3,500 2,080,000 1,200 82,000 24,000 1,480,000 2,840 1,860,000 656 72,100 17,500 1,290,000
22 Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan

EXPLANATION

Phosphorus load computed with multiple-vertical depth-integrated measurements

Phosphorus load computed with fixed-point measurements

Instantaneous discharge

300

600

900

1,200

1,500

Discharge, in cubic meters per second

Jan. 2015 Apr. 2015 July 2015 Oct. 2015

Date

1,000

2,000

3,000

4,000

5,000

Phosphrus load, in kilograms per day

Dec. 17, 2014Mar. 18, 2015Apr. 9, 2015May 4, 2015May 29, 2015Aug. 12, 2015Aug. 26, 2015

Sept. 1, 2015

Sept. 23, 2015

Sept. 30, 2015

Oct. 21, 2015Nov. 18, 2015

Figure 10. Comparison of phosphorus loads computed by use of multiple-vertical depth-integrated (MVDI) and 

fixed-point measurements and instantaneous discharge at U.S. Geological Survey station 041686401 Trenton 

Channel of Detroit River at Grosse Ile, Michigan, November 2014 to November 2015.
References 23

Summary

The Detroit River separates the United States and Canada 

as it flows from Lake St. Clair to Lake Erie. The Trenton 

Channel is a 13-kilometer-long branch of the Detroit River 

that flows to the west of Grosse Ile before rejoining the Detroit 

River near the mouth of Lake Erie. The U.S. Environmental 

Protection Agency has listed both the Trenton Channel and 

Detroit River as Areas of Concern because of Beneficial Use 

Impairments such as interrupted drinking-water services, loss 

of aquatic life, and reduced recreational use. About 22 percent 

of the Detroit River flows past the western side of Gross Ile 

through the Trenton Channel. Flow from the Trenton Channel 

rejoins the Detroit River near its mouth, just before it flows 

into Lake Erie. The U.S. Geological Survey, in cooperation 

with the U.S. Environmental Protection Agency and Environment Canada, investigated concentrations and loads of 

nutrients (total phosphorus, orthophosphate, total nitrogen, 

and ammonia), suspended sediment, and flow velocities at 

U.S. Geological Society station 041686401 Trenton Channel 

of Detroit River at Grosse Ile, Mich., (Trenton Channel Site) 

from November 2014 through November 2015. The site was 

selected to better understand the distribution of constituents 

and loading that is contributing to eutrophication in Lake Erie. 

Also, the site was chosen for study to improve future sampling 

efforts in Trenton Channel. Three water-quality sampling 

methods—multiple-vertical depth-integrated (MVDI), fixedpoint sampling, and discrete sampling—were compared to 

describe the distribution of nutrients, chloride, and suspended 

sediment. Also, flow velocity data were collected by acoustic 

Doppler current profiling (ADCP) throughout this study period 

to understand the distribution of velocity in the sampled transect of Trenton Channel. 

Maps of flow velocities were developed using the Velocity Mapping Toolbox and are displayed in plan and streamwise 

view near the sampling cross section. Plan view velocity maps 

display depth averaged velocity in comparison to sampling 

locations, where higher than average velocities are apparent 

approximately 200 meters (m) from the west bank of Trenton 

Channel. Transverse streamwise velocity components as well 

as secondary flow patterns confirm plan view velocity maps 

and show the distribution of velocity. Secondary flow vectors 

suggest the presence of counter-rotating helical flow cells, 

these cells could contribute to distribution of constituents. 

Flow depths at the Trenton Channel Sampling Cross Section 

range from 4.75 to 8.75 m, with an average depth of 6–8 m. 

Velocity maps provide the velocity and bathymetry throughout 

the sampled cross section of Trenton Channel. 

MVDI, fixed-point, and discrete samples were collected 

on 12 different days from November 2014 to November 

2015. MVDI and fixed-point samples were collected for each 

sampling event, and four sampling events included a set of 

discrete samples. All sampling methods tested for selected 

nutrients, chloride, and suspended sediment. Both tile and 

boxplot graphs of constituent concentrations show heterogeneity horizontally and homogeneity vertically throughout the 

cross section. 

Differences between MVDI and fixed-point sampling 

results likely arise in part from the unsampled part of the cross 

section not accounted for in the fixed-point sample. Simple 

linear-regressions models developed regression equations to 

estimate MVDI concentrations for future sampling. 

Constituent loads were developed using ADCP discharge 

values and concentrations derived from MVDI and fixed-point 

methods. Constituent loads closely followed trends in concentrations collected from both MVDI and fixed-point methods. 

Phosphorus loads in particular were analyzed and higher loads 

were seen in the winter months of this study, directly related to 

higher phosphorus concentrations are evident in both MVDI 

and fixed-point methods. This relation of phosphorus loads 

and concentrations directly relates to the influence of concentrations on phosphorus loads. 

In conclusion, this investigative study was intended to 

provide information to our cooperators regarding the distribution of constituents, velocities, and sampling applications for 

the Trenton Channel. The importance of continuing future 

investigations to fully understand the Trenton Channel of the 

Detroit River is paramount, but the information in this report 

begins to pave the way for effective management decisions 

and potential for a healthy water system.

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For additional information, contact:

Director, Upper Midwest Water Science Center

U.S. Geological Survey

6520 Mercantile Way, Suite 5

Lansing, MI 48911

or visit our website at: https://mi.water.usgs.gov/

Publishing support provided by the 

Madison and West Trenton Publishing Service Centers
Totten and Duris—Spatial Distribution of Concentrations and Loads Using Different Sampling Methods, Trenton Channel, Michigan—Scientific Investigations Report 2018–5141

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185141