Peña Blanca Sampling Site Bernalillo Sampling Site

November 10, 2011

Number of wetted mapped mesohabitats

70

0 10 20 30 40 50 60

71,327 square meters

N/O

9

70

22

21

57

20

62

61

43

66

39

68

42

18

1

2

9

4

12

37

106 ̊21’30”

35 ̊34’

35 ̊33’40”

106 ̊21’40” 106 ̊21’20”

A

0 50 100 150 200 METERS

0 125 250 375 500 FEET

37,144 square meters

November 11, 2011

0 10 20 30 40 50 60

Number of wetted mapped mesohabitats

17

N/O

N/O

12

13

10

1

17

5

7

4 3

6

2

15

16

9 8

14

0 50 100 150 200 METERS

0 125 250 375 500 FEET

106 ̊33’30”

35 ̊19’15”

35 ̊19’

35 ̊19’7.5”

35 ̊18’52.5”

106 ̊33’37.5”

B

U.S. Geological Survey hydrologist delineates 

backwaters at Peña Blanca sampling site. 

Photograph by Daniel K. Pearson, U.S. Geological 

Survey, November 10, 2011.

A B

Upper end of Bernalillo sampling site showing submerged 

bar/riffle/run complex (from left to right) in the foreground 

and cut bank in the background. Photograph by Daniel K. 

Pearson, U.S. Geological Survey, November 11, 2011.

Mapped Mesohabitat Features—Continued

 A total of eight different types of wetted mesohabitats 

were mapped across the entire study area: riffles, runs, 

pools, isolated pools, forewaters, backwaters, embayments, 

and flats. The only sampling site that contained all 8 wetted 

mesohabitat types was Abeytas on June 7, 2012, but 10 of 

the 13 sampling sites mapped in summer 2012 contained 

at least 7 of the 8 potential wetted mesohabitat types. In 

contrast, only 3 out of 15 sampling sites (Peña Blanca, La 

Orilla, and Barelas) that were mapped in winter 2011–12 

contained as many as seven different wetted mesohabitat 

types, and all 3 of these sampling sites were located in 

the most upstream part of the study area (3 of the 4 most 

upstream sampling sites). La Joya contained the fewest 

types of wetted mesohabitats in summer 2012 with five, 

whereas Los Lunas I and Rio Salado contained the fewest 

types of wetted mesohabitats in winter 2011–12 with three 

each. The average number of different wetted mesohabitat 

types per site mapped in winter 2011–12 and summer 2012 

were 5.3 and 6.8, respectively. In general, decreases in 

streamflow between winter 2011–12 and summer 2012 led 

to increased complexity in terms of the number of different 

types of wetted mesohabitats that were mapped at each 

sampling site. Barelas was the only sampling site where 

a greater number of wetted mesohabitats was mapped in 

winter 2011–12 compared to summer 2012.

Decreases in streamflow between winter 2011–12 and 

summer 2012 also led to increased complexity in terms of 

the total number of wetted mesohabitats that were mapped 

at each sampling site. More than half of the sampling sites 

that were mapped during winter 2011–12 contained fewer 

than 40 mesohabitats. During summer 2012, more than 40 

mesohabitats were mapped at all of the sites except for the 

Rio Salado site, where 40 mesohabitats were mapped. In 

winter 2011–12, the largest number of wetted mesohabitats 

mapped at a sampling site was 70 at Peña Blanca, and 

the smallest was 16 at Lemitar. In summer 2012, more 

than 100 wetted mesohabitats were mapped at three 

different sampling sites (Barelas, Los Lunas I, and Arroyo 

del Tajo) with Los Lunas I having the most at 145. The 

average number of wetted mesohabitats mapped in winter 

2011–12 was 38.1, whereas the average number of wetted 

mesohabitats mapped in summer 2012 was 84.5. In other 

words, decreases in streamflow between winter 2011–12 

and summer 2012 resulted on average in more than twice as 

many wetted mesohabitats at each sampling site in summer 

2012 relative to winter 2011–12.

In many cases, decreases in streamflow between 

winter 2011–12 and summer 2012 also led to increased 

complexity in terms of the total number of channel bars 

mapped. Channel bars are defined as a transitory parcel 

of land surrounded by water and typically either devoid 

of or containing annual vegetation (table 2). Reductions 

in stage associated with decreased streamflow resulted in 

the emergence of channel bars in areas that were shallow 

wetted mesohabitats, particularly flats and shallow runs, 

under higher streamflow conditions (figs. 8A and 8B show 

an example of this change in channel complexity at the Los 

Lunas I site). The emergence of channel bars contributes to 

the creation of additional wetted mesohabitats and higher 

complexity (particularly along the margins and at the 

downstream end of the channel bars) because of the flowaltering effects caused by the channel bars (figs. 8A and 8B). 

Los Lunas I had the most channel bars (32) of any 

of the reaches in winter 2011–12 and the second most in 

summer 2012 (44), and not surprisingly, it had the second 

most wetted mesohabitats in winter 2011–12 (59) and 

the most in summer 2012 (145). The average and median 

number of channel bars mapped in winter 2011–12 was 

16.0 and 13.0, respectively, whereas the average and 

median number of channel bars mapped in summer 2012 

was 20.5 and 19, respectively. Figure 8C shows the relation 

between the number of channel bars and the number of 

wetted mesohabitats mapped at each of the 15 sampling 

sites on the Middle Rio Grande during winter 2011–12 and 

summer 2012. 

Least-squares linear regression analyses were done 

to assess the relations between the number of wetted 

mesohabitats and the number of channel bars. In leastsquared linear regression analyses, the R-squared (R2

) or 

coefficient of determination is one indicator of the goodness 

of fit, that is, how well the regression equation fits the data 

(Iman and Conover, 1982; Helsel and Hirsch, 2002).

The largest R2 value was 0.89, which was measured at 

each of the three sites that were sampled in February 2012 

(San Pedro, Bosque del Apache I, and Bosque del Apache 

II); the identical R2 values for these three sites were not 

surprising because these three sampling sites are in close 

proximity to one another at the downstream part of the 

study area. There was also a relatively strong correlation 

(R2=0.78) between the number of channel bars and the 

number of wetted mesohabitats for all sites sampled in June 

and August 2012; however, the correlation in sites sampled 

in November and December 2011 was relatively low 

(R2=0.38).

Another factor that can contribute to channel 

complexity is bed-substrate composition. The bed-substrate 

composition of the Peña Blanca and Bernalillo sites was 

dominated by coarse-grained bed materials, particularly 

coarse gravels and cobble in samples collected in winter 

2011–12 (fig. 9). Downstream from these two sampling 

sites, the Rio Grande is characterized by a broader, more 

low-gradient channel dominated by sand. Fine-grained silts 

and clays are more prevalent in the mid-reach sampling 

sites including Los Lunas I and II, Abeytas, La Joya, and 

Rio Salado. The increase in silts and clays at these sampling 

sites could be the result of finer-grained contributions from 

two large tributaries to the Rio Grande, the Rio Puerco and 

Rio Salado, both of which join 

the Rio Grande downstream 

from Albuquerque (fig. 3).

Consistent with the 

preceding discussion, decreases 

in streamflow typically led to 

increases in channel complexity 

in terms of the number of 

different wetted mesohabitat 

types present, total number 

of mesohabitats present, and 

the number of channel bars. 

Decreases in streamflow 

also led to reductions in 

wetted area for all sampling 

sites mapped in both winter 

2011–12 and summer 2012. 

A graphical representation 

of discharge measured at or 

near each sampling site as it 

relates to channel complexity 

(represented by the number of 

wetted mesohabitats mapped) is 

shown in figure 10. In general, 

sampling sites that were mapped 

at higher discharge during 

winter 2011–12 resulted in 

the lowest number of wetted 

mesohabitats mapped, whereas 

sampling sites mapped at 

lower discharge in summer 

2012 resulted in the highest 

number of wetted mesohabitats. Lower discharge rates 

result in increased mesohabitat fragmentation, increased 

numbers of slack water mesohabitats (isolated pools, 

backwaters, forewaters, and embayments), smaller (area) 

mesohabitats, greater numbers of mesohabitats, and a 

more braided stream channel. For higher discharge rates, 

smaller mesohabitats are flooded, and the stream channel 

is simplified overall, resulting in fewer slack water 

mesohabitats, larger (area) mesohabitats, and a stream 

channel that is less braided. Based on field experience, it is 

expected that during high magnitude discharge conditions 

when the channel is bankfull, each reach should consist of 

no more than a few mesohabitats.

Maps showing the mesohabitats for each of the 15 

sites are presented in sheets 3–7. Maps are arranged 

from upstream to downstream order and grouped by 

MRGBI reach name. Numbered mesohabitats labeled 

in yellow correspond to the subset of mesohabitats 

where Rio Grande silvery minnows were caught. 

Numbered mesohabitats outlined in black on maps 

correspond to the subset of mesohabitats where physical 

habitat measurements (and water-quality properties 

were measured in summer 2012) and fish collection were 

attempted. In addition, graphs showing mesohabitat 

characteristics and selected photographs of field 

activities and site conditions are shown for each site.

Number of wetted mesohabitat types

0

1

2

3

4

5

6

7

8

9

Wetted area, in square meters

Number of wetted mesohabitats Number of channel bars

November and December 2011 February 2012 June and August 2012

Sampling period

EXPLANATION

U.S. Geological Survey sampling sites

A.

B.

C.

D.

160

140

120

100

80

60

40

20

0

50

45

40

35

30

25

20

15

10

5

0

120,000

100,000

80,000

60,000

40,000

20,000

0

PNB BRN LOR BAR PAD LL1 LL2 ABY LJY RSL LEM ATJ SPD BA1 BA2

Figure 7. Number of A, wetted mesohabitat types mapped; B, wetted 

mesohabitats mapped; C, channel bars mapped; and D, wetted area at 15 

sampling sites on the Middle Rio Grande, winter 2011–12 and summer 2012.

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50

Number of channel bars

Number of wetted mesohabitats

November and December 2011

February 2012

June and August 2012

 

Sampling periods

EXPLANATION

A.

B.

C.

Least-squares linear regression lines

November and December 2011

February 2012

June and August 2012

R2=0.78

R2

=0.38

R2

=0.89

Note: R2 is coefficient of determination

Figure 8. Comparison of differences in channel complexity at the Los Lunas I site during A, November 12, 2011, and B, June 5, 

2012, following a reduction in stage; C, correlation between the number of channel bars and the number of wetted mesohabitats 

mapped at each site during winter 2011–11 and summer 2012.

Hardpan

Boulder (greater than 256)

Cobble (greater than 64 and less than or equal to 256)

Coarse gravel (greater than 12 and less than or equal to 64)

Fine gravel (greater than 4 and less than or equal to 12)

Sand (greater than 0.0625 and less than or equal to 2)

Silt and clay (less than or equal to 0.0625)

Substrate categories (size in millimeters)—

EXPLANATION

Area-weighted substrate composition, in percent

A. Winter 2011–12

U.S. Geological Survey sampling sites

0

B. Summer 2012 Not Sampled Not Sampled

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

PNB BRN LOR BAR PAD LL1 LL2 ABY LJY RSL LEM ATJ SPD BA1 BA2

U.S. Geological Survey sampling sites

PNB BRN LOR BAR PAD LL1 LL2 ABY LJY RSL LEM ATJ SPD BA1 BA2

Figure 9. Area-weighted substrate composition at 15 sampling sites on the Middle Rio Grande, A, winter 2011–12; and B, summer 2012.

0

20

40

60

80

100

120

140

160

0 200 400 600 800 1000 1200

Discharge, in cubic feet per second

Number of wetted mesohabitats mapped

PNB

BRN

LOR

BAR*

PAD

LL1

LL2* ABY

LJY

RSL

LEM

ATJ

SPD

BA1

BA2*

LOR

BAR*

PAD

LL1

LL2

ABY

LJY

RSL

LEM

ATJ

SPD*

BA1

BA2

SPD

BA2

NOTE: Discharge was not measured in the field at locations indicated with *; plotted discharge in these cases is the daily mean discharge one day after the site was mapped

for the nearest U.S. Geological Survey streamflow-gaging station upstream from the site.

November and December 2011

February 2012

June and August 2012

Sampling periods

EXPLANATION

Figure 10. Graphical representation of discharge as it relates to channel complexity (represented by the number of wetted 

mesohabitats mapped).

86,252 square meters

August 11, 2012

0 10 20 30 40 50 60

Number of wetted mapped mesohabitats

93

N/O

November 16, 2011

0 10 20 30 40 50 60

Number of wetted mapped mesohabitats

40

N/O 104,256 square meters 86,252 square meters

August 11, 2012

0 10 20 30 40 50 60

Number of wetted mapped mesohabitats

93

N/O

November 16, 2011

0 10 20 30 40 50 60

Number of wetted mapped mesohabitats

40

N/O 104,256 square meters

C

Looking upstream from western edge of channel bar 

towards the bottom end of the large channel bar that 

occupies mid-channel at the top of the La Orilla reach. 

Photograph by Daniel K. Pearson, U.S. Geological Survey, 

August 13, 2012.

34

28

38

1

30

4

16

40

5

14

22

20

8 15

0 50 100 150 200 METERS

0 125 250 375 500 FEET

35 ̊9’30”

35 ̊9’15“

35 ̊9’

106 ̊40’30” 106 ̊40’15”

2*

*Habitat parameters were not measured at 

this location, but fish collection was attempted.

35 ̊9’30”

35 ̊9’15”

35 ̊9’

87

48

64

70

5

68

3

53

86

82

89

80

84

4

8

81

10

74

19

48

49

51

17

50

13

36

33

12

45

25

46

106 ̊40’30” 106 ̊40’15”

C

0 50 100 150 200 METERS

0 125 250 375 500 FEET

Winter 2011–12

November 10, 2011

Winter 2011–12

November 16, 2011

Summer 2012

August 11, 2012

Winter 2011–12

November 11, 2011

La Orilla Sampling Site

Fish Assemblage Composition and Mapped Mesohabitat Features Over a Range of Streamflows

in the Middle Rio Grande, New Mexico, Winter 2011–12, Summer 2012

By

Daniel K. Pearson, Christopher L. Braun, and J. Bruce Moring

2015 Printed on recycled paper

ISBN 978-1-4113-4010-7

9 7 8141 1 3401 0 7

ISSN 2329-1311 (print)

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3350

ABBREVIATIONS and EXPLANATION

pools

riffles

forewaters

backwaters

flats

isolated pools

channel bar*

point bar*

*Not included in wetted mesohabitat area 

donut graphs or bar graphs showing 

number of wetted mesohabitats mapped

flat

riffle

run

pool

isolated pool

backwater

forewater

embayment

runs

Base from Middle Rio Grande Conservation District,

March–May 2012, 0.5-foot resolution compressed mosaic,

New Mexico State Plane Central Zone,

North American Datum of 1983

Base from Bureau of Reclamation,

February 2012, 1.5-foot resolution compressed mosaic,

New Mexico State Plane Central Zone,

North American Datum of 1983

Base credit in maps for Peña Blanca, Bernalillo, La Orilla,

Barelas, Los Padillas, Los Lunas I, and Los Lunas II (sheets 3 and 4) 

Base credit in maps for Abeytas, La Joya, Rio Salado, Lemitar, Arroyo del Tajo, San Pedro,

Bosque del Apache I, and Bosque del Apache II (sheets 5, 6, and 7)

U.S. Geological Survey sampling

sites short names and map identifier

Peña Blanca, PNB

Bernalillo, BRN

La Orilla, LOR

Barelas, BAR

Los Padillas, PAD

Los Lunas I, LL1

Los Lunas II, LL2

Abeytas, ABY

La Joya, LJY

Rio Salado, RSL

Lemitar, LEM

Arroyo del Tajo, ATJ

San Pedro, SPD

Bosque del Apache I, BA1

Bosque del Apache II, BA2

45,744 square meters**

Wetted mesohabitat area

NOTE: Mesohabitat area donut plots are scaled relative to one another as a function of area.

NOTE: Numbered mesohabitats labeled in yellow correspond to the subset of mesohabitats where Rio Grande silvery minnows were caught.

NOTE: Numbered mesohabitats that are outlined in black on maps correspond to the subset of mesohabitats where physical habitat measurements

 (and water-quality properties were measured in summer 2012) and fish collection was attempted. 

August 11, 2012

0 10 20 30 40 50 60

Number of wetted mapped mesohabitats

93

N/O (not observed)

Total number

of wetted 

mesohabitats 

mapped

Date site was mapped

**Total areal extent of wetted

mesohabitat mapped 

Photo identifier and direction facing when

photograph was taken

A

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3350

Sheet 3 of 7

Prepared in cooperation with the

U.S. Army Corps of Engineers, Albuquerque District, and the U.S. Fish and Wildlife Service

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, 

Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://dx.doi.org/10.3133/sim3350

Suggested citation: Pearson, D.K., Braun, C.L., and Moring, J.B., 2015, Fish assemblage 

composition and mapped mesohabitat features over a range of streamflows in the Middle 

Rio Grande, New Mexico, winter 2011–12, summer 2012: U.S. Geological Survey Scientific 

Investigations Map 3350, 7 sheets, http://dx.doi.org/10.3133/sim3350.