AcknowledgementsUNM Hydrogeoecology Group

NSF Grant DEB-9903973

Middle Rio Grande Conservancy District

Bosque del Apache National Wildlife Refuge

City of Albuquerque Open Space Division

New Mexico State Land Office

Rio Grande Nature Center

Belen Consolidated Schools

ContactsSamuel F. Gray 505-277-5732 samgray@unm.edu

Jennifer F. Schuetz 505-277-5732 jschuetz@sevilleta.unm.edu

Manuel C. Molles, Jr. 505-277-3050 molles@sevilleta.unm.edu

HYDROLOGIC CONNECTIVITY OF NATIVE RIPARIAN FORESTS

ALONG THE MIDDLE RIO GRANDE, NEW MEXICO

S.F. Gray, J.F. Schuetz, and M.C. Molles, Jr.

Department of Biology, University of New Mexico, Albuquerque, NM 87131

AbstractThe native riparian ecosystem of the Middle Rio Grande in New Mexico is in decline and is aging. This riparian forest, or bosque, is dependent on the annual flood pulse that in the past 50 years has been nearly eliminated by dams, diversions and drought. We are studying the difference in hydrologic connectivity between four flood sties and four nonflood sites within a 160 km stretch of the middle Rio Grande from Cochiti Dam to the Elephant Butte Reservoir. These hydrologic factors include river levels, groundwater depth and soil moisture. The relationship among these factors will help us understand hydrologic differences in flood and nonflood sites and what is critical in maintaining the native riparian ecosystem. Results from this study will be used to help inform policy makers on potential tool such as managed floods that could be used to restore the native bosque of the Middle Rio Grande.

Introduction

•The flood pulse that once normally occurred throughout the Rio Grande Valley has been greatly diminished. This has a negative impact on native plant and animal populations, wood and leaf decomposition rates and soil bacteria and fungi (Ellis, Crawford, and Molles 2002).

•Life cycles of plants and animals in floodplain ecosystems are correlated to the annual timing, duration and river levels produced from the flood pulse (Junk, Bayley, and Sparks 1989).

•Natural overbank flooding has been severely restricted in the past 60 years, and the last major floods that produced large-scale cottonwood establishments occurred in 1941and 1942.

•Flooding has been shown to decrease air and soil temperatures and increase water holding capacities of soils. These factors may be important to the life cycles and activities of soil and surface organisms (Ellis, Molles, and Crawford 1996).

•Three years of experimental flooding indicates a strong relationship between surface water and ground water. Increased ammonium levels in the soil, increased soil respiration, and changing soil structure and composition were observed, including lowered salinity (Ellis, Molles, and Crawford 1996).

•Reinstating the historical hydrograph of the Rio Grande can help restore the native riparian ecosystem, supported by results from three years of experimental and natural flooding (Ellis, Molles, and Crawford 1996).

Literature CitedEllis L.M., Crawford C.S. and M.C. Molles Jr.. 2002.The role of the flood pulse in ecosystem-level processes in southwestern riparian forests: a case study from the Middle Rio Grande.Flood pulsing in wetlands: restoring the natural hydrological balance, p. 51.

Ellis L.M., Molles M.C., Jr., and C.S. Crawford. 1996. Seasonal flooding and riparian forest restoration in the Middle Rio Grande Valley. Final report, U.S Fish and Wildlife Service, District 2, Albuquerque, New Mexico.

Junk, W.L., Bayley P.B. and R.E. Sparks. 1989. The flood pulse concept in river-floodplain systems, p.110-127. In D.P. Dodge Proceedings of the International Large River Symposium. Can. Spec. Publ. Fish. Aquat.Sci. 106.

Surface Soil Moisture at Flood and Nonflood Sites (2002)

2002

Jan Mar May Jul Sep Nov

Mo

istu

re C

onte

nt

0.1

0.2

0.3

0.4

0.5

Rio

Gra

nd

e D

isch

arg

e in

Be

rna

rdo

(cf

s)

1

50

100

500

1000

5000

Nonflood Sites

Flood Sites

River Flow

Surface Soil Moisture at Flood and Nonflood Sites (2001)

2001

Jan Mar May Jul Sep Nov

Moi

stur

e C

onte

nt0.1

0.2

0.3

0.4

0.5

Rio

Gra

nde

Dis

char

ge in

Ber

nard

o (c

fs)

1

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Nonflood Sites

Flood Sites

River Flow

Dry river bed of the Rio Grande at Bosque del Apache 7/17/02

Soil Moisture at Flood Sites (2001)

2001

Apr May Jun Jul Aug Sep Oct Nov Dec

Vol

umet

ric w

ater

con

tent

(m

L/g

soil)

0.12

0.16

0.20

0.24

0.28

0.32

0.36

Rio

Gra

nde

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ge in

Ber

nard

o (c

fs)

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2000

25 cm below ground40 cm below ground55 cm below ground70 cm below ground85 cm below ground100 cm below groundRio Grande Flow (cfs)

MonsoonrainsFlood pulse

Soil Moisture at Nonflood Sites (2001)

2001

Apr May Jun Jul Aug Sep Oct Nov Dec

Vol

umet

ric w

ater

con

tent

(m

L/g

soil)

0.12

0.16

0.20

0.24

0.28

0.32

Rio

Gra

nde

Dis

char

ge in

Ber

nard

o (c

fs)

1

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MonsoonrainsFlood pulse

Obtaining soil moisture readings

Recording water table depths

View of Rio Grande under normal flow conditions

Depth to Water Table in Flood and Nonflood Sites (2001 and 2002)

Jan Mar May Jul Sep Nov

Dep

th to

Wa

ter

Tab

le (

cm)

40

60

80

100

120

140

160

180

Flood Sites 2001

Nonflood Sites 2001

Flood Sites 2002

Nonflood Sites 2002

Soil Moisture at Nonflood Sites (2002)

2002

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Vo

lum

etric

wat

er c

ont

ent (

mL

/g s

oil)

0.12

0.16

0.20

0.24

0.28

0.32

Rio

Gra

nde

Dis

char

ge in

Ber

nar

do (

cfs)

1

50

500

1000

2000

MonsoonrainsNo flood pulse

Soil Moisture at Flood Sites (2002)

2002

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Vo

lum

etric

wat

er c

ont

ent (

mL

/g s

oil)

0.12

0.16

0.20

0.24

0.28

0.32

0.36

Rio

Gra

nde

Dis

char

ge in

Ber

nar

do (

cfs)

1

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2000

MonsoonrainsNo flood pulse

Groundwater depths were significantly higher at flood sites than nonflood sites in 2001 (p=0.001) and 2002 (p=0.032)