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 [email protected]
Jennifer F. Schuetz 505-277-5732 [email protected]
Manuel C. Molles, Jr. 505-277-3050 [email protected]
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
50
100
500
1000
5000
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
Dis
char
ge in
Ber
nard
o (c
fs)
1
50
500
1000
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
50
500
1000
2000
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
50
500
1000
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)