Introduction
1
Introduction • The Rio Grande’s flows are about half of what they were 60 years ago, and half of the wetlands in the Middle Rio Grande have been lost in just 50 years (Crawford et al. 1993). • Overbank flooding in late spring/early summer due to snowmelt runoff occurs in a very limited area only in years with above-average snowfall. The last major floods in the Middle Rio Grande that produced large-scale cottonwood establishment occurred in the springs of 1941 and 1942. • Cottonwood germination, which require sand bars and adequate moisture from high river flows (Braatne et al. 1996), has declined substantially. • Without changes in water management, the Rio Grande bosque (riparian forest) will be dominated by exotic species, namely salt cedar (Tamarix ramosissima) and Russian Olive (Elaeagnus angustifolia) over the next 50 to 100 years (Howe and Knopf 1991). • Restoration of native bosque along the hydrologically altered and highly controlled Rio Grande would require instituting managed late spring/early summer floods in years with good water availability that coincide with the historical peak in snowmelt discharge. Literature Cited Braatne, J.H., S.B. Rood and P.E. Heilman. 1996. Life history, ecology and conservation of riparian cottonwoods in North America. In Biology of Populus and its Implications for Management and Conservation. Edited by R.F. Stettler, H.D. Bradshaw, Jr., P.E. Heilman and T.M. Hinckley. NRC Research Press, Ottawa, Ontario, Canada. pp. 57-85. Crawford, C.S., A.S. Culley, R. Leutheuser, M.S. Sifuentes, L.H. White, and J.P. Wilber. 1993. Middle Rio Grande Ecosystem: Bosque Biological Management Plan. U.S. Fish and Wildlife Service, District 2, Albuquerque, New Mexico, 291 pp. Howe, W.H., and F.L. Knopf. 1991. On the imminent decline of the Rio Grande cottonwoods in central New Mexico. Southwestern Naturalist 36: 218-224. Acknowledgements UNM 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 Contacts Jennifer F. Schuetz 505- 277-5732 [email protected] du Jean-Luc Cartron 505- 277-5732 [email protected] Manuel C. Molles, Jr. 505-277-3050 [email protected] Cliff N. Dahm 505-277- 2850 [email protected] Abstract Over the past 50 years, volume and timing of the Rio Grande’s flow, including the annual flood pulse, have been altered due to damming and diversion of the river. As a result, the river is largely isolated from its riparian forest, or bosque, and the native cottonwood forest is aging, is not regenerating, and is being invaded by exotics. Restoration of native bosque may require restoring the annual flood pulse and thus the hydrologic connection between the river and its floodplain. To determine the current extent of hydrologic connectivity within a 160 km stretch of the Middle Rio Grande in New Mexico, we are investigating the relationship among river flow, groundwater depth and soil moisture at 4 flood and 4 nonflood sites. United States Geological Survey station data are used to monitor river flow at various locations within our study reach. Pressure transducers at each site measure groundwater depths throughout the year. Water content of the top 30 cm of soil at each site is measured using a water content reflectometer, and soil moisture from 25 to 100 cm below ground is measured using a neutron probe. Preliminary analysis of pressure transducer data suggests that flood sites have a higher water table than nonflood sites, and analyses of neutron probe data suggest that soil moisture is higher at flood sites. In addition, soil moisture and depth to groundwater are negatively correlated. Results will help us inform policy-makers on potential tools, such as managed seasonal flooding in years with adequate water availability, to help restore the native bosque and the hydrologic connectivity between the river and its floodplain. Flood site with native understory of willow and other species, relatively healthy cottonwoods, and a small quantity of coarse woody debris and litter on forest floor Nonflood site with non-native understory of salt cedar and Russian Olive, older cottonwoods, and a large quantity of coarse woody debris and litter on forest floor Is the water table higher at flood sites than at nonflood sites? Yes (P=0.002) Taking soil moisture readings with a neutron probe What distinguishes flood sites from nonflood sites? Is it… Elevation of wells in relation to the river? Distance of site to the river? Soil type, hydraulic conductivity, stratigraphy? Groundwater well with pressure transducer Downloading pressure transducer Is soil moisture at flood sites more responsive to river flow than soil moisture at nonflood sites? … Perhaps (to be investigated) Soil M oisture atN onflood Sites (2001) 2001 Apr M ay Jun Jul Aug Sep O ct N ov D ec Volum etric w atercontent(m L/g soil) 0.12 0.16 0.20 0.24 0.28 0.32 R io G rande D ischarge in Albuquerque (cfs) 300 500 800 1000 2000 3000 4000 M onsoon rains Flood pulse Soil M oisture atFlood Sites (2001) 2001 Apr M ay Jun Jul Aug Sep O ct N ov D ec Volum etric w atercontent(m L/g soil) 0.12 0.16 0.20 0.24 0.28 0.32 0.36 R io G rande D ischarge in Albuquerque (cfs) 300 500 800 1000 2000 3000 4000 25 cm below ground 40 cm below ground 55 cm below ground 70 cm below ground 85 cm below ground 100 cm below ground R io G rande D ischarge (cfs) M onsoon rains Flood pulse Are groundwater levels at flood sites more responsive to river flow than groundwater levels at nonflood sites? …Perhaps (to be investigated) D epth to W aterTable ofAll Sites (2001) 2001 Apr M ay Jun Jul Aug Sep O ct D epth to W aterTable (cm ) 40 60 80 100 120 140 160 180 200 LL BLNB BDAC BLN BDOC SHK AOP RGNC Flood Sites N onflood Sites Are soil moisture levels higher at flood sites than at nonflood sites? Yes Are depth to groundwater and soil moisture correlated? Yes, depth to groundwater and soil moisture are correlated at all depths (i.e. 25, 40, 55, 70, 85 and 100 cm below ground). D epth to w atertable (cm ) 60 80 100 120 140 160 180 200 Soil w atercontent(m L/g soil) 0.05 0.10 0.15 0.20 0.25 0.30 0.35 R elationship Betw een D epth to W aterTable and Soil M oisture 40 cm Below G round LL BLNB BLN BDAC RGNC AOP SH K BDOC R 2 = 0.83 P = 0.002 R elationship Betw een D epth to W aterTable and Soil M oisture 100 cm Below G round D epth to w atertable (cm ) 60 80 100 120 140 160 180 200 Soil w atercontent(m L/g soil) 0.0 0.1 0.2 0.3 0.4 0.5 R 2 = 0.9 P = 0 LL BLNB BLN BDAC RGNC AOP SH K BDOC Soil M oisture 40 cm Below G round (2001) P =0.044 2001 Apr M ay Jun Jul Aug Sep O ct N ov D ec Volum etric w atercontent(m L/g soil) 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 Flood Sites N onflood Sites LL BLNB BDAC BLN BDOC SHK AOP RGNC Soil M oisture 25 cm Below G round (2001) P =0.028 2001 Apr M ay Jun Jul Aug Sep O ct N ov D ec Volum etric w atercontent(m L/g soil) 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 N onflood Sites Flood Sites LL BDAC BLN BLNB AOP SHK BDOC RGNC Belen (Flood)and Bernardo (N onflood)D epth to W aterTable 2001 G row ing Season 2001 Apr M ay Jun Jul Aug Sep O ct N ov 1 D epth to W aterTable (cm ) -50 0 50 100 150 200 R io G rande D ischarge in Bernardo (cfs) 1 50 100 500 1000 5000 Belen (flood site)centerw ell Bernardo (nonflood site)centerw ell R io G rande flow (cfs)atBernardo,N M
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Are depth to groundwater and soil moisture correlated? Yes, depth to groundwater and soil moisture are correlated at all depths (i.e. 25, 40, 55, 70, 85 and 100 cm below ground). - PowerPoint PPT Presentation
Transcript of Introduction
Introduction• The Rio Grande’s flows are about half of what they were 60 years ago, and half of the wetlands in the Middle Rio Grande have been lost in just 50 years (Crawford et al. 1993).
• Overbank flooding in late spring/early summer due to snowmelt runoff occurs in a very limited area only in years with above-average snowfall. The last major floods in the Middle Rio Grande that produced large-scale cottonwood establishment occurred in the springs of 1941 and 1942.
• Cottonwood germination, which require sand bars and adequate moisture from high river flows (Braatne et al. 1996), has declined substantially.
• Without changes in water management, the Rio Grande bosque (riparian forest) will be dominated by exotic species, namely salt cedar (Tamarix ramosissima) and Russian Olive (Elaeagnus angustifolia) over the next 50 to 100 years (Howe and Knopf 1991).
• Restoration of native bosque along the hydrologically altered and highly controlled Rio Grande would require instituting managed late spring/early summer floods in years with good water availability that coincide with the historical peak in snowmelt discharge.
Literature CitedBraatne, J.H., S.B. Rood and P.E. Heilman. 1996. Life history, ecology and conservation of riparian cottonwoods in
North America. In Biology of Populus and its Implications for Management and Conservation. Edited by R.F. Stettler, H.D. Bradshaw, Jr., P.E. Heilman and T.M. Hinckley. NRC Research Press, Ottawa, Ontario,
Canada. pp. 57-85.
Crawford, C.S., A.S. Culley, R. Leutheuser, M.S. Sifuentes, L.H. White, and J.P. Wilber. 1993. Middle Rio Grande Ecosystem: Bosque Biological Management Plan. U.S. Fish and Wildlife Service, District 2, Albuquerque,
New Mexico, 291 pp.
Howe, W.H., and F.L. Knopf. 1991. On the imminent decline of the Rio Grande cottonwoods in central New Mexico. Southwestern Naturalist 36: 218-224.
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
ContactsJennifer F. Schuetz 505-277-5732 [email protected]
Jean-Luc Cartron 505-277-5732 [email protected]
Manuel C. Molles, Jr. 505-277-3050 [email protected]
Cliff N. Dahm 505-277-2850 [email protected]
Cliff S. Crawford 505-277-3411 [email protected]
AbstractOver the past 50 years, volume and timing of the Rio Grande’s flow, including the annual flood pulse, have been altered due to damming and diversion of the river. As a result, the river is largely isolated from its riparian forest, or bosque, and the native cottonwood forest is aging, is not regenerating, and is being invaded by exotics. Restoration of native bosque may require restoring the annual flood pulse and thus the hydrologic connection between the river and its floodplain. To determine the current extent of hydrologic connectivity within a 160 km stretch of the Middle Rio Grande in New Mexico, we are investigating the relationship among river flow, groundwater depth and soil moisture at 4 flood and 4 nonflood sites. United States Geological Survey station data are used to monitor river flow at various locations within our study reach. Pressure transducers at each site measure groundwater depths throughout the year. Water content of the top 30 cm of soil at each site is measured using a water content reflectometer, and soil moisture from 25 to 100 cm below ground is measured using a neutron probe. Preliminary analysis of pressure transducer data suggests that flood sites have a higher water table than nonflood sites, and analyses of neutron probe data suggest that soil moisture is higher at flood sites. In addition, soil moisture and depth to groundwater are negatively correlated. Results will help us inform policy-makers on potential tools, such as managed seasonal flooding in years with adequate water availability, to help restore the native bosque and the hydrologic connectivity between the river and its floodplain.
Flood site with native understory of willow and other species, relatively healthy cottonwoods, and a small quantity of coarse woody debris and litter on forest floor
Nonflood site with non-native understory of salt cedar and Russian Olive, older cottonwoods, and a large quantity of coarse woody debris and litter on forest floor
Is the water table higher at flood sites than at nonflood sites? Yes (P=0.002)
Taking soil moisture readingswith a neutron probe
What distinguishes flood sites from nonflood sites? Is it…
Elevation of wells in relation to the river?
Distance of site to the river?
Soil type, hydraulic conductivity, stratigraphy?
Groundwater well with pressure transducer
Downloading pressure transducer
Is soil moisture at flood sites more responsive to river flow than soil moisture at nonflood sites? … Perhaps (to be investigated)
Soil Moisture at Nonflood Sites (2001)
2001
Apr May Jun Jul Aug Sep Oct Nov Dec
Vol
um
etr
ic w
ate
r co
nten
t (m
L/g
soi
l)
0.12
0.16
0.20
0.24
0.28
0.32
Rio
Gra
nde
Dis
char
ge in
Alb
uque
rqu
e (c
fs)
300
500
800
1000
2000
3000
4000
MonsoonrainsFlood pulse
Soil Moisture at Flood Sites (2001)
2001
Apr May Jun Jul Aug Sep Oct Nov Dec
Vol
um
etr
ic w
ate
r co
nten
t (m
L/g
soi
l)
0.12
0.16
0.20
0.24
0.28
0.32
0.36
Rio
Gra
nde
Dis
char
ge in
Alb
uque
rqu
e (c
fs)
300
500
800
1000
2000
3000
4000
25 cm below ground40 cm below ground55 cm below ground70 cm below ground85 cm below ground100 cm below groundRio Grande Discharge (cfs)
MonsoonrainsFlood pulse
Are groundwater levels at flood sites more responsive to river flow than groundwater levels at nonflood sites? …Perhaps (to be investigated)Depth to Water Table of All Sites (2001)
2001
Apr May Jun Jul Aug Sep Oct
Dep
th to
Wat
er T
able
(cm
)
40
60
80
100
120
140
160
180
200
LL
BLNB
BDAC
BLN
BDOCSHK
AOP
RGNC
Flood Sites
Nonflood Sites
Are soil moisture levels higher at flood sites than at nonflood sites? Yes
Are depth to groundwater and soil moisture correlated?
Yes, depth to groundwater and soil moisture are correlated at all depths (i.e. 25, 40, 55, 70, 85 and 100 cm below ground).
Depth to water table (cm)
60 80 100 120 140 160 180 200
Soi
l wat
er c
ont
en
t (m
L/g
so
il)
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Relationship Between Depth to Water Tableand Soil Moisture 40 cm Below Ground
LL
BLNB
BLN
BDAC
RGNC
AOP
SHKBDOC
R2 = 0.83P = 0.002
Relationship Between Depth to Water Tableand Soil Moisture 100 cm Below Ground
Depth to water table (cm)
60 80 100 120 140 160 180 200
Soi
l wat
er c
onte
nt (
mL/
g so
il)
0.0
0.1
0.2
0.3
0.4
0.5
R2 = 0.9P = 0
LL
BLNB
BLN BDAC
RGNC
AOPSHKBDOC
Soil Moisture 40 cm Below Ground (2001)P=0.044
2001
Apr May Jun Jul Aug Sep Oct Nov Dec
Vol
umet
ric w
ater
con
tent
(m
L/g
soil)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Flood Sites
Nonflood Sites
LL
BLNBBDAC
BLN
BDOCSHKAOP
RGNC
Soil Moisture 25 cm Below Ground (2001)P=0.028
2001
Apr May Jun Jul Aug Sep Oct Nov Dec V
olum
etric
wat
er c
onte
nt (
mL/
g so
il)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Nonflood Sites
Flood Sites LL
BDACBLNBLNB
AOPSHKBDOC
RGNC
Belen (Flood) and Bernardo (Nonflood) Depth to Water Table2001 Growing Season
2001
Apr May Jun Jul Aug Sep Oct Nov 1
Dep
th to
Wa
ter
Tab
le (
cm)
-50
0
50
100
150
200
Rio
Gra
nd
e D
isch
arg
e in
Be
rna
rdo
(cfs
)
1
50
100
500
1000
5000
Belen (flood site) center wellBernardo (nonflood site) center well Rio Grande flow (cfs) at Bernardo, NM
