Remote sensing and isotopic analysis to determine the contribution of snow- and ice-melt to streamflow in the Nepal Himalaya. Presented by Mark Williams at the "Perth II: Global Change and the World's Mountains" conference in Perth, Scotland in September 2010.

1. The Niwot Ridge Mountain Biosphere Reserve:
Tipping points in high-elevation ecosystems
in response to changes in climate and
atmospheric deposition
Mark Williams, University of Colorado

2. High-elevation areas are important
bellwethers of global change:
we need long-term research

3. Glaciated
valley SADDLE

4. External Drivers: Temperature
 Increasing air temperature since early 1980’s
 Summer air temps warming fastest
 Earlier lake ice-out
dates
5ºC increase in 25 years

5. External Drivers: Precipitation
 Greater precipitation with increasing elevation
 Increases in the winter months (more snow)
 Summer drought starting in 2000

6. External Drivers: N deposition
• Increased rates of N deposition (wetfall)
• N loading increases, despite drought

7. ARIKAREE D1 CLIMATE
GLACIER
ROCK
GLACIER
GREEN
LAKE 4
3,600 m

8. Earlier Snowmelt 2-6 days decade-1

9. Precipitation Effects on Streamflow
GL4 225-ha
MART 8-ha

10. Wet Year vs. Dry Year
-Increasing subsurface
pathways.
-- Snowmelt peak is not
snow – old, reacted water
(talus + baseflow) is
pushed out by infiltrating
snow.
-- Source of baseflow
changes and volumes are
not significantly different.

11. Arikaree glacier is dying
Drought
Tipping point
Arikaree Glacier: Mass balance (Bn), cm water equivalent.

12. N dep + warming T = N saturation
N Critical load:
Aquatic
4 Kg N/ ha/ yr
Annual VWM concentrations of nitrate increase at all stream sites

13. Stoichiometric controls on N-
cycling
Scatterplot of NO3- vs. DOC: NO3- ratio
for eight sites in Green Lakes Valley.

14. Saddle site

15. how much N input does it take to produce a change in
species composition? (= N critical load using biotic
response)
Addressed experimentally in
species rich dry meadow, using
additions of 2, 4, 6 g N/m2/yr

16. species composition response:
50 treatment x year P < 0.01
Carex rupestris
40
projected cover (%)
N added:
Carex rupestris
30 0
2
20
4
10 6
0
96
98
00
02
04
06
08
19
19
20
20
20
20
20
Treatment specific rate of change in cover
similar response for Trisetum spicatum

17. Empirical estimation of N critical load for plant
species responses in alpine dry meadows
4
(% projected cover/yr)
change in Carex cover
3
2
1
0
-1 0 1 2 3 4 5 6 7
-2 -1
0.0 N input (g N m yr )
N Critical load:
score (value /year)
Change in DCA1
10-40 Kg N/ ha/
-2.5
yr
-5.0
Whole community response
-7.5
-1 0 1 2 3 4 5 6 7
-2 -1
N input (g N m yr )

18. Woody Willow Encroachment

19. Willow Encroachment Experiment
Factorial manipulation of N
(fertilizer), snow (snowfence),
summer temperature (open-
topped chambers), in all possible
combinations
+ Addition of Salix glauca
seedlings

20. Shrub growth benefits from
increased N, snow, and temperature
Salix growth in height after 2 years (cm)

21. Feedbacks to ecosystem processes
 Willow encroachment
increases litter, N availability,
Net N mineralization
(mg N/g soil/30 days)
and snow depth.
 These effects may accelerate
encroachment
Absent Present
Willows

22. Summary
• Disappearing glaciers
• Snowmelt occurring earlier
• Drought years little discharge because of
groundwater deficit
• Increasing N deposition increases nitrate in
streamflow
• Critical loads for terrestrial veg 10 kg/ha/yr
• Shrub invasion of alpine

23. QUESTIONS?