1. Landscape Limnology: Nutrient Fluxes &
Biotic Stability in Complex Mountain Watersheds
Wayne Wurtsbaugh,
Michelle Kang & Dave Epstein
Watershed Sciences Department &
Ecology Center
Utah State University
IALS Meeting, Snowbird, 14 April 2009

2. Landscape Ecology ≠ Lakes}
Kratz, Soranno et al. 1991, 1999
Hershey et al. 1999
Riera et al. 2000
Lake placement in watersheds
Synchrony of lake processes }
Chemical interactions across stream-lake landscapes
Baron and Campbell 1997
Hillbricht-Ilkowska 1999
Kling et al {
Insect communities & processes at lake outlets
Richardson & Mackay 1991
Fisher (1997)
Wiens (2002) {
Landscape ecology
of streams

3. Stream–Lake Interaction Project
How do lakes and streams interact in mountain watersheds?
Utah State University
Univ. of Wyoming
Montana State Univ.

4. An important question: How do complex patterns of lakes and streams influence ecosystem function?
Boulder Chain Lakes Watershed, White Cloud Mountains, Idaho A B E C D

5. Sawtooth
Mountains, ID
Study site

6. Characteristics: Twin Lakes
Watershed Characteristics
Elevations m
Granitic, glaciated
Pristine
Precipitation: 80 cm yr -1
1.8 kg NO3- ha-1 yr -1
(N and P limitation of algae)
Characteristics: Twin Lakes

7. Lower reaches vegetated with lodgepole pine

8. Like many montane watersheds, nutrient transport is closely tied to spring snowmelt
~85% of N flux
during 2-month
runoff period
J F M A M J J A S O N D

9. Size-frequency Distribution of Lakes in Sawtooths
Of the 220 lakes analyzed, most are quite small
(modal size ca m2)
Only 0–4% of watershed areas are covered by lakes

10. Streams are tiny features in the landscape
Only 0.3% of watershed area
Sawtooth stream lengths_WS areas_Decker Dec 03B

11. Watershed differences: the have and have nots
Yellow Belly Creek
Watershed
“Lake-less”
South Alturas Ck.

12. Watershed Streams Lakes % Stream Lakes %
Area (ha) Perimeter (km)
Watershed Streams Lakes % Stream Lakes %
Lake Lake
“Lakeless” % % ..(N.Alturas)
Yellow Belly % %

13. PHYSICAL COMPARISONS OF WATERSHEDS WITH AND WITHOUT MAJOR LAKES
Watershed Volumes Residence Time
(1000 m3) @ mean discharge (days)
Stream Lakes % lake
“Lakeless” (N. Alturas) %
Yellow Belly %

14. How Does Having Lakes High in the Watershed Influence the Function of the Final Lake? Do high lakes starve lower ones of nutrients? Do high lakes “buffer” the flux of nutrients making algal populations more stable in lakes below?
“Lakeless”
Stanley Lake
Yellow Belly Creek
Watershed

15. Yellow Belly Creek Watershed
Lakes are dissolved nutrient traps whereas streams are “sources” of dissolved nutrients 16
2.5
2.0 12
Temp
1.5
Temperature (°C)
NO3 (µM) ± S.E. 8
1.0 4
NO3
0.5
Yellow Belly Creek Watershed
Lake
Lake
Lake 2 4 6 8 10 12
Distance from inflow of headwater lake (km)
Yellow Belly Watershed

16. Increasing Lake Area Higher in Watershed Decreases Nutrients in Lowest Lakes (5 watersheds compared)

17. Increasing Lake Area Higher in Watershed Decreases Mean Annual Phytoplankton (Chl a) in Lowest Lakes

18. Increasing Lake Area Higher in Watershed Decreases Phytoplankton Seasonal Variability of Lakes Low in Watershed
Few upstream lakes
Large upstream lakes

19. Increasing Lake Area Higher in Watershed Decreases Phytoplankton Seasonal Variability of Lakes Low in Watershed
Few upstream lakes
Large upstream lakes

20. Summary
When lakes are present in watersheds, they dominate water area & volume of the channalized flow, and thus interactions with radiation & gas exchange.
The large volumes greatly increase water & nutrient residence times.

21. Summary
Many ecological functions are dependent on lake-stream interactions
Upstream lakes trap nutrients, lowering nutrient levels in down-valley lakes (and streams)
Algal populations in down-valley lakes are lowered when upstream lakes trap nutrients
However, algal populations are more stable if upstream lakes buffer the flux of nutrients
The spatial patterning of streams and lakes is thus a crucial factor influencing watershed function

22. Closing photo
FIN