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

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. 2000 { Insect communities & processes at lake outlets Richardson & Mackay 1991 Fisher (1997) Wiens (2002) { Landscape ecology of streams

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

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

Sawtooth Mountains, ID Study site

Characteristics: Twin Lakes Watershed Characteristics Elevations 1900 - 3250 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

Lower reaches vegetated with lodgepole pine

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

Size-frequency Distribution of Lakes in Sawtooths Of the 220 lakes analyzed, most are quite small (modal size ca. 2500 m2) Only 0–4% of watershed areas are covered by lakes

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

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

Watershed Streams Lakes % Stream Lakes % Area (ha) Perimeter (km) Watershed Streams Lakes % Stream Lakes % Lake Lake “Lakeless” 9.1 3.9 30% 4.4 0.7 14% ..(N.Alturas) Yellow Belly 5.2 143 96% 31.5 10.0 24%

PHYSICAL COMPARISONS OF WATERSHEDS WITH AND WITHOUT MAJOR LAKES Watershed Volumes Residence Time (1000 m3) @ mean discharge (days) Stream Lakes % lake “Lakeless” (N. Alturas) 6.6 22.8 77.6% 2 Yellow Belly 16 9145 99.8% 101

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

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

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

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

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

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

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.

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

Closing photo FIN