How Will Climate Change Affect Trophic Processes and Productivity in

Freshwater-Riparian Ecosystems?

Mark S. Wipfli

USGS Cooperative Fish and Wildlife Research UnitSchool of Fisheries and Ocean Sciences & Dept of Biology and Wildlife

Institute of Arctic BiologyUniversity of Alaska Fairbanks

I. Aquatic Food Webs

II. Climate Change Effects on Food Webs

• Freshwater habitat loss from drying

• Water temperature increases

• Terrestrial vegetation cover changes

• Nutrient loading – from land and sea

Today’s talk

FISH BIRDS

nutrients

algae and aquatic plants

herbivorous invertebrates

carnivorous invertebrates

Aquatic food web (streams, wetlands)

Baxter et al. 2005

Aquatic food web & riparian linkages

Terrestrial prey ingestion by fishes

Cutthroat trout

May June July Aug Sept Oct0.0

1.0

0.2

0.4

0.6

0.8

Pro

port

ion

of t

erre

stria

l pr

ey in

gest

ed

Juvenile coho salmon

Dolly Varden char

Wipfli 1997

Climate Change Effects

• Freshwater habitat loss from drying

• Water temperature increases

• Terrestrial vegetation cover changes

• Nutrient loading – from land and the sea

Climate Change Effects

• Freshwater habitat loss from drying

Riordan et al. 2006

↑ drying = ↓ aq habitat, ↓ aq production Result:

Climate Change Effects

• Water temperature increases

Shrinking water body size, warmer soil and air temps, and longer growing seasons will all likely lead to higher water temperatures

↑ temps = ↑ aq production (to a point), ∆ community composition

Result:

Climate Change Effects on Vegetation

• Expansion of shrubs (alder, willow, dwarf birch) and spruce along aquatic habitats.

Sturm et al. 2001

Kugururok R

Climate Change Effects

• Terrestrial vegetation cover changes (valley bottom)

USDA Coop Ext

Invertebrates on riparian plants

0

0.5

1

1.5

2

2.5

3

Alder

Spruce

Hemlo

ck

Salm

onberry

Stink

curra

nt

Blueb

erryIn

ve

rte

bra

te m

as

s (

mg

) /

lea

f m

as

s (

g)

Allen et al. 2003

Coniferous

Deciduous

Result:

↑ rip veg = ∆ food supply ↑ litter ↑ invert production (?) ∆ invert community comp

Tape et al. 2006

1949

2000

Kugururok River

Climate Change Effects

• Terrestrial vegetation cover changes (headwaters)

Active stream channels and gravel bars in 1949 are now colonized by shrubs – alder, willow, dwarf birch.

Spruce riparian

Inve

rteb

rate

bio

mas

s ex

port

ed(m

g dr

y m

ass·

m-3 w

ater

)

0

2

4

6

Conifer Alder

p < 0.05

Piccolo and Wipfli 2002

Aq. invertebrate drift density

Maybeso Drainage

Alder riparian

Result:

↑ deciduous veg = ↑ food for aq consumers

Sturm et al. 2005

Climate Change Effects

• Nutrient loading – from land

Result (?):

↑ nutrients (N + P) = ↑ aq production ∆ invert composition

Hobbie et al. 1999Benstead et al. 2005

Stream nutrient addition studies led to higher aq production in Kuparuk studies.

Bilby et al. 1996, 1998Heintz 2004Wipfli et al. 1998, 2003, 2004

Anadromous fish runs enrich streams with nutrients

• Shown to increase aquatic productivity in Alaska & the PNW

↑ nutrients (N + P) = ↑ aq production (all trophic levels) ↑ fish growth rates, production, lipid levels

Climate Change Effects

• Warming ocean currents

Salmon distributions shift northward (Welch et al. 1998)

Climate Change Effects

• Nutrient loading – from the sea

Result (?):

↑ nutrients (N + P) = ↑ aq production ∆ invert community composition

Summary – hypothesized climate change effects

• Increased temperatures = ↑ invertebrate production ∆ invertebrate community composition ∆ seasonal occurrence

• Terrestrial veg expansion = ↑ invertebrate abundance ∆ invertebrate community composition ∆ seasonal occurrence

• Nutrient loading = ↑ invertebrate production ∆ invertebrate community composition

∆ seasonal occurrence

Summary – hypothesized climate change effects

• Increased temperatures = ↑ invertebrate production ∆ invertebrate community composition ∆ seasonal occurrence

• Terrestrial veg expansion = ↑ invertebrate abundance ∆ invertebrate community composition ∆ seasonal occurrence

• Nutrient loading = ↑ invertebrate production ∆ invertebrate community composition

∆ seasonal occurrence

Summary – hypothesized climate change effects

• Increased temperatures = ↑ invertebrate production ∆ invertebrate community composition ∆ seasonal occurrence

• Terrestrial veg expansion = ↑ invertebrate abundance ∆ invertebrate community composition ∆ seasonal occurrence

• Nutrient loading = ↑ invertebrate production ∆ invertebrate community composition

∆ seasonal occurrence

Summary – hypothesized climate change effects

Physical processes dictate biological outcomes in riverine systems

Erosion & sediment deposition

Riparian plant community development

Leaf litterinputs

Terrestrial invertebrateinputs

Terrestrial ecosystem

Freshwater ecosystem

Elevated basal food resources for fish & other consumers

Questions?!?