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How Will Climate Change Affect Trophic Processes and Productivity in Freshwater-Riparian Ecosystems? Mark S. Wipfli USGS Cooperative Fish and Wildlife Research Unit School of Fisheries and Ocean Sciences & Dept of Biology and Wildlife Institute of Arctic Biology University of Alaska Fairbanks

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slide1

How Will Climate Change Affect Trophic Processes and Productivity in Freshwater-Riparian Ecosystems?

Mark S. Wipfli

USGS Cooperative Fish and Wildlife Research Unit

School of Fisheries and Ocean Sciences & Dept of Biology and Wildlife

Institute of Arctic Biology

University of Alaska Fairbanks

slide2

Today’s talk

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

slide3

Aquatic food web (streams, wetlands)

BIRDS

FISH

carnivorous invertebrates

herbivorous invertebrates

algae and aquatic plants

nutrients

slide5

1.0

0.8

0.6

0.4

0.2

0.0

Aug

Sept

Oct

June

July

May

Terrestrial prey ingestion by fishes

Juvenile coho salmon

Cutthroat trout

Proportion of terrestrial prey ingested

Dolly Varden char

Wipfli 1997

slide6

Climate Change Effects

• Freshwater habitat loss from drying

• Water temperature increases

•Terrestrial vegetation cover changes

• Nutrient loading – from land and the sea

slide7

Climate Change Effects

• Freshwater habitat loss from drying

Riordan et al. 2006

Result:

↑ drying =↓ aq habitat, ↓ aq production

slide8

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

Result:

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

slide9

Climate Change Effects

• Terrestrial vegetation cover changes (valley bottom)

Climate Change Effects on Vegetation

Kugururok R

Sturm et al. 2001

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

slide10

Result:

↑ rip veg =∆ food supply

↑litter

↑invert production (?)

∆invert community comp

USDA Coop Ext

Invertebrates on riparian plants

3

2.5

Deciduous

2

1.5

Invertebrate mass (mg) / leaf mass (g)

1

Coniferous

0.5

0

Alder

Spruce

Hemlock

Blueberry

Salmonberry

Stink currant

Allen et al. 2003

slide11

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.

Kugururok River

1949

2000

Tape et al. 2006

slide12

Spruce riparian

6

p < 0.05

4

Invertebrate biomass exported

(mg dry mass·m-3 water)

2

0

Alder

Conifer

Alder riparian

Aq. invertebrate drift density

Maybeso Drainage

Result:

↑ deciduous veg =

↑ food for aq consumers

Piccolo and Wipfli 2002

slide13

Climate Change Effects

• Nutrient loading – from land

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

Hobbie et al. 1999

Benstead et al. 2005

Result (?):

↑ nutrients (N + P) =

↑ aq production

∆invert composition

Sturm et al. 2005

slide14

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

Bilby et al. 1996, 1998

Heintz 2004

Wipfli et al. 1998, 2003, 2004

slide15

Climate Change Effects

• Warming ocean currents

Salmon distributions shift northward (Welch et al. 1998)

slide16

Climate Change Effects

• Nutrient loading – from the sea

Result (?):

↑ nutrients (N + P) =

↑ aq production

∆invert community composition

slide17

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

slide18

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

slide19

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

slide20

Summary – hypothesized climate change effects

Physical processes dictate biological outcomes in riverine systems

Leaf litter

inputs

Terrestrial

invertebrate

inputs

Elevated basal food resources for fish & other consumers

Riparian plant

community

development

Erosion &

sediment

deposition

Terrestrial

ecosystem

Freshwater

ecosystem