Ellen Wohl Geosciences Colorado State University

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1 Headwater Rivers & Carbon Storage Ellen Wohl Geosciences Colorado State University

2 Context Regional Setting C Pools along Front Range Rivers Implications

3 Context Watersheds are sites for * terrestrial & aquatic CO 2 removal thru photosynthesis transport of living & decomposing organic C in surface & ground waters storage of organic C for widely varying lengths of time

4 Aufdenkampe et al., 2011 Amount of C rivers deliver to oceans is a fraction of that entering rivers from terrestrial ecosystems atmosphere 1.2 land 2.7 rivers, lakes, wetlands 0.9 ocean 0.6 geosphere

5 Headwaters are important significantly contribute to CO 2 outgassing via microbial activity (Battin et al., 2007) transient storage greatly affects nutrient uptake secondary channels, logjams, algal mats, hyporheic, floodplain (Battin et al., 2008, 2009) storage also affects sequestration at time scales of years

6 vegetation soil landslides gradual erosion C C Pools vegetation dead wood floodplain stream litter duff roots fossil C from bedrock

7 Basic research questions Where are carbon and fine sediment stored in a mountainous headwater river network? What is the magnitude of storage in different segments of the river network? What are the mechanisms facilitating storage? How might mechanisms and magnitude of storage change with anthropogenic alteration of rivers and the greater landscape?

8 Regional Setting Colorado Front Range mountain rivers, with varying valley morphology, as reflected in process domains based on elevation (hydroclimatology) valley geometry (lateral confinement) biotic drivers (forest age, beavers) unconfined confined

Basin-scale heterogeneity (bedrock jointing, glaciation) 10 2-10 3 m, 10 3-10 5 y differences in valley geometry (confined/unconfined) Reach-scale heterogeneity (logjams, beaver

9 Basin-scale heterogeneity (bedrock jointing, glaciation) m, y differences in valley geometry (confined/unconfined) Reach-scale heterogeneity (logjams, beaver dams) m, y differences in channel geometry (single-thread/multi-thread) Unit-scale heterogeneity differences in C retention & biological uptake upstream from jam

10 mountain river sluices? not quite

11 Unconfined valleys have the potential for a multi-thread channel planform driven by biota channel-spanning logjams (old-growth forest) beaver dams (beaver)

12 Channel-spanning logjams & multi-thread channels old-growth forest logjams multi-thread channels

bank erosion, overbank flow avulsion/ multi-thread wood recruitment treefall ramped piece logjam upstream alluviation for length of > 2X channel width (persistent)

13 bank erosion, overbank flow avulsion/ multi-thread wood recruitment treefall ramped piece logjam upstream alluviation for length of > 2X channel width (persistent) threshold based on gradient & channel width/valley-bottom width shallow, wide valley steep, narrow valley upstream alluviation for length of 1-2X channel width (transient) Wohl, 2011

14 Beaver dams & multi-thread channels disturbance? aspen high water table beaver multi-thread channels aspen & willow Polvi & Wohl, 2012

15 prior to intensive human manipulation of forests & rivers, patches of old-growth & beavers more widespread headwater multi-thread channels more common greater complexity & retention

Historical changes loss of old-growth forest (globally, reduced forest cover by half & nearly eliminated old growth) currently 6-12 million beaver in North America historically, more

16 Historical changes loss of old-growth forest (globally, reduced forest cover by half & nearly eliminated old growth) currently 6-12 million beaver in North America historically, more like million evidence of much more extensive beaver activity on east side RMNP e.g., Upper Beaver Meadows beaver-induced sedimentation accounts for 30-50% of post-glacial sediments

17 C Pools along Front Range Rivers Objectives quantify C in different reservoirs in diverse valley types 7 valley types based on lateral confinement channel planform (single vs multi-thread) biota (old-growth or younger forest, beaver)

18 C Pools floodplain soils floodplain coarse wood instream coarse wood floodplain fine organic matter litter duff floodplain vegetation live standing trees dead standing trees tree regeneration (understory) shrubs herbaceous plants roots (trees, shrubs, herbaceous)

Methods 100 m valley length 11 transects at 10 m spacing soil thickness at 10 m increments all floodplain & instream wood biomass trees: dbh, height, % live & dead canopy along transects understory

19 Methods 100 m valley length 11 transects at 10 m spacing soil thickness at 10 m increments all floodplain & instream wood biomass trees: dbh, height, % live & dead canopy along transects understory trees: count by height class (3 growth stages) along transects shrubs, herbaceous: estimation of cover (0.5 x 0.5 m) plot along transects litter, duff: sample 0.2 x 0.2 m plots along transects roots: estimate values from literature

20 Preliminary Results channel surveys on eastern side of Rocky Mountain NP > 120 river km in 16 drainages of total river length surveyed 14% beaver meadows 11% unconfined (3% unconfined multi-thread) 32% partly confined 43% confined (23% old-growth)

21 maps by Nick Sutfin

22 Where are carbon and fine sediment stored in a mountainous headwater river network? Because of greater valley bottom area, greater sediment thickness, & greater basal area of forest, predominantly in beaver meadows & unconfined, old-growth valley segments What is the magnitude of storage in different segments of the river network? Unconfined valley segments < 25% of total river length, but contain 75% of the C in valley bottoms (~ 20% of total C in watershed)

23 Megagrams of carbon old-growth single-thread old-growth multi-thread long abandoned beaver meadow newly abandoned beaver meadow old-growth younger old-growth younger 2000 wood vegetation sediment unconfined partly confined confined Wohl et al., in review

24 What are the mechanisms facilitating storage? Variations in rock erodibility, glacial history & biotic drivers How might mechanisms and magnitude of storage change with anthropogenic alteration of rivers and greater landscape?

25 In the absence of biotic drivers, valley geometry does not change, but channel-valley bottom interactions change & C in living and dead biomass changes plan beaver meadow side water sediment nutrients water sediment nutrients

26 Implications leaky rivers as biotic drivers lost Front Range rivers not unique in terms of simplification alternative stable states for rivers in terms of logjams beavers Wohl & Beckman, in press Polvi & Wohl, 2012 restoration?

27 How do individual segment W c /W v scale with increasing drainage area? How does floodplain turnover time vary among segment types? With increasing drainage area? What is role of disturbance (fire, flood, debris flow, blowdown, insects)?

28 Timing is everything

References Aufdenkampe et al., 2011, Riverine coupling of biogeochemical cycles between land, oceans, and atmosphere. Frontiers in Ecology 9, 53-60. Battin et al.

29 References Aufdenkampe et al., 2011, Riverine coupling of biogeochemical cycles between land, oceans, and atmosphere. Frontiers in Ecology 9, Battin et al., 2007, Microbial landscapes: new paths to biofilm research. Nature Reviews 5, Battin et al., 2008, Biophysical controls on organic carbon fluxes in fluvial networks. Nature Geoscience 1, Battin et al., 2009, The boundless carbon cycle. Nature Geoscience 2, Polvi & Wohl, 2012, The beaver meadow complex revisited the role of beavers in post-glacial floodplain development. Earth Surface Processes & Landforms 37, Wohl, 2011, Threshold-induced complex behavior of wood in mountain streams. Geology 39, Wohl & Beckman, in press, Leaky rivers: implications of the loss of longitudinal fluvial disconnectivity in headwater streams. Geomorphology. Wohl et al. in review. Mechanisms of carbon storage in mountainous headwater rivers. Nature Communications.

Prepared By: Tom Parker Geum Environmental Consulting, Inc.

Prepared By: Tom Parker Geum Environmental Consulting, Inc. Topics covered: Definition of riparian and floodplain restoration Floodplain attributes as a basis for developing criteria for restoration designs