Completed Projects

Here’s what we’ve completed thus far:

Crossing A Threshold: The Legacy of 19th-Century Logging on Logjams and Carbon Storage in Front Range Headwater Streams – Natalie Beckman, PhD Dissertation

Natalie’s dissertation work tested the hypothesis that wood loads and logjams in streams draining old-growth forests differ significantly from those in younger forests. Beckman (2013) describes the primary findings from the work, including: streams in old-growth forests contain greater volumes of large wood, more closely spaced ramp and bridge pieces that can act as key pieces to form channel-spanning logjams, and more logjams per kilometer of stream. Logjams in old-growth forests trap a greater volume of organic matter: riparian forest stand age and valley geometry explain 73% of the variation in organic carbon in the form of wood and finer organic matter stored within a stream. Natural disturbances such as wildfires and blowdowns tend to increase the amount of organic carbon stored within streams, whereas human disturbances such as logging reduce carbon storage within streams. Size of jams, number of jams per kilometer of stream, and carbon storage within jams correlate most strongly with reach-scale variables rather than exhibiting consistent downstream trends, implying that management to retain or reintroduce large wood and logjams is most effective at the reach-scale. Increased total wood load and decreased spacing between key pieces are the most effective characteristics for promoting formation of logjams within a stream.

References

Beckman N. 2013. Crossing a threshold: the legacy of 19th-century logging on logjams and carbon storage in Front Range headwater streams. PhD dissertation, Colorado State University.

Beckman ND, Wohl E. 2014. Organic carbon storage in mountainous headwater streams: the role of old-growth forest and logjams. Water Resources Research 50: 2376-2393.

Beckman ND, Wohl E. 2014. Effects of forest stand age on the characteristics of logjams in mountainous forest streams. Earth Surface Processes and Landforms 39: 1421-1431.

Great River Wood Dynamics, Slave River and Great Slave Lake, Canada – Natalie Kramer, PhD Dissertation

Natalie’s dissertation focused on the dynamics of large wood in the Mackenzie River drainage basin of Canada. The Mackenzie River basin is a primary source of large wood to the Arctic Ocean, yet previous work on organic carbon dynamics in the Mackenzie and other Arctic river basins has focused on dissolved organic carbon and finer particulate organic carbon outputs to the ocean, rather than on organic carbon outputs in the form of large wood. Natalie’s work focused particularly on wood transport in the Slave River, a tributary to Great Slave Lake. Among her findings most relevant to carbon dynamics is that large wood entering Great Slave Lake is retained within the lake, rather than being transported downstream into the mainstem Mackenzie River. Some of the wood entering the Slave River delta forms large accumulations that block distributary channels. Much of the wood that is transported through the delta and enters the lake is transported by wind and water currents to limited portions of the lake shoreline. The repeated deposition of driftwood on these portions of the shoreline over centuries has facilitated accumulation of sediment and germination of vegetation on the wood-vegetation deposits. Natalie described these deposits as ‘driftcretions’ and distinguished different depositional morphologies, from mats to low ridges that record individual large storms (Kramer and Wohl, 2015). Driftwood deposited on the margins of Great Slave Lake thus forms a carbon deposit in its own right, but also facilitates trapping and retention of other organic matter containing carbon. Additional publications from Natalie’s dissertation include: a statistical examination of how different time-sampling intervals influence estimates of quantity of driftwood transport as recorded in time-lapse photographs (Kramer and Wohl, 2014); an extensive literature review and synthesis of quantitative and qualitative patterns of wood transport in rivers (Kramer and Wohl, 2017); and an examination of influences on large wood transport and storage along the Slave River using multiple lines of evidence (Kramer et al., 2017, Water Resources Research).

References

Kramer N. 2016. Great river wood dynamics, Slave River and Great Slave Lake, Canada. PhD dissertation, Colorado State University.

Kramer N, Wohl E. 2014. Estimating fluvial wood discharge using time-lapse photography with varying sampling intervals. Earth Surface Processes and Landforms 39: 844-852.

Kramer N, Wohl E. 2015. Driftcretions: the legacy impacts of driftwood on shoreline morphology. Geophysical Research Letters 42: 5855-5864.

Kramer N, Wohl E. 2017. Rules of the road: a qualitative and quantitative synthesis of large wood transport through drainage networks. Geomorphology 279: 74-97.

Kramer N, Wohl E, Hess-Homeier B, Leisz S. 2017. The pulse of driftwood export from a very large forested river basin over multiple time scales, Slave River, Canada. Water Resources Research 53: 1928-1947.

 Spatiotemporal Variability of Floodplain Sediment and Organic Carbon Retention in Mountain Streams of the Colorado Front Range – Nicholas Sutfin, PhD Dissertation

A pilot study of organic carbon storage along river corridors in the Colorado Front Range quantified carbon stored within downed, dead wood and floodplain sediment in relation to varying valley geometry. The pilot study suggested that relatively wide, low gradient valley segments were disproportionately important in storing organic carbon at the network scale (Wohl et al., 2012). Nick’s dissertation work greatly expanded this pilot study, with detailed quantification of organic carbon storage in 24 valley segments. As a population, these valley segments ranged in elevation from 2100 to 3050 m and had contributing drainage areas of 10 to 200 km2. Sutfin (2016) describes the primary findings from the work. Depth-averaged mean soil organic carbon content can be accurately estimated using systematic random sampling at approximately 10 locations. Soil organic carbon content correlates with soil moisture, sample depth, grain size, elevation of the floodplain surface relative to the active channel, thickness of soil at the sampling location, and valley geometry. Older pooled mean 14C ages of floodplain sediment at sites above 2900 m elevation compared to ages at sites below 2400 m elevation support previous work indicating elevational differences in flooding and floodplain disturbance regime in the Colorado Front Range. Observations of floodplain disturbance during the September 2013 flood indicate the amount of disturbed floodplain area increases exponentially downstream. Laterally unconfined valley segments store more organic carbon per unit area. Unconfined valley segments with single, rather than anabranching, channels tend to have saturated soils and store the greatest amounts of organic carbon. Additional journal articles based on this work are pending.

References

Suftin NA. 2016. Spatiotemporal variability of floodplain sediment and organic carbon retention in mountain streams of the Colorado Front Range. PhD dissertation, Colorado State University.

Sutfin NA, Wohl EE, Dwire KA. 2016. Banking carbon: a review of organic carbon storage and physical factors influencing retention in floodplains and riparian ecosystems. Earth Surface Processes and Landforms 41: 38-60.

Wohl E, Dwire K, Sutfin N, Polvi L, Bazan R. 2012. Mechanisms of carbon storage in mountainous headwater rivers. Nature Communications 3: 1263. Doi:10.1038/ncomms2274.

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Instream Wood Loads and Channel Complexity in Headwater Southern Rocky Mountain Streams Under Alternative States  – Bridget Livers, PhD Dissertation

Bridget’s dissertation research was conducted as part of a large, multidisciplinary research project that examined the effects of riparian forest stand age and disturbance history on mountain stream ecosystems. The study design focused on three populations of stream segments in the Southern Rockies of Colorado and Wyoming: streams draining old-growth forests; streams draining younger forests with a history of only natural disturbances such as wildfire or blowdowns; and streams draining younger forests with a management history as a result of timber harvest or other activities that occurred at least several decades before the study. Although analyses are ongoing for the biological data, preliminary results suggest that old-growth and naturally disturbed forests are significantly different than managed forests, even if the stand age of the naturally disturbed and managed forests are similar. These differences largely stem from significantly greater instream wood loads in old-growth and naturally disturbed forests. Greater wood loads equate to greater physical complexity, or spatial heterogeneity, in channels and floodplains and to greater organic carbon storage within channels (Livers and Wohl, 2016). Differences in wood load and physical complexity between streams in old-growth and naturally disturbed forests versus streams in managed forests reflect alternative states of stream ecosystem form and function, with the less complex and retentive state existing as a legacy from historical timber harvest and log floating. Additional journal articles based on this work are pending.

References

Livers Gonzalez B. 2016. Instream wood loads and channel complexity in headwater Southern Rocky Mountain streams under alternative states. PhD dissertation, Colorado State University.

Livers B, Wohl E. 2016. Sources and interpretation of channel complexity in forested subalpine streams of the Southern Rocky Mountains. Water Resources Research 52: 3910-3929.

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Evaluating Carbon Storage in Subalpine Lake Deltas in the Colorado Front Range and Washington Central Cascades – Dan Scott, MS Thesis

Dan’s thesis focused on understanding the contribution of subalpine lake deltas to the mountain river carbon pool. Subalpine lake deltas, potentially acting as the first long-term stop for carbon in a headwater network, provide a carbon storage record that largely reflect the carbon dynamics of their upstream basins. The study focused on comparing the magnitude of carbon storage in subalpine lake deltas between the Colorado Front Range and the Washington Central Cascades to evaluate the dominant controls on that storage in each region. Subalpine lake deltas are hot spots of carbon storage on the landscape, storing high concentrations of organic carbon, despite their small size on the landscape. Geomorphic factors that influence the transport, decomposition, and stability of organic carbon both in the upstream watershed and on the delta exert a stronger control on carbon storage than climate or primary production (Scott, 2015 ; Scott and Wohl, In Review). This project, along with the work of Nick Sutfin, provides the basis for Dan’s dissertation research, which broadens the scope of this investigation of carbon storage to entire mountain river basins.

References

Scott, DN. 2015. Evaluating Subalpine Lake Delta Carbon Storage in the Colorado Front Range and Washington Central Cascades. MS Thesis. Colorado State University.

Scott DN & Wohl E. 2017. Evaluating carbon storage in subalpine lake deltas. Earth Surface Processes and Landforms 42: 1472-1481.

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