I recently submitted revisions to our manuscript examining the linkages between hydrology and floodplain erosion and sedimentation over a 60-year period. Using lidar, aerial imagery, field measurements, and hydrologic analysis of USGS stream gauge data, we found that the rate of decline in river flows (slope of the recession limb) is strongly linked to the area of floodplain eroded during periods between aerial images used in the study. We also find that pointbar lateral accretion is linked to the duration of overbank flows and conduct a floodplain fine sediment budget. The preprint of the article currently in review can be found on the Earth and Space Center Open Archive here. Check out the word cloud of the manuscript text to get a brief summary of the emphasis of the manuscript and much of my research!
I have been working with the Cleveland Metroparks and the Northeast Ohio Regional Sewer District to gain access to logjams along rivers and streams in open spaces of parks and urban watersheds. I am investigating (1) the volume of wood and carbon storage in these streams, (2) watershed, forest, and channel characteristics linked with logjam occurrence and wood volume, (3) how logjams are altering channel morphology and sediment dynamics. Our observations have already influenced management decisions not to remove two of the logjams previously tagged for removal!
Leaving the logjams in place provides me with the opportunity to monitor them over time including, changes in channel shape or morphology, the size of sediment (like sand, cobbles or boulders), erosion of river banks, and the accumulation of sediment. I will continue to monitor three of the logjams, which show evidence of facilitating river flow outside of the channel and onto the floodplain and the development of side channels. This type of hydrologic connectivity or water across the floodplain creates critical aquatic and riparian (near the river) habitat including invertebrates, frogs, fish, and birds like the great blue heron.
Although these logjams create a much more dynamic river and encourage erosion along the river banks and the deposition of sediment, no infrastructure appears to be at risk. Common practice and plans for some of the jams I have investigated is to removed the jams because they pose risk for infrastructure (e.g., roads, buildings, bridges). Allowing the logjams to remain in place provides the benefits of creating improved diversity of healthy habitat in and near the streams. Part of this increase in healthy ecosystems is an increased ability for the stream to flow up and out of the channel on what is called the floodplain. This reduces flood damage downstream because it slows down water as is spreads out and flows over grasses, around trees, and through other vegetation. In doing so, these spaces become buffers that facilitate what are call ecosystem services – a societal benefit produced by natural ecosystem processes – by filtering nutrients, carbon, and other contaminants from surface water. Some of this occurs through hyporheic exchange, which is when water moving with the stream flows beneath the stream bed and banks. Logjams in urban areas also filter out garbage and trash, which my colleague, Anne Jefferson at Kent State, is currently examining in her research.
My research shows that logjams may reduce otherwise high amounts of floodplain sediment storage in unconfined valleys, provide hotspots for the transformation of organic matter, and thus limit carbon storage in the Colorado Rocky Mountains. A manuscript currently in review expanded upon the last portion of my dissertation, which examined the role of channel morphology and logjams on floodplain sedimentation and organic carbon storage, to include fluorescence analysis of dissolved organic matter in surface water and sediment through collaboration with Laurel Lynch and Tim Fegel. This complemented surveys of 24 study reaches, over 600 sediment samples, and used five years of logjam surveys in and around Rocky Mountain National Park. The preprint is available here, for the manuscript currently in review. Our results inform two conceptual models described below.
Figure 5. Conceptual figure of sediment dynamics in (A) confined, (B) multithread, and (C) unconfined systems and observed dissolved organic matter dynamics in (D) single thread-multithread-single thread transitional stream segments. (A) Shear stress (τ) is a function of the specific weight of water (γ), stream gradient (S), and flow depth (h), which changes with discharge (Q). In multithread channels (B) where Qt = Q1 + Q2 + Q3 + … Qn for n number of channels, flow depth is not additive as is Qt so h, and thus τ, decrease substantially across the valley bottom. Increased transit time and hyporheic exchange in multithread channels facilitates extraction and mixing of terrestrial and microbial organic matter (OM) from floodplain sediment, increasing the transformation and mineralization of OM and resulting in higher OM diversity within multithread and downstream (D) systems. Unconfined single-thread channels have high in situ OM inputs from seasonal sedges and evidence of groundwater inputs that may cause higher observed OC concentrations (C).
The Natural Inquirer, a publication by the U.S. Forest Service that provides science education and outreach to middle school and high school students, featured one of our papers on the influence of beaver dams and logjams on carbon storage along river valleys. I was happy to be a part of this so that our research can be used to educate others about land-use management and the influence of surface processes on carbon dynamics and climate change.
The article even covers the global carbon cycle…
with mention of how wildfires are a significant part of the carbon cycle, a growing aspect of my research.
I am happy to announce that the Cleveland Teen Science Cafe’s inaugural cafe was a great success! A paleoanthropologist at the Cleveland Museum of Natural History (CMNH), Dr. Yohannes Haile-Selassie – who recently published an article in Nature about a 3.8 million-year old skull of a hominin species in the Woranso-Mille region of Ethiopia – led the first cafe. Students from the public high school, Cleveland School of Science and Medicine (CSSM), received free admission to the CMNH and attended the cafe where Dr. Haile-Selassie talked about what he does as a paleoanthropologist, outlined his recent discovery, and led the students in talking about how to identify and distinguish different species.
This fall, I have been working with a math teacher at the CSSM public high school, Manuel Mendoza, with guidance from Michelle Hall, the President of Science Education Solutions, Inc. and Co-Director and Founder of the Teen Science Cafe (TSC) Network to start Cleveland’s first TSC. Our first year of cafes is supported by the Case Western Reserve University Gelfand STEM Center. With the help of Mr. Mendoza and graduate students from our department, Sara Gutierrez and Jemila Edmonds, we recruited a core group of committed Teen Leaders to organize and lead the CLE TSCafe.
The goal of this effort is to engage high school students from the Cleveland area in STEM fields with an emphasis on sciences. By finding engaging presenters with an effort to include those from underrepresented groups and minorities to lead the cafes, we hope to inspire and help encourage pursuit of higher education in science fields among participating teens who represent the diversity of the Cleveland area. With other public schools showing interest in participating, the long-term goal for CLE TSC will be to develop several groups of Teen Leaders from different areas in Cleveland, where the cafe presenters will lead a series of engaging cafes.
From my experience as a student and a professor, field experiences early in the semester provide experiential learning opportunities that can spark interest and understanding that simply can not be matched in the classroom. This is why I designed a field trip to Cuyahoga Valley National Park (CVNP) for my Geomorphology class at Case Western Reserve University. Early this fall, after learning about fundamental unifying concepts in geomorphology, weathering, erosion, and soils, we took a trip to CVNP.
This field trip emphasized how to maintain a field book and take detailed observations of study sites. In the field trip guide, I asked students to make sketches, answer several questions, and discuss various topics related to what we covered in class and what we talked about in the field. Topics included: weathering and erosion, river incision, landslides, basin evolution, glaciation and glacial till, numeric and relative dating methods, soil development, and interpretation of past environmental conditions. Exciting highlights include the ~300 million-year-old Sharon Conglomerate shown below with cross-bedded sandstone and honey comb weathering.
I also prepared the students with materials about the field trip site in a brief lab exercise where they downloaded kmz files of United States Geological Survey (USGS) 7.5 minute quadrangle topographic maps from USGS TopoView and geologic maps from the USGS and the Association of American State Geologists (AASG), National Geologic Map Database, and projected kmz files onto Google Earth topography.
This field trip served as an introduction to geomorphology in the field prior to our next field trip, which was a quantitative analysis of channel geometry and hydraulics of the Chagrin River to investigate potential fish habitat for reintroduction of species of interest.
Earlier this semester, my geomorphology class had an introduction to photogrammetry, using Agisoft Photoscan to explore ways of visualizing our environment and the surface of Earth using technology. Thanks to Ben Gorham at the Freedman Center for Digital Scholarship and the Kelvin Smith Library at Case Western Reserve University for introducing the students to the optimal techniques and the Agisoft Photoscan software! Here are some 3-D models of completed photogrammetry products, including two of a glacial erratic pillow basalt left behind in northeastern Ohio from Canada after the retreat of the Laurentide ice sheet following the last glacial maximum!
Case Western Reserve University highlighted my most recent publication in Nature Communications about floods, floodplain sediment, wildfire, climate, and erosion along Rocky Mountain rivers. The journalist and author of the article, Mike Scott, asked me about similarities and parallels with urban rivers in the East. Check it out!
A portion of my dissertation research that quantified the duration fine sediment resides along the area adjacent to a river before being eroded (floodplain sediment residence time) and examined the role of valley geometry on the impact of extreme floods was just published in Nature Communications.
This paper shows that mountain streams at higher elevation in the Colorado Rocky Mountains store fine floodplain sediment for longer durations (>1200 years) than those below the Pleistocene glacial terminal moraine (<200 years). In addition to differences in glacial history associated with elevation, these differences in floodplain sediment residence times reflect differences in dominant vegetation and forest type, wildfire regime, hydroclimatic regime, and resulting hydrologic runoff response. Additionally, one high-elevation site with evidence of more recent wildfires in the last 400 years exhibits shorter residence times (<200 yrs).
These findings suggest that wildfire and projected increases in the the frequency and intensity of wildfires and extreme floods are likely to reduce sediment storage and residence times along mountain river corridors. Potential decrease in fine floodplain sediment retention along rivers is extremely important for carbon dynamics and ecosystems services, the stability of floodplains and risk to commonly associated societal infrastructure, and the fate and transport of contaminants including contaminated sediment from mines.
Difference between pre- and post-flood lidar complement 52 radiocarbon ages (used to estimate residence times) in identifying stream power, and valley confinement as significant predictors for floodplains disturbance in response to extreme floods. This means that while differences in vegetation, wildfire, and hydrology associated with elevation regulate the geomorphic response along river corridors of the study area, the shape of the valley and the landscape’s ability to dissipate energy during floods is also a determining factor as to where fine sediment will remain stable or be eroded.
This research was partially funded by my NSF Doctoral Dissertation Research Improvement Grant, two graduate student research grants from the Geological Society of America Quaternary Geology and Geomorphology Division, the Colorado Scientific Society, and scholarships from the Colorado State University Warner College of Natural Resources and Department of Geosciences.
Our research, led by Postdoctoral Fellow at Cornell University, Laurel Lynch, was just published in Nature Communications. This work expanded upon some of my PhD research and study sites in Rocky Mountain National Park and utilized Dr. Lynch’s expertise in biogeochemistry to examine the influence of hydrologic connectivity and channel complexity on aquatic carbon dynamics. Our findings show that river corridors with complex river channels in beaver meadows with beaver dams, canals, and multiple channels of flow across a single valley bottom create disparate zones with differences in organic carbon and metabolite composition. These spatial differences in organic carbon composition occur during low flow conditions in the late summer following peak flow.
During peak flow conditions in early June as a result of mountain snowmelt, organic carbon composition is similar across all channels. High flow causes water in numerous channels to become more connected and forces water from beneath the river channel and floodplain to the surface for mixing. These results are important for ecosystem productivity affected by land use management regarding the complexity of river channels, which society has a tendency to intentionally decrease. Changes in hydrologic flow regime associated with a shifting climate can also alter the functionality of these systems so that connectivity is decreased in complex channels, limiting temporal variation in connectivity in unaltered systems.