Grand Canyon Hydrogeology- Isotopic and geochemical tracers of groundwater flow in the Shivwits Plateau, Grand Canyon National Park

As the impacts of global climate change on water resources continue to become more apparent, characterization and management of strained groundwater resources will be needed. Ambient geochemical tracers from discrete sampling could aid in characterizing spring systems through determining flow paths, recharge areas, and carbon cycling. This study explores the novel use of δ13C of dissolved organic carbon (DOC), δ13C of dissolved inorganic carbon (DIC) and fluorescent dissolved organic matter (fDOM), together with water isotopes, major ions, and saturation indices, to characterize springs of the Shivwits Plateau in Grand Canyon National Park. Values of carbon isotopes and fDOM for all springs reflect source values for regional surface vegetation and heterotrophic degradation of terrestrial DOM. Principal component analyses show that springs can be grouped into four groups by geochemical variability: 1) a shallow epikarst system, 2) a flow path through gypsiferous beds of the Toroweap Formation on the eastern side of the plateau, 3) a short, canyon slope runoff-dominated flow path, and 4) a deeper complex flow system in the Redwall Limestone characteristic of mixing of all other flow systems. As appropriations from the Colorado River already exceed its annual streamflow, characterizing groundwater resources for water supply in an increasingly arid climate will be paramount. These results demonstrate the effectiveness of geochemical techniques for groundwater flow characterization, particularly in inaccessible environments.

*Wilson, J.W., Erhardt, A.M. and Tobin, B.W., Using δ13C of dissolved inorganic carbon and dissolved organic carbon as tracers to characterize karst spring systems of the Shivwits Plateau at Grand Canyon National Park. In revision after review at Hydrogeology Journal.

Hyporheic Zone Geochemistry- Forepole Creek, Huntington, West Virginia

This ongoing project is in collaboration with Dr. Bill Ford (UK School of Agriculture)

Wetland environments are frequently thought of as buffer regions for nutrient fluxes into major waterways.   Agricultural and environmental runoff brings nitrogen, phosphorous, and trace metals into the wetland system that changes in geochemical conditions can either mobilize or entrain within the sediment.  Given the nutrient-driven occurrences of harmful algal blooms on the Ohio river, it is critical to characterize the role of backwater wetland systems in either preventing or enhancing these events. Specifically, the impact of hyporheic zone interactions must be characterized to understand microbial activity. Here we show results from the sampling of subsurface waters along the Fourpole Creek in Huntington, W.V.  This backwater system fills during high water levels on the Ohio River, trapping both catchment water and Ohio River overflow.  We utilized a multi-proxy geochemical approach to characterize changes in the geochemistry of the interstitial waters both along the creek and across the floodplain.

Overall, the hyporheic zone can be identified as the upper 9 inches below the sediment-water interface. This region shows different trace metal and carbon sources than deeper samples, consistent with enhanced microbial activity. Additionally, the analysis of d18O, D17O, and dD show that the hyporheic zone waters are isotopically distinct from the underlying water, consistent with higher degrees of flux of fresh water and nutrients. Finally, we see changes in the d13C DIC down the depth profile, supporting the hyporheic zone as a region of carbon cycling.

 These results are consistent with recycling of nutrients in the hyporheic zone, likely resulting in enhanced nitrogen removal via denitrification. Future work will expand this record to more sample locations during and after flood events. 

Erhardt, A.M., Ford. W.A., 2018. Geochemical characterization of hyporheic zone geochemistry in a backwater system: a case study from Fourpole Creek, Huntington, WV.  Geological Society of America Annual Meeting.  Oral Presentation.

Erhardt, A.M., *Young, H.A., Ford, W.I., 2018. Isotope tracers of pore water geochemistry variability across a backwater wetland- a case study from the Fourpole Creek Watershed, Huntington, WV.  American Society of Agricultural and Biosystems Engineers Annual Meeting.  Invited Keynote Presentation  

*Young, H.A., Ford, W.I., Erhardt, A.M., 2018. Pore water geochemistry variability across a backwater wetland- a case study from the Fourpole Creek Watershed, Huntington, WV. Southeast Geological Society of America. Poster Presentation

*Undergraduate Researcher

Freshwater Mussel Shell Geochemistry- Licking River, KY

This ongoing project is in collaboration with Dr. Wendel Haag (Kentucky Department of Fish and Wildlife), Dr. David Weisrock (UK Biology), and Dr. Steven Price (UK Forestry and Natural Resources).

Freshwater mussel shells are sensitive recorders of environmental change and impacts of human activity on the ecosystem. Mussels grow by forming new bands on their shell seasonally between warm and cold cycles, providing a seasonal record as old as the mussel shell. These seasonal records, up to 50 years long, can be reconstructed through the isotopic analysis of the regular banding of the shell. This study presents a comparative study of the isotopic composition of water and sediment with that of mussel shell organic and inorganic material to evaluate freshwater mussels as recorder of diet and environmental conditions in the Licking River of Kentucky.

Mussel shells representing 12 locations and seven species were collected from the two main branches of the Licking River. The organic d13C and d15N from the periostracum and d13C, d18O, and the d15N of the prismatic layer were measured on the outermost growth band on all samples considered, along with multiple growth horizons on a subset of samples. To calibrate this data set, water and sediment samples were collected across a seasonal cycle, with sampling at February, May, and August 2018.  Samples were analyzed for d18O and dD of water, d13C of DIC, and organic d13C and d15N of sediment. 

 Preliminary data of mussel shells from the Licking River in Kentucky show relationships linked to location, as well as differences between species. There is a general trend of isotope values for both inorganic carbon and oxygen that vary by stream location (upstream/downstream), as well as variability between the two main forks of the Licking River. Additionally, carbonate-bound d15N was compared to the d15N the outer periostracum at the same growth horizon. The results across 22 samples, including five species, were the same within analytical error. 

These results will be placed in the context of the impact human activity has on freshwater systems, including multiple human constructed dams along the river as well as any changes in land use. Sampling sites are located on both sides of four dams, as well as spatially distributed to allow changes resulting from human activity to be visible. These results will also provide greater insight into the seasonal cycles of mussel growth and diet, and whether either has been affected by human activity within the length of the mussel’s seasonal records.

*Wilson, J., Haag, W., Weisrock, D., Price, S., Erhardt, A.M., 2018. Variation in stable isotopes of freshwater mussel shells in the Licking River of Kentucky. Geological Society of America. Poster Presentation.

*Bechtol, C., Haag, W., Price, S., Weisrock, D., Erhardt, A.M., 2018.  Changes in Kentucky’s Licking River effect on isotopes of freshwater mussel shells. Southeast Geological Society of America. Poster Presentation

Erhardt, A.M., Weisrock, D., Price, S., Haag, W. 2017. Variation in stable isotopes of freshwater mussel shells in a Kentucky river system. American Geophysical Union. Poster Presentation.

*Undergraduate Researcher