Dissertation Defense: Fischer Young

Sep 12 2022 9:00 am
University of Montana or Zoom

Dissertation Defense | Fischer Young

Location: University of Montana; Education Building Room 214 (ED 214)

Date and Time: September 12th, 2022 at 9:00 am

Virtual option for those not in Missoula, MT:

Note that Zoom attendees will have limited functionality to minimize technical difficulties



Characterizing Riverine Carbon: A spatiotemporal study of organic and inorganic carbon variability and evaluation of methods for quantifying pCO2


Carbon is a critical component of aquatic ecosystems. For inland waters, carbon is a basal resource for biological communities and is a key component of trophic transfer through ingestion and respiration processes. Additionally, carbon acts as a key biogeochemical tracer that can track chemical, physical, and biological processes from the terrestrial landscape to inland waters to the ocean. Riverine carbon, however, can be challenging to characterize and interpret due to the complexity of its sources and sinks along a riverine continuum. Included in this work are the biogeochemically relevant forms of carbon such as dissolved inorganic carbon (DIC), the partial pressure of carbon dioxide (pCO2), and dissolved organic carbon (DOC). Together, these forms of carbon along with spectrophotometric pH, temperature, total alkalinity, and ionic strength were measured and analyzed to evaluate a novel method for quantifying freshwater pCO2 and to assess the spatial and temporal variability of inorganic and organic carbon along the upper Clark Fork River (UCFR), MT, USA.

Overall, the method for calculating pCO2 showed an ~4-fold improvement in accuracy, compared to an infrared reference, when using an indicator-based pH instead of electrochemical pH. Moreover, this method was validated through a 19-d field application in the UCFR. This method was then used to calculate pCO2 on 275 discrete samples to estimate the air-water CO2 flux along the UCFR. The UCFR was a source of CO2 to the atmosphere with a river-wide average air-water CO2 flux of 80 ± 140 mmol m-2 d-1 (n = 275). The magnitude of the air-water CO2 flux was primarily driven by riverine pH, discharge, and season. Additionally, DOC variability along the UCFR was assessed through the Nutrient Processing Domain framework where stream reaches were designated by functional space. DOC dynamics were strongly linked to changes in discharge, characteristic of a snowmelt dominated system, where reaches along the UCFR occupied diluter, enhancer, compiler, conduit, and consumer domains dependent on season, reach, and hydraulic loads. This work characterized the carbon dynamics of ~215 km of the UCFR from ~3500 discrete samples over 4 years to better understand carbon sources, sinks, and variability along the UCFR.