Dissolved Organic Carbon and the Potential Role to Stream Acidity in the Great Smoky Mountains National Park

A substantial societal shift towards environmental awareness has focused research efforts on the impacts of pollution on natural landscapes. Improvements to pollutant regulations and technology have resulted in sizeable reductions of atmospheric deposition of anthropogenic acids, especially nitrates and sulfates, which has altered the role of these ions in the environment. As such, understandings of environmental chemistry dynamics have required regular updating.

Through the National Park Service Vital Signs monitoring program, increases in precipitation pH observed in Great Smoky Mountains National Park (GRSM) has been attributed to the reduction of inorganic acid concentrations. Unfortunately, these improvements have not been uniformly reflected in stream waters across the park. As such, intra-soil and stream water chemical interactions require scrutiny for an explanation. Specifically, the dissolved organic carbon (DOC) concentrations are targeted within this research to determine their impact.

GRSM stream waters were monitored on a bimonthly basis throughout the year of 2020. Ambient baseflow DOC concentrations were quantified, ranging from -1to 9.38 mg L^-1, and general variations between watersheds were revealed that restrict direct comparisons from one watershed to another. Positive relationships for DOC concentrations with elevation, drainage area, and drainage density were then determined. Additionally, DOC concentrations were found to have correlations with calcium, potassium, nitrate, and acid neutralizing capacity. Stepwise regression analysis then determined a predictive model for DOC concentrations with calcium and potassium having positive relationships and nitrate having a negative relationship.

Overall, this study established a foundational characterization of DOC concentrations in GRSM streams and suggests indirect consequences to reductions in inorganic acid deposition, likely through soil-based interactions. Continued analysis beyond the research presented here is best directed to DOC compositional evaluations to quantify and understand organic acids, soil solution analysis to determine contained DOC interactions, and temporal trends to enhance predictability and appropriate management.