TEMPORAL VARIATION IN PH, ALKALINITY, AND TOTAL INORGANIC CARBON IN WESTERN LAKE SUPERIOR TRIBUTARIES

Inorganic carbon in aquatic systems can be a source or a sink of atmospheric carbon dioxide, affect the pH, and shift the speciation of other chemical species (such as metals).  It is also the carbon source for aquatic organic matter production via photosynthesis and influences the quality of life for heterotrophic organisms. However, temporal variation in inorganic carbon cycling in freshwater has not yet been well constrained.  This study focuses on sites in three tributaries of different sizes in the Lake Superior watershed to investigate how key inorganic carbon system variables (pH, total alkalinity (TA), and total inorganic carbon (TIC)) are affected by seasonality and to compare this to inter-annual variability. For one tributary site, variations across storm events and a diurnal cycle are also studied. Across seasons, pH, TIC, and TA showed minima in spring and were highest in summer. During the storm events, changes in pH and TA were up to ~60% and ~55% respectively, of the seasonal variation in the tributary.  Specific trends during storms appeared related to event duration, total precipitation, and prior precipitation amounts. Over a diurnal cycle measured near the summer solstice, pH increased to a midday maximum and then decreased; TIC and TA increased throughout the day, likely due to the increased influence of groundwater as the stream recovered from a rain event that occurred 4 days prior. Comparing pH data across all four temporal scales, interannual variability is highest, followed by seasonal variability, which is ~40% of interannual variability.

Primary Presenter: Elizabeth Minor, Large Lakes Observatory (eminor@d.umn.edu)

Authors:

Payton Kittaka, WRS Program, University of Minnesota  (kita085@d.umn.edu)

Joel Hoffman, US EPA  (Hoffman.Joel@epa.gov)

Christopher Filstrup, NRRI, University of Minnesota Duluth  (filstrup@d.umn.edu)

Elizabeth Minor, University of Minnesota Duluth  (eminor@d.umn.edu)