Rivers are important contributors of carbon, nutrients, and other chemical species, providing the link between biogeochemical cycling on land and the coastal oceans. Appropriate physico-chemical characterizations of rivers are important for accurately studying these biogeochemical processes. In specific, river carbon chemistry has an important spatiotemporal variability, which has not been well constrained due to data limitations. The sparseness of data results in larger uncertainties when estimating changes in carbon cycling within these river regions, including estimates of pH, CO₂, and calcium carbonate saturation states. A relevant aspect to properly characterizing rivers, and thus accurately modelling the inorganic carbon system, is ionic strength (i.e., specific conductance). Here we present a novel method to measure ionic strength based on spectrophotometric pH methods, which improves both the accuracy and precision of ionic strength measurements compared to more traditional conductometric instruments. The impacts of these measurement improvements on inorganic carbon system parameter estimations was investigated near the Mississippi River Delta and Tampa Bay, two regions within the Gulf of Mexico that are strongly influenced by river runoff. Our findings suggest that ionic strength errors can cause significant biases in calculations of pH, CO₂ fluxes, and calcium carbonate saturation. Thus, accurate measurements of ionic strength are a critical component to obtaining an accurate picture of the inorganic carbon system variability in river influenced coastal margins.

Primary Presenter: Katelyn Schockman, NOAA Atlantic Oceanographic and Meteorological Laboratory (katelyn.schockman@noaa.gov)

Authors:

Katelyn Schockman, NOAA/University of Miami  (katelyn.schockman@noaa.gov)

Robert Byrne, University of South Florida  (rhbyrne@usf.edu)

Christopher Moore, U.S. Geological Survey  (csmoore@usgs.gov)

Fabian Gomez, NOAA/Northern Gulf Institute  (fabian.gomez@noaa.gov)

Rik Wanninkhof, NOAA  (rik.wanninkhof@noaa.gov)