CDFLOW: A 30-year dataset of CO₂ in U.S. flowing freshwaters

Presenting the data pipeline and workflow for the compilation of CDFLOW.

Abstract

Carbon dioxide (CO₂) concentrations in the atmosphere have been steadily increasing since the mid-twentieth century. This rise in CO₂ has been shown to affect a wide range of ecosystems and organisms, with a number of negative effects of elevated CO₂ documented for marine organisms. Less is known about the dynamics of CO₂ in freshwaters, but the potential exists for freshwater organisms to be challenged by elevated CO₂. CO₂ dynamics in flowing freshwaters exhibit more variability than in lakes or the ocean, yet it remains important to understand changes in CO₂ despite any background fluctuations. Direct measures of CO₂ in freshwater are limited making it challenging to define spatial or temporal trends in CO₂ levels. However, CO₂ can be estimated from pH, temperature, and alkalinity—commonly collected water quality metrics. We used the National Water Quality Monitoring Council data portal as a source of water quality metrics and the program PHREEQC to estimate CO₂ in flowing freshwaters across 50,000 sites spanning the lower 48 US states from 1990 to 2020. Site data for water chemistry measurements were spatially joined with the National Hydrology Dataset to define sites. CDFLOW presents an opportunity for spatiotemporal analysis of CO₂ trends across the United States over the past 30 years.