SPATIOTEMPORAL PATTERNS IN pCO2 IN AN IMPOUNDED URBAN STREAM SYSTEM WITH A HISTORY OF HARMFUL ALGAL BLOOMS

Intense photosynthesis-driven carbon fixation can cause CO₂ undersaturation in eutrophic surface waters, potentially turning them into air CO₂ sinks especially in summer. In the context of rising air CO₂ levels and associated gains in air-to-water CO₂ flux over time, an increased carbon supply from air could be a contributing factor to positive trends in harmful algal bloom intensities. We determined spatiotemporal patterns in surface pCO₂ in an impounded, eutrophic, urban stream system in West Texas with a history of harmful algal blooms. We took monthly measurements (early-to-mid afternoon) over two years above the dam spillways of four artificial lakes and used field water temperature and pH and lab-measured total alkalinity (Alk) to estimate pCO₂. Alk was moderate-to-high in all lakes (overall lake medians, ~1200-1800 μmol/L). Three of the lakes had overall and seasonal median pCO₂ values well below air pCO₂ values (lowest individual lake values ranged from 6 to 37 μatm), and their seasonal median values of dissolved oxygen showed oversaturation year-round. The overall median pH in these three lakes ranged from 8.6 to 8.9. These observations indicate that eutrophic urban lakes can maintain high levels of productivity and be daytime sinks of air CO₂ year-round. Although algal communities may take carbon directly from Alk (bicarbonate), the severity of CO₂ depletion in three of the study lakes suggests they are carbon-limited, and therefore that the ongoing increase in air CO₂ levels could potentially lead to the intensification of their algal blooms.

Primary Presenter: Reynaldo Patino, U.S. Geological Survey (at Texas Tech University) (reynaldo.patino@ttu.edu)

Authors:

Reynaldo Patino, U.S. Geological Survey (at Texas Tech University)  (reynaldo.patino@ttu.edu)

Samantha Lehker, Texas Tech University  (slehker@outlook.com)