Year-round daytime pCO2 undersaturation in an instream series of urban reservoirs with a history of harmful algal blooms

Reynaldo Patino; Samantha Lehker

doi:10.1080/20442041.2025.2544581

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Year-round daytime pCO2 undersaturation in an instream series of urban reservoirs with a history of harmful algal blooms

Reynaldo Patino·Samantha Lehker

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Abstract

Daytime water quality was determined monthly over two years in an instream series of four urban reservoirs with recurring blooms of Prymnesium parvum —a cool-season toxigenic species. Temperature, pH, and laboratory-measured total alkalinity were used to estimate p CO 2 . System-wide, p CO 2 was negatively associated with dissolved oxygen. Chlorophyll- a , phycocyanin (cyanobacterial pigment), and P. parvum were negatively associated with p CO 2 and positively with dissolved oxygen. Three reservoirs were productive and, during daytime, p CO 2 -undersaturated year-round or near-year-round, while a fourth (third in the series) was unproductive and mostly p CO 2 -oversaturated. Seasonal phycocyanin and chlorophyll- a patterns indicated that cyanobacterial and eukaryotic ( P. parvum included) phytoplankton growth drives daytime CO 2 depletion in the productive reservoirs during the warm and cool seasons, respectively. The system’s moderate alkalinity (HCO 3 − ) may serve as an alternative carbon source for photosynthesis; however, the persistent depletion of CO 2 and the energetic cost of using HCO 3 − are consistent with a scenario where phytoplankton growth is CO 2 -limited. Daytime p CO 2 undersaturation across seasons has been rarely reported, but this study indicated it occurs more often than recognized. The non-monotonic spatial patterns in productivity and carbonate system conditions across the study reservoirs indicate that localized influences from a heterogeneous urban landscape may help shape individual lake metabolism.

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Inland Waters Article

Source-reported bounding extent: 33.52159454590185° to 33.64162038185367° latitude; -101.93988097783505° to -101.77150820869511° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Reynaldo Patino, Samantha Lehker. 2026-01-23. Year-round daytime pCO2 undersaturation in an instream series of urban reservoirs with a history of harmful algal blooms. https://doi.org/10.1080/20442041.2025.2544581

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