Systematic Review of Dissolved Oxygen in Streams and Rivers: Advances, Challenges, and Opportunities

Dissolved oxygen (DO) has been extensively studied in streams and rivers. Despite this breadth of research, the processes governing DO are rarely quantified concurrently with whole-ecosystem measurements. To address this gap, we synthesize 230 empirical studies (1964-2024) to evaluate how, where, and with what methods oxygen exchanges—the processes by which oxygen enters and leaves streams—have been measured. We organize oxygen exchanges into five groupings, treating whole-stream metabolism as an integrative category of four underlying process domains: (1) water column, (2) benthic, (3) the hyporheic zone and sediments, and (4) surface-atmosphere exchange. Across the literature, estimates of whole-stream metabolism and gas exchange dominate, reported in 66% and 18% of studies, respectively, while underlying process domains were collectively reported in fewer than 16% of studies and jointly quantified in less than 7%. Where units permitted comparison, estimates of respiration in benthic, hyporheic, and underlying sediments were among the most variable exchanges yet least frequently measured. Together, these patterns indicate that our current understanding of stream oxygen dynamics relies heavily on integrative, reach-scale metabolism estimates, while the processes that generate these signals remain poorly resolved due to methodological and disciplinary silos. We identify key challenges and opportunities for synthesizing oxygen exchanges, emphasizing standardized reporting, concurrent measurements, and cross-site comparisons to advance integrated assessments of DO exchanges across streams and rivers.