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

Jasmine Krause, Erin R. Hotchkiss, Cassandra Knutson, Matthew Cohen, Adam Scott Ward 

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.