Temporal Variations in Dissolved Oxygen Concentrations Observed in a Shallow Floodplain Aquifer

Dissolved oxygen (DO) concentrations play an important role in many groundwater biogeochemial processes, yet assessments of temporal variations are lacking. In this study, we examined daily DO concentrations using a continuously‐reading optical DO probe in a shallow floodplain setting in Iowa to (i) quantify fluctuations across two growing seasons; (ii) examine hydrologic controls on DO values; and (iii) model daily DO concentrations using easily measured variables. DO concentrations exhibited both rapid and long‐term changes in concentrations over time, rapidly increasing and decreasing more than 1 mg/l in response to precipitation recharge and stream stage increase over the span of several hours and days. On 40% of the monitoring days in this study, DO concentrations increased, on average, 0.2–0.4 mg/l from one day to the next. DO concentrations decreased approximately 5–6 mg/l from spring through late summer and fall, likely owing to microbial and root respiration. Daily DO concentrations were successfully modelled using a combination of hydrologic (groundwater level and river stage) and temperature variables ( r 2  > 0.7). Improved understanding of temporal controls on groundwater DO patterns is needed to help clarify the dynamics of many biogeochemical processes. Copyright © 2014 John Wiley & Sons, Ltd.