Subsurface Fe (II) affects concentrations of dissolved O₂ in streamwater

Area of Science:

• Ecohydrology
• Biogeochemistry
• Environmental Science

Background:

• The groundwater-surface water interface is crucial for aquatic ecosystems, featuring redox gradients.
• Groundwater inflow of reduced substances, like iron(II), impacts stream water oxygen budgets.

Purpose of the Study:

• To experimentally quantify the effect of iron(II)-rich groundwater inflow on dissolved oxygen (DO) in stream and hyporheic zones.
• To investigate the influence of sediment type and flow rate on these processes.

Main Methods:

• Simulated groundwater inflow of iron(II) into a flume system with varying sediment content and flow rates.
• Weekly monitoring of iron(II), iron(III), dissolved organic carbon (DOC), and dissolved oxygen (DO) in open and pore waters over five weeks.

Main Results:

• Iron(II) inflow substantially decreased DO concentrations in both pore and open waters.
• Oxygen uptake rates increased significantly with iron(II) inflow, contributing 17-21% to overall oxygen consumption.
• Iron(II) treatment increased dissolved organic carbon, suggesting a link between iron mobilization and DOC.

Conclusions:

• Hyporheic and riparian redox processes, including iron(II) inflow, critically affect stream oxygen budgets.
• These processes are vital to consider for understanding and managing stream ecosystem health.