Resumen
Low impact development (LID) best management practices (BMPs) collect, infiltrate, and treat stormwater runoff, and increase recharge to aquifers. Understanding the controls on reduction/oxidation (redox) conditions within LID BMPs is important for groundwater management because outflow from some LID BMPs can recharge aquifers and affect groundwater quality. Here we evaluate redox conditions of urban stormwater runoff in a LID infiltration trench in San Francisco, California, and quantify the relation between water saturation (%) and temperature (°C) and resulting dissolved oxygen (DO) concentrations, redox dynamics, and O2 reduction rates. The DO fluctuations have an inverse response to the duration of saturation of the trench. Anoxic (<0.5 mg/L) conditions often occurred within hours of stormwater events and persisted from a few hours to two days, which indicate that microbial respiration can be a limiting factor for DO. Temperature of stormwater runoff was not a statistically significant control on DO. The estimated O2 reduction rate is 0.003 mg·L?1·min?1, which is two to five orders of magnitude higher than in groundwater from previous studies. Higher rates of O2 reduction are a function of the more oxic and organic-rich stormwater runoff that drives faster microbial O2 reduction. Our findings have important implications for the design of infiltration trenches and other LID BMPs to achieve desired redox conditions for infiltrating stormwater toward minimizing groundwater contamination.