Dissolved organic carbon (DOC) quantity and chemical quality alters microbial metabolism for stream function. Carbon amendments are used in remediation to improve microbial populations, respiration, and precipitate dissolved metals. However, it is not as well understood how newly added DOC compares to natural carbon in an urban, mining area where stream metabolism is suppressed. This project focuses on the urban stream Lone Elm Reach, Joplin, MO, which is located within the Tri-State Mining District and existing superfund program. High levels of lead and cadmium above EPA water quality criteria for chronic aquatic life exposure provide on-going motivation for remediation. Water was collected in winter and late summer 2022, directly from the anoxic mine discharge, and at the receiving stream, upstream, and downstream of the mine discharge. After ICP-MS analyses, we found the water samples to have abundant dissolved ions that interfere with carbon analysis. For example, sulfur = 117 mg/L, calcium = 293 mg/L and sodium= 14.7 mg/L and iron, a known optical interferant was measured at 7.99 mg/L in the mine adit. Thus, we utilized a novel column clean-up method to isolate stream DOC and remove ion interference to < 1 mg/L per target ion. We compared the stream carbon quality to the carbon quality of leachate from biochar and engineered soil, materials that may be used in future remediation efforts. We then ran absorbance on isolated stream DOC and leachate DOC from materials used in remediation to understand quality via optical metrics of SUVA ₂₅₄, E₂:E₃, Spectral Slopes, and Slope Ratio. Preliminary results show that E₂:E₃ ratios of the carbon from the leachates are significantly lower, i.e. more visible wavelength absorbing similar to humic acids, than in-stream carbon via a one-way ANOVA. Biological oxygen demand (BOD) tests are currently underway to provide context for how different carbon may alter biological activity when compared to in-situ carbon BOD results. The overall goal of this work is to understand how remedial carbon amendments could encourage healthy microbial respiration, which could help flocculate heavy metals long-term.

Elli Castonguay

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