Mine Drainage Residual Additions to Lake Sediments Alter Phosphorus and Trace Metal Distributions

Abstract

AbstractA greenhouse microcosm study investigated the impacts of recovered iron oxyhydroxide mine drainage residuals (MDRs) on phosphorus (P) and trace metal distributions at the sediment layer/water column interface in Grand Lake o’ the Cherokees, a large reservoir receiving waters impacted by both historic mining and current agricultural land uses. Each mesocosm included 5 kg of lake sediment and 20 L of on-site groundwater. Three treatments were examined in triplicate: control (C) with no additions, low MDR (LM) with 0.3 kg added MDR, and high MDR (HM) with 0.9 kg added MDR. In the first 10 days, aqueous soluble reactive phosphorous (SRP) concentrations decreased likely due to colonizing biomass uptake with no significant differences among the three treatments. LM and HM treatments showed delayed peaks in dissolved oxygen (DO) and lesser peaks in chlorophyll-a (Chl-a) concentrations compared to the C treatment, indicating MDR addition may suppress biomass growth. During days 11 to 138, the C treatment demonstrated increasing pH, decreasing ORP, and biomass decay resulting in significantly increased SRP concentrations. In LM and HM treatments, sufficient P sorption by the MDR maintained low SRP concentrations. Although the MDRs are derived from metal-rich mine waters, all aqueous concentrations were below both hardness-adjusted acute and chronic criteria, except for Pb with regard to the chronic criterion. Metal concentrations in sediments were below the Tri-State Mining District (TSMD)–specific Sediment Quality Guidelines (SQGs). MDR additions may serve as stable long-term P sinks to prevent P release from dead biomass, decrease internal P cycling rates, and mitigate eutrophication, with limited concern for trace metal release.