Phytostabilization of Fluvial Tailings Deposits in the Clark Fork River Floodplain

Abstract

Butte, Montana is the site of a world class copper deposit that has been mined nearly continuously since the 1870's. Tailings deposits, a legacy of early mining practices, are abundant in the floodplain of the Clark Fork River, which has its headwaters near Butte. Tailings released by large-scale flooding in the early 1900's form a patchwork in the floodplain. Waters that contact the pyriterich tailings are generally acidic and contain elevated copper, zinc, and arsenic levels.Thinner tailings deposits (e.g. less than 15 cm) are fully oxidized and have become naturally re-vegetated. In areas with thicker tailings deposits, low pH (3 to 4.5) persists and tailings are devoid of vegetation. Evaporation from bare tailings concentrates metal sulfate salts at or near the surface. The bare tailings are susceptible to erosion and water flowing across the tailings dissolves metals and contributes metal loads to the Clark Fork River. In the middle and late 1980's, large fish kills occurred in the Clark Fork after thunderstorms rinsed soluble metals, especially copper, into the river.In 1990 and 1991, 4 km of the Clark Fork River near Warm Springs, Montana, was reclaimed using liming and both deep and conventional tillage techniques to reduce the mobility of metals in the floodplain and to allow reestablishment of vegetation. Successful stabilization of the floodplain soils has been amply demonstrated and phytostabilization was proposed as a cornerstone of the remediation efforts for the Clark Fork River superfund site. Environmental monitoring of the Clark Fork Demonstration project over a 14 year period is described in this paper.

Quantitative trait loci (QTL) and candidate genes associated with trace element concentrations in perennial grasses grown on phytotoxic soil contaminated with heavy metals

“…Concentrations of As and Pb in some of the plants examined in this study were below possible toxicity thresholds of 30 mg As or 10-100 mg Pb kg −1 forage for cattle, sheep, and other livestock (Table 1), but the principle threat of As and Pb to livestock actually comes also from direct ingestion of contaminated soils, such as the Clark Fork soil sample used in this experiment, because plants tend to exclude these toxic non-essential elements (Underwood and Suttle 2001;National Research Council 2005). Aside from toxicities of individual heavy metals to various plants and animals, contamination of the Clark Fork River floodplain with mixture of different heavy metals had a devastating effect on the riparian vegetation and aquatic wildlife (Moore and Luoma 1990;Nimick and Moore 1991;EPA 2004;Hochella et al 2005) with a relatively small number of plant species, including basin wildrye, able to grow on this site (Neuman and Schafer 2006).…”

“…However, basin wildrye grows up to 2 m tall in good native habitats, such as the native Clark Fork River landscape, with roots that extend at least that deep. The depth of contaminated sediment on the Clark Fork River floodplain shows patchlike variation (Neuman and Schafer 2006) and the concentration of heavy metals also varies by depth (Brumbaugh et al 1994). Areas with thicker tailings deposits are devoid of vegetation, whereas thinner deposits less than 15 cm thick are fully oxidized with natural vegetation (Neuman and Schafer 2006).…”

“…The depth of contaminated sediment on the Clark Fork River floodplain shows patchlike variation (Neuman and Schafer 2006) and the concentration of heavy metals also varies by depth (Brumbaugh et al 1994). Areas with thicker tailings deposits are devoid of vegetation, whereas thinner deposits less than 15 cm thick are fully oxidized with natural vegetation (Neuman and Schafer 2006). Thus, relatively deep root systems may enable basin wildrye to escape contaminated topsoil in some parts of the Clark Fork River floodplain.…”

“…Conversely, under natural aerobic soil conditions As and Mo are taken up as the oxyanions AsO 4 3− (arsenate) and MoO 4 2− (molybdate), which have increasing solubility at higher pH levels. Soils of the Clark Fork river floodplain were limed to counteract acid-forming contaminants, raise the pH, and promote plant growth (EPA 2004;Neuman and Schafer 2006). With a pH of 7.6 in this experimental soil, Cu 2+ and Pb 2+ are essentially immobilized while Cd 2+ and Zn 2+ have intermediate levels of mobility (McKenzie 1980;Stumm 1992;Grossl et al 1994 (McKenzie 1980;Stumm 1992;Grossl et al 1994).…”

“…Genetic mapping populations derived from hybrids of North American perennial wildrye species, basin wildrye (Leymus cinereus) and creeping wildrye (Leymus triticoides), have been used to identify QTLs controlling mineral concentrations in relationship to the nutritional quality of forages grown on fertile pastureland and the risk of hypomagnesemia in grazing animals (Larson and Mayland 2007). Basin wildrye also displays relatively high tolerance to heavy metals (Paschke et al 2000;Paschke and Redente 2002) and is often used for reclamation of mine-land soils including phytotoxic soils along the Clark Fork River, in western Montana, which was contaminated with high levels of As, Cd, Cu, Pb, Zn, and acid-forming compounds (Moore and Luoma 1990;Nimick and Moore 1991;Brumbaugh et al 1994;EPA 2004;Hochella et al 2005;Neuman and Schafer 2006). The basin wildrye germplasm 'Washoe' was collected from a natural population growing on a site contaminated with As and other heavy metals near a defunct smelter stack (EPA 1996a;Redente et al 2002), near the Clark Fork River of western Montana, for specific purposes of mineland reclamation (Marty 2003).…”