Environmental effects of copper mine tailings reclamation with biosolids

Anaerobically digested biosolids (treated sewage sludge) were applied to Copper mine tailings (pH 8.0) in Princeton, B.C. to determine how well biosolids could achieve land reclamation on a site prone to wind erosion in a semi-arid climate (350 mm mean annual precipitation). In October 1992, biosolids at 62, 77 (two plots), and 179 Mg/ha were applied to four 0.5 ha plots with manure spreaders. In 1993, vegetation established on all sites without irrigation which reduced wind erosion. The 77 Mg/ha treatment led to the best vegetation quality and yield in the first growing season. Yield increased from 300 kg/ha (Control) to 5500 kg/ha (77 Mg/ha). In October 1993, additional biosolids were applied to the 62 and one of the 77 Mg/ha plots to test if it is beneficial to apply biosolids in two applications rather than one larger application. Yields in 1994 were generally lower than in 1993 reflecting lower precipitation. Alfalfa established well on all sites and was the dominant legume while brome and fescue were dominant grasses. Vegetation samples showed no micronutrient or metal toxicity problems. Notable trends in both growing seasons included: foliar Mo concentrations were lower; foliar Cu:Mo ratios were higher; cattle and deer grazing did not hamper growth; soil pH decreased whereas concentrations of Total P, Bray-P, TKN-N, NH₃-N, NO₃-N, Fe, and Hg increased with increasing application rates. Nitrate below 60 cm was negligible for all plots except the 179 Mg/ha and split application plots in 1994. N leaching losses were below 4-8% of applied TKN-N. Metal concentrations were below the CCME criteria for agricultural and residential soils except for Cu. Well water samples met the Canadian Drinking Water Guidelines.