GOLD‐MINING EFFECTS ON HEAVY METALS IN STREAMS, CIRCLE QUADRANGLE, ALASKA¹

Abstract

Placer gold mining, which extracts gold from buried or exposed alluvia, is often conducted on or near streams. Such mining has the potential to adversely affect water quality. Other heavy metals associated with the gold (such as arsenic, cadmium, lead, zinc, and copper) may be freed to enter streams. Mercury may also enter streams if miners are using it to recover fine particles of gold. These heavy metals are toxic and thus may be harmful to the aquatic life of the streams receiving effluent or runoff from placer mines. In 1982 we sampled two streams intensively ‐ one heavily mined and one unmined ‐ for total recoverable arsenic, mercury, lead, zinc, and copper. Only mercury was not significantly higher in concentration in the mined streams. In 1983 we sampled two stream pairs three times, and 10 other sites at least once, for total and dissolved arsenic, cadmium, mercury, lead, zinc, and copper. Mercury and cadmium were not significantly elevated in mined streams, but the concentrations of total arsenic, lead, zinc, and copper, and dissolved arsenic and zinc were significantly higher in streams below active placer mining sites than in these that were not being mined or those that had never been mined. Additionally, total arsenic, lead, zinc, and copper and dissolved arsenic and copper became elevated after mining began in 1983 on a previously unmined stream.

EFFECTS OF PLACER MINING DISCHARGE ON HEALTH AND FOOD OF ARCTIC GRAYLING1

“…Our objectives were to document changes in food habits, survival, and well-being as a result of exposure of the fish to placer mining discharges; and to relate any effects, direct or indirect, to the concentration of placer mining sediments. Placer mining discharge results in complex changes in heavy metal concentrations , water quality, and hydrology (Bjerklie and LaPerriere, 1985). The relative importance of these factors on grayling ecology was not the scope of our study nor, to our knowledge, that of related studies.…”

“…Other characteristics of water were also affected downstrEam by the placer mining effluent. Bjerklie and LaPerriere (1985) found total iron to be Twelvemile Creek, in 1982 and1983. Other heavy metals, particularly dissolved arsenic, zinc, and copper, which are more critical to aquatic biota, were elevated downstream by placer mining effluents in the same study area during 1982area during and 1983area during (LaPerriere, et al, 1985.…”

“…Twelvemile Creek, the unmined stream, had no detectable settleable solids.Turbidities were considerably higher in Birch Creek than in Twelvemile Creek; during cage experiments, they often exceeded 1000 NTU during the day and peaked at 2000-3000 NTU at midnight. Total residue averages were seven times higher in Birch Creek than in Twelvemile Creek in 1983 and often ten times higher in 1982(Bjerklie and LaPerriere, 1985). of Placer Mining Discharge on Health and Food of Arctilc Grayling…”

Physical and biological controls on fine sediment transport and storage in rivers

“…Biofilms comprise a mixture of heterotrophic (e.g., fungi, bacteria, protozoa) and autotrophic (e.g., cyanobacteria, algae, chemosynthetic bacteria) organisms, with many of the latter highly dependent on light. As such, the attenuation of light caused by increased sediment loads (either suspended or deposited) adversely affects the photosynthetic component of biofilms (Vermaat & De Bruyne, ), shifting the balance of these two traits, and thus the net primary production of affected biofilms (LaPerriere et al, ; Lloyd, Koenings, & Laperriere, ; Rivier & Seguier, ; Van Nieuwenhuyse & LaPerriere, ). For the sessile photosynthetic components, the absence of light caused by burial beneath depositing sediment can be catastrophic and the only option can be to produce resting stages to endure the period until erosion brings them to the surface once more.…”

EFFECTS OF PLACER GOLD MINING ON PRIMARY PRODUCTION IN SUBARCTIC STREAMS OF ALASKA1

“…Anchor and frazil ice begin forming in late September. Detailed data on water quality and hydrology are given by Bjerklie and LaPerriere (1985), LaPerriere, et al (1985), Peterson (1973), and Van Nieuwenhuyse (1983); a selected portion is summarized in Table 1.…”