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

Abstract

Turbidity, total residues, settleable solids, vertical light extinction, and primary production were measured in mined and unmined streams located in the interior highlands of Alaska. Undisturbed streams had low turbidities (< 1 NTU), total residue concentrations averaging 120 mg i1, and undetectable settleable solids. During active mining, turbidity, total residues, and settleable solids levels in a moderately mined stream averaged 170 NTU, 201 mg l1, and <0.1 ml i1, respectively. In a heavily mined stream, turbidity and total residues were two orders of magnitude higher than in unmined streams and settleable solids nearly always exceeded 0.2 ml 1. Vertical extinction coefficients and turbidity were positively correlated. In undisturbed streams gross primary productivity (g-O2m2d) ranged from 0.20 shortly after spring breakup to a maximum of 1.20 in early fall. Productivity in the moderately mined stream was reduced by 50 percent while photosynthetic efficiency doubled. Primary production was undetectable in a heavily mined stream. Maximum standing crops of periphyton measured as chlorophyll a occurred in fall in an undisturbed stream after 13 weeks of exposure and ranged from 4.5 to 11.8 mg-chl a m2. The highest chlorophyll a densities recorded in the moderately mined stream was 3.8 mg m2, and no chlorophyl a was detected in the heavily mined stream. (

Impacts of Open Placer Gold Mining on Aquatic Communities in Rivers of the Khentii Mountains, North-East Mongolia

“…Direct effects for example result from an increase of shear stress causing elevated drift rates of organisms (Berry et al, 2003) or clogging of respiratory organs. Indirect effects for macroinvertebrates result from lowered benthic biofi lm biomass and food quality due to light limitation (Van Nieuwenhuyse & LaPerriere, 1986, Ryan, 1991 and deposition of fi ne sediments. This results in a bottomup control of benthic invertebrate biomass and abundance (Wagener & LaPerriere, 1985;Wood & Armitage, 1997;Fossati et al, 2001) and benthic invertebrates diversity (Quinn et al, 1992).…”

“…Numerous authors have reported on the effects for the ecosystem itself (Newcombe & MacDonald, 1991) or specifi c components, e.g. primary production (Van Nieuwenhuyse & LaPerriere, 1986), macroinvertebrates (Wagener & LaPerriere, 1985) or fi sh (Pentz & Kostaschuk, 1999;McLeay et al, 1987). Although in Mongolia mining is seen to be a major threat to river ecosystems and its biocoenoses (Grayson, 2003;Ocock et al, 2006), little is known about the sitespecifi c impact and the scientifi c basis for targeted regional management given the specifi c situation for Mongolia.…”

Compromised Rivers: Understanding Historical Human Impacts on Rivers in the Context of Restoration

“…Downstream accumulation can reduce the river capacity and cause more flooding. Water quality is degraded by the increase in suspended sediment, which further degrades the aquatic habitat for a variety of species (Wagener andLaPerriere 1985, Van Nieuwenhuyse andLaPerriere 1986). The remaining coarse lag can be too large to provide spawning gravel for fish, whereas the finer sediment carried downstream can preferentially fill pools and cover spawning gravel downstream.…”

Hood River Production Program Review, Final Report 1991-2001.

“…Literature indicated that suspended solids have positive and negative effects on salmonids. Some of these effects include changes in rearing density Sigler et al 1994), distribution (Scrivener et al 1994;Sigler et al 1984;Gregory 1993;Bisson and Bilby 1982;Sevizi and Martens 1992), growth rates (Sigler et al 1984;Murray and Rosenau 1989;Newcombe and MacDonald 1991), foraging behavior and efficiency (Tippets and Moyle 1978;Gregory 1990;Ginetz and Larkin 1975;Gregory and Levings 1998;Murray and Rosenau 1989;Gregory and Northcote 1993), physiological stress (Redding et al 1987, Sigler et al 1984Servizi and Martens 1987;Servizi and Martens 1992), predator avoidance (Gregory 1993;Gregory and Levings 1998) and primary production (Lloyd et al 1987;Van Nieuwenhuyse, 1983;Van Nieuwenhuyse and LaPerriere 1986).…”