| Abstract: | 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 1?1, and undetectable settleable solids. During active mining, turbidity, total residues, and settleable solids levels in a moderately mined stream averaged 170 NTU, 201 mg 1?1, and < 0.1 ml 1?1, 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?1. Vertical extinction coefficients and turbidity were positively correlated. In undisturbed streams gross primary productivity (g-O2m?2d?1) 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 m?2. The highest chlorophyll a densities recorded in the moderately mined stream was 3.8 mg m?2, and no chlorophyl a was detected in the heavily mined stream. |
