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 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.     

三亚电厂码头航道泥沙洄淤预测

本文从波浪掀沙和潮流输沙问题入手，对三亚电厂码头二种拟建方案的航道泥沙洄淤进行了预测。预测结果表明：航道的淤积强度呈自北向南递增的趋势，航道的南段淤积最重。在航道的北段，长山村方案淤积较重；在航道的南段，梅村方案的淤积较重。总体上看，二种方案均不属严重淤积。如果根据两种方案的洄淤分布特征对航道走向做适当调整，可望进一步改善航道的防淤效果。     

减少泥沙沿岸搬运 延缓拦门沙的淤积速度──米草生态工程在防治黄河改道中的作用初探

黄河口水动力作用的最显著特点是径流方向（ＷＥ）和潮流方向（ＳＮ）近于垂直。这一特点有利于三角洲的横向扩展［１］，但另一方面，由于沿岸流异常发育，加快了河口沉积速度，促进了拦门沙的发育，使河口处的河床抬高，泄流不畅，不利于黄河口外水下河道的自然下切延伸，最终诱发改道。米草生态工程可以通过防止泥沙沿岸搬运，降低海水含沙量，从而降低拦门沙的发育速度，保护黄河水下河道，最终起到降低河口变动频率，防治黄河改道的作用。