We developed photographic techniques to characterize coarse (>2‐mm) and fine (≤2‐mm) streambed particle sizes in 12 streams in Anchorage, Alaska. Results were compared with current sampling techniques to assess which provided greater sampling efficiency and accuracy. The streams sampled were wadeable and contained gravel—cobble streambeds. Gradients ranged from about 5% at the upstream sites to about 0.25% at the downstream sites. Mean particle sizes and size‐frequency distributions resulting from digitized photographs differed significantly from those resulting from Wolman pebble counts for five sites in the analysis. Wolman counts were biased toward selecting larger particles. Photographic analysis also yielded a greater number of measured particles (mean = 989) than did the Wolman counts (mean = 328). Stream embeddedness ratings assigned from field and photographic observations were significantly different at 5 of the 12 sites, although both types of ratings showed a positive relationship with digitized surface fines. Visual estimates of embeddedness and digitized surface fines may both be useful indicators of benthic conditions, but digitizing surface fines produces quantitative rather than qualitative data. Benefits of the photographic techniques include reduced field time, minimal streambed disturbance, convenience of postfield processing, easy sample archiving, and improved accuracy and replication potential.
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iii Contents NATIONAL WATER-QUALITY ASSESSMENT PROGRAM ……………………………………… iv What kind of water-quality information does the NAWQA Program provide? …………… v INTRODUCTION TO THIS REPORT …………………………………………………………… vi SUMMARY OF MAJOR FINDINGS …………………………………………………………… Stream and River Highlights …………………………………………………………… GroundWater Highlights ………………………………………………………………… INTRODUCTION TO THE COOK INLET BASIN ………………………………………………… Diverse topography results in diverse climate and hydrology …………………………… Most of the basin is undeveloped ……………………………………………………… Human activities affect water quality and aquatic biota ………………………………… Most drinking water comes from rivers and streams …………………………………… Results from this study provide a benchmark for measuring changes to come ………… MAJOR FINDINGS …………………………………………………………………………… Water quality in streams and rivers in the Cook Inlet Basin is affected by natural features and human activities ………………………………………………………… Pesticides detected in an urban stream in Anchorage also were detected in urban streams throughout the Nation …………………………………………… Many volatile organic compounds were present in an urban stream in Anchorage at low concentrations ……………………………………………… Nitrate concentrations were low in streams, but phosphorus commonly exceeded criteria for preventing nuisance plant growth ……………………… Concentrations of dissolved organic carbon were highest in streams draining wetlands Urban streams are contaminated by fecal-indicator bacteria ………………………… Streams and rivers in the Cook Inlet Basin are colder than other rivers nationally …… Some streambed and lakebed sediments in Cook Inlet Basin are contaminated by trace elements and organic compounds ………………………………………… Trace elements are present at naturally large concentrations in streambed sediments Concentrations of lead in lakebed sediments have decreased since the 1970s ………… Chemically persistent organic contaminants were detected in urban lakebed sediments but were detected only infrequently in streambed sediments or fish tissues …………………………………………………………………… Semivolatile organic compounds were detected infrequently in streambed sediments Aquatic communities are adversely affected by a variety of natural and human-induced stresses ……………………………………………………………… Degradation of water quality and stream ecosystems occurs early in the process of watershed urbanization …………………………………………… Natural and human factors affect groundwater quality ……………………………………… Low levels of pesticides and volatile organic compounds were detected in ground water …………………………………………………………………… Concentrations of nutrients in ground water were low ………………………………… Concentrations of radon in ground water are a health concern ………………………… Arsenic in ground water is a national concern ………………………………………… STUDY UNIT DESIGN ………………………………………………………………………… REFERENCES CITED ………………………………………………………………………… GLOSSARY …………………………………………………………………………………… APPENDIX-Water-Quality Data from the Cook Inlet Basin in a National Context ………… National Water-Quality Assessment Program The Cook Inlet Basin is one of 51 water-quality assessments init...
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