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Scientific Investigations Report 2004-5021

Water-Quality, Biological, and Physical-Habitat Conditions at Fixed Sites in the Cook Inlet Basin, Alaska, National Water-Quality Assessment Study Unit, October 1998-September 2001

National Water-Quality Assessment Program

By Timothy P. Brabets and Matthew S. Whitman



The Cook Inlet Basin study unit of the U.S. Geological Survey National Water-Quality Assessment Program comprises 39,325 square miles in south-central Alaska. Data were collected at eight fixed sites to provide baseline information in areas where no development has taken place, urbanization or logging have occurred, or the effects of recreation are increasing. Collection of water-quality, biology, and physical-habitat data began in October 1998 and ended in September 2001 (water years 1999-2001).

The climate for the water years in the study may be categorized as slightly cool-wet (1999), slightly warm-wet (2000), and significantly warm-dry (2001). Total precipitation was near normal during the study period, and air temperatures ranged from modestly cool in water year 1999 to near normal in 2000, and to notably warm in 2001. Snowmelt runoff dominates the hydrology of streams in the Cook Inlet Basin. Average annual flows at the fixed sites were approximately the same as the long-term average annual flows, with the exception of those in glacier-fed basins, which had above-average flow in water year 2001.

Water temperature of all streams studied in the Cook Inlet Basin remained at 0 oC for about 6 months per year, and average annual water temperatures ranged from 3.3 to 6.2 degrees Celsius. Of the water-quality constituents sampled, all concentrations were less than drinking-water standards and only one constituent, the pesticide carbaryl, exceeded aquatic-life standards. Most of the stream waters of the Cook Inlet Basin were classified as calcium bicarbonate, which reflects the underlying geology. Streams in the Cook Inlet Basin draining areas with glaciers, rough mountainous terrain, and poorly developed soils have low concentrations of nitrogen, phosphorus, and dissolved organic carbon compared with concentrations of these same constituents in streams in lowland or urbanized areas. In streams draining relatively low-lying areas, most of the suspended sediment, nutrients, and dissolved organic carbon are transported in the spring from the melting snowpack. The urbanized stream, Chester Creek, had the highest concentrations of calcium, magnesium, chloride, and sodium, most likely because of the application of de-icing materials during the winter. Several volatile organic compounds and pesticides also were detected in samples from this stream.

Aquatic communities in the Cook Inlet Basin are naturally different than similar sites in the contiguous United States because of the unique conditions of the northern latitudes where the Cook Inlet Basin is located, such as extreme diurnal cycles and long periods of ice cover. Blue-green algae was the dominant algae found at all sites although in some years green algae was the most dominant algae. Macroinvertebrate communities consist primarily of Diptera (true flies), Ephemeroptera (mayflies), and Plecoptera (stoneflies). Lowland areas have higher abundance of aquatic communities than glacier-fed basins. However, samples from the urbanized stream, Chester Creek, were dominated by oligochaetes, a class of worms. Most of the functional feeding groups were collector-gatherers. The number of taxa for both algae and macroinvertebrates were highest in water year 2001, which may be due to the relative mild winter of 2000—2001 and the above average air temperatures for this water year.

The streams in the Cook Inlet Basin typically are low gradient. Bank substrates consist of silt, clay, or sand, and bed substrate consists of coarse gravel or cobbles. Vegetation is primarily shrubs and woodlands with spruce or cottonwood trees. Canopy angles vary with the size of the stream or river and are relatively low at the smaller streams and high at the larger streams. Suitable fish habitat, such as woody debris, pools, cobble substrate, and overhanging vegetation, is found at most sites.

Of the human activities occurring in the fixed site basins — high recreational use, logging, and urbanization — based on the multiple lines of evidence used in the NAWQA program, only urbanization was noted to have measurably affected the water quality. High recreational use and logging may be affecting site-specific areas within the Kenai River and Ninilchik River basins, respectively, but these effects, if any, were not seen at the respective sampling sites.


Methods of Data Collection and Analysis
Description of Study Area
Climate of the Cook Inlet Basin
Water-Quality, Biological, and Physical-Habitat Conditions at Fixed Sites
Comparisons Among All Fixed Sites
Summary and Conclusions
References Cited
Appendix A
Appendix B
Appendix C

This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

Download the report (PDF, 6.3 MB)

Other downloadable items:

Algal taxa and densities of richest-targeted-habitat (RTH) samples collected at fixed sites in the Cook Inlet Basin study unit. (table 15, 124 KB)


Algal taxa and densities of depositional-targeted-habitat (DTH) samples collected at fixed sites in the Cook Inlet Basin study unit, Alaska. (table 16, 131 KB)


Algal taxa present for qualitative-multi-habitat (QMH) samples collected at fixed sites in the Cook Inlet Basin study unit, Alaska. (table 17, 226 KB)


Macroinvertebrate taxa and densities for richest-targeted-habitat (RTH) samples collected at fixed sites in the Cook Inlet Basin study unit, Alaska. (table 18, 84 KB)


Macroinvertebrate taxa for qualitative-multi-habitat (QMH) samples collected at fixed sites in the Cook Inlet Basin study unit, Alaska. (table 19, 124 KB)


Fish taxa and numbers of fish collected at fixed sites in the Cook Inlet Basin study unit, Alaska. (table 20, 34 KB)


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For additional information contact:

Alaska Science Center, Water Resources Office
U.S. Geological Survey
4230 University Drive, Suite 201
Anchorage, AK 99508-4664

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