Introduction

In September 2002, fish on the west side of Hood Canal near Hoodsport, Washington (fig. 1) were observed to be under stress from low concentrations of dissolved oxygen. This observation prompted the Washington State Department of Fish and Wildlife to temporarily close parts of Hood Canal to some types of fishing during October. In 2003, low dissolved‑oxygen conditions worsened, some fish kills were observed as early as June, and about 30 percent of rockfish were killed by October (http://www.hoodcanal.washington.edu/documents/document.jsp?id=1453, accessed Nov. 15, 2005). Low concentrations of dissolved oxygen in Hood Canal during late summer and early autumn have been observed as far back as the 1950s (Collias and others, 1974). Available data suggest that even though dissolved-oxygen concentrations vary from year to year, dissolved-oxygen conditions recently have been more frequently low, and the duration of low concentrations is more persistent (http://www.hoodcanal.washington.edu/observations/historicalcomparison.jsp, accessed January 29, 2006).

In 2003, the U.S. Geological Survey (USGS) was asked by Congress to study the causes of low dissolved-oxygen concentrations in Hood Canal in collaboration with the Hood Canal Dissolved Oxygen Program (HCDOP). The HCDOP is a partnership of organizations that monitor and study Hood Canal, and evaluate potential corrective actions to address the low dissolved oxygen problem. There are more than 30 HCDOP partners, among them Puget Sound Action Team; Washington State Departments of Ecology, Health, Fish and Wildlife, and Natural Resources; Jefferson, Kitsap and Mason Counties; Skokomish and Port Gamble S’Klallam Tribes; Hood Canal Coordinating Council; Hood Canal Salmon Enhancement Group; University of Washington; and the USGS. After consultation with the HCDOP partners, the USGS began to assess the loadings of nitrogen-based compounds to Hood Canal. A study focusing on the nutrient input from surface water landward of The Great Bend was initiated in 2004 because the instances of low dissolved oxygen are most severe in this region. As part of the study, surface water-quality data were collected in the southern part of Hood Canal drainage area.

Purpose and Scope

Samples were collected during summer base-flow conditions and analyzed for nutrients, major ions, organic carbon, suspended sediment, and the ratio of ¹⁵N to ¹⁴N (δ¹⁵N) of nitrate to obtain a better understanding of the nutrient concentrations in the rivers that are discharging into the southern part of Hood Canal as well as possible sources of those nutrients. Samples also were collected during spring rain events along the Union River, Tahuya River, Mission Creek, and three smaller drainage basins to assess whether nutrient concentrations are elevated in surface water due to increased runoff. This report examines the longitudinal distribution of nutrients, major ions, organic carbon, suspended sediment, and δ¹⁵N collected by the USGS along the Union, Tahuya, and Skokomish Rivers during summer base-flow conditions as well as concentrations of nutrients from six sites located along various rivers and creeks in the southern part of the Hood Canal during the spring.

Acknowledgments

The authors would like to thank U.S. Geological Survey Washington Water Science Center staff Joseph Gilbert, Greg Justin, Karen Payne, and student intern Matt Groce for their assistance in locating sites and sample collection.

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