COPPER, CADMIUM, AND ZINC CONCENTRATIONS IN JUVENILE CHINOOK SALMON AND SELECTED FISH-FORAGE ORGANISMS (AQUATIC INSECTS) IN THE UPPER SACRAMENTO RIVER, CALIFORNIA MICHAEL K. SAIKI1∗ , BARBARA A. MARTIN1 , LARRY D. THOMPSON2 and DANIEL WELSH2 1 U.S. Geological Survey, Biological Resources Division, Western Fisheries Research Center, Dixon Duty Station, 6924 Tremont Road, Dixon, California 95620, U.S.A.; 2 U.S. Fish and Wildlife
Service, Sacramento Fish and Wildlife Office, 2800 Cottage Way, Suite W-2605, Sacramento, California 95825, U.S.A. (∗ author for correspondence, e-mail: [email protected]
(Received 11 April 2000; accepted 11 November 2000)
Abstract. This study assessed the downstream extent and severity of copper (Cu), cadmium (Cd), and zinc (Zn) contamination from acid mine drainage on juvenile chinook salmon (Oncorhynchus tshawytscha) and aquatic insects over a roughly 270-km reach of the Sacramento River below Keswick Reservoir. During April–May 1998, salmon were collected from four sites in the river and from a fish hatchery that receives water from Battle Creek. Salmon from river sites were examined for gut contents to document their consumption of various invertebrate taxa, whereas salmon from river sites and the hatchery were used for metal determinations. Midge (Chironomidae) and caddisfly (Trichoptera) larvae and mayfly (Ephemeroptera) nymphs were collected for metal determinations during April–June from river sites and from Battle and Butte creeks. The fish hatchery and Battle and Butte creeks served as reference sites because they had no history of receiving mine drainage. Salmon consumed mostly midge larvae and pupae (44.0%, damp-dry biomass), caddisfly larvae (18.9%), Cladocera (5.8%), and mayfly nymphs (5.7%). These results demonstrated that insects selected for metal determinations were important as fish forage. Dry-weight concentrations of Cu, Cd, and Zn were generally far higher in salmon and insects from the river than from reference sites. Within the river, high metal concentrations persisted as far downstream as South Meridian (the lowermost sampling site). Maximum concentrations of Cd (30.7 µg g−1 ) and Zn (1230 µg g−1 ), but not Cu (87.4 µg g−1 ), in insects exceeded amounts that other investigators reported as toxic when fed for prolonged periods to juvenile salmonids. Keywords: Chironomidae, Ephemeroptera, fish gut contents, heavy metals, Oncorhynchus tshawytscha, Trichoptera
1. Introduction For over a century, fish kills from metal pollution have occurred in the Sacramento River at or below the mouth of Spring Creek, a small tributary that receives runoff from Iron Mountain Mine in Shasta County, California (Finlayson and Wilson, 1979). In 1963, the Spring Creek Debris Dam (which forms Spring Water, Air, and Soil Pollution 132: 127–139, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.
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Creek Reservoir) was constructed partly to control the flow of acid-mine wastewater into Keswick Reservoir, an afterbay for Shasta Dam on the Sacramento River. Since then, remedial activities have occurred at Iron Mountain Mine to reduce the production of acid mine drainage and to remove dissolved metals by treating some of the most contaminated waters. Although flow from Spring Creek Debris Dam is regulated specifically to prevent acute heavy-metal toxicity in salmonids inhabiting the Sacramento River, uncontrolled flows still occur during severe rainstorms (usually in winter or spring) when flood waters overtop the dam. During such events, dissolved concentrations of copper (Cu), cadmium (Cd), and zinc (Zn) measured at Keswick Dam can exceed toxic thresholds for juvenile chinook salmon, Oncorhynchus tshawytscha, and steelhead, O. mykiss (Finlayson and Wilson, 1989). However, high body burdens of Cu, Cd, and Zn have been documented in aquatic insects during low-rainfall periods (summer and fall) when low concentrations of dissolved metals typically occur in the Sacramento River below Keswick Dam (Saiki et al., 1995; Cain et al., 2000). Laboratory studies indicate that juvenile salmonids can suffer high mortality, poor growth, and other adverse biological effects when fed metal-contaminated natural foods (Woodward et al., 1994, 1995). Moreover, diet-borne metals can be more important than water-borne metals in reducing fish survival and growth (Woodward et al., 1994). These findings suggest that juvenile salmonids in the Sacramento River could be exposed year-around (not just during the rainy season) to harmful levels of Cu, Cd, and Zn through consumption of metal-contaminated forage organisms. The purpose of this study was to gather additional field evidence for the U.S. Fish and Wildlife Service’s Natural Resources Damage Assessment Program as a first step in assessing damages to the chinook salmon fishery from metal pollution caused by acidic drainage from Iron Mountain Mine. Specific objectives of this study were (i) to identify the most important fish-forage organisms consumed by juvenile chinook salmon by documenting their gut contents, and (ii) to determine the spatial (longitudinal) extent and severity of Cu, Cd, and Zn contamination by measuring the concentrations of these metals in juvenile salmon and their forage (aquatic insects).
2. Study Area A total of six sampling sites was established on the Sacramento River system in Shasta, Tehama, Sutter, and Butte counties (Figure 1). Four sites were on the Sacramento River below Keswick Reservoir as follows (in longitudinal order from upstream to downstream): within the City of Redding (Lake Redding, latitude 40◦ 35 40 N, longitude 122◦ 23 55 W); adjacent to Jellys Ferry Road (Jellys Ferry, latitude 40◦ 20 54 N, longitude 122◦ 10 55 W); near the City of Corning (Woodson Bridge, latitude 39◦ 54 31 N, longitude 122◦ 05 29 W); and near the City of Me-
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Figure 1. Map of the study area.
ridian (South Meridian, latitude 39◦ 06 47 N, longitude 121◦ 54 12 W). Woodson Bridge is located about 20 kilometers above Hamilton City, the downstream extent to which water temperature is believed to be suitable for spawning by chinook salmon (U.S. Fish and Wildlife Service-California Department of Fish and Game, 1987). The remaining two sites – Battle Creek at Jellys Ferry Road (Battle Creek, latitude 40◦ 23 23 N, longitude 122◦ 10 43 W) and Butte Creek at the Upper Butte Basin Wildlife Area (Butte Creek, latitude 39◦ 22 41 N, longitude 121◦ 53 08 W) – had no documented history of heavy metal contamination and served as reference sites. Due to concerns over rare or endangered species, we were not permitted to sample fish from Battle and Butte creeks. However, juvenile chinook salmon were obtained from the Coleman National Fish Hatchery (latitude 40◦ 24 10 N, longitude 122◦ 08 28 W), which receives water from Battle Creek, to represent reference conditions.
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3. Materials and Methods
Juvenile chinook salmon were collected during April–May 1998 from the Sacramento River for gut analysis and heavy metal determinations, and from the Coleman National Fish Hatchery for heavy metal determinations. In addition, aquatic insects were collected during April–June 1998 from the river and from Battle and Butte creeks for heavy metal determinations. This time frame coincided with or immediately followed the rainy season when the Sacramento River can receive uncontrolled spills of metal-laden acid-mine drainage from Spring Creek Debris Dam. Juvenile chinook salmon were captured with a small-mesh beach seine operated by U.S. Fish and Wildlife Service personnel from the Northern Central Valley Fishery Resource Office in Red Bluff, California, and the Sacramento-San Joaquin Estuary Fishery Resource Office in Stockton, California. According to proposed daily fork length criteria for the four runs of chinook salmon occurring in the Sacramento River (S. Greene, Environmental Services Office, California Department of Water Resources, Sacramento, unpublished data), fish used in this study were mostly progeny of fall-run adults. For gut analysis, the first 25 fish from each site were weighed and measured for total length, then preserved in 10% formalin. About four days later, the fish were transferred into 70% isopropyl alcohol and stored until gut analysis could be performed. Gut analysis was performed by using dissection to remove stomach contents from the anterior end of the esophagus to the pyloric sphincter, identifying food items with the help of taxonomic keys (Usinger, 1971; Merrit and Cummins, 1978; Pennak, 1978), then measuring the damp-dry biomass of each taxonomic category. For heavy metal determinations, juvenile chinook salmon were weighed and measured, then as many as 15 individuals were divided into composite samples containing five fish each. The composite samples were rinsed in site water to remove mud or other debris, then wrapped in clean plastic sheets (Saran Wrap) and double-bagged in plastic ziplock bags. The bagged samples were chilled on wet ice until returning from the field (within 6 hr), at which time they were stored frozen in a chest freezer (–10 ◦ C) until shipment to the analytical laboratory. Three representative taxa of immature aquatic insects – midges (Chironomidae), mayflies (Ephemeroptera), and caddisflies (Trichoptera) – were chosen for heavy metal determinations because they occurred in the study area (Saiki et al., 1995; Cain et al., 2000) and are generally important as prey items for juvenile chinook salmon (Moyle, 1976; Merz and Vanicek, 1996). Aquatic insects were collected by placing small-mesh dipnets and screen barrier (kick) nets immediately downstream from a riffle, then overturning rocks or vigorously shaking submerged logs and other debris. Midges, mayflies, and caddisflies were collected with plastic forceps by hand-sorting through the material retained by the downstream nets. These samples were rinsed in site water to remove loosely associated debris, then wrapped
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in plastic sheets (Saran Wrap), double-bagged in plastic ziplock bags, chilled on wet ice, and stored frozen after returning from the field. Samples of juvenile chinook salmon and aquatic insects were shipped on dry ice to a federally approved contract laboratory (Research Triangle Institute, Research Triangle Park, NC) for determination of moisture content and Cu, Cd, and Zn concentrations. The samples were prehomogenized in a food processor, then a portion of each sample was freeze-dried for determination of moisture content. Samples were homogenized by grinding with a mill, then passed through a 1-mm (mesh size) screen. Homogenized subsamples were digested in concentrated nitric acid (Baker Instra-analyzed Reagent for trace metals analysis, 70.0–71.0% HNO3) and heat from a water bath at 85±2 ◦ C for 45 min, followed by addition of hydrogen peroxide and reheating for an additional 15 min. After cooling, the subsamples were placed into a CEM MDS-2000 microwave oven to concentrate the digestate, then deionized water was added to achieve the desired volume. Each digestate was then subjected to atomic spectroscopic determination of Cu, Cd, and Zn by using either a Leeman Labs Plasma Spec I sequential spectrometer or an ES2000 simultaneous spectrometer. Quality assurance measures included analyses of procedural blanks, duplicate samples, spiked samples, and standard reference materials. Measurements of procedural blanks yielded the following results: Cu, 0.000–0.0500 µg; Cd, 0.000 µg; and Zn, 0.050–0.220 µg. For duplicate samples, relative percent difference (RPD) values varied as follows: for percent moisture,