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Metals

Of 18 metals analyzed, only cadmium, mercury, silver and strontium were not detected in 94 samples. Cadmium was detected in only two samples, mercury in 37 samples, silver was not detected in any of the samples, and strontium was detected in only four samples (Normandeau 1999b).
The metal consistently found in the highest concentrations was manganese. This metal is commonly detected in river sediments due to its high relative abundance in the natural environment.
Concentrations of manganese in individual sediment samples collected from the Lower Snake River during this investigation ranged from 250 ppm to 1,044 ppm with an average concentration of 430 ppm (Normandeau 1999b). In comparison, the concentration of manganese in sediment samples collected upstream of the study area by the USGS (Clark and Maret 1998), ranged from 370 ppm to 1,000 ppm with an average concentration of 564 ppm.
No consistent trends in sediment metal concentrations were observed going downstream from Lower Granite Lake to Lake Sacajawea (Table 19). When compared with the results obtained by the USGS (Clark and Maret 1998) in their investigation of the Snake River upstream of the study area several trends do become apparent. In the USGS investigation bed sediments were collected and analyzed for a broad range of trace elements. Upstream concentrations of arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc (USGS) were lower than downstream concentrations.
Concentration values for metals in sediments are also available for the lower Columbia River drainage basin (Bi-State Study and 1997 Corps Survey). Of the reported values for the metals arsenic, cadmium, copper, lead, mercury, nickel, silver, and zinc in these previous investigations, only the concentration of arsenic and lead were found to be slightly higher for the samples collected from the Lower Snake River during this investigation.
Table 19. Summary of mean metal concentrations for sediment samples collected during Phase 2 (1997) in the Lower Snake River (Corps 1999).

Metal (mg/kg)	Ice Harbor	Lower Monumental	Little Goose	Lower Granite
Arsenic Barium Beryllium Cadmium Chromium Cobalt Copper Lead Manganese Mercury Molybdenum Nickel Selenium Silver Strontium Thallium Vanadium Zinc	6.3 170.6 0.6 ND 20.2 10.9 20.8 10.5 510.1 0.1 0.3 14.2 1.6 ND 0.1 0.2 45.1 52.5	3.9 157.2 0.6 ND 17.7 8.2 16.8 8.8 384.6 0.1 0.2 12.4 1.4 ND 0.1 0.2 37.9 45.0	6.0 192.7 0.7 ND 22.4 11.1 24.8 12.6 475.2 0.1 0.2 15.6 1.3 ND ND 0.2 47.2 57.3	5.2 180.8 0.7 0.1 23.0 12.0 29.8 12.9 408.9 0.1 0.3 16.6 1.5 ND 0.1 0.2 60.9 61.4
Note: all concentrations in mg/kg (ppm) Ice Harbor Dam - Lake Sacajawea Lower Monumental Dam - Lake West Little Goose Dam - Lake Bryan Lower Granite Dam - Lower Granite Lake

Table 20. Summary of Mean Nutrient Concentrations for Sediment Samples Collected During Phase 2 (1997) in the Lower Snake River (Corps 1999).

Parameter	Ice Harbor	Lower Monumental	Little Goose	Lower Granite
Ammonia Total Kjeldahl Nitrogen Nitrate/Nitrite Total Organic Nitrogen Total Organic Matter Phosphorus Bicarbonate Sulfate pH (standard units)	81.3 1317.1 0.7 1235.7 2.5 37.7 7.7 6.9	59.6 1146.1 0.6 1086.7 2.2 38.2 8.4 6.9	64.3 1344.1 0.7 1280.0 3.3 35.0 10.5 7.1	75.7 1746.5 1.4 1671.3 5.2 34.1 17.9 6.8
All results in mg/kg unless otherwise noted Ice Harbor Dam - Lake Sacajawea Lower Monumental Dam - Lake West Little Goose Dam - Lake Bryan Lower Granite Dam - Lower Granite Lake

A total of 84 of the sediment samples were analyzed for a number of chemical parameters, designated as the nutrient group (although not all of the parameters are true nutrients). The sediments were analyzed for: ammonia, total Kjeldahl nitrogen (TKN), nitrogen as nitrate/nitrite, total organic nitrogen, total organic matter, pH, phosphorus bicarbonate and sulfate. The mean reach concentrations for each of the nutrient group parameters are summarized in Table 20. No screening levels have been established under the DMEF (Corps 1998c) for nutrients, and comparison with water quality standards is not appropriate.

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