Thomas E. Cleasby

Influence of in‐stream diel concentration cycles of dissolved trace metals on acute toxicity to one‐year‐old cutthroat trout (Oncorhynchus clarki lewisi)

Extrapolating results of laboratory bioassays to streams is difficult, because conditions such as temperature and dissolved metal concentrations can change substantially on diel time scales. Field bioassays conducted for 96 h in two mining-affected streams compared the survival of hatchery-raised, metal-naïve westslope cutthroat trout (Oncorhynchus clarki lewisi) exposed to dissolved (0.1-microm filtration) metal concentrations that either exhibited the diel variation observed in streams or were controlled at a constant value. Cadmium and Zn concentrations in these streams increased each night by as much as 61 and 125%, respectively, and decreased a corresponding amount the next day, whereas Cu did not display a diel concentration cycle. In High Ore Creek (40 km south of Helena, MT, USA), survival (33%) after exposure to natural diel-fluctuating Zn concentrations (range, 214-634 microg/L; mean, 428 microg/L) was significantly (p = 0.008) higher than survival (14%) after exposure to a controlled, constant Zn concentration (422 microg/L). Similarly, in Dry Fork Belt Creek (70 km southeast of Great Falls, MT, USA), survival (75%) after exposure to diel-fluctuating Zn concentrations (range, 266-522 microg/L; mean, 399 microg/L) was significantly (p = 0.022) higher than survival (50%) in the constant-concentration treatment (392 microg/L). Survival likely was greater in these diel treatments, both because the periods of lower metal concentrations provided some relief for the fish and because toxicity during periods of higher metal concentrations was lessened by the simultaneous occurrence each night of lower water temperatures, which reduce the rate of metal uptake. Based on the present study, current water-quality criteria appear to be protective for streams with diel concentration cycles of Zn (and, perhaps, Cd) for the hydrologic conditions tested.

Water-quality trends for selected sites in the Boulder River and Tenmile Creek watersheds, Montana, based on data collected during water years 1997-2013

In the Boulder River and Tenmile Creek watersheds in southwestern Montana, there was intensive mining during a 40-year period after the discovery of gold in the early 1860s. Potential effects from the historic mining activities include acid-mine drainage and elevated concentrations of potentially toxic trace elements from mining remnants such as waste rock and tailing piles. In support of remediation efforts, water-quality monitoring by the U.S. Geological Survey began in 1997 in the Boulder River and Tenmile Creek watersheds and has continued to present (2014). The U.S. Geological Survey, in cooperation with the U.S. Forest Service, investigated temporal trends in water quality at 13 sites, including 2 adit (or mine entrance) sites and 11 stream sites. The primary purpose of this report is to present results of trend analysis of specific conductance, selected trace-elements (cadmium, copper, lead, zinc, and arsenic), and suspended sediment for the 13 sites. For the stream sites, multiple linear regression of constituent concentrations on time, streamflow, and season was used for flow-adjusted trend analysis. For the adit sites, relations between constituent concentrations and streamflow were much weaker than for the stream sites. Thus, streamflow was not included in multiple linear regression trend models for the adit sites, and the trend results represent temporal changes in unadjusted concentrations. The datasets for the sites in the Boulder River and Tenmile Creek watersheds were not specifically designed for trend analysis. All of the study sites have variability in withinyear sampling frequency. However, the within-year sampling frequency was similar among most sites in individual years. Although the study datasets are not ideally suited for precise definition of temporal trends, generally strong similarity in sample-collection characteristics of the datasets among most sites provides a reasonable basis for relative comparisons of trend results among sites. Trend results for the adit sites in the Boulder River watershed (Bullion Mine adit [site 2] and Crystal Mine adit [site 6]) do not provide clear evidence of substantial trending during June 2003 through September 2013. Water quality of the adit sites probably is affected by complex processes that are not well defined in the study datasets. As such, the trend-analysis structure of the study might not be suitable for accurate description of temporal trends in water quality at the two adit sites. Trend results for most stream sites in the Boulder River watershed for water years 2000–13 (water year is the 12-month period from October 1 through September 30 and is designated by the year in which it ends) indicate decreasing trends in flow-adjusted specific conductance, in flow-adjusted concentrations (FACs) for most filtered and unfiltered-recoverable trace elements, and in suspended sediment. Overall, magnitudes of the decreasing trends in FACs of metallic contaminants are largest for Bullion Mine tributary at mouth (site 3), Jack Creek at mouth (site 4), and Cataract Creek at Basin (site 8). For sites 3, 4, and 8, magnitudes of decreasing trends generally ranged from about -5 to -10 percent per year. Notably, the watersheds upstream from sites 3, 4, and 8 have been targeted by substantial remediation activities. Overall, magnitudes of decreasing trends in FACs of metallic contaminants are considered intermediate for Basin Creek at Basin (site 5), High Ore Creek near Basin (site 9), and Boulder River below Little Galena Gulch (site 10). For sites 5, 9, and 10, the magnitudes of the decreasing trends generally ranged from about -2 to -5 percent per year. Decreasing trends in FACs of metallic contaminants for Boulder River above Kleinsmith Gulch (site 1) and Cataract Creek above Uncle Sam Gulch (site 7) generally are minor to small (ranging from about -1 to -2 percent per year) and for most metallic contaminants the changes are within fairly small ranges at generally low FACs. The watershed of site 1 has smaller mining effects than most other study sites. The watersheds of site 1 and 7 have not been targeted by substantial remediation activities. Consideration of trend patterns among all stream sites in the Boulder River watershed provides strong evidence that remediation activities are the primary cause of decreasing trends in metallic contaminants. Trend results for sites in the Tenmile Creek watershed generally are more variable and difficult to interpret than for sites in the Boulder River watershed. Trend results for Tenmile Creek above City Diversion (site 11) and Minnehaha Creek near Rimini (site 12) for water years 2000–13 indicate decreasing trends in FACs of cadmium, copper, and zinc. The magnitudes of the decreasing trends in FACs of copper Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana, Based on Data Collected During Water Years 1997–2013 By Steven K. Sando, Melanie L. Clark, Thomas E. Cleasby, and Elliott P. Barnhart 2 Water-Quality Trends for Selected Sites in the Boulder River and Tenmile Creek Watersheds, Montana generally are moderate and statistically significant for sites 11 and 12. The magnitudes of the decreasing trends in FACs of cadmium and zinc for site 11 are minor to small and not statistically significant; however, the magnitudes for site 12 are moderate and statistically significant. In general, patterns in FACs for Tenmile Creek near Rimini (site 13) are not well represented by fitted trends within the short data collection period, which might indicate that the trend-analysis structure of the study is not appropriate for describing trends in FACs for site 13. The large decreasing trend in FACs of suspended sediment is the strongest indication of change in water quality during the short period of record for site 13; however, this trend is not statistically significant.