This study was conducted to better understand total residual chlorine (TRC) dynamics and ambient toxicity in two chlorine‐contaminated streams in eastern Tennessee. The study used stepwise logistic analysis of Ceriodaphnia survival and water quality factors measured in 169 7‐d chronic toxicity tests of water from four sites in one stream to determine the factors significantly affecting the survival. The 7‐d mean concentrations of TRC and a measure of day‐to‐day variation in TRC concentration in each test were included as dominant factors in explaining Ceriodaphnia mortality. The logistic regression model correctly predicted the mortality or survival in individual Ceriodaphnia in 89.9% of the cases and had a low rate of false positives and false negatives. A simpler pass‐or‐fail model, which used a Ceriodaphnia survival criterion of 60%, yielded slightly better results (correctly predicted outcomes, 91.7%). We also measured TRC concentrations in situ by monitoring at two sites in one of the streams and at one site in the other stream. This monitoring showed that TRC concentrations in both streams varied approximately three‐fold in daily cycles, with TRC concentrations at night greater than those during the day. Laboratory and field experiments indicated that the diel cycles in TRC were probably driven by sunlight and stream periphyton. Two key points emerged from this study. First, the analysis show that logistic regression can be used effectively to relate temporally varying chemical conditions to the outcomes of static‐renewal ambient toxicity tests. In some situations, this method of analysis is more appropriate than other methods, such as ANOVA, that there are used to evaluate dose‐response patterns. Second, diel changes in TRC in streams, apparently caused by sunlight and periphyton, can be large and have important implications for predicting the fate and ecological effects of this widespread contaminant.

Steelhead (Oncorhynchus mykiss) populations have declined throughout their range in the last century and many populations, including those of the Snake River Basin are listed under the Endangered Species Act of 1973. The reasons for their decline are many and complex, but include habitat loss and degradation, overharvesting, and dam construction. The 2008 Biological Opinion calls for an increase in the abundance of female steelhead through an increase in iteroparity (i.e., repeat spawning) and this can be realized through a combination of reconditioning and in-river survival of migrating kelts. The goal of this study is to provide the data necessary to inform fisheries managers and dam operators of Snake River kelt migration patterns, survival, and routes of dam passage. Steelhead kelts (n = 487) were captured and implanted with acoustic transmitters and passive integrated transponder (PIT)-tags at the Lower Granite Dam (LGR) Juvenile Fish Facility and at weirs located in tributaries of the Snake and Clearwater rivers upstream of LGR. Kelts were monitored as they moved downstream through the Federal Columbia River Power System (FCRPS) by 15 autonomous and 3 cabled acoustic receiver arrays. Cabled receiver arrays deployed on the dam faces allowed for three-dimensional tracking of fish as they approached the dam face and were used to determine the route of dam passage. Overall, 27.3% of the kelts tagged in this study successfully migrated to Martin Bluff (rkm 126, as measured from the mouth of the Columbia River), which is located downstream of all FCRPS dams. Within individual river reaches, survival per kilometer estimates ranged from 0.958 to 0.999; the lowest estimates were observed in the immediate forebay of FCRPS dams. Steelhead kelts tagged in this study passed over the spillway routes (spillway weirs, traditional spill bays) in greater proportions and survived at higher rates compared to the few fish passed through powerhouse routes (turbines and juvenile bypass systems). The results of this study provide information about the route of passage and subsequent survival of steelhead kelts that migrated through the Snake and Columbia rivers from LGR to Bonneville Dam in 2013. These data may be used by fisheries managers and dam operators to identify potential ways to increase the survival of kelts during their seaward migrations. Passage Times and Travel Rates Forebay residence and tailrace egress times were consistent among LGR, LGS, and LMN in 2013. Median forebay residence times were less than 2.00 hours at all dams and median tailrace egress times were approximately 0.50 hours. Median project passage time in this study ranged from 2.00 (LMN) to 3.06 (LGR) hours. Overall, passage times were lowest for fish that passed LMN. Of the kelts captured and tagged in the tributaries, those released in Fish Creek, which migrated the greatest distance through fluvial habitats, travelled fastest to Red Wolf Bridge (rkm 743; median = 88.2 vi Many people made valuable contributions to this study and deserve acknowledgment.

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Survival studies of juvenile Pacific salmon Oncorhynchus spp. implanted with acoustic tags have been conducted at hydroelectric dams within the Federal Columbia River Power System in the Columbia and Snake rivers between 2010 and 2014 to assess compliance with the dam passage survival standards stipulated in the 2008 Biological Opinion. For juvenile yearling Chinook Salmon O. tshawytscha and steelhead O. mykiss that migrate downstream in the spring, dam passage survival (defined as survival from the upstream dam face to the tailrace mixing zone) must be ≥ 96%, and for subyearling Chinook Salmon that migrate downstream in summer, dam passage survival must be ≥ 93%. Precision requirement stipulates a standard error ≤ 1.5% (i.e., a 95% confidence interval of ± 3%). A total of 29 compliance tests have been conducted at six of eight main‐stem dams in the Federal Columbia River Power System, using over 109,000 acoustic‐tagged salmonid smolts. Of these 29 compliance studies, 23 met the survival standards and 26 met the precision requirements. Of the six dams evaluated to date, individual survival estimates range from 0.9597 to 0.9868 for yearling Chinook Salmon, from 0.9534 to 0.9952 for steelhead, and from 0.9076 to 0.9789 for subyearling Chinook Salmon. Averages across the six dams exceed the survival standards for all three migrant populations. Received November 9, 2015; accepted February 16, 2016 Published online June 27, 2016

Recovery dynamics in a previously disturbed stream were investigated to determine the influence of a series of remedial actions on stream recovery and to evaluate the potential application of bioindicators as an environmental management tool. A suite of bioindicators, representing five different functional response groups, were measured annually for a sentinel fish species over a 15 year period during which a variety of remedial and pollution abatement actions were implemented. Trends in biochemical, physiological, condition, growth, bioenergetic, and nutritional responses demonstrated that the health status of a sentinel fish species in the disturbed stream approached that of fish in the reference stream by the end of the study. Two major remedial actions, dechlorination and water flow management, had large effects on stream recovery resulting in an improvement in the bioenergetic, disease, nutritional, and organ condition status of the sentinel fish species. A subset of bioindicators responded rather dramatically to temporal trends affecting all sites, but some indicators showed little response to disturbance or to restoration activities. In assessing recovery of aquatic systems, application of appropriate integrative structural indices along with a variety of sensitive functional bioindicators should be used to understand the mechanistic basis of stress and recovery and to reduce the risk of false positives. Understanding the mechanistic processes involved between stressors, stress responses of biota, and the recovery dynamics of aquatic systems reduces the uncertainty involved in environmental management and regulatory decisions resulting in an increased ability to predict the consequences of restoration and remedial actions for aquatic systems.

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