A two—part study was undertaken to investigate the adaptive value of carotenoid pigmentation to calanoid copepods and the costs in terms of visually selective predation. A comparative survey of copepod populations documented the distribution of pigmented forms and suggested the importance of water temperature, lake depth, and elevation to copepod pigmentation. Estimates of photodamaging irradiance and yearly temperature regime were constructed from the primary survey variables and compared for their correlation with copepod pigmentation. Yearly temperature regime is directly related to elevation and is most important in explaining variation in copepod pigmentation. Copepods are most darkly pigmented in the coldest lakes. Phytoplankton pigment concentration is not limiting to the pigmentation of calanoid copepods. Laboratory experiments demonstrated that carotenoid pigments can be photoprotective to calanoid copepods exposed to strong sunlight, yet field experiments failed to demonstrate photodamage when copepods were allowed to migrate vertically in enclosures. Respirometry experiments have shown that pigmented copepods respire faster in the light than in the dark, while unpigmented copepods do not. This metabolic facilitation by light helps to explain literature accounts of the sunlight—related behavior of pigmented zooplankton. Laboratory and field experiments with predators confirmed that vertebrate predators select pigmented calanoid copepods, but that common invertebrate predators are not visually selective. Trout are highly visually selective predators. Although salamanders are visually selective in laboratory enclosures, they are inefficient at capturing calanoid copepods in nature. Pigments are adaptive to calanoid copepods because they facilitate a metabolic increase and provide photoprotection when the animals are illuminated. Pigments are rarely found in the zooplankton, however, because zooplankton are continuously exposed to predation by visually selective predators. In cold environments with short growing seasons, as at high elevations, the advantages of pigmentation at least partially outweigh the costs in terms of selective predation, thus shifting the balance in favor of pigmentation.

We used scuba observations to determine summer habitat use and the effects of piers on the littoral‐zone fish community in Lake Tahoe, California–Nevada. Habitat complexity declined with depth. Over 50% of the littoral zone less than 2 m deep was composed of complex boulder substrates, but this substrate represented less than 10% of the habitat between 10 and 18 m deep. A severe drought lowered the surface elevation of the lake 2 m and reduced the wetted complex rocky habitat by 20% between the 0‐ and l0‐m isobaths (referenced to the mean lake level of 1,899 m above sea level). The dominant littoral‐zone fish, adult Lahontan redsides Richardsonius egregius, were found at depths ranging from 1–10 m over substrates, but at somewhat greater depths (3–10 m) over cobble–boulder substrates. Juvenile Lahontan redsides were concentrated around boulders at depths of 1–3 m, and their densities were much lower than the densities of adults. Adult tui chub Gila bicolor and rainbow trout Oncorhynchus mykiss were also most often associated with complex boulder habitats. The daytime densities and species composition of fishes associated with piling‐supported piers did not differ significantly from adjacent no‐pier areas, whereas the densities of Lahontan redsides, tui chubs, Lahontan speckled dace Rhynichthys osculus robustus, and Tahoe suckers Catostomus tahoensis associated with the complex structure of rock‐crib piers were significantly higher than in adjacent no‐crib areas. Fish density increased 5–12‐fold at night relative to the observed daytime densities in the pier, rock‐crib, no‐pier, and no‐crib transects.

During summer 1980, dense swarms of the calanoid copepod Diaptomus tyrrelli formed during midday in several areas of the nearshore surface of Lake Tahoe, California‐Nevada. Swarms were most consistently found immediately adjacent to rocks in pools protected from wave action. Swarms were as dense as 11,354 copepods·liter−1 and composed primarily of adult males. They were not formed passively by currents. Swarming copepods have greater mating success than midlake copepods. Swarming may offer some protection from fish predation. The high densities and small size of swarms indicate that they could severely alter estimates of zooplankton density when they are included in integrated net tows.

We examined land‐use and water quality monitoring data for 10 watersheds of tributary streams to Lake Tahoe, California‐Nevada, to describe relationships between watershed disturbance and water quality degradation from nonpoint sources. Discharge‐weighted annual average concentrations of nitrate (as NO3‐N), soluble P, total P and suspended sediment were plotted against the proportion of each watershed represented as disturbed and imperviously covered land of various land‐use classes. Comparisons between land‐use and runoff water quality demonstrated significant relationships between increased coverage and disturbance in the watersheds and decreased water quality. The concentrations of NO3‐N, total P, and suspended sediment in the streams increased significantly with the disturbance of high hazard lands (erodible soils, steep slopes, stream environment zones). Increased disturbance of lower hazard lands (less erodible soils) resulted in increases in the concentrations of soluble and total P. The patterns of significance and slopes of the relationships demonstrated increased nonpoint source water quality degradation with increased land disturbance in these Sierra Nevada watersheds.

Severe effects of selenium (Se) occurred among birds feeding and nesting at Kesterson Reservoir (San Joaquin Valley, California, USA) in 1983 to 1985. This paper describes the integration of site monitoring, risk assessment, and management actions conducted after the effects of Se were discovered. Selenium contamination of the site occurred over just a few years, but actions to resolve the contamination issues required >20 y. The reservoir, a series of 12 ponds totaling about 1280 acres (518 hectares), served for storage and evaporation of subsurface agricultural drainage. Selenium concentrations in reservoir inflow in 1983 were about 300 µg/L, primarily as selenate; within the ponds it was biogeochemically reduced to other inorganic and organic forms and bioaccumulated by biota or deposited to sediments. An estimated 9000 kg of Se were delivered to Kesterson in 1981–1986. A 1985 order required cleanup and abatement of the reservoir, so the United States Bureau of Reclamation and the US Department of the Interior undertook actions and studies to reduce hazards to birds. In 1988, about 1 million cubic yards (764 500 m3) of soil were used to fill portions of the reservoir, transforming it into terrestrial habitat. Intensive monitoring began in 1989 to assess the impact of the reservoir on wildlife, provide a basis for adjusting site management, verify the effectiveness of cleanup actions, and provide a basis for modifying future monitoring. Monitoring continued until 2014, with modifications and management actions based on results of 2 risk assessments (1993 and 2000). Monitoring results in 2013–2014 showed that Se concentrations were relatively stable over time and risks to wildlife were low. From the initial problem discovery to the conclusion of actions taken to remediate the site, combining responsive, reactive, and adaptive monitoring; modeling; risk assessment; and mitigation actions proved effective in solving the problem so that risks to wildlife were reduced to minimal levels. Integr Environ Assess Manag 2020;16:257–268. © 2019 SETAC