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Observations from a granitic watershed within a Mediterranean climate reveal the hydrologic and critical zone functioning of a perennial stream headwater and its upslope contributing area within a meadow system in the Sierra Nevada, California. Chemical analysis (diagnostic tools of mixing models, end member mixing analysis, tritium, etc.) and physical data (stream stage, piezometers, soil water, snowpack, etc.) indicate there are two primary pathways of water input into a headwater stream sourced from a mountain meadow. One input is a shallower and younger subsurface pathway with water that resembles snowpack chemistry, and the other a deeper and older subsurface pathway with water that reflects the chemistry of the groundwater derived from the contributing hillslopes. Multi‐year observations reveal that regardless of snowpack amount, during the period of peak hillslope infiltration, shallow and deep pathways in the hillslope behave similarly to initiate headwater streams. However, during summer dry periods, similarities in active pathways within the meadow center are not maintained between high and low snowpack years. With less snow, perennial groundwater discharge within the meadow center is eliminated, becoming only a seasonal source at the meadow's outlet. At the meadow's edge, geophysically observed downslope thinning in saprolite thickness creates reduced lateral transmissivity and initiation points for headwater streams via enhanced groundwater discharge of upslope water. Combined, these findings suggest how loss of snowpack and critical zone structure can together mediate hydrologic function in a wet meadow system in a Mediterranean climate. Creating new understanding about the stability of hydraulic functioning in headwater wet‐meadow systems under a changing climate. Plain Language Summary: A new combination of data sets collected over several years in the Sierra Nevada Mountains of California reveal how smaller wet meadows sustain headwater streamflow, or not, during years of higher or lower snowpack or drought. The location of streamflow generation at these sites may be strongly tied to the shape and characteristics of the weathered bedrock in the shallow subsurface. Findings from this study show how underground flow pathways of water can function to promote year‐round headwater stream sources in mountain environments with wet‐winter, dry‐summer climates, when large snowpacks are present. However, long‐term the prevalence of seasonal surface flooding in these headwater wet meadows may decrease as climate warms and snowpacks continue to decline and become more variable from year to year. Key Points: During low snow years, perennial surface saturation is lost within the meadow, but streamflow is sustained year‐round at the meadow's baseExistence of these groundwater‐fed meadows is related to regular surface saturation caused by downslope thinning of saproliteTogether, this suggests that under continued snowpack decline, regular surface saturation may be lost in mountain meadow systems [ABSTRACT FROM AUTHOR]

The Sierra Nevada Yellow-Legged Frog (Rana sierrae) has generally been viewed as a lake species, but it has increasingly been found in streams, including in the northern part of its range where it is particularly at risk. Developing effective conservation strategies has been hindered by a lack of knowledge of its basic ecological requirements in stream habitats. To address this information gap, we investigated the demography, habitat use, and movements of stream populations of this federally endangered species. We conducted capture–mark–recapture of adults, quantitatively described stream channel and riparian vegetation characteristics, and collected habitat use data at four northern Sierra Nevada mountain streams, counted egg masses at three central Sierra Nevada streams, and radio-tracked individuals at three central and southern Sierra Nevada streams. Stream populations in the northern range were very small with maximum abundances of <15 individuals, and apparent survival probability ranged from 0.57–0.81. In contrast, one southern Sierra Nevada stream had a large count of 547 adults. Egg mass counts ranged from 22–104 per stream. We found frogs in diverse headwater streams ranging from perennial to intermittent flow regimes, pool versus riffle dominated, and low to high channel gradient, and they used diverse microhabitats within these streams. In these stream habitats, frogs moved little over four-day survey periods but were capable of moving longer distances of up to 1248 m over the summer. Conservation and management of the at-risk R. sierrae are most likely to be effective when built on comprehensive quantitative information on basic ecological requirements in all habitats used by the species. [ABSTRACT FROM AUTHOR]

Basic information on species distribution and abundance is often lacking, even for common species. The historically abundant Mountain Yellow-legged ( Rana sp.) and Pacific Treefrog ( Pseudacris sp.) species complexes occur sympatrically and are exposed to similar threats. We evaluated the status of these species complexes on national forest lands in the Sierra Nevada, California as part of a long-term bioregional amphibian monitoring program. To determine occupancy and abundance indices, we surveyed all lentic and a sample of lotic habitats in 208 small watersheds (2-4 km2) selected using an unequal probability design where watersheds occupied previously had a higher likelihood of being selected. For Rana sp., results corroborated other assessments that the taxon has declined substantially. We found breeding activity in an estimated 0.04 (SE = 0.01) of watersheds rangewide, 0.47 (SE = 0.04) of watersheds with locality data from 1990-2001, and 0.02 (SE = 0.03) of watersheds with locality data prior to 1990. Less than 10% of the watersheds contained large numbers of frogs (>500 tadpoles or 100 adults + subadults). In contrast, treefrogs were still distributed widely, with breeding occurring in an estimated 0.25 (SE = 0.01) of watersheds rangewide and 0.95 (SE = 0.02) of watersheds where the taxon was assumed to have occurred historically. The status of Rana sp. is consistent with broad-scale predictions that highly aquatic, specialized anuran species have an increased extinction risk. The delayed recognition of the severity of Rana sp. declines underscores the value of an early warning monitoring system for all species including common ones. [ABSTRACT FROM AUTHOR]

The emerging pathogen, Batrachochytrium dendrobatidis (Bd), causes a fatal amphibian disease called chytridiomycosis, and has impacted amphibian biodiversity. Amphibian declines were first noticed in the 1970s and 1980s, decades before Bd was discovered (1998). In the Sierra Nevada mountains (California, USA), mass die-offs of Yosemite toads (Anaxyrus canorus) occurred in the late 1970s. In this study, we investigated the historical and contemporary Bd presence on A. canorus. We used a retrospective analysis to determine Bd presence/absence on 719 museum specimens collected between 1915 and 2005, and on an additional 1678 samples collected from live animals in the wild (2004–2012). For the 1678 contemporary dataset, we developed a statistical model to identify biotic and abiotic drivers of Bd infection likelihood. We found that: 1) Bd emerged coincident with historical declines; 2) Bd is currently widely distributed throughout the species range; 3) life stage, elevation, and precipitation regime were associated with Bd infection likelihood; and, 4) the juvenile life stage was the most highly infected, with some having Bd infection loads surpassing a mortality threshold identified in other species. In combination, our results suggest that Bd may have played a significant yet unrecognized role in the decline of A. canorus. Additionally, we find evidence that Bd may continue to affect survival and recruitment, depressing population growth and increasing extinction risk in remaining populations. These represent key insights for efforts to recover this species across its historical range and may also be important in hundreds of other species that declined before Bd was discovered. [ABSTRACT FROM AUTHOR]