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At least 163 records · Page 9Linked to original sources

USGS1988

A climatic-limnologic model of diatom succession for paleolimnological interpretation of varved sediments at Elk Lake, Minnesota

Sediment traps placed in the profundal region of Elk Lake, north central Minnesota during the 1979 spring and 1983-84 fall and spring seasons monitored seasonal diatom production for two climatically distinctive periods. The spring of 1979 was one of the coldest and wettest on record. Ice out at Elk Lake was 10 days later than average, and spring circulation was short. Fragilaria crotonensis dominated the late spring and early summer diatom production in association with Synedra and Cyclotella species, perhaps because rates of phosphorus supply were low compared to silica. The winter of 1983-84 was drier than usual, and the early but cold spring of 1984 caused ice out at Elk Lake to be about 1 week earlier than normal. Spring storms promoted a long and full circulation that allowed Stephanodiscus minulutus to bloom, presumably in response to increased phosphorus loading related to deep and vigorous circulation. The two dominant diatoms in Elk Lake, F. crotonensis and S. minutulus may reflect climatic patterns that control lake circulation. The climatically regulated occurrence of these diatoms is generally, but not specifically, comparable to their distribution in lake surface sediments throughout Minnesota. A combination of regional and lake-specific studies on the controls of diatom succession and distribution provides climatic insights for interpreting paleolimnogical records of diatoms. ?? 1988 Kluwer Academic Publishers.

Journal of Paleolimnology↗

USGS1994

Relationships between atmospheric circulation and snowpack in the Gunnison River basin, Colorado

In this study, winter mean 700 mbar height anomalies over the eastern North Pacific Ocean and the western USA are related to variability in snowpack accumulations measured on or about 1 April at 21 snowcourse stations within and near the Gunnison River basin in Colorado. Results indicate that lower than normal snowpack accumulations are primarily associated with positive 700 mbar height anomalies (anomalous anticyclonic circulation) over the western USA. Moist air from the Pacific Ocean is moved to the north of the western USA along the western margin of the anomalous anticyclonic circulation. In contrast, higher than normal snowpack accumulations are associated with negative 700 mbar height anomalies (anomalous cyclonic circulation) over the western USA and over most of the eastern North Pacific Ocean. The anomalous cyclonic circulation over the western USA enhances the movement of moisture from the Pacific Ocean into the southern and central parts of the West. Results also indicate that variability in winter mean 700 mbar height anomalies can explain over 50% of the variability in snowpack accumulations in the Gunnison River basin. The significant linear relationships between 700 mbar height anomalies and snowpack accumulations in the Gunnison River basin can be used in conjunction with general circulation model simulations of 700 mbar height anomalies for future climatic conditions to estimate future snowpack accumulations in the Gunnison River basin.

Journal of Hydrology↗

USGS2020

Spatial and temporal diving behavior of non-breeding common murres during two summers of contrasting ocean conditions

Successful foraging of marine predators depends on environmental conditions, which also influence prey availability. Neutral or negative El Niño Southern Oscillation and Pacific Decadal Oscillation ocean conditions during the summer of 2013 and strongly positive conditions during the summer of 2015 in the northern California Current System provided a case study to evaluate a marine predator's response to anomalously warm conditions. We used satellite transmitters with saltwater switches to track movements and estimate dive behavior among non-breeding common murres (Uria aalge) off Oregon prior to and during a marine heatwave. We quantified differences in space-use between years, applied linear mixed models to determine environmental influences (e.g. sea surface temperature, surface salinity, chlorophyll a, ocean depth, and calendar date) on dive frequency and dive duration, and contrasted dive activity between time of day, year, and sexes. The majority of birds dispersed away from capture locations, which were situated near the southern range limit of their population. In both years, murres used the Salish Sea and the Columbia River plume; however, murres spent more time foraging in the Columbia River plume and in continental slope habitat during the marine heatwave of 2015. During 2015, dive frequency was reduced, and dive durations were almost twice as long during daytime indicating deeper or more dispersed prey. Increased dive frequency was positively associated with temperature, chlorophyll a, and crepuscular periods. Cluster analysis of dive activity and the top-ranked predictive dive duration model revealed associations between longer-duration dives and decreased dive frequency, marine slope habitat, and cooler ocean temperatures. Murres were relatively inactive throughout the night and we found no sex differences in dive activity. Changes in common murre foraging tactics were associated with ocean warming and revealed selectivity in spatial and temporal use of foraging habitats. Productive marine features including the Columbia River plume provided refuge for murres during apparently poor ocean conditions associated with the marine heatwave. Identifying refuge areas used by highly mobile species experiencing varying ocean conditions is critical for adaptive marine spatial planning that can accommodate a changing ocean climate.

California↗

USGS2009

Trends in streamflow in the Yukon River Basin from 1944 to 2005 and the influence of the Pacific Decadal Oscillation

Streamflow characteristics in the Yukon River Basin of Alaska and Canada have changed from 1944 to 2005, and some of the change can be attributed to the two most recent modes of the Pacific Decadal Oscillation (PDO). Seasonal, monthly, and annual stream discharge data from 21 stations in the Yukon River Basin were analyzed for trends over the entire period of record, generally spanning 4-6 decades, and examined for differences between the two most recent modes of the PDO: cold-PDO (1944-1975) and warm-PDO (1976-2005) subsets. Between 1944 and 2005, average winter and April flow increased at 15 sites. Observed winter flow increases during the cold-PDO phase were generally limited to sites in the Upper Yukon River Basin. Positive trends in winter flow during the warm-PDO phase broadened to include stations in the Middle and Lower Yukon River drainage basins. Increases in winter streamflow most likely result from groundwater input enhanced by permafrost thawing that promotes infiltration and deeper subsurface flow paths. Increased April flow may be attributed to a combination of greater baseflow (from groundwater increases), earlier spring snowmelt and runoff, and increased winter precipitation, depending on location. Calculated deviations from long-term mean monthly discharges indicate below-average flow in the winter months during the cold PDO and above-average flow in the winter months during the warm PDO. Although not as strong a signal, results also support the reverse response during the summer months: above-average flow during the cold PDO and below-average flow during the warm PDO. Changes in the summer flows are likely an indirect consequence of the PDO, resulting from earlier spring snowmelt runoff and also perhaps increased summer infiltration and storage in a deeper active layer. Annual discharge has remained relatively unchanged in the Yukon River Basin, but a few glacier-fed rivers demonstrate positive trends, which can be attributed to enhanced glacier melting. A positive trend in annual flow during the warm PDO near the mouth of the Yukon River suggests that small increases in flow throughout the Yukon River Basin have resulted in an additive effect manifested in the downstream-most streamflow station. Many of the identified changes in streamflow patterns in the Yukon River Basin show a correlation to the PDO regime shift. This work highlights the importance of considering proximate climate forcings as well as global climate change when assessing hydrologic changes in the Arctic.

Journal of Hydrology↗

USGS2001

Sources of global warming in upper ocean temperature during El Niño

Global average sea surface temperature (SST) from 40°S to 60°N fluctuates ±0.3°C on interannual period scales, with global warming (cooling) during El Niño (La Niña). About 90% of the global warming during El Niño occurs in the tropical global ocean from 20°S to 20°N, half because of large SST anomalies in the tropical Pacific associated with El Niño and the other half because of warm SST anomalies occurring over &sim;80% of the tropical global ocean. From examination of National Centers for Environmental Prediction [ Kalnay et al. , 1996] and Comprehensive Ocean-Atmosphere Data Set [ Woodruff et al. , 1993] reanalyses, tropical global warming during El Niño is associated with higher troposphere moisture content and cloud cover, with reduced trade wind intensity occurring during the onset phase of El Niño. During this onset phase the tropical global average diabatic heat storage tendency in the layer above the main pycnocline is 1–3 W m −2 above normal. Its principal source is a reduction in the poleward Ekman heat flux out of the tropical ocean of 2–5 W m −2 . Subsequently, peak tropical global warming during El Niño is dissipated by an increase in the flux of latent heat to the troposphere of 2–5 W m −2 , with reduced shortwave and longwave radiative fluxes in response to increased cloud cover tending to cancel each other. In the extratropical global ocean the reduction in poleward Ekman heat flux out of the tropics during the onset of El Niño tends to be balanced by reduction in the flux of latent heat to the troposphere. Thus global warming and cooling during Earth's internal mode of interannual climate variability arise from fluctuations in the global hydrological balance, not the global radiation balance. Since it occurs in the absence of extraterrestrial and anthropogenic forcing, global warming on decadal, interdecadal, and centennial period scales may also occur in association with Earth's internal modes of climate variability on those scales.

Journal of Geophysical Research C: Oceans↗

USGS2003

Importance of a stochastic distribution of floods and erosion thresholds in the bedrock river incision problem

Fluvial erosion of bedrock occurs during occasional flood events when boundary shear stress exceeds a critical threshold to initiate incision. Therefore efforts to model the evolution of topography over long timescales should include an erosion threshold and should be driven by a stochastic distribution of erosive events. However, most bedrock incision models ignore the threshold as a second‐order detail. In addition, climate is poorly represented in most landscape evolution models, so the quantitative relationship between erosion rate and measurable climatic variables has been elusive. Here we show that the presence of an erosion threshold, when combined with a well‐constrained, probabilistic model of storm and flood occurrence, has first‐order implications for the dynamics of river incision in tectonically active areas. First, we make a direct calculation of the critical shear stress required to pluck bedrock blocks for a field site in New York. Second, we apply a recently proposed stochastic, threshold, bedrock incision model to a series of streams in California, with known tectonic and climatic forcing. Previous work in the area has identified a weak relationship between channel gradient or relief and rock uplift rate that is not easily explained by simpler detachment‐limited models. The results with the stochastic threshold model show that even low erosion thresholds, which are exceeded in steep channels during high‐frequency flood events, fundamentally affect the predicted relationship between gradient and uplift rate in steady state rivers, in a manner consistent with the observed topography. This correspondence between theory and data is, however, nonunique; models in which a thin alluvial cover may act to inhibit channel incision in the low uplift rate zone also provide plausible explanations for the observed topography. Third, we explore the broader implications of the stochastic threshold model to the development of fluvial topography in active tectonic settings. We suggest that continued field applications of geomorphic models, including physically meaningful thresholds and stochastic climate distributions, are required to advance our knowledge of interactions among surficial, climatic, and crustal processes.

California↗

USGS2012

Quantifying soil surface change in degraded drylands: shrub encroachment and effects of fire and vegetation removal in a desert grassland

Woody plant encroachment, a worldwide phenomenon, is a major driver of land degradation in desert grasslands. Woody plant encroachment by shrub functional types ultimately leads to the formation of a patchy landscape with fertile shrub patches interspaced with nutrient-depleted bare soil patches. This is considered to be an irreversible process of land and soil degradation. Recent studies have indicated that in the early stages of shrub encroachment, when there is sufficient herbaceous connectivity, fires (prescribed or natural) might provide some reversibility to the shrub encroachment process by negatively affecting shrub demography and homogenizing soil resources across patches within weeks to months after burning. A comprehensive understanding of longer term changes in microtopography and spatial patterning of soil properties following fire in shrub-encroached grasslands is desirable. Here, we investigate the changes in microtopography with LiDAR (light detection and ranging), vegetation recovery, and spatial pattering of soil properties in replicated burned, clipped, and control areas in a shrub-grass transition zone in the northern Chihuahuan Desert four years after prescribed fire or clipping. Results indicate a greater homogeneity in soil, microtopography, and vegetation patterning on burned relative to clipped and control treatments. Findings provide further evidence that disturbance by prescribed fire may allow for reversal of the shrub encroachment process, if the event occurs in the early stages of the vegetation shift. Improved understanding of longer-term effects of fire and associated changes in soil patterning can inform the use and role of fire in the context of changing disturbance regimes and climate.

Chihuahuan Desert↗

USGS2021

Quantifying the response of nitrogen speciation to hydrology in the Chesapeake Bay Watershed using a multilevel modeling approach

Excessive nitrogen (N) inputs to coastal waters can lead to severe eutrophication and different chemical forms of N exhibit varying levels of effectiveness in fueling primary production. Efforts to mitigate N fluxes from coastal watersheds are often guided by models that predict changes in N loads as a function of changes in land use, management practices, and climate. However, relatively little is known on the impacts of such changes on the relative fractions of different N forms. We leveraged a long-term dataset of N loads from over 100 river stations to investigate how the fraction, that is, the ratio of to total N ( /TN), changes as a function of spatio-temporal changes in TN loads in the Chesapeake Bay watershed. We built a hierarchical model that separates the response of to changes in TN load occurring at different scales: Across river stations, where differences in TN loads are largely driven by spatial differences in anthropogenic inputs, and within stations, where inter-annual variability in hydrology is a key driver of changes in TN loads. Results suggest that while increases in TN loads resulting from changes in anthropogenic inputs lead to an increase in the fraction, a decrease in the fraction may occur when increases in TN loads are driven by increased streamflow. These results are especially relevant in watersheds that may experience changes in N loads due to both management decisions and climate-driven changes in hydrology.

Chesapeake Bay watershed↗

USGS2025

Detection of deer at remote camera sites in relation to snow conditions

In the rain-snow transition zone of the Pacific Northwest, climate change is expected to alter the incidence of rain-on-snow and freeze-thaw events, which will change snow density and hardness dynamics. In winter, the ability of economically and ecologically important wildlife species, such as deer ( Odocoileus spp.), to efficiently move through the landscape and access forage is mediated by snow conditions. Therefore, snow properties such as density and hardness can directly affect how energetically costly it is for these animals to survive. However, little is known about whether and how ungulates use habitats based on snow density and hardness. We deployed a stratified network of remote camera stations in complex forested terrain in Latah County, Idaho, USA, to remotely measure snow depth and detect deer. We also collected snow density and hardness measurements throughout the winter. We used these data to determine the degree to which the probability of deer presence at cameras could be explained by snow conditions and air temperature. Snow depth and density had negative relationships with the probability of deer presence, while ram resistance (a proxy for snow hardness) had a marginal positive effect. We were able to estimate snow conditions important to deer in winter 2020–2021 primarily using data obtained from cameras. This provides an important proof-of-concept that can be applied at different sites and climate conditions to gain a deeper understanding of how deer are affected by snowpack properties. These methods can be used by managers to determine how ungulates are affected by snow depth, density, and hardness collectively and subsequently inform ungulate management in a changing climate.

Idaho↗

USGS2020

Modeling larval American Shad recruitment in a large river

Climate change is altering the spatial and temporal patterns of temperature and discharge in rivers, which is expected to have implications for the life stages of anadromous fish using those rivers. We developed an individual-based model to track American Shad Alosa sapidissima offspring within a coarse template of spatially and temporally variable habitat conditions defined by a combination of temperature, river velocity, and prey availability models. We simulated spawning at each river kilometer along a 142-km reach of the Connecticut River on each day (April 1–August 31) to understand how spawning date and location drive larval recruitment differentially across years and decades (1993–2002 and 2007–2016). For both temperature and flow, interannual variation was large in comparison to interdecadal differences. Variation in simulated recruitment was best explained by a combination of season-specific spawning temperature and location along the course of the river. The greatest potential recruitment occurred during years in which June temperatures were relatively high. In years when June and July were warmer than average, maximum recruitment resulted from spawning taking place at the upstream portion of the modeled reach. Model scenarios (stationary or passive-drift larvae; and dams or no dams) had predictable effects. We assumed that the pools above dams had negative impacts on eggs and yolk-sac larvae that may have been deposited there. Allowing eggs and larvae to drift passively with the current reduced spatial differences in recruitment success among spawning sites relative to stationary eggs and larvae. Our results demonstrate the importance of spatiotemporal environmental heterogeneity for producing positive recruitment over the long term. In addition, our results suggest the importance of successful passage of spawners to historical spawning sites in the Connecticut River upstream of Vernon Dam, especially as conditions shift with climate change.

New Hampshite, Massachutsetts↗

USGS1985

Carboniferous paleogeographic, phytogeographic, and paleoclimatic reconstructions

Two revised paleogeographic reconstructions of the Visean and Westphalian C-D stages are presented based on recent paleomagnetic, phytogeographic, stratigraphic, and tectonic data. These data change the positions of some continental blocks, and allow the definition of several new ones. The most important modifications that have been incorporated in these reconstructions are: (1) a proposed isthmus linking North America and Siberia across the Bering Strait; and (2) the separation of China and Southeast Asia in six major blocks, including South China, North China, Shan Thai-Malaya, Indochina, Qangtang, and Tarim blocks. Evidence is presented that suggests that at least the South China, Shan Thai-Malaya, and Qangtang blocks were derived from the northern margin of Gondwana. Multivariate statistical analysis of phytogeographic data from the middle and late Paleozoic allow definition of a number of different phytogeographic units for four time intervals: (1) the Early Devonian, (2) Tournaisian—early Visean, (3) Visean, and (4) late Visean—early Namurian A. Pre-late Visean—early Namurian A floral assemblages from South China show affinities with northern Gondwana floras suggesting a southerly position and provides additional support for our reconstruction of South China against the northern margin of Gondwana. There is a marked decrease in the diversity of phytogeographic units in the Namurian and younger Carboniferous. This correlates closely with the time of assembly of most of Pangaea. The general pattern of Carboniferous phytogeographic units corresponds well with global distribution of continents shown on our paleogeographic reconstructions. In addition, we have constructed paleoclimatic maps for the two Carboniferous time intervals. These maps stress the distribution of rainfall, as this should be strongly correlated with the floras. There is marked change in the rainfall patterns between the Visean and Westphalian C-D. This change corresponds with the closing of the Appalachian-Ouachita ocean between Laurussia and Gondwana, and reflects the removal of a low-latitude moisture source that probably gave rise to monsoonal conditions along the northern margin of Gondwana in the Visean and earlier times. As well, the presence of a substantial heat source at high elevation in the Late Carboniferous significantly influenced the distribution of climatic belts.

International Journal of Coal Geology↗

USGS2009

Spatial and temporal variation in distribution of larval lake whitefish in eastern Lake Ontario: signs of recovery?

The lake whitefish ( Coregonus clupeaformis ) is one of the native Lake Ontario fishes that declined severely over the past century. Recent evidence of larval lake whitefish production in a historic spawning area (Chaumont Bay) might signal a recovery of this species in New York waters. We surveyed coastal and open water areas to evaluate densities and estimate total abundance of larval lake whitefish in Chaumont Bay. Other historic spawning areas and embayments with appropriate spawning and nursery habitat were also surveyed, but only a few larvae were found outside of Chaumont Bay. Lake whitefish larvae were found in every embayment sampled within Chaumont Bay, with larval densities of nearly 600/1000 m 2 in some samples. Greatest abundances occurred in the northern sectors and near the mouth of the bay. Open water densities were generally less than half that of nearshore sites. The total bay-wide estimate for 2005 was approximately 644,000 lake whitefish larvae, but dropped to 230,000–400,000 in 2006 and 2007, respectively. Mean larval growth rates (0.36 mm/day) did not differ by year, but were consistently higher in early May than in late April. Lake whitefish production in Chaumont Bay is encouraging for this species, but the cause and persistence of the decline after 2005 can be determined only by continued monitoring. Other possible bottlenecks of survival may exist at juvenile and adult stages and could significantly affect recruitment dynamics. This species is sensitive to normal climatic fluctuations and increased variability associated with global climatic change could make winter nursery conditions unfavorable for this species.

Journal of Great Lakes Research↗

USGS2012

Modeling thermal dynamics of active layer soils and near-surface permafrost using a fully coupled water and heat transport model

Thawing and freezing processes are key components in permafrost dynamics, and these processes play an important role in regulating the hydrological and carbon cycles in the northern high latitudes. In the present study, we apply a well-developed soil thermal model that fully couples heat and water transport, to simulate the thawing and freezing processes at daily time steps across multiple sites that vary with vegetation cover, disturbance history, and climate. The model performance was evaluated by comparing modeled and measured soil temperatures at different depths. We use the model to explore the influence of climate, fire disturbance, and topography (north- and south-facing slopes) on soil thermal dynamics. Modeled soil temperatures agree well with measured values for both boreal forest and tundra ecosystems at the site level. Combustion of organic-soil horizons during wildfire alters the surface energy balance and increases the downward heat flux through the soil profile, resulting in the warming and thawing of near-surface permafrost. A projection of 21st century permafrost dynamics indicates that as the climate warms, active layer thickness will likely increase to more than 3 meters in the boreal forest site and deeper than one meter in the tundra site. Results from this coupled heat-water modeling approach represent faster thaw rates than previously simulated in other studies. We conclude that the discussed soil thermal model is able to well simulate the permafrost dynamics and could be used as a tool to analyze the influence of climate change and wildfire disturbance on permafrost thawing.

Journal of Geophysical Research D: Atmospheres↗

USGS2021

Lagged wetland CH4 flux response in a historically wet year

While a stimulating effect of plant primary productivity on soil carbon dioxide (CO 2 ) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH 4 ) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH 4 emissions (FCH 4 ) is complicated by confounding influences of water table level and temperature on CH 4 production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH 4 at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US-Los) and Allequash Creek (US-ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US-Los being larger in scale and having a more open canopy. Co-located sites with multi-year observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH 4 without interference due to differing climate. Daily average FCH 4 from US-Los reached a maximum of 47.7 ηmol CH 4 m −2 s −1 during the study period, while US-ALQ was more than double at 117.9 ηmol CH 4 m −2 s −1 . The lagged influence of GPP on temperature-normalized FCH 4 ( T air -FCH 4 ) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH 4 at US-ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH 4 due to this study has implications for climate modeling and more accurate carbon budgeting.

Journal of Geophysical Research: Biogeosciences↗

USGS2017

Growth strategies and threshold responses to water deficit modulate effects of warming on tree seedlings from forest to alpine

1.Predictions of upslope range shifts for tree species with warming are based on assumptions of moisture stress at lower elevation limits and low temperature stress at high elevation limits. However, recent studies have shown that warming can reduce tree seedling establishment across the entire gradient from subalpine forest to alpine via moisture limitation. Warming effects also vary with species, potentially resulting in community shifts in high elevation forests. 2.We examined the growth and physiology underlying effects of warming on seedling demographic patterns. We evaluated dry mass (DM), root length, allocation above- and belowground, and relative growth rate (RGR) of whole seedlings, and their ability to avoid or endure water stress via water-use efficiency and resisting turgor loss, for Pinus flexilis, Picea engelmannii and Pinus contorta seeded below, at, and above treeline in experimentally warmed, watered, and control plots in the Rocky Mountains, USA. We expected that growth and allocation responses to warming would relate to moisture status and that variation in drought tolerance traits would explain species differences in survival rates. 3.Across treatments and elevations, seedlings of all species had weak turgor-loss resistance, and growth was marginal with negative RGR in the first growth phase (-0.01 to -0.04 g/g/d). Growth was correlated with soil moisture, particularly in the relatively small-seeded P. contorta and P. engelmannii. P. flexilis, known to have the highest survivorship, attained the greatest DM and longest root but was also the slowest growing and most water-use-efficient. This was likely due to its greater reliance on seed reserves. Seedlings developed 15% less total DM, 25% less root DM, and 11% shorter roots in heated compared to unheated plots. Higher temperatures slightly increased DM, root length and RGR where soils were wettest, but more strongly decreased these variables under drier conditions. 4.Synthesis: The surprising heat-inhibition of tree seedling establishment at the cold edge of forests appears to have a physiological basis: newly germinated seedlings have poor moisture stress tolerance, which appears related to marginal initial growth and heavy reliance on seed reserves. Variation in these attributes among tree species at treeline helps explain their different climate responses.

Journal of Ecology↗

USGS2023

Progradational-to-retrogradational styles of Palaeogene fluvial fan successions in the San Juan Basin, New Mexico

Basin-scale outcrop analyses of fluvial architecture in the Palaeogene San Juan Basin, New Mexico, document lateral and vertical trends in channel, floodplain and palaeosol characteristics. Herein, the uppermost part of the Palaeocene Nacimiento Formation and lower Eocene Cuba Mesa and Regina Members of the San Jose Formation are identified as deposits of large fluvial fans based on trends observed across the basin. Stratigraphic trends suggest two packages originated by fluvial fan progradation. Progradation of the lower fan system provides a new explanation for the transitional nature of a disconformity at the Nacimiento–San Jose Formation contact, previously thought to be a low-angle unconformity. The two fan systems are separated by a retrogradational interval that culminates in a depositional hiatus at the contact between the Cuba Mesa and Regina Members. This, combined with poor age constraints, indicates that the duration of the disconformity at the base of the Cuba Mesa Member may have been overestimated. Furthermore, the succession is interpreted as deposits of variable-discharge rivers, based on the combined abundance of upper flow regime and high deposition rate sedimentary structures indicative of intense flooding events, preservation of in-channel bioturbation and paedogenic modification indicating periods of prolonged dryness, lack of identifiable bar strata and alternations of poorly drained and well-drained floodplain deposits with pedofacies indicating alternating wet–dry cycles. This dataset adds to a growing body of evidence linking the formation of large fluvial fans to discharge variability and thus to hydroclimates with significant inter- and intra-annual precipitation variability and intense rainfall. A long-term stratigraphic shift from poorly drained to well-drained floodplain deposits across two progradational fan successions indicates that a predictive model suggesting downstream decreases in soil drainage conditions is not encompassing of all large fan systems, and instead suggests a transition to a more arid climate across the Palaeocene–Eocene boundary.

New Mexico↗

USGS2009

Using time-dependent models to investigate body condition and growth rate of the giant gartersnake

Identifying links between phenotypic attributes and fitness is a primary goal of reproductive ecology. Differences in within-year patterns of body condition between sexes of gartersnakes in relation to reproduction and growth are not fully understood. We conducted an 11-year field study of body condition and growth rate of the giant gartersnake Thamnophis gigas across 13 study areas in the Central Valley of California, USA. We developed a priori mixed effects models of body condition index (BCI), which included covariates of time, sex and snout-vent length and reported the best-approximating models using an information theoretic approach. Also, we developed models of growth rate index (GRI) using covariates of sex and periods based on reproductive behavior. The largest difference in BCI between sexes, as predicted by a non-linear (cubic) time model, occurred during the mating period when female body condition (0.014??0.001 se) was substantially greater than males (-0.027??0.002 se). Males likely allocated energy to search for mates, while females likely stored energy for embryonic development. We also provided evidence that males use more body energy reserves than females during hibernation, perhaps because of different body temperatures between sexes. We found GRI of male snakes was substantially lower during the mating period than during a non-mating period, which indicated that a trade-off existed between searching for mates and growth. These findings contribute to our understanding of snake ecology in a Mediterranean climate. ?? 2009 The Zoological Society of London.

Journal of Zoology↗

USGS2021

Current distribution and abundance of Kohala forest birds in Hawai‘i

The Kohala volcano is home to the most spatially isolated population of Hawaiian forest birds on Hawai‘i Island and contains one of the few native bird populations in the state that has not been monitored since the original Hawai‘i Forest Bird Survey (HFBS) in 1979. We surveyed 143 stations across 13 transects in Pu‘u ‘O ‘Umi Natural Area Reserve on Kohala from February through April 2017 and compared our results to data from the 1979 HFBS conducted at 80 stations across three transects in the same location as our study site. We detected 2806 individuals of 15 species and measured relative abundance, relative occurrence, and density for seven species. We observed changes in species densities ranging from −8.4% (Hawai‘i ‘Elepaio, Chasiempis sandwichensis ) to +714% (‘I‘iwi, Drepanis coccinea ). Equivalence testing showed meaningful increases in population densities for all but one species, the Hawai‘i ‘Elepaio. The increases in population densities on Kohala are in stark contrast to the widespread declines in population densities of native species elsewhere in Hawai‘i. Relative occurrence was greater in 2017 than in 1979 for all species except Hawai‘i ‘Elepaios and House Finches ( Haemorhous mexicanus ), and relative abundance increased for all species except Hawai‘i ‘Elepaios, House Finches, and Melodious Laughing Thrushes ( Garrulax canorus ). We also documented the range expansion of Japanese Bush Warblers ( Cettia diphone ) in Kohala. Our results indicate that this spatially isolated avian community remains biologically diverse, and most population densities are increasing in the study area. Our results provide a framework for future surveys and a baseline for understanding possible changes in population and community dynamics as birds respond to climate change and avian disease on Kohala volcano.

Hawai'i↗