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USGS2020

Effect of an environmental flow on vegetation growth and health using ground and remote sensing metrics

Understanding the effectiveness of environmental flow deliveries along rivers requires monitoring vegetation. Monitoring data are often collected at multiple spatial scales. For riparian vegetation, optical remote sensing methods can estimate growth responses at the riparian corridor scale, and field‐based measures can quantify species composition; however, the extent to which these different measures are duplicative or complementary is important to understand when planning monitoring programmes with limited resources. In this study, we analysed riparian vegetation growth in the delta of the Colorado River in response to an experimental pulse flow. Our goal was to compare ground‐based measurements of vegetation structure and composition with satellite‐based Landsat radiometric variables, such as the normalized difference vegetation index (NDVI). We made this comparison in 21 transects following the delivery of 131.8 million cubic meters (mcm) of water in the stream channel during the spring of 2014 as a pulse flow and 38.4 mcm as base flows. Vegetation cover increased 14% and NDVI increased 0.02 (15%) by October 2015, and both variables returned to pre‐pulse flow values in October 2016. Observed changes in vegetation structure and composition did not persist after the second year. The highest increase in vegetation cover in October 2014 and October 2015 resulted from species that could respond rapidly to additional water such as reeds ( Arundo donax and Phragmites australis ), cattail ( Typha domingensis ), and herbaceous plants. Dominant shrubs, saltcedar ( Tamarix spp.) and arrowweed ( Pluchea sericea ), both indicative of nonrestored habitats showed variable increases in cover, and native trees ( Salicaceae family) presented low increases (1%). The strong NDVI–vegetation cover relationship indicates that NDVI is appropriate to detect changes at the riparian corridor scale but needs to be complemented with ground data to determine the contributions by different species to the observed trends.

Colorado River↗

USGS2011

Response of an algal assemblage to nutrient enrichment and shading in a Hawaiian stream

To investigate the effects of nitrate enrichment, phosphate enrichment, and light availability on benthic algae, nutrient-diffusing clay flowerpots were colonized with algae at two sites in a Hawaiian stream during spring and autumn 2002 using a randomized factorial design. The algal assemblage that developed under the experimental conditions was investigated by determining biomass (ash-free dry mass and chlorophyll a concentrations) and composition of the diatom assemblage. In situ pulse amplitude-modulated fluorometry was also used to model photosynthetic rate of the algal assemblage. Algal biomass and maximum photosynthetic rate were significantly higher at the unshaded site than at the shaded site. These parameters were higher at the unshaded site with either nitrate, or to a lesser degree, nitrate plus phosphate enrichment. Analysis of similarity of diatom assemblages showed significant differences between shaded and unshaded sites, as well as between spring and autumn experiments, but not between nutrient treatments. However, several individual species of diatoms responded significantly to nitrate enrichment. These results demonstrate that light availability (shaded vs. unshaded) is the primary limiting factor to algal growth in this stream, with nitrogen as a secondary limiting factor.

Hawaii↗

USGS1986

Evaluation of coded wire tags for marking lake trout

Among hatchery-reared lake trout ( Salvelinus namaycush ) of the 1979-1982 year classes stocked in New York waters of Lake Ontario, more than 3 million fish were marked with a coded wire tag (CWT) plus an adipose fin clip, and 1.5 million with only conventional fin clips. Altogether, 7,640 tags were recovered from fish collected with bottom trawls and gill nets or caught by anglers during 1980-1983. One person was able to extract and decipher 200 or more CWTs per day with about a 1% error rate in reading and recording codes. Presence of the CWT did not affect growth. The adipose fin clip did not regenerate. The occurrence of fish with an adipose fin clip but no CWT resulted primarily from the regeneration of paired fins among fish marked with a combination of the adipose fin and a paired fin. Loss of CWTs between marking and stocking (generally 4-5 months for fish stocked in spring and 1-8 d for fish stocked in fall) declined from nearly 11% for the 1979 year class stocked as fall fingerlings to less than 3% for the 1981 and 1982 year classes - a difference that primarily reflected improvements in instrumentation and tagging technique. The rate of CWT loss after the marked fish were stocked was probably less than 1% per year. The CWT is a reliable method for marking hatchery-reared lake trout. A large number of experimental groups can be uniquely marked, and fish from each group can be accurately identified throughout their life. Use of this technique should greatly facilitate evaluations of genetic strain, hatchery experience, condition at time of stocking, season of stocking, size at stocking, method of stocking and other factors that affect poststocking survival and performance of lake trout stocked in the Great Lakes.

North American Journal of Fisheries Management↗

USGS1999

Duck plague

Duck plague is caused by a herpesvirus. Infection often results in an acute, contagious, and fatal disease. As with many other herpesviruses, duck plague virus can establish inapparent infections in birds that survive exposure to it, a state referred to as latency. During latency, the virus cannot be detected by standard methods for virus isolation. Studies of domestic species of waterfowl have detected multiple strains of the virus that vary in their ability to cause disease and death. Little is known about the response of wild waterfowl to strain differences. Duck plague outbreaks are thought to be caused when birds that carry the virus shed it through fecal or oral discharge, thus releasing the virus into food and water with which susceptible birds may have contact. Experimental studies have demonstrated spontaneous virus shedding by duck plague carriers during spring. Changes in the duration of daylight and onset of breeding are thought to be physiological stresses that stimulate virus shedding at this time of year. The carriers are immune to the disease, but the virus shed by them causes infection and disease among susceptible waterfowl. Bird-to-bird contact and contact with virus that has contaminated the environment perpetuate an outbreak. Scavenging and decomposition of carcasses of infected birds also contaminate the environment by releasing viruses from tissues and body fluids. Virus transmission through the egg has been reported, but the role of the egg in the disease cycle remains to be resolved.

Information and Technology Report↗

USGS2019

Experimental study on the impact of thermal maturity on shale microstructures using hydrous pyrolysis

Hydrous pyrolysis was applied to four low-maturity aliquots from the Utica, Excello, Monterey, and Niobrara Shale Formations in North America to create artificial maturation sequences, which could be used to study the impact of maturation on geochemical and microstructural properties. Modified Rock-Eval pyrolysis, reflectance, organic petrology, and Fourier transform infrared spectroscopy (FTIR) were employed to analyze their geochemical properties, while gas adsorption (CO 2 and N 2 ) was used to characterize their pore structures (pores < 200 nm). Organic petrography using white and blue light (fluorescence) before and after hydrous pyrolysis showed that amorphous organic matter cracked into solid bitumen, oil, and gas during hydrous pyrolysis. A reduction of the CH 2 /CH 3 ratio in hydrous pyrolysis residues was observed from FTIR analysis. Rock-Eval pyrolysis showed that kerogens in the four samples were dissimilar, and hydrous pyrolysis residues showed smaller hydrogen index and Sh2 values than starting materials. Results from CO 2 and N 2 gas adsorption analysis showed that pore structures (micropore volume, micropore surface area, meso-macropore volume, and meso-macropore surface area) changed significantly during hydrous pyrolysis. However, changes in pore structure were dissimilar among the four samples, which was attributed to different activation energies of organic matter. A thermodynamic fractal model showed a decrease in fractal dimensions of Utica, Monterey, and Excello after hydrous pyrolysis, indicating a decrease in surface roughness. The pore size heterogeneity in the Utica sample increased as hydrous pyrolysis temperature increased, whereas the pore size heterogeneity distributions in the Monterey and Excello decreased based on the N 2 adsorption data.

Energy & Fuels↗

USGS2012

Probing the Earth's strength: Can we measure small stress at high pressure?

Simulating the conditions and processes that occur in the Earth's deep interior has been a major goal of experimental geophysics since the 1920s. In particular, pioneers such as P. W. Bridgman, David Griggs, Hugh Heard, Mervyn Paterson, William Brace, and their colleagues sought to establish the basic relations between differential stresses and rock and mineral deformation under pressure-temperature conditions that favor such inelastic processes as brittle fracture, frictional sliding, plastic deformation, and dynamic metamorphism. This work has been applied to diverse problems in the Earth sciences, including the physical nature of earth quake sources, the forces that drive and resist plate movement, deformation under partial-melting conditions at the tops of mantle plumes, the flexure of the lithosphere, post-glacial rebound, and the origin of the preferred orientation of minerals and the resultant seismic anisotropy and metamorphic textures.

Eos, Transactions, American Geophysical Union↗

USGS2005

Distribution, foraging behavior, and capture results of the spotted bat (Euderma maculatum) in central Oregon

The spotted bat (Euderma maculatum) has been virtually unknown in Oregon despite the existence of potential habitat in many areas of the state. In 2002 and 2003 we searched for spotted bats along the John Day, Deschutes, and Crooked Rivers and at a remote dry canyon southeast of the city of Bend in central Oregon. The species was documented through the use of mist-nets, a bat detector, and recognition of audible spotted bat calls. Spotted bats were found at 11 locations in 6 Oregon counties. Nightly activity patterns of spotted bats were unpredictable. Spotted bats were found in 78% of search areas but on only 48% of survey nights. We observed spotted bats foraging above fields and low upland slopes adjacent to rivers and creeks and along the rims of cliffs. Estimated flying heights of spotted bats ranged from 3 m to 50 m aboveground. The species was difficult to capture and was captured only after considerable experimentation with methods and materials. Three spotted bats were captured toward the end of the project in 2003 and accounted for only 0.5% of all bats captured during the study. Although we attached radio transmitters to 2 spotted bats, we found no roost locations. We believe additional spotted bat surveys in Oregon are warranted, especially in higher-elevation habitats, but recommend that to increase their effectiveness, surveys accommodate the unique foraging behavior of the species.

Western North American Naturalist↗

USGS2019

Geese mediate vegetation state changes with parallel effects on N cycling that leave nutritional legacies for offspring

Along the coastal fringe of the Yukon–Kuskokwim River Delta in southwestern Alaska, geese maintain grazing lawns dominated by a rhizomatous sedge that, when ungrazed, transitions to a taller, less palatable growth form that is taxonomically described as a different species. Nutrients recycled in goose feces, in conjunction with grazing, are critical to the rapid, nutritious growth of grazing lawns, and selective foraging on lawns has positive life‐history consequences for goslings. To examine whether bidirectional vegetation shifts were accompanied by parallel changes in N cycling, we studied how 15 N‐urea and 13 C 15 N‐glycine were processed through soils and plants of native and recently reverted vegetation states. Biomass and plant 15 N uptake from plots reverted to the tall growth form using exclosures and from those shifted to grazing lawns by experimental clipping and then goose grazing were identical to their native counterparts. Total recovery of 15 N within the tall vegetation types was significantly greater than within grazing lawns, although when expressed on a per‐gram biomass basis, percentage of 15 N recovery was significantly higher in grazing lawns compared with the tall vegetation state. Patterns of 13 C enrichment in CO 2 soil efflux showed rapid use of 13 C‐glycine as a respiratory substrate within the first hour following injection, with both the timing and magnitude of efflux occurring at similar time points for all four vegetation types. However, higher soil respiration rates and a shorter half‐life for 13 C‐glycine in soils from tall meadows resulted in a greater proportional loss of 13 CO 2 compared with grazing lawns. Despite daily‐to‐weekly tidal inundation, all of 15 N from labeled substrates could be accounted for within 1 m of the injection grid from soils of both states after 30 d, with significant levels of 15 N in soils and vegetation after one year. Geese have remarkably high fidelity to brood‐rearing areas, returning as adults to the same grazing lawns where they were raised as goslings. Our data suggest that the role fecal‐derived nutrients play in the positive feedback loop between geese and their food resources can provide a long‐term legacy that spans generations.

Alaska↗

USGS2023

Assessing contaminants of emerging concern in the Great Lakes Ecosystem: A decade of method development and practical application

Assessing the ecological risk of contaminants in the field typically involves consideration of a complex mixture of compounds which may or may not be detected via instrumental analyses. Further, there are insufficient data to predict the potential biological effects of many detected compounds, leading to their being characterized as contaminants of emerging concern (CECs). Over the past several years, advances in chemistry, toxicology, and bioinformatics have resulted in a variety of concepts and tools that can enhance the pragmatic assessment of the ecological risk of CECs. The present Focus article describes a 10+- year multiagency effort supported through the U.S. Great Lakes Restoration Initiative to assess the occurrence and implications of CECs in the North American Great Lakes. State-of-the-science methods and models were used to evaluate more than 700 sites in about approximately 200 tributaries across lakes Ontario, Erie, Huron, Michigan, and Superior, sometimes on multiple occasions. Studies featured measurement of up to 500 different target analytes in different environmental matrices, coupled with evaluation of biological effects in resident species, animals from in situ and laboratory exposures, and in vitro systems. Experimental taxa included birds, fish, and a variety of invertebrates, and measured endpoints ranged from molecular to apical responses. Data were integrated and evaluated using a diversity of curated knowledgebases and models with the goal of producing actionable insights for risk assessors and managers charged with evaluating and mitigating the effects of CECs in the Great Lakes. This overview is based on research and data captured in approximately about 90 peer-reviewed journal articles and reports, including approximately about 30 appearing in a virtual issue comprised of highlighted papers published in Environmental Toxicology and Chemistry or Integrated Environmental Assessment and Management . Environ Toxicol Chem 2023;42:2506–2518. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Environmental Toxicology and Chemistry↗

USGS2025

Reaction kinetics and accelerant effects of sulfides in early mature hydrocarbon generation using hydrous pyrolysis

Hydrocarbon generation in organic-rich sediments is influenced by the molecular organic composition and relative abundance of associated minerals. Certain mineral-derived elements act as catalysts and reaction intermediaries, facilitating early-stage hydrocarbon formation in potential source rocks. This study investigated the role of sulfur contributed from pyrite as an accelerant in thermal reaction, focusing on its effects on early maturation and consequent hydrocarbon generation from gilsonite (low-sulfur solid petroleum). Hydrous pyrolysis (HP) experiments were conducted on mixtures of gilsonite and pyrite in varying ratios (1:0.1, 1:0.5, 1:1, 1:2, and 1:10 w/w gilsonite:pyrite) at 320, 350, and 370 °C for 72 h. Untreated and thermally altered residues were analyzed using solid bitumen reflectance (BR o , %), total organic carbon (TOC) content, programmed temperature pyrolysis, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) to evaluate the potential accelerant role of pyritic sulfur in hydrocarbon formation. The results show HP residues at 320 and 350 °C with greater pyrite concentrations had higher BR o , while reflectance values were similar in the 370 °C residues, regardless of pyrite concentration, suggesting enhanced reaction at lower thermal conditions. Increasing pyrite content systematically decreased hydrogen index (HI) values while increasing the transformation ratio (TR) and production index (PI), indicating enhanced conversion of organic matter to hydrocarbons with increasing pyrite concentrations. Gas yields increased with pyrite addition, particularly at 350 °C, confirming secondary cracking effects. However, gas production stabilized or declined at higher pyrite loadings (1:10), suggesting alternative reaction pathways such as coke formation. Our data indicate the presence of pyrite lowers the activation energy for thermal cracking, shifting peak experimental hydrocarbon generation temperatures downward by 20–30 °C, with the most pronounced accelerant effects observed at moderate pyrite concentrations (1:0.5 and 1:1). The thermodynamic framework reveals that pyrite stability is influenced by experimental conditions, with pyrrhotite formation favored in the presence of gilsonite due to reduced oxygen fugacity. Pyrite transformation to pyrrhotite, as observed through XRD, SEM-EDS, and predicted by thermodynamic data, further supports the accelerant role of S, as pyrrhotite exhibits a higher hydrogen transfer potential, promoting early oil generation. These findings highlight the importance of pyrite in modulating hydrocarbon generation pathways in organic-rich systems.

Journal of Analytical and Applied Pyrolysis↗

USGS2024

On the survival and habitat use of hatchery-reared cisco (Coregonus artedi) in Lake Erie

Cisco ( Coregonus artedi ) have been extirpated from Lake Erie in North America since the 1960s, but they once supported one of the largest Laurentian Great Lakes fisheries. Numerous potential impediments to rehabilitation have been identified, including summer habitat refugia and predation. We used acoustic telemetry to investigate the thermal habitat use and survival of hatchery-reared adult cisco in Lake Erie. Fish were experimentally released (n = 50 per site) offshore at Dunkirk, New York, in the eastern basin and Huron, Ohio, in the central basin. Cisco in both basins found suitable summer oxythermal habitat in the metalimnion, suggesting that coldwater habitat availability is likely not an impediment for reestablishment. However, track end dates or predation dates were distributed across only four months with the last detection at 155 days. Predation sensors combined with temperature values during digestion indicated different potential predators: lake trout ( Salvelinus namaycush ) for the Dunkirk group and walleye ( Sander vitreus ) for the Huron group. Additionally, digestion temperatures of two tags indicated bird predation was also important, likely underestimated and suggested substantial use of the epilimnion by tagged fish. The results highlight the need for additional studies to address stocking optimization questions in support of future reintroduction experiments and related cisco conservation efforts.

Lake Erie↗

USGS2008

Inverse modeling of surface-water discharge to achieve restoration salinity performance measures in Florida Bay, Florida

The use of numerical modeling to evaluate regional water-management practices involves the simulation of various alternative water-delivery scenarios, which typically are designed intuitively rather than analytically. These scenario simulations are used to analyze how specific water-management practices affect factors such as water levels, flows, and salinities. In lieu of testing a variety of scenario simulations in a trial-and-error manner, an optimization technique may be used to more precisely and directly define good water-management alternatives. A numerical model application in the coastal regions of Florida Bay and Everglades National Park (ENP), representing the surface- and ground-water hydrology for the region, is a good example of a tool used to evaluate restoration scenarios. The Southern Inland and Coastal System (SICS) model simulates this area with a two-dimensional hydrodynamic surface-water model and a three-dimensional ground-water model, linked to represent the interaction of the two systems with salinity transport. This coastal wetland environment is of great interest in restoration efforts, and the SICS model is used to analyze the effects of alternative water-management scenarios. The SICS model is run within an inverse modeling program called UCODE. In this application, UCODE adjusts the regulated inflows to ENP while SICS is run iteratively. UCODE creates parameters that define inflow within an allowable range for the SICS model based on SICS model output statistics, with the objective of matching user-defined target salinities that meet ecosystem restoration criteria. Preliminary results obtained using two different parameterization methods illustrate the ability of the model to achieve the goals of adjusting the range and reducing the variance of salinity values in the target area. The salinity variance in the primary zone of interest was reduced from an original value of 0.509 psu2 to values 0.418 psu2 and 0.342 psu2 using different methods. Simulations with one, two, and three target areas indicate that optimization is limited near model boundaries and the target location nearest the tidal boundary may not be improved. These experiments indicate that this method can be useful for designing water-delivery schemes to achieve certain water-quality objectives. Additionally, this approach avoids much of the intuitive type of experimentation with different flow schemes that has often been used to develop restoration scenarios. ?? 2007 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2006

Evaluation of the factors controlling the time-dependent inactivation rate coefficients of bacteriophage MS2 and PRD1

Static and dynamic batch experiments were conducted to study the effects of temperature and the presence of sand on the inactivation of bacteriophage MS2 and PRD1. The experimental data suggested that the inactivation process can be satisfactorily represented by a pseudo-first-order expression with time-dependent rate coefficients. The time-dependent rate coefficients were used to determine pertinent thermodynamic properties required for the analysis of the molecular processes involved in the inactivation of each bacteriophage. A combination of high temperature and the presence of sand appears to produce the greatest disruption to the surrounding protein coat of MS2. However, the lower activation energies for PRD1 indicate a weaker dependence of the inactivation rate on temperature. Instead, the presence of air-liquid and air-solid interfaces appears to produce the greatest damage to specific viral components that are related to infection. These results indicate the importance of using thermodynamic parameters based on the time-dependent inactivation model to better predict the inactivation of viruses in groundwater. ?? 2006 American Chemical Society.

Environmental Science & Technology↗

USGS2022

Hydrologic restoration decreases greenhouse gas emissions from shrub bog peatlands in southeastern US

Peatlands play a disproportionate role in the global carbon cycle. However, many peatlands have been ditched to lower the water table and converted into agriculture, which contributes to anthropogenic greenhouse gas emissions. Hydrologic restoration of drained peatlands could offset greenhouse gas emissions from these actions, but field examples that consider various greenhouse gases are still rare. Here, we examined emissions of carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) from soils in drained shrub bogs in North Carolina, USA, before and after hydrologic restoration. We used static chamber methods and a before-and-after, control-impact (BACI) experimental design. We found that hydrologic manipulation (akin to restoration) increased water table levels by 65%, even with the impact of two hurricanes before and one after hydrologic manipulation. Increased water table levels led to a 58% decrease in CO 2 fluxes, and an increase in CH 4 (251%) and N 2 O fluxes (85%). Water table depth and soil temperature explained 43% of variation in CO 2 , while water table depth explained 25% and 18% of variation in CH 4 and N 2 O fluxes, respectively. Despite the increases in CH 4 and N 2 O, the higher magnitude of fluxes and large decline in CO 2 lead to an overall lowering of greenhouse gas emissions after hydrologic restoration. Our results suggest that raising the water table in this shrub bog peatland decreased overall greenhouse gas emissions, illustrating that hydrologic restoration of peatlands can be a valuable climate mitigation practice.

North Carolina↗

USGS2012

Roost networks of northern myotis (Myotis septentrionalis) in a managed landscape

Maternity groups of many bat species conform to fission–fusion models and movements among diurnal roost trees and individual bats belonging to these groups use networks of roost trees. Forest disturbances may alter roost networks and characteristics of roost trees. Therefore, at the Fernow Experimental Forest in West Virginia, we examined roost tree networks of northern myotis ( Myotis septentrionalis ) in forest stands subjected to prescribed fire and in unmanipulated control treatments in 2008 and 2009. Northern myotis formed social groups whose roost areas and roost tree networks overlapped to some extent. Roost tree networks largely resembled scale-free network models, as 61% had a single central node roost tree. In control treatments, central node roost trees were in early stages of decay and surrounded by greater basal area than other trees within the networks. In prescribed fire treatments, central node roost trees were small in diameter, low in the forest canopy, and surrounded by low basal area compared to other trees in networks. Our results indicate that forest disturbances, including prescribed fire, can affect availability and distribution of roosts within roost tree networks.

West Virginia↗

USGS2013

Development of a novel flow cytometric approach to evaluate fish sperm chromatin using fixed samples

The integrity of the paternal DNA is essential for the accurate transmission of genetic information, yet fertilization is not inhibited by chromatin breakage. Some methods are available for the sensitive detection of DNA damage and can be applied in studies of environmental toxicology, carcinogenesis, aging, and assisted reproduction techniques in both clinical and experimental settings. Because semen samples obtained from remote locations undergo chromatin damage prior to laboratory assessment, the present study was undertaken to evaluate treatments for effective chromatin staining in the development of a DNA fragmentation assay using fixed milt from yellow perch (Perca flavescens). Similar to the sperm chromatin structure assay (SCSA), susceptibility of nuclear DNA to acid-induced denaturation was measured by flow cytometry (FCM). Use of 10% buffered formalin for milt fixation allowed easier peak discrimination than 4% paraformaldehyde. The effects of time and temperature of incubation in 0.08 N HCl were evaluated in order to determine the ideal conditions for promoting DNA decondensation and making strand breaks more available for staining and detection by FCM. The best results were obtained with incubation at 37°C for 1 minute, followed by cold propidium iodide staining for 30 minutes.

Conference Paper↗

USGS2014

Energetic demands of immature sea otters from birth to weaning: Implications for maternal costs, reproductive behavior and population-level trends

Sea otters ( Enhydra lutris ) have the highest mass-specific metabolic rate of any marine mammal, which is superimposed on the inherently high costs of reproduction and lactation in adult females. These combined energetic demands have been implicated in the poor body condition and increased mortality of female sea otters nearing the end of lactation along the central California coast. However, the cost of lactation is unknown and currently cannot be directly measured for this marine species in the wild. Here, we quantified the energetic demands of immature sea otters across five developmental stages as a means of assessing the underlying energetic challenges associated with pup rearing that may contribute to poor maternal condition. Activity-specific metabolic rates, daily activity budgets and field metabolic rates (FMR) were determined for each developmental stage. Mean FMR of pre-molt pups was 2.29±0.81 MJ day −1 and increased to 6.16±2.46 and 7.41±3.17 MJ day −1 in post-molt pups and dependent immature animals, respectively. Consequently, daily energy demands of adult females increase 17% by 3 weeks postpartum and continue increasing to 96% above pre-pregnancy levels by the average age of weaning. Our results suggest that the energetics of pup rearing superimposed on small body size, marine living and limited on-board energetic reserves conspire to make female sea otters exceptionally vulnerable to energetic shortfalls. By controlling individual fitness, maternal behavior and pup provisioning strategies, this underlying metabolic challenge appears to be a major factor influencing current population trends in southern sea otters ( Enhydra lutris nereis ).

California↗

USGS2015

Growth-climate relationships across topographic gradients in the northern Great Lakes

Climatic conditions exert important control over the growth, productivity, and distribution of forests, and characterizing these relationships is essential for understanding how forest ecosystems will respond to climate change. We used dendrochronological methods to develop climate–growth relationships for two dominant species, Populus tremuloides (quaking aspen) and Pinus resinosa (red pine), in the upper Great Lakes region to understand how climate and water availability influence annual forest productivity. Trees were sampled along a topographic gradient at the Marcell Experimental Forest (Minnesota, USA) to assess growth response to variations in temperature and different water availability metrics (precipitation, potential evapotranspiration (PET), cumulative moisture index (CMI), and soil water storage). Climatic variables were able to explain 33–58% of the variation in annual growth (as measured by ring-width increment) for quaking aspen and 37–74% of the variation for red pine. Climate–growth relationships were influenced by topography for quaking aspen but not for red pine. Annual ring growth for quaking aspen decreased with June CMI on ridges, decreased with temperature in the November prior to the growing season on sideslopes, and decreased with June PET on toeslopes. Red pine growth increased with increasing July PET across all topographic positions. These results indicate the sensitivity of both quaking aspen and red pine to local climate and show several vulnerabilities of these species to shifts in water supply and temperature because of climate change.

Minnesota↗