University of Maine

About: University of Maine is a education organization based out in Orono, Maine, United States. It is known for research contribution in the topics: Population & Ice sheet. The organization has 8637 authors who have published 16932 publications receiving 590124 citations. The organization is also known as: University of Maine at Orono.

Responses of atmospheric methane consumption by soils to global climate change

Abstract: Soils consume about 40 Tg methane from the atmosphere annually. Thus, soils contribute significantly to the atmospheric methane budget. However, responses of atmospheric methane consumption to climate change are uncertain. Predicting these responses requires an understanding of the effect on methane consumption of specific variables (temperature and soil water content) as well as interactions among parameters (methane, ammonium, water content). Key considerations involve the limitations of diffusive transport and controls of methane diffusivity; limitation of methanotrophic activity by water stress; relatively slow growth rates of methane-oxidizing bacteria on atmospheric methane; ammonium toxicity. Interactions among these parameters may be particularly important, and lead to responses contrary to those predicted from changes in temperature and water content alone. Results from a number of analyses indicate that atmospheric methane consumption is especially sensitive to anthropogenic disturbances, which typically decrease activity. Continued increases in wet and dry ammonium deposition are likely to exacerbate inhibition resulting from changes in land use. Changes in hydrological regimes could further decrease activity if dry periods increase water stress at soil depths currently colonized by methanotrophs. Future trends in the soil methane sink are likely to lead to enhanced accumulation of atmospheric methane.

Investigating peatland stratigraphy and hydrogeology using integrated electrical geophysics

Abstract: Hydrology has been suggested as the mechanism controlling vegetation and related surficial pore-water chemistry in large peatlands. Peatland hydrology influences the carbon dynamics within these large carbon reservoirs and will influence their response to global warming. A geophysical survey was completed in Caribou Bog, a large peatland in Maine, to evaluate peatland stratigraphy and hydrology. Geophysical measurements were integrated with direct measurements of peat stratigraphy from probing, fluid chemistry, and vegetation patterns in the peatland. Consistent with previous field studies, ground-penetrating radar (GPR) was an excellent method for delineating peatland stratigraphy. Prominent reflectors from the peat-lake sediment and lake sediment-mineral soil contacts were precisely recorded up to 8 m deep. Two-dimensional resistivity and induced polarization imaging were used to investigate stratigraphy beneath the mineral soil, beyond the range of GPR. We observe that the peat is chargeable, and that IP imaging is an alternative method for defining peat thickness. The chargeability of peat is attributed to the high surface-charge density on partially decomposed organic matter. The electrical conductivity imaging resolved glaciomarine sediment thickness (a confining layer) and its variability across the basin. Comparison of the bulk conductivity images with peatland vegetation revealed a correlation between confining layer thickness and dominant vegetation type, suggesting that stratigraphy exerts a control on hydrogeology and vegetation distribution within this peatland. Terrain conductivity measured with a Geonics EM31 meter correlated with confining glaciomarine sediment thickness and was an effective method for estimating variability in glaciomarine sediment thickness over approximately 18 km 2 . Our understanding of the hydrogeology, stratigraphy, and controls on vegetation growth in this peatland was much enhanced from the geophysical study.

Seasonal carcass composition and energy balance of female black ducks in Maine

Abstract: Female Black Ducks (Anas rubripes) collected in Maine during the summer, fall, and winter of 1974-1976 showed significant seasonal variation in body weight, nonfat dry weight, gizzard and pectoral muscle weight, and fat, moisture, and protein content Variation of body weight within and among seasons was correlated more strongly with carcass protein content, and with fat content during seasons of heavy lipid deposition, than with three structural size variables (culmen, tarsus, and sternum) Regression equations including fat and protein as independent variables accounted for 80-90% of the annual and seasonal variation in body weight; structural size variables alone accounted for less than 30% Immature females averaged 54 and 99 g lighter, and carried 54 and 59 g less fat than adults during the fall and winter Ducks of both age classes lost weight in December and January Adult and immature females metabolized 59 and 64 g of fat and 17 and 25 g of protein in winter compared with 46 g of fat during the nesting season Nutrient reserves are thus equally as important for the winter survival of these birds as for successfurl eproduction Seasonalc hangesi n carcass composition suggest that (1) fat deposited in late fall provides an energy reserve during winter, (2) a reduction in lean weight during winter may lower daily energy requirements and increase the effective amount of energy reserves, and (3) declining body weights during late winter may be an endogenous rhythm that reflects a shift in the expected benefits of an energy reserve compared to the costs of carrying additional weight

Modeling Englacial Radar Attenuation at Siple Dome, West Antarctica, Using Ice Chemistry and Temperature Data

Abstract: [1] The radar reflectivity of an ice-sheet bed is a primary measurement for discriminating between thawed and frozen beds. Uncertainty in englacial radar attenuation and its spatial variation introduces corresponding uncertainty in estimates of basal reflectivity. Radar attenuation is proportional to ice conductivity, which depends on the concentrations of acid and sea-salt chloride and the temperature of the ice. We synthesize published conductivity measurements to specify an ice-conductivity model and find that some of the dielectric properties of ice at radar frequencies are not yet well constrained. Using depth profiles of ice-core chemistry and borehole temperature and an average of the experimental values for the dielectric properties, we calculate an attenuation rate profile for Siple Dome, West Antarctica. The depth-averaged modeled attenuation rate at Siple Dome (20.0 ± 5.7 dB km−1) is somewhat lower than the value derived from radar profiles (25.3 ± 1.1 dB km−1). Pending more experimental data on the dielectric properties of ice, we can match the modeled and radar-derived attenuation rates by an adjustment to the value for the pure ice conductivity that is within the range of reported values. Alternatively, using the pure ice dielectric properties derived from the most extensive single data set, the modeled depth-averaged attenuation rate is 24.0 ± 2.2 dB km−1. This work shows how to calculate englacial radar attenuation using ice chemistry and temperature data and establishes a basis for mapping spatial variations in radar attenuation across an ice sheet.