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M. O'Brien

Publications and source records attributed to M. O'Brien.

6 recordsLinked to original sources
USGS2009

Geoelectrical measurement and modeling of biogeochemical breakthrough behavior during microbial activity

We recorded bulk electrical conductivity ( σ b ) along a soil column during microbially-mediated selenite oxyanion reduction. Effluent fluid electrical conductivity and early time σ b were modeled according to classic advective-dispersive transport of the nutrient medium. However, σ b along the column exhibited strongly bimodal breakthrough which cannot be explained by changes in the electrical conductivity of the pore fluid. We model the anomalous breakthrough by adding a conduction path in parallel with the fluid phase, with a time dependence described by a microbial population-dynamics model. We incorporate a delay time to show that breakthrough curves along the column satisfy the same growth model parameters and offer a possible explanation based on biomass-limited growth that is delayed with distance from influent of the nutrient medium. Although the mechanism causing conductivity enhancement in the presence of biomass is uncertain, our results strongly suggest that biogeochemical breakthrough curves have been captured in geoelectrical datasets.

Geophysical Research Letters↗
USGS2005

Broad-scale predictors of canada lynx occurrence in eastern North America

The Canada lynx (Lynx canadensis) is listed as a threatened species throughout the southern extent of its geographic range in the United States. Most research on lynx has been conducted in the western United States and Canada; little is known about the ecology of lynx in eastern North America. To fill critical knowledge gaps about this species, we modeled and mapped lynx occurrence using habitat and weather data from 7 eastern states and 3 Canadian provinces. Annual snowfall, road density, bobcat (L. rufus) harvest, deciduous forest, and coniferous forest were compared at 1,150 lynx locations and 1,288 random locations. Nineteen a priori models were developed using the information-theoretic approach, and logistic regression models were ranked using Akaike's Information Criterion (AIC) and by our ability to correctly classify reserved data (Kappa). Annual snowfall and deciduous forest predicted lynx presence and absence for a reserved dataset (n = 278) with 94% accuracy. A map of the probability of lynx occurrence throughout the region revealed that 92% of the potential habitat (i.e., >50% probability of occurrence) was concentrated in a relatively contiguous complex encompassing northern Maine, New Brunswick, and the Gaspe?? peninsula of Quebec. Most of the remaining potential habitat (5%) was on northern Cape Breton Island in Nova Scotia. Potential habitat in New Hampshire, Vermont, and New York was small (1,252 km2), fragmented, and isolated (>200 km) from known lynx populations. When federally listed as threatened in the contiguous United States in 2000, inadequate regulations on federal lands were cited as the primary threat to Canada lynx. However, the majority of potential lynx habitat in the eastern United States is on private lands and continuous with potential habitat in Canada. Therefore, lynx conservation in eastern North America will need to develop partnerships across national, state, and provincial boundaries as well as with private landowners.

Journal of Wildlife Management↗