Philip A. Robertson

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There is much interest in biogeochemical processes that occur at the interface between soils and streams since, at the scale of landscapes, these habitats may function as control points for fluxes of nitrogen (N) and other nutrients from terrestrial to aquatic ecosystems. Here we examine whether a thermodynamic perspective can enhance our mechanistic and(More)
Nitrous oxide (N2O) is a major greenhouse gas (GHG) product of intensive agriculture. Fertilizer nitrogen (N) rate is the best single predictor of N2O emissions in rowcrop agriculture in the US Midwest. We use this relationship to propose a transparent, scientifically robust protocol that can be utilized by developers of agricultural offset projects for(More)
Trace gas fluxes often show temporal variability on the order of hours and accurate quantification may be difficult without continuous or near-continuous measurements. We developed an automated near-continuous trace gas analysis system (NCTGAS) to measure soil-atmosphere gas fluxes on a several-times-per-day basis. In this system, air is circulated in a(More)
A variety of disinfection procedures were tested on two strains of scrapie agent, treated either as brain macerates (autoclaving) or as 10% homogenates (chemical treatments). It is suggested that a given treatment should produce a titre loss, of both strains of scrapie, of at least 10(4) units before it be regarded as useful for the disinfection of the(More)
[1] Site preference (SP), the difference in dN between the central and outer nitrogen atoms in N2O, is a powerful approach for apportioning fluxes of N2O from soils to nitrification and denitrification (Sutka et al., 2006). A critical aspect of the use of SP data to apportion sources of N2O to nitrification and denitrification is the need to evaluate data(More)
Numerous ecological studies use Principal Components Analysis (PCA) for exploratory analysis and data reduction. Determination of the number of components to retain is the most crucial problem confronting the researcher when using PCA. An incorrect choice may lead to the underextraction of components, but commonly results in overextraction. Of several(More)
The natural removal of NO3 by denitrification within riparian zones of streams and rivers is an area of considerable interest owing to its potential to minimize the impacts of excess anthropogenic loadings. In this study we utilize natural variations in stable N isotopic compositions of NO3 and NH4 within a transect of shallow wells extending 4 m inland(More)
[1] Agricultural lime can be a source or a sink for CO2, depending on whether reaction occurs with strong acids or carbonic acid. Here we examine the impact of liming on global warming potential by comparing the sum of Ca and Mg to carbonate alkalinity in soil solutions beneath unmanaged vegetation versus limed row crops, and of streams and rivers in(More)
The woody vegetation and associated soil-site variables from a range of upland to swamp sites were measured using 480 0.04 ha plots from Little Black Slough, Goose Pond and Horseshoe Lake in Illinois, and Mingo Wildlife Refuge, Missouri. Multiple regression, correlation, and factor analysis were used to relate soil-site data to vegetation structure and(More)