Modelling nitrogen fluxes at the landscape scale

The distribution and impacts of different nitrogen pollutants are inextricably linked. To understand the problem fully, the interactions between the different pollutants need to be taken into account. This is particularly important when it comes to abatement techniques, since measures to reduce emissions of one nitrogen pollutant can often lead to an increase in another. This project represents a step towards greater understanding of these issues by linking together new and existing nitrogen flux models into a larger framework. The modelling framework has been constructed and some of the nitrogen flows between fields, farms and the atmosphere have been modelled for a UK study area for typical farm management scenarios.     

Rapid amino acid cycling in arctic and antarctic soils

Amino acids constitute one of the largest inputs of organic nitrogen (N) to most polar soils and have been hypothesized to be important in regulating vegetational succession and productivity in Arctic ecosystems. Our understanding of amino acid cycling in these soils, however, is poor. The aim of this study was to investigate the size and rate of turnover of the amino acid pool in a range of Arctic and Antarctic soils. Our results indicate that in polar soils with either high or low ornithogenic inputs the amino acid pool is small in comparison to the inorganic N pool (NO^–₃ and NH⁺₄). The free amino acid pool constituted only a small proportion of the total dissolved organic nitrogen (DON) pool in these soils. Here we show that these low concentrations may be due to rapid use by the soil microbial community in both Arctic and Antarctic soils. The turnover of the amino acid pool in soil was extremely rapid, with a half-life ranging from 2 to 24 h, indicating that this N pool can be turned over many hundred times each summer when polar soils are frequently unfrozen. The implications of amino acids in N cycling and plant and microbial nutrition are discussed.     

Impact of Land Use on Soluble Organic Nitrogen in Soil

Although it has been hypothesized that soluble organic nitrogen (SON) plays a central role in regulating productivity in some terrestrial ecosystems, the factors controlling the size of the SON pool in soil remain poorly understood. Therefore our principal aim in this work was to assess the impact of seven different land use systems (rough and managed grassland, deciduous and coniferous woodland, heathland, wetland and tilled land) on the size of the SON and inorganic N (NO ₃ ^– , NH ₄ ⁺ ) pools in the surface soil layer (0–15 cm). After extraction with deionised water, we found that in most cases the size of the water extractable organic N (WEON) pool was similar in size to the inorganic N pool. In contrast, the KCl extractable organic N (KClEON) pool constituted the dominant form of soluble N in soils under all land uses, perhaps indicating that significant amounts were held on the soil exchange phase. In contrast to inorganic N, which varied significantly with land use, the size of the KClEON and WEON pool was similar for all land uses with the exception of KClEON in tilled land, where significantly lower amounts were observed. We conclude that SON constitutes an important soil N pool in a broad range of land uses, and that its role in microbial N assimilation, plant nutrition and ecosystem responses to atmospheric N deposition warrants further attention. SAFRD, University of Newcastle, Newcastle-upon-Tyne, NE1 7RU, U.K.     

Best Management Practices for Silvicultural Chemicals and the Science Behind Them

Silvicultural chemicals include fertilizers and pesticides applied for forest management. All states east of the Rockies have at least some form of silvicultural chemical best management practices (SCBMPs) and it is widely accepted that SCBMPs effect some protection of water quality. All SCBMPs recommend handling and application precautions and a minimum width streamside management zone (SMZ) on each side of streams for protection of water quality and aquatic ecosystems. Typically these zones increase in width as stream width increases. In areas where cold-water fish are present, additional widths are designated for their protection. Minimum SMZ widths range from 8 to 91 meters on each side of the stream bank for intermittent and perennial streams. Most SMZ recommendations do not cover ephemeral drainages, ditches or canals. SMZs are generally described as being site specific with width dependent on slope, soil type and other conditions as well as the stream's designation as perennial or intermittent. The science behind SCBMPs is often elusive. Spray drift can be controlled through proper selection and use of application technology while considering site specific conditions. SMZs greatly reduce the amount of herbicides reaching streams. Available toxicological data and research on aquatic ecosystem impacts from herbicide use suggest that additional protection from silvicultural chemicals may not be necessary. However, there is evidence to suggest that protection of ephemeral and intermittent channels can further reduce entry of silvicultural chemicals into streams and also reduce sedimentation. This may be the most fruitful area of research we can pursue in light of the knowledge gaps listed.     

Lightweight Concrete Containing an Alkaline Resistant Starch-Based Aquagel

Starch aquagel-based lightweight concrete has properties similar to those of other lightweight concrete products. However, starch aquagels are unstable in the strongly alkaline conditions typical of Portland Cement-based concrete and may interfere with the setting process. The effect of alkali treatments on the physical, mechanical, and functional properties of starch aquagels and aquagels from starch/polymer blends was investigated. Starch was blended at 100–115°C in a twin-screw extruder with five different polymers to determine whether the blends improved alkaline resistance. Polymer blends containing 5%, 15%, and 30% of the polymer hydrated and formed aquagels when equilibrated in water for 24 h. However, equilibrium moisture content was lower for the blends compared to the starch control. Aquagels equilibrated in 0.15 N NaOH swelled, lost compressive strength and had greater than 90% moisture. The blend of starch and 30% PVOH absorbed less moisture and was more resistant to alkaline dissolution in 1 N NaOH than the other blends tested making it a more suitable material for aquagel-based concrete. The moisture content of starch-based aquagels and mixing time were critical factors in determining setting times. The size of aquagel blends had a minor effect on density and compressive strength.     

Radiogenic Lead Isotopes and Time Stratigraphy in the Hudson River, New York

Radionuclide, radiogenic lead isotope and trace metal analyses on fine-grained sediment cores collected along 160 km of the upper and tidal Hudson River were used to examine temporal trends of contaminant loadings and to develop radiogenic lead isotopes both as a stratigraphic tool and as tracers for resolving decadal particle transport fluxes. Very large inputs of Cd, Sb, Pb, and Cr are evident in the sediment record, potentially from a single manufacturing facility. The total range in radiogenic lead isotope ratios observed in well-dated cores collected about 24 km downstream of the plant is large (e.g., maximum difference in ²⁰⁶Pb/²⁰⁷Pb is 10%), characterized by four major shifts occurring in the 1950s, 1960s, 1970s and 1980s. The upper Hudson signals in Cd and radiogenic lead isotopes were still evident in sediments collected 160 km downstream in the tidal Hudson. The large magnitude and abrupt shifts in radiogenic lead isotope ratios as a function of depth provide sensitive temporal constraints that complement information derived from radionuclide analyses to significantly improve the precision of dating assignments. Application of a simple dilution model to data from paired cores suggests much larger sediment inputs in one section of the river than previously reported, suggesting particle influxes to the Hudson have been underestimated.     

Measurements of PCB Fluxes into the Atmosphere from a Site Receiving Stabilized Dredged Material

A 50 ha known contaminated site in Bayonne, New Jersey, U.S.A. is permitted to receive up to 3 × 10⁶ m³ of sediment dredged from navigation channels in the New York/New Jersey Harbor. Much of the sediment is expected to contain low to moderate concentrations of industrial and agricultural chemicals, including Polychlorinated Biphenyls (PCBs). The dredged material brought to the site is stabilized with cement and then placed as a capping and grading layer. The flux of PCBs from drying stabilized dredged material has been estimated from measurements of PCB air concentrations at two heights above the ground along with micrometeorological observations. A statistically significant gradient in PCB concentrations has been consistently measured in the first 3 m above the ground. Observed PCB fluxes were highest over freshly placed stabilized dredged sediment and decreased as it cured. The highest flux observed in this study was 7214 ng/m²/h, but during subsequent sampling intervals at the same site, the flux estimates decreased by an order of magnitude over a 5-day interval.     

How clean is clean enough? Maintaining thermal protective clothing under field conditions in the oil and gas sector.

The purpose of this research was to develop practical care procedures to help maintain the protective quality of flame resistant workwear laundered by workers in the field. Based on observed field conditions, experiments were conducted that simulated domestic laundry procedures. The first experiment involved two flame resistant (FR) fabrics, contaminated or not contaminated with oil. Independent variables also included detergent type and laundry pre-treatment. Other laundry parameters were controlled. Results indicated that it is easier to maintain the FR performance of the FR-treated blend than it is for the aramid fabric. It is hypothesized that energy generated by initial ignition of oil on the specimens triggers the FR mechanism of the treatment, which in turn inhibits further combustion. A second experiment using larger specimens and a domestic washing machine also supported the hypothesized mechanism.     

Towards a model of safety climate measurement.

In this study, a survey instrument was developed to measure safety climate. A review of the scientific literature as well as consultation with an expert panel was used to determine the survey's dimensions. Next, the survey was administered, first as a pilot study (n = 15) and then as a full scale study (n = 229), to employees of the City of Cincinnati Department of Public Works. The psychometric integrity of the survey was assessed according to validity, reliability and utility criteria. Results are presented and discussed.     

Transition to self‐directed work teams: implications of transition time and self‐monitoring for managers' use of influence tactics

In the face of heightened competitive pressures, elevated quality expectations, and calls for worker empowerment, more and more organizations have turned to self‐directed work teams (SDWTs). A review of the literature devoted to SDWTs suggests that managers often struggle with the transition to SDWTs because of the required shift in control to SDWT members. To promote the development of work teams, managers must modify their use of influence tactics in direct response to the control shift. In this study, we explore changes in managers' usage of influence tactics during the transition to SDWTs within a large aluminum manufacturing plant. Analyses of longitudinal data show that despite the new team environment, managers' use of influence tactics was focused at the individual level. We also found that transition time accounts for variance in managers' choices of influence tactics. Finally, an exploratory analysis suggests that high as opposed to low self‐monitoring managers may be more prone to increase their usage of soft influence tactics and decrease their usage of hard influence tactics over the course of the transition; the influence behavior of low self‐monitoring managers remained unchanged. Implications for future research are discussed. Copyright © 2004 John Wiley & Sons, Ltd.