The distribution of Salmonella enterica serovars and subtypes in surface water from five agricultural regions across Canada.

Serovar prevalence of the zoonotic pathogen, Salmonella enterica, was compared among 1624 surface water samples collected previously from five different Canadian agricultural watersheds over multiple years. Phagetyping, pulsed field gel electrophoresis (PFGE), and antimicrobial resistance subtyping assays were performed on serovars Enteritidis, Typhimurium, and Heidelberg. Serovars and subtypes from surface water were compared with those from animal feces, human sewage, and serovars reported to cause salmonellosis in Canadians. Sixty-five different serovars were identified in surface water; only 32% of these were isolated from multiple watersheds. Eleven of the 13 serovars most commonly reported to cause salmonellosis in Canadians were identified in surface water; isolates of these serovars constituted >40% of the total isolates. Common phagetypes and PFGE subtypes of serovars associated with illness in humans such as S. Enteritidis and S. Typhimurium were also isolated from surface water and animal feces. Antimicrobial resistance was generally low, but was highest among S. Typhimurium. Monitoring of these rivers helps to identify vulnerable areas of a watershed and, despite a relatively low prevalence of S. enterica overall, serovars observed in surface water are an indication of the levels of specific S. enterica serovars present in humans and animals.

Investigation of an Escherichia coli environmental benchmark for waterborne pathogens in agricultural watersheds in Canada.

Canada's National Agri-Environmental Standards Initiative sought to develop an environmental benchmark for low-level waterborne pathogen occurrence in agricultural watersheds. A field study collected 902 water samples from 27 sites in four intensive agricultural watersheds across Canada from 2005 to 2007. Four of the sites were selected as reference sites away from livestock and human fecal pollution sources in each watershed. Water samples were analyzed for Campylobacter spp., Salmonella spp., Escherichia coli O157:H7, Cryptosporidium spp., Giardia spp., and the water quality indicator E. coli. The annual mean number of pathogen species was higher at agricultural sites (1.54 ± 0.07 species per water sample) than at reference sites (0.75 ± 0.14 species per water sample). The annual mean concentration of E. coli was also higher at agricultural sites (491 ± 96 colony-forming units [cfu] 100 mL(-1)) than at reference sites (53 ± 18 cfu 100 mL(-1)). The feasibility of adopting existing E. coli water quality guideline values as an environmental benchmark was assessed, but waterborne pathogens were detected at agricultural sites in 80% of water samples with low E. coli concentrations (<100 cfu 100 mL(-1)). Instead, an approach was developed based on using the natural background occurrence of pathogens at reference sites in agricultural watersheds to derive provisional environmental benchmarks for pathogens at agricultural sites. The environmental benchmarks that were derived were found to represent E. coli values lower than geometric mean values typically found in recreational water quality guidelines. Additional research is needed to investigate environmental benchmarks for waterborne pathogens within the context of the "One World, One Health" perspective for protecting human, domestic animal, and wildlife health.

Sources of nitrite in streams of an intensively cropped watershed.

The sources of high in-stream nitrite (NO2(-)) concentrations were investigated in two major streams located in an intensively cropped watershed in Quebec, Canada. Nitrogen retention was determined to evaluate the dynamics in relation to nitrogen transport along both stream branches during summer-low-water and fall-recharge regimes. In the first stream branch, NO2(-) and ammonium (NH4(+)) showed removal patterns during summer-low-water and fall-recharge periods, whereas, in the second branch, NO2(-) and NH4(+) exports occurred during both hydrologic regimes. The study also demonstrated that seepage water is a source of NO2(-) instream, which varies within the watershed stream branches and with the hydrologic regime. The results highlighted a significant reductive microbial activity in seepage water from either denitrification or dissimilatory nitrate reduction to ammonium (DNRA), leading to nitrate (NO3(-)) consumption. Differences in groundwater NO3(-) concentrations feeding each stream branch may have significantly influenced NH4(+) and NO2(-) concentrations found in seepage water, which potentially resulted in quantitatively significant NO2(-) formation.

Nitrogen fertilizer impact on the Wilmot watershed aquifer in Prince Edward Island, Canada.

The objective of this study is to estimate the soil N flux from the vadose zone to the aquifer of the Wilmot watershed (Prince Edward Island, Canada) for a typical three-year cropping rotation (barley-red clover-potato). A conceptual model estimates that 199-221 tons of N were yearly available for leaching at the watershed scale. A significant portion of this N amount was available for leaching at the end of the crop season representing 80-90% of the annual N balance. Drainage water nitrate concentrations were significantly higher after the potato-rotation year than during the crop season. Low nitrate concentrations were measured at spring thaw indicating that most of the nitrate available from the preceding potato crop season was likely leached at the end of fall or during winter. Early spring ionic exchange membrane sampling show a large availability of nitrate in soil possibly throughout winter as well, resulting from soil N mineralization and nitrification over the winter period. These findings are corroborated by the isotope natural abundance analysis of nitrate in groundwater implying that nitrifiers are significantly active during winter, as well as during the crop season, and that leaching of soil nitrates with seasonal signals takes place whenever recharge is occurring.

Indicator of risk of water contamination by phosphorus from Canadian agricultural land.

The indicator of risk of water contamination by phosphorus (IROWC_P) is designed to estimate where the risk of water P contamination by agriculture is high, and how this risk is changing over time based on the five-year period of data Census frequency. Firstly developed for the province of Quebec (2000), this paper presents an improved version of IROWC_P (intended to be released in 2008), which will be extended to all watersheds and Soil Landscape of Canada (SLC) polygons (scale 1:1, 000, 000) with more than 5% of agriculture. There are three objectives: (i) create a soil phosphorus saturation database for dominant and subdominant soil series of SLC polygons--the soil P saturation values are estimated by the ratio of soil test P to soil P sorption capacity; (ii) calculate an annual P balance considering crop residue P, manure P, and inorganic fertilizer P--agricultural and manure management practices will also be considered; and (iii) develop a transport-hydrology component including P transport estimation by runoff mechanisms (water balance factor, topographic index) and soil erosion, and the area connectivity to water (artificial drainage, soil macropores, and surface water bodies).

Self-organization in a multicore fiber laser array.

We explain an observed spontaneous transition to the high-brightness, in-phase array state of a seven-core ytterbium-doped fiber laser array [IEEE Photonics Technol. Lett. 13, 439 (2001)]. The responsible mechanism is nonlinear refraction, and either in-phase or antiphase array modes can be selected by control of pump intensity. The phenomenon appears to be robust and scalable.

Quenching and enhancement of an optical nonlinearity by a phase-conjugate mirror.

The nonlinear polarizabilities of a two-level atom and a nonlinear oscillator in front of a resonant phase-conjugate mirror are calculated as functions of the mirror reflectivity. The effect of the mirror is to quench the nonlinearity of the two-level system and most anharmonic oscillators. In the case of a weakly anharmonic oscillator the nonlinear polarizability can be extremely large.

Optical quadratic processor using four-wave mixing in BaTiO(3).

A method has been demonstrated for performing quadratic operations by using four-wave mixing in BaTiO(3) crystals. The processor performs a parallel vector-matrix-vector multiplication. System operation and performance are discussed.

Transverse-mode instability and chaos in an optical cavity with phase-conjugate mirror.

We calculate the effect of pump-intensity variation on the mode structure of an optical cavity with a phaseconjugate mirror operated in the linear regime. Instabilities and chaos are predicted under conditions similar to those observed by Valley and Dunning [Opt. Lett. 9, 513 (1984)].

Improvement of phase-conjugate beam fidelity in degenerate four-wave mixing by focused probe fields.

It is shown that signal-beam fidelity in degenerate four-wave mixing, which is affected by the finite beam widths of the pump beams, may be largely restored over a wide range of spatial frequencies. The technique consists of focusing the probe beam into the mixing cell. This permits restoration of up to about 90%of the principal distortion effect.

Conversion of a wideband frequency-modulated signal to amplitude modulation through dispersion in an optical fiber.

Our calculation shows that, by means of group-velocity dispersion of an optical fiber, a cw frequency-modulated signal evolves into an intense and sharp pulse. The results compare favorably with an earlier analysis of a narrowband FM system. In particular, the minimum fiber length needed for maximum FM-AM conversion may be considerably reduced.

Geometrical characterization of liquid core fibers by measurement of thermally induced mode cutoffs and interference.

Transmitted and scattered intensity in liquid core fibers have been measured as a function of temperature and v values of cutoff points obtained which are in good agreement with weakly guiding mode theory. We also report observation of oscillations in the transmitted intensity which we interpret to be caused by interference between modes. We show that measurement of the period of these oscillations can be used to make high-precision nondestructive measurements of core radius and core ellipticity along the fiber length.

FM-AM conversion by material dispersion in an optical fiber.

We show that material and guide dispersion may be used effectively in an optical fiber to convert an FM signal to an AM signal after it traverses a certain minimum fiber length. This length depends on material and modal dispersion of the guide. An upper limit to the fiber length is established and is shown to be related to laser linewidth. We also discuss laser-mode selection and conversion in multimode fibers.