Residual soil nitrate after potato harvest

Nitrogen loss by leaching is a major problem, particularly with crops requiring large amounts of N fertilizer. We evaluated the effect of N fertilization and irrigation on residual soil nitrate following potato (Solanum tuberosum L.) harvests in the upper St-John River valley of New Brunswick, Canada. Soil nitrate contents were measured to a 0.90-m depth in three treatments of N fertilization (0, 100, and 250 kg N ha(-1)) at two on-farm sites in 1995, and in four treatments of N fertilization (0, 50, 100, and 250 kg N ha(-1)) at four sites for each of two years (1996 and 1997) with and without supplemental irrigation. Residual soil NO3-N content increased from 33 kg NO3-N ha(-1) in the unfertilized check plots to 160 kg NO3-N ha(-1) when 250 kg N ha(-1) was applied. Across N treatments, residual soil NO3-N contents ranged from 30 to 105 kg NO3-N ha(-1) with irrigation and from 30 to 202 kg NO3-N ha(-1) without irrigation. Residual soil NO3-N content within the surface 0.30 m was related (R2 = 0.94) to the NO3-N content to a 0.90-m depth. Estimates of residual soil NO3-N content at the economically optimum nitrogen fertilizer application (Nop) ranged from 46 to 99 kg NO3-N ha(-1) under irrigated conditions and from 62 to 260 kg NO3-N ha(-1) under nonirrigated conditions, and were lower than the soil NO3-N content measured with 250 kg N ha(-1). We conclude that residual soil NO3-N after harvest can be maintained at a reasonable level (<70 kg NO3-N ha(-1)) when N fertilization is based on the economically optimum N application.     

Variations in benthic community structure in a sub-tropical estuary

Abundances of macroinfaunal invertebrates in sand dollar (Dendraster excentricus) beds and in adjacent areas free of sand dollars were studied at 10 intertidal sites in the Pacific Northwest region of the USA and Canada. Each site was sampled once in late summer of 1977. There were no significant differences in overall diversity of species between the beds and adjacent areas; nor did cluster analysis indicate a sand dollar bed community. However, a polychaete (Armandia brevis) was significantly more abundant inside the beds than just outside them. Conversely, in comparison to the beds, adjacent regions contained significantly more specimens of the following species: a bivalve (Transennella tantilla), several tubicolous crustaceans (Corophium spp., Ampelisca agassizi, and Leptochelia savignyi) and two polychaetes (Glycinde polygnatha and Malacoceros arenicola). Sediment characteristics at each study site were not correlated with the presence or absence of sand dollars; moreover, a comparison among the 10 sites revealed no sediment characteristics typical of sand dollar beds. At most of the sites, significantly fewer tube-building invertebrates occurred inside sand dollar beds than outside. The discussion considers the possibility that mechanical disturbance by the sand dollars tends to exclude some macroinvertebrates (especially tubicolous ones) from sand dollar beds.     

Measures of flow variability for great lakes tributaries

Design of monitoring programs for load estimation is often hampered by the lack of existing chemical data from which to determine patterns of flux variance, which determine the sampling program requirements when loads are to be calculated using flux-dependent models like the Beale Ratio Estimator. In contrast, detailed flow data are generally available for the important tributaries. For pollutants from non-point sources there is often a correlation between flow and pollutant flux. Thus, measures of flow variability might be calibrated to flux variability for well-known watersheds, after which flow variability could be used as a proxy for flux variability to estimate sampling needs for tributaries for which adequate chemical observations are lacking.Three types of measures of flow variability were explored: ratio measures, which are of the form q _x/q_y, where q _xis the flow corresponding to the percentile x, and y=100–x; spread measures, of the form (q _x–q_y)/q_m, where q _mis the median flow; and the coefficient of variation of the logs of flows. In the latter, flows are log transformed because flow distributions are often approximately log-normal. Three ratio measures were evaluated, based on the percentiles (10,90), (20,80), and (25,75). The analogous spread measures were also evaluated; the spread measure based on percentiles (25,75) is derived from the commonly used fourth spread of non-parametric statistics. The ratio measures and the spread measures are scale independent, and thus are measures only of the shape of the distribution. The coefficient of variation is also scale independent, but in log space.Values of these measures of flow variability for 120 Great Lakes tributaries are highly intercorrelated, although the relationship is often non-linear. The coefficient of variation of the log of the flows is also well correlated with the coefficient of variation of fluxes of suspended solids, total phosphorus, and chloride, for a smaller set of rivers where the existence of abundant chemical data allows comparison.Tributaries with abnormal distributions often show up as outliers when one measure of flow variability is plotted against another. Several examples are discussed.     

DETECTING REDUCTIONS IN SEDIMENT LOADS ASSOCIATED WITH OHIO'S CONSERVATION RESERVE ENHANCEMENT PROGRAM1

ABSTRACT: Small systematic changes in loads or concentrations of water quality constituents are difficult to detect against the background of short term fluctuations (“noise”) that result from weather and climate effects. Minimum Detectable Change Analysis (MDCA) uses prior knowledge of a water quality constituent to determine how much change must occur (e.g., from implementation of conservation practices) for the change to be statistically significant. In this paper we use MDCA to determine whether the goal of the Ohio Lake Erie Conservation Reserve Enhancement Program (CREP), to reduce sediment loads by an average of 6 percent over 10 years, represents a large enough change to be detected. We conclude that this amount of change is unlikely to be detected as statistically significant, even with the high frequency sampling program planned for evaluating it. The minimum detectable change ranges from about 7 to 9 percent for three different rivers.     

Functional models for colloid retention in porous media at the triple line

Spectral confocal microscope visualizations of microsphere movement in unsaturated porous media showed that attachment at the Air Water Solid (AWS) interface was an important retention mechanism. These visualizations can aid in resolving the functional form of retention rates of colloids at the AWS interface. In this study, soil adsorption isotherm equations were adapted by replacing the chemical concentration in the water as independent variable by the cumulative colloids passing by. In order of increasing number of fitted parameters, the functions tested were the Langmuir adsorption isotherm, the Logistic distribution, and the Weibull distribution. The functions were fitted against colloid concentrations obtained from time series of images acquired with a spectral confocal microscope for three experiments performed where either plain or carboxylated polystyrene latex microspheres were pulsed in a small flow chamber filled with cleaned quartz sand. Both moving and retained colloids were quantified over time. In fitting the models to the data, the agreement improved with increasing number of model parameters. The Weibull distribution gave overall the best fit. The logistic distribution did not fit the initial retention of microspheres well but otherwise the fit was good. The Langmuir isotherm only fitted the longest time series well. The results can be explained that initially when colloids are first introduced the rate of retention is low. Once colloids are at the AWS interface they act as anchor point for other colloids to attach and thereby increasing the retention rate as clusters form. Once the available attachment sites diminish, the retention rate decreases.     

Whale watch or no watch: the Australian whale watching tourism industry and climate change

Whale watching is a billion dollar industry worldwide. One of the most popular species for whale watching is the humpback whale (Megaptera novaeangliae). The migratory corridors, feeding, resting and calving sites which are used for whale watching may be influenced by changing ocean currents and water temperatures. Here, we used an innovative approach addressing the emerging issue of climate change on the whale watch industry. This involved participatory modelling using key stakeholders for the whale watching industry to develop a systems conceptualisation model for evaluating the potential effects of climate change based on a case study from the east coast of Australia. This participatory approach allowed us to identify the causal linkages (including feedback pathways) between different “Elements” of the system within which the whale watching industry operates. It also allowed us to integrate multiple drivers covering socio-economic and environmental aspects including climate change (e.g. temperature), policy (e.g. number of boats), ecology (e.g. number of whales) and socio-economics (e.g. number of tourists) to evaluate the changes in the overall system. We then developed a Bayesian belief network model from the systems conceptualisation on which stakeholders identified a priority issue (Profitability). Stakeholders provided the structure and the quantification of this model, and a sensitivity analysis was carried out to help identify important intervention points for the industry. Overall, our research illustrates how such a modelling process can assist local tourism operators and authorities in making rational management decisions within a holistic or systems-based framework and its approach is applicable to other regions.     

Transformation products and reaction kinetics of fragrances in advanced wastewater treatment with ozone

The reaction of the fragrance compounds 4,6,6,7,8,8-hexamethyl-1,3,4,7-tetrahydrocyclopenta[g]isochromene (HHCB), 1-(3,5,5,6,8,8-hexamethyl-6,7-dihydronaphthalen-2-yl)ethanone (AHTN), 1-tert-butyl-3,5-dimethyl-2,4,6-trinitrobenzene (musk xylene/MX), 1-(4-tert-butyl-2,6-dimethyl-3,5-dinitrophenyl)ethanone (musk ketone/MK), and 1-(2,3,8,8-tetramethyl-1,3,4,5,6,7-hexahydronaphthalen-2-yl)ethanone (OTNE) with ozone in tap water as well as waste water treatment plant (WWTP) effluents is described. Several transformation products are characterized by means of gas chromatography coupled to mass spectrometry. One transformation product (HHCB-Lactone) was confirmed by means of a true standard. Musk xylene and musk ketone do not react with ozone under the conditions used in this study. AHTN and HHCB reacted slowly to a multitude of transformation products, while OTNE reacted quickly to several stable transformation products. The reaction constants and half lives are used to predict removal efficiencies for full scale reactors.     

First detection of an NSAID, flunixin, in sheep's wool using GC-MS

Exposure to the nonsteroidal anti-inflammatory drug (NSAID) diclofenac resulted in the near extinction of three species of Gyps vultures on the Indian subcontinent. Other NSAIDs present in the environment, including flunixin, may pose a similar risk. In the course of a study to determine the feasibility of detecting NSAIDs in keratinous matrices (i.e., hair, nails and feathers) using GC-MS, wool opportunistically collected from a sheep treated with flunixin was analysed for residues. Flunixin was detected qualitatively in external wool wash and extract samples. While residues of veterinary agents and pesticides have previously been found in sheep’s wool, our preliminary investigation provides the first instance of an NSAID being detected in this matrix. Here we provide the sample preparation methods and GC-MS parameters used to enable further refinement as part of ongoing conservation and consumer quality control measures.     

Transformation of sulfaquinoxaline by chlorine and UV light in water: kinetics and by-product identification

Sulfaquinoxaline (SQX) is an antimicrobial of the sulfonamide class, frequently detected at low levels in drinking and surface water as organic micropollutant. The main goal of the present study is the evaluation of SQX reactivity during chlorination and UV irradiations which are two processes mainly used in water treatment plants. The SQX transformation by chlorination and UV lights (254 nm) was investigated in purified water at common conditions used for water disinfection (pH =?7.2, temperature =?25 °C, [chlorine] =?3 mg L^?1). The result shows a slow degradation of SQX during photolysis compared with chlorination process. Kinetic studies that fitted a fluence-based first-order kinetic model were used to determine the kinetic constants of SQX degradation; they were equal to 0.7?×?10^?4 and 0.7?×?10^?2 s^?1corresponding to the half time lives of 162 and 1.64 min during photolysis and chlorination, respectively. In the second step, seven by-products were generated during a chlorination and photo-transformation of SQX and identified using liquid chromatography with electrospray ionization and tandem mass spectrometry (MS-MS). SO₂ extrusion and direct decomposition were the common degradation pathway during photolysis and chlorination. Hydroxylation and isomerization were observed during photodegradation only while electrophilic substitution was observed during chlorination process.