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We applied 5 pesticides, along with bromide as a conservative tracer, at 2 field sites (Northland and Manawatu, North Island of New Zealand), and their distributions in the soil profile were monitored through soil core and suction cup sampling for 18 months. Field-measured values were simulated using LEACHM, HYDRUS-1D, GLEAMS, and SPASMO models and compared against the measured datasets at both these sites. All 4 models predicted the measured dataset for each of the compounds with reasonable degree of accuracy; however, some discrepancies were observed. Prediction by GLEAMS was by far the best, as indicated by the goodness of fit parameters. Pesticide leaching parameters, organic carbon partition coefficient (Koc), and degradation half-life ([T.sub.1/2]) were optimised using the PEST optimisation package. For diazinon and terbuthylazine the parameters obtained for each of the models were generally close to the literature range. However, Koc and [T.sub.1/2] values for atrazine, hexazinone, and procymidone were found to be slightly lower than the available literature range data. Additional keywords: models, atrazine, diazinon, hexazinone, procymidone, terbuthylazine, bromide., Introduction Simulation models typically integrate theoretical concepts, empirical knowledge, numerical algorithms, and statistical considerations to predict environmental parameters of interest. Such models are increasingly used world-wide to predict the fate [...]

Five pesticides, atrazine, diazinon, hexazinone, procymidone, and terbuthylazine, were applied to a Kiripaka bouldery clay loam located near Whangarei, Northland, New Zealand, and a Himatangi sand located near Palmerston North, Manawatu, along with bromide and deuterated water as tracers. Their transport and persistence were monitored for 18 months using soil sampling down to a maximum of 1 m and 8 suction cups at each site located between 0.2 and 1.5 m down the profile. There was rapid leaching of the tracers as well as hexazinone at both sites. Procymidone was much less mobile than the tracers but was very persistent, with significant amounts still present in the profile after 18 months. Atrazine, terbuthylazine, and diazinon had relatively low persistence, mainly due to rapid degradation, and possibly volatilisation for diazinon, with < 10% remaining after 6 months at both sites. There was evidence of preferential flow at the Northland site, which is consistent with the highly structured soil profile and intense rainfall that occurred at the site in the month following pesticide application. Batch sorption experiments measured lower [K.sub.oc] values for the topsoil samples than generally observed in the literature for all 5 pesticides. This indicates that these pesticides will be much more mobile in the Northland Kiripaka soil and slightly more mobile in the Manawatu Himatangi soil than would be expected from the literature values. Additional keywords: atrazine, diazinon, hexazinone, procymidone, terbuthylazine, bromide, deuterated water., Introduction While the majority of groundwaters in New Zealand appear free from pesticide contamination (Ministry for the Environment 1997), recent New Zealand-wide targeted surveys in 1998 and 2004 have detected [...]

This paper presents results using the Burgers equation in spherical coordinates for the investigation of soil water dynamics around porous cup samplers under field conditions. The analysis reveals that the yield (V) of the porous suction-cup sampler is a power function of inflow duration (7) and source moisture strength (A). It also shows that the shock front velocity and moving boundary of the front are both power functions of A and time. The analysis further demonstrates that the asymptotic shock front velocity derived from a similarity solution is the samefor different versions of Burgers equation, indicating the validity of different versions of Burgers equation for the same flow patterns. The observation using time domain reflectometry shows that a moisture shock was induced around the sampler following application of a vacuum, which justifies the application of Burgers equation. The values of A were derived using field data to determine the location and the front velocity of the shock. Additional keywords: soil-water flow, TDR., Introduction In this paper, we aim to investigate the transient movement of water towards a porous cup sampler, which can be regarded theoretically as a spherical sink. In this case, [...]