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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, [...]

A hydrological framework encompassing nitrogen (N), phosphorus (P) and microbial (E. coli) transfer from land to water was developed to provide a consistent and rapid approach for assessing the potential impacts of land activity on water quality in New Zealand. A flow partition approach was used to route precipitation via surface and subsurface pathways from land to water. The framework included a typology-based inventory that estimates annual yields of transportable N and P from land, a regional-scale spatial layer that attenuates N in groundwater, and literature-based estimates of E. coli concentrations in surface runoff and artificial drainage. Application of the framework in four catchments highlighted the importance of local catchment knowledge of dominant hydrological processes that was needed to ensure flow partitions derived were a realistic representation of transport processes. While the approach was promising, additional refinements are needed to improve process representation (e.g. effects of groundwater lags) and ensure input data (e.g. soil attributes) have appropriate resolution to describe hydrological pathways. We contend that such a framework would provide a consistent and relatively rapid approach for identifying contaminant transfer pathways from land to water that can inform assessments of the potential consequences of land use change and intensification. [ABSTRACT FROM AUTHOR]

Monte Carlo uncertainty analysis, model calibration and optimization applications in hydrology, usually involve a very large number of forward transient model solutions, often resulting in computational bottlenecks. Parallel processing can significantly reduce overall simulation time, benefiting from the architecture of modern computers. This work investigates system performance using two realistic flow and transport modeling scenarios, applied to various modeling hardware, to provide information on the expected performance of parallel simulations and inform investment decisions. We investigate how performance, measured in terms of speedup and efficiency, changes with increasing number of parallel processes. We conclude that the maximum performance achieved by parallelization can range from 40% to 100% of the theoretical limit, with the lower increases associated with multi‐CPU servers. The number of parallel processes required to maximize performance is application dependent, and in contrast to common practice, often needs to be significantly larger than the total number of system CPU cores. Further testing is required to better understand how the physical problem being simulated affects the optimal number of parallel processes needed. Finally, when laptops are considered for modeling applications, careful consideration should be given not only to the specifications but also to the intended use designated by the manufacturer. [ABSTRACT FROM AUTHOR]