Systematic parameter fitting for conceptual models of catchment hydrology

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Heterogeneity in catchment properties: a case study of Grey and Buller catchments, New Zealand

International audienceThe scaling behaviour of landscape properties, including both morphological and landscape patchiness, is examined using monofractal and multifractal analysis. The study is confined to two neighbouring meso-scale catchments on the west coast of the South Island of New Zealand. The catchments offer a diverse but largely undisturbed landscape with population and development impacts being extremely low. Bulk landscape properties of the catchments (and their sub-basins) are examined and show that scaling of stream networks follow Hack's empirical rule, with exponents ?0.6. It is also found that the longitudinal and transverse scaling exponents of stream networks equate to ?l ?0.6 and ?w? 0.4, indicative of self-affine scaling. Catchment shapes also show self-affine behaviour. Further, scaling of landscape patches show multifractal behaviour and the analysis of these variables yields the characteristic parabolic curves known as multifractal spectra. A novel analytical approach is adopted by using catchments as hydrological cells at various sizes, ranging from first to sixth order, as the unit of measure. This approach is presented as an alternative to the box-counting method as it may be much more representative of hydro-ecological processes at catchment scales. Multifractal spectra are generated for each landscape property and spectral parameters such as the range in ? (Holder exponent) values and maximum dimension at ?0, (also known as the capacity dimension Dcap), are obtained. Other fractal dimensions (information Dinf and correlation Dcor) are also calculated and compared. The dimensions are connected by the inequality Dcap?Dinf?Dcor. Such a relationship strongly suggests that the landscape patches are heterogeneous in nature and that their scaling behaviour can be described as multifractal. The quantitative parameters obtained from the spectra may provide the basis for improved parameterisation of ecological and hydrological models. Keywords: fractal, multifractal, scaling, landscape, patchines

Cloning and characterisation of the lpxA gene in Campylobacter jejuni.

Lipopolysaccharides (LPS) are important structural components of the outer membrane of Gram-negative bacteria. Lipid A anchors LPS molecules in the outer membrane and is also the sole LPS component necessary for endotoxic shock induction. UDP-N-acetylglucosamine acyltransferase is encoded by the lpxA gene. In Escherichia coli K12 and Salmonella typhimurium, this enzyme completes the first step in lipid A synthesis. The lpxA gene product is essential for the production ofLPS in these organisms as null mutations in lpxA are lethal. The aim of the study was to characterise lipid A biosynthesis in Campylobacter jejuni. C. jejuni appears to contain three lipid A types, one of which is similar to the lipid A species in E. coli. In this study it was proposed that C. jejuni contains an enzyme that is functionally analogous to LpxA from E. coli. The initial aim was to clone the gene necessary for the production of LpxA in C. jejuni. An E. coli temperature-sensitive mutant defective in LpxA activity provided a model with which to study the effect of acyltransferase deficiency on cell viability. A C. jejuni plasmid expression library was electroporated into E. coli lpxA mutant SM101 cells and transformants were screened for their ability to survive at the previous non-permissive temperature (42°C) on minimal media containing ampicillin. Plasmid DNA from one transformant able to restore the full length LPS in lpxA defect in SM101 was analysed. Nucleotide sequence has shown the gene order to be JabZ-lpxA as in E. coli and the predicted amino acid sequence from the 'lpxA' gene from C. jejuni displayed strong amino acid similarity to the 3' end of the UDP-N-acetylglucosamine acyltransferase protein from E. coli, S. typhimurium, Rickettsia rickettsii, Yersinia enterocolitica and Haemophilus influenzae. While this gene from C. jejuni F38011 was capable of rescuing the temperature-sensitive defect of KLC 4177 (SM101), growth curves and viable plate counts reveal that rescue is not complete. A second allele of lpxA, cloned from C. jejuni strain NZRM 1958 has shown a similar arrangement of genes (fabZ-lpxA) although differences in primary amino acid sequence between the alleles were revealed

Assessment of irrigation shortfall using WATHNET in the Otago region of New Zealand

Knowledge of the likely rainfall and river flow for a coming season can improve management of an overall water resources system without unduly compromising either the environmental or productive behaviour of the system. The objective of this study has been to assess the probability of irrigation demand shortfalls, i.e. soil moisture deficits, for a typical “run of the river” irrigation scheme so as to identify the duration and severity of potential shortfalls. In this study a multi-objective linear programming tool WATHNET has been used to build and run a model of the irrigation scheme. The focus of this study has been on how to use predictions of 3-monthly rainfall and temperature to estimate potential daily water available for irrigation. The method uses Monte-Carlo simulations, to produce multiple replicates of equally likely sequences of river flows, rainfall and potential evaporation values. A sub-set of the equally likely sequences is then selected using prediction information of the likely seasonal climate outlook from NIWA’s Climate Update. The selected sequences, which are biased towards the seasonal climate prediction, are then used as inputs to multiple model runs. By using the output from all the “biased” model runs a probability distribution can be made of water availability for irrigation. The methodology has been demonstrated using the Shag River Irrigation Scheme located in the Otago region of New Zealand. The results compare the predicted soil moisture variation over two three-month periods with retrospective simulations based on the observed rainfalls, river flows and potential evaporation values. Results suggest that WATHNET can simulate 3-month soil moisture dynamics. In order to develop WATHNET as a tool to assess probabilities of irrigation shortfall it needs to be validated using measurements of soil moisture variations over an irrigation season at sites with different soil types

An analysis of the effects of parameter uncertainty in deterministic hydrologic models

The uncertainty in the output of deterministic models, due to the uncertainty in the parameters of the model, is analyzed and compared to current procedures of using average values for the uncertain parameters. The present analysis considers an analytical rainfall-runoff flood frequency model where the infiltration parameter is considered as a stochastic variable. The same conceptual procedure can be used to analyze fixed but uncertain (unknown) parameters. The extension to analyzing parameter uncertainty in large simulation models is indicated, and the importance of such analyses is discussed