Palmerston North, New Zealand
Palmerston North, New Zealand

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Muller K.,The New Zealand Institute for Plant and Food Research Ltd | Deurer M.,Manawatu Mail Center | Newton P.C.D.,Agresearch Ltd.
Agriculture, Ecosystems and Environment | Year: 2010

We hypothesized that elevated atmospheric carbon dioxide concentration [CO2] as a feature of climate change promotes the occurrence of soil water repellency (SWR) which reduces soil carbon mineralization and thus increases carbon sequestration. Soil surface transects under elevated (475μLL-1) and ambient atmospheric [CO2] in a long-term Free Air Carbon Dioxide Enrichment experiment were sampled at a high spatial resolution. All samples were hydrophobic at the time of the sampling. At the micro-scale, the differences in degree and persistence of SWR, soil organic matter (SOM) content, microbial respiration rates (MRR) and water content between the treatments were not significant. SWR was not correlated with SOM or MRR. A strong correlation between water contents and SWR parameters demonstrated the importance of SWR for water redistribution. At the meso-scale of disc infiltrometry, infiltration rates were reduced by SWR, and were higher under ambient than under elevated [CO2]. This corroborates the tendency of reduced SWR under elevated [CO2] observed at the micro-scale. SWR showed a spatial structure, exhibiting short ranges. SOM and MRR showed no spatial pattern at the scale analyzed, emphasizing that SWR did not contribute to an increase of the long-term terrestrial C sink in response to increased atmospheric [CO2]. © 2010 Elsevier B.V.

Schofield M.R.,University of Kentucky | Barker R.J.,University of Otago | Taylor P.,Manawatu Mail Center
Biometrics | Year: 2013

Summary: We use Bayesian methods to explore fitting the von Bertalanffy length model to tag-recapture data. We consider two popular parameterizations of the von Bertalanffy model. The first models the data relative to age at first capture; the second models in terms of length at first capture. Using data from a rainbow trout Oncorhynchus mykiss study we explore the relationship between the assumptions and resulting inference using posterior predictive checking, cross validation and a simulation study. We find that untestable hierarchical assumptions placed on the nuisance parameters in each model can influence the resulting inference about parameters of interest. Researchers should carefully consider these assumptions when modeling growth from tag-recapture data. © 2013, The International Biometric Society.

McArthur K.J.,Manawatu Mail Center | Roygard J.,Manawatu Mail Center | Clark M.,Manawatu Mail Center
Journal of Hydrology New Zealand | Year: 2010

Nitrogen (N) and phosphorus (P) enrichment of waterways can affect their ecological, aesthetic and recreational values by causing excessive growth of nuisance algae and other organisms, collectively known as periphyton. In the past, P was commonly thought to be the 'limiting nutrient' for periphyton growth in many of the Manawatu-Wanganui region's rivers. Management of the Manawatu River in particular relied on reducing P inputs from point sources at low flows to avoid nuisance periphyton growth. Long-term State of the Environment data on N and P were analysed against river flow for a number of sites in the region's river catchments. This paper presents the results from this analysis for the Manawatu and Rangitikei catchments. Nutrient limitation status was found to vary at and between a number of sites in the Manawatu catchment and this variation was highly influenced by river flow. Specific low flow investigations of water quality in two catchments found large spatial variation in limiting nutrient status at a number of sites on the same day, within the same sub-catchment. The One Plan (Manawatu-Wanganui combined Regional Plan and Policy Statement) proposes management of both N and P at all flows lower than substrate-disturbing floods (20th percentile flow). As more is learned about the interactions between nutrient concentration, flow and periphyton growth in enriched river catchments, it becomes clear that the best approach is a catchment- specific framework, based on the combined management of N and P, at relevant flow regimes. © (2010) New Zealand Hydrological Society.

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