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Astorga A.,University of Oulu | Astorga A.,Massey University | Astorga A.,Finnish Environment Institute | Death R.,Massey University | And 5 more authors.
Ecology and Evolution | Year: 2014

To define whether the beta diversity of stream invertebrate communities in New Zealand exhibits geographical variation unexplained by variation in gamma diversity and, if so, what mechanisms (productivity, habitat heterogeneity, dispersal limitation, disturbance) best explain the observed broad-scale beta diversity patterns. We sampled 120 streams across eight regions (stream catchments), spanning a north-south gradient of 12° of latitude, and calculated beta diversity (with both species richness and abundance data) for each region. We explored through a null model if beta diversity deviates from the expectation of stochastic assembly processes and whether the magnitude of the deviation varies geographically. We then performed multimodel inference analysis on the key environmental drivers of beta diversity, using Akaike's information criterion and model and predictor weights to select the best model(s) explaining beta diversity. Beta diversity was, unexpectedly, highest in the South Island. The null model analysis revealed that beta diversity was greater than expected by chance in all eight regions, but the magnitude of beta deviation was higher in the South Island, suggesting differences in environmental filtering and/or dispersal limitation between North and South Island. Habitat heterogeneity was the predominant driver of beta diversity of stream macroinvertebrates, with productivity having a secondary, and negative, contribution. This is one of the first studies accounting for stochastic effects while examining the ecological drivers of beta diversity. Our results suggest that local environmental heterogeneity may be the strongest determinant of beta diversity of stream invertebrates, more so than regional- or landscape-scale variables. © 2014 The Authors. Source


Wood S.A.,Cawthron Institute | Wood S.A.,University of Waikato | Depree C.,NIWA - National Institute of Water and Atmospheric Research | Brown L.,Horizons Regional Council | And 2 more authors.
PLoS ONE | Year: 2015

Proliferations of the benthic mat-forming cyanobacteria Phormidium have been reported in rivers worldwide. Phormidium commonly produces natural toxins which pose a health risk to animal and humans. Recent field studies in New Zealand identified that sites with Phormidium proliferations consistently have low concentrations of water column dissolved reactive phosphorus (DRP). Unlike other river periphyton, Phormidium mats are thick and cohesive, with water and fine sediment trapped in a mucilaginous matrix. We hypothesized that daytime photosynthetic activity would elevate pH inside the mats, and/or night time respiration would reduce dissolved oxygen. Either condition could be sufficient to facilitate desorption of phosphates from sediment incorporated within mats, thus allowing Phormidium to utilize it for growth. Using microelectrodes, optodes and pulse amplitude modulation fluorometry we demonstrated that photosynthetic activity results in elevated pH (<9) during daytime, and that night-time respiration causes oxygen depletion (<4mg L-1) within mats. Water trapped within the mucilaginous Phormidium mat matrix had on average 320-fold higher DRP concentrations than bulk river water and this, together with elevated concentrations of elements, including iron, suggest phosphorus release from entrapped sediment. Sequential extraction of phosphorus from trapped sediment was used to investigate the role of sediment at sites on the Mangatainoka River (New Zealand) with and without Phormidium proliferations. Deposition of fine sediment (<63 μm) was significantly higher at the site with the most extensive proliferations and concentrations of biological available phosphorus were two-to four-fold higher. Collectively these results provide evidence that fine sediment can provide a source of phosphorus to support Phormidium growth and proliferation. © 2015 Wood et al.This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Source


Stapleton G.,University of Brighton | Howse J.,University of Brighton | Bonnington A.,Horizons Regional Council | Burton J.,University of Brighton
CEUR Workshop Proceedings | Year: 2014

Ontology engineering is becoming more important, given the rapid rise of data in this information age. To better understand and reason about this data, ontologies provide us with insight into its structure. With this comes the involvement of a wide range of stakeholders, such as information analysts, software engineers, lawyers, and domain experts, alongside specialist ontology engineers. These specialists are likely to be adept at using existing approaches to ontology development, typically description logic or one of its various stylized forms. However, not all stakeholders can readily access such notations, which often have a very mathematical style. Many stakeholders, even including fluent ontology engineers, could benefit from visual approaches to ontology engineering, provided those approaches are accessible. This paper presents ongoing research into a diagrammatic approach to ontology engineering, outlining key research advances that are required. Source


Douglas G.B.,Agresearch Ltd. | McIvor I.R.,Plant and Food Research | Manderson A.K.,Agresearch Ltd. | Koolaard J.P.,Agresearch Ltd. | And 3 more authors.
Land Degradation and Development | Year: 2013

Shallow landslides occur globally on soil-mantled hilly and mountainous terrain. In New Zealand, they are a nation-wide problem, particularly on pastoral hill country grazed by livestock. On these landscapes, trees are planted at low densities, often <70 stems per hectare (sph), to reduce landslide occurrence, but there has been limited quantification of their effectiveness in this role. This study determined the reduction in landslide occurrence at 65 sites planted with spaced trees (53×Populus, 6×Salix, 6×Eucalyptus) following rainstorm events. Sites had a mean slope angle of 27 degrees and soils were predominantly silt or sand-loams. Tree density across all sites was 32-65sph, height was 8-43m, canopy radius was 1-10m and trunk diameter was 18-99cm. Trees reduced landslide occurrence by 95 per cent compared to paired pasture control sites (0·4 per cent vs. 7·9 per cent scar area, respectively), and scars occurred on fewer sites with trees than pasture (10 vs. 45). For the 10 tree sites with scars, their area was <3·5 per cent, except at one site where it was 11·3 per cent. There were no significant differences between species in their effectiveness in reducing landslide occurrence. Analyses were partially successful in discriminating between sites with and without shallow landslides and identified some attributes with potentially useful discriminatory power. Aspect, mean slope angle and tree density did not feature significantly in the analyses because they were homogeneous across site groups. The study verified the large benefit from wide-spaced tree planting on sites susceptible to shallow landslides. © 2011 John Wiley & Sons, Ltd. Source


Parfitt R.,Landcare Research | Frelat M.,Landcare Research | Dymond J.,Landcare Research | Clark M.,Horizons Regional Council | Roygard J.,Horizons Regional Council
New Zealand Journal of Agricultural Research | Year: 2013

Dissolved phosphorus (P) from various sources contributes to periphyton growth in rivers. The Manawatu catchment is in the southern North Island, and since it flows through pastoral farmland with soft rock geology, it carries nitrogen, P and sediment that lead to growth of periphyton. We estimated long-term average sediment P in rivers in the catchment above Palmerston North (PNth) (3910 km2) with the NZeem® model, and also measured the total P on the bed of the river. The annual loss of P in eroded sediment made up 95% of the P flux, (1500 t P yr-1 at PNth); 96% of the erosion occurred under pastures and 4% under forest. Dissolved P was measured at Hopelands and at PNth, and its origins-point sources, forests, the bed of the river and farmland-were assessed. The annual average dissolved P was estimated to be 75 t P at PNth, with 34 t P coming from sheep and beef farms, and this could be reduced with targeted planting of trees; 19 t P came from dairy farms, and could be reduced with changes to management of effluent, limiting soil Olsen P to the optimum agronomic range, and excluding cows from streams, banks and channels. Dissolved P from point sources (15 t P) could be decreased with changes to management of effluent. During low flows, sediment on the bed of the river released approximately 1.3 t dissolved P. These particulate-bound P losses could be reduced by targeted planting of trees on highly erodible land. The Upper Manawatu Water Management Zones (a priority catchment for mitigation) above Hopelands Bridge were also modelled. Council programmes to reduce soil erosion and total P, and to reduce dissolved P during low flow have the potential to reduce P loads in the river. Monitoring of P in the river should be carried out to define a more precise base line, and to monitor improvements to water quality as the programmes progress. © 2013 The Royal Society of New Zealand. Source

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