Establishing riverine nutrient criteria using individual taxa thresholds

Nutrient enrichment is one of the most pervasive impacts on aquatic ecosystems globally. Approaches to establish nutrient criteria that safeguard aquatic ecosystem health are highly variable and, in many instances, criteria are derived from correlations between in-situ nutrient concentrations and biological indices. Summarising entire assemblages with a single index can result in a substantial loss of information and potentially weaker relationships. In this study, we compared the derivation of nutrient criteria using biological indices and those from individual taxa for rivers and streams in New Zealand. Random forest models, including nutrient concentrations, were built to predict two biological indices and individual taxa across New Zealand's river monitoring network. For all acceptable models, the response of the biological indices and individual taxa to increasing Dissolved Inorganic Nitrogen (DIN) and Dissolved Reactive Phosphorus (DRP) were then predicted for every river reach across the nation, and nutrient concentrations that protected 80% of taxa were then identified. Models for the biological indices were poor but were good for most of the taxa, with nutrient concentrations almost always being the most influential factor. To ensure persistence of at least 80% of the taxa within a river reach, we estimated that DIN (Dissolved Inorganic Nitrogen) concentrations would need to be below 0.57–1.32 mg/L, and DRP (Dissolved Reactive Phosphorus) concentrations below 0.019–0.033 mg/L, depending on the river type. In general, high order, low slope rivers and streams required more stringent nutrient criteria than steep, low order streams. The link between nutrient concentrations and biological indices were weak and likely suffer from the loss of information from summarising an entire assemblage into a single numeric. We consider that the derivation of nutrient criteria for waterways should also examine the individual relationships with the taxa in a river system to establish protection for a desired proportion of taxa

Reaction calorimetry applied to kinetic problems. The design and construction of an isothermal calorimeter with heat compensation by the Peltier effect, and the application of the calorimeter in the study of reaction kinetics in solvent/water mixtures.

An isothermal calorimeter controlled by the Peltier effect has been designed and constructed in order to investigate reaction rates in solventwater mixtures. Because a thermal method was used a constant temperature environment was essential and this was achieved by using a water bath controlled to + 0.0010C. This callorinieter has been used to study the alkaline hydrolysis of methyl acetate in dimethylsulphoxide, and tetrahydrofuran - water mixtures at 15, 25 and 35 [degrees]C. The results of other investigations on similar reactions have been reviewed and an attempt has been made to correlate the electrostatic theories of Laidler and Eyring, and Amis and jaffe with these results. Finally, because it appears that specific solvent interactions play a major part in the reaction rates the role of water in the reaction mechanism has been examined. A mechanistic explanation has been proposed in order to correlate the rate of reaction with the composition of water-solvent mixtures which justifies the Laidler and Eyring treatment of solvent effects on ion-molecule reactions.Bradford Universit

Trophic cascade direction and flow determine network flow stability

The mechanisms for maintenance of food web structure and function in the face of frequent disturbance has been a question in ecology for many years. Local point-wise stability of theoretical food webs or robustness assessment of empirical binary food webs are the two principal techniques that have been used to address this question. However, many theoretical webs are often small, constructed randomly or from theoretical algorithms (such as Cascade or Niche models), and assume Lotka-Volterra dynamics. Whilst the binary webs used also assume all interactions are equal and that webs are donor controlled. Recent dynamic stability analysis of empirical quantitative webs has sought to improve this assessment. Here we investigate how aquatic food web structure and the direction of trophic cascades interact to affect the robustness of total carbon flow between species after a disturbance. The robustness of the 18 food webs is higher if predator control dominates. Webs with predator control were however stabilised by weak indirect interactions and short food chains