Eric O. Goodwin

Can Weighted Useable Area Predict Flow Requirements of Drift-Feeding Salmonids? Comparison with a Net Rate of Energy Intake Model Incorporating Drift–Flow Processes

AbstractWe compared a process-based invertebrate drift and drift-feeding net rate of energy intake (NREI) model and a traditional hydraulic-habitat model (using the RHYHABSIM [River Hydraulics and Habitat Simulation] software program) for predicting the flow requirements of 52-cm Brown Trout Salmo trutta in a New Zealand river. Brown Trout abundance predicted by the NREI model for the constant drift concentration–flow scenarios were asymptotic or linear, depending on drift concentration, increasing through the mean annual low flow (MALF; 17 m3/s). However, drift concentration increased with flow, consistent with passive entrainment. The predicted fish abundance–flow relationship based on flow-varying drift concentration increased logistically, and more steeply, with flow through the MALF and beyond. Predictions for the relationship between weighted useable area (WUA) and flow were made for three sets of drift-feeding habitat suitability criteria (HSC) developed on three midsized and one large New Zealand ...

Finding reference: a comparison of modelling approaches for predicting macroinvertebrate community index benchmarks

ABSTRACT Reference benchmarks are needed to assess the contemporary status of rivers and to establish restoration targets. We developed predictive models to estimate site-specific reference values for a macroinvertebrate community index (MCI), which is used to indicate a range of human impacts on wadeable streams. We compared three statistical modelling approaches – general linear, boosted regression tree (BRT) and random forest (RF) – and tested the effect of spatial scale on predictive accuracy by developing national and regional BRT models. Using fitted flexible models (BRT, RF) and resetting predictors to reflect natural state provided the most accurate predictions of reference condition. Variation in reference MCI predictions from national and regional models was within the range observed from methodological and temporal variability. The proportion of native vegetation in upstream catchments was the primary predictor of MCI scores in all models, while secondary predictors varied regionally.

Thresholds in ecosystem structural and functional responses to agricultural stressors can inform limit setting in streams

Setting numeric in-stream objectives (limits, criteria) to inform limits on catchment loads for major land-use stressors is a promising policy instrument to prevent ecosystem degradation. Management objectives can be informed by thresholds identified from stressor–response shapes of ecological indicators based on field survey data. Use of multiple structural and functional indicators and different organism groups provides multiple lines of evidence to make objectives more robust. We measured a suite of ecological indicators during a regional field survey in New Zealand. We built flexible boosted regression tree (BRT) models with a predictor set consisting of nutrient, sediment, and environmental variables and investigated the fitted functions for different types of thresholds across each stressor gradient. Congruence of impact initiation (II) thresholds for N among macroinvertebrate metrics and 2 periphyton indicators provided multiple lines of evidence for ecosystem change with small increases in N concentrations above background levels. Impact cessation (IC) on macroinvertebrate metrics at total N = ~0.5 mg/L (below N concentrations that saturate important ecosystem processes) highlighted sensitivity of macroinvertebrate communities to eutrophication. We found few stressor–response relationships for sediment. We suggest use of sediment-specific macroinvertebrate metrics and a reliable measure of deposited fine sediment in the future. Few indicators responded to phosphorus (P) concentration. Limited information for setting P objectives highlights the need to develop alternative indicators of P loading. Statistical analysis based on single-stressor inferential threshold models suggested that these models carry high risk of identifying spurious thresholds and are less suitable for setting management objectives. II and IC thresholds of multiple ecological indicators can be used to set robust objectives aimed at different levels of protection of ecosystem health.

Optimising conditions for growth and xanthophyll production in continuous culture of Tisochrysis lutea using photobioreactor arrays and central composite design experiments

ABSTRACT The production of valuable metabolites from microalgae represents a potentially sustainable source of a range of products that can be difficult to synthesise directly. Microalgae respond to the dynamic and often subtly shifting growth environment in a complex way. The optimal conditions for growth can be quite different to those needed for optimal product generation, depending on the nature of the biosynthesis of that product. This is especially so for secondary metabolites. A combination of a multi-vessel photobioreactor array, where certain growth conditions can be monitored and controlled precisely together with an experimental design matrix has been used to determine the optimal combination of temperature, irradiance and pH for a group of xanthophylls including fucoxanthin in the algae Tisochrysis lutea in continuous culture. Continuous culture as a mode is more suited for industrial production than batch mode in which the media constituents and algal population change dramatically over time. The central composite design experiment matrix has a range of set values for each parameter being investigated that bracket the optimal conditions. The three parameters investigated in this work (temperature, irradiance and pH) are major factors influencing algal growth. The method can be applied to other parameters that might affect growth or might affect production of a metabolite of interest, such as a nutrient level. The combined approach has been used previously to indicate optimal growth conditions for biomass generation and this work is one of the first to apply it to the generation of an algal product of interest.

Molecular Characterisation and Co-cultivation of Bacterial Biofilm Communities Associated with the Mat-Forming Diatom "Didymosphenia geminata"

Didymosphenia geminata (Lyngbye) M. Schmidt is a stalked freshwater diatom that is expanding its range globally. In some rivers, D. geminata forms thick and expansive polysaccharide-dominated mats. Like other stalked diatoms, D. geminata cells attach to the substratum with a pad of adhesive extracellular polymeric substance. Research on D. geminata and other diatoms suggests that bacterial biofilm composition may contribute to successful attachment. The aim of this study was to investigate the composition and role of bacterial biofilm communities in D. geminata attachment and survival. Bacterial biofilms were collected at four sites in the main stem of a river (containing D. geminata) and in four tributaries (free of D. geminata). Samples were characterised using automated rRNA intergenic spacer analysis and high-throughput sequencing (HTS). Mat-associated bacteria were isolated and their effect on the early establishment of D. geminata cells assessed using co-culturing experiments. ARISA and HTS data showed differences in bacterial communities between samples with and without D. geminata at two of the four sites. Samples with D. geminata had a higher relative abundance of Sphingobacteria (p < 0.01) and variability in community composition was reduced. Analysis of the 76 bacteria isolated from the mat revealed 12 different strains representing 8 genera. Co-culturing of a Carnobacterium sp. with D. geminata reduced survival (p < 0.001) and attachment (p < 0.001) of D. geminata. Attachment was enhanced by Micrococcus sp. and Pseudomonas sp. (p < 0.001 and p < 0.01, respectively). These data provide evidence that bacteria play a role in the initial attachment and on-going survival of D. geminata, and may partly explain observed distribution patterns.