Roger G. Young

Roger G. YoungCawthron Institute | CI · Coastal and Freshwater Group

· BSc (Hons), PhD
  • 2
  • 86
  • About
    Research items
    Research Experience
    Feb 1998
    Team leader - Freshwater Sciences
    • Team leader - Freshwater Sciences
    Current institution
    Cawthron Institute | CI
    Current position
    • Team leader - Freshwater Sciences
    Top co-authors
    Projects (2)
    Archived project
    LAWA is a web tool that enables scientists and the general public to find out about the state of New Zealand's environment - all on one website. It informs you if it is safe for you to swim in a particular river, or at a specific beach, what the air quality is like in your suburb or what projects your local community group has got planned. Go and check it out at
    Research Items (86)
    Setting numeric in-stream objectives (limits, criteria) to inform limits on catchment loads for major landuse 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 inNconcentrations above background levels. Impact cessation (IC) on macroinvertebrate metrics at total N 5 ~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.
    Effective ecosystem management requires a robust methodology to analyse, remedy and avoid ecosystem damage. Here we propose that the overall conceptual framework and approaches developed over millennia in medical science and practice to diagnose, cure and prevent disease can provide an excellent template. Key principles to adopt include combining well-established assessment methods with new analytical techniques and restricting both diagnosis and treatment to qualified personnel at various levels of specialization, in addition to striving for a better mechanistic understanding of ecosystem structure and functioning, as well as identifying the proximate and ultimate causes of ecosystem impairment. In addition to applying these principles, ecosystem management would much benefit from systematically embracing how medical doctors approach and interview patients, diagnose health condition, select treatments, take follow-up measures, and prevent illness. Here we translate the overall conceptual framework from medicine into environmental terms and illustrate with examples from rivers how the systematic adoption of the individual steps proven and tested in medical practice can improve ecosystem management.
    Toxic cyanobacterial proliferations in water bodies can cause serious environmental and public health issues, as well as having economic effects. Increased inputs of nutrients and fine sediment caused by forestry have been hypothesised as possible causes of increased Phormidium-dominated proliferations in New Zealand rivers. Little is known about the effect of these proliferations on river ecosystem functioning. In the present study, we evaluated five sites along the Maitai River (New Zealand) differing in pine plantation cover of their catchments. We hypothesised that Phormidium biofilms would trap more sediments and recycle more phosphorus than diatoms, that Phormidium proliferations would increase with forestry cover in the catchment and that the varying abundance of Phormidium would affect river ecosystem functioning. Phormidium did not trap more sediment or recycle more phosphorus (measured as alkaline phosphate activity) than diatom biofilms. However, the cover of Phormidium did increase with the proportion of forestry in the catchment. Organic matter decomposition rates (measured as loss of tensile strength of standard cotton strips) varied very little among sites, whereas river ecosystem metabolism increased with the abundance of Phormidium, especially in the lower part of the river. The results of the present study suggest that pine forestry does promote Phormidium biofilm abundance and affect ecosystem functioning in the Maitai River.
    Proliferations of the benthic anatoxin-producing cyanobacterium Phormidium are increasing in prevalence in cobble-bed rivers worldwide. This proliferation is of particular concern when rivers are used as sources of drinking water or for recreation. Little is known about the physicochemical variables promoting proliferations, and our existing knowledge is based on data from only a few rivers. We assessed Phormidium cover, physicochemical variables, and anatoxin concentrations at 10 sites in 7 New Zealand rivers every week for 2 y. Generalized additive mixed models (GAMMs) identified dissolved inorganic N (DIN) over the accrual period <0.8 mg/L, dissolved reactive P accrual <0.005 mg/L, water temperatures >157C, and conductivity as having positive and statistically significant effects on % Phormidium cover. Flow intensity, expressed relative to the long-term median, had a positive effect up to 0.4� the median flow and a negative effect when >0.5� the median flow. Quantile regression models showed marked variability among sites in relation to the flow intensity required to reduce % Phormidium cover (90th percentile ranged 0.65–249� the long-term median flow). Anatoxins were detected in variable concentrations in samples from 7 of the 10 sites. GAMMs identified strong relationships between elevated toxin concentrations and low conductivity and increasing % Phormidium cover, and significantly lower toxin concentrations when DIN was <0.2 mg/L. These data demonstrate that multiple physicochemical variables influence Phormidium proliferations and toxin concentrations and indicate that the relative importance of these variables differs among rivers and sites.
    The setting of numeric instream objectives (effects-based criteria) and catchment limits for major agricultural stressors, such as nutrients and fine sediment, is a promising policy instrument to prevent or reduce degradation of stream ecosystem health. We explored the suitability of assemblage thresholds, defined as a point at which a small increase in a stressor will result in a disproportionally large change in assemblage structure relative to other points across the stressor gradient, to inform instream nutrient and sediment objectives. Identification and comparison of thresholds for macroinvertebrate, periphyton and bacterial assemblages aimed at making the setting of objectives more robust and may further provide a better understanding of the underlying mechanisms of nutrient and fine sediment effects. Gradient forest, a novel approach to assemblage threshold identification based on regression tree-based random forest models for individual taxa, allowed inclusion of multiple predictors to strengthen the evidence of cause-and-effect between stressors and multispecies responses. The most prominent macroinvertebrate and periphyton assemblage threshold across the nitrogen (N) gradient was located at very low levels and mainly attributed to declines of multiple taxa. This provided strong evidence for stream assemblages being significantly affected when N concentrations exceed reference conditions and for effects cascading through the ecosystem. The most prominent macroinvertebrate assemblage threshold across a gradient of suspended fine sediment was also located at very low levels and attributed to declines of multiple taxa. However, this threshold did not correspond with periphyton assemblage thresholds, suggesting that the sensitivity of macroinvertebrate assemblages is unrelated to sediment effects on periphyton assemblages. Overall, the spectrum of N concentrations and fine sediment levels within which these stream assemblages changed most dramatically were relatively narrow given the wide gradients tested. We conclude that assemblage thresholds can inform the setting of generic instream nutrient and sediment objectives for stream ecosystem health. For example, the most stringent objective for instream N concentration should be set at values similar to reference concentrations for full protection of sensitive taxa or overall stream biodiversity. To avoid severe degradation of stream biodiversity, the least stringent N objective should stay well below the point where significant turnover subsided. This article is protected by copyright. All rights reserved.
    Stream metabolism (gross primary production and ecosystem respiration) is increasingly used to assess waterway health because mean values are responsive to spatial variation in land use, but little is known about how human land use influences the temporal variability of stream metabolism. We investigated daily variation in dissolved O2 (DO) concentrations and calculated mean and within-season variation in gross primary production (GPP) and ecosystem respiration (ER) rates at 13 stream sites across a landuse intensity gradient in the Auckland region, New Zealand, over 9 y. Based on generalized linear mixed models, mean daily GPP (0.1–12.6 g O2 m⁻² d⁻¹) and ER (1.8–29.6 g O2 m⁻² d⁻¹) and seasonal variation in stream metabolism were significantly related to landuse intensity with higher variability associated with higher values of a landuse stress score. Overall, mean daily rates and day-to-day variation in GPP and ER were greatest in summer and least in winter. We recommend summer monitoring over a minimum 5-d period to assess stream health. Our results show that human land use affects the mean and the temporal variability of DO and stream metabolism. This finding has important consequences for characterizing in-stream processes and the resilience of stream ecosystems. Only long-term temporal monitoring provides the data needed to assess fully how streams function.
    a b s t r a c t Anatoxins are powerful neuromuscular blocking agents produced by some cyanobacteria. Consumption of anatoxin-producing cyanobacterial mats or the water containing them has been linked to numerous animal poisonings and fatalities worldwide. Despite this health risk, there is a poor understanding of the environmental factors regulating anatoxin pro-duction. Non-axenic Phormidium autumnale strain CAWBG557 produces anatoxin-a (ATX), homoanatoxin-a (HTX) and their dihydrogen-derivatives dihydroanatoxin-a (dhATX) and dihydrohomoanatoxin-a (dhHTX). The effects of varying nitrogen and phosphorus con-centrations on the production of these four variants were examined in batch mono-cultures. The anatoxin quota (anatoxin per cell) of all four variants increased up to four fold in the initial growth phase (days 0e9) coinciding with the spread of filaments across the culture vessel during substrate attachment. Dihydroanatoxin-a and dhHTX, accounted for over 60% of the total anatoxin quota in each nitrogen and phosphorus treatment. This suggests they are being internally synthesised and not just derived following cell lysis and environmental degradation. The four anatoxin variants differed in their response to varying nitrogen and phosphorus concentrations. Notably, dhATX quota significantly decreased (P 0.03) when nitrogen and phosphorus concentrations were elevated (nitrogen ¼ 21 mg L À1 ; phosphorus ¼ 3 mg L À1), while HTX quota increased when the phosphorus concentrations were reduced (ca. < 0.08 mg L À1). This is of concern as HTX has a high toxicity and anatoxin producing P. autumnale blooms in New Zealand usually occur in rivers with low water column dissolved reactive phosphorus.
    Integrating multiple measures of stream health into a combined metric can provide a holistic assessment of the ecological integrity of a stream. The aim of this study was to develop a multimetric index (MMI) of stream integrity based on predictive modelling of national data sets of water quality, macroinvertebrates, fish and ecosystem process metrics. We used a boosted regression tree approach to calculate an observed/expected score for each metric prior to combining metrics in a MMI based on data availability and the strength of predictive models. The resulting MMI provides a geographically meaningful prediction of the ecological integrity of rivers in New Zealand, but identifies limitations in data and approach, providing focus for ongoing research.
    Irrigation development is being promoted by the New Zealand government alongside the need to set catchment limits for water takes and to protect water quality. This paper presents results of an integrated catchment management assessment of the potential water quality consequences from the proposed Waimea water augmentation project near Nelson, New Zealand. The assessment comprised four components: 1. Modelling nutrient leaching through the soil profile for six land uses, irrigated and dryland, and four soil groups using the SPASMO model 2. Assessing attenuation of nitrogen carried via three aquifers from the bottom of the soil profile to potentially sensitive receiving waters (springs, river and coast) 3. Recommending water quality limits which protect the values and uses of those receiving waters, 4. Scoping possible Good Management Practices (GMPs) which would reduce the risks of water quality limits being exceeded when increased irrigation is implemented. Full irrigation is modelled to increase nitrogen concentrations entering groundwaters by 23% and in a hypothetical worst case by up to 50% if the entire plains were converted to irrigated market gardening. These increases, however, are mitigated (diluted) by increased drainage rates to groundwater of 6% and 19% respectively caused by the increased irrigation. Nitrogen is diluted and dispersed within the aquifers with attenuation of around 50% in the unconfined aquifer and 0-40% in the confined aquifers. In the river, water quality is expected to improve when the water augmentation scheme is operating, because of the dilution offered by the uncontaminated flow releases from the dam. Spring-fed streams fed by upwelling water from the unconfined and Upper Confined aquifers already have high - Albeit declining - nitrate concentrations 4.6-14 mg/L, a legacy of past land use. Those springs are identified as 'choke points' for system management because potential nitrate limits based on toxicity to aquatic species may be exceeded.
    The ecological responses of large rivers to human pressure can be assessed at multiple scales using a variety of indicators, but little is known about how the responses of ecological indicators vary over small spatial scales. We sampled phytoplankton, zooplankton and macroinvertebrates and measured river metabolism and cotton strip breakdown rates (loss in tensile strength) in contrasting habitats along a 21-km urban-industrial reach on a constrained section of the Waikato River, New Zealand's longest river. Rates of gross primary production (2.8–7.8 g O2/m2/d) and ecosystem respiration (3.5–12.7 g O2/m2/d) did not differ consistently between near-shore (2–3 m from river side) and far-shore (ca. 10 m from side) locations, urban and industrial reaches or between autumn and spring sampling occasions. Rates of cotton decay (−k) ranged from 0.014 to 0.112 per day and were typically faster at far-shore locations and in the section of river receiving industrial inputs, but slower in spring compared with autumn. Nonmetric multidimensional scaling analysis of phytoplankton and zooplankton data did not reveal spatial patterns relating to pressure or location (embayment, edge, mid-river). However, the macroinvertebrate ordination suggested distinct communities for the mid-river benthos compared with near-shore communities and a distinction between sites in the urban reach and the industrial reach. Our results suggest that large-river macroinvertebrate communities and cotton decay rates can be influenced to varying degrees by reach-scale pressures and local habitat conditions. Monitoring designs in spatially complex rivers should account for habitat heterogeneity that can lead to differences in structural and functional indicator responses.
    Functional indicators are being increasingly used to assess waterway health but their responses to pressure in non-wadeable rivers have not been widely documented or applied in modern survey designs that provide unbiased estimates of extent. This study tests the response of river metabolism and loss in cotton strip tensile strength across a land use pressure gradient in non-wadeable rivers of northern New Zealand, and reports extent estimates for river metabolism and decomposition rates. Following adjustment for probability of selection, ecosystem respiration (ER) and gross primary production (GPP) for the target population of order 5–7 non-wadeable rivers averaged −7.3 and 4.8 g O2 m−2 d−1, respectively, with average P/R < 1 indicating dominance by heterotrophic processes. Ecosystem respiration was <−3.3 g O2 m−2 d−1 for 75% of non-wadeable river length with around 20% of length between −10 and −20 g O2 m−2 d−1. Cumulative distribution functions of cotton strength loss estimates indicated a more-or-less linear relationship with river km reflecting an even spread of decay rates (range in k 0.0007–0.2875 d−1) across non-wadeable rivers regionally. A non-linear relationship with land cover was detected for GPP which was typically <5 g O2 m−2 d−1 where natural vegetation cover was below 20% and greater than 80% of upstream catchment area. For cotton strength loss, the relationship with land cover was wedge-shaped such that sites with >60% natural cover had low decay rates (<0.02 d−1) with variability below this increasing as natural cover declined. Using published criteria for assessing waterway health based on ER and GPP, 232–298 km (20–29%) of non-wadeable river length was considered to have severely impaired ecosystem functioning, and 436–530 km (42–50%) had no evidence of impact on river metabolism.
    Global demand for freshwater has led to unprecedented levels of water abstraction from riverine systems. This has resulted in large alterations in natural river flows. The deleterious impacts of reduced flows on fish and macroinvertebrate abundances have been thoroughly investigated; in contrast, there is a limited understanding of the potential for changes in the abundance of nuisance benthic algal/cyanobacterial blooms. In New Zealand, Phormidium sp. blooms are common in numerous rivers during summer low flows. In this study, an in-stream habitat assessment is used to examine the relationship between Phormidium habitat availability and reducing flows. Over 650 observations of Phormidium mats, from seven sites (Hutt River, lower North Island, New Zealand), were used to construct habitat suitability curves for depth, velocity and substrate. Preference curves were fitted using both the ‘forage ratio’ and ‘quantile regression’ methods. Phormidium growth, observed at all seven sites, increased significantly from upstream (uppermost site, 5.2% mat cover) to downstream (63.5%). The habitat suitability curves revealed Phormidium had a large tolerance to velocity, depth and substrate type. Consequently, decreases in flow had only negligible effects on available Phormidium habitat. During periods of stable flow, Phormidium abundance positively correlated with increased nitrogen concentrations, potentially explaining the large variation in Phormidium cover from upstream to downstream. Quantile regression generated habitat suitability criteria were a more accurate predictor of available Phormidium habitat than the forage ratio criteria. Copyright © 2013 John Wiley & Sons, Ltd.
    Responses of macroinvertebrate communities to human pressure are poorly known in large rivers compared with wadeable streams, in part because of variable substrate composition and the need to disentangle pressure responses from underlying natural environmental variation. To investigate the interaction between these factors, we sampled macroinvertebrates from the following: (i) submerged wood; (ii) littoral substrates < 0.8 m deep; and (iii) inorganic substrates in deep water (> 1.5 m) benthic habitats in eleven 6th- or 7th-order New Zealand rivers spanning a catchment vegetation land cover gradient. Cluster analysis identified primary site groupings reflecting regional environmental characteristics and secondary groupings for moderate gradient rivers reflecting the extent of catchment native vegetation cover. Low pressure sites with high levels of native vegetation had higher habitat quality and higher percentages of several Ephemeroptera and Trichoptera taxa than sites in developed catchments, whereas developed sites were more typically dominated by Diptera, Mollusca and other Trichoptera. Partial regression analysis indicated that the combination of underlying environment and human pressure accounted for 77–89% of the variation in Ephemeroptera, Trichoptera and Plecoptera taxa richness, %Diptera and %Mollusca, with human pressure explaining more variance than underlying environment for %Mollusca. Analysis of replicate deepwater and littoral samples from moderate gradient sites at the upper and lower ends of the pressure gradient indicated that total Trichoptera and Diptera richness and %Diptera responded to land use differences in these boatable river catchments. Responses to human pressure were substrate specific with the combination of littoral and deepwater substrates providing the most consistent response and yielding the highest number of taxa. These results indicate that multiple substrate sampling is required to document the biodiversity and condition of boatable river macroinvertebrate communities and that spatial variation in the underlying natural environment needs to be accounted for when interpreting pressure–response relationships. Copyright © 2012 John Wiley & Sons, Ltd.
    Benthic Phormidium mats can contain high concentrations of the neurotoxins anatoxin-a and homoanatoxin-a. However, little is known about the co-occurrence of anatoxin-producing and non-anatoxin-producing strains within mats. There is also no data on variation in anatoxin content among toxic genotypes isolated from the same mat. In this study, 30 Phormidium strains were isolated from 1 cm(2) sections of Phormidium-dominated mats collected from three different sites. Strains were grown to stationary phase and their anatoxin-a, homoanatoxin-a, dihydroanatoxin-a and dihydrohomoanatoxin-a concentrations determined using liquid chromatography-mass spectrometry. Each strain was characterized using morphological and molecular (16S rRNA gene sequences) techniques. Eighteen strains produced anatoxin-a, dihydroanatoxin-a or homoanatoxin-a. Strains isolated from each mat either all produced toxins, or were a mixture of anatoxin and non-anatoxin-producing genotypes. Based on morphology these genotypes could not be separated. The 16S rRNA gene sequence comparisons showed a difference of at least 17 nucleotides among anatoxin and non-anatoxin-producing strains and these formed two separate sub-clades during phylogenetic analysis. The total anatoxin concentration among toxic strains varied from 2.21 to 211.88 mg kg(-1) (freeze dried weight), representing a 100 fold variation in toxin content. These data indicate that both the relative abundance of anatoxin and non-anatoxin-producing genotypes, and variations in anatoxin producing capability, can influence the overall toxin concentration of benthic Phormidium mat samples.
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    The mitigating effects of fish passes to aid fish dispersal are well recognised; however, non-sports fish species, juveniles and weak swimmers have mostly been neglected when developing solutions to fish passage issues. We studied the juvenile (fork length, FL <60 mm) swimming ability of a weakly swimming fish species, īnanga (Galaxias maculatus), up an artificial ramp to evaluate the effects of fish size, ramp slope (5°, 15°, 25°), water velocity and the potential need for resting opportunities (pools) for a successful ascent. Water velocity significantly increased and fish passage success significantly decreased with ramp angle, with only one fish passing the 25° ramp. On average, fish had to be 10 mm larger to ascend a 15° ramp angle than at 5°. Pools did not enhance passage success in this study. To facilitate fish passage at barriers for weakly swimming fish species like juvenile īnanga, ramps should provide a rough surface substrate and have an optimal angle of 5° for a 3-m ramp.
    The influences of geology and land use on macroinvertebrate communities were investigated in the Motueka River catchment, New Zealand. Comparisons of functional feeding groups, multivariate community composition and biotic indices (MCI, QMCI, %EPT) were made between native forest stream reaches that differed in subcatchment geology (ultramafic, hard sedimentary, granite, gravel, karst) and between stream reaches surrounded by different land uses (native forest, exotic forest and pasture) within two of these geologies (granite, gravel). Differences in invertebrate community density and taxon richness were greater across the three land uses in the same geology than among the five geologies. Macroinvertebrate communities in streams flowing through native forest had greater numbers of shredders, and higher MCI scores than pastoral streams. Exotic forest macroinvertebrate communities were similar to the native forest communities in granite geology, but distinct from both native and pastoral communities in sites with underlying gravel geology. The results demonstrate that there is potential for underlying geology to influence the magnitude of land use impacts on invertebrate communities. The geologies within a catchment should be accounted for when considering the consequences of land development on river and stream communities.
    Scientific monitoring of river health is well established and has a significant role to play in environmental assessment by communities, managers and policy makers. Cultural indicators help to articulate cultural values, assess the state of the environment from a cultural perspective and assist with establishing a role for Māori in environmental monitoring. We reviewed the philosophies behind cultural and scientific monitoring of river health and compared the results from the two approaches at 25 sites in the Motueka and Riwaka catchments. Both scientific and cultural indicators suggested a decrease in river health in relation to increased land-use pressure. There were also correlations between the results from the two approaches suggesting cultural indicators could be used in a similar manner as scientific indicators to set environmental benchmarks. Using scientific approaches alongside culturally based monitoring provides a wealth of knowledge to understand better what we mean by river health. The two approaches can be regarded as complementary and reflect two different knowledge systems and perspectives.
    The effects of coastal floodgates on fish distribution are largely unknown. In this study, we used Dual-frequency Identification Sonar (DIDSON) to assess the effect of tidal floodgates on movement of diadromous juvenile galaxiids in a New Zealand estuarine system and test the suitability of DIDSON as a tool for monitoring behaviour of small fish. DIDSON allowed observations of juvenile galaxiid movements over 24 h through contrasting gated and un-gated culverts. More than twice as many fish were recorded passing the un-gated culvert than the gated culvert. Movement occurred during the day and night and was highest at the un-gated culvert just before high tide. By contrast, movement past the gated culvert was highest during low tide, when the gate was open. DIDSON is suitable for discretely observing in situ behaviour of small fish at night or in turbid water and will assist to identify design and operational needs for fish-friendly floodgates.
    Success at integrated catchment management (ICM) requires the ongoing participation of different stakeholders in an adaptive and learning-based management process. However, this can be difficult to achieve in practice because many initiatives fail to address the underlying social process aspects required. We review emerging lessons around how to engage stakeholders in ways that support social learning. We focus on the experience of an ICM research programme based in the Motueka catchment in New Zealand and provide a simple framework for distinguishing a range of conversations across different communities of practice. We highlight the need to use multiple engagement approaches to address different constituent needs and opportunities, and to encourage the informal conversations that spring up around these. We then illustrate the range of platforms for dialogue and learning that were used in the programme during 10 years of ICM research. Finally, a number of lessons are described from across the programme to guide research leaders and managers seeking to improve collaboration in other integrated science, management and policy initiatives.
    Hydrographic and water quality surveys of the Motueka River and its river plume were conducted during a moderate flood event (peak flow of 420 m3/s) to assess the source and fate of faecal contaminants transported into Tasman Bay. Escherichia coli (E. coli) and enterococci concentrations in the river were up to 10000 and 7300 Most Probable Number (MPN)/100 ml during peak flow, respectively. A coastal survey revealed a shallow low-salinity plume that extended at least 6 km into Tasman Bay and the region's largest aquaculture management areas (AMAs). Mussels within the influence of the river plume, including those collected within an AMA, had E. coli and enterococci concentrations as high as 1300 and 2200 MPN/100 g tissue, respectively. Application of microbial source tracking markers using end-point PCR assays identified the presence of faecal contamination from ruminant animals (cows, sheep) in water and mussel samples. The detection of ruminant faecal contamination within shellfish located 6 km offshore highlights the close connection between land use and the quality of New Zealand's highly valued coastal resources.
    The monthly mass transport of nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), total nitrogen (TN), dissolved reactive phosphorus (DRP), total phosphorus (TP) and dissolved reactive silica (DRSi) from the Motueka River catchment into Tasman Bay (South Island, New Zealand) was estimated for the period 2005–2009 based on observed historical relationships between recorded river flows and the associated measured concentrations of each nutrient. The resulting average annual loading estimates for TN, TP and DRSi ranged from 397–829, 25–72 and 4053–6576 tonnes, respectively, over the 5-year period. Large seasonal variations in nutrient loadings were also estimated with the highest rates generally, but not always, occurring during winter. The observed patterns suggest that phytoplankton biomass within the river outwelling plume may also vary in response to seasonal and inter-annual variations in catchment nutrient loading rates with potential follow-on food web effects including the growth of cultured GreenshellTM mussels. The estimated average annual TN loading rate (2005–2009) from the Motueka River catchment (613 tonnes) is only c. 20% of the annual loss of nitrogen based on extrapolated literature values for denitrification rates in Tasman Bay. We therefore suggest that, under the present land use scenario in the Motueka catchment, there is little potential for resulting dysfunctional river plume ecosystem enrichment effects to occur.
    This study examined whether element:Ca ratios within the otoliths of juvenile brown trout could provide accurate trace element signatures for specific natal tributaries, and attempted to match these to trace element natal signatures found within the otoliths of adult trout caught in the main stem rivers of the same catchment. The trace element signatures of juvenile trout otoliths were analysed from a sample of eight tributaries representing the main sub-catchments of the Motueka River catchment, New Zealand. Trace element signatures were determined using laser ablation inductively coupled plasma mass spectrometry, and differentiated using linear discriminant function analysis with an overall cross-validated classification success of 96.8%. Temporal stability in element:Ca ratios was investigated by repeat collections of juvenile fish over two years. Natal signatures from 11 of 23 adult trout sampled from the catchment main stems were matched to one of the eight tributary signatures showing recruitment sources to be spread relatively evenly throughout the catchment. This study demonstrates the potential of using otolith trace element analysis to determine the natal origins of freshwater fish within a catchment.
    Storm-induced Escherichia coli pulses in the Motueka River (2074 km2) and the Sherry River (78.4 km2) are modelled. The model focuses on the catchment outlets, representing key processes, including E. coli transfer to and from the river bed, with account taken of the hysteresis in, and non-linear, non-stationary, response of E. coli concentrations to river stormflows. The model fits the Motueka River observations well, but less well in the Sherry River. A greatly simplified description of headwater and riparian inputs is satisfactory at the larger catchment scale where near-field, in-channel processes dominate the response. Spatial heterogeneity in rainfall-run-off and faecal sources probably contribute to the poorer fit in the smaller catchment. Despite using a relatively small number of driving variables and parameters, the model has the potential to predict real-time E. coli input to Tasman Bay in river plumes causing shellfish and bathing beach contamination.
    This paper provides an overview of the Motueka integrated catchment management (ICM) research programme. This research was based on the thesis that achieving ecosystem resilience at a catchment scale requires active measures to develop community resilience. We define a generic adaptive planning and action process, with associated knowledge management and stakeholder involvement processes, and illustrate those processes with observations from five research themes: (1) water allocation; (2) land use effects on water; (3) land and freshwater impacts on the coast; (4) integrative tools and processes for managing cumulative effects; and (5) building human capital and facilitating community action. Our research clearly illustrates the benefits for effective decision-making of carrying out catchment scale science and management within collaborative processes which patiently develop trusting relationships. We conclude that coastal catchments should be managed as a holistic continuum from ridge tops to the sea and that some processes like floods or loss of community resilience have decadal consequences, which support the need for long-term monitoring and investment.
    We tested the hypothesis that differences in top-level predators could mediate the importance of top-down versus bottom-up forces in stream food chains using three streams dominated by Galaxias (fish native to New Zealand) and three dominated by brown trout (Salmo trutta) (an introduced species). These two fish species have quite different predation strategies and energetic requirements. Periphyton in the Galaxias streams formed relatively low biomass (indicative of high invertebrate grazing), whereas periphyton in two of the three trout streams formed relatively high biomass (indicative of lower grazing pressure). Periphyton biomass response to inorganic nutrient enrichment varied by fish type. Invertebrate densities on artificial substrates were higher in the Galaxias streams, with the exception of chironomids. Nutrient enrichment of periphyton led to increases in total invertebrate densities, but these increases were greater in the Galaxias streams where invertebrate predation was thought to be lower. Our results suggest that the specific feeding behavior traits of the consumers should be considered when investigating trophic cascades or predicting effects of bottom-up nutrient enrichment on autotrophy.
    We tested the assumptions and predictions of a foraging model for drift-feeding fish. We used three-dimensional videography to describe the foraging behavior of brown trout, Salmo trutta, mapped water depth and velocity in their foraging area, sampled invertebrate drift to determine length class specific drift densities, and captured trout to determine the size composition of their diet. The model overestimated the fish's prey capture rate and gross energy intake rate by a factor of two. Most of this error resulted from the fact that prey detection probabilities within the fish's foraging area averaged only half the expected value. This was the result of a rapid decrease in capture probability with increasing lateral distance from the fish's focal point. Some of the model's assumptions were accurate: equations for predicting reaction distance and minimum prey size supported reliable predictions of the shape and size of the fish's foraging area and the size composition of the diet. Other assumptions were incorrect: fish detected prey within the predicted reaction volume, not on its upstream surface as expected, fish intercepted prey more slowly than the expected maximum sustainable swimming speed, and fish captured about two-thirds of their prey downstream of their focal point, rather than upstream.
    Longitudinal patterns of ecosystem metabolism were measured in a 310-km grassland river continuum (Taieri River, New Zealand) during two consecutive summer-autumn periods with contrasting discharge (average 1993-1994 = 76.8 m(3) . s(-1); 1994-1995 = 6.6 m(3) . s(-1)). Metabolism was estimated from diel oxygen curves using the single-station open-channel regression method. Ratios of gross primary production (<0.3-9.6 g O-2 . m(-2). day(-1)) to community respiration (0.7-9.8 g O-2 . m(-2). day(-1)) ranged to 6.5, while net daily metabolism ranged from -8.2 to 6.2 g O-2 . m(-2). day(-1). Only the upper 70 lan of the river was autotrophic during 1993-1994, while most of the river was autotrophic during 1994-1995. Light saturation of gross primary production by natural communities of autotrophs (bankside light intensities greater than or equal to 250 mu mol . m(-2). s(-1)) was observed only in the headwaters during 1993-1994, but throughout the continuum during 1994-1995. Patterns of gross primary production were controlled by fluctuations in water depth and turbidity that determined light availability. In regions with oceanic climates, river discharge varies widely within and between years. In such regions autotrophic river reaches should extend down continua during low-discharge periods, and retreat during high discharge. This conceptual model explains how hydrological variability may control longitudinal patterns of river metabolism.
    1. Modification of natural landscapes and land-use intensification are global phenomena that can result in a range of differing pressures on lotic ecosystems. We analysed national-scale databases to quantify the relationship between three land uses (indigenous vegetation, urbanisation and agriculture) and indicators of stream ecological integrity. Boosted regression tree modelling was used to test the response of 14 indicators belonging to four groups – water quality (at 578 sites), benthic invertebrates (at 2666 sites), fish (at 6858 sites) and ecosystem processes (at 156 sites). Our aims were to characterise the ecological response curves of selected functional and structural metrics in relation to three land uses, examine the environmental moderators of these relationships and quantify the relative utility of metrics as indicators of stream ecological integrity.
    This report critically assesses the concept of ecological integrity (EI) and its application in freshwater management. EI integrates a wide range of ecological values related to the structural and functional processes of ecosystems, making it particularly appealing for management application. EI is not inherently empirical, but it can be useful where its components are rigorously defined and appropriate ecological metrics are used to quantify these components. We analysed a number of published definitions of EI to arrive at our own working definition, which included four core components: nativeness, pristineness, diversity and resilience. We then developed a methodology for assessing EI based on the quantification of these components, recognising that this requires identifying ecosystems of interest and, if possible, establishing their reference conditions. Several indices that could be used to measure each of the four core components were then evaluated using a standard set of assessment criteria. For stream ecosystems, distributions of native species and habitat ecotyping can be used to reduce geographical variability in EI. In contrast, for lakes, ecotyping is not as useful and EI can instead be defined and assessed as the degree of departure of key metrics from threshold levels delimiting unfavourable conditions. We conclude with a list of potentially useful metrics for assessing EI in New Zealand streams and lakes, and provide information on how these might be combined in a multimetric index of EI.
    Alteration of urban streams by culverts is common throughout the world and is known to impede freshwater fish movement. The main objectives were therefore to investigate how different culvert characteristics (e. g. height, length, angle, perched v. non-perched) and habitat variables (e. g. water velocity, riverbed gradient) affect the passage success of juvenile inanga (Galaxias maculatus), a weak-swimming migratory fish. We determined whether passage of juvenile G. maculatus could be improved by installing a ramp at thirteen replicate in situ culverts in Nelson City, New Zealand. As expected, none of the 400 fish tested were able to pass undercut (i.e. perched) culverts before ramp installation (0% passage), compared with the 250 fish (65% passage) that were able to pass non-perched culverts. Significantly more fish (44% passage) reached perched culvert outlets when aided by the ramp. Passage success with the ramp depended on its length and angle, with fewer fish passing longer or steeper ramps. To provide upstream passage for weak-swimming species such as juvenile (fork length<60 mm) G. maculatus, ramp length and angle should not exceed three metres and 20 degrees, respectively. With passage requirements known and mitigation processes in place, urban fish populations might be able to be sustained.
    1. Broad-scale assessment of stream health is often based on correlative relationships between catchment land-use categories and measurements of stream biota or water chemistry. Few studies have attempted to characterise the response curves that describe how measures of ecosystem function change along gradients of catchment land use, or explored how these responses vary at broad spatial scales. 2. In autumn 2008, we conducted a survey of 84 streams in three bioregions of New Zealand to assess the sensitivity of functional indicators to three land-use gradients: percentage of native vegetation cover, percentage of impervious cover (IC) and predicted nitrogen (N) concentration. We examined these relationships using general linear models and boosted regression trees to explore monotonic, non-monotonic and potential threshold components of the response curves. 3. When viewing the responses to individual land-use gradients, four of five functional indicators were positively correlated with the removal of native vegetation cover and N. In general, weaker and less responsive models were observed for the IC gradient. An analysis of the response to multiple stressors showed δ15N of primary consumers and gross primary productivity (GPP) to be the most responsive functional indicators to land-use gradients. The multivariate models identified thresholds for change in the relationship between the functional indicators and all three land-use gradients. Apparent thresholds were <10%IC, between 40 and 80% loss of native vegetation cover and at 0.5 and 3.2 mg L−1 N. 4. The strength of regression models and the nature of the response curves suggest that measures of ecosystem function exhibit predictable relationships with land use. Furthermore, the responses of functional indicators varied little among three bioregions. This information provides a strong argument for the inclusion of functional indicators in a holistic assessment of stream health.
    Can we develop land use policy that balances the conflicting views of stakeholders in a catchment while moving toward long term sustainability? Adaptive management provides a strategy for this whereby measures of catchment performance are compared against performance goals in order to progressively improve policy. However, the feedback loop of adaptive management is often slow and irreversible impacts may result before policy has been adapted. In contrast, integrated modelling of future land use policy provides rapid feedback and potentially improves the chance of avoiding unwanted collapse events. Replacing measures of catchment performance with modelled catchment performance has usually required the dynamic linking of many models, both biophysical and socio-economic-and this requires much effort in software development. As an alternative, we propose the use of variable environmental intensity (defined as the ratio of environmental impact over economic output) in a loose coupling of models to provide a sufficient level of integration while avoiding significant effort required for software development. This model construct was applied to the Motueka Catchment of New Zealand where several biophysical (riverine water quantity, sediment, E. coli faecal bacteria, trout numbers, nitrogen transport, marine productivity) models, a socio-economic (gross output, gross margin, job numbers) model, and an agent-based model were linked. An extreme set of land use scenarios (historic, present, and intensive) were applied to this modelling framework. Results suggest that the catchment is presently in a near optimal land use configuration that is unlikely to benefit from further intensification. This would quickly put stress on water quantity (at low flow) and water quality (E. coli). To date, this model evaluation is based on a theoretical test that explores the logical implications of intensification at an unlikely extreme in order to assess the implications of likely growth trajectories from present use. While this has largely been a desktop exercise, it would also be possible to use this framework to model and explore the biophysical and economic impacts of individual or collective catchment visions. We are currently investigating the use of the model in this type of application.
    Management of the effects of water quality and flow on fisheries requires an understanding of the factors that control fish movements. We used radiotelemetry to monitor the movements of adult brown trout Salmo trutta in a New Zealand river over 11 months (September 2004 to August 2006) and linked those movements to the changes in flow and water temperature. Individual fish moved up to 41 km during the study. However, most fish moved less than 1 km. All of the trout that showed little movement throughout the summer were living in relatively deep pools that presumably provided cover. The rates of movement declined steadily over the spring–summer period, as flow decreased and water temperature increased. The percentage of fish moving was positively related to the average daily flow during the interval between tracking occasions and negatively related to the average daily water temperature, less than 20% of the tagged fish moving once temperatures were above 19°C. A severe, 50-year flood occurred in March 2005 and was associated with the mortality of 60–70% of the remaining tagged fish, confirming that flood-induced mortality can affect a substantial proportion of an adult brown trout population.
    Integrative research projects are becoming more common and inherently face challenges that singlediscipline or multi-disciplinary projects seldom do. It is difficult to learn what makes a successful integrative research project as many of these challenges and solutions often go unreported. Using the New Zealand Integrated Catchment Management (ICM) for the Motueka River research program, we reflect on the demands confronting research programs attempting to operate in an integrative interdisciplinary manner. We highlight seven key lessons that may help others learn of the benefits and difficulties that confront scientists and stakeholders involved in undertaking similar research. These are (1) clarify the goal and work with key people; (2) manage expectations; (3) agree on integrative concepts and face the challenge of epistemology; (4) leadership; (5) communication in an atmosphere of mutual trust and respect; (6) acknowledge that different modes of learning mean that a wide range of knowledge products are needed; and (7) measure and celebrate success. The recognition that many environmental problems can only be solved through the creation of new knowledge and through social processes that engage the research and management domains has been a major benefit of the research program.
    1. The value of measuring ecosystem functions in regular monitoring programs is increasingly being recognised as a potent tool for assessing river health. We measured the response of ecosystem metabolism, organic matter decomposition and strength loss, and invertebrate community composition across a gradient of catchment impairment defined by upstream landuse stress in two New Zealand streams. This was performed to determine if there were consistent responses among contrasting functional and structural indicators.
    To assess whether reaches of the Motueka River (New Zealand) that gain water from groundwater were likely to represent significant cold-water refugia for brown trout during periods of high water temperatures, water temperature was monitored for more than 18 months in two gaining reaches of the Motueka River and three reaches that were predicted to be losing water to groundwater. These data were used to predict brown trout (Salmo trutta) growth in gaining and losing reaches. Groundwater inputs had a small effect on water temperature at the reach-scale and modelling suggests that the differences observed were unlikely to result in appreciable differences in trout growth. Several coldwater patches were identified within the study reach that were up to 3.5°C cooler than the mainstem, but these were generally shallow and were unlikely to provide refuge for adult trout. The exception was Hinetai Spring, which had a mean water temperature of close to 16°C during the period January-March, when temperatures in the mainstem regularly exceeded 19°C. Trout were observed within the cold-water plume at the mouth of Hinetai Stream, which would allow them to thermoregulate when mainstem temperatures are unfavourable while still being able to capitalise on food resources available in the mainstem.
    A large river study was conducted as part of the Cross Departmental Research Pool (CDRP) ecological integrity project to (i) provide an overview of the macroinvertebrate faunas of large rivers, including those in deep-water habitats, and (ii) to elucidate links between these faunas, river function and anthropogenic stressors. Eleven sites on 6th-order or 7th-order rivers were sampled; four in the South Island and seven in the North Island. We measured (i) macroinvertebrate communities colonising wood, riffles (where present), littoral habitats (<1 m deep) and deepwater habitats (>1.5 m deep) (ii) ecosystem metabolism using a single-station open-channel approach based on natural changes in dissolved oxygen concentration over a 24-hour period, and (iii) wood and cellulose breakdown. Relationships were investigated between these response variables and reach-scale assessments of habitat quality, underlying upstream and segment environmental variables provided in the Freshwater Environments of New Zealand (FWENZ) database, and anthropogenic pressure variables provided by the Waters of National Importance (WONI) database.
    River health monitoring traditionally has made use of structural measurements (water quality or taxonomic composition of aquatic organisms). We argue that a more complete assessment of river health should include functional metrics, such as rates of organic matter decomposition and ecosystem metabolism. Leaf breakdown links the characteristics of riparian vegetation with the activity of both aquatic invertebrates and microbial organisms and is affected by natural and human-induced variation in a wide range of environmental factors. Measurement of leaf breakdown is relatively simple and has modest equipment requirements. River metabolism (gross primary productivity and ecosystem respiration) measures the rates of production and use of organic C in river ecosystems as a whole, providing a direct estimate of the food base that determines life-supporting capacity. Metabolism measurements require more sophisticated equipment than do measurements of leaf breakdown, but improvements in technology have made metabolism measurements relatively easy. We review the factors that influence leaf breakdown and river metabolism and pay particular attention to the effects of human-induced environmental stressors. We also describe how measurements can be standardized and suggest criteria for interpreting functional measures in terms of river ecosystem health. Last, we consider the strengths and weaknesses of both methods as functional measures and provide recommendations for their use as biomonitoring tools.
    A conceptual model of integrated catchment management (ICM) is presented in which ICM is defined as a process to achieve both ecosystem resilience and community resilience. It requires not only biophysical knowledge developed by hydrologists and other environmental scientists, but an active partnership with catchment communities and stakeholders to break the 'paradigm lock' described by the UNESCO-HELP programme. This paper reports observations from ICM research in the Motueka HELP demonstration basin in the upper South Island of New Zealand. The Motueka occupies 2 170 km2 of land yet the river effects are felt on the seabed more than 50 km2 off- shore, so the true 'catchment' is larger. A hydrologically temperate mountainous catchment with horticultural, agricultural, plantation forestry and conservation land uses, the Motueka also hosts an internationally recognised brown trout fishery. Land and water management issues driving ICM research include water allocation conflicts between instream and irrigation water uses, impacts on water quality of runoff from intensifying land uses, catchment impacts on coastal productivity and aquacul- ture, and how to manage catchment processes in an integrated way that addresses cumulative effects of development. Collaboration with catchment stakeholders can be viewed as having two primary purposes: • Building knowledge and commitment of resource users towards sustainable resource management (collaborative learning) • Stakeholder involvement in resource management itself (governance). Examples are presented of a Collaborative Learning Group on Sediment learning of their differing perspectives on fine sedi - ment impacts, and a Catchment Landcare Group working with scientists to improve water quality in their river. Success fac- tors for water user committees making decisions about water resource management include creating opportunities to commu- nicate and build trust, share scientific knowledge on the issue, and willingness to compromise. Functioning catchment groups have potential to take on delegated governance responsibility for meeting agreed water quality and other community goals. Finally a scenario modelling framework IDEAS (Integrated Dynamic Environmental Assessment System) is presented, in which environmental indicators such as nutrient fluxes are simulated alongside socio-economic indicators such as job num - bers and catchment GDP for a range of land and marine use options.
    EXECUTIVE SUMMARY River health monitoring, which has traditionally concentrated on the use of structural measurements (such as water quality or the composition of aquatic communities), should be complemented in the future by functional indicators, such as rates of ecosystem metabolism and organic matter decomposition, to provide a more complete assessment of the state of these environments. This report summarises the results of a three-year project on the potential and application of functional indicators in New Zealand and identifies where future efforts on this topic should be focused. Guidelines on the interpretation of functional indicator measurements are provided along with simple protocols for indicator measurement. A series of case-studies were conducted during the project to provide regional council staff with practical experience of the techniques and assist with protocol development. Four measures of organic matter decomposition were trialled in the case studies-mass loss of leaves, toughness loss of leaves, tensile strength loss of cotton strips, and mass loss of wooden sticks. Some interesting patterns in decomposition were observed with decomposition rates reflecting differences in land use and water quality. After considering the results from the case studies, wooden stick mass loss appeared to be the most suitable measurement of organic matter decomposition for regular river health monitoring. Within-site variability was high for both leaf toughness loss and cotton strip strength loss making them less attractive options. Leaf mass loss is relatively easy to measure and responds to a broad range of stressors. However, collecting leaves and assembling leaf bags is time consuming and variation among leaves, even from the same tree, means that comparisons among sites or over time may be compromised by differences in the original leaf material. In contrast, wooden stick mass loss is easy to measure and wooden sticks are cheap, easily sourced and have a relatively consistent composition. Ecosystem metabolism was also trialled in a series of case-studies. Rates of gross primary production (GPP) and ecosystem respiration (ER) responded to gradients in water quality and indicated changes in the sources of energy driving river ecosystems at different locations. Plots of GPP versus light intensity were used to indicate the importance of light in controlling ecosystem processes/functioning. The single-station open-system approach to measuring ecosystem metabolism appears to be feasible for regular river health monitoring, and could be adapted to enable automated real time assessments from permanent sites where dissolved oxygen is measured. We have a full set of data on water quality, invertebrates, leaf mass loss, leaf toughness loss, cotton strip strength loss, wooden stick mass loss, and ecosystem metabolism for nine sites along the length of the Motueka River, enabling comparisons among these different measures of ecosystem health. There were surprisingly few correlations among the health indicators, suggesting that each indicator is measuring different attributes of the ecosystem. This indicates that functional indicators are complementary to existing monitoring techniques and provide additional information about the health of river ecosystems. Two approaches can be used to interpret results from functional indicators; a reference site approach where measurements from test sites are compared with those from appropriate reference sites, or an absolute values approach where information from a range of reference sites is used to develop a set of criteria that can be compared with results from any test site. At this stage, organic matter decomposition data need to be interpreted using the reference site approach, whereas either approach is suitable for interpreting measurements of ecosystem metabolism since we have developed a set of criteria for the absolute values approach that should be appropriate for most New Zealand rivers. This project has demonstrated the potential of functional indicators and provided a framework for their use in measuring river health in New Zealand. Several councils have already incorporated functional indicators in their regular monitoring programmes. However, there will undoubtedly be refinements as familiarity with the techniques and understanding of the variability in responses to a variety of impacts improves.
    We examined the effects of land use, geology, and longitudinal position within the river network on water quality and thermal regime at 23 sites within the Motueka River catchment. The con-centrations of suspended solids, nitrate nitrogen, total nitrogen, Escherichia coli, and Campylobacter were higher at sites draining pastoral and horticultural land than in similar-sized native or plantation forest streams. Average daily mean temperature and mini-mum temperature in summer and maximum winter temperature were higher in unshaded pastoral and horticultural streams than at native forest sites. Dif-ferences in water quality and thermal regime were also observed among sites with contrasting geology. Conductivity, pH, and minimum winter temperatures were highest at sites draining marble terrain. In con-trast, longitudinal patterns in water quality and tem-perature regime along the 120-km length of the river were relatively weak, although longitudinal patterns in amplitude of daily temperature fluctuation matched theoretical predictions. In this study, differ-ences in land use appeared to have the strongest influence on most water quality and thermal vari-ables examined. However, geology was an impor-tant factor explaining variation in certain variables (e.g., pH and conductivity). Longitudinal patterns in water quality and temperature were relatively weak and in many instances were linked with longitudi-nal patterns in land use and geology rather than catchment location alone.
    Angling pressure is increasing in many recreational trout fisheries throughout the world. There is a strong perception among anglers that trout become harder to catch after being disturbed by other anglers, thus affecting the quality of their angling experience. However, there is little scientific evidence to support or refute this perception. We measured the response to angling pressure in two rivers in New Zealand: The remote Ugly River and the more heavily fished Owen River. Both of these rivers have fisheries for brown trout Salmo trutta. The numbers of trout seen and caught over the length of four 3-d angling trips were compared between rivers. The behavioral responses to angling of naïve trout in the Ugly River were compared with those of Owen River trout and trout that had been angled previously from the Ugly River. The proportion of the trout population in the study reaches caught by two anglers after four 3-d trips was estimated as between 11% and 23% in the Owen River and up to 47% in the Ugly River. The most marked behavioral response to angling pressure was in the Ugly River, where trout that had been caught and released or merely disturbed by anglers were rarely seen over the following days. No such hiding response was observed in the Owen River. A learning response was also evident, as trout that had been fished previously were more likely to be scared by anglers or required smaller, low-profile flies before being caught than naïve trout. Faced with increasing angling pressure, anglers can perhaps cope with the observed learning response by improving their techniques to outsmart trout. However, the hiding response observed in the remote river indicates that controls on angling, such as access restrictions, may be required to maintain quality angling experiences in these wilderness fisheries.
    The water quality impact of a herd of 246 dairy cows crossing a stream ford was documented. Two cow crossings produced plumes of turbid water associated with very high concentrations of faecal indicator bacteria (Escherichia coli) and high suspended solids (SS) and total nitrogen (TN). On the first crossing, towards the milking shed, the cows were tightly-bunched and produced a sharp spike of contamination (E. coli peaking at 50 000 cfu/100 ml). After milking, the cows wandered back across the stream as individuals or small groups, and contaminants were less elevated, albeit for a longer period. Light attenuation, measured continuously by beam transmissometer, correlated closely with E. coli, SS, and TN, permitting the total yield of these contaminants to be estimated. Contaminant yields for the two crossings were very similar, suggesting that time taken and whether or not cows are herded may not greatly influence water quality impact. The cows defecated c. 50 times more per metre of stream crossing than elsewhere on the raceway. This study has shown that cattle accessing stream channels can cause appreciable direct water contamination, suggesting that excluding cattle from streams will have major water quality benefits.
    Drainage is considered the primary function of many lowland waterways throughout New Zealand, but drains also provide habitat for many valued species. Aquatic plant growth and sediment accumulation can decrease drainage efficiency, making drain maintenance necessary. However, the importance of other functions provided by these waterways may be overlooked during drain maintenance. In this study we measured water levels, plant cover, water quality, and invertebrate community composition in spring-fed drains before and after mechanical excavation and herbicide (diquat) application. A control drain was also monitored. Many eels and other aquatic fauna were amongst the material removed from the drain by the excavator. Invertebrate densities recorded after excavation were half of those recorded shortly before clearance, but recovered within 1 month. Aquatic plant cover had returned to 80% of pre-excavation levels within 6 months. We observed no acute toxic effects of diquat application on aquatic invertebrates; however, survival of invertebrates living among overhanging vegetation was reduced. Aquatic invertebrate taxonomic richness decreased at the sprayed site after diquat application, probably due to an increase in detritus within the drain. We did not observe a decrease in oxygen concentration associated with the decay of aquatic plants after treatment. Plant cover returned to pre-treatment levels within 6 months of diquat treatment, but was dominated by aquatic plants rather than overhanging terrestrial vegetation. The use of weed rakes, rather than standard excavator buckets, should be encouraged to reduce the removal of eels and other aquatic organisms during mechanical excavation. Manual return of eels to drains following mechanical excavation could also be considered.
    We assessed whether taxonomic structure and density of aquatic drift could be predicted from the benthos in three New Zealand rivers. The three main orders contributing to both the benthos and drift were Ephemeroptera, Diptera, and Trichoptera. Drift and benthic densities for all taxa and all rivers combined were not significantly correlated (adults inclusive and exclusive). There were significant positive correlations between benthic and drift densities for the three main drifting orders—Ephemeroptera, Diptera, and Trichoptera when data from all rivers were combined. However, these relationships were not always detected in individual rivers. The propensity for Deleatidium to drift was negatively related to chlorophyll a concentration; suggesting density‐dependent drift mediated by food limitation. Drift was reduced when periphyton chlorophyll a concentration was high in relation to benthic Deleatidium density. This highlights an unexpected effect of periphyton proliferation on invertebrate drift and drift‐feeding fishes. Despite finding some correlations between benthic and drifting communities, defining general relationships between benthic and drifting communities is challenging given the complexity of density‐dependent and density‐independent mechanisms that influence invertebrate drift.
    Current conceptual models of river ecosystems differ in their predictions of the dependence of food webs on organic matter from upstream sources versus that produced within the river channel or in the adjacent riparian zone. Model suitability may vary at the valley segment scale, however, due to the role of channel type in determining sources of organic matter. We analyzed stable isotopes to assess sources of organic matter for consumers in a grassland river (Taieri River, New Zealand) that flows through two distinct valley segments with contrasting channel types - bedrock confined (n = 2 upstream reaches) versus alluvial floodplain (n = 2 downstream reaches). We tested predictions that: (a) riverine consumer production is based on valley-segment scale sources of organic matter, and (b) upstream-downstream linkage of food webs via organic matter transported from bedrock confined to alluvial floodplain channels is weak. δ13C and δ15N values for consumers in confined reaches indicated that primary production from the channel was their primary food source during summer, but terrestrial vegetation was important during winter. In comparison, terrestrial vegetation was the major food source in one floodplain reach, but aquatic primary production appeared to be the major food source in the other floodplain reach. When considered simultaneously, δ13C and δ15N values for consumers and their food sources indicated little overlap between channel types and negligible linkage of food webs by organic matter transported from confined to floodplain valley segments. These results suggest that the floodplain may be the primary contributor of carbon and nitrogen to riverine food webs in floodplain valley segments. Local factors, rather than upstream-downstream linkage between confined and floodplain valley segments, appear to be determinants of trophic resources for consumers in floodplain reaches of this grassland river. This conclusion supports models viewing river channels traversing discrete valley segments as being independent with regard to food web dynamics.
    We compared raw drift‐dive counts of adult brown trout (Salmo trutta Linnaeus 1758) with population estimates calculated from mark‐resight techniques on two occasions in two back‐country rivers near Nelson, New Zealand. Trout were caught by angling and marked with colour‐coded dart tags between 1 and 7 days before drift dives were carried out. Drift‐dive counts in the Owen and Ugly Rivers were 57–66% and 21–43%, respectively, of the population estimates calculated using the mark‐resight techniques. Although underwater census is the cheapest and easiest way to census adult trout populations in clear‐water rivers, a large proportion of the trout population may not be seen in rivers with abundant in‐stream cover. Raw drift‐dive counts provide an index of relative abundance that is useful for monitoring changes in trout populations of specific river reaches over time. However, for comparisons between rivers more accurate population estimates are required. We recommend a combined approach of raw drift‐dive counts and the use of mark‐resight techniques to provide the best estimates of trout numbers. As many trout as possible should be tagged to improve the accuracy of mark‐resight studies.
    1. We used stable isotopes to study the temporal (early summer versus autumn) pattern of use of terrestrial and aquatic sources of organic carbon by consumers in two bedrock-confined reaches of a grassland river in New Zealand. 2. The major sources of organic carbon available to primary consumers were expected to be terrestrial leaf-litter and biofilm from the stream channel. These putative carbon sources showed no significant change in mean δ13C between summer and autumn. Leaf litter (mean δ13C<−26.25) was depleted in 13C compared to biofilm (mean δ13C>−19.92). 3. In contrast to leaf litter and biofilm, the δ13C of consumers changed over time, being enriched in 13C in the autumn compared with early summer. Both the magnitude (>5‰ in some cases) and rapidity of this shift (<3 months) was surprising. 4. A two-source mixing model indicated that, during early summer, terrestrial carbon comprised> 50% of tissue carbon for 15 of the 17 taxa of aquatic consumers analysed. During autumn, terrestrial carbon comprised> 50% of the tissue carbon of only five of 25 taxa. Because the mean δ13C of putative food sources was consistent over time, the shift in δ13C values for consumers is attributed to a change in relative amounts of terrestrial and aquatic carbon available for consumption. 5. Because seston consists of a mixture of many particles of diverse origin, it may provide an integrated measure of catchment-wide sources of organic matter entering a stream channel. Like the tissues of most consumers, mean δ13C values for seston showed a significant shift toward 13C enrichment. This indicated that the relative availability of terrestrial carbon decreased from summer to autumn. 6. The actual quantity of carbon contributed to the stream food-web by this potential terrestrial–aquatic link is unknown. Although terrestrial carbon may comprise a high proportion of the tissue carbon of consumers prior to summer, the majority of secondary production (and carbon sequestration) probably occurs during early summer as a consequence of rising temperature and high quality food in the form of biofilm.
    We measured ecosystem metabolism and organic matter transport seasonally in five streams draining catchments dominated by native forest, exotic pine plantation, grazed tussock grassland, or developed pasture. All streams are tributaries of the Taieri River in southeastern New Zealand. Whole-stream metabolism was estimated by both two-station and single-station open-channel methods, allowing comparison between these techniques. Transfer of oxygen across the stream surface was estimated using reaeration coefficients determined from three different procedures: tracer gas injections (propane), analysis of the oxygen record, and empirical velocity-depth equations. Measurements of gross primary production (GPP) and community respiration (CR) showed differences among streams that reflected method rather than ecosystem process. The ratio of GPP:CR and net ecosystem metabolism, however, showed strong concordance among methods, suggesting that bias involved in standardizing estimates to areal units may be more important than differences among methods. The two-station approach appeared to cope more adequately with steep slope, high bed roughness, and low GPP than did the single-station method. However, in tranquil and productive streams, both methods worked well. When differences between methods were accounted for, results emphasized how differences in terrestrial landscapes may markedly affect ecosystem processes within streams. Shading by the heavy canopy at the native forest site, turbidity at the pasture site, and the valley walls at one of the tussock grassland sites appeared to limit GPP. CR was high in the native forest site, due to a large supply of organic material from the riparian zone. Concentrations of seston were highest at the developed pasture site, apparently a result of intensive grazing and associated bank failure. The organic content of seston was highest in the native forest site and lowest in the pasture site. Organic carbon spiraling length in the pasture site was longer than average for a stream of its size, whereas spiraling length in the native forest site was short when compared to similar-sized streams elsewhere. Changes in catchment land use and riparian vegetation, as well as reach-specific geomorphic factors, alter light availability and organic matter supply, which are fundamental factors controlling organic matter production, respiration, and transport in streams.
    1. The impact of agricultural activities on waterways is a global issue, but the magnitude of the problem is often not clearly recognized by landowners, and land and water management agencies. 2. The Pomahaka River in southern New Zealand represents a typical lowland catchment with a long history of agricultural development. Fifteen sites were sampled along a 119-km stretch of the river. Headwater sites were surrounded by low-intensity sheep farming, with high-intensity pasture and dairying occurring in the mid-reach and lower reaches. 3. Water clarity decreased significantly from about 6 m in the headwaters to less than 2 m in the lower reaches. Benthic sediment levels increased significantly downriver, peaking at 35 mg m−−2 below several tributaries with high-intensity agriculture in their catchments. Periphyton levels were also significantly greater in the lower reaches than the headwaters, and coincided with increased nitrogen (DIN) and phosphorus (SRP) concentrations. 4. Macro-invertebrate species richness did not change significantly throughout the river, but species composition did with Ephemeroptera, and to a lesser extent, Plecoptera and Trichoptera dominating the headwater sites (where there was high water clarity, and low nutrient and periphyton levels). Downriver these assemblages were replaced by molluscs, oligochaetes and chironomids. 5. Canonical correspondence analysis indicated that agricultural intensity and physical conditions associated with agriculture activity (e.g. impacted waters, high turbidity and temperature) were strongly associated with the composition of benthic assemblages at differing reaches down the Pomahaka River. 6. The present results indicate that quantifying agricultural intensity within a catchment, particularly relative livestock densities, may provide a useful tool for identifying threshold levels above which river health declines.
    1. We determined the longitudinal pattern of organic matter concentration, quality, size composition and spiralling length along a 310-km grassland river system (Taieri River, New Zealand). 2. Organic seston concentration (0.24–4.05 mg ash-free dry mass (AFDM) l–1) and dissolved organic carbon (DOC) concentration (2.3–5.7 mg C l–1) showed no obvious longitudinal patterns. In contrast, there was a significant downstream increase in inorganic seston concentration (0.13–13.73 mg ash l–1), presumably because of a downstream increase in the proportion of the catchment developed for agriculture. 3. Although there was a trend toward increasing particle size in the first 25 km of the river continuum, organic seston was primarily composed of ultrafine particles (0.6–30 μm) at all study sites. The ratio of coarse (> 250 μm) to ultrafine organic seston decreased logarithmically down the continuum. Organic content generally decreased with particle size. Ultrafine particles, however, had significantly higher organic fractions than fine (60–100 μm) and very fine (30–60 μm) particles. 4. Daily organic carbon turnover length ranged from 10 to 98 km and increased downstream. This is consistent with other studies along river continua and suggests that organic carbon turnover length is largely controlled by the relationship between channel dimensions and discharge, rather than the presence of specific retention devices. 5. Concentrations and nutritional quality of organic seston and concentrations of DOC were highest in an unconstrained floodplain reach in the upper river. These data suggest that new material enters the river channel in this reach, potentially providing an important energy source for the river community downstream. The effect of this reach on the longitudinal pattern of organic matter concentration and quality emphasizes how changes in channel form can alter river ecosystem structure and function.
    1. We compare the rates and mechanisms of processing of tussock (Chionochloa spp.) leaf litter in six New Zealand streams draining grassland catchments that contrast in the extent to which they have been developed for pasture. 2. Rates of processing, measured as rate of weight loss of leaf packs and rate of leaf softening, were at the slow end of the spectrum for vascular plant processing. Processing was faster at developed sites, mediated mainly through the influence of oxidized nitrogen concentration on microbial activity. 3. Few invertebrate shredders colonized leaf packs and it is unlikely that invertebrates had an appreciable effect on leaf processing in our study streams, which do not effectively retain leaf litter. Very small headwater tributaries appear to retain leaf litter and possess a more abundant shredder community. 4. Measures of leaf processing in our six streams were significantly correlated with Petersen's (1992) RCE score of stream condition. We discuss the potential for using rate of leaf litter processing as a method of bioassessment. 5. Even the most degraded stream in our study is classed as ‘good’ using the RCE inventory system. Human impact in the Taieri River is relatively small compared with the degradation observed in some parts of the world.
    abstractive demands,against flows required for maintenance,of in-stream values in small streams. In many ,cases these streams do not ,have flow data and there is limited information on the in-stream values to be protected. Unfortunately, the in-stream values ofsmall streams are often perceived to be relatively low, despite the fact that they are often important habitat for native fish and key spawning,and rearing areas for sports fish. Technical methods,to assess flow requirements in larger streams and rivers are relatively well developed. However, these methods are not necessarily applicable to small streams because most research on the ,flow requirements of aquatic ,life has been carried out on larger rivers and the equations used in hydraulic models,work poorly in small,turbulent streams. These techniques are also time consuming,and expensive and often can not be justified on a small stream. In most cases, decisions on water allocation and environmental,flows in small streams currently are based on historic flow,methods,(e.g. minimum,flow at the 1 in 5-year low flow) and thus require transfer of flow records from the nearest flow recorder, which is usually on a nearby larger stream or river and thus not necessarily a good predictor of flows in the small stream of interest. Abstractions from groundwater ,and seepage galleries have the potential to drop ,ground water levels causing springs and nearby ,small streams ,to recede ,or dry ,up. These concerns led to two ,small stream studies in Marlborough ,and Tasman. The first study was of the values and threats across a range of spring-fed waterways,on the Wairau Plain in conjunction with the Marlborough District Council. The second was an assessment of some techniques to guide,management,of water abstraction in a small headwater stream inthe,Motueka ,River catchment ,as part ,of the ,Motueka ,integrated catchment management,(ICM) project (see
    Decline in the Motueka trout fishery in the mid-1990's has been linked by some observers to increased input of sediment into the river, mainly from the Separation Point Granite terrain. This is believed to have increased the proportion of the riverbed that is covered in sand and silt and affected trout spawning, food supply, and habitat (such as the density of pools in the catchment). However, there is currently no scientific evidence to support this contention, to determine where the major sediment sources are and whether they are natural or linked to land use practices, or to clearly determine whether other factors may have played a role in the observed decline in trout numbers. In addition, elevated sediment loads may also affect marine ecosystems and aquaculture, and there is a need to understand sediment delivery to Tasman Bay and redistribution within the bay. Further, understanding rates of gravel supply and sediment transport dynamics is fundamental to management of gravel extraction and bank stability within the catchment. This poster outlines the progress we are making to determine the spatial pattern of sediment generation, delivery and transport and its impacts on freshwater and marine habitats.
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