Doug J. Booker

Establishment of reference or baseline conditions of chemical indicators in New Zealand streams and rivers relative to present conditions

The management of streams and rivers can be aided by knowledge of reference conditions. Data from >1000 sites across New Zealand was used to develop a technique to estimate median ammoniacal-N, clarity, Escherichia coli, filterable reactive phosphorus, nitrate-N, suspended solids, and total nitrogen and phosphorus values under reference conditions for streams and rivers as classified by the River Environment Classification (REC). The REC enabled us to account for natural variation in climate, topography and geology when estimating reference conditions. Values for minimally disturbed sites (i.e. <5% in intensive agriculture) were generally within the confidence limits for estimated reference values. Metrics that described: (1) the percentage of anthropogenic contribution to analyte values; and (2) the degree of enrichment beyond the reference conditions, showed that lowland sites classified as warm-wet, warm-dry or cool-dry exhibited the greatest anthropogenic input and enrichment. The consideration of natural variation by REC class informs the setting of water quality objectives through avoiding water quality limits or targets that are either too restrictive, and impossible to meet (e.g. below reference conditions), or too high, such that they have little ecological benefit. We recommend reference conditions be considered by regulatory authorities when assessing water quality impacts, objectives and limits.

Does one size fit all? An evaluation of length–weight relationships for New Zealand's freshwater fish species

Length–weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length–weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length–weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length–weight relationships was also assessed. Location, in particular, generated different length–weight relationships for 65% of the species examined. Length–weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R2>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand.

Can bottom-up procedures improve the performance of stream classifications?

Top-down methods for defining stream classifications are based on a conceptual model or expert-defined rules, whereas bottom-up methods use biological training data and statistical modelling. We compared the performance of six classification methods for explaining the taxonomic composition of invertebrate and fish assemblages recorded at 327 and 511 sites, respectively, distributed throughout France. Classification 1 and 2 were top-down classifications; The European Water Framework System A (WFDa,) and the French Hydro-ecoregions (HER 2). Four bottom-up classification procedures of increasing complexity were defined based on 11 variables that included watershed characteristics describing climate, topography, and geology, and site characteristics including elevation, bed slope and temperature. Classification 3 was defined using matrix correlation (MC) to select a combination of variable categories that produced the best discrimination of the observed taxonomic composition. Classification 4 and 5 were defined by clustering the sites based on their taxonomic data and then using linear discriminant analysis (LDA) and Random forests (RF) to discriminate the clusters based on the environmental variables. Classification 6 was defined using generalized dissimilarity modelling (GDM). Our hypothesis was that the bottom-up classifications would perform better because they flexibly accommodate complex relationships between compositional and environmental variation. We tested the classifications using the classification strength statistic (CS). The RF-based classification fitted the taxonomic patterns better than GDM or LDA and these latter classifications generally fitted better than the MC, WFDa or HER classifications. Cross validation analysis showed that differences in predictive CS (i.e. the CS statistics produced from sites not used in defining the classifications) were often significant. However, these differences were generally small. Gains in predictive performance of classifications appear to be small relative to the increase in complexity in the manner in which environmental variables are combined to define classes.

Estimating periphyton standing crop in streams: a comparison of chlorophyll a sampling and visual assessments

Abstract Periphyton standing crop is often measured as chlorophyll a but there is increasing interest in using visual assessments of periphyton cover. Visual methods are rapid and require no sample analysis, but can be regarded as subjective with high inter-operator variability. We investigated variability in periphyton standing crop across operators, rivers and time, as determined visually and from chlorophyll a measurements. We found that visual assessments (comprising percentage cover estimates of up to eight periphyton categories) distinguished sites and occasions as effectively as chlorophyll a. Furthermore, an estimate of chlorophyll a could be derived from the visual assessments. Because our surveys were conducted in only three rivers, general applicability of the derivation of estimated chlorophyll a from the visual assessments warrants further investigation. The current recommendation of 20 views was sufficient for realistic visual assessments of average cover. Overall, our results indicated that inter-operator variability in visual assessments need not be a major concern, given adequate training.

Characterizing disturbance regimes of mountain streams

Abstract: Characterizing biologically relevant stream disturbance regimes is challenging, but necessary to answer questions about disturbance effects on ecological processes. No universally accepted approach exists for characterizing stream regimes. Our goal was to evaluate approaches that can be applied to test effects of disturbance on benthic organisms. We defined disturbance as events or environmental conditions caused by changes in stream discharge that affect the stability or habitability of the stream bed. We used several metrics to describe disturbance regimes of mountain streams that were not permanently gauged in 1 catchment, and considered the trade-off between effort required to obtain the data and the quality of information gained. We used an innovative photographic method to assess substrate particle movement empirically as a benchmark for comparison to other indicators of channel stability and to metrics describing hydrologic variability relevant to streambed stability. We used a model selection procedure to choose the best combination of individual variables to explain variation in substrate particle movement and included those variables in a multivariate axis of disturbance that can be applied to evaluate effects of disturbance on benthic organisms. Individual variables with the highest explanatory power were maximum daily increase in discharge and the Pfankuch index of channel stability. Substrate particle size and stream size (drainage basin area) were related to the multivariate index of disturbance, but channel gradient was not. Protocols used to measure substrate stability and to obtain the multivariate index of disturbance were labor intensive, but our analyses indicate it may be reasonable to use more easily measured variables (e.g., Pfankuch index) to estimate disturbance to benthic organisms at local scales, although explanatory power may be reduced. Our analyses provide a menu of options to estimate variation in local disturbance regimes of ungauged mountain streams that may not be adequately explained by extrapolation from hydrographs of gauged streams.

Relative influence of local and landscape-scale features on the density and habitat preferences of longfin and shortfin eels

The relative structural influence of local-scale versus landscape-scale habitat features on size-class matrices of both longfin (Anguilla dieffenbachia) and shortfin (Anguilla australis) eels collected along six different New Zealand rivers (10 river-year combinations) are quantified using variance decomposition. The total explained variation of these species and size-class matrices was related to both local-scale and landscape-scale variables, and some proportion was shared between these two scales. When compared with landscape-scale variables, local-scale physical habitat variables such as water velocity and fish cover explained more about patterns in the size-distribution of longfin eels. The opposite situation was true for shortfin eels whose size-distribution was more strongly related to landscape-scale variables such as distance from sea and channel slope. These findings suggest that management of river flows is required to ensure flow regimes that maintain availability of suitable local-scale hydraulic conditions, and that biodiversity conservation efforts need to be targeted at protecting a gradient of rivers across New Zealands river landscape.

Quantifying the Hydrological Effect of Permitted Water Abstractions across Spatial Scales

Water abstraction from rivers and aquifers has considerable potential to alter flow regimes, thereby influencing the physical, chemical, and ecological well-being of freshwater ecosystems. The economic and social benefits of abstraction need to be balanced against its potentially deleterious consequences for hydrologically-driven ecological functions, ecosystem services, cultural values, and recreation. In New Zealand, recent legislation states that limits for the use of water resources should be set for all waterbodies to manage the potential cumulative impacts of abstraction and reduce allocation of the hydrological resource in over-allocated catchments. These limits must comprise at least a predefined minimum flow (the flow at which all abstraction must cease) and a total allocation (the maximum rate of abstraction summed across upstream abstractions). Over-allocation occurs when the sum of all upstream abstractions exceeds the total allocation. A national database describing consents to abstract water was collated. A replicable, transferable, and objective method was applied to calculate total allocation at the national, catchment, and reach scales across the entire country. Total allocation for each catchment was expressed by mapping Weighted Allocation Impact; an index that integrates magnitude and spread of water resource allocation across entire catchments. Results show that existing consents have caused over-allocation in several catchments, prompting questions about how to reduce abstraction in these locations.

Relationships between Maori values and streamflow: tools for incorporating cultural values into freshwater management decisions

ABSTRACT This study aimed to develop quantitative relationships for Maori cultural values supported by streamflow. We examined the results of a Cultural Flow Preference Study (CFPS) for five streams in Canterbury, New Zealand, and used mixed effects models to quantify how observed streamflow supported scores for Overall Health (OH). Relationships between streamflow and OH differed between sites and assessors within each site. Ignoring differences between sites and assessors, there was a positive relationship that explained 5% of the variation between streamflow and OH. After accounting for differences between sites and assessors, there was a positive relationship that explained 53% and 62% of the variation respectively. Flow attributes sustaining cultural values are based on the characteristics of the site and relationships change between rivers. Our study provides a transferable framework for developing cultural health–flow relationships that will enable Maori to be involved from the outset of any environmental flow assessment.

Communicating biophysical conditions across New Zealand's rivers using an interactive webtool

ABSTRACT Scientific research is often targeted towards predicting broad-scale patterns in biophysical variables, with spatial data traditionally communicated using static figures and written descriptions in scientific journals and reports. However, inaccessibility and lack of flexibility mean that these communication methods have often hindered research uptake by resource managers and decision-makers. We used R shiny to develop an interactive webtool that maps estimates of 109 biophysical variables, including hydrology, ecology and water quality metrics across the New Zealand digital river network. NZ River Maps is freely available online and can be used to visualise regional patterns, identify site-specific characteristics and overlay regional planning layers. Interactive webtools improve on traditional communication methods by allowing inspection of predictions for selected sites and plotting of spatial patterns. The ability to quickly visualise and quantify relevant spatial data has enabled better communication of research outputs to provide robust and transparent inputs into environmental management.