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There is growing recognition that multiple forms of uncertainty influence policy reform, but we need case studies illustrating how uncertainties influence reform, and strategies used to manage uncertainties in practice. We present a case study of how science was generated and incorporated into national water policy. We estimated turbidity (suspended fine sediment) reference states throughout the river network of New Zealand. A key decision-problem was: how region-specific should reference states be? We developed classifications of the national river network that grouped rivers with similar turbidity regimes into classes at four spatial resolutions. Choosing a classification was complicated by ontological uncertainties. Scientific actors framed these ontological uncertainties in different ways, introducing framing uncertainties (‘ambiguities’) into the decision-making process. Well-established statistical techniques were employed to objectively identify the most parsimonious classification, but those techniques had little impact on decision-making. Reframing ontological uncertainties in terms of risks to management objectives was required to reconcile divergent frames, and showed that the classification with the highest resolution was the most credible option. Nonetheless, local governments highlighted that the most credible classification was not the most relevant or legitimate one in light of implementation constraints. The final decision was made against a backdrop of ambiguities, was partially subjective, and balanced trade-offs among credibility, relevance and legitimacy. Looking ahead, ambiguities could be reduced by framing decision problems in terms of risks to management objectives. A barrier to doing this is the short duration of policy windows, so translational science must take place when such windows are shut.

A method for objectively estimating reference states for suspended fine sediment (turbidity) is presented. To be fit for water policy development and implementation the method had to satisfy four requirements: (1) the method must not be dependent on data from minimally-disturbed reference sites; (2) the method must facilitate characterization of reference states throughout heterogeneous river networks, given patchy data; (3) the classification of reference states must be relevant and legitimate to end-users; (4) the method should provide several classifications of reference states at different spatial resolutions allowing selection of the resolution yielding the most parsimonious classification of reference states throughout the network. Implementing the method involves two stages: (1) Development of a river classification based on sediment supply and retention regimes (defining ‘turbidity classes’) at multiple spatial resolutions. (2) At each resolution, for each turbidity class, estimation of a reference state based on relationships between turbidity and anthropogenic stressors, then objective selection of the resolution yielding the most parsimonious classification of reference states throughout the network. Implementing the method requires a river network GIS and turbidity data within classes, preferably from monitoring sites spanning the domains of the anthropogenic stressor variables used for model-based estimation of reference states.•A method is presented for estimating reference states for suspended fine sediment (turbidity) throughout spatially heterogeneous river networks.•Development of the method was guided by the requirements of policy analysts during reform of water policy in New Zealand.•The method presented was used to develop fine sediment regulatory thresholds of national water policy., Graphical abstract Image, graphical abstract

Increasing urbanisation in the future will put mounting stresses on the receiving environments around those urban centres due to increased sedimentation and contaminant runoff. Emerging contaminants (ECs) are an extensive array of chemicals and many are not under regulatory action. Within New Zealand likely future pressures from ECs will be in both urban centres and rural areas due to intensive agriculture, although at present there is a lack of information on the state of the environment in both sectors. This study was initiated to gauge the distribution of ECs in the urban environment by measuring concentrations of flame retardants, plasticisers, alkylphenols, herbicides and pesticides, steroid oestrogens, pharmaceuticals and heavy metals in sediment from 13 estuarine sites around Auckland, New Zealand's biggest city. Total polybrominated diphenyl ether (PBDE) flame retardant concentrations ((7)ΣPBDE) ranged from 0.55 to 573 ng/g (dw). The phthalate plasticiser di(2-ethylhexyl)phthalate (DEHP) was measured at up to 11,500 ng/g from one site. Nonylphenol (NP) was found at up to 32,000 ng/g at one site adjacent to the city's major wastewater treatment plant (WWTP). However, median concentrations of NP were 153 ng/g, suggesting this site was not representative of the region. Nonylphenol mono- and di-ethoxylates (NPEO1,2) had highest concentrations (1600 ng/g) at a marina. Highest glyphosate concentrations (up to 950 ng/g) were observed at residential sites. Steroid oestrogens were detected at extremely low concentrations (maximum 2.2 ng/g), while all other pesticides or herbicides were not detected at any sites. Multi-residue analysis of 46 pharmaceuticals showed presence of 21 compounds at one or more sites, with average concentrations ranging from 0.16 to 7.66 ng/g. Generally, environmental concentrations of ECs were similar to those reported world-wide. However, comparisons for pharmaceuticals were problematic, due to very few studies on pharmaceutical concentrations in estuarine sediments, with most focussed on sewage and stream water phases.

Increasing concentrations of anthropogenic contaminants in wild kai (food) of cultural, recreational and economic importance to the indigenous Māori of New Zealand is a potential human health risk. Contaminants that are known to bioaccumulate through the food chain (e.g., organochlorine pesticides (OCPs), PCBs and selected heavy metals) were analysed in important kai species including eel (Anguilla sp.), brown trout (Salmo trutta), black flounder (Rhombosolea retiaria) and watercress (Nasturtium officinale) from important harvesting sites in the region of South Canterbury. Eels contained relatively high wet weight concentrations of p,p′-DDE (8.6–287 ng/g), PCBs (32ΣPCB; 0.53–58.3 ng/g), dieldrin (< 0.05–16.3 ng/g) and Σchlordanes (0.03–10.6 ng/g). Trout and flounder contained lower concentrations of organochlorines than eels, with p,p′-DDE wet weight concentrations ranging from 2.2 to 18.5 ng/g for trout and 6.4 to 27.8 ng/g for flounder. Total arsenic wet weight concentrations were below detection limits for eels but ranged from 0.27 to 0.89 μg/g for trout and 0.12 to 0.56 μg/g for flounder. Mercury concentrations ranged from 0.02 to 0.56 μg/g, 0.11 to 0.50 μg/g and 0.04 to 0.10 μg/g (ww) for eel, trout and flounder respectively. Lifetime excess cancer risk was calculated through established risk assessment procedures, highlighting dieldrin, ΣPCBs and p,p′-DDE in eels and arsenic in trout and flounder as primary contaminants of concern. A second non-cancer chronic health risk assessment indicated that mercury and PCBs were a potential concern in eels and mercury in trout. A cumulative lifetime cancer risk assessment showed potential health risk for consumption of some species, even at low consumption rates and provided the basis for establishing recommended dietary consumption limits for harvest sites within the study region.

The potential for stressors to interact or elicit different responses depending on ecological setting can confound the use of contaminant guidelines or predictions from laboratory-based ecotoxicological studies. However, predicting and identifying multiple stressor effects is challenging because of the wide range of treatment combinations needed for laboratory experiments and the difficulty of conducting field experiments across a range of conditions that may influence stress responses. In this study we analyse density responses apparent in the natural populations of 46 macrofaunal taxa to stressors representing habitat requirements (sediment particle size), food (sediment organic content) and heavy metal contamination (copper, zinc and lead). Simple responses to either a single stressor or stressors acting additively were less apparent in our regression-based models than multiplicative effects. We also investigated whether species that exhibited a unimodal abundance distribution in response to a habitat factor were more likely to exhibit differential responses to contaminants than species that exhibited monotonic responses to habitat factors. This proved to be the case, although not all unimodal abundance distributions were related to differential responses. The results of this study suggest that regression analysis, together with well-designed, large-scale, field surveys, offer a good method for describing and predicting effects of multiple stressors and helping to both target experiments and scale-up their results.

Heavy metals and metalloids were measured in freshwater mussels ( Hyridella menziesi ) and sediments in the upper Waikato River, New Zealand. Mercury (Hg) concentrations ranged 35-fold in sediments (0.025-0.87 mg kg −1 dry wt) and 144-fold in mussels (0.091-13.1 mg kg −1 dry wt). Arsenic (As) concentrations ranged 190-fold in sediments (7.9–1520 mg kg −1 dry wt) and only 10-fold in mussels (15.0–153 mg kg −1 dry wt). There was no significant correlation between sediment total concentrations of either Hg or As and mussel tissue levels. Sediment quality guidelines were exceeded for Hg and As at most sites and for copper, chromium, iron and manganese at a few sites. Tissue concentrations exceeded levels considered to be safe for human consumption for Hg at Lake Aratiatia and As at several sites. Transplant experiments with caged mussels were used to measure uptake and depuration rates of Hg and As. Half-lives for mussel uptake and depuration of Hg were 6–12 months. Arsenic uptake rates could not be determined but the depuration showed a half-life of about 2.5 months. Physiological measurements were consistent with increased food availability at some sites rather than contaminant effects. These results highlight the need to understand biochemical changes induced by factors that are independent of environmental concentrations of contaminants, such as the influence of food levels and the potential for metabolic adaptation in biomonitoring organisms.

The concentrations of resin acids and chlorophenolic compounds were measured in river sediments above and below the effluent discharge point of a New Zealand bleached kraft pulp and paper mill. No significant concentrations of resin acids were found at background sites. Background concentrations of total chlorophenolic compounds ranged from −1 to 35 ng g −1 . Elevated concentrations of both compound classes were observed downstream of the mill. Total concentrations immediately below the discharge point were 76.6 ug g −1 and 30.7 ng g −1 dry weight respectively for the resin acids and chlorophenolic compounds. Chlorophenolic compound concentrations declined to background levels 20 km downstream whereas resin acids reached background concentrations after 38 km. Shallow surficial sediments were shown to contain the majority of the organic compounds.

Periphyton biomass on natural substrata at 26 sites above and below point source discharges in 7 New Zealand streams was compared with maximum potential values predicted by a laboratory calibrated model to determine the extent to which biomass was controlled by nutrients. Point-source enrichment, which increased dissolved reactive phosphorus (DRP) from 6 to 100 times the saturation level (about 25 μg/l) in five streams, was found to substantially increase biomass at all enriched sites in four streams. In two of these streams, biomass below the enrichment inputs was about 1200 mg chl a/m2. Overall, biomass averaged only 35 ± 44% of that predicted from phosphorus, velocity and temperature using the model. Furthermore, aesthetically nuisance biomass levels (i.e. > 200 mg chl a/m2) were observed at only 7 of the 19 downstream sites. In many cases, the lower than expected biomass levels were associated with high macroinvertebrate grazer densities, riparian shading or unsuitable attachment surfaces. These factors, therefore, appear to have exercised more control on periphyton biomass than nutrients, and may offer more effective alternatives for biomass control in enriched streams than lowering DRP below biomass saturating levels.

Modifications to an electrolytic respirometric system are described which facilitate precise measurements of BOD progressions for low substrate concentration (BOD 5 −3 ) as found in natural waters receiving organic enrichment. Samples may be incubated at any desired temperature or dissolved oxygen concentration with automatic hourly monitoring of the BOD progression. Subsamples may be withdrawn at any time without interference to the measurement. The system is independent of atmospheric temperature and pressure fluctuations and has a detection sensitivity of 0.05 mg of oxygen. Nomographs are presented to enable the maximum dissolved oxygen deficit, and the “apparent lag” time to be estimated. CO 2 removal, which may result in an extended lag phase, need not be used for BOD values below 50 g m −3 provided adequate buffering is supplied.

Benthic oxygen uptake rates (BUR) were measured for sewage fungus biofilms in rivers using a recirculating chamber in situ and ranged from 3.8 to 70.2 g O2m−2 d−1. In all chamber studies, BUR decreased with time during measurements. These decreases in BUR were reproducible and shown to be the result of decreasing dissolved oxygen (DO) concentrations. For a given run, a geometric relationship (log BUR linearly related to log DO) provided best fit to the data. An oxygen transfer exponent (OTE) with units of m d−1 was measured as the slope of this log-log plot. For repeated BUR runs with constant flow velocity and comparable substrate conditions the OTE value has been found to be constant. Estimated OTE values varied from 0.28 to 4.12 m d−1, being influenced by the flow velocity, biofilm morphology and age, and the concentration of substrate in the overlying water. Calculated depths of DO penetration into the river biofilms (depths 2–10 mm) ranged from 0.35 to 3.5 mm with apparent dispersion coefficients of 0.37−8.9 × 10−3cm2s−1. These results indicated that turbulent biofilm/water exchange dominates nutrient mass transfer process in river biofilms.

Benthic oxygen uptake rates (BUR) were measured for sewage fungus biofilms in rivers using a chamber in situ . The accuracy of the chamber measurements of BUR were tested by determining a river oxygen mass balance. This demonstrated that the chamber BUR values were within the range calculated when operated at the river boundary velocity (0.25 m s −1 , measured 0.05 m above bed). The maximum BUR value recorded was 70.2 g m −2 d −1 at 7.0 g m −3 dissolved oxygen (DO) concentration with a median value of 18 g m −2 d −1 . The large BUR response to flow velocity, increasing 1.9-fold for a doubling of flow velocity (0.125-0.25 m s −1 ), suggested a turbulent mass transfer process predominate for nutrient exchange between river biofilms and the overlying flow. Biofilm respiratory decay coefficients for homogenised biofilms were k = 0.375 – 0.100 day −1 (base e) giving a respiratory half-life of 1.85–5.54 days. These measurements suggest that intermittant effluent loading to rivers with biofilms established is unlikely to result in substantial respiratory decline unless the with-holding period is of the order of days.