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Degradation of aquatic ecosystems by fine sediment is a global environmental problem, and damages reflect particle properties as well as mass concentration. We studied sediment-related water qualit...

The planting of degraded land with tree plantations may be effective at improving land use sustainability and profitability but it can also have significant effects on stream hydrology. In this pai...

Water is an important component of many recreational opportunities and New Zealand invests significant resources in recreational water quality (RWQ) monitoring to assess risks to public health. How...

Water pollution control is challenging in catchments affected by ‘informal’ urban development. Lake Pampulha, an impoundment that is a major tourist focus within the municipality of Belo Horizonte, Minas Gerais state, Brazil, provides an example of degradation of aquatic environments by disorganised urbanization. We evaluated the current recreational suitability of the lake using state government monitoring data (2012-2017) with reference to Brazilian legislation and a water quality index for contact recreation in Brazilian freshwaters, considering E. coli (indicating faecal pollution and microbial hazards), cyanobacterial density (health risks and aesthetic quality), turbidity (aesthetics and safety associated with visual clarity), and pH (safety and eye-comfort). Our results show that, despite investments in pollution control, the recreational water quality of Lake Pampulha remains very poor. Contact recreation was most limited by persistent cyanobacterial blooms, but also faecal contamination and low visual water clarity. The effects of high phosphorus loading and faecal contamination from unsewered domestic wastewater is exacerbated by a tropical climate, promoting stable thermal stratification (favouring cyanobacterial dominance) and turbid wet-season runoff. Water quality indexing is a powerful tool not just for interpreting and communicating multiple metrics affecting water resources, but also for guiding rehabilitation efforts and tracking progress.

Estuaries are biogeochemically and physically dynamic environments, resulting in diverse optical water properties that vary in space and time. This natural variability challenges effective monitoring. We develop semi-empirical linear models of the two main water clarity aspects, visual clarity and light penetration, as functions of more routinely monitored and/or modelled water quality measures, to simplify approximations and allow more expansive modelling in space and time. At multiple points along salinity gradients in six northern New Zealand estuaries, we made discrete measurements of horizontal black disk visibility (yBD) and downwelling irradiance attenuation (Kd(PAR)), with surface concentrations of the main light-attenuating constituents (LACs): total suspended solids (TSS), coloured dissolved organic matter (CDOM – ag(340)), and phytoplankton chlorophyll a (Chl.a). Estuaries on the east coast (Tauranga and Tairua Harbours) were relatively clear compared to those on the west coast (Kaipara and Raglan Harbours). Although Kd(PAR) (controlling light penetration and euphotic zone depth) and yBD (inversely proportional to beam attenuation at 550 nm, controlling visual clarity) were strongly corelated over all estuaries (r2 > 0.8), there were small, yet significant, differences between regression lines in different estuaries. This suggests regional differences in light scattering and absorption properties of the LACs. Variability in water clarity was mainly accounted for by TSS alone in west coast Kaipara Harbour sub-estuaries (r2 > 0.7), while in east coast estuaries, TSS was a weak predictor (r2 0.7). West coast Raglan Harbour had intermediary responses. In most cases, the inclusion of CDOM significantly improved estuary models, but Chl.a was a significant term only in a few cases, such as during one survey on the Kaipara River sub-estuary. Co-linearity of LACs was an issue in some cases for semi-empirical models. The application of a literature-derived Lambert-Beer Law (LBL) type model to our data more effectively partition the contributions of the LACs, which confirmed and quantified differences between west coast (TSS dominant), and east coast (TSS + CDOM) estuaries. Although we expect that ‘simple’ semi-empirical models will have wide practical application for estimating visual clarity and light penetration in estuaries in New Zealand and elsewhere, consideration of all LACs in an LBL type model is advised across entire estuaries, and local verification and ‘tuning’ is desirable.

We assessed the reproducibility of river state-of-environment (SoE) water quality measurements in the Wellington Region, New Zealand (NZ). Field staff from GWRC and NIWA conducted 29 side-by-side water sampling and in-situ measurements at six river sites of diverse water quality for 12 variables measured routinely in river SoE monitoring across NZ. Field measurements of water temperature, dissolved oxygen, electrical conductivity and visual clarity agreed closely with strong numerical similarity (within 10%). Numerical similarity ranged widely for laboratory measurements, from strong for nitrate-nitrite-nitrogen to weak for turbidity, dissolved reactive phosphorus, and ammoniacal-nitrogen. Numerical agreement was very weak for laboratory pH (which is problematic) and E. coli–which is ‘tolerable’ for many applications given good correlation (R = 0.94) over a 2000-fold concentration range. The findings of our inter-agency comparison have contributed to quality assurance recommendations in the NZ National Environmental Monitoring Standard (NEMS) for water quality.

Sunlight exposure of streams controls their thermal regime and light availability for photosynthesis. Restoring riparian shade to formerly forested streams in cleared land is an important step in the restoration of stream ecological health. Methods exist for measuring existing stream shade, but management tools are needed for predicting future shade as riparian plantings grow. We refine an existing geometrically-based numerical model for diffuse lighting which can be linked to models of tree growth to investigate how shade changes over time. The model predicts ‘diffuse non-interceptance’ (difn) which is an index of long-term averaged lighting. Shade of real (meandering) streams is bounded by two computationally straightforward cases: a perfectly straight channel (canyon model) and a channel meandering so tightly that its shade geometry ‘collapses’ to that of a circular pool (cylinder model). In this paper, we verify model results against measurements of shading made with a canopy analyzer instrument in precisely-constructed physical models of both the cylinder and canyon cases. For both canyon and cylinder geometries the observed and predicted difn matched closely (over a wide range of the ratio tree height to stream width, h/w) corroborating the numerical model. As expected, light exposure at the channel mid-point was higher than at channel edges, highlighting the need to consider variations in lighting across the channel when predicting water temperature and aquatic plant growth. Over the range of h/w where difn changes rapidly, shade was appreciably higher for the cylinder than the canyon case.

Restoring riparian shade to formerly forested streams in cleared land is an important step in the restoration of stream ecological health. In a companion paper, we validated a numerical model for diffuse non-interceptance (difn) against measurements made in precisely-constructed physical models for two simplified geometries ‘canyon’ and ‘cylinder’ with trees lacking canopy ‘shape’. In this paper, we extend the model to include canopy ‘shape’ by representing trees as ellipses or kites, and quantifying shading from canopy overhang of the channel. The ratio of tree height (h) to stream width (w) strongly influences stream shade and is a key parameter when scoping riparian revegetation. Canopy width, overhang and viewpoint affect stream shade and could profitably be included in water temperature and aquatic plant growth models. Tree shape has a second-order effect on shade, most noticeably near the stream banks. The model predicts shade assuming a sky of uniform radiance (viz., it predicts shade to diffuse radiation) on the premise that difn is a useful index of long-term averaged light exposure. The model successfully reproduced the trajectory of shade reductions following riparian restoration predicted using a published physically-based model, confirming its suitability for scoping riparian shade restoration. While it would be feasible to include direct radiation in the model, this would require additional input data and computational effort.

This article overviews community-based water monitoring (CBWM) in Aotearoa-New Zealand (NZ). CBWM was strongly boosted in NZ around 2000 by the development of the Stream Health Monitoring and Assessment Kit (SHMAK) and the Wai Care community initiative. Reform of freshwater management in NZ may be one driver for renewed interest recently in CBWM. Because professionals perceive volunteer-monitoring data as unreliable, they currently give little support to volunteer monitoring. To address their concern, we compared CBWM with measurements by regional authorities (RAs) – the main water management agencies in NZ. Agreement was encouragingly close for a comprehensive range of variables, including the important state-of-environment (SoE) indicators: visual clarity, Escherichia coli and macroinvertebrates. Community volunteers need and want ongoing professional support and encouragement, and, fortunately, there are important benefits for water management agencies, including engagement of citizens in water management and use of volunteer data. Professional support for CBWM in NZ could include: advice and encouragement, training, database development and quality assurance. Current research and development is focused on improving resources and systems for volunteer monitoring, notably with upgrading of the SHMAK. We are enlisting volunteers, equipped with improved tools and support systems, to assess the benefits of riparian rehabilitation and the suitability of water for swimming.

Swimming is a popular activity in Aotearoa-New Zealand (NZ). Two variables that strongly influence swimming suitability of waters are faecal contamination, as indicated by the bacterium Escherichia coli, and visual clarity as it affects aesthetics and safety with respect to submerged hazards. We show that E. coli and visual clarity are inversely related overall in NZ rivers (R = −0.54), and more strongly related in many individual rivers, while similar (but positive) correlations apply also to turbidity. This finding, apparently reflecting co-mobilisation of faecal contamination and fine sediment, suggests that visual clarity, measured or estimated from appearance of submerged features, should be a valuable indicator of faecal contamination status and (more generally) swimming suitability. If swimmers were to avoid river waters

Seagrass meadows are important estuarine habitats, and in recent decades, have suffered global declines. Fine sediment pollution is recognised as a major cause of decline, usually attributed to the combined effects of reduction of photosynthetically available radiation (PAR) and burial. However, intruded fine sediment affects the seagrass rhizosphere and this interacts with reduced irradiance to affect seagrass performance. We undertook a 2 × 2 factorial mesocosm experiment, to examine the interaction between substrate muddiness and irradiance on seagrass growth and survival over a six-week period. The seagrass Zostera muelleri was grown on two substrates from the same estuary: (1) an inner estuary substrate with high mud content (42 %) from a location where seagrass formerly grew; and (2) an outer estuary substrate with moderate mud content (20 %) from a location at which seagrass persists. Two irradiance levels were used: (1) low (6.3 mol quanta m−² d−¹) and (2) very low (2.3 mol quanta m−² d−¹) both above a published compensation irradiance (Ec) of 1.9 mol quanta m−² d−¹. Belowground biomass and rhizome growth were significantly reduced by substrate muddiness but not detectably affected by irradiance. Shoot growth, was reduced by both reduced irradiance and increased muddiness, with a significant interaction. We conclude that muddification of substrates imposes an increased irradiance requirement for Z. muelleri to cope with adverse rhizosphere conditions, which should be taken into account when planning seagrass conservation and restoration interventions.

This review collates research into fine sediment as a stressor of seagrass and emphasizes the multiple modes of action of this contaminant. The article is based on a bibliographic database search that identified 201 articles describing sediment impacts on seagrasses. Articles were classified by one of three non-exclusive modes of action: 1) light reduction; 2) smothering (burial), and 3) effects via rhizosphere physico-chemistry. Most citations (104) investigated multi-mode impacts of sediments, but the most frequently investigated single mode was light reduction (57 citations), followed by substrate rhizosphere chemistry (31) then smothering effects (6). Mud with high organic content is particularly problematic and smaller seagrasses are particularly vulnerable. Research gaps include polyphasic approaches, and studies of interactions between smothering, rhizosphere biogeochemistry and light climate. Identifying the thresholds of seagrass health indicators under mud stress should benefit coastal resource management, enabling improved decision-making and implementation of protective actions.

This study compared light and dark disinfection of faecal bacteria/viral indicator organisms (E. coli and MS2 (fRNA) bacteriophage) and human viruses (Echovirus and Norovirus) in Wastewater Treatment Pond (WTP) mesocosms. Stirred pond mesocosms were operated in either outdoor sunlight-exposed or laboratory dark conditions in two experiments during the austral summer. To investigate wavelength-dependence of sunlight disinfection, three optical filters were used: (1) polyethylene film (light control: transmitting all solar UV and visible wavelengths), (2) acrylic (removing most UVB 5-log E. coli and MS2 phage removal (from ~1.0 × 106 to

Relationships between land use and water quality are complex with interdependencies, feedbacks, and legacy effects. Most river water quality studies have assessed catchment land use as areal coverage, but here, we hypothesize and test whether land use intensity – the inputs (fertilizer, livestock) and activities (vegetation removal) of land use – is a better predictor of environmental impact. We use New Zealand (NZ) as a case study because it has had one of the highest rates of agricultural land intensification globally over recent decades. We interpreted water quality state and trends for the 26 years from 1989 to 2014 in the National Rivers Water Quality Network (NRWQN) – consisting of 77 sites on 35 mostly large river systems. To characterize land use intensity, we analyzed spatial and temporal changes in livestock density and land disturbance (i.e., bare soil resulting from vegetation loss by either grazing or forest harvesting) at the catchment scale, as well as fertilizer inputs at the national scale. Using simple multivariate statistical analyses across the 77 catchments, we found that median visual water clarity was best predicted inversely by areal coverage of intensively managed pastures. The primary predictor for all four nutrient variables (TN, NOx, TP, DRP), however, was cattle density, with plantation forest coverage as the secondary predictor variable. While land disturbance was not itself a strong predictor of water quality, it did help explain outliers of land use–water quality relationships. From 1990 to 2014, visual clarity significantly improved in 35 out of 77 (34∕77) catchments, which we attribute mainly to increased dairy cattle exclusion from rivers (despite dairy expansion) and the considerable decrease in sheep numbers across the NZ landscape, from 58 million sheep in 1990 to 31 million in 2012. Nutrient concentrations increased in many of NZ's rivers with dissolved oxidized nitrogen significantly increasing in 27∕77 catchments, which we largely attribute to increased cattle density and legacy nutrients that have built up on intensively managed grasslands and plantation forests since the 1950s and are slowly leaking to the rivers. Despite recent improvements in water quality for some NZ rivers, these legacy nutrients and continued agricultural intensification are expected to pose broad-scale environmental problems for decades to come.

Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280–320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems. ISSN:2050-7887 ISSN:2050-7895

Long-term survival of pathogenic microorganisms in streams enables long-distance disease transmission. In order to manage water-borne diseases more effectively we need to better predict how microbes behave in freshwater systems, particularly how they are transported downstream in rivers. Microbes continuously immobilize and resuspend during downstream transport owing to a variety of processes including gravitational settling, attachment to in-stream structures such as submerged macrophytes, and hyporheic exchange and filtration within underlying sediments. We developed a stochastic model to describe these microbial transport and retention processes in rivers that also accounts for microbial inactivation. We used the model to assess the transport, retention, and inactivation of Escherichia coli in a small stream and the underlying streambed sediments as measured from multitracer injection experiments. The results demonstrate that the combination of laboratory experiments on sediment cores, stream reach-scale tracer experiments, and multiscale stochastic modeling improves assessment of microbial transport in streams. This study (1) demonstrates new observations of microbial dynamics in streams with improved data quality than prior studies, (2) advances a stochastic modeling framework to include microbial inactivation processes that we observed to be important in these streams, and (3) synthesizes new and existing data to evaluate seasonal dynamics.

Turbidity is often monitored continuously as a proxy for suspended sediment in catchment sediment load studies, but is less often applied to measuring optical ‘loads’ as they affect water quality in downstream waters. We added measurements of visual clarity, from which light (beam) attenuation can be estimated, to auto-sampler monitoring over storm events in tributary rivers of the Kaipara Harbour, a large barrier enclosed estuary complex in northern New Zealand. This paper presents, for the first time, evidence of the mutual relationships between turbidity, total suspended sediment (TSS), and visual clarity, from water samples collected under event flow conditions. The mutual relationships between turbidity, TSS and visual clarity for our monitoring sites were fairly close over about three orders of magnitude (TSS ranging from about 1–1000 mg L−1). Our results show that visual clarity (and hence light attenuation) can be predicted from turbidity, at least as precisely as more traditional predictions of TSS from turbidity. The estimation of light attenuation and corresponding load estimates from visual clarity measurements, for relatively little marginal extra effort, extends the environmental relevance and application of suspended sediment monitoring.

Both microbial metabolism and pathogen retention and remobilization are dependent on downstream transport of fine particles, which migrate in a series of deposition and resuspension events. All fine particles, including clay minerals, particulate organic carbon, nutrients and microbes, are often considered to be transported similarly in the environment because of a lack of specific observations comparing their relative transport. We conducted a tracer injection study to compare the transport and retention of the fecal indicator bacterium Escherichia coli, synthetic inert fluorescent fine particles, and a dissolved conservative tracer. We found that the fluorescent fine particles and bacteria were transported similarly, with both having greater retention than the solute tracer. We used a stochastic model to evaluate in-stream retention and migration of the solute, fluorescent particles, and E. coli. The best-fit model parameters indicate that different stream reaches had varied retention characteristics, but always showed greater retention of fluorescent particles and E. coli compared to the solute tracer. Direct measurements within known retention areas after the injection showed that the majority of the fluorescent particles and E. coli were retained near the sediment–water interface in macrophyte stands or filtered within the top 3 cm of the streambed sediment. Both the tracer particles and E. coli were retained within these regions for multiple months following the injection experiment. The stochastic model properly captured the wide range of storage timescales and processes we observed in the stream. Our results demonstrate the importance of the streambed sediment and in-stream macrophytes as short- and long-term reservoirs for fine organic particles and microbes in streams.

The Sherry River, a tributary of the Motueka River (Tasman District, upper South Island, New Zealand), has somewhat degraded water quality related to a high proportion of the catchment being used for pastoral agriculture (which comprises 30% dairying). We undertook a campaign to estimate loads of phosphorus, nitrogen and Escherichia coli for comparison with other dairy-impacted catchments and against which to measure future reductions in pollutants in the Sherry River, expected from changed management practices. Monthly water quality sampling in the Sherry River was augmented with storm chasing for one year (October 2008 to October 2009). Loads of pollutants in events increased disproportionately with event peak flow, probably because the proportion of overland flow increases systematically with increasing event size. Stormflows (occurring 9.5% of the time) transported 33% of the total flow from the Sherry River, and between 22% (for nitrate) and 92% (for E. coli) of pollutant loads.

Deforestation in New Zealand has led to increased soil erosion and sediment loads in rivers. Increased suspended fine sediment in water reduces visual clarity for humans and aquatic animals and reduces penetration of photosynthetically available radiation to aquatic plants. To mitigate fine-sediment impacts in rivers, catchment-wide approaches to reducing soil erosion are required. Targeting soil conservation for reducing sediment loads in rivers is possible through existing models; however, relationships between sediment loads and sediment-related attributes of water that affect both ecology and human uses of water are poorly understood. We present methods for relating sediment loads to sediment concentration, visual clarity, and euphotic depth. The methods require upwards of twenty concurrent samples of sediment concentration, visual clarity, and euphotic depth at a river site where discharge is measured continuously. The sediment-related attributes are related to sediment concentration through regressions. When sediment loads are reduced by soil conservation action, percentiles of sediment concentration are necessarily reduced, and the corresponding percentiles of visual clarity and euphotic depth are increased. The approach is demonstrated on the Wairua River in the Northland region of New Zealand. For this river we show that visual clarity would increase relatively by approximately 1.4 times the relative reduction of sediment load. Median visual clarity would increase from 0.75m to 1.25m (making the river more often suitable for swimming) after a sediment load reduction of 50% associated with widespread soil conservation on pastoral land. Likewise euphotic depth would increase relatively by approximately 0.7 times the relative reduction of sediment load, and the median euphotic depth would increase from 1.5m to 2.0m with a 50% sediment load reduction.

Optical water quality (OWQ) relates the composition of waters to their light transmission and thereby light availability for aquatic plants, visual range for aquatic animals, and suitability for re...

Reduction of visual clarity in streams by diffuse sources of fine sediment is a cause of water quality impairment in New Zealand and internationally. In this paper we introduce the concept of a load of optical cross section (LOCS), which can be used for load-based management of light-attenuating substances and for water quality models that are based on mass accounting. In this approach, the beam attenuation coefficient (units of m–1) is estimated from the inverse of the visual clarity (units of m) measured with a black disc. This beam attenuation coefficient can also be considered as an optical cross section (OCS) per volume of water, analogous to a concentration. The instantaneous ‘flux’ of cross section is obtained from the attenuation coefficient multiplied by the water discharge, and this can be accumulated over time to give an accumulated ‘load’ of cross section (LOCS). Moreover, OCS is a conservative quantity, in the sense that the OCS of two combined water volumes is the sum of the OCS of the individual water volumes (barring effects such as coagulation, settling, or sorption). The LOCS can be calculated for a water quality station using rating curve methods applied to measured time series of visual clarity and flow. This approach was applied to the sites in New Zealand's National Rivers Water Quality Network (NRWQN). Although the attenuation coefficient follows roughly a power relation with flow at some sites, more flexible loess rating curves are required at other sites. The hybrid mechanistic–statistical catchment model SPARROW (SPAtially Referenced Regressions On Watershed attributes), which is based on a mass balance for mean annual load, was then applied to the NRWQN dataset. Preliminary results from this model are presented, highlighting the importance of factors related to erosion, such as rainfall, slope, hardness of catchment rock types, and the influence of pastoral development on the load of optical cross section.

Blue Lake, a remote sub-alpine lake, in Nelson Lakes National Park, New Zealand, has exceptional optical purity. Horizontal sighting range ('visibility') on six visits approached 80 m, the theoretical limit based on accepted light-attenuation coefficients for pure water, making Blue Lake the most visually clear freshwater yet reported. Blue Lake is characterized by blue-violet hues seen only in the clearest natural waters. Light penetration is as expected for pure water, except in the ultraviolet to blue spectrum where light-attenuation is increased slightly by very low ('oceanic') concentrations of colored dissolved organic matter. Particulate concentrations are extremely low, comparable to those in the Southeast Pacific Gyre, and the lake is hyper (ultra) oligotrophic (Chlorophyll a concentrations ∼ 0.014 mg m ―3 ). Continuous monitoring of beam attenuation (532 nm) over 18 months demonstrated consistently high visual clarity, except for short-lived episodes following turbid inflows from ephemeral streams. The dominant inflow to Blue Lake comes from springs emerging from the face of landslide debris separating the lake from nearby glacial Lake Constance. The optical purity of Blue Lake apparently reflects efficient removal of particles and dissolved organic matter during groundwater flow from Lake Constance to these springs. Blue Lake may be valuable in aquatic optics research for testing optical instruments and models.

River water quality reflects land use in the catchment (mobilizing diffuse pollution) as well as point source discharges. In New Zealand (NZ) diffuse pollution vastly outweighs point sources which have largely cleaned up over many decades. Because NZ has good geospatial data on physiographic variables, land cover and agricultural statistics, and time series on water quality at the national scale over several decades, the country is a natural laboratory for investigating water quality response to land use/disturbance and associated diffuse pollution "pressures". We interpreted water quality state and trends for the 26 years from 1989 and 2014 in the National Rivers Water Quality Network (NRWQN), consisting of 77 sites on 35 mostly large river systems with an aggregate catchment amounting to half of NZ's land area. To characterize water quality pressures, we used multiple land use datasets spanning 1990–2012, plus recently-developed 8-day land-disturbance datasets using MODIS imagery. Current state and directions of change in visual clarity and nitrate-nitrite-nitrogen provide a particularly valuable summary of impact, respectively from mobilization of fine particulate matter and soluble nutrients. We show that the greatest impact on river water quality in NZ over the 1989–2014 period is high-producing pastures with their high nutrient inputs to support high densities of livestock. While land disturbance was not itself a strong predictor of water quality, it did help explain outliers of land use-water quality relationships, especially those with large areas of plantation forest. Plantation forestry was strongly associated with water quality impacts, particularly on visual clarity and particulate nutrients when land disturbed for harvesting generated sediment runoff and nutrient mobilization. In all, our study demonstrates how interdisciplinary combinations of expertise including geospatial analysis, land management, remote-sensing, and water quality can advance understanding of broad-scale and long-term impacts of land use change on river water quality.

Use of water for leisure activities has long been prevalent in human societies, especially where the climate is favorable. Water resources with appealing conditions for primary contact recreational activities include rivers, waterfall plunge pools, dams and lakes, as well as sea coasts. Recreational use has specific demands for water quality, particularly as regards risks to human health such as exposure to pathogenic organisms, toxic substances, and submerged hazards. In Brazil, there is insufficient monitoring of bathing water conditions and currently used methodology has some limitations particularly the lack of guidance on interpretation of variables other than faecal bacterial indicators. The objectives of this study were: (1) to establish variables contributing to assessment of freshwater bathing conditions in Brazil; (2) to develop an integrated index of suitability-for-use for bathing in Brazil; and (3) to improve the methodology for assessing bathing water quality in Brazil. Based on a metadata analysis and consultation with Brazilian water professionals, a water quality index was developed incorporating the variables: Escherichia coli, cyanobacterial density, turbidity (visual clarity) and pH. This index should advance the management of recreational waters in Brazil, by improving the evaluation of freshwater bathing conditions and protecting the health of frequent users.

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...

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.

Davies-Colley, Robert J., David G. Smith, Robert C. Ward, Graham G. Bryers, Graham B. McBride, John M. Quinn, and Mike R. Scarsbrook, 2011. Twenty Years of New Zealand’s National Rivers Water Quality Network: Benefits of Careful Design and Consistent Operation. Journal of the American Water Resources Association (JAWRA) 47(4):750-771. DOI: 10.1111/j.1752-1688.2011.00554.x Abstract: This paper reviews New Zealand’s National Rivers Water Quality Network (NRWQN), which is now in its third decade of monitoring. The NRWQN is noteworthy for being operationally stable throughout its history, and the resulting consistency is increasingly valuable for detecting water quality trends and for “anchoring” temporary special purpose monitoring campaigns. The NRWQN was carefully designed following considerable effort to learn from monitoring experiences elsewhere. Monthly visits are made to 77 sites (all near hydrometric stations) on 35 river systems that cumulatively drain about one half of the national landscape. “Core” (routinely measured) variables are: conductivity, pH, temperature, dissolved oxygen, visual clarity, turbidity, colored dissolved organic matter, fecal indicator bacteria, and different forms of nitrogen and phosphorus (italics indicate field measurements). Associated benthic biological monitoring comprises monthly visual assessment of periphyton and annual sampling for macro-invertebrates. We overview the conception, design, initiation, and operational history of the NRWQN, and highlight the diverse applications of its datasets including numerous scientific applications, national-scale modeling of material fluxes, and state-of-environment reporting and practical water management at both regional and national scale. The qualified success of the NRWQN can probably be attributed to careful (and parsimonious) design and consistent operation.

Action is increasingly being taken in New Zealand and elsewhere to restore ecological function to streams through planting of riparian zones. We used simulation modelling to explore the relative performance of three strategies to restore the riparian zone of a pastoral stream to native forest by: (1) passive regeneration; (2) planting then abandonment of a Pinus radiata plantation; and (3) active restoration by planting selected native trees. We linked the forest model LINKNZ with a shade and temperature model (sWAIORA), and a wood model (OSU_STREAMWOOD) to simulate recovery trajectories for key forest stream attributes in hypothetical streams (1.3–14.0 m channel width) in the central North Island, New Zealand. Both active restoration strategies outperformed passive regeneration in shade, temperature and stream wood volume for most of the simulation time (800 years). Although the abandoned pine plantation provided greatest shade initially (

The mechanisms of interaction between stream life and habitat are often complex and poorly understood. We explored the response of a freshwater crayfish (Paranephrops planifrons) to the functions of large wood with a view towards possible future use of wood in stream restoration in New Zealand. We compared three sub‐reach types within a native forest stream in the central North Island, New Zealand; complex wood‐rich, simple (straight) woodless, and geomorphically complex woodless. Stable logs embedded across the channel created considerable habitat heterogeneity, particularly diversity of substrate, water depths and velocities, that was associated with a significantly higher abundance and biomass of crayfish compared with a straight woodless reach. Although undercut banks in woodless sub‐reaches also supported abundant crayfish, wood increased the proportion of stream area used as habitat, apparently by providing surrogate edge habitat. Wood appeared to increase stream complexity by retaining str...

Although the geomorphic and ecological importance of large wood in streams and rivers is well recognized, most studies consider only dead wood in channels. However, we have observed that living parts of trees are often found within active channels and that this “livewood” shares functions with both instream dead wood and live riparian trees, while also providing some functions unique to living woody material within a channel. We describe the mechanisms that produce livewood and illustrate its characteristics and influences on riparian and stream ecosystems with examples from Europe, North America, and New Zealand. We hypothesize that, compared with dead wood in channels, livewood (a) persists longer because of greater stability and greater resistance to decay, and (b) imparts greater structural complexity (with associated hydraulic roughness and retentiveness). The phenomenon of livewood implies that a broader range of tree species and sizes than previously considered may contribute functionally important...

We measured inherent and apparent optical properties and computed ‘optical closure’ in four lakes on the South Island of New Zealand, ranging very widely in reflectance. Optical properties were measured by modern instruments deployed from boats, with supporting laboratory measurements on water samples. The radiative transfer model, Hydrolight, was used with measured inherent optical properties to predict characteristics of the light field for comparison with field measurements. Two glacier-fed lakes were strongly light-scattering and weakly light-absorbing, with optical properties dominated by glacial flour. In marked contrast, two humic-stained wetland lakes were strongly light-absorbing and weakly light-scattering, with optical properties dominated by colored dissolved organic matter. Very good optical “closure” (i.e., agreement of modeled with measured characteristics of the light field) was obtained for all apparent optical properties examined in all but the most strongly light-scattering lake. Closure was achieved when systematic spectral bias in absorption in this lake, possibly caused by multiple scattering in the field absorption meter, was corrected using laboratory absorption measurements. The highest and lowest measured and modeled water-leaving radiances exceeded the previous range for such studies by a factor of 5. The good optical closure observed over a very wide (200-fold) range of reflectance increases confidence in our ability to specify inputs for radiative transfer modeling while highlighting the enduring challenge of accurately measuring absorption in highly scattering waters and backscattering in highly absorbing waters.

This paper summarises findings from the Pathogen Transmission Routes Research Program, describing pathogen pathways from farm animals to water bodies and measures that can reduce or prevent this transfer. Significant faecal contamination arises through the deposition of faeces by grazing animals directly into waterways in New Zealand. Bridging of streams intersected by farm raceways is an appropriate mitigation measure to prevent direct deposition during herd crossings, whilst fencing stream banks will prevent access from pasture into waterways by cattle that are characteristically attracted to water. Riparian buffer strips not only prevent cattle access to waterways, they also entrap microbes from cattle and other animals being washed down‐slope towards the stream in surface runoff. Microbial water quality improvements can be realised by fencing stock from ephemeral streams, wetlands, seeps, and riparian paddocks that are prone to saturation. Soil type is a key factor in the transfer of faecal m...

Wood abundance in streams is an indicator of its likely geomorphological and ecological importance. However, wood volume estimates can be highly variable, due in part to natural variability and the methodology used to characterize it. We measured wood volume in streams of similar sizes and riparian forest conditions using extended field surveys and simulation modelling. We surveyed a total of 3·1 km along four tributary streams of New Zealand's Waihaha River to obtain an estimate of wood volume in streams with similar basin positions (second order), forest types (podocarp/hardwood forest), disturbance histories (post volcanic eruption of Taupo ca. 180 AD) and stream sizes (2–3 m bankfull width). A ‘sliding window’ analysis was conducted whereby the wood volume was calculated for a ‘window’ (i.e., reach survey of fixed length) that was progressively moved upstream in 10 m increments. The resulting frequency distributions of wood volume were bimodal and represented the range and relative proportion of reach volumes possible from the wood surveys. The wood volume based on all streams surveyed (23 m3/100 m) was equivalent to the 64th percentile of the sliding window distribution, suggesting that a randomly placed study reach would be likely to underestimate wood volume. The bimodal distribution was attributed to the inclusion/exclusion of relatively large (≥10 m3), but rare (0·3 logs/100 m) logs. We also examined the variability of reach-level wood volume estimates (200 m and 400 m) for the Waihaha tributaries using the model OSU StreamWood. The volume frequency distributions from the simulations were similar to those from the empirical approach, except that they were unimodal. We attribute the unimodal distribution to the greater number of reach-scale estimates used in the simulations (n = 2000). The two independent approaches characterized the variation of wood volumes possible for this forest type and stream width. Copyright © 2007 John Wiley & Sons, Ltd.

We surveyed the amount and geomorphic role of wood in 18 pristine native forest streams (channel width: 3-6 m) throughout New Zealand, and quantified the characteristics associated with piece stability and geomorphic effect. Wood piece numbers (18-66 per 100 m) and volumes (85-470 m 3 ha -1 ) were similar to or greater than found in many streams throughout the world. Forest type and geographic location had no discernable influence on wood abundance at a particular site, possibly due to the confounding influences of local features (e.g., tree fall regime) and methodology ('snap-shot' survey of a dynamic system). Half the pieces that were geomorphically active had moved, suggesting that stable pieces did not necessarily dominate geomorphic activity. Tree ferns were an important contributor to wood abundance in many of the streams studied.

The optical character of waste stabilization ponds (WSPs) is of concern for several reasons. Algal photosynthesis, which produces oxygen for waste oxidation in WSPs, is influenced by attenuation of sunlight in ponds. Disinfection in WSPs is influenced by optical characteristics because solar UV exposure usually dominates inactivation. The optical nature of WSPs effluent also affects assimilation by receiving waters. Despite the importance of light behaviour in WSPs, few studies have been made of their optical characteristics. We discuss simple optical measures suitable for routine monitoring of WSPs (including at sites remote from laboratories): optical density of filtrates – an index of dissolved coloured organic (humic) matter, visual clarity – to provide an estimate of the beam attenuation coefficient (a fundamental quantity needed for optical modelling) colour (hue) – as an indicator of general WSP ‘condition’ and irradiance attenuation quantifying depth of light penetration. The value of optical characterisation of WSPs is illustrated with reference to optical data for WSPs in NZ (including high-rate algal ponds) treating dairy cattle wastewater versus domestic sewage. We encourage increased research on optical characteristics of WSPs and the incorporation of optical measures in monitoring and modelling of WSP performance

Advanced pond systems (APS), incorporating high-rate ponds, algal settling ponds, and maturation ponds, typically achieve better and more consistent disinfection as indicated by Escherichia coli than conventional waste stabilisation ponds. To see whether this superior disinfection extends also to enteric viruses, we studied the removal of somatic phages (‘model’ viruses) in a pilot-scale APS treating sewage. Measurements through the three aerobic stages of the APS showed fairly good removal of somatic phage in the summer months (2.2 log reduction), but much less effective removal in winter (0.45 log reduction), whereas E. coli was removed efficiently (>4 logs) in both seasons. A very steep depth-gradient of sunlight inactivation of somatic phage in APS pond waters (confined in silica test tubes) is consistent with inactivation mainly by solar UVB wavelengths. Data for F-RNA phage suggests involvement of longer UV wavelengths. These findings imply that efficiency of virus removal in APS will vary seasonally with variation in solar UV radiation.

The radiation environment of streams is of major ecological importance because it controls stream thermal regime and light availability for photosynthesis. Therefore, methods are needed for measuring stream shade in practical riparian management. The quantity ‘diffuse non-interceptance’ (difn), defined as the proportion of incident lighting received under a sky of uniform brightness and best estimated from fish-eye images, is useful for general specification of light exposure. For routine measurement of difn along stream reaches we recommend using a matched pair of simple light sensors (e.g. photosynthetically available radiation sensors) under conditions of complete overcast (which has almost uniform brightness). Methods are also needed for predicting future light exposure as riparian plantings grow and increasingly shade the stream. A simple model is outlined for predicting difn at the channel centre as a function of channel dimensions (stream width, w ) and riparian plant character (foliage density, canopy height, h). The model reproduces the broad empirical trend of increasing shade with increasing h / w ratio. Future model refinement will aim to quantify the increase in shade moving from channel centre to edge under an overhanging canopy.

Riparian tree planting is widely recognised as a means to improve water quality and stream habitat. However, shading of riparian pasture grasses can lead to channel widening, and riparian shade may limit the growth of macrophytes and algae that assimilate dissolved nutrients from the water column. We investigated concerns that riparian management could lead to increased yields of nutrients and sediments through a conceptual modelling exercise. A simple model of the trade-off between interception of nutrients in runoff by forest buffers versus reduction of in-stream uptake due to shade, predicted that a buffer strip alongside a small headwater stream would reduce nutrient export, while a buffer strip instigated as an isolated patch alongside a larger stream (c. >2.5 km2 upstream catchment size) would increase nutrient export, as the relative amount of nutrients trapped by the buffer decreases as the nutrient load present in the stream water increases. However, in these larger streams with width exceeding approximately 6 m, sufficient light may reach the streambed for plant and algal growth, which in turn would promote instream nutrient processing. At the peak of streambank erosion after planting, predicted total sediment yield (hillslope plus bank sources) was appreciably higher than the hillslope pasture yield, but sediment yield stabilised c. 35–40 years after planting. When planting was extended over 40 years in the model, the sediment yield never exceeded that in pasture before planting. This conceptual modelling exercise shows that riparian tree planting programmes should commence in the headwaters and progress downstream to avoid nutrient yield increases. Significant sediment yield from bank stored sediment of small streams can be expected until the channel reaches the more stable, original forested width, but progressive planting may decrease the peak loads of sediment.

Two‐stage oxidation ponds have traditionally been used for the treatment of dairy‐farm wastewater in New Zealand, but are now considered unsuitable to discharge to waterways. The first full‐scale dairy‐farm advanced pond system (APS), a low‐cost and effective upgrade option for traditional ponds was evaluated over a 2‐year period. The system consisted of an anaerobic pond (AP) (the first pond of traditional oxidation pond systems), a high rate pond (HRP), a pair of algae settling ponds (ASP) and a maturation pond (MP) (which all replace the second pond of traditional systems). APS effluent quality was considerably higher than that of traditional ponds, with respective median effluent concentrations of biological oxygen demand: 43 versus 98 g m−3, total suspended solids: 87 versus 198 g m−3, ammoniacal nitrogen: 39 versus 106 gm−3, total phosphorus: 19 versus 27 g m−3, and Escherichia coli of 918 versus 70 000 MPN/100 ml. APS show great promise for upgrading traditional dairy‐farm oxidation ponds ...

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 cross...

Studies of disinfection in conventional waste stabilisation ponds (WSPs) suggest that sunlight is an important factor, sometimes interacting with elevated dissolved oxygen and pH. Shallow depth and mixing in ecologically engineered high rate ponds (HRPs) enable greater exposure of wastewater to sunlight than in conventional WSPs, and we hypothesised that the reported efficient disinfection in HRPs may reflect this. We conducted two experiments on disinfection in a pilot-scale HRP treating dairy farm wastewater. The HRP was operated in batch mode so that removal of Escherichia coli could be followed by sampling over time (2 days). In both experiments, E. coli removal was rapid during daylight hours and slow overnight. The data were well-fitted by a simple model with a dark die-off term evaluated using night data, and a sunlight exposure term evaluated using day-time data. Dissolved oxygen and pH appeared to have little influence on inactivation rate over the measured range of pH (8.0–9.2) and DO (0–22 g m−3). Overall, about 75% of the total E. coli inactivation in the HRP was attributable to sunlight action.

Stream sediments have been recognised as an in-channel store of faecal contamination that can be mobilised during floods or other sediment-disturbing events. We studied this store of faecal contamination by creating artificial floods during dry weather when, in the absence of overland flow from the catchment, the only source of faecal bacteria was stores within the channel. Artificial floods, created by releasing water from a supply reservoir, increased the E. coli concentration in the water column by two orders of magnitude, from a background level of 10 2 cfu per 100 mL to over 10 4 cfu per 100 mL. The bacterial peak concentrations and yields declined systematically through a triplicate flood series. The size of the total in-channel store, calculated as the sum of yields of an infinite series of artificial floods, was approximately 10 8 cfu m −2 of streambed area. Direct measurements of sediment E. coli found few sites (only those associated with cattle crossings) with areal concentrations as high as 10 8 cfu m −2 , consistent with flood yields. Concentrations of E. coli in the biofilms on exposed rocks were orders of magnitude lower, indicating that exposed rocks were not a source of E. coli released by the artificial floods.