R. J. Davies-Colley

Inactivation of faecal indicator micro-organisms in waste stabilisation ponds: interactions of environmental factors with sunlight

Sunlight exposure is considered to be the most important cause of “natural” disinfection in waste stabilisation ponds (WSPs). We examined the influence of dissolved oxygen (DO), pH, and particulate and dissolved constituents in WSP effluent, on sunlight inactivation of faecal micro-organisms, using small reactors operated under controlled physico-chemical conditions. Inactivation of both enterococci and F-RNA phages increased strongly as DO was increased, and also depended on light-absorbing pondwater constituents, but pH was not influential over the range investigated (7.5 to 10). Inactivation of E. coli increased strongly when pH increased above 8.5, as well as being strongly dependent on DO. Inactivation of F-DNA phage was independent of the factors investigated. These results are consistent with the F-DNA phages being inactivated as a result of direct DNA damage by UVB in sunlight, whereas the other three microbiological indicators are inactivated as a result of photo-oxidative damage, although the target of damage is apparently different. Our findings of diverse influences of physico-chemical conditions suggest difficulties in interpreting data for a single micro-organism to indicate WSP effluent quality. However, sunlight remains the factor of over-riding importance, and disinfection in WSPs may be enhanced by increasing sunlight exposure.

Water quality impact of a dairy cow herd crossing a stream

Abstract 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.

Advanced pond system for dairy‐farm effluent treatment

Abstract 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 in New Zealand, particularly in areas where land irrigation is unsuitable.

Integrated catchment management—interweaving social process and science knowledge

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.

Modelling storm-event E. coli pulses from the Motueka and Sherry Rivers in the South Island, New Zealand

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.

“Livewood”: Geomorphic and Ecological Functions of Living Trees in River Channels

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 wood to channels. We encourage the study of livewood in a range of forest-stream ecosystems to test our hypotheses and further our understanding of how forests interact with rivers and streams.

A water quality index for recreation in Brazilian freshwaters

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.

Nitrogen, phosphorus and E. coli loads in the Sherry River, New Zealand

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.

Faecal contamination and visual clarity in New Zealand rivers: Correlation of key variables affecting swimming suitability

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 <1.6 m black disc visibility (a long-established NZ guideline for swimming) they would also avoid microbial hazards (E. coli <550 cfu/100 mL about 99% of the time in NZ rivers). However, urban-affected rivers might sometimes be microbially contaminated when still clear. Water management agencies should measure visual clarity together with E. coli in river surveillance. Real-time information on swimming suitability could then be based on continuous monitoring of turbidity locally calibrated to both visual clarity and E. coli.