Quantitative microbial risk assessment modelling for the use of reclaimed water in irrigated horticulture

Reuse of treated sewage effluent for the irrigation of horticultural crops is being propounded and practiced as a means of alleviating pressure on freshwater resources. Concerns have been raised. however, as to the risk to human health, primarily disease, associated with this practice. Quantitative Microbial Risk Assessment (QMRA) is a useful tool for estimating this risk. We describe how QMRA works and the current state of knowledge of the components of QMRA models for the horticultural reuse scenario.

Near-surface distributions of soil water and water repellency under three effluent irrigation schemes in a blue gum (Eucalyptus globulus) plantation

Water repellent soils are difficult to irrigate and susceptible to preferential flow, which enhances the potential for accelerated leaching to groundwater of hazardous substances. Over 5 Mha of Australian soil is water repellent, while treated municipal sewage is increasingly used for irrigation. Only if a critical water content is exceeded will repellent soils become wettable. To avoid excessive loss of water from the root zone via preferential flow paths, irrigation schemes should therefore aim to keep the soil wet enough to maintain soil wettability. Our objective was to monitor the near-surface water content and water repellency in a blue gum (Eucalyptus globulus) plantation irrigated with treated sewage. The plantation's sandy soil surface was strongly water repellent when dry. For 4 months, three rows of 15 blue gum trees each received no irrigation, three other rows received 50% of the estimated potential water use minus rainfall, and three more rows received 100%. During this period, 162 soil samples were obtained in three sampling rounds, and their water content (% dry mass) and degree of water repellency determined. Both high and low irrigation effectively wetted up the soil and eliminated water repellency after 2 (high) or 4 (low) months. A single-peaked distribution of water contents was observed in the soil samples, but the water repellency distribution was dichotomous, with 44% extremely water-repellent and 36% wettable. This is consistent with a threshold water content at which a soil sample changes from water repellent to wettable, with spatial variability of this threshold creating a much wider transition zone at the field scale. We characterized this transition zone by expressing the fraction of wettable samples as a function of water content, and demonstrated a way to estimate from this the wettable portion of a field from a number of water content measurements. To keep the plantation soil wettable, the water content must be maintained at a level at which a significant downward flux is likely, with the associated enhanced leaching. At water contents with negligible downward flux, the field is water repellent, and leaching through preferential flow paths is likely. Careful management is needed to resolve these conflicting requirements.

The effect of increased water prices on construction

The research aimed to investigate the effect an increase in water prices would have on construction. It was found that while there is a considerable amount of water embodied in construction the actual effect of a water tax on construction would be minimal unless implemented at the highest rate.

Statutory verification of water rights: the 'insuperable' difficulties of propertising water entitlements

The abolition of riparian entitlements in the early stages of colonial Australia and the vesting of these rights in the Crown represented a turning point for the evolution of private water rights. The extinguishment of common law rights connected to vested land interests and the introduction of new, unaligned statutory entitlements provided a new and fundamentally different system for the creation and regulation of private water entitlements. Unlike riparian entitlements, in the absence of express definition, statutory water entitlements may only be verified as property where such a construction is consistent with the nature and scope of the entitlement. In this respect, the statutory framework has disaggregated the propertisation of water rights from land ownership and linked the process to broader statutory interpretation principles. The shift away from institutional property has generated concerns about the interpretive approaches appropriate for the verification of legislative water entitlements. This article examines the existing interpretive approaches and argues that the blurring of the propertisation process with the separate issue of whether any change or modification of such water rights attracts s 51(xxxi) of the Commonwealth Constitution has produced a situation where core property indicia is increasingly overshadowed by legislative defeasibility. In the recent High Court decision of ICM Agriculture Pty Ltd v Commonwealth, the focus of the majority judgements upon the inherent susceptibility of legislative entitlements to variation or extinguishment acted as a catalyst for the non-propertisation of statutory bore water licences in New South Wales. The emphasis the majority judgements gave to legislative defeasibility precluded a full and balanced assessment of other highly relevant property indicia, in particular the expectation interests of the holders. Conflating property and constitutional evaluation in this way is inappropriate in an era where entitlements to natural resource interests are increasingly statute based and the verification process has significant social and economic repercussions. Determining whether a statutory entitlement constitutes property requires a careful balancing of legislative intent, social and environmental context and individual expectation and the vicissitudes of a regulatory context should not eclipse this process.

Assessing health risk of reclaimed water using human cell culture.

For risk analysis of reclaimed water, current animal and toxicity testing may not detect subtle effects such as interactions that could contribute to complex diseases such as cancers that develop over a long period of time. There is a need for assays that can be validated against known human physiological processes. We have previously validated sensitive human cell culture assays for their responsiveness to agents that induce carcinogenesis in vivo. In this initial study we analysed the effects of three batches of reclaimed water on human colonic cells. At concentrations of up to 10-fold, they had no significant effect on the cellular markers, indicating an overall lack of biological activity. The assay has potential but needs to be refined to maximise its sensitivity.

The role of herbivorous water birds in aquatic systems through interactions with aquatic macrophytes, with special reference to the Bewick’s Swan – Fennel Pondweed system

The role of aquatic macrophytes in stimulating biodiversity and maintaining clear waters is currently undisputed. The management of (eutrophic) shallow waters is therefore often directed at (re-)establishing macrophyte domination. In contrast, the role of water birds has long been considered of minor importance for the functioning of fresh water ecosystems. Indeed, in terms of biomass and production, water birds constitute only a minor part of these systems. However, water birds may graze heavily on water plants under certain circumstances, and the question arises whether herbivorous water birds have an important indirect effect on shallow fresh water systems. Mainly illustrated with the interaction between Bewick’s Swans and Fennel Pondweed, we present data on the role that water plants may play in the life of water birds and how water birds may impact water plants’ fitness in terms of survival, production, dispersal and competitive ability. It appears that water plants may be crucial for water birds during periods of high-energy requirements, such as migration. Despite the plants’ costs associated with water bird grazing, the interaction between water birds and water plants varies in nature from an apparent predator–prey relationship to a mutually beneficial interaction depending on the context and the perspective. For the case of the Bewick’s Swan–Fennel Pondweed interaction, regular bird grazing is sustainable and may actually favour the plant’s dispersal. Thus, Bewick’s Swans themselves may in fact play a crucial role in establishing and maintaining the Fennel Pondweed rich staging sites between the swans’ wintering and breeding grounds, which are vital for the swans’ successful migration.