Quantitative microbial risk assessment models for consumption of raw vegetables irrigated with reclaimed water

Quantitative microbial risk assessment models for estimating the annual risk of enteric virus infection associated with consuming raw vegetables that have been overhead irrigated with nondisinfected secondary treated reclaimed water were constructed. We ran models for several different scenarios of crop type, viral concentration in effluent, and time since last irrigation event. The mean annual risk of infection was always less for cucumber than for broccoli, cabbage, or lettuce. Across the various crops, effluent qualities, and viral decay rates considered, the annual risk of infection ranged from 10–3 to 10–1 when reclaimed-water irrigation ceased 1 day before harvest and from 10–9 to 10–3 when it ceased 2 weeks before harvest. Two previously published decay coefficients were used to describe the die-off of viruses in the environment. For all combinations of crop type and effluent quality, application of the more aggressive decay coefficient led to annual risks of infection that satisfied the commonly propounded benchmark of ≤10–4, i.e., one infection or less per 10,000 people per year, providing that 14 days had elapsed since irrigation with reclaimed water. Conversely, this benchmark was not attained for any combination of crop and water quality when this withholding period was 1 day. The lower decay rate conferred markedly less protection, with broccoli and cucumber being the only crops satisfying the 10–4 standard for all water qualities after a 14-day withholding period. Sensitivity analyses on the models revealed that in nearly all cases, variation in the amount of produce consumed had the most significant effect on the total uncertainty surrounding the estimate of annual infection risk. The models presented cover what would generally be considered to be worst-case scenarios: overhead irrigation and consumption of vegetables raw. Practices such as subsurface, furrow, or drip irrigation and postharvest washing/disinfection and food preparation could substantially lower risks and need to be considered in future models, particularly for developed nations where these extra risk reduction measures are more common.

Estimates of Heterozostera tasmanica, Zostera muelleri and Ruppia megacarpa distribution and biomass in the Hopkins Estuary, western Victoria, by GIS

Knowledge of the spatial arrangement of the seagrass distribution and biomass within the Hopkins Estuary is an essential step towards gaining an understanding of the functioning of the estuarine ecosystem. This study marks the first attempt to map seagrass distribution and model seagrass biomass and epiphyte biomass along depth gradients by the use of global positioning system (GPS) and geographical information system (GIS) technologies in the estuary. For mapping seagrass in small estuaries, ground-surveying the entire system is feasible. Three species of seagrasses, Heterozostera tasmanica (Martens ex Aschers), Zostera muelleri (Irmisch ex Aschers) and Ruppia megacarpa (Mason), were identified in the Hopkins Estuary. All beds investigated contained a mixed species relationship. Three harvest techniques were trialed in a pilot study, with the 25 × 25-cm quadrat statistically most appropriate. Biomass of seagrasses and epiphytes was found to vary significantly with depth, but not between sites. The average estimate of biomass for total seagrasses and their epiphytes in the estuary in January 2000 was 222.7 g m^–2 (dry weight). Of the total biomass, 50.6% or 112.7 g m^–2 (dry weight) was contributed by seagrasses and 49.4% of the biomass (110.0 g m^–2) were epiphytes. Of the 50.6% of the total biomass represented by seagrasses, 39.3% (87.5 g m^–2) were leaves and 11.3% (25.2 g m^–2) were rhizomes. The total area of seagrasses present in the Hopkins Estuary was estimated to be 0.4 ± 0.005 km², with the total area of the estuary estimated to be 1.6 ± 0.02 km² (25% cover). The total standing crop of seagrasses and epiphytes in the Hopkins Estuary in January 2000 was estimated to be 102.3 ± 57 t in dry weight, 56% (56.9 ± 17 t, dry weight) seagrasses and 44% (45.4 ± 19 t, dry weight) epiphytes. Of the seagrass biomass, 39% (39.7 ± 13 t, dry weight) was contributed by leaves and 17% (17.3 ± 7 t, dry weight) by rhizomes.

A new modelling approach to simulate preferential flow and transport in water repellent media: parameter sensitivity, and effects on crop growth and solute leaching

A modified version of the popular agrohydrological model SWAP has been used to evaluate modelling of soil water flow and crop growth at field situations in which water repellency causes preferential flow. The parameter sensitivity in such situations has been studied. Three options to model soil water flow within SWAP are described and compared: uniform flow, the classical mobile-immobile concept, and a recent concept accounting for the dynamics of finger development resulting from unstable infiltration. Data collected from a severely water-repellent affected soil located in Australia were used to compare and evaluate the usefulness of the modelling options for the agricultural management of such soils.

The study shows that an assumption of uniform flow in a water-repellent soil profile leads to an underestimation of groundwater recharge and an overestimation of plant transpiration and crop production. The new concept of modelling taking finger dynamics into account provides greater flexibility and can more accurately model the observed effects of preferential flow compared with the classical mobile–immobile concept. The parameter analysis indicates that the most important factor defining the presence and extremity of preferential flow is the critical soil water content.

Comparison of the modelling results with the Australian field data showed that without the use of a preferential flow module, the effects of the clay amendments to the soil were insufficiently reproduced in the dry matter production results. This means that the physical characteristics of the soil alone are not sufficient to explain the measured increase in production on clay amended soils. However, modelling with the module accounting for finger dynamics indicated that the preferential flow in water repellent soils that had not been treated with clay caused water stress for the crops, which would explain the decrease in production.

Regional-scale models for relating land cover to basin surface-water quality using remotely sensed data in a GIS

Plant-based management systems implementing deep-rooted, perennial vegetation have been identified as important in mitigating the spread of secondary dryland salinity due to its capacity to influence water table depth. The Glenelg Hopkins catchment is a highly modified watershed in the southwest region of Victoria, where dryland salinity management has been identified as a priority. Empirical relationships between the proportion of native vegetation and in-stream salinity were examined in the Glenelg Hopkins catchment using a linear regression approach. Whilst investigations of these relationships are not unique, this is the first comprehensive attempt to establish a link between land use and in-stream salinity in the study area. The results indicate that higher percentage land cover with native vegetation was negatively correlated with elevated in-stream salinity. This inverse correlation was consistent across the 3 years examined (1980, 1995, and 2002). Recognising the potential for erroneously inferring causal relationships, the methodology outlined here was both a time and cost-effective tool to inform management strategies at a regional scale, particularly in areas where processes may be operating at scales not easily addressed with on-site studies.

Appraisal of random and systematic land cover transitions for regional water balance and revegetation strategies

This study describes the use of landscape transition analysis as a means for effective basin management. Land cover transitions from 1995 to 2002 were analyzed using a cross-tabulation matrix for an important economic zone in south-west Victoria, Australia. Specifically, the matrix was used to determine whether the transitions were random or systematic. Random landscape transitions occur when a land cover replaces other land covers in proportion to their availability. Systematic landscape transitions occur when there are deviations from random patterns, and land use types ‘target’ other land use types for replacement. The analysis was conducted with 11 land cover categories and showed that dryland pastures have been systematically losing area to dryland crops and blue gum (Eucalyptus globulus) plantations. Dryland crops have systematically expanded in the north-east of the catchment, an area where increasing in-stream salinization has occurred concurrently with this transition. The systematic expansion of the blue gum plantations has been predominantly in the south-west of the catchment and has the potential to reduce stream flows and groundwater recharge in an already water-stressed region, as blue gums use more water than the dryland pastures they are replacing. All other transitions were largely random. These findings have implications for land use planning in the study area for regional water balance and revegetation strategies. Landscape transition analysis is a cost-effective means of contributing to the management of water resources at a regional scale, and is highly recommended for future basin planning.

Association of reduced riparian vegetation cover in agricultural landscapes with coarse detritus dynamics in lowland streams

Studies were conducted on streams flowing through agricultural floodplains in south-eastern Australia to quantify whether reductions in riparian canopy cover were associated with alterations to the input and benthic standing stocks of coarse allochthonous detritus. Comparisons were made among three farmland reaches and three reaches within reserves with intact cover of remnant overstorey trees. Detritus inputs to these reaches were measured monthly over 2 years using litter traps. Direct inputs to streams within the reserves were relatively high (550–617 g ash free dry weight (AFDW) m^–2 year^–1), but were lower at farmland reaches with the lowest canopy covers (83–117 gAFDW m^–2 year^–1). Only a minor fraction of the total allochthonous input (<10%) entered any of the study reaches laterally. The mean amounts of benthic detritus were lowest in the most open farmland reaches. Standing stocks of benthic detritus were found to be highly patchy across a large number of agricultural streams, but were consistently very low where the streamside canopy cover was below ~35%. Canopy cover should be restored along cleared agricultural streams because allochthonous detritus is a major source of food and habitat for aquatic ecosystems. Given the absence of pristine lowland streams in south-eastern Australia, those reaches with the most intact remnant overstorey canopies should be used to guide restoration.

Ecology of Pittosporum undulatum Vent. (Pittosporaceae) an environmental weed in south east Australia

Pittosporum undulatum Vent. (Sweet Pittosporum) is a densely foliaged tall shrub or small tree, native to the wet forests of south east Australia, This species now functions as a serious environmental weed in a range of habitats in Australia and on other continents and islands throughout the temperate, sub-tropical and tropical zones. This study investigated some of the ecological causes and consequences of P. undulatum invasion across a range of habitat types in south east Australia. Key aspects of P. undulatum biology and ecology investigated in the current study include; patterns of morphological variation across the range of habitats occupied (as a measure of the species’ plasticity), dispersal ecology and seed germinability, population structure and spatial pattern, community relationships and the ecological impacts of invasion. Phenotypic plasticity is considerable in P. undulatum. No clear patterns of geographic variation emerged from a study of leaf morphological attributes across the current range of this species on mainland south east Australia. The pattern of morphological variation is particularly complex in Victoria, where the invasion of this species is most advanced. The species’ adaptability to a range of environments and environmental conditions will likely promote further range expansion. The abundant winter fruit crop produced by functionally female P. undulatum plants attracts a suite of generalist opportunistic frugivores, which feed on P. undulatum fruits and seeds at various stages of fruit dehiscence, thereby enhancing dispersal opportunities for this species. P. undulatum seed collected from natural and invasive populations, at two stages of fruit maturity and from the scats and pellets of dispersal agents, displayed high germinability. European Blackbirds and Pied Currawongs are implicated as the main avian dispersal agents of P undulatum in south east Australia. The broader ecological implications of developing relationships between invasive fleshy-fruited bird-dispersed plant species and adaptive frugivores are likely to be considerable. The distribution of P. undulatutn seedlings was significantly negatively correlated with adult conspecifics and significantly positively correlated with trees and shrubs of other genera. This pattern reflects the importance of both firugivorous dispersal agents and the species’ germination and establishment requirements, in shaping the contagious distribution pattern typical of this species. These analyses suggest that recruitment opportunities for conspecific seedlings are limited beneath the canopy of adult conspecifics. Densities of P. undulatum were on average, 2.7 times higher in invaded populations, compared to the natural populations sampled. A male-bias was evident in all populations and no relationships between reproductive activity and the density of seedlings and juveniles were evident. Invading populations of P. undulatum impose substantial changes on ecosystem-level properties and functions. Mean species richness and cover-abundance declined notably once P. undulatum cover-abundance exceeded 20% at the invaded sites and 60% at the natural sites sampled. The natural communities sampled displayed comparatively greater resilience to the competitive effects of P. undulatum, but community attributes were affected at high densities and cover-abundance of this species. The cover-abundance of herbs and grasses declined most substantially with increasing P. undulatum at invaded sites, whereas, at the natural sites sampled, the species’ structural analogues appeared to be most affected by increasing P. undulatum cover-abundance. This study has demonstrated that the ecological consequences of P. undulatum population expansion are substantial and contribute to changes in the composition and successional trajectory of affected communities. These processes ultimately lead to the loss and simplification of biodiversity values and the homogenisation of affected habitats. P. undulatum has the potential to emerge as one of south east Australia's most serious environmental weed species.

Influence of land cover on water resources

The influence of land cover on water quality and quantity was examined using a multidisciplinary approach that integrated land use maps, historical databases, and statistical modelling. Systematic changes in the Glenelg Hopkins landscape were identified, in addition to a relationship between greater proportions of vegetation and better water quality.

Effects of snow cover on the timing and success of reproduction in high-Arctic pink-footed geese Anser brachyrhynchus

During four breeding seasons, 2003–2006, we studied the relationship between snow cover and nesting performance in pink-footed geese (Anser brachyrhynchus) in a key breeding site on Svalbard. Snow cover in late May, i.e., at the time of egg laying of geese, was derived from MODIS satellite images. Snow cover had a profound cascading effect on reproductive output via the number of nesting pairs and timing of nesting, which affected nest success, while there was only a tendency for a negative effect on clutch size. Hence, we estimated a five-fold difference in the number of young produced (to post-hatching) between years with little snow and years with high snow cover. The results from the study area correlated with whole-population productivity estimates recorded in autumn. Thus, snow cover derived from MODIS satellite images appears to provide a useful indicator of the breeding conditions in the Arctic.

Assessment of spatiotemporal varying relationships between rainfall, land cover and surface water area using geographically weighted regression

Traditional regression techniques such as ordinary least squares (OLS) are often unable to accurately model spatially varying data and may ignore or hide local variations in model coefficients. A relatively new technique, geographically weighted regression (GWR) has been shown to greatly improve model performance compared to OLS in terms of higher R 2 and lower corrected Akaike information criterion (AICC). GWR models have the potential to improve reliabilities of the identified relationships by reducing spatial autocorrelations and by accounting for local variations and spatial non-stationarity between dependent and independent variables. In this study, GWR was used to examine the relationship between land cover, rainfall and surface water habitat in 149 sub-catchments in a predominately agricultural region covering 2.6 million ha in southeast Australia. The application of the GWR models revealed that the relationships between land cover, rainfall and surface water habitat display significant spatial non-stationarity. GWR showed improvements over analogous OLS models in terms of higher R 2 and lower AICC. The increased explanatory power of GWR was confirmed by the results of an approximate likelihood ratio test, which showed statistically significant improvements over analogous OLS models. The models suggest that the amount of surface water area in the landscape is related to anthropogenic drainage practices enhancing runoff to facilitate intensive agriculture and increased plantation forestry. However, with some key variables not present in our analysis, the strength of this relationship could not be qualified. GWR techniques have the potential to serve as a useful tool for environmental research and management across a broad range of scales for the investigation of spatially varying relationships.