A Numerical and Field Investigation of Surface Heat Fluxes from Small Wind-Sheltered Waterbodies in Semi-Arid Western Australia

Shelterbelts are used for a variety of purposes in agricultural environments, primarily because of their ability to improve the downwind microclimate. Excessive evaporative losses from small, agricultural water supply reservoirs in semi-arid Western Australia motivated a combined numerical modelling and field investigation into the potential for using shelterbelts to reduce evaporation from these open waterbodies. A numerical model of the disturbed momentum and turbulence fields in the region modified by the wind-shelter was employed and accounted for the presence of a waterbody downwind. The model was coupled with conservation equations for heat and moisture and sensible and latent heat fluxes were estimated from the simulated momentum, temperature and humidity fields. The numerical simulations were tested against four days of field data from two experiments conducted in the agricultural districts of southwest Western Australia that measured boundary-layer evolution over a variety of small waterbodies protected by artifical and natural wind-shelters. The model provided good predictions of windspeed during neutral conditions, but inadequate specification of the upwind boundary during non-neutral stabilities resulted in the model failing to capture any sensitivity to atmospheric stability as seen in the field data. Despite this limitation, the temperature and humidity fields were adequately captured by the model, and evaporative mass flux predictions also agreed well with estimates taken from water-balance measurements. It is concluded that well-designed wind-shelters can reduce evaporation from open waterbodies by 20–30% as a result of reductions in the velocity scales responsible for removing moisture from the water surface. The model can be used to estimate the values of various shelterbelt design parameters (e.g., porosity, height) that could be applied in the field to provide optimum evaporation reductions.     

Database of PCDD/PCDF levels in ambient air and in samples related to the pulp and paper industry

A literature and questionnaire survey has been carried out in order that a database be developed for PCDD/PCDF levels in ambient air. The data received to date and entered into the database indicates that standardization in methodologies and reporting is required. The overall response to the survey, even with reminders, was disappointing.     

Examining the potential impacts of sea level rise on coastal wetlands in north-eastern NSW,Australia

The coastal wetlands of north-eastern New South Wales (NSW) Australia are increasingly being affected by anthropogenic factors such as urbanisation, residential development and agricultural development. However, little is known about their vulnerability to sea level rise as a result of climate change. The aim of this research is to predict the potential impact of sea level rise (SLR) on the coastal wetland communities. Sea Level Affecting Marshes Model (SLAMM) was used to predict the potential impacts of sea level rise. Geographic Information System (GIS) was used for mapping and analysis. It was found that a meter rise in sea level could decrease coastal wetlands such as Inland fresh marshes from about 225.67 km² in February 2009 to about 168.04 km² by the end of the century in north-eastern NSW, Australia. The outcomes from this research can contribute to enhancing wetland conservation and management in NSW.     

Accumulation,fractionation and release of oil by the intertidal clam Macoma balthica

The bivalve mollusc Macoma balthica accumulated hydrocarbons during 180 days of continuous exposure to Prudhoe Bay crude oil in seawater dispersions with nominal concentrations of 0.03, 0.3 and 3.0 mg l^-1. The mollusc's ability to concentrate oil from seawater increased with decreasing oil-in-water concentration. Decreases in oil burden began after 30 to 120 days (depending on the oil concentration) and continued for at least 60 days after exposure to oil ceased. Aliphatic and aromatic hydrocarbons were fractionated in markedly different ways by the bivalve. Branched and cyclic aliphatics in the molecular weight-range dodecane through hexadecane were preferentially retained over straightchain and their higher homologs. Larger and more substituted aromatic compounds were selectively concentrated. There appeared to be no selective concentration of aromatic sulphur compounds.Please address requests for reprints to Dr. D. G. Shaw at the Institute of Marine Science     

A survey of drinking water supplies in the Province of Ontario for dioxins and furans

A survey of drinking water supplies in the Province of Ontario was initiated in 1983 to determine the extent of their contamination by polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). This drinking water survey arose from concerns regarding the discovery of PCDDs and PCDFs in sport fish from western Lake Ontario in the early 1980's.A total of 49 water supplies throughout all Regions of Ontario have been examined to date. Water supplies in the vicinity of chemical industries and pulp and paper mills were sampled more frequently; as many as 20 times. Detection limits were in the low parts per quadrillion (ppq) range for all tetra- to octachlorinated PCDDs and PCDFs.As of February 1989, 4, 347 results were received for 399 raw and treated water samples. Only 37 positive results were reported, constituting less than 1 percent of the total number of results. The O₈CDD congener accounted for 36 of the 37 positive results. The 2,3,7,8- TCDD isomer was not detected in any sample.     

Validation studies of an automated preconcentration water sampler (APS) for chlorinated dibenzo-p-dioxins and dibenzofurans

An Automated Preconcentration Sampler (APS) was developed by the Ontario Ministry of the Environment (MOE) and Carleton University for the determination of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in drinking water. The APS employs a two-stage particulate filtration system followed by an XAD-2 resin column. Field and laboratory testing of the APS is required to validate the device before it is put into regular service.The capacity of the APS filtration system is 30 L for a 4 Formazin Turbidity Unit (FTU) input water turbidity and greater than 50 L for a typical treated water. Flushing of a clean XAD-2 resin column with 200 L of spiked water showed that the optimum flowrate in terms of spike breakthrough is equal to three times the resin bed volume per minute. This flowrate is used for APS operation. Testing also showed that no spike breakthrough occurred after 200 L of clean water was flushed through a spiked XAD-2 resin column at flowrates in excess of the APS operating flowrate. Spike testing was also carried out on the filters and results are pending. An analytical comparison between the present MOE sampling and analytical procedure and the proposed APS sampling and analytical procedure using a PCDD/PCDF source water is planned.     

Methane emissions of beef cattle on forages: efficiency of grazing management systems

Fermentation in the rumen of cattle produces methane (CH4). Methane may play a role in global warming scenarios. The linking of grazing management strategies to more efficient beef production while reducing the CH4 emitted by beef cattle is important. The sulfur hexafluoride (SF6) tracer technique was used to determine the effects of best management practices (BMP) grazing compared with continuous grazing on CH4 production in several Louisiana forages during 1996-1998. Cows and heifers (Bos taurus) grazed common bermudagrass [Cynodon dactylon (L.) Pers.], bahiagrass (Paspalum notatum Flugge), and ryegrass (Lolium multiflorum Lam.) pastures and were wintered on bahiagrass hay with supplements of protein molasses blocks (PMB), cottonseed meal and corn (CSMC), urea and corn (URC), or limited ryegrass grazing (LRG). Daily CH4 emissions were between 89 and 180 g d(-1) for young growing heifers and 165 to 294 g d(-1) for mature Simbrah cows. Heifers on "ad lib" ryegrass in March and April produced only one-tenth the CH4 per kg of gain as heifers on LRG of 1 h. Using BMP significantly reduced the emission of CH4 per unit of animal weight gain. Management-intensive grazing (MIG) is a BMP that offers the potential for more efficient utilization of grazed forage crops via controlled rotational grazing and more efficient conversion of forage into meat and milk. Projected CH4 annual emissions in cows reflect a 22% reduction from BMP when compared with continuous grazing in this study. With the BMP application of MIG, less methane was produced per kilogram of beef gain.