MERCURY CONTAMINATION AND FLOODPLAIN SEDIMENTATION FROM FORMER GOLD MINES IN NORTH GEORGIA1

ABSTRACT: Gold was discovered in Georgia in 1829 and mined until about 1940 in the Dahionega Gold Belt of the north Goorgia Piedmont. Streams there are characterized by gravel beds and fine sandy to silty banks. Historical mining-related alluvium is clearly distinguished from prehistoric alluvium because it is contaminated with mercury (Hg), which was used by miners to amalgamate gold. Mercury concentrations in historical floodplain sediments range from 0.04 to 4.0 mg kg^?1, exceeding background (0.04 mg kg¹) by as much as two orders of magnitude near the core of the mining district and decreasing in the downstream direction. Low levels (≤ 0.1 mg kg¹) of Hg are established within about 10–15 km from the source mines. The mercury-contaminated sediment exceeds sediment quality guidelines set by many agencies, and is a significant nonpoint source for mercury pollution. Hydraulic mining of saprolite, which began in 1868, and cutting of forests associated with mining and settlement caused unusually rapid sedimentation (1–3 cm yr^?l) and floodplain aggradation in the region. After mining ceased, streams adjusted by downcutting and forming an historical-age terrace. A new floodplain is currently being formed as streams migrate lateraily and erode the mining-related sediment of the historical terrace. High magnitude floods are contained within the confines of the historical terrace, thus limiting quantities of over-bank sedimentation, causing channel bank erosion, and transmitting high sediment yields to reservoirs in the region.     

Volatilization of mercury from natural water by a broad-spectrum Hg-resistantBacillus pasteurii strain DR2

Summary A broad-spectrum mercury-resistant bacterial strain was isolated from contaminated water and was identified as Bacillus pasteurii strain DR2. It could volatilize Hg-compounds including organomercurials from its growth media. It utilized several aromatic compounds as a sole source of carbon. The bacterial strain eliminated HgCl₂ from sterile river water and the presence of benzene, toluene, naphthalene and nitrobenzene at 1 mM concentration in the system increased the rate of mercury volatilization, the volatilization rate being highest with benzene. When 1.7×10⁷ cells of this bacterial strain were added per ml of non-sterile water the bacterial strain volatilized more than 90 percent of mercury from mercuric chloride and organo-mercurials like PMA, thiomersol and methoxy ethyl mercuric chloride (MEMC). In the absence of this bacterial strain the volatilization of PMA and MEMC due to the presence of other Hg-resistant organisms in nonsterile polluted water ranged between 20–25 percent and of HgCl₂ was about 40 percent. However, in the presence of B. pasteurii DR2 volatilization of these Hg-compounds from non-sterile water increased by 20–40 percent. In the presence of 1 mM benzene the rate of mercury volatilization was even higher. In all the cases the rate of volatilization was higher in the first seven days than in the next seven days.Professor A. Mandal, MSc, PhD is Head of the Department of Biochemistry at the University College of Science, 35 Ballygunge Circular Road, Calcutta 700019, to whom correspondence should be addressed. His co-workers are Dr K. Pahan, Postdoctoral Associate, Department of Cell Biology and Paediatrics, Medical University of South Carolina, USA; Dr J. Chaudhuri, Senior Lecturer, Department of Molecular Biology, BKC College, Calcutta, India; Dr D.K. Ghosh, Postdoctoral Associate, Department of Biochemistry, University College of Science, Calcutta, India; Dr R. Gachhui, Postdoctoral Associate, The Cleveland Clinic Foundation, Cleveland, USA; and Dr S. Ray, Postdoctoral Associate, The Johns Hopkins University School of Hygiene and Public Health, Department of Biochemistry, Baltimore, USA.     

Impact of crude oil pollution on species number and live standing herbaceous crop biomass

Summary The impact of crude oil spill on the number of plant species and the above-ground live standing crop biomass (AGLSCB) of a herbaceous plant community was assessed. The spillage had a devastating effect on the herbaceous community and especially on the component herbaceous annuals. At least 80–90% of the species were absent in the affected areas in comparison to nearby unaffected areas, most of these being annuals. Perennial species were generally less affected. The total herbaceous production for a period of 12 months in the polluted areas was 885.1 gm^–2 compared with 4860.7 gm^–2 for the unaffected areas. The average monthly production in the polluted areas was 73.8 gm^–2 compared with 405.0 gm^–2 for the unaffected areas.Dr Debojit Baruah is the senior author of this paper and he is a research scholar at Dibrugarh University. Dr Sarada K. Sarma is a Pofessor in the Botany Department of Guwahati University in Assam.     

Fly ash for the treatment of Zn(II) rich effluents

Summary The ability of fly ash to remove Zn(II) from water by adsorption has been tested at different concentrations, temperatures and pH of the solution. It was found that low adsorbate concentration, small particle size of adsorbent and higher temperature favoured the removal of Zn(II) from aqueous solution. The Langmuir isotherm was used to represent the equilibrium data at different temperatures. The apparent heat of adsorption has been found to be 17.325 Kcal mol^–1, which indicates the process to be endothermic. The uptake of Zn(II) is diffusion controlled and the mass transfer coefficient is 3.56 × 10^–5 cm s ^–1.The maximum removal was noted at pH 7.5. Dr V.N. Singh is Professor and Head of the Department of Applied Chemistry, Dr A.K. and Prof. D.P. Singh are members of the Department of Mining Engineering; all are situated in the Institute of Technology at Banaras Hindu University.     

Mobility of oil and other sludge constituents during oily sludge treatment by landfarming

Five levels of oily sludge application were made to the surface layer of a desert sandy soil in Kuwait. The migration of the constituents of the sludge to subsurface soil layers was investigated at intervals over a period of 29 months. The data show very limited mobility to subsurface soil layer (40–70 cm depth) but not to 70–90 cm depth. The environmental impact of the added sludge is related to soil pH and to the Zn equivalent value of the sludge. Zn equivalent for the soil treated with oily sludge was 612 mg kg⁻¹, which is much lower than permissible limits. This soil can accept more than 1000 t ha⁻¹ from this type of sludge. However, due to the heterogeneous composition of sludge the Zn equivalent value should be calculated for each batch. Addition of oily sludge to the desert soil susceptible to wind erosion had a significant effect on minimizing soil loss under wind tunnel conditions. This effect is attributed to aggregation of the soil particles in the surface soil layers.     

Toxicity and uptake of mercurials in a cyanobacterium

Nostoc calcicola cells exposed to mercuric chloride (0.05–0.25 M), methyl mercuric chloride (0.05–0.15 M) and the fungicide ceresan (phenyl mercuric acetate; 0.05–0.20 M) showed sensitivity in the sequence: methyl mercury3) over phenyl mercuric acetate (0.51×10³); inorganic mercury occupied the intermediate position with a bioconcentration factor of 1.32×10³. The data infer that larger molecules of organomercurials may not be taken up by cells at the rate and extent comparable to the smaller species.     

Bacteriological quality of spring water in Bahrain

Summary The bacteriological quality of untreated spring waters in Bahrain were evaluated. Samples were collected from 12 natural springs and analysed for total plate count, total coliform, total faecal coliform, total faecal streptococci and occurrence ofShigella andSalmonella. The total bacterial counts ranged from 2.4×10¹ to 1.6×10⁴ CFU mL^–1 with an average of 2.8×10³.The coliform organisms were present in all springs. Faecal coliforms were present in 11 out of 12 springs studied, and three springs were heavily contaminated. Based on criteria which used the ratio of faecal coliform to faecal streptococci, all springs studied may be contaminated with human wastes, except one spring which may be contaminated with animal wastes. NeitherSalmonella norShigella were detected in any of the spring waters. It is concluded that the spring waters studied are unsuitable for human consumption unless disinfected.Dr Abdulrahman O. Musaiger is the senior author, to whom correspondence should be addressed. He is Head of the Nutrition Unit at the Bahrain Public Health Directorate. Mr Zakaria A. Khunji is a qualified microbiologist and the nutritionist at the Unit. Mr Hussain A. Mohana is a graduate and technician in charge of the food and water microbiology section at the Public Health Laboratory, Ministry of Health, Bahrain.     

Metal contamination of surface water,sediment and <Emphasis Type="Italic">Tympanotonus fuscatus</Emphasis> var. <Emphasis Type="Italic">radula</Emphasis> of Iko River and environmental impact due to Utapete gas flare station,Nigeria

Inter-seasonal studies on the trace metal load of surface water, sediment and Tympanotonus fuscatus var. radula of Iko River were conducted between 2003 and 2004. The impact of anthropogenic activities especially industrial effluent, petroleum related wastes, gas flare and episodic oil spills on the ecosystem are remarkable. Trace metals analyzed included cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni), vanadium (V) and zinc (Zn). Sediment particle size analysis revealed that they were characteristically psammitic and were predominantly of medium to fine grained sand (>73%), less of silt (<15%) and clay (<10%). These results correlated with low levels of trace elements such as Pb (0.03 ± 0.02 mg kg⁻¹), Cr (0.22 ± 0.12 mg kg⁻¹), Cd (0.05 ± 0.03 mg kg⁻¹), Cu (0.04 ± 0.02 mg kg⁻¹) and Mn (0.23 ± 0.22 mg kg⁻¹) in the sediment samples. This observation is consistent with the scarcity of clayey materials known to be good scavengers for metallic and organic contaminants. Sediments indicated enhanced concentration of Fe, Ni and V, while other metal levels were relatively low. The concentrations of all the metals except Pb in surface water were within the permissible levels, suggesting that the petroleum contaminants had minimal effect on the state of pollution by trace metals in Iko River. Notably, the pollutant concentrations in the sediments were markedly higher than the corresponding concentrations in surface water and T. fuscatus tissues, and decreased with distance from point sources of pollution.     

Causes and effects of siltation on the environment of Nepal

Summary The present investigation was carried out in 1986, and is based upon about 20 years of river discharge data (1960s to 1980s). There are three important river-systems in Nepal - Sapt Kosi River system in East Nepal, Sapt Gandaki River system in mid- Nepal, and Karnali River system in West Nepal. The average annual highest rainfall is 3,685 mm yr^–1, and the greatest mean annual suspended sediment load (1.434 g L^–1) was recorded in Sapt Gandaki, while the water discharge from Sapt Kosi (1,747 m³ s^–1) was the highest and so also was the silt discharge (0.4 million ton day^–1). The correlation between water discharge and silt discharge was found to be statistically highly significant as verified by correlation and regression analyses.An abatement of human interference in the catchment areas of these rivers, and fodder/fuelwood plantation through the active participation of local people in their marginal land to decrease the human pressure on natural forests, are considered the two major easy, effective and economic methods to control the siltation hazard that is causing extensive deterioration to the environment in Nepal.Dr Govind P.S. Ghimire is Reader and Associate Professor in the Central Department of Botany at Tribhuvan University. Mr B.K. Uprety is an ecologist working on the Environmental Impact Study Project of His Majesty's Government, Nepal.     

A Baseline Study on Water Resources of the Tourist Island, Pulau Perhentian, Peninsular Malaysia, from an Ecological Perspective

Ambient water quality and bacterial populations in the water resources of Pulau Perhentian, a Marine Park of Malaysia, were studied during a peak tourist arrival, off-monsoon period. The overall water and bacteriological quality of swimming/boating sites in the island is at an acceptable condition, although the conductivity (0.88–60 mS m^–1) due to high dissolved solid concentrations is slightly high, when compared with the recommended standard and published guidelines for the protection/maintenance of recreation water and its aesthetic enjoyment (Universiti Malaya, Department of Environment, Malaysia, 1986). However, the bacteriological quality of the drinking/bathing water wells is poor, with faecal coliform counts (2 up to 1,600 MPN per 100 ml sample water) exceeding the permissible levels defined for raw water supplies (with or without treatment). This suggests that the groundwater, seepage and run-off into the wells is contaminated. Contrary to the belief of the water users being interviewed in a social survey, the untreated drinking/bathing water is not bacteria-free. The excessive counts are attributable to deoxygenated conditions (12–42 percent corresponding to 0.9–3.3 mg l^–1) prevailing in the wells, high total suspended solids (up to 202 mg l^–1) which promote bacterial growth, lack of adequate sewerage systems to receive effluents from lavatories of dwellings, chalets and resorts, as well as the lack of centralised water treatment plants and storage tanks to cope with water scarcity and waterway contamination.     

Monitoring effects of a controlled subsurface carbon dioxide release on vegetation using a hyperspectral imager

A hyperspectral imaging system was used to monitor vegetation during a subsurface controlled release of carbon dioxide (CO₂). From August 3 to 10, 2007, 0.3 tons CO₂/day were released through a 70 m horizontal pipe located at a nominal depth of 1.8 m below the surface. Hyperspectral images of alfalfa plants were collected during the controlled release and used along with classification tree analysis to study changes in the reflectance spectra as a function of perpendicular distance from the horizontal pipe. Changes in the reflectance spectra near the red edge (650–750 nm) were observed over the course of the controlled release experiment for plants within a perpendicular distance of 1 m of the release pipe. These results indicate monitoring vegetation over a carbon sequestration site has the potential to allow monitoring of the integrity of the CO₂ storage.     

Decolorization and Complete Degradation of Methyl Red by a Mixed Culture

Synthetic dyes, azo dyes in particular, are widely found in the effluents from textile industries. The persistence and toxicity of these compounds cause adverse impacts in the receiving streams. A mixed culture isolated from a domestic wastewater treatment plant was found to remove the colour of the azo dye, methyl red, efficiently. Total decolorization and degradation occurred within 18 h. The mixed culture could degrade 700 mgl^–1 of methyl red efficiently in the presence of 200 mgl^–1 of glucose, whereas in the absence of glucose it could degrade only 100 mgl^–1 of methyl red. The mixed culture, when suspended in phosphate buffer along with methyl red at 100 mgl^–1 concentration could degrade methyl red efficiently within 2 h of incubation. The pH of the medium decreased continuously during degradation. After the complete removal of initial methyl red, another 100 mgl^–1 was added to the culture filtrate and incubated further. The mixed microbial cultures could degrade methyl red efficiently through three cycles but further degradation was not possible as the pH of the medium decreased to 3.5.     

Impact of Vegetative Cover on Runoff and Soil Erosion at Hillslope Scale in Lanjaron, Spain

Soil loss and surface runoff patterns over a four-year period (1997–2000) were studied in erosion plots from three hillslopes under different vegetative covers (Rosmarinus officinalis, Triticum aestivum and natural-spontaneous vegetation) in Lanjaron (Alpujarras) on the south flank of the Sierra Nevada of southeast Spain. The erosion plots were located on the hillslopes at 35.5% incline, at 1,480 m in altitude and with 41.8 m² (21 m×1.9 m) in area. The vegetative covers were tested for effectiveness in controlling the surface runoff and soil loss production. The highest runoff and erosion values, ranging from 114.1 to 1.7 mmyr^–1 and from 14,564.3 to 6.6 kgha^–1yr^–1, respectively, over the entire study period, were measured under the Triticum aestivum. In the Rosmarinus officinalis, runoff ranged from 7.9 to 1.3 mmyr^–1 and erosion from 156.4 to 2.3 kgha^–1yr^–1, while on the hillslope under natural-spontaneous vegetation, runoff ranged from 4.4 to 0.9 mmyr^–1 and erosion from 322.3 to 2.2 kgha^–1yr^–1. According to the results the vegetative covers of Rosmarinus officinalis and natural-spontaneous vegetation reduced the soil losses by 99 and 98%, with respect to the Triticum aestivum, and the runoff losses by 94 and 96%, respectively. Also, the Rosmarinus officinalis and natural-spontaneous plants influenced infiltration by intercepting much of the rainfall water respect to the Triticum aestivum. Monitoring allowed more direct linkages to be made between management practices and their impacts on runoff and soil erosion, thereby enabling to identify problems and take appropriate preventive measures to improve the management practices.     

Upstream Channel Changes Following Dam Construction and Removal Using a GIS/Remote Sensing Approach1

Abstract: This study used an innovative GIS/remote sensing approach to study historical river channel changes in the Huron River, a wandering gravel‐bedded river in northern Ohio. Eight sets of historical aerial photographs (1958‐2003) span the construction of a low‐head dam (1969), removal of the spillway (1994), and removal of the dam itself (2002). Construction of the dam modified stream gradients >4 km upstream of the small impounded reservoir. This study tracked changes in the polygon size, shape, and centroid position of 12 sand‐gravel bars through a study reach 0.2‐4.1 km upstream of the dam. These bars were highly responsive, tending to migrate obliquely downstream and toward the outer bank at rates up to 9 m/year. Historical changes in the size and position of the bars can be interpreted as the downstream translation of one or more sediment waves. Prior to dam construction, a sediment wave moved downstream through the study reach. Following construction of the dam, this sediment wave became stationary and degraded in situ by dispersion. The growth of bars throughout the study reach during this time interval resulted in a progressive increase in channel sinuosity. Removal of the spillway rejuvenated downstream translation of a sediment wave through the study reach and was followed by a reduction in channel sinuosity. These results illustrate that important geomorphologic changes can occur upstream of low‐head dams. This may be a neglected area of research about the effects of dams and dam removals.     

Morphologie effects of channelization: the case of the Neebing-McIntyre floodway,Thunder Bay,Ontario, Canada

The Neebing-McIntyre floodway in Thunder Bay, Ontario, Canada, has been constructed with a relatively straight and uniform trapezoidal channel, compared with the prechannelized sinuous reaches of the Neebing and the McIntyre rivers. The flow regime of the floodway also contrasts significantly with the prechannelized regime, because of the combination of discharges from these rivers into a new channel and the regulation of flows by a diversion structure. The maximum channel capacity of the floodway is about 284 m³ s^–1 (175-year regional flood), compared with about 40 m³ s^–1 and 60 m³ s^–1, respectively, for the Neebing and the McIntyre. According to regime theories, the construction of a straight and trapezoidal channel has upset the equilibrium of the stream system and therefore should lead to some accelerated erosion and sedimentation processes in the new channel immediately after construction. Erosion potential is particularly high during higher discharge events, when flow velocities are expected to be greater than the prechannelized velocities of the Neebing and the McIntyre. The overall sediment yield of the watershed is low (71t km^–2 yr^–1), compared with other documented watersheds of North America, but the rates of deposition in the floodway are relatively high, mainly due to the backwater effect of Lake Superior. Unless maintained by constant channel work, the floodway will tend to fill up with sediment, until a postconstructional equilibrium is reestablished.     

Assessment of Endocrine‐Disrupting Chemicals Attenuation in a Coastal Plain Stream Prior to Wastewater Treatment Plant Closure

The U.S. Geological Survey is conducting a combined pre/post‐closure assessment at a long‐term wastewater treatment plant (WWTP) site at Fort Gordon near Augusta, Georgia. Here, we assess select endocrine‐active chemicals and benthic macroinvertebrate community structure prior to closure of the WWTP. Substantial downstream transport and limited instream attenuation of endocrine‐disrupting chemicals (EDCs) was observed in Spirit Creek over a 2.2‐km stream segment downstream of the WWTP outfall. A modest decline (less than 20% in all cases) in surface water detections was observed with increasing distance downstream of the WWTP and attributed to partitioning to the sediment. Estrogens detected in surface water in this study included estrone (E1), 17β‐estradiol (E2), and estriol (E3). The 5 ng/l and higher mean estrogen concentrations observed in downstream locations indicated that the potential for endocrine disruption was substantial. Concentrations of alkylphenol ethoxylate (APE) metabolite EDCs also remained statistically elevated above levels observed at the upstream control site. Wastewater‐derived pharmaceutical and APE metabolites were detected in the outflow of Spirit Lake, indicating the potential for EDC transport to aquatic ecosystems downstream of Fort Gordon. The results indicate substantial EDC occurrence, downstream transport, and persistence under continuous supply conditions and provide a baseline for a rare evaluation of ecosystem response to WWTP closure.     

Upstream Sediment‐Control Dams: Five Decades of Experience in the Rapidly Eroding Dahan River Basin,Taiwan

Sedimentation is emerging as a key issue in sustainable reservoir management. One approach to controlling reservoir sedimentation is to trap sediment in hydraulic structures upstream of the reservoir. In the 1,163‐km² catchment of the Dahan River (Taiwan) over 120 “sabo” dams were built to reduce sediment yield to Shihmen Reservoir. Built in 1963 for water supply, Shihmen has lost over 40% of its 290‐Mm³ storage capacity to sedimentation. Most of these upstream structures were small, but three had capacities >9 Mm³. Field measurements and historical data from the Water Resources Agency show most smaller dams had filled with sediment by 1976. The three largest were full or nearly so by 2007, when one (Barlin Dam) failed, releasing a pulse of 7.5 Mm³, most of its 10.4 Mm³ stored sediment downstream. The Central Range of Taiwan is rapidly eroding (denudation rates 3‐6 mm/yr), so geologically high loads make sediment problems manifest sooner. Even in other environments, however, eventually small dams built upstream of large reservoirs are likely to fill themselves, creating multiple small sediment‐filled reservoirs, some located in sites inaccessible to mechanical removal. Our analysis suggests sabo dams do not offer a long‐term basis for controlling reservoir sedimentation in such a high‐sediment yield environment. Sustainable solutions must somehow pass sediment downstream, as would be accomplished by a sediment bypass around Shihmen Reservoir, as now being studied.     

Legacy Effects of Colonial Millponds on Floodplain Sedimentation,Bank Erosion,and Channel Morphology,Mid‐Atlantic,USA1

Abstract: Many rivers and streams of the Mid‐Atlantic Region, United States (U.S.) have been altered by postcolonial floodplain sedimentation (legacy sediment) associated with numerous milldams. Little Conestoga Creek, Pennsylvania, a tributary to the Susquehanna River and the Chesapeake Bay, is one of these streams. Floodplain sedimentation rates, bank erosion rates, and channel morphology were measured annually during 2004‐2007 at five sites along a 28‐km length of Little Conestoga Creek with nine colonial era milldams (one dam was still in place in 2007). This study was part of a larger cooperative effort to quantify floodplain sedimentation, bank erosion, and channel morphology in a high sediment yielding region of the Chesapeake Bay watershed. Data from the five sites were used to estimate the annual volume and mass of sediment stored on the floodplain and eroded from the banks for 14 segments along the 28‐km length of creek. A bank and floodplain reach based sediment budget (sediment budget) was constructed for the 28 km by summing the net volume of sediment deposited and eroded from each segment. Mean floodplain sedimentation rates for Little Conestoga Creek were variable, with erosion at one upstream site (?5 mm/year) to deposition at the other four sites (highest = 11 mm/year) despite over a meter of floodplain aggradation from postcolonial sedimentation. Mean bank erosion rates range between 29 and 163 mm/year among the five sites. Bank height increased 1 m for every 10.6 m of channel width, from upstream to downstream (R² = 0.79, p < 0.0001) resulting in progressively lowered hydraulic connectivity between the channel and the floodplain. Floodplain sedimentation and bank erosion rates also appear to be affected by the proximity of the segments to one existing milldam, which promotes deposition upstream and scouring downstream. The floodplain and bank along the 28‐km reach produced a net mean sediment loss of 5,634 Mg/year for 2004‐2007, indicating that bank erosion was exceeding floodplain sedimentation. In particular, the three segments between the existing dam and the confluence with the Conestoga River (32% of the studied reach) account for 97% of the measured net sediment budget. Future research directed at understanding channel equilibria should facilitate efforts to reduce the sediment impacts of dam removal and legacy sediment.     

Performance assessment of a wastewater treatment plant producing effluent for irrigation in Egypt

A conventional activated sludge treatment facility was the subject of this study. The assessment was directed at determining the characteristics of the raw wastewater, the quality of the treated effluent and the efficiency of the various treatment units. Furthermore, the water quality along the effluent irrigation canal was monitored. The assessment of the quality of the treated effluent for irrigation is based on the guidelines established by the World Health Organization and the Egyptian decree 9/89 for the use of wastewater in agriculture. The results of the study indicated that the concentration of the raw wastewater was considered moderate. The mean values of the COD (Chemical Oxygen Demand), BOD (Biological Oxygen Demand) and total suspended solids (TSS) were around 250, 102 and 142 mg l–1, respectively. This was attributed to the high quantities of wastewater from industrial sources. The overall efficiency of the treatment facility was good. The mean residual COD, BOD and TSS were 25, 8 and 21 mg l–1 and the corresponding percentage removal values were 90, 92 and 85%, respectively. The maximum percentage removal of oil and grease was 84% with a mean residual concentration of 24 mg l–1. The total viable count (22°C and 37°C), faecal coliform and aecal streptococci were reduced by 99.9% compared to only 99.5% for Salmonella. Bacteriological examination of the dried sludge indicated a reduction of nine logs of faecal coliform and faecal streptococci, as compared to thickened sludge. Analysis of the Ni, Cu, Pb and Cr in the dried sludge indicated that their concentrations are within the permissible limits. Zinc exceeded the consent standards by 50%. The results of the analyses of samples collected at the beginning of the irrigation canal indicated insignificant changes from the characteristics of the final effluent. Samples collected at a distance of 2km along the irrigation canal showed mean reductions in the COD and BOD of 28.6 and 47%, respectively, which could be attributed to sedimentation and/or a self-purification effect. An increase in the total nitrogen, total phosphorus and total viable count was also recorded, which could be due to seepage from the agricultural land. From the data available it is evident that the treated wastewater could be used for restricted irrigation. The design and implementation of a monitoring programme is recommended.     

Destruction of Wetlands and Waterbird Populations by Dams and Irrigation on the Murrumbidgee River in Arid Australia

The Lowbidgee floodplain is the Murrumbidgee Rivers major wetland in southeastern Australia. From more than 300,000 ha in the early 1900s, at least 76.5% was destroyed (58%) or degraded (18%) by dams (26 major storages), subsequent diversions and floodplain development. Diversions of about 2,144,000 ML year^–1 from the Murrumbidgee River come from a natural median flow of about 3,380,000 ML year^–1 providing water for Australias capital, hydroelectricity, and 273,000 ha of irrigation. Diversions have reduced the amount of water reaching the Lowbidgee floodplain by at least 60%, from 1888 to 1998. About 97,000 ha of Lowbidgee wetland was destroyed by development of the floodplain for an irrigation area (1975–1998), including building of 394 km of channels and 2,145 km of levee banks. Over 19 years (1983–2001), waterbird numbers estimated during annual aerial surveys collapsed by 90%, from an average of 139,939 (1983–1986) to 14,170 (1998–2001). Similar declines occurred across all functional groups: piscivores (82%), herbivores (87%), ducks and small grebe species (90%), large wading birds (91%), and small wading birds (95%), indicating a similar decline in the aquatic biota that formed their food base. Numbers of species also declined significantly by 21%. The Lowbidgee floodplain is an example of the ecological consequences of water resource development. Yanga Nature Reserve, within the Lowbidgee floodplain, conserved for its floodplain vegetation communities, will lose these communities because of insufficient water. Until conservation policies adequately protect river flows to important wetland areas, examples such as the Lowbidgee will continue to occur around the world.