Temporal and spatial distributions of sediment mercury at salt pond wetland restoration sites, San Francisco Bay, CA, USA

Decommissioned agricultural salt ponds within south San Francisco Bay, California, are in the process of being converted to habitat for the benefit of wildlife as well as water management needs and recreation. Little is known of baseline levels of contaminants in these ponds, particularly mercury (Hg), which has a well established legacy in the Bay. In this study we described spatial and short-term temporal variations in sediment Hg species concentrations within and among the Alviso and Eden Landing salt ponds in the southern region of San Francisco Bay. We determined total Hg (Hg_t) and methylmercury (MeHg) in the top 5 cm of sediment of most ponds in order to establish baseline conditions prior to restoration, sediment Hg_t concentrations in a subset of these ponds after commencement of restoration, and variation in MeHg concentrations relative to sediment Hg_t, pH, and total Fe concentrations and water depth and salinity in the subset of Alviso ponds. Inter-pond differences were greatest within the Alviso pond complex, where sediment Hg_t concentrations averaged (arithmetic mean) 0.74 μg/g pre and 1.03 μg/g post-restoration activity compared to 0.11 μg/g pre and post at Eden Landing ponds. Sediment Hg_t levels at Alviso were fairly stable temporally and spatially, whereas MeHg levels were variable relative to restoration activities across time and space. Mean (arithmetic) sediment MeHg concentrations increased (2.58 to 3.03 ng/g) in Alviso and decreased (2.20 to 1.03 ng/g) in Eden Landing restoration ponds during the study. Differences in MeHg levels were related to water depth and pH, but these relationships were not consistent between years or among ponds and were viewed with caution. Factors affecting MeHg levels in these ponds (and in general) are highly complex and require in-depth study to understand.     

Occurrence of pathogens on vegetables harvested from soils irrigated with contaminated streams

The study assesses the contamination level, the seasonal distribution and the toxigenicity of pathogens isolated from irrigated vegetables and the water used for irrigation. A total of 196 samples of water used for irrigation and 326 irrigated vegetables were obtained from Kawo drain, Sabon Gari drain and River Galma and examined using standard procedures for coliform and viable counts and the presence of E. coli, Salmonella and Vibrio during the dry and wet seasons. Irrigation water from Kawo drain had significantly higher coliform counts by location and season than water from the other two locations. Although all the vegetables had coliform counts higher than the recommended standard (range 3.40-6.38 log(10) cfuml(-1)), amaranthus had significantly higher (P<0.05) counts than other vegetables during the dry season. Salmonella was significantly more likely to be detected during the dry season than during the wet (OR 4.91, 1.07相似文献   

Occurrence of polycyclic aromatic hydrocarbons in water and sediment samples from KwaZulu Natal Province,South Africa

Solid‐phase extraction (SPE) and ultrasonic extraction (UE) techniques followed by Gas Chromatography‐Mass Spectrometry (GC‐MS) have been modified for qualitative and quantitative analysis of polycyclic aromatic hydrocarbons (PAHs) in water and sediment samples. Percentage recoveries of PAHs ranged from 85 to 121% in water and 82 to 117% in sediment samples. The limits of detection (LOD) and limits of quantification (LOQ) ranged from 0.02 to 0.2 and 0.05 to 0.5 µg/L for SPE while for UE, they were between 0.008–0.09 and 0.02–0.30 µg/kg, respectively. The concentration levels of PAHs (naphthalene, acenaphthene, acenaphthylene, fluorine, anthracene, phenanthrene and pyrene) detected in water samples were 0.071–2.7, 2.0–10.4 and 2.5–3.5 µg/L in wastewater, river water, and dam water, respectively. In sediment samples, concentration levels of PAHs were between 2.8–42.0 and 2.8–3.9 µg/kg, in river and dam sediment, respectively.     

The fate of oil and oil—dispersant mixtures in freshwater ponds

The fate, distribution and composition of oil and oil—dispersant mixtures were studied in a series of five, lined, inground ponds containing sandy gravel sediment and mesotrophic water. Norman Wells crude oil and Corexit 9527 were added at nominal concentrations of 100 and 20 ppm, respectively, to two of the ponds, and the crude oil alone was added at 100 ppm to a third pond. The water surface, water column, the sediment, pond liner and attached biota were systematically sampled for a year. While only about 2% of the oil remained in the water column of the pond with no dispersant addition, in the pond with the dispersant, about 10% of the oil persisted in the water for several weeks. Most of the oil initially dispersed in the water returned to the water surface, then eventually sank to the sediment. Thinner surface films showed a higher dispersant content than the thicker slicks, and the thinner films had higher infrared carbonyl absorption. Final distribution calculations revealed that about 45% of the oil had degraded in the oil—dispersant-treated ponds during the one year study, while only 23% could not be accounted for in the oil pond. Changes in the oil composition during the experiment were similar in all ponds, with no evidence to suggest that the dispersant affected oil composition in any special manner.     

Septage disposal in waste recycling ponds

Experiments were carried out to investigate the feasibility of septic tank sludge (septage) disposal into pilot-scale waste recycling ponds for the production of algae and fish. A septage loading of 100 kg COD ha⁻¹ day⁻¹ to four 4-m² single-stage ponds resulted in the production of algal biomass and dissolved oxygen in the pond water, suitable for Tilapia growth. Some microbiological investigations of this waste recycling scheme were undertaken using ten earth ponds (each with the dimensions of 20 × 10 × 1.3 m: length × width × depth). It was found that the densities of coliform bacteria and bacteriophages in the pond water and sediment tended to increase with increased septage loadings and loading periods. The ponds fed with septage at the loading of 100 kg COD ha⁻¹ day⁻¹ were found to contain higher densities of these microorganisms than those of the control pond without septage feeding. The possible public health impact resulting from this practice was assessed.     

Mobility and profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans in sediment of Ya-Er Lake, China

The sediment of Ya-Er Lake had been heavily polluted by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from the former chloralkali industry. The total amounts of PCDD/Fs and I-TEQ decreased along the water flow direction and also decreased from top to bottom layers of sediment cores. Sediment of Pond 1 was dominated by PCDF. especially TCDF. In contrast, in the other four ponds, PCDD dominated in all layers and octachlorinated dibenzo-p-dioxin (OCDD) predominated in all of the homologues. When homologue profiles from sediments and water samples were compared using principal component analysis (PCA), the first two principal components represented 95.2% of the variance in the data. The first component explained 75.9% of the variance and the second one 19.3%. Two clusters were most distinct, presenting a shift in PCDD/Fs composition from PCDF to heptachlorinated dibenzo-p-dioxin (HpCDD) and OCDD in sediments and water from Pond I to Ponds 2-5. The pattern variation between Pond I and Ponds 2-5 in Ya-Er Lake was most likely due to the change of process in the chemical plant after the dams between the ponds were built. The results of the present study also showed that log Koc of PCDD/Fs calculated from data of sediment and water in the field were comparable with theoretical log Koc. The results also implied that the concentrations of PCDD/Fs in water and sediments could be predicted from each other by log Koc.     

Toxicity testing for controlling urban wet-weather pollution: advantages and limitations

Toxicity of Combined Sewer Overflows (CSOs) and stormwater was studied at 15 sites in Southern Ontario, using a battery of seven bioassays. The highest frequencies of severe and moderate toxicity (19% and 24%, respectively) were found at highway runoff sites; frequencies of CSO toxicity were much lower (from 6.6% to 13%, for moderate and severe toxicity combined). Stormwater ponds contributed to toxicity reduction, with respect to both water and sediment downstream of ponds. Conventional toxicity testing was found useful for screening and assessing potential receiving water impacts, but was somewhat limited by the dynamic nature and large variety of wet-weather pollution sources.     

Sources of water to the seawater well which supplies the fish ponds in Eilat Implications for fishpond management

The sources of water to the well supplying the fishponds in Eilat were determined using a simple mass balance approach, in which the concentration of various components in the source waters were measured and a series of simultaneous equations solved to determine the hydrological budget. It was calculated that 80% of the water supplied to the well was recycled pond water, 10% was seawater and 10% was sewage effluent. On the basis of major ion determinations, it was shown that there could be no significant contribution from natural groundwater.This method of water supply has both disadvantages and benefits. The fishpond system was operated to produce gilthead seabream and grey mullet in the pond and oysters on the pond effluent. The major disadvantage was that the excess nutrients supplied in the inflow may have limited the total biomass of fish which could be grown in the ponds by making them more susceptible to mass mortalities due to both high oxygen or high ammonia/low oxygen concentrations.The benefits include the high productivity of diatoms due to the nutrients supplied which enabled there to be a successful oyster culture. In addition, 95–97% of the nitrogen supplied in the sources was as ammonium which is toxic to fish. After passage through the aerobic groundwater, 97% of the dissolved nitrogen was in the form of nitrate. At the same time, the coliform counts were reduced to undetectable levels. The major ion composition of the pond was enriched 25% relative to seawater because the evaporated seawater was replaced by sewage effluent. Despite this unusual ionic composition fish, oysters and prawns were grown successfully in these ponds.     

The limitation of the ratio of fecal coliforms to total coliphage as a water pollution index

The fecal coliform populations of raw sewage, sewage lagoon effluent, and river water were determined using the most probable number technique. The total coliphage populations of the three water sources were determined using Escherichia coli B (ATCC 11303-1) host cells. The ratios of fecal coliforms to coliphage in the three water samples were 87:1, 4.2:1, and 0.15:1, respectively. The ratio of fecal coliforms to coliphage in stored raw sewage decreased from 87:1 to about 1:1 within 7 days at 20°C and within 28 days at 4°C. These changing ratios resulted from the greater longevity of the coliphage compared with that of the coliform bacteria. The use of the ratio of fecal coliforms to coliphage is not considered reliable as an index of when a fecal pollution event occurred because the ratio is influenced by prior contamination, presence of sediment, chlorination, and temperature.     

Statistics of enumerating total coliforms in water samples by membrane filter procedures

A commonly used assumption is that the microbial counts of a given water sample are randomly distributed according to Poisson statistics and, in particular, that replicate analyses of the same sample are so distributed. Using Fisher's index of dispersion, as well as a newly developed test, analysis of prior data on membrane filter total coliform organisms in a variety of water samples indicated that, in many cases, the assumption of Poisson statistics was incorrect, but that the data were consistent with a negative binomial distribution. This finding has significance in the interpretation of total coliform counts for regulatory as well as research purposes, and further research to delineate the responsible mechanisms is required.     

Occurrence of Giardia cysts and Cryptosporidium oocysts in raw and treated water from two water treatment plants in Selangor, Malaysia

The occurrence of Giardia cysts and Cryptosporidium oocysts was determined both in the raw water and the treated waters from two water treatment plants in Selangor, Malaysia between July 1994 and January 1995. At each treatment plant, raw and treated water samples were collected fortnightly on 10 separate occasions. Physical parameters, including dissolved oxygen, pH, temperature, conductivity, turbidity and free and total chlorine were measured, and samples were also taken for faecal coliform analyses. The isolation and enumeration of cysts and oocysts was according to UK standard methods. Whilst Giardia cysts were detected in 90% of the raw water samples (range 0–60 cysts per litre) no Cryptosporidium oocysts were detected. Higher concentrations of cysts were detected in the raw water of the first treatment plant. All raw water samples were faecally contaminated, as faecal coliform counts ranged from 4.6 × 10⁴ to 1.3 × 10⁵ colony forming units per 100 ml. No correlation between the concentration of Giardia cysts and the concentration of faecal coliforms could be demonstrated statistically, nor was there any correlation between the concentration of Giardia cysts and the physical parameters tested for any of the raw waters. No cysts, oocysts or faecal coliforms were detected in samples of treated water.     

Inactivation of indigenous coliform bacteria in unfiltered surface water by ultraviolet light

This study examined the potential for naturally occurring particles to protect indigenous coliform from ultraviolet (UV) disinfection in four surface waters. Tailing in the UV dose-response curve of the bacteria was observed in 3 of the 4 water samples after 1.3-2.6-log of log-linear inactivation, implying particle-related protection. The impact of particles was confirmed by comparing coliform UV inactivation data for parallel filtered (11 microm pore-size nylon filters) and unfiltered surface water. In samples from the Grand River (UVT: 65%/cm; 5.4 nephelometric turbidity units (NTU)) and the Rideau Canal (UVT: 60%/cm; 0.84 NTU), a limit of approximately 2.5 log inactivation was achieved in the unfiltered samples for a UV dose of 20 mJ/cm2 while both the filtered samples exhibited >3.4-log inactivation of indigenous coliform bacteria. The results suggest that particles as small as 11 microm, naturally found in surface water with low turbidity (<3NTU), are able to harbor indigenous coliform bacteria and offer protection from low-pressure UV light.     

The effect of drinking water treatment on the spatial heterogeneity of micro-organisms: implications for assessment of treatment efficiency and health risk

The effect of drinking water treatment (ferric coagulation, floc blanket clarification, rapid sand filtration) on the spatial heterogeneity of five species of micro-organism was studied at pilot scale. It was found that the spatial heterogeneity of vegetative bacteria (namely total coliform and heterotrophic (22 degrees C; 3 d) bacteria) was little affected by treatment. Indeed, counts of total coliform bacteria within 500 l volumes of treated water were Poisson distributed (i.e. showed minimum variation). In contrast, treatment appeared to increase the spatial heterogeneity (or clustering) of both aerobic spores indigenous to the raw water and Bacillus subtilis var niger spores added to the raw water. Furthermore, B. subtilis var niger spores added to the raw water were detected in the treated water 25 h after termination of spiking to the raw water. The effect on C. parvum oocysts added to the raw water could not be determined because few oocysts broke through treatment into the treated water. Indeed oocyst removals of 5-6 logs were apparent. "Species-specific" differences in the removal ratios were also demonstrated. It is concluded that audits for treatment processes based on single 100 ml "spot" samples for spores will tend to over-estimate the net spore removal and hence underestimate the public health risk. Spatial heterogeneity of counts in treated water contributes to explaining why no "ideal" surrogate has been identified for treatment plant performance.     

A comparison of toxicity tests conducted in the laboratory and in experimental ponds using cadmium and the fathead minnow (Pimephales promelas)

Acute toxicity tests were conducted in the laboratory with fathead minnows (Pimephales promelas) to determine the 96-h LC₅₀ of cadmium under three conditions: (1) in laboratory water, (2) in water from experimental ponds, and (3) in pond water underlain by sediment. Cadmium was then applied at doses equivalent to the estimated LC₅₀ values to 0.07-ha ponds containing caged fathead minnows. A cadmium ion selective electrode, ultrafiltration, and equilibrium calculations were used to determine cadmium speciation, and several water quality characteristics were measured to correlate differences in mortality between test systems (laboratory and field) with observed differences in water quality. The LC₅₀ estimates (mg l⁻¹) for the bioassays were 4.39 for the laboratory water, 3.52 for the pond water with sediment, and 2.91 for the pond water. Concentrations of Cd²⁺ decreased and those of cadmium in the particulate (> 1.2 μm) and 300,000 mol. wt (0.018–1.2 μm) fractions increased over the 96-h; cadmium in these fractions was believed to consist of colloidal sized CdCO₃ precipitates. Concentrations of Cd²⁺ decreased at different rates between test systems, regulated by the degree of CdCO₃(s) supersaturation which in turn depended on pH and total metal concentrations. Differences in toxicity in the laboratory tests were attributed to differences in water hardness and Cd²⁺ concentrations. Mortality of fathead minnows was low (0–10%) during the 96-h test period in the ponds due to the higher pH, which produced supersaturated conditions resulting in the rapid formation of nontoxic CdCO₃ precipitates and a more rapid decrease in Cd²⁺ concentrations as compared to the laboratory bioassays.     

Modelling of coliform removal in 186 facultative and maturation ponds around the world

The paper presents a very extensive evaluation of the coliform decay in facultative and maturation ponds, based on data from 186 different ponds in the world. The ponds encompass a very wide diversity in terms of physical and operating conditions, covering most situations encountered in practice. The median values for the coliform removal efficiencies were 1.8 log units (98% removal) for primary facultative ponds, 1.0 log units for secondary facultative ponds (90% removal) and 1.2 log units (94% removal) for each maturation pond in the series. Two equations to be used for design purposes were derived for estimating the die-off coefficient K(b) (dispersed flow, 20 degrees C) in facultative and maturation ponds. The first equation led to a slightly better fitting with the observed logarithm of the effluent coliform concentrations (R2 = 0.874), and related K(b) with the pond detention time t and depth H (K(b) = 0.682 H(-1.286) t(-0.103)). The other equation also led to a satisfactory fitting (R2 = 0.845), but was slightly simpler, depending only on the pond depth (K(b) = 0.549 H(-1.456)).     

Growth of blue-green algae in the Manukau (New Zealand) oxidation ponds—I. Growth potential of oxidation pond water and comparative optima for blue-green and green algal growth

Water sampled from the Manukau oxidation ponds between 6 December 1973 and 12 July 1974 was tested for its ability to support blue-green algal growth. A local blue-green algal isolate of Anabaena grew well on membrane filtered pond water throughout the year, however the unfiltered water sustained Anabaena only when the resident green algal populations, in particular Chlorella, were low.Temperature and pH optima for growth of Anabaena and the Manukau pond algal dominant, Chlorella, were found to be significantly different: 28–35°C and pH 9–10 and 23–28°C and pH 7–8 respectively. The ambient conditions of the ponds favoured growth of Chlorella over blue-green algae during the period of study.     

Distribution of indicator bacteria in Canyon Lake, California

The spatial and temporal distributions of indicator bacteria in a small, multiple-use source drinking water reservoir in Southern California, USA were quantified over the period August 2001-July 2002. High levels of total and fecal coliform bacteria were present in Canyon Lake (annual geometric mean concentrations+/-SEM of 3.93+/-0.02 and 3.02+/-0.03 log cfu/100mL, respectively), while comparatively low levels of enterococci and E. coli were found (1.16+/-0.02 log cfu/100mL and 0.30+/-0.03 log MPN/100mL, respectively). As a result, these different indicator bacteria yielded quite divergent indices of water quality, with 72.1% of all surface samples (n=294) exceeding the USEPA single-sample limit of 400 cfu/100mL fecal coliform bacteria, while none (0%) of the samples exceeded the single-sample limit for E. coli (n=194). Regression analyses found a positive correlation between total and fecal coliform bacteria (R=0.50, significant at p<0.001) and between enterococci and E. coli (R=0.51, significant at p<0.001), but no correlation or inverse correlations were found between coliform concentrations and enterococci and E. coli levels. External sources responsible for the high total and fecal coliform bacteria were not identified, although laboratory studies demonstrated growth of the coliform bacteria in lake water samples. Enterococci and E. coli were not observed to grow, however. Bacteria concentrations varied relatively little laterally across the lake, although strong vertical gradients in fecal coliform and enterococcus bacteria concentrations were present during summer stratification, with concentrations about 10x higher above the thermocline when compared with surface concentrations. In contrast, total bacteria, total virus and total coliform bacteria levels were unchanged with depth. Seasonal trends in bacteria concentrations were also present. This study shows that the choice of indicator bacteria and sampling depth can both strongly affect the apparent microbial water quality of a lake or reservoir.     

Microbiological aspects of fish grown in treated wastewater

Tilapia, common carp and silver carp were reared in treated domestic wastewater. The most sensitive to this environment was the silver carp, followed by common carp and tilapia. In healthy clean fish, bacteria were not found in the blood or the muscles. They were present in small numbers in various organs and in concentrations of 10⁶–10⁷ g⁻¹ in the digestive tract content. In fish exposed to treated wastewater for the entire growing period, bacteria were found in the muscles. The number of bacteria recovered from various organs ranged between 10⁴–10⁶ g⁻¹ and their concentration in the digestive tract content was 10⁸–10⁹ g⁻¹. The number of bacteria in the pond water determined the presence and concentration of bacteria in the fish. The number of bacteria that caused their appearance in the muscles of fish has been named the “threshold concentration”. Considering the public health aspects, fish can be reared in treated wastewater provided the bacteriological quality of the water is compatible with the “threshold concentration” levels of the fish grown in the ponds. The suitability of E. coli (fecal coliform bacteria) as indicators for the bacteriological quality of fish grown in wastewater-fed ponds is examined.     

Characterizing nutrient dynamics with relation to changes in partial pressure of CO2 in a tropical sewage‐fed aquaculture pond situated in a Ramsar wetland

The changes in nutrient dynamics (nitrate, ammonium, silicate, phosphate and iron concentration) vis‐à‐vis partial pressure of CO₂ in water [pCO₂(water)] from tropical sewage‐fed aquaculture ponds (East Kolkota Wetlands, India) were analysed by means of a microcosm. A significant relationship between these nutrient’s removal from the system and reduction in pCO₂(water) was observed (with few exceptions). These water bodies acted as significant sources of CO₂ in pre‐monsoon and monsoon seasons despite having substantial quantity of chlorophyll‐a to make it a net autotrophic system. The study revealed that if conditions favourable for optimum photosynthesis can be maintained in these ponds, the CO₂ source character of these ponds can be reversed. In the post‐monsoon season, when the pH of the water column was high, the system acted as sink for CO₂ which suggests the use of lime to prevent these systems from becoming hypereutrophic and carbon source at the same time.     

Influence of physico‐chemical factors on the coliform bacteria in a closed‐lake water system

This investigation is concerned with an examination of the coliform group of micro‐organisms responsible for causing pollution in drinking waters. Bacterial counts (MPN) were correlated with certain physical and chemical factors, viz. electrical conductivity, pH, temperature, Ca‐Mg hardness, inorganic nitrogen substances, inorganic sulphate and phosphate contents of the water. The coliform counts (MPN) varied with seasonal variations and changes in the properties of the water bodies. An inverse correlation of bacterial counts was noted with the dissolved inorganic nitrogenous compounds like ammonia, nitrite and nitrate. Similar observations were made when compared with dissolved salts of phosphate and sulphate.