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At least 127 records · Page 7Linked to original sources
PubMed2001

Geographical and genetic distances among zooplankton populations in a set of interconnected ponds: a plea for using GIS modelling of the effective geographical distance.

In systems of interconnected ponds or lakes, the dispersal of zooplankton may be mediated by the active population component, with rivulets and overflows functioning as dispersal pathways. Using a landscape-based approach, we modelled the effective geographical distance among a set of interconnected ponds (De Maten, Genk, Belgium) in a Geographic Information System (GIS) environment. The first model (the Landscape Model; LM) corrects for the presence of direct connections among ponds and was based on the existing landscape structure (i.e. network of connecting elements among ponds, travelling distance and direction of the current). A second model (the Flow Rate Model; FRM) also incorporated field data on flow rates in the connecting elements as the driving force for the passive dispersal of the active zooplankton population component. Finally, the third model (the Dispersal Rate Model; DRM) incorporated field data on zooplankton dispersal rates. An analysis of the pattern of genetic differentiation among Daphnia ambigua populations inhabiting 10 ponds in the pond complex reveals that the effective geographical distance as modelled by the flow rate and the dispersal rate model provide a better approximation of the true rates of genetic exchange among populations than mere Euclidean geographical distances or the landscape model that takes into account solely the presence of physical connections.

Alleles↗
PubMed2002

Giardia and Cryptosporidium removal from waste-water by a duckweed (Lemna gibba L.) covered pond.

AIMS: To determine the ability of duckweed ponds used to treat domestic waste-water to remove Giardia and Cryptosporidium. METHODS AND RESULTS: The influent and effluent of a pond covered with duckweed with a 6 day retention time was tested for Giardia cysts, Cryptosporidium oocysts, faecal coliforms and coliphage. Giardia cysts and Cryptosporidium oocysts were reduced by 98 and 89%, respectively, total coliforms by 61%, faecal coliforms by 62% and coliphage by 40%. There was a significant correlation between the removal of Giardia cysts and Cryptospordium oocysts by the pond (P < 0.001). Influent turbidity and parasite removal were also significantly correlated (Cryptosporidium and turbidity, P=0.05; Giardia and turbidity, P=0.01). CONCLUSIONS: The larger organisms (parasites) probably settled to the bottom of the pond, while removal of smaller bacteria and coliphages in the pond was not as effective. SIGNIFICANCE AND IMPACT OF THE STUDY: Duckweed ponds may play an important role in wetland systems for reduction of Giardia and Cryptosporidium.

Animals↗
PubMed2003

The fate of heavy metals (Zn, Cu, Pb, Cd and Cr) in an integrated wastewater treatment plant: two phase anaerobic reactor (RAP) - high rate algal pond (HRAP).

Removal of heavy metals (Zn, Cu, Pb, Cd and Cr) by an integrated wastewater treatment system, Two Phase Anaerobic Reactor (RAP) - High Rate Algal Pond (HRAP), was investigated. Results indicate a good reduction of these micro-pollutants by this system. Global elimination rates of treatment system are 80%, 87%, 38%, 60% and 63%, respectively for Zn, Cu, Pb, Cd and Cr. Primary treatment (RAP) was not involved in this reduction. Metal concentrations detected in RAP effluent are higher than those detected in raw wastewater. However, the essential metal removal was ensured by the HRAP and thetwo maturation ponds. Sedimentation of metals adsorbed on suspended matters is the principal factor that intervened in metal elimination by these ponds. Indeed, metal analysis of wastewater dissolved and particulate fractions showed that the majority of these cations was in particulate fraction, notably for Zn, Cu, Cd and Cr. Their distribution between these fractions evolved towards their solubilization, during the treatment. Otherwise, metal sediment analysis of different ponds showed that sludges accumulate important quantities of metals, especially in RAP sludges. Thereafter, Zn, Cu and Cd concentrations increased in HRAP sludges, but Pb and Cr contents decreased. However, in maturation pond sludges metal quantities are lower. On the other hand, metal contents in sludges are variable from upstream to downstream of each pond.

Adsorption↗
PubMed2004

Seasonal performance of constructed wetland and winter storage pond for sewage treatment in Korea.

A pilot study was performed from July 1998 to December 2002 to examine the feasibility of a constructed wetland system for sewage treatment in small communities of Korea. To maintain treatment performance during the winter period, an intermittent-discharge pond was connected to the wetland; its effects were evaluated from December 2001 to April 2003. The subsurface flow (SSF) wetland was satisfactory for treating sewage with good removal efficiency even during the winter period. The wetland effluent concentrations of BOD5 and TSS were often higher in winter than in the growing season, but this was explained by the higher loading rates, rather than lower removal efficiency. The relatively poor-quality wetland effluent was further polished during winter in the pond. The upper layer of the pond water column became remarkably clear immediately after ice melt. Overall, the wetland system was found to be adequate for treating sewage with stable removal efficiency, and the intermittent-discharge pond was found to be effective for further polishing if necessary. Therefore, a wetland and subsequent pond system is recommended as a practical alternative for treating sewage in small communities in Korea, and partial discharge of pond water in March is suggested.

Ecosystem↗
PubMed2005

Multi-stage ponds-wetlands ecosystem for effective wastewater treatment.

The performance of the Dongying multi-stage ponds-wetlands ecosystem was investigated in this work. Study of the removal of different pollutants (BOD(5), COD, SS, TP, TN, NH(3)-N, etc.) in different temperature seasons and different units in this system indicated that effluent BOD(5) and SS were constant to less than 11 mg/L and 14 mg/L throughout the experimental processes; but that the removal efficiencies of pollutants such as TP, TN, NH(3)-N, COD varied greatly with season. The higher the temperature was, the higher was the observed removal in this system. Additionally, each unit of the system functioned differently in removing pollutants. BOD(5) and SS were mainly removed in the first three units (hybrid facultative ponds, aeration ponds and aerated fish ponds), whereas nitrogen and phosphates were mainly removed in hydrophyte ponds and constructed reed wetlands. The multi-stage ponds-wetlands ecosystem exhibits good potential of removing different pollutants, and the effluent quality meet several standards for wastewater reuse.

Ecosystem↗
PubMed2004

Laser defocusing effects on laser ablation inductively coupled plasma-atomic emission spectrometry: different ablation interactions between the laser and low-alloy steel, Fe pellets, and a pond sediment pellet.

The ablation interaction between a laser and solid samples, which affects the analytical performance for laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES), was studied. The emission intensities of elements observed by LA-ICP-AES (LA-ICP-AES element signal intensities) for different solid samples were measured under different laser defocusing conditions with a fixed laser output energy. It was found that the optimum laser defocusing conditions were dependent on the different solid samples with different sample characteristics, and also on the different elements with different elemental characteristics in each solid sample. A low-alloy steel, pellets containing different Fe concentrations (0 - 100% Fe pellet), and a pond sediment pellet were used as different solid samples. The variations of the LA-ICP-AES Fe signal intensities observed under different laser defocus conditions were completely different between the low-alloy steel and the pond sediment pellet. The changes in the LA-ICP-AES Fe signal intensities for 90 and 100% Fe pellets were similar to that of the low-alloy steel. However, pellets with lower Fe concentrations (less than 70%) showed different trends and the defocusing behavior became closer to that of the pond sediment pellet. The LA-ICP-AES signal intensities of other elements were also evaluated, and were compared for different solid samples and different defocusing behavior. It was observed that the changes in the LA-ICP-AES signal intensities of almost all elements in the pond sediment pellet showed a similar trend to those of Fe for different laser defocus positions; that is, the elemental fractionation for these elements in the pond sediment pellet seemed to be relatively small. On the contrary, it was found that the LA-ICP-AES Si, Ti, and Zr signal intensities for low-alloy steel showed different trends compared to those of other elements, including Fe, under different defocusing conditions; that is, the elemental fractionation observed for the low-alloy steel was larger than that of the pond sediment pellet. From these results, different ablation interactions between the laser and the different solid samples were considered, and attributed to the sample characteristics, such as the matrix, hardness, and conductivity. Elemental fractionation was attempted to be explained by using elemental characteristics, such as the melting point and ionization energy of the elements.

Journal Article↗
PubMed2005

Effects of using retention-pond water for dust abatement on performance of feedlot steers and carriage of Escherichia coli O157 and Salmonella spp.

OBJECTIVE: To evaluate the effects of using retention-pond water for dust abatement on performance of feedlot steers and carriage of Escherichia coli O157 and Salmonella spp. DESIGN: Matched cohort studies. ANIMALS: 2 groups of feedlot steers comprising 3,510 (pathogen carriage) and 3,737 (performance) animals housed in a large commercial feedlot in the Texas Panhandle. PROCEDURE: Steers were systematically allocated to treatment pens approximately 60 days after arrival (pathogen carriage) or at arrival (performance). For evaluation of pathogen carriage, feces and hide swab specimens were collected from 25 animals in each pen within 10 days of slaughter. Samples were submitted for bacterial culture for E. coli O157 and were tested with a polymerase chain reaction-based assay for Salmonella spp. For evaluation of performance, pen weights of animals were obtained at arrival and slaughter and feed delivered to each pen was recorded. The exposure of interest for both studies was application of retention-pond water through fixed high-pressure sprinklers. RESULTS: Carriage of E. coli O157 and Salmonella spp and animal performance were not adversely affected by exposure to retention-pond water. Prevalences of E. coli O157 in feces, on hides, and either in feces or on hides for those exposed to retention-pond water were 8.3%, 8.9%, and 15.4%, respectively; prevalences for those unexposed to retention-pond water were 11.4%, 15.4%, and 22.6%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that use of retention-pond water for dust abatement in feedlot pens does not adversely affect pathogen carriage or animal performance.

Animals↗
PubMed2001

Performance of WSSV-infected and WSSV-negative Penaeus monodon postlarvae in culture ponds.

In a survey of 27 Penaeus monodon culture ponds stocked with postlarvae (approximately PL10) at medium density (approximately 40 shrimp m(-2)), single-step nested white spot syndrome virus (WSSV) PCR was used to measure the WSSV infection rates in the shrimp populations within 1 mo after stocking. Seven ponds were initially WSSV-free, and the shrimp in 5 of these were harvested successfully. In the ponds (n = 6) where detection rates were higher than 50%, mass mortality occurred during the growth period, and none of these ponds was harvested successfully. In a subsequent study, P. monodon brooders were classified into 3 groups according to their WSSV infection status before and after spawning: brooders that were WSSV-positive before spawning were assigned to group A; spawners that became WSSV-positive only after spawning were assigned to group B; and group C consisted of brooders that were still WSSV-negative after spawning. WSSV screening showed that 75, 44 and 14%, respectively, of group A, B and C brooders produced nauplii that were WSSV-positive. Most (57%; 16/28) of the brooders in group A produced nauplii in which the WSSV prevalence was high (>50%). When a pond was stocked with high-prevalence nauplii from 1 of these group A brooders, an outbreak of white spot syndrome occurred within 3 wk and only approximately 20% of the initial population survived through to harvest (after 174 d). By contrast, 2 other ponds stocked with low-prevalence and WSSV-negative nauplii (derived respectively from 2 brooders in group B), both had much higher survival rates (70 to 80%) and yielded much larger (approximately 3x by weight) total harvests. We conclude that testing the nauplii is an effective and practical screening strategy for commercially cultured P. monodon.

Animals↗
PubMed2002

The influence of thermal stratification on the hydraulic behavior of waste stabilization ponds.

Thermal stratification, which is characterized by a high vertical thermal gradient, is usually observed in deep lakes. However, although waste stabilization ponds have small depths, their high turbidity provides favorable conditions for the occurrence of this phenomenon, mainly during summer. During that time of the year, the layers nearest to the surface concentrate a larger amount of thermal energy compared to the deeper layers, which results in a temperature difference between the surface and the bottom of the pond. As a consequence a density profile appears, with the less dense layers located at the surface of the pond and the densest ones close to the bottom. This stratification in the water column induces alterations in the flow pattern and a decrease of the useful volume of the pond. This paper presents a mathematical model developed to forecast the conditions of thermal stratification in waste stabilization ponds and the volume actually used for wastewater treatment. With these values it is possible to correct the average residence time of the liquid in the pond. The theoretical results were compared with experimental observations, and maximum differences of 15% between the calculated and observed temperature profiles were found.

Forecasting↗
PubMed2002

Influence of load distribution and recycle rate in step-fed facultative ponds.

This study presents the results of research on a wastewater treatment system with four identical facultative ponds in series with step-feeding and recirculation (SFFPR). Four modes of distribution of the influent were studied, which were (in percentages of the inflow per pond): C1 = 25/25/25/25; C2 = 50/20/20/10; C3 = 50/50/0/0; C4 = 100/0/0/0. The organic loading applied to the four ponds overall was around 200 kg BOD5/ha.d. The distribution C4 = 100/0/0/0 was selected for studying the recycle rate. Three recycling rates were studied: 0.5Q, 1Q and 2Q. COD and BOD5 removal efficiencies were high whatever the step-feed distribution. For the distribution C1 and C2, the four ponds were homogeneous. The equal distribution of organic loading rate in C2 distribution was most beneficial for algal growth. For piston pattern distributions (C3 and C4), the ponds receiving the highest loading showed a bacterial biomass higher than that of the primary production. Increasing the recirculation rate seemed to lead towards homogenisation of the ponds, while a decrease appeared to lead to their individualisation and increased their productivity. The SFFPR constitutes a stage of the treatment process which can replace the facultative stage; it produces a high effluent quality and decreases land area requirements.

Bacteria↗
PubMed2002

Treatment of piggery wastes in waste stabilization ponds.

The piggery industry produces high effluent loads. This is due to the high concentration of animals kept in a confined space, foods with high protein content that are not well assimilated by the animals, and poor on-farm water management. In this study, we present the characteristics, design, site selection, soil study, and the construction of a pilot pond system for a family farm located in a warm climate area. The design includes a solids sedimentation phase, an anaerobic pond, a facultative pond and three maturation ponds. Once the system had reached steady state, the organic and bacterial kinetic constants were determined for each pond. The control parameters were determined and the dissolved oxygen and removal efficiency profiles were obtained. The results indicate that the effluent from the second maturation pond complies with the Official Mexican Standard for reuse in agriculture ("1000 FC/100 ml).

Agriculture↗
PubMed2002

Assessment of stormwater impacts on an urban stream with a detention pond.

Impacts of urban development on a small creek with an on-stream stormwater pond, which was built to mitigate the effects of a 13-ha commercial plaza on creek flows, were assessed by investigations of the creek-pond system hydrology, water and sediment chemistry and toxicity, and benthic communities. The hydrology and conventional pollutant loadings of this system were dominated by the creek catchment (4.5 km2), which contributed more than 95% of the total flow; the rest was contributed by the plaza runoff which was less polluted than typical residential runoff. Conventional bioassays (Daphnia magna, Microtox) did not indicate any confirmed acute toxicity in the creek flow, plaza drainage, or pond outflow. However, sediments accumulated in the pond were rather polluted and several sediment bioassays (including Sediment Microtox) indicated their severe toxicity. In benthic community assessments, taxa richness and total counts of benthic organisms did not change much when moving from upstream to downstream of the pond. Thus, the pond accumulates sediments and toxicants and thereby prevents further degradation of the creek condition downstream of the plaza drainage outfall.

Animals↗
PubMed2001

Quality status and optimum utilisation of village pond water--a case study.

The village ponds, which used to be useful institutions have become a source of nuisance and environmental pollution. Therefore, an effort was made to determine the quality of water stored in village ponds and to develop a strategy for its optimum utilization. Two village ponds were selected randomly in each block of Ludhiana district of Punjab State for detailed investigations. The comparative study of the quality of pond water vis-a-vis, quality standards for irrigation and rearing of fish has revealed that the quality of pond water is not only suitable for irrigation and development of fisheries, but also rich in nutrients, which is an added advantage. The study has revealed that the renovation of village ponds will have positive affect on environment, rural economy and ground water regime in declining water table areas.

Agriculture↗
PubMed2003

Waste stabilisation ponds upgrading at Blenheim and Seddon, New Zealand--case studies.

Waste stabilisation ponds (WSP) have been a popular form of wastewater treatment in New Zealand both for large cities and small communities. Most WSP were constructed from 1960 to 1985 and were single ponds or a primary and secondary pond in series of similar size. Since 1995, improvements comprising primary and maturation ponds, with four to six cells in series have been constructed or retrofitted to original two cell ponds. The Seddon and Blenheim ponds include in-bank rock filters between maturation cells as a lower cost way of providing this feature for reduction of solids. Operating results show reduced variability in final effluent quality for BOD and SS. In addition, very good reductions of faecal coliform and enterococci have been achieved along with good reductions of ammonia and total nitrogen for most of the year except the middle of winter. Extensive use of rock as rip-rap bank protection and in the rock filters, appears to have provided sufficient extra surface area for a nitrifying biofilm to develop.

Ammonia↗
PubMed2003

Mixing and its impact on faecal coliform removal in a stabilisation pond.

Faecal coliform removal in stabilisation ponds is highly dependent on shortest water retention times. Tracer tests have been performed in a 3,300 m2 and 1.0 m deep pond, located in Southern France, to measure the retention times and bring light on the main influencing factors and mechanisms. Tracer concentrations were monitored at the outlet and 60 locations within the pond--at the surface, mid depth and the bottom of the water column. Pond water temperatures were measured at different depths and locations, together with pH, DO and redox potential. Wind velocity and rainfall were recorded. Water quality was monitored at the inlet, outlet and within the pond. Water retention times were shown to be strongly affected by weather conditions. Windy periods appeared to favour mixing regardless of the season. In sunny periods of spring and summer, a clear stratification was observed during daytime and vanished gradually during the night, suggesting alternation of mixed and stratified hydrodynamic patterns. This alternation was shown to influence microorganism contents within and at the outlet of the pond. Accurate prediction of shortest water retention times and disinfection performance requires 3D unsteady state fluid dynamic models that are able to take the influence of wind and water temperature distribution into account.

Disinfection↗
PubMed2003

The spatial significance of water quality indicators in waste stabilization ponds--limitations of residence time distribution analysis in predicting treatment efficiency.

Over the past fifty years, considerable research in waste stabilization pond operation has led to the development of a number of models used to describe the hydraulic regime and predict treatment efficiency. Models range in complexity from plug or completely mixed simplifications to computational fluid dynamics (CFD) models which are able to predict flow hydraulics at a local level. Information about the exit age of pond effluent can be used to estimate pollutant decay. However, a mechanistic approach to understanding pond operation highlights the importance of knowing both the time and spatial history of pond effluent. A CFD model of a large pond system was constructed to demonstrate various hydraulic scenarios under different boundary conditions. Two scenarios were compared to visually demonstrate the effects of differing hydraulic conditions. Typical mechanistic models were applied to each condition to quantify biological differences. This simple example indicates that integrating biological and localised flow models will lead to a more holistic understanding of pond operation and treatment efficiency.

Bioreactors↗
PubMed2003

Effect of duckweed cover on greenhouse gas emissions and odour release from waste stabilisation ponds.

Treatment of wastewater in stabilisation pond systems prevents the negative environmental impact of uncontrolled disposal of sewage. However, even a natural treatment system may generate secondary negative environmental impacts in terms of energy consumption, emission of greenhouse gases and emission of odorous compounds. Whereas natural systems have an advantage over electro-mechanical systems in that they use less hardware and less energy, it is not yet known whether secondary environmental effects in the form of greenhouse gas emissions are lower for these systems. This research intends to be a first step in the direction of answering this question by assessing gas emissions from two types of natural systems, namely algae-based and duckweed-based stabilisation ponds. The H2S volatilisation from laboratory scale pond-reactors has been determined by drawing the air above the water surface continuously through a solution of 1 M NaOH for absorption of sulphide. The amount of H2S that volatilised from the algae pond-reactor, and was trapped in the NaOH trap, was found to be 2.5-86 mg/m2/day. The H2S volatilisation from the duckweed pond-reactor was found to be negligible, even though the sulphide concentration was 9.7 mg/l S(2-). The duckweed cover was a physical barrier for volatilisation, since bubbles were trapped in the cover. In addition the duckweed layer was found to be afavourable environment for both aerobic sulphide oxidisers (Beggiatoa gigantae) as well as for photosynthetic purple sulphur bacteria belonging to the genus Chromatium. These may also have contributed to the prevention of H2S volatilisation. Results on methane emissions were not conclusive so far, but the same mechanisms that prevent H2S volatilisation may also prevent methane volatilisation. Therefore it was concluded that duckweed covers on stabilisation ponds may reduce the emission of both odorous and greenhouse gases.

Adsorption↗
PubMed2004

Environmental impacts of two kind of ponds for shrimp production at Northwest Mexico.

Aquaculture offers a major opportunity for the economic development of Baja California Sur (BCS), Mexico. The severely limited freshwater supply and the geographic isolation of the state place limits on other productive activities. Despite the aridity, the natural vegetation of BCS is diverse and structurally complex with a high percentage (20%) of endemic species. In this work we compare the environmental impacts produced by two kinds of aquaculture systems: coastal ponds vs. inland ponds. Construction and operation of coastal ponds does not require destruction of the natural vegetation and, as is true for inland ponds. Coastal ponds are also compatible with conservation of mangroves, sea grasses and sensitive habitats for fish and mollusks. To reduce the negative impacts of aquaculture and to protect the vegetation of Baja California Sur, we recommend the use of coastal ponds for shrimp production.

Animals↗